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Research ArticleInfluence of Filler from a Renewable Resourceand Silane Coupling Agent on the Properties ofEpoxidized Natural Rubber Vulcanizates

Wiphawadee Pongdong1 Charoen Nakason2

Claudia Kummerloumlwe3 and Norbert Vennemann3

1Department of Rubber Technology and Polymer Science Faculty of Science and Technology Prince of Songkla UniversityPattani Campus Pattani 94000 Thailand2Faculty of Science and Industrial Technology Prince of Songkla University Surat Thani Campus Surat Thani 84000 Thailand3Faculty of Engineering and Computer Science Osnabruck University of Applied Sciences Albrechtstrasse 3049076 Osnabruck Germany

Correspondence should be addressed to Norbert Vennemann nvennemannhs-osnabrueckde

Received 25 November 2014 Revised 8 February 2015 Accepted 10 February 2015

Academic Editor Cengiz Soykan

Copyright copy 2015 Wiphawadee Pongdong et alThis is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Rice husk ash (RHA) was used as a reinforcing filler in epoxidized natural rubber (ENR) with various loading levels (0 10 20and 30 phr) and silica filled ENR was also studied for comparison The effects of RHA content on cure characteristics mechanicalproperties dynamicmechanical properties and thermoelastic behavior of the filled ENR composites were investigated It was foundthat the incorporation of RHA significantly affected the cure characteristics and mechanical properties That is the incorporationof RHA caused faster curing reactions and increased Youngrsquos modulus and tensile strength relative to the unfilled compound Thismight be attributed to the metal oxide impurities in RHA that enhance the crosslinking reactions thus increasing the crosslinkdensity Further improvements in the curing behavior and the mechanical properties of the filled composites were achieved byin situ silanization with bis(triethoxysilylpropyl) tetrasulfide (Si69) It was found that the rubber-filler interactions reinforced thecompositesThis was indicated by the decreased damping characteristic (tan 120575) and the other changes in the mechanical propertiesFurthermore the ENR composites with Si69 had improved filler dispersion Temperature scanning stress relaxation (TSSR) resultssuggest that the metal oxide impurities in RHA promote degradation of the polymer network at elevated temperatures

1 Introduction

Natural rubber (NR) is a natural biosynthesis polymer thathas been widely used for numerous applications becauseof its excellent mechanical and elastic properties Howeverthe application of NR is limited due to some drawbacksThat is NR is highly susceptible to degradation becauseof the double bonds in the main chain Several ways tomodify natural rubber molecules have been proposed toovercome these problems including the incorporation ofsome functional groups onto the NR molecules Epoxidationhas been one of the most popular alternatives modifyingthe molecular structure of NR by adding epoxide groups

onto the NR molecules Epoxidized natural rubber (ENR)has improved heat and oil resistance and low air permeabilityand viscosity However ENR with low epoxide content stillretains the strain crystallization tendency of natural rubberFurthermore the polarity of ENR increases with the degreeof epoxidation [1]

Reinforcement of rubber and polymer materials by par-ticulate fillers is a common practice for improving the serviceproperties and reducing the production cost The mostimportant fillers are the conventional synthetic fillers carbonblack and silica Production of these conventional fillers ishighly energy-consuming Therefore alternative fillers fromrenewable resources are of considerable interest improving

Hindawi Publishing CorporationJournal of ChemistryVolume 2015 Article ID 796459 15 pageshttpdxdoiorg1011552015796459

2 Journal of Chemistry

the overall sustainability of filled rubber production Ricehusk ash (RHA) is obtained by burning the agricultural ricehusk waste and it mainly consists of amorphous silica andresidual carbon black from combustionThe amount of silicain RHA varies between 55 and 97wt depending on thecombustion conditions Rice is the staple food of over halfof the worldrsquos population and about one-fifth of the worldrsquospopulation is engaged in rice cultivation The global riceproduction was about 750 million tons in 2013 and the huskscontribute about one-fifth by weight of the harvested anddried crops The husks contain about 20 silica Thereforesilica containing rice husk ash is generated in excess of 30million tons per year [2] Some prior research has assessed theproperties of silica ash to obtain an in-depth understandingof its behavior and has specifically tried to identify suitablemodifications to improve its performance as fillerThe poten-tial of RHA as a filler material for polymer composites hasbeen investigated with various polymers such as polyethylene(PE) [3 4] polypropylene (PP) [5] [styrene butadiene rubber(SBR)] + [linear low-density polyethylene (LLDPE)] blends[6] and polyurethane (PU) [7] In RHArubber compositesenhanced curing rate was observed with increased RHAloading levels in EPDM while contrary trends were observedin silica composites [8] In a comparative study of the curecharacteristics processability and mechanical properties ofNREPDM blends filled with RHA silica or carbon blackthe RHA filling gave the best resilience properties [9] It wasalso found that the incorporation of RHA in natural rubberresulted in lowered Mooney viscosity and shortened curetime and improved hardness but decreased tensile strengthand tear strength [10]

Influences of the two types of RHA namely black ricehusk ash (BRHA silica content of 54) and white ricehusk ash (WRHA silica content of 95) on the mechanicalproperties of epoxidized natural rubber with 50 moleepoxide (ie ENR-50) were investigated in [11] It wasfound that the WRHA exhibits overall superior vulcanizateproperties to those with BRHA The effects of RHA on theproperties of unmodified natural rubber compared withENR-50 composites were also reported [12] The resultsindicated that the NR composites exhibited longer scorchand cure times with higher tensile strength and elongationat break but lower tensile modulus than that of the ENR-50composites

To improve the mechanical properties of polymer com-posites filler surfaces have been treated with various typesof coupling agents However the most commonly used cou-pling agent in rubber compounds is bis(triethoxysilylpropyl)tetrasulfide (Si69) The effects of Si69 on the properties ofRHA filled natural rubber (NR) were investigated in [13]No improvement was found in the mechanical properties ofRHA filled vulcanizates with the silane coupling agent (Si69)This was presumably caused by the lack of silanol groups onthe RHA surfaces The effects of coupling agent (Si69) anda chemical treatment of RHA filled natural rubber were alsoinvestigated in [14] In this case the silane coupling agentmarginally improved the performance of rubber vulcanizates

In this work RHA filled ENR-25 composites with variousfiller contents were prepared Cure characteristics tensile

properties dynamical mechanical thermal analysis (DMTA)crosslink density thermoelastic properties and relaxationbehavior of RHA filled ENR-25 vulcanizates were investi-gated Furthermore an in situ modification of silica withthe silane coupling agent in the ENR-25 compounds wasinvestigated The silane coupling agent was directly addedto the internal mixer during the mixing of RHA and ENR-25 The silanization reaction might take place under themixing conditions A conventional commercial precipitatedsilica was also used as the filler to prepare composites forcomparisons between alternative fillers

2 Experimental

21 Materials Epoxidized natural rubber (ENR) with25mol epoxide was prepared in house by using preparationmethod described elsewhere [15] The high ammonia (HA)concentrated natural rubber latex used as raw materialin the preparation of ENR was manufactured by YalaLatex Industry Co Ltd (Yala Thailand) The ENR with a25mol level of epoxide groups was prepared via performicepoxidation by reacting NR latex with in situ performicacid generated from a reaction of formic acid (94 puritymanufactured by Riedel De Haen (Seelze Germany)) andhydrogen peroxide (50wt manufactured by Riedel DeHaen (Seelze Germany)) Characterization of the preparedENR was also performed by 1H-NMR Mooney viscometerand DSC Results confirmed that it was the ENR with26mol epoxide having 966 (ML 1 + 4) 100∘C and Tg ofminus4265∘CThe RHA filler was supplied byThunyakit NakhonPathom Rice Mill Co Ltd (Nakhon Pathom Thailand)The silica Ultrasil 7000GR was manufactured by EvonikIndustries (Essen Germany) The bis(triethoxysilylpropyl)tetrasulfide (Si69) was manufactured by Evonik Industries(Essen Germany) and was used as a silane coupling agentThe sulfur used as a curing agent was manufactured byPergan GmbH (Bocholt Germany) The N-tert-butyl-2benzothiazolesulfenamide (Santocure TBBS) used as anaccelerator was manufactured by Rhein Chemie RheinauGmbH (Mannheim Germany) The 13-diphenylguanidine(DPG) used as an secondary accelerator was manufacturedby Evonik Industries (Essen Germany) The zinc oxideused as a cure activator was manufactured by Lanxess(Leverkusen Germany) The other cure activator namelystearic acid was manufactured by Unichema InternationalBV (Gouda Netherlands)

22 Characterization of RHA RHAwas obtained from burn-ing of the rice husks during the rice manufacturing processWhen the burning is incomplete the result is carbonized ricehusks (CRH) Typically the particles of RHA or CRH arereduced in size by milling and further by grinding and aresieved through 120-mesh screen The powder of this typethat we obtained was placed in aluminum crucibles and putin a muffle furnace (Thermolyne 6000 furnace BarnsteadInternational Dubuque USA) and a heat treatment wasperformed at 700∘C for 6 h [16] This caused reduction of thecarbonaceous material and increased the relative content ofsilicon oxide The chemical composition and the functional

Journal of Chemistry 3

Table 1 Compounding formulation

Ingredients Gum RHA10 RHA10-Si69 RHA20 RHA20-Si69 RHA30 RHA30-Si69 S30 S30-Si69ENR-25 100 100 100 100 100 100 100 100 100ZnO 5 5 5 5 5 5 5 5 5Stearic acid 1 1 1 1 1 1 1 1 1Wingstay-L 1 1 1 1 1 1 1 1 1TBBS 06 06 06 06 06 06 06 06 06Sulfur 2 2 2 2 2 2 2 2 2RHA mdash 10 10 20 20 30 30 mdash mdashSilicaa mdash mdash mdash mdash mdash mdash mdash 30 30TESPT mdash mdash 001 mdash 002 mdash 003 mdash 24DPG mdash mdash 0003 mdash 0005 mdash 0008 mdash 03aSilica (Ultrasil 7000GR)

groups of the RHA were characterized by X-ray fluorescencespectrometer (XRF) and by Fourier transform infrared spec-troscopy (FT-IR) Also the particle size distribution of RHAwas analyzed by a particle size analyzer (Beckman CoulterLS 230 Vernon Hills Illinois USA) The surface area ofRHA was also determined by the Brunauer-Emmett-Teller(BET)methodThe structure of RHA particles was visualizedby scanning electron microscopy (SEM) (JSM-6510LA JeolLtd Akishima Japan) The density was measured by anultrapycnometer Finally the pH of the RHAwas determinedusing the procedure described in ASTM D1512

23 Mixing and Vulcanization The rubber compounds wereprepared using the compounding formulation shown inTable 1 The Haake Rheocord 600 laboratory internal mixer(Thermo Electron Corporation Karlsruhe Germany) witha fill factor of 07 was used to mix the rubber and otherchemicals at 80∘C at a rotor speed of 40 rpm The ENR-25was first masticated and compounded with various contentsof RHA (10 20 and 30 phr labeled as RHA

10 RHA

20 and

RHA30 resp) Furthermore the compounds without filler

(gum ENR-25) as well as ENR-25 compounded with 30 phrof silica (S

30) were prepared as control samples for com-

parisons The bis(triethoxysilylpropyl) tetrasulfide couplingagent (Si69)was alsomixedwithRHAor silica (labels RHA

10-

Si69 RHA20-Si69 RHA

30-Si69 and S

30-Si69) It is noted

that the contents of Si69 and DPG used in this formulationwere fixed based on the specific surface areas of the fillersaccording to [17]

Si69 content (phr) = 000053 times 119876 times 119862119879119860119861

DPG content (phr) = 000012 times 119876 times 119862119879119860119861(1)

where 119876 is the filler content (phr) and CTAB is the specificsurface area of silica or RHA (m2g)

Cure characteristics of the rubber compounds were thenstudied by using a rotorless rheometer D-MDR 3000 (Mon-tech Werkstoffprufmaschinen GmbH Buchen Germany) at160∘C for 30minThe compounds were then vulcanized in anelectrically heated plate press (Polystat 200 T type Schwaben-thanWustermark Germany) under 70-bar pressure at 160∘C

The rubber vulcanizates were eventually conditioned for 24 hbefore testing and characterization

24 Mechanical Properties Mechanical properties in termsof tensile strength and modulus were determined using auniversal tensile testing machine (Hounsfield Tensometermodel H 10KS Hounsfield Test Equipment Co Ltd SurreyUK)Themachinewas operated at room temperature with anextension speed of 500mmmin according to the proceduresdescribed in ASTMD412 Dumbbell-shaped specimens weredie-cut from the vulcanized rubber sheets using ASTM dietype C

25 Dynamic Mechanical Properties Dynamic mechanicalproperties of the rubber vulcanizates were measured usingan advanced rheometric expansion system rheometer (modelARES-RDA WFCO TA Instruments Ltd New Castle TheUnited States) The instrument was operated in the torsionmode at a frequency of 10Hz and at dynamic strain ampli-tude of 05 The temperatures range was set from minus60 to20∘C with a heating rate of 2∘Cmin

26 Crosslink Density Apparent crosslink densities of therubber vulcanizates were determined using a swellingmethod Rectangular 10 times 10 times 2mm test pieces were usedThe samples were weighted before immersing into tolueneand were left in the dark under ambient conditions for sevendays The swollen samples were then removed and excessliquid on the specimen surfaces was removed by blotting withfilter paperThe specimens were then dried in an oven at 60∘Cuntil constant weight [18] The final weights of the sampleswere then compared with their original weights beforeimmersion into toluene The apparent crosslink density wascalculated by using the Flory-Rehner equation [19]

] =minus (ln (1 minus 120601

120588) + 120601120588+ 1205941206012120588)

1198811(12060113

120588 minus 1206011205882) (2)

where ] is the crosslink density (molm3) 120601120588is the volume

fraction of rubber in a swollen network1198811refers to themolar

volume of toluene and 120594 is the Flory-Huggins interaction


Table 2 Physical properties of rice husk ash (RHA) and silica

Properties RHA SilicaMean particle size (120583m) 383 0018Surface area (m2g) 091 173Density (gcm3) 218 210pH 920 650

parameter between toluene and rubber where a value of 04was used for 120594 according to the literature [20]

It is noted that the volume fraction of filler had to besubtracted in the calculation of the volume fraction of rubberin a swollen network (120601

120588) Thus the volume fraction of

rubber in a swollen network was determined by

120601120588=

1

(1 + ((119898 minus 119898119889) 119898119889)) sdot (120588

119901120588119904) (3)

where 119898 is the mass of the swollen sample 119898119889is the mass

after drying of the sample 120588119901is density of the polymer and

120588119904is density of the solvent [21]

27 Temperature Scanning Stress Relaxation The thermoe-lastic behavior of each rubber vulcanizate was determinedby using a TSSR meter (Brabender Duisburg Germany)operated at a constant tensile strain of 50 A dumbbell-shaped specimen (type 5A ISO 527) was placed in anelectrically heated test chamber regulated to the initial 23∘Ctemperature for 2 h This is to allow the decay of short-time relaxation processes The sample was then heated witha constant heating rate of 2∘Cmin until the stress relaxationwas complete or the sample ruptured From the resultingstress-temperature curve or force-temperature curve thenonisothermal relaxation modulus 119864(119879) can be obtainedspecifically for the used constant heating rate ]Therelaxationspectrum 119867(119879) was obtained by differentiating 119864(119879) withrespect to temperature 119879 according to [21ndash23]

119867(119879) = minus119879[119889119864 (119879)

119889119879]V=const (4)

28 Morphological Properties Microstructures of the rubbervulcanizates were studied by scanning electron microscopy(SEM) (model JSM-6510LA Jeol Ltd Akishima Japan) Thesample surfaces were first prepared by cryogenic fracturingand were then coated with a thin layer of gold under vacuumconditions before characterization by SEM

3 Results and Discussion

31 Characteristics of RHA and Silica Thephysical propertiesin terms of particle size surface area density and pH ofRHA and silica are summarized in Table 2 It can be seenthat the mean particle size of RHA is considerably largerthan that of the silica Ultrasil 7000GR That is the mass-average particle size based on the particle size distributioncurve of RHA (Figure 1) is approximately 383 120583m while thecommercial silica shows very small particles with a mean

Table 3 Chemical compositions of RHA

Chemical composition Concentration ()Silicon dioxide (SiO2) 9104Potassium oxide (K2O) 370Phosphorus pentoxide (P2O5) 136Calcium oxide (CaO) 196Magnesium oxide (MgO) 045Alumina (Al2O3) 052Iron oxide (Fe2O3) 060Manganese oxide (MnO) 032Barium oxide (BaO) 003Lead oxide (PbO) 005Rubidium oxide (Rb2O) 002

001 01 1 10 100

0

2

4

6

Diff

eren

tial v

olum

e (

)

Particle diameter (120583m)

Figure 1 Particle size distribution curve of RHA

Figure 2 SEM micrograph of RHA particle

particle size of about 0018 120583m (Table 2) Also the BETsurface area of RHA is considerably lower than that of thesilica particles Furthermore it is seen that pH is higherfor RHA than for the silica This might be attributed to thepresence of impurities in particular metal oxides as shownin Table 3The topography of RHA particles characterized bySEM technique is shown in Figure 2 It is seen that the RHAparticles are irregular in shape with smooth surface


Table 4 Cure characteristics of gum and filled ENR-25 vulcanizates with various RHA contents or 30 phr of silica with and without silanecoupling agent (Si69)

Sample Min torque(119872119871 dNm)

Max torque(119872119867 dNm)

Delta torque(119872119867ndash119872119871 dNm)

Scorch time(1199051199042 min)

Cure time(11990590 min)

Gum 114 56 446 384 816RHA10 144 573 429 310 461

RHA20 155 615 460 270 428

RHA30 182 771 589 240 459

RHA10-Si69 116 597 481 148 289

RHA20-Si69 123 668 545 127 269

RHA30-Si69 136 817 681 103 273

S30 513 1445 932 367 1954S30-Si69 461 1672 1211 268 928

4000 3000 2000 1000

1115

1087

3439

Silica

Rice husk ash

Tran

smitt

ance

()

3433788

468

802

473

Wave number (cmminus1)

Figure 3 FTIR spectra of RHA and silica

Figure 3 shows the infrared spectra of RHA and silicaIt is seen that the absorption peak at a wave number of3433 cmminus1 which is assigned to the stretching vibration ofsilanol groups and the hydrogen bonds between water andadjacent (vicinal) silanols (ndashOH) is observed in both spectraAlso the absorption peak at the wave number 1087 cmminus1which is assigned to the asymmetrical stretching vibrationof SindashOndashSi is observed Furthermore the absorption peaksat wave numbers 788 and 468 cmminus1 which represent thecharacteristic bands of amorphous silica are also observedin both samples [13 24] It is therefore concluded that theRHA and silica show similar infrared spectra indicating thecharacteristics of silica Also in the spectrum of RHA thecharacteristic peak of hydrocarbon is not observed Thisconfirms that burning in the muffle furnace at 700∘C for 6 hcompletely eliminated the carbon content in the RHA

32 Cure Characteristics Figure 4 shows the curing curves ofthe gum and the filled ENR-25 compounds with various con-tents of RHAandwith 30 phr of silica with andwithout silanecoupling agent (Si69) Plateau curing curves were observedfor the gum and the RHA filled compounds However the

5 10 15 20 25 300

4

8

12

16

20

Gum vulcanizates Without silane

With silaneTime (min)

RHA10RHA10-Si69

RHA20RHA30RHA20-Si69

S30

S30-Si69

Gum ENR-25

Torq

ue (d

Nmiddotm

)

RHA30-Si69

Figure 4 Cure curves of gum and filled ENR-25 vulcanizates withvarious contents of RHA and 30 phr silica with and without silanecoupling agent (Si69)

reversion phenomenon with decreasing torque was observedfor the filled ENR-25 compounds with RHA-Si69 This isattributed to the restructuring and changing crosslink struc-tures of rubber vulcanizates after themaximumvulcanization[25] Also the breakdown of monosulfidic and ether linkagescontributes to the reversion in the ENRnetworks [26] On theother hand the silica filled ENR-25 compound (S

30) exhibits

marching curing with increasing torque with cure retarda-tion This might be attributed to reactions between the silicaand the zinc oxide accelerator which subsequently lowers theability to form zinc complex intermediates and slows downthe vulcanization process In addition the incorporation ofthe silane coupling agent enhanced the cure characteristics byforming filler-silane-ENR linkages That is all silane treatedcompounds exhibit short cure times (119905

90) and scorch times

(1199051199042) and high torque differences or delta torques as shown in

Table 4


Step (2)

Step (1)

Si

O

OHHO

SiO

Silica

C

C

C

CO H+

ENR

SiO O O

Si

O

H OH

C

H C

HO

SiO

O

OSiO

C CO

H

HC

C

O

H

H

2HC

2HC

CH2

CH3

CH3

CH2

CH2

CH2

CH2

CH2

3HC

3HC

3HC

2HC

2HC

Scheme 1 Possible chemical interaction between ENR and silica

In Table 4 it is also clear that scorch and cure timeswere shortened by increasing the content of RHAThis mightbe attributed to the presence of metal oxides in the RHAwhich enhances crosslinking reactions and increases curerates of the rubber compounds [9ndash14] However at equal fillerloading levels of 30 phr the RHA exhibited shorter scorchand cure times than the silica The most probable factorto account for this observation is the specific surface areawith low specific surface allowing less hydroxyl groups onthe RHA surfaces [27 28] This reduces the cure retardationby the adsorption of curatives In Table 4 the 119872

119867and 119872

119871

increased with the loading level of RHA That is addition offiller usually increases the modulus and significantly reducesthe chain mobility of rubber macromolecules The relativelyhigh 119872

119871and cure torque of silica filled ENR compound

with 30 phr indicates its high stiffness caused by the silicaparticulates This stiffness also restricts the chain mobilitydue to obstruction by the filler particles and probably bythe strong interaction between silica and the ENR matrixFurther the expected increase in modulus is partly due tothe inclusion of rigid filler particles in the soft matrix whileanother contribution arises from the filler-rubber interac-tions The latter effect relates to the smaller particle size andcorrespondingly high specific surface area of silica (Table 2)In the ENR compounds with silane coupling agent all filledrubber vulcanizates exhibit low119872

119871but high119872

119867and torque

difference (ie delta torque) This may be attributed to theinvolvement of silanemolecules in vulcanization resulting inchemical linkages being established between the silane andthe filler together with the ENR-25 matrix The vulcanizateproperties are enhanced by the silane coupling agent throughthe polymer-polymer and polymer-filler interactions It isnoted that an increase in delta torque indicates an increase incrosslink density Also shortened scorch and cure times wereobserved in the filled ENR-25 with the silane coupling agentThismight be due to the presence of sulfur atoms in the silanecoupling agent (Figure 5) Otherwise the functional groupsthat link the coupling agent to the rubber molecules formdouble bonds which are activated by the addition of an activesulfur compound or by the generation of a radical moiety

Si (CH2)3 (CH2)3S4 Si

OC2H5

OC2H5

OC2H5

H5C2O

H5C2O

H5C2O

Figure 5 Chemical structure of silane coupling agent Si69

in order to have simultaneous crosslinking of rubber andthe coupling agent molecules with comparable reaction rateduring the curingThe silane coupling agent also increases theamount of sulfur in the rubber compounds which may causecrosslinking reactions and hence shorten the scorch and curetimes

33 Mechanical Properties The effects of the various fillerloadings with alternative fillers and the use of silane couplingagent on the mechanical properties of ENR-25 vulcanizatesin terms of Youngrsquos modulus tensile strength and elongationat break are shown in Figures 6 to 8 In Figure 6 it isseen that the Youngrsquos modulus increased with RHA contentThe incorporation of RHA particles restricts the mobilityof rubber molecular chains and hence increases materialstiffness This result agrees with the increase of delta torquein Table 4 It is also seen that the filled ENR vulcanizatesexhibited higher Youngrsquos moduli and tensile strengths thanthe gumvulcanizate Furthermore these properties increasedslightly with the loading level of RHAThis may be attributedto the dilution effect togetherwith the reinforcement becauseof chemical interactions between the RHA particles and theENRmatrix It is noted that the RHA surfaces carry hydroxylgroups and other oxygen compounds (Table 2) These caninteract with the epoxide groups in ENR molecules and apotential reaction is shown in Scheme 1 That is the silanolgroups on the silica surfaces can interact with the epoxiderings in ENR molecules during mixing andor vulcanizingAlso chemical linkages form from silanol groups reactingwith the ring opening products of ENR possibly with thereaction model shown in Figure 9(a) In Figures 6 and 7 itis also seen that the silane coupling agent in RHA increased


0 10 20 3000

05

10

15

20

25

30

Filler content (phr)

RHARHA-Si69

Youn

grsquos m

odul

uss (

MPa

)

S30

S30

-Si69

Figure 6 Youngrsquos modulus of gum and filled ENR-25 vulcanizateswith various RHA contents and 30 phr of silica with and withoutsilane coupling agent (Si69)

Youngrsquos modulus and tensile strength of the filled ENR-25vulcanizates This might be due to an increased crosslinkdensity caused by the new linkages of silica-Si69-ENR-25 asschematically shown in Figure 9(b) It is also seen that theYoungrsquos modulus (Figure 6) and tensile strength (Figure 7)of silica filled ENR-25 vulcanizates with silane couplingagent were higher than those of the RHA filled vulcanizatesThis might be attributed to the high specific surface ofsilica particles which allows extensive chemical interactionsbetween filler and rubber thus enhancing polymer-fillerinteraction

In Figures 7 and 8 it is also seen that increasing thecontent of RHA increased the tensile strength but decreasedthe elongation at break of the RHA filled ENR-25 vulcan-izates This is due to the RHA particles lowering chainmobility of rubber molecules together with the increasedchemical interactions between the RHA particles and theENR matrix with a high reinforcing effect Furthermore theincorporation of silane coupling agent increased the tensilestrength but decreased the elongation at break This mightbe due to the surfaces of RHA providing hydroxyl groupsand other oxygen compounds (Table 3) which may formhydrogen bonds with the organosilane coupling agent andthe epoxide groups in ENR molecules In Figure 8 it is alsoseen that the silica filled ENR-25 vulcanizate showed lowerelongation at break than that of the RHA filled ENR-25composite This might be due to the high polarity of silicathatmay cause poor filler distribution and increase filler-fillerinteractions This is corroborated by the large silica agglom-erates observed in the SEM micrograph of Figure 14(d) It istherefore concluded that the rubber vulcanizate with silanecoupling agent showed high mechanical properties in terms

0 10 20 300

4

8

12

16

20

Tens

ile st

reng

th (M

Pa)


RHARHA-Si69

S30

S30-Si69

Figure 7 Tensile strength of gum and filled ENR-25 vulcanizateswith various RHA contents and 30 phr of silica with and withoutsilane coupling agent (Si69)

0 10 20 300

200

400

600

800

1000

Elon

gatio

n at

bre

ak (M

Pa)


RHARHA-Si69

S30S30-Si69

Figure 8 Elongation at break of gumand filled ENR-25 vulcanizateswith various RHA contents and 30 phr of silica with and withoutsilane coupling agent (Si69)

of Youngrsquos modules and tensile strength but low elongationat break That is the silane coupling agent might contributeto good filler dispersion in the elastomeric matrix and toimproved adhesion between the two phases Typically thecoupling agents are bifunctional molecules (Figure 5) whichare capable of establishing molecular bridges at the interface


SiSi

SiSi

Si

O O

O

O

O

OH

OH

OH

OH

O

O

Sx

Sx

OH

O

OHO

HO O

Sx

Filler particle

(a)

HO

Filler particle

Si

Si

SiSi

O

O

O

O

O

O

O

O

OH

OH

OH

O Sx

OH

O O

HO

Si

SiOEt

EtO Sx

SxSx

(CH2)3

(b)

Figure 9The proposed reactionmodels for RHA or silica dispersed in ENR-25matrix (a) without silanization (b) with silane coupling agent(Si69)

Table 5 Storage moduli at 20∘C loss moduli and maximum damping factor of gum and filled ENR-25 vulcanizates with 30 phr of RHA orsilica with and without silane coupling agent (Si69)

Sample Storage modulus1198661015840(MPa)

Loss modulus11986610158401015840 (times105) (MPa)

Maximum damping factortan 120575max

Gum 74696 287 277RHA30 84164 322 269

RHA30-Si69 142810 391 196

S30 292750 325 134S30-Si69 301750 358 141

between the polymermatrix and filler surface as illustrated inFigure 9(b) Hence they enhance the rubber-filler adhesionimprove reinforcement effects and give superior mechanicalproperties

34 Dynamic Properties It is well recognized that the stor-age modulus of a particulate filled polymer composite isinfluenced by the effective interfacial interaction between theinorganic filler particles and the polymer matrix In generala stronger interfacial interaction between the matrix andthe filler gives a superior storage modulus of the composite[29] Dynamic mechanical thermal analysis (DMTA) wasexploited to characterize the RHA and silica filled ENR-25 vulcanizates Figure 10 shows the storage modulus (1198661015840)the loss modulus (11986610158401015840) and the loss tangent of gum ENR-25 vulcanizates and filled ENR-25 with 30 phr of RHA orsilica with and without silane Si69 In Figure 10(a) it is seenthat in the glassy region at temperatures below minus55∘C thechanges in 1198661015840 were small That is the modulus-temperaturecurves are plateaus It is also seen that the various types ofrubber vulcanizates had the following rank order by storagemodulus gum vulcanizate lt RHA filled ENR-25 lt RHA

filled ENR-25 with Si69 lt silica filled ENR-25 lt silica filledENR-25 with Si69 (Table 5) Therefore the incorporationof RHA or silica in ENR-25 increased the modulus fromthe gum vulcanizates This is due to interactions betweenthe silanol groups in silica and the polar functional groupsin ENR molecules (Figure 9(a)) Also the addition of Si69increased the reinforcement effects of RHA or silica fillersin the vulcanizates (in RHA

30-Si69 and S

30-Si69) This is

simply due to the reactions between the silanol groups ofsilica the epoxide groups in ENR and the organosilane(Figure 9(b)) Therefore the incorporation of Si69 increasedthe rubber-filler interactions and consequently enhanced thestorage modulus [30] It is noted that the silica filled ENR-25 vulcanizates with and without Si69 show higher modulithan the RHA filled vulcanizates This might be due tothe more restricted molecular mobility due to the greaterinteractions between the silica and the rubber matrix InFigure 10(a) it is also seen that increasing the temperaturecaused an abrupt drop in the storage modulus before thetransition and the rubbery regions In these regions it isseen that the storage modulus increased with filler Thiscould be explained by the higher stiffness of the filled rubbervulcanizates and the hydrodynamic effects associated with


minus60 minus50 minus40 minus30 minus20 minus10 0 10 20

Temperature (∘C)

102

103

104

105

106

107

RHA30

RHA30-Si69S30S30-Si69 Gum ENR-25

Stor

age m

odul

usG

998400(M

Pa)

(a)


Temperature (∘C)

101

102

103

104

105

106

RHA30

RHA30-Si69S30Gum ENR-25

Loss

mod

ulus

G998400998400

(MPa

)S30-Si69

(b)

0

1

2

3


Temperature (∘C)

RHA30


tan 120575

(c)

Figure 10 (a) Storage modulus (b) loss modulus and (c) tan 120575 as a function of temperature of ENR-25 gum and filled vulcanizates with30 phr of RHA and silica with and without silane coupling agent (Si69)

the strong interactions between filler and rubber moleculesAlso the highest modulus of RHA filled ENR-25 vulcanizateswas found with Si69Thismight be due to increased chemicalrubber-filler interactions

In Figure 10(b) it is clear that the gum vulcanizate showsthe lowest loss modulus which might be related to themobility of the rubber molecular chains [30] It is also seenthat loss modulus peaks were comparatively broad for the

filled ENR-25 samples RHA30 RHA

30-Si69 S

30 and S

30-

Si69 This might be due to an increased energy absorptioncaused by the fillers Other reasons might be the chemicalinteractions in RHA

30-Si69 and S

30-Si69 together with the

interactions between ENR-25 and RHA or silica particleswhich restrict molecular mobility

The ratio of lossmodulus to storagemodulus is referred toas the internal damping or the loss tangent (tan 120575) and is an


indicator characterizing the dynamic behavior of materialsThe storage moduli at 20∘C (1198661015840) the maximum loss moduli(11986610158401015840) and the variation of maximum damping factor areshown in Table 5 and in Figure 10(c) It is seen that thegum vulcanizates show the lowest storage modulus and lossmodulus but the highest tan 120575 values in the glass transitionregion This indicates a large degree of mobility and hencegood damping characteristics and elastomeric propertiesTan120575 relates to the impact resistance and damping of amaterial which mainly depend on the nature of the matrixthe filler and their interface Furthermore there is frictionaldamping due to slippage in the unbound regions at theinterface of filler and matrix or interfacial delaminationand energy is dissipated by crack propagation in the matrixall of these phenomena relate to the damping properties[29] The damping peak usually occurs in the glass tran-sition region and is associated with the movement of sidegroups or low molecular-weight units within the rubbermolecules Therefore a high maximum of the damping peakor the damping factor (tan 120575max) or the peak area indicateshigh molecular mobility as observed in the ENR-25 gumvulcanizates (Figure 10(c)) In Table 5 it is clear that thegum vulcanizate shows the highest tan 120575max indicating goodmobility and damping characteristics In Figure 10(c) it isalso seen that the incorporation of fillers in the ENR-25vulcanizates decreased the damping characteristics and gavelow and broad damping peaks This might be attributed tothe filler retarding the mobility of rubber chains restrictingthe segmental motions of the rubber molecules by the strongfiller-rubber interactions It is also seen that the RHA

30-Si69

showed a lower tan 120575max than the one without silane couplingagent This may be attributed to the silane coupling agentimproving the filler-rubber interaction The decreased valueof tan 120575max suggests a relatively high filler-rubber interaction[31] The temperature at which the tan 120575 peak appears isan estimated value of the glass transition temperature (119879

119892)

and the height of the peak can be used to quantitate thereinforcement of rubber In Figure 10(c) slight differencesare seen in the 119879

119892for the gum vulcanizate and the RHA

filled ENR-25 with or without silane coupling agent (Si69)That is the filler shifted the 119879

119892for filled rubber vulcanizates

especially in the RHA filled ENR-25 with silane couplingagent towards higher temperatures This might be attributedto the crosslinking that restricts the mobility of the polymerchains or other increased rubber-filler interactions It isalso seen that the silica filled ENR-25 vulcanizate showedhigher storage (1198661015840) and lossmoduli (11986610158401015840) but lowermaximumdamping factor (tan 120575max) than the RHA filled ENR-25vulcanizates with or without silane coupling agent and thesame goes for the unfilled gums This might be due to thehigh polarity of silica with high polymer-filler and filler-fillerinteractions Hence the silica gives high reinforcing effectsand strongly restricts the segmental motions of rubber

35 Crosslink Density Figure 11 and Table 6 show the appar-ent crosslink densities based on the Flory-Rehner equation(equation (2)) for the gumand the filled ENR-25 vulcanizateswith various contents of RHA or silica with and without

0 10 20 300

50

100

150

200

250

300

RHA RHA-Si69


Appa

rent

cros

slink

den

sity

(mol

m3)

S30

S30-Si69

Figure 11 Apparent crosslink densities of gum and filled ENR-25vulcanizates with various RHAcontents and 30 phr of silica with andwithout silane coupling agent (Si69)

Table 6 Crosslink densities of gum and filled ENR-25 vulcanizateswith various RHA contents and 30 phr of silica with and withoutsilane coupling agent (Si69)

Sample Crosslink density (molm3)Gum 8336 plusmn 141RHA10

9233 plusmn 274RHA20


12987 plusmn 195RHA10-Si69 10092 plusmn 573

RHA20-Si69 13601 plusmn 316


S30

17637 plusmn 350S30-Si69 28225 plusmn 280

Si69 It can be seen that the apparent crosslink densityincreased with the RHA content In general the crosslinkdensity is the number of linkages between rubber moleculesper unit volume In the filled rubber vulcanizates the fillerparticles act as additional multifunctional crosslinking sitesinteracting physically andor chemically with the rubbermolecules That is the rubber-filler linkages contribute effec-tively increasing the crosslink density Obviously the numberof linkages increasedwithRHAor silica loadingThe additionof Si69 also increased the crosslink density especially at thehigh 20 and 30 phr filler concentrations The increases inapparent crosslink density may be caused by two differentcrosslinking reactions namely the interaction of hydroxylgroups on silica ash surfaces with the polar functionalgroups in ENR molecules (Figure 9(a)) and the crosslink-ing of SiO

2-Si69-rubber (Figure 9(b)) [32] It is also seen


0 50 100 150 20000

03

06

09

12

RHA30RHA30-Si69

S30

S30-Si69

Gum ENR-25

Temperature (∘C)

Stre

ss120590

(MPa

)

Figure 12 Stress as a function of temperature of gum and filledENR-25 vulcanizates with 30 phr of RHAand silica with andwithoutsilane coupling agent (Si69)

that the apparent crosslink density correlates well with themechanical properties that is modulus and tensile strength(Figures 6 and 7) and the dynamic mechanical properties(Figure 10) In Figure 11 it is also seen that the silica filledENR-25 vulcanizate had a higher crosslink density with Si69than without it and surpassed all the RHA filled ENR-25vulcanizatesThis might be due to the high specific surface ofsilica with hydroxyl groups on the surfaces giving chemicalinteractions The higher amount of chemically bound rubbercontent significantly improves filler dispersionwith less filler-filler interaction and higher reinforcement [33]

36 Temperature Scanning Stress Relaxation Thethermoelas-tic and relaxation behavior of the ENR-25 vulcanizates werecharacterized by the temperature scanning stress relaxation(TSSR) technique from an initial elongation of 1205760 = 50and with a heating rate of 2∘Cmin This technique hasbeen used to examine the relaxation behavior in relationto crosslink density for polymer blends as well as for filledrubber composites [21ndash23 34] Generally it can be expectedthat the stress at a constant extension initially increases withtemperature due to the entropic elasticity of rubber and athigher temperatures the physical and chemical relaxationswill counteract this trend In particular the debonding ofbound rubber from the filler surfaces the cleavage of sulfurbridges and the scission of polymer main chains contributeto relaxation

Figure 12 shows the stress as a function of the temperaturefor gum and filled ENR-25 vulcanizates with 30 phr of RHAor silica with and without silane coupling agent (Si69) Itcan be seen that initially the stress slightly increased withtemperature as expected because of the entropy effect Stressrelaxation that is the decrease of stress occurred at highertemperatures with the stress approaching zero Severe stressrelaxation is caused by thermooxidative chain scission andby degradation of crosslinks in particular cleavage of the

0 50 100 150 200

0

5

10

15

RHA30

RHA30-Si69S30

S30-Si69

Gum ENR-25

Temperature T (∘C)

Nor

mal

ized

rela

xatio

n sp

ectr

umH(T

)1205900

Figure 13 Normalized relaxation spectrums as a function oftemperature of gum and filled ENR-25 vulcanizates with 30 phr ofRHA and silica with and without silane coupling agent (Si69)

sulfur bridges which occurs at temperatures above 130∘C Incontrast the physically induced relaxation of polymer-fillerinteractions occurs at lower temperatures Also the adsorbedpolymer layer or glassy layer with polymer segments restrictsthe polymer chain mobility at the filler surface and reducesreinforcement of the vulcanizates At high temperaturesthe weak physical interactions between filler particles andpolymer segments can be overcome by thermal energy andthe polymer segments are released from the filler surface if anexternal stress is applied This is evidenced by the decreasingtrend of stress with increasing temperature that depends onthe amount of desorbed polymer segments This is evidentin the silica filled vulcanizates and can also be seen in theRHA filled vulcanizates In Figure 12 it is also seen that theinitial stress 120590

0increases with incorporation of filler This

could be explained by the higher stiffness of the filled rubbervulcanizate and by the hydrodynamic effects associated withstrong interactions between filler and rubber moleculesTherefore the incorporation of RHA or silica in ENR-25increased the initial stress relative to the gum vulcanizatesMoreover with silica filler the initial stress was higher withsilane coupling agent Si69 than without it This is attributedto the high crosslink density caused by chemical filler-rubberinteractions or to the strong polymer-filler interactionsThiscorrelates well with the trends in the mechanical propertiesnamely tensile strength and Youngrsquos modulus and with thecrosslink density However the addition of RHA leads todifferent results with respect to the initial stress The RHAfilled ENR-25 had slightly higher initial stress without silanecoupling agent Si69 The small amount of silane couplingagent used together with the low specific surface area of RHAthat reduced the availability of hydroxyl groups may havecaused the low initial stresses

Figure 13 shows the relaxation spectra 119867(119879) calculatedusing (4) To facilitate comparisons the spectra were nor-malized to show 119867(119879) relative to the initial stress It can be


(a) (b)

(c) (d)

(e)

Figure 14 SEM micrographs of gum and filled ENR-25 vulcanizates with 30 phr of RHA and silica with and without silane coupling agent(Si69) (a) gum vulcanizates (b) RHA

30 (c) RHA

30-Si69 (d) S

30 (e) S

30-Si69

seen that the relaxation spectrum of the pure ENR-25 gumvulcanizate exhibits a dominant peak at about 150∘C and abroadening shoulder peak at about 170 to 190∘CThese peaksare attributed to polymer network degradation caused by thecleavage of sulfur linkages and scission of the polymer mainchains That is the dominant peak at 150∘C corresponds tothe cleavage of long polysulfidic bonds (ndashCndashSxndashCndash) whereas

the shoulder peak at about 170 to 190∘C represents the dis-sociation of short monosulfidic and disulfidic linkages (ndashCndashSndashCndash) and the scission of main polymer chains which mightoccur at this higher temperature due to the higher bindingenergies [35] This reflects the higher binding energy of thendashCndashSndashCndash and ndashCndashCndash compared to the polysulfidic linkages(ndashCndashSxndashCndash) the thermal stability of the composite network


correlates with the highest peak temperature obtained fromthe relaxation spectra Therefore the peaks of the relaxationspectrum reflect thermal stability The relaxation spectra ofsilica filled vulcanizates differ significantly from the unfilledvulcanizates in that the peak at 170ndash190∘C almost vanishesHowever the peak at 150∘C is more or less unaffected by theaddition of silica Also a broad small peak is recognizable inthe relaxation spectra of the silica filled vulcanizates at thelower temperatures from 30 to 90∘C This is attributed to therelease of polymer segments of the glassy layer or of adsorbedpolymer layer from the filler surface [22]

In Figure 13 it is seen that addition of RHA leads to adifferent relaxation behavior That is the peaks are shiftedtowards lower temperaturesThis is presumably caused by themetal impurities in RHA which may promote degradationof the polymer network Furthermore the silanization ofRHA resulted in new chemical linkages between the polymersegments and the RHA particles This is obviously indicatedby the peak in the temperatures from 30 to 60∘C whichreflects the debonding of the glassy layer or adsorbed polymerlayer at the RHA interface The RHA filled ENR-25 vulcan-izates without Si69 have a recognizable small peak whilewith silanization that peak vanishes Furthermore the peakis much smaller than for the silica filled ENR-25 vulcanizatebecause of the difference in specific surface areas

37 Scanning Electron Microscopy Figure 14 shows SEMmicrographs of cryogenically fractured surfaces of the gumas well as the RHA and silica filled ENR-25 vulcanizatesIt is seen that the gum vulcanizate had a smooth fracturedsurface with some white ZnO particles in Figure 14(a)However the fractured surfaces of the filled vulcanizateswere rougher because of silica agglomerates Also it is clearthat the silica filled ENR vulcanizates exhibited poor fillerdistribution with rubber-rich areas indicating high filler-filler interaction (Figure 14(b)) This should lower Youngrsquosmodulus and the tensile strength Better distributions of fillerparticles are observed in the silanized samples in Figure 14(c)of RHA

30-Si69 and Figure 14(e) of S

30-Si69 This is attributed

to the functional groups of organosilane interacting withthe hydroxyl groups on silica particles and dominating thefiller-filler interactions to prevent agglomeration The RHAparticles in the ENR (Figure 14(b)) are much larger than thesilica particles This lowers the mechanical properties thecrosslink density and the reinforcement relative to the silicafiller The finer dispersion of RHA particles is observed oncomparing RHA

30-Si69 to S

30-Si69 This might be due to

the silica ash particles of RHA being more embedded in therubber blendmatrix In Figure 14 it is also seen that the Si69-treated ENR-25 filled vulcanizates exhibited improved phasecontinuity and homogeneity at the filler-rubber interfacesThis is due to the high shear mixing that dispersed particleswhile simultaneously Si69 and hydroxyl groups on RHAsurfaces interacted to prevent filler reagglomeration

4 Conclusions

Themain objective of this studywas to demonstrate the use ofrice husk ash (RHA) as an alternative filler for natural rubber

It was found that the incorporation of RHAenhanced the cur-ing characteristics of rubber and the mechanical propertiesof the vulcanizate Furthermore the RHA offers processingadvantages over silica because theRHAENR-25 vulcanizatesexhibited shorter optimum cure times and lower maximumtorques Moreover as the filler concentration increases thetensile modulus and tensile strength slightly increased butthe elongation at break decreased due to reinforcing effectsThe storage modulus was also found to increase with theloading level of RHA in the composites This is due to theincreased material stiffness The filler surface treatment withsilane coupling agent improved all of the filled vulcanizatesPolar functional groups in the rubber matrix as well as theRHA concentration had significant effects on themechanicalproperties of RHAENR-25 vulcanizates That is the polarfunctional groups combined with finely structured silica ashpromoted crosslink density degree of reinforcement andmechanical strength Moreover the in situ silanization withSi69 increased the storagemodulus and the loss modulus anddecreased the loss tangent (tan 120575) due to increased crosslink-ing and strong filler-rubber interactions Alsomorphologicalstudies indicated that the reinforcement trends observedmatched filler dispersion in the rubber matrix affected bythe chemical interactions between ethoxy groups of Si69 andENR Temperature scanning stress relaxation (TSSR) wasused to investigate the relaxation behavior of materials as afunction of temperature It was found that the metal oxidesin RHA promoted the degradation and deterioration of theENR networks Furthermore the silanization of RHA alsoresulted in chemical linkages between polymer segments andthe RHA particles However we found higher reinforcementof ENR-25 vulcanizates with silica and Si69 than with RHAand Si69 This is because of the small particle size and highspecific surface area of silica and the functional SindashOHgroupson silica surfaces Nevertheless the rice husk ash (RHA) hasgreat potential for use as reinforcement in rubber compositesimproving mechanical and other related properties

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors gratefully acknowledge the Thailand ResearchFund (TRF) through the Royal Golden Jubilee PhD Program(Grant no PHD00542553) and the Project Based PersonnelExchange Programme (PPP 2012) of the German AcademicExchange Service (DAAD) and TRF for their financial sup-portThey are also thankful for the kind support of Universityof Applied Science Osnabruck Germany for use of researchfacilities and the other support

References

[1] C S L Baker and I R Gelling ldquoEpoxidized natural rubbermdashanew synthetic polymerrdquo Rubber World vol 191 no 6 pp 15ndash20 1985


[2] Food and Agriculture Organization of the United Nations RiceMarket Monitor vol 16 Food and Agriculture Organization ofthe United Nations 2013

[3] Q Zhao B Zhang H Quan R C M Yam R K K Yuen andR K Y Li ldquoFlame retardancy of rice husk-filled high-densitypolyethylene ecocompositesrdquo Composites Science and Technol-ogy vol 69 pp 2675ndash2681 2009

[4] H-S Kim S Kim H-J Kim and H-S Yang ldquoThermal prop-erties of bio-flour-filled polyolefin composites with differentcompatibilizing agent type and contentrdquo Thermochimica Actavol 451 no 1-2 pp 181ndash188 2006

[5] H G B Premalal H Ismail and A Baharin ldquoComparison ofthemechanical properties of rice husk powder filled polypropy-lene composites with talc filled polypropylene compositesrdquoPolymer Testing vol 21 no 7 pp 833ndash839 2002

[6] A I Khalf and A A Ward ldquoUse of rice husks as potential fillerin styrene butadiene rubberlinear low density polyethyleneblends in the presence of maleic anhydriderdquo Materials andDesign vol 31 no 5 pp 2414ndash2421 2010

[7] H D Rozman Y S Yeo G S Tay and A Abubakar ldquoThemechanical and physical properties of polyurethane compositesbased on rice husk and polyethylene glycolrdquo Polymer Testingvol 22 no 6 pp 617ndash623 2003

[8] S Siriwardena H Ismail and U S Ishiaku ldquoA comparison ofwhite rice husk ash and silica as fillers in ethylene-propylene-diene terpolymer vulcanizatesrdquo Polymer International vol 50no 6 pp 707ndash713 2001

[9] W Arayapranee and G L Rempel ldquoA comparative study ofthe cure characteristics processability mechanical propertiesageing and morphology of rice husk ash silica and carbonblack filled 75 25NREPDMblendsrdquo Journal of Applied PolymerScience vol 109 no 2 pp 932ndash941 2008

[10] W Arayapranee N Naranong and G L Rempel ldquoApplicationof rice husk ash as fillers in the natural rubber industryrdquo Journalof Applied Polymer Science vol 98 no 1 pp 34ndash41 2005

[11] Z A M Ishak and A A Bakar ldquoAn investigation on thepotential of rice husk ash as fillers for epoxidized natural rubber(ENR)rdquo European Polymer Journal vol 31 no 3 pp 259ndash2691995

[12] S Attharangsan H Ismail M A Bakar and J Ismail ldquoTheeffect of rice husk powder on standardMalaysian natural rubbergrade L (SMR L) and epoxidized natural rubber (ENR 50) com-positesrdquo Polymer-Plastics Technology and Engineering vol 51no 3 pp 231ndash237 2012

[13] P Sae-Oui C Rakdee and P Thanmathorn ldquoUse of rice huskash as filler in natural rubber vulcanizates in comparison withother commercial fillersrdquo Journal of Applied Polymer Sciencevol 83 no 11 pp 2485ndash2493 2002

[14] H M Da Costa L L Y Visconte R C R Nunes and C R GFurtado ldquoThe effect of coupling agent and chemical treatmenton rice husk ash- filled natural rubber compositesrdquo Journal ofApplied Polymer Science vol 76 no 7 pp 1019ndash1027 2000

[15] DDerouet P Intharapat QN Tran F Gohier andCNakasonldquoGraft copolymers of natural rubber and poly(dimethyl(acryl-oyloxymethyl)phosphonate) (NR-g-PDMAMP) or poly(dim-ethyl(methacryloyloxyethyl)phosphonate) (NR-g-PDMMEP)from photopolymerization in latexmediumrdquo European PolymerJournal vol 45 no 3 pp 820ndash836 2009

[16] V P Della I Kuhn and D Hotza ldquoRice husk ash as an alternatesource for active silica productionrdquoMaterials Letters vol 57 pp818ndash821 2002

[17] L Guy S Daudey P Cochet and Y Bomal ldquoNew insights inthe dynamic properties of precipitated silica filled rubber usinga new high surface silicardquo Kautschuk Gummi Kunststoffe vol62 no 7-8 pp 383ndash391 2009

[18] S Thongsang and N Sombatsompop ldquoDynamic reboundbehavior of silicanatural rubber composites fly ash particlesand precipitated silicardquo Journal of Macromolecular Science PartB Physics vol 46 no 4 pp 825ndash840 2007

[19] P J Flory and J Rehner Jr ldquoStatisticalmechanics of cross-linkedpolymer networks II SwellingrdquoThe Journal of Chemical Physicsvol 11 no 11 pp 521ndash526 1943

[20] P J Flory ldquoMolecular size distribution in three dimensionalpolymers II Trifunctional branching unitsrdquo Journal of theAmerican Chemical Society vol 63 no 11 pp 3091ndash3096 1941

[21] N Vennemann K Bokamp and D Broker ldquoCrosslink densityof peroxide cured TPVrdquo Macromolecular Symposia vol 245-246 pp 641ndash650 2006

[22] N Vennemann M Wu and M Heinz ldquoThermoelastic prop-erties and relaxation behavior of S-SBRsilica vulcanizatesrdquoRubber World vol 246 no 6 pp 18ndash23 2012

[23] N Vennemann Characterization of Thermoplastic Elastomersby Means of Temperature Scanning Stress Relaxation Measure-ments Thermoplastic Elastomers A El-Sonbati Ed InTechRijeka Croatia 2012

[24] J Kruzelak C Kysela and I Hudec ldquoElastomeric magneticcompositesmdashcuring and propertiesrdquo Kautschuk Gummi Kunst-stoffe vol 61 no 9 pp 424ndash428 2008

[25] B T Poh C P Kwok and G H Lim ldquoReversion behaviour ofepoxidized natural rubberrdquo European Polymer Journal vol 31no 3 pp 223ndash226 1995

[26] M P Wagner ldquoReinforcing silicas and silicatesrdquo Rubber Chem-istry and Technology vol 49 no 3 pp 703ndash774 1976

[27] H M da Costa L L Y Visconte R C R Nunes and C R GFurtado ldquoRice husk ash filled natural rubber III Role of metaloxides in kinetics of sulfur vulcanizationrdquo Journal of AppliedPolymer Science vol 90 no 6 pp 1519ndash1531 2003

[28] A S Hashim B Azahari Y Ikeda and S Kohjiya ldquoThe effect ofbis(3-triethoxysilylpropyl) tetrasulfide on silica reinforcementof styrene-butadiene rubberrdquoRubberChemistry andTechnologyvol 71 no 2 pp 289ndash299 1998

[29] S Thongsang W Vorakhan E Wimolmala and N Som-batsompop ldquoDynamic mechanical analysis and tribologicalproperties of NR vulcanizates with fly ashprecipitated silicahybrid fillerrdquo Tribology International vol 53 pp 134ndash141 2012

[30] M Jacob B Francis SThomas and K T Varughese ldquoDynami-cal mechanical analysis of sisaloil palm hybrid fiber-reinforcednatural rubber compositesrdquo Polymer Composites vol 27 no 6pp 671ndash680 2006

[31] Y Y Luo Y QWang J P Zhong C Z He Y Z Li and Z PengldquoInteraction between fumed-silica and epoxidized natural rub-berrdquo Journal of Inorganic and Organometallic Polymers andMaterials vol 21 no 4 pp 777ndash783 2011

[32] A K Manna P P de D K Tripathy S K de and D G PeifferldquoBonding between precipitated silica and epoxidized naturalrubber in the presence of silane coupling agentrdquo Journal ofApplied Polymer Science vol 74 no 2 pp 389ndash398 1999

[33] W Keawsakul K Sahakaro W K Dierkes and J W MNoordermeer ldquoOptimization of mixing conditions for silica-reinforced natural rubber tire tread compoundsrdquoRubber Chem-istry and Technology vol 201 pp 277ndash294 2012


[34] S Pichaiyut C Nakason C Kummerlowe and N VennemannldquoThermoplastic elastomer based on epoxidized natural rub-berthermoplastic polyurethane blends influence of blendingtechniquerdquo Polymers for Advanced Technologies vol 23 no 6pp 1011ndash1019 2012

[35] N Vennemann C Schwarze and C Kummerlowe ldquoDetermi-nation of crosslink density and network structure of NR vul-canizates by means of TSSRrdquo Advanced Materials Research vol844 pp 482ndash485 2013

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


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Applied ChemistryJournal of



Theoretical ChemistryJournal of


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Analytical ChemistryInternational Journal of


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ElectrochemistryInternational Journal of



CatalystsJournal of


the overall sustainability of filled rubber production Ricehusk ash (RHA) is obtained by burning the agricultural ricehusk waste and it mainly consists of amorphous silica andresidual carbon black from combustionThe amount of silicain RHA varies between 55 and 97wt depending on thecombustion conditions Rice is the staple food of over halfof the worldrsquos population and about one-fifth of the worldrsquospopulation is engaged in rice cultivation The global riceproduction was about 750 million tons in 2013 and the huskscontribute about one-fifth by weight of the harvested anddried crops The husks contain about 20 silica Thereforesilica containing rice husk ash is generated in excess of 30million tons per year [2] Some prior research has assessed theproperties of silica ash to obtain an in-depth understandingof its behavior and has specifically tried to identify suitablemodifications to improve its performance as fillerThe poten-tial of RHA as a filler material for polymer composites hasbeen investigated with various polymers such as polyethylene(PE) [3 4] polypropylene (PP) [5] [styrene butadiene rubber(SBR)] + [linear low-density polyethylene (LLDPE)] blends[6] and polyurethane (PU) [7] In RHArubber compositesenhanced curing rate was observed with increased RHAloading levels in EPDM while contrary trends were observedin silica composites [8] In a comparative study of the curecharacteristics processability and mechanical properties ofNREPDM blends filled with RHA silica or carbon blackthe RHA filling gave the best resilience properties [9] It wasalso found that the incorporation of RHA in natural rubberresulted in lowered Mooney viscosity and shortened curetime and improved hardness but decreased tensile strengthand tear strength [10]

Influences of the two types of RHA namely black ricehusk ash (BRHA silica content of 54) and white ricehusk ash (WRHA silica content of 95) on the mechanicalproperties of epoxidized natural rubber with 50 moleepoxide (ie ENR-50) were investigated in [11] It wasfound that the WRHA exhibits overall superior vulcanizateproperties to those with BRHA The effects of RHA on theproperties of unmodified natural rubber compared withENR-50 composites were also reported [12] The resultsindicated that the NR composites exhibited longer scorchand cure times with higher tensile strength and elongationat break but lower tensile modulus than that of the ENR-50composites

To improve the mechanical properties of polymer com-posites filler surfaces have been treated with various typesof coupling agents However the most commonly used cou-pling agent in rubber compounds is bis(triethoxysilylpropyl)tetrasulfide (Si69) The effects of Si69 on the properties ofRHA filled natural rubber (NR) were investigated in [13]No improvement was found in the mechanical properties ofRHA filled vulcanizates with the silane coupling agent (Si69)This was presumably caused by the lack of silanol groups onthe RHA surfaces The effects of coupling agent (Si69) anda chemical treatment of RHA filled natural rubber were alsoinvestigated in [14] In this case the silane coupling agentmarginally improved the performance of rubber vulcanizates

In this work RHA filled ENR-25 composites with variousfiller contents were prepared Cure characteristics tensile

properties dynamical mechanical thermal analysis (DMTA)crosslink density thermoelastic properties and relaxationbehavior of RHA filled ENR-25 vulcanizates were investi-gated Furthermore an in situ modification of silica withthe silane coupling agent in the ENR-25 compounds wasinvestigated The silane coupling agent was directly addedto the internal mixer during the mixing of RHA and ENR-25 The silanization reaction might take place under themixing conditions A conventional commercial precipitatedsilica was also used as the filler to prepare composites forcomparisons between alternative fillers

2 Experimental

21 Materials Epoxidized natural rubber (ENR) with25mol epoxide was prepared in house by using preparationmethod described elsewhere [15] The high ammonia (HA)concentrated natural rubber latex used as raw materialin the preparation of ENR was manufactured by YalaLatex Industry Co Ltd (Yala Thailand) The ENR with a25mol level of epoxide groups was prepared via performicepoxidation by reacting NR latex with in situ performicacid generated from a reaction of formic acid (94 puritymanufactured by Riedel De Haen (Seelze Germany)) andhydrogen peroxide (50wt manufactured by Riedel DeHaen (Seelze Germany)) Characterization of the preparedENR was also performed by 1H-NMR Mooney viscometerand DSC Results confirmed that it was the ENR with26mol epoxide having 966 (ML 1 + 4) 100∘C and Tg ofminus4265∘CThe RHA filler was supplied byThunyakit NakhonPathom Rice Mill Co Ltd (Nakhon Pathom Thailand)The silica Ultrasil 7000GR was manufactured by EvonikIndustries (Essen Germany) The bis(triethoxysilylpropyl)tetrasulfide (Si69) was manufactured by Evonik Industries(Essen Germany) and was used as a silane coupling agentThe sulfur used as a curing agent was manufactured byPergan GmbH (Bocholt Germany) The N-tert-butyl-2benzothiazolesulfenamide (Santocure TBBS) used as anaccelerator was manufactured by Rhein Chemie RheinauGmbH (Mannheim Germany) The 13-diphenylguanidine(DPG) used as an secondary accelerator was manufacturedby Evonik Industries (Essen Germany) The zinc oxideused as a cure activator was manufactured by Lanxess(Leverkusen Germany) The other cure activator namelystearic acid was manufactured by Unichema InternationalBV (Gouda Netherlands)

22 Characterization of RHA RHAwas obtained from burn-ing of the rice husks during the rice manufacturing processWhen the burning is incomplete the result is carbonized ricehusks (CRH) Typically the particles of RHA or CRH arereduced in size by milling and further by grinding and aresieved through 120-mesh screen The powder of this typethat we obtained was placed in aluminum crucibles and putin a muffle furnace (Thermolyne 6000 furnace BarnsteadInternational Dubuque USA) and a heat treatment wasperformed at 700∘C for 6 h [16] This caused reduction of thecarbonaceous material and increased the relative content ofsilicon oxide The chemical composition and the functional






10 RHA

20 and





10-

Si69 RHA20-Si69 RHA

30-Si69 and S












120588) + 120601120588+ 1205941206012120588)

1198811(12060113

120588 minus 1206011205882) (2)











120601120588=

1

(1 + ((119898 minus 119898119889) 119898119889)) sdot (120588

119901120588119904) (3)





119867(119879) = minus119879[119889119864 (119879)

119889119879]V=const (4)






001 01 1 10 100

0

2

4

6

Diff

eren

tial v

olum

e (

)












Gum 114 56 446 384 816RHA10 144 573 429 310 461

RHA20 155 615 460 270 428

RHA30 182 771 589 240 459

RHA10-Si69 116 597 481 148 289

RHA20-Si69 123 668 545 127 269

RHA30-Si69 136 817 681 103 273

S30 513 1445 932 367 1954S30-Si69 461 1672 1211 268 928

4000 3000 2000 1000

1115

1087

3439

Silica

Rice husk ash

Tran

smitt

ance

()

3433788

468

802

473





5 10 15 20 25 300

4

8

12

16

20



RHA10RHA10-Si69


S30

S30-Si69

Gum ENR-25

Torq

ue (d

Nmiddotm

)

RHA30-Si69



30) exhibits




Table 4


Step (2)

Step (1)

Si

O

OHHO

SiO

Silica

C

C

C

CO H+

ENR

SiO O O

Si

O

H OH

C

H C

HO

SiO

O

OSiO

C CO

H

HC

C

O

H

H

2HC

2HC

CH2

CH3

CH3

CH2

CH2

CH2

CH2

CH2

3HC

3HC

3HC

2HC

2HC



119867and 119872

119871




119871but high119872

119867and torque



OC2H5

OC2H5

OC2H5

H5C2O

H5C2O

H5C2O





0 10 20 3000

05

10

15

20

25

30


RHARHA-Si69

Youn

grsquos m

odul

uss (

MPa

)

S30

S30

-Si69




0 10 20 300

4

8

12

16

20

Tens

ile st

reng

th (M

Pa)


RHARHA-Si69

S30

S30-Si69


0 10 20 300

200

400

600

800

1000

Elon

gatio

n at

bre

ak (M

Pa)


RHARHA-Si69

S30S30-Si69




SiSi

SiSi

Si

O O

O

O

O

OH

OH

OH

OH

O

O

Sx

Sx

OH

O

OHO

HO O

Sx

Filler particle

(a)

HO

Filler particle

Si

Si

SiSi

O

O

O

O

O

O

O

O

OH

OH

OH

O Sx

OH

O O

HO

Si

SiOEt

EtO Sx

SxSx

(CH2)3

(b)






Gum 74696 287 277RHA30 84164 322 269

RHA30-Si69 142810 391 196

S30 292750 325 134S30-Si69 301750 358 141




30-Si69 and S

30-Si69) This is




Temperature (∘C)

102

103

104

105

106

107

RHA30


Stor

age m

odul

usG

998400(M

Pa)

(a)


Temperature (∘C)

101

102

103

104

105

106

RHA30


Loss

mod

ulus

G998400998400

(MPa

)S30-Si69

(b)

0

1

2

3


Temperature (∘C)

RHA30


tan 120575

(c)





30-Si69 S

30 and S

30-


30-Si69 and S






30-Si69


119892)







0 10 20 300

50

100

150

200

250

300

RHA RHA-Si69


Appa

rent

cros

slink

den

sity

(mol

m3)

S30

S30-Si69









S30





0 50 100 150 20000

03

06

09

12

RHA30RHA30-Si69

S30

S30-Si69

Gum ENR-25

Temperature (∘C)

Stre

ss120590

(MPa

)





0 50 100 150 200

0

5

10

15

RHA30

RHA30-Si69S30

S30-Si69

Gum ENR-25


Nor

mal

ized

rela

xatio

n sp

ectr

umH(T

)1205900







(a) (b)

(c) (d)

(e)


30 (c) RHA

30-Si69 (d) S

30 (e) S

30-Si69










30-Si69 to S



4 Conclusions





Acknowledgments


References















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of






10 RHA

20 and





10-

Si69 RHA20-Si69 RHA

30-Si69 and S












120588) + 120601120588+ 1205941206012120588)

1198811(12060113

120588 minus 1206011205882) (2)











120601120588=

1

(1 + ((119898 minus 119898119889) 119898119889)) sdot (120588

119901120588119904) (3)





119867(119879) = minus119879[119889119864 (119879)

119889119879]V=const (4)






001 01 1 10 100

0

2

4

6

Diff

eren

tial v

olum

e (

)












Gum 114 56 446 384 816RHA10 144 573 429 310 461

RHA20 155 615 460 270 428

RHA30 182 771 589 240 459

RHA10-Si69 116 597 481 148 289

RHA20-Si69 123 668 545 127 269

RHA30-Si69 136 817 681 103 273

S30 513 1445 932 367 1954S30-Si69 461 1672 1211 268 928

4000 3000 2000 1000

1115

1087

3439

Silica

Rice husk ash

Tran

smitt

ance

()

3433788

468

802

473





5 10 15 20 25 300

4

8

12

16

20



RHA10RHA10-Si69


S30

S30-Si69

Gum ENR-25

Torq

ue (d

Nmiddotm

)

RHA30-Si69



30) exhibits




Table 4


Step (2)

Step (1)

Si

O

OHHO

SiO

Silica

C

C

C

CO H+

ENR

SiO O O

Si

O

H OH

C

H C

HO

SiO

O

OSiO

C CO

H

HC

C

O

H

H

2HC

2HC

CH2

CH3

CH3

CH2

CH2

CH2

CH2

CH2

3HC

3HC

3HC

2HC

2HC



119867and 119872

119871




119871but high119872

119867and torque



OC2H5

OC2H5

OC2H5

H5C2O

H5C2O

H5C2O





0 10 20 3000

05

10

15

20

25

30


RHARHA-Si69

Youn

grsquos m

odul

uss (

MPa

)

S30

S30

-Si69




0 10 20 300

4

8

12

16

20

Tens

ile st

reng

th (M

Pa)


RHARHA-Si69

S30

S30-Si69


0 10 20 300

200

400

600

800

1000

Elon

gatio

n at

bre

ak (M

Pa)


RHARHA-Si69

S30S30-Si69




SiSi

SiSi

Si

O O

O

O

O

OH

OH

OH

OH

O

O

Sx

Sx

OH

O

OHO

HO O

Sx

Filler particle

(a)

HO

Filler particle

Si

Si

SiSi

O

O

O

O

O

O

O

O

OH

OH

OH

O Sx

OH

O O

HO

Si

SiOEt

EtO Sx

SxSx

(CH2)3

(b)






Gum 74696 287 277RHA30 84164 322 269

RHA30-Si69 142810 391 196

S30 292750 325 134S30-Si69 301750 358 141




30-Si69 and S

30-Si69) This is




Temperature (∘C)

102

103

104

105

106

107

RHA30


Stor

age m

odul

usG

998400(M

Pa)

(a)


Temperature (∘C)

101

102

103

104

105

106

RHA30


Loss

mod

ulus

G998400998400

(MPa

)S30-Si69

(b)

0

1

2

3


Temperature (∘C)

RHA30


tan 120575

(c)





30-Si69 S

30 and S

30-


30-Si69 and S






30-Si69


119892)







0 10 20 300

50

100

150

200

250

300

RHA RHA-Si69


Appa

rent

cros

slink

den

sity

(mol

m3)

S30

S30-Si69









S30





0 50 100 150 20000

03

06

09

12

RHA30RHA30-Si69

S30

S30-Si69

Gum ENR-25

Temperature (∘C)

Stre

ss120590

(MPa

)





0 50 100 150 200

0

5

10

15

RHA30

RHA30-Si69S30

S30-Si69

Gum ENR-25


Nor

mal

ized

rela

xatio

n sp

ectr

umH(T

)1205900







(a) (b)

(c) (d)

(e)


30 (c) RHA

30-Si69 (d) S

30 (e) S

30-Si69










30-Si69 to S



4 Conclusions





Acknowledgments


References















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of








120601120588=

1

(1 + ((119898 minus 119898119889) 119898119889)) sdot (120588

119901120588119904) (3)





119867(119879) = minus119879[119889119864 (119879)

119889119879]V=const (4)






001 01 1 10 100

0

2

4

6

Diff

eren

tial v

olum

e (

)












Gum 114 56 446 384 816RHA10 144 573 429 310 461

RHA20 155 615 460 270 428

RHA30 182 771 589 240 459

RHA10-Si69 116 597 481 148 289

RHA20-Si69 123 668 545 127 269

RHA30-Si69 136 817 681 103 273

S30 513 1445 932 367 1954S30-Si69 461 1672 1211 268 928

4000 3000 2000 1000

1115

1087

3439

Silica

Rice husk ash

Tran

smitt

ance

()

3433788

468

802

473





5 10 15 20 25 300

4

8

12

16

20



RHA10RHA10-Si69


S30

S30-Si69

Gum ENR-25

Torq

ue (d

Nmiddotm

)

RHA30-Si69



30) exhibits




Table 4


Step (2)

Step (1)

Si

O

OHHO

SiO

Silica

C

C

C

CO H+

ENR

SiO O O

Si

O

H OH

C

H C

HO

SiO

O

OSiO

C CO

H

HC

C

O

H

H

2HC

2HC

CH2

CH3

CH3

CH2

CH2

CH2

CH2

CH2

3HC

3HC

3HC

2HC

2HC



119867and 119872

119871




119871but high119872

119867and torque



OC2H5

OC2H5

OC2H5

H5C2O

H5C2O

H5C2O





0 10 20 3000

05

10

15

20

25

30


RHARHA-Si69

Youn

grsquos m

odul

uss (

MPa

)

S30

S30

-Si69




0 10 20 300

4

8

12

16

20

Tens

ile st

reng

th (M

Pa)


RHARHA-Si69

S30

S30-Si69


0 10 20 300

200

400

600

800

1000

Elon

gatio

n at

bre

ak (M

Pa)


RHARHA-Si69

S30S30-Si69




SiSi

SiSi

Si

O O

O

O

O

OH

OH

OH

OH

O

O

Sx

Sx

OH

O

OHO

HO O

Sx

Filler particle

(a)

HO

Filler particle

Si

Si

SiSi

O

O

O

O

O

O

O

O

OH

OH

OH

O Sx

OH

O O

HO

Si

SiOEt

EtO Sx

SxSx

(CH2)3

(b)






Gum 74696 287 277RHA30 84164 322 269

RHA30-Si69 142810 391 196

S30 292750 325 134S30-Si69 301750 358 141




30-Si69 and S

30-Si69) This is




Temperature (∘C)

102

103

104

105

106

107

RHA30


Stor

age m

odul

usG

998400(M

Pa)

(a)


Temperature (∘C)

101

102

103

104

105

106

RHA30


Loss

mod

ulus

G998400998400

(MPa

)S30-Si69

(b)

0

1

2

3


Temperature (∘C)

RHA30


tan 120575

(c)





30-Si69 S

30 and S

30-


30-Si69 and S






30-Si69


119892)







0 10 20 300

50

100

150

200

250

300

RHA RHA-Si69


Appa

rent

cros

slink

den

sity

(mol

m3)

S30

S30-Si69









S30





0 50 100 150 20000

03

06

09

12

RHA30RHA30-Si69

S30

S30-Si69

Gum ENR-25

Temperature (∘C)

Stre

ss120590

(MPa

)





0 50 100 150 200

0

5

10

15

RHA30

RHA30-Si69S30

S30-Si69

Gum ENR-25


Nor

mal

ized

rela

xatio

n sp

ectr

umH(T

)1205900







(a) (b)

(c) (d)

(e)


30 (c) RHA

30-Si69 (d) S

30 (e) S

30-Si69










30-Si69 to S



4 Conclusions





Acknowledgments


References















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of








Gum 114 56 446 384 816RHA10 144 573 429 310 461

RHA20 155 615 460 270 428

RHA30 182 771 589 240 459

RHA10-Si69 116 597 481 148 289

RHA20-Si69 123 668 545 127 269

RHA30-Si69 136 817 681 103 273

S30 513 1445 932 367 1954S30-Si69 461 1672 1211 268 928

4000 3000 2000 1000

1115

1087

3439

Silica

Rice husk ash

Tran

smitt

ance

()

3433788

468

802

473





5 10 15 20 25 300

4

8

12

16

20



RHA10RHA10-Si69


S30

S30-Si69

Gum ENR-25

Torq

ue (d

Nmiddotm

)

RHA30-Si69



30) exhibits




Table 4


Step (2)

Step (1)

Si

O

OHHO

SiO

Silica

C

C

C

CO H+

ENR

SiO O O

Si

O

H OH

C

H C

HO

SiO

O

OSiO

C CO

H

HC

C

O

H

H

2HC

2HC

CH2

CH3

CH3

CH2

CH2

CH2

CH2

CH2

3HC

3HC

3HC

2HC

2HC



119867and 119872

119871




119871but high119872

119867and torque



OC2H5

OC2H5

OC2H5

H5C2O

H5C2O

H5C2O





0 10 20 3000

05

10

15

20

25

30


RHARHA-Si69

Youn

grsquos m

odul

uss (

MPa

)

S30

S30

-Si69




0 10 20 300

4

8

12

16

20

Tens

ile st

reng

th (M

Pa)


RHARHA-Si69

S30

S30-Si69


0 10 20 300

200

400

600

800

1000

Elon

gatio

n at

bre

ak (M

Pa)


RHARHA-Si69

S30S30-Si69




SiSi

SiSi

Si

O O

O

O

O

OH

OH

OH

OH

O

O

Sx

Sx

OH

O

OHO

HO O

Sx

Filler particle

(a)

HO

Filler particle

Si

Si

SiSi

O

O

O

O

O

O

O

O

OH

OH

OH

O Sx

OH

O O

HO

Si

SiOEt

EtO Sx

SxSx

(CH2)3

(b)






Gum 74696 287 277RHA30 84164 322 269

RHA30-Si69 142810 391 196

S30 292750 325 134S30-Si69 301750 358 141




30-Si69 and S

30-Si69) This is




Temperature (∘C)

102

103

104

105

106

107

RHA30


Stor

age m

odul

usG

998400(M

Pa)

(a)


Temperature (∘C)

101

102

103

104

105

106

RHA30


Loss

mod

ulus

G998400998400

(MPa

)S30-Si69

(b)

0

1

2

3


Temperature (∘C)

RHA30


tan 120575

(c)





30-Si69 S

30 and S

30-


30-Si69 and S






30-Si69


119892)







0 10 20 300

50

100

150

200

250

300

RHA RHA-Si69


Appa

rent

cros

slink

den

sity

(mol

m3)

S30

S30-Si69









S30





0 50 100 150 20000

03

06

09

12

RHA30RHA30-Si69

S30

S30-Si69

Gum ENR-25

Temperature (∘C)

Stre

ss120590

(MPa

)





0 50 100 150 200

0

5

10

15

RHA30

RHA30-Si69S30

S30-Si69

Gum ENR-25


Nor

mal

ized

rela

xatio

n sp

ectr

umH(T

)1205900







(a) (b)

(c) (d)

(e)


30 (c) RHA

30-Si69 (d) S

30 (e) S

30-Si69










30-Si69 to S



4 Conclusions





Acknowledgments


References















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


Step (2)

Step (1)

Si

O

OHHO

SiO

Silica

C

C

C

CO H+

ENR

SiO O O

Si

O

H OH

C

H C

HO

SiO

O

OSiO

C CO

H

HC

C

O

H

H

2HC

2HC

CH2

CH3

CH3

CH2

CH2

CH2

CH2

CH2

3HC

3HC

3HC

2HC

2HC



119867and 119872

119871




119871but high119872

119867and torque



OC2H5

OC2H5

OC2H5

H5C2O

H5C2O

H5C2O





0 10 20 3000

05

10

15

20

25

30


RHARHA-Si69

Youn

grsquos m

odul

uss (

MPa

)

S30

S30

-Si69




0 10 20 300

4

8

12

16

20

Tens

ile st

reng

th (M

Pa)


RHARHA-Si69

S30

S30-Si69


0 10 20 300

200

400

600

800

1000

Elon

gatio

n at

bre

ak (M

Pa)


RHARHA-Si69

S30S30-Si69




SiSi

SiSi

Si

O O

O

O

O

OH

OH

OH

OH

O

O

Sx

Sx

OH

O

OHO

HO O

Sx

Filler particle

(a)

HO

Filler particle

Si

Si

SiSi

O

O

O

O

O

O

O

O

OH

OH

OH

O Sx

OH

O O

HO

Si

SiOEt

EtO Sx

SxSx

(CH2)3

(b)






Gum 74696 287 277RHA30 84164 322 269

RHA30-Si69 142810 391 196

S30 292750 325 134S30-Si69 301750 358 141




30-Si69 and S

30-Si69) This is




Temperature (∘C)

102

103

104

105

106

107

RHA30


Stor

age m

odul

usG

998400(M

Pa)

(a)


Temperature (∘C)

101

102

103

104

105

106

RHA30


Loss

mod

ulus

G998400998400

(MPa

)S30-Si69

(b)

0

1

2

3


Temperature (∘C)

RHA30


tan 120575

(c)





30-Si69 S

30 and S

30-


30-Si69 and S






30-Si69


119892)







0 10 20 300

50

100

150

200

250

300

RHA RHA-Si69


Appa

rent

cros

slink

den

sity

(mol

m3)

S30

S30-Si69









S30





0 50 100 150 20000

03

06

09

12

RHA30RHA30-Si69

S30

S30-Si69

Gum ENR-25

Temperature (∘C)

Stre

ss120590

(MPa

)





0 50 100 150 200

0

5

10

15

RHA30

RHA30-Si69S30

S30-Si69

Gum ENR-25


Nor

mal

ized

rela

xatio

n sp

ectr

umH(T

)1205900







(a) (b)

(c) (d)

(e)


30 (c) RHA

30-Si69 (d) S

30 (e) S

30-Si69










30-Si69 to S



4 Conclusions





Acknowledgments


References















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0 10 20 3000

05

10

15

20

25

30


RHARHA-Si69

Youn

grsquos m

odul

uss (

MPa

)

S30

S30

-Si69




0 10 20 300

4

8

12

16

20

Tens

ile st

reng

th (M

Pa)


RHARHA-Si69

S30

S30-Si69


0 10 20 300

200

400

600

800

1000

Elon

gatio

n at

bre

ak (M

Pa)


RHARHA-Si69

S30S30-Si69




SiSi

SiSi

Si

O O

O

O

O

OH

OH

OH

OH

O

O

Sx

Sx

OH

O

OHO

HO O

Sx

Filler particle

(a)

HO

Filler particle

Si

Si

SiSi

O

O

O

O

O

O

O

O

OH

OH

OH

O Sx

OH

O O

HO

Si

SiOEt

EtO Sx

SxSx

(CH2)3

(b)






Gum 74696 287 277RHA30 84164 322 269

RHA30-Si69 142810 391 196

S30 292750 325 134S30-Si69 301750 358 141




30-Si69 and S

30-Si69) This is




Temperature (∘C)

102

103

104

105

106

107

RHA30


Stor

age m

odul

usG

998400(M

Pa)

(a)


Temperature (∘C)

101

102

103

104

105

106

RHA30


Loss

mod

ulus

G998400998400

(MPa

)S30-Si69

(b)

0

1

2

3


Temperature (∘C)

RHA30


tan 120575

(c)





30-Si69 S

30 and S

30-


30-Si69 and S






30-Si69


119892)







0 10 20 300

50

100

150

200

250

300

RHA RHA-Si69


Appa

rent

cros

slink

den

sity

(mol

m3)

S30

S30-Si69









S30





0 50 100 150 20000

03

06

09

12

RHA30RHA30-Si69

S30

S30-Si69

Gum ENR-25

Temperature (∘C)

Stre

ss120590

(MPa

)





0 50 100 150 200

0

5

10

15

RHA30

RHA30-Si69S30

S30-Si69

Gum ENR-25


Nor

mal

ized

rela

xatio

n sp

ectr

umH(T

)1205900







(a) (b)

(c) (d)

(e)


30 (c) RHA

30-Si69 (d) S

30 (e) S

30-Si69










30-Si69 to S



4 Conclusions





Acknowledgments


References















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


SiSi

SiSi

Si

O O

O

O

O

OH

OH

OH

OH

O

O

Sx

Sx

OH

O

OHO

HO O

Sx

Filler particle

(a)

HO

Filler particle

Si

Si

SiSi

O

O

O

O

O

O

O

O

OH

OH

OH

O Sx

OH

O O

HO

Si

SiOEt

EtO Sx

SxSx

(CH2)3

(b)






Gum 74696 287 277RHA30 84164 322 269

RHA30-Si69 142810 391 196

S30 292750 325 134S30-Si69 301750 358 141




30-Si69 and S

30-Si69) This is




Temperature (∘C)

102

103

104

105

106

107

RHA30


Stor

age m

odul

usG

998400(M

Pa)

(a)


Temperature (∘C)

101

102

103

104

105

106

RHA30


Loss

mod

ulus

G998400998400

(MPa

)S30-Si69

(b)

0

1

2

3


Temperature (∘C)

RHA30


tan 120575

(c)





30-Si69 S

30 and S

30-


30-Si69 and S






30-Si69


119892)







0 10 20 300

50

100

150

200

250

300

RHA RHA-Si69


Appa

rent

cros

slink

den

sity

(mol

m3)

S30

S30-Si69









S30





0 50 100 150 20000

03

06

09

12

RHA30RHA30-Si69

S30

S30-Si69

Gum ENR-25

Temperature (∘C)

Stre

ss120590

(MPa

)





0 50 100 150 200

0

5

10

15

RHA30

RHA30-Si69S30

S30-Si69

Gum ENR-25


Nor

mal

ized

rela

xatio

n sp

ectr

umH(T

)1205900







(a) (b)

(c) (d)

(e)


30 (c) RHA

30-Si69 (d) S

30 (e) S

30-Si69










30-Si69 to S



4 Conclusions





Acknowledgments


References















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



Temperature (∘C)

102

103

104

105

106

107

RHA30


Stor

age m

odul

usG

998400(M

Pa)

(a)


Temperature (∘C)

101

102

103

104

105

106

RHA30


Loss

mod

ulus

G998400998400

(MPa

)S30-Si69

(b)

0

1

2

3


Temperature (∘C)

RHA30


tan 120575

(c)





30-Si69 S

30 and S

30-


30-Si69 and S






30-Si69


119892)







0 10 20 300

50

100

150

200

250

300

RHA RHA-Si69


Appa

rent

cros

slink

den

sity

(mol

m3)

S30

S30-Si69









S30





0 50 100 150 20000

03

06

09

12

RHA30RHA30-Si69

S30

S30-Si69

Gum ENR-25

Temperature (∘C)

Stre

ss120590

(MPa

)





0 50 100 150 200

0

5

10

15

RHA30

RHA30-Si69S30

S30-Si69

Gum ENR-25


Nor

mal

ized

rela

xatio

n sp

ectr

umH(T

)1205900







(a) (b)

(c) (d)

(e)


30 (c) RHA

30-Si69 (d) S

30 (e) S

30-Si69










30-Si69 to S



4 Conclusions





Acknowledgments


References















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



30-Si69


119892)







0 10 20 300

50

100

150

200

250

300

RHA RHA-Si69


Appa

rent

cros

slink

den

sity

(mol

m3)

S30

S30-Si69









S30





0 50 100 150 20000

03

06

09

12

RHA30RHA30-Si69

S30

S30-Si69

Gum ENR-25

Temperature (∘C)

Stre

ss120590

(MPa

)





0 50 100 150 200

0

5

10

15

RHA30

RHA30-Si69S30

S30-Si69

Gum ENR-25


Nor

mal

ized

rela

xatio

n sp

ectr

umH(T

)1205900







(a) (b)

(c) (d)

(e)


30 (c) RHA

30-Si69 (d) S

30 (e) S

30-Si69










30-Si69 to S



4 Conclusions





Acknowledgments


References















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0 50 100 150 20000

03

06

09

12

RHA30RHA30-Si69

S30

S30-Si69

Gum ENR-25

Temperature (∘C)

Stre

ss120590

(MPa

)





0 50 100 150 200

0

5

10

15

RHA30

RHA30-Si69S30

S30-Si69

Gum ENR-25


Nor

mal

ized

rela

xatio

n sp

ectr

umH(T

)1205900







(a) (b)

(c) (d)

(e)


30 (c) RHA

30-Si69 (d) S

30 (e) S

30-Si69










30-Si69 to S



4 Conclusions





Acknowledgments


References















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


(a) (b)

(c) (d)

(e)


30 (c) RHA

30-Si69 (d) S

30 (e) S

30-Si69










30-Si69 to S



4 Conclusions





Acknowledgments


References















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of








30-Si69 to S



4 Conclusions





Acknowledgments


References















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of














































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of













Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of










Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

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Research Article Influence of Filler from a Renewable Resource …downloads.hindawi.com/journals/jchem/2015/796459.pdf · properties of unmodi ed natural rubber, compared with ENR-