Mechanical, Chemical, And Curing Characteristics of Cardanol–Furfural-based Novolac Resin for Application in Green Coatings

Mechanical, chemical, and curing characteristics of cardanolfurfural-based novolac resin for application in green coatings

Riya Srivastava, Deepak Srivastava

American Coatings Association 2015

Abstract The present research work focuses on themechanical, chemical, and curing characteristics ofnovolac resin based on renewable resource materialssuch as cardanol and furfural. Cardanol, a metasubsti-tuted phenol, is a renewable organic resource obtainedas a byproduct of the cashew industry. Furfural, anaromatic aldehyde, is also a renewable resourceobtained as an agricultural waste product. Novolacresin has been synthesized by the condensation ofcardanol with furfural in the presence of an oxalic acidcatalyst and using varied molar proportions of thereacting monomers. The reaction was performed at120C. The progress of the reaction was monitored bydetermining the free formaldehyde and free phenolcontent. The prepared cardanolfurfural-based novo-lac resins were further characterized by various tech-niques such as infrared and nuclear magneticresonance spectroscopic analysis. The resins werecured using the most suitable agent, hexamethylene-tetramine. The differential scanning calorimetric tech-nique was used to investigate the curing behavior ofthe prepared samples. The cured film samples wereused for the determination of mechanical propertiessuch as adhesion, flexibility, scratch hardness, gloss,and impact resistance; these cured film samples werealso used to observe the effect of various chemicals andsolvents (chemical resistance properties) such as sul-furic acid, acetic acid, sodium hydroxide, sodiumcarbonate and methanol, methyl ethyl ketone, xylene,and deionized water, respectively, on the surface of thefilm. The resulting coatings based on prepared carda-

nolfurfural resin were found to have excellentmechanical and chemical resistance properties.

Keywords Renewable resource, Cardanol, Furfural,FTIR, NMR, DSC, Coatings

Introduction

Increasing environmental concerns have opened sig-nificant opportunities for polymers from renewableresources. The utilization of renewable resources inpolymers and coating applications is receiving increas-ing attention and has been the subject of keen interestamong both academic and industrial researchers.13

The need to reduce the use of petrochemical-derivedmonomers in the manufacture of polymers is evident asa result of spiraling cost and the high rate of depletionof petrochemical-derived stocks. This requires theinvestigation and use of renewable resources whichcan serve as alternative feedstocks of monomers forthe polymer industry.4 Among the renewable re-sources, cashew nut shell liquid (CNSL), an agricul-tural renewable resource material obtained as abyproduct of the cashew processing industry, is uniquein that it possesses phenolic moiety with an unsatu-rated 15-carbon side chain, as shown in Scheme 1.5

Cardanol, a natural metasubstituted alkyl phenol fromCNSL, can be regarded as a versatile and valuable rawmaterial for polymer production,68 and like phenol, itcan be condensed with active hydrogen-containingcompounds to yield a series of phenolic resins, forinstance, base-catalyzed resoles and acid-catalyzednovolacs.9 Resins derived from CNSL/cardanol arewidely employed in the field of surface coatings,adhesives, and laminates, and have several miscella-neous applications.10

Furfural, the heteroaryl aldehyde, is obtained as anagricultural waste product which has an extensive

R. Srivastava, D. Srivastava (&)Department of Plastic Technology, H. B. TechnologicalInstitute, Kanpur 208002, Indiae-mail: [email protected]

R. Srivastavae-mail: [email protected]

J. Coat. Technol. Res., 12 (2) 303311, 2015

DOI 10.1007/s11998-014-9630-7

303

application in the formation of resins.11 Several resinshave been prepared by using cardanyl acrylate andfurfural in the presence of an acid catalyst and aselective organic compound, and their thermal prop-erties have been studied.12

Novolac resins based on phenolfurfural havealready been discussed in previous publications.9,10

The synthesis of cardanolformaldehyde resins havebeen reported earlier.1315 However, these have somelimitations, like weak chemical stability, low flexibility,and weak impact resistance.16 Therefore, the cardanolformaldehyde resins may be further modified byreplacing formaldehyde with an aromatic aldehydesuch as furfural in the presence of a suitable catalyst toimprove the chemical and mechanical stability of suchcardanol-novolac resins. Since the study of mechanical,chemical, and curing properties of cardanolfurfuralresins has hardly been investigated so far, the presentwork is concerned with the mechanical, chemical, andcuring characteristics of cardanolfurfural resin forapplication in green coatings, as these coatings arederived from renewable resources (cardanol and fur-fural).

Experimental

Materials

Cardanol was procured from M/s Dheer GramodyogLtd., Kanpur, India. Furfural (A.R. grade) wasobtained from Qualikems Fine Chemicals Pvt. Ltd.,New Delhi, India, and was used for formylation.Succinic acid and hexamethylenetetramine (HMTA)were received from Central Drug House Ltd. (CDH),Mumbai and New Delhi, India, respectively. Methanolwas used to dissolve the free catalyst and was receivedfrom M/s Thomas Baker Chemicals Ltd., Mumbai,India. Powdered soap was procured from the localmarket.

Analysis of cardanol

Cardanol was subjected to extensive analysis for thedetermination of iodine value, viscosity, and specificgravity as per the procedures mentioned in IS-Standard840-1964 (refer to Table 1).

Methods

Synthesis of cardanolfurfural-based novolac resin

Cardanolfurfural-based novolac resins were synthe-sized from cardanol and furfural in the mole ratios 1:0.5,1:0.6, 1:0.7, and 1:0.8 using oxalic acid as a catalyst by amethod published in the literature for cardanolform-aldehyde resin.16 Four samples of cardanolfurfuralnovolacs were prepared using four different mole ratiosas mentioned earlier (refer to Table 2). Under warmconditions, the catalyst (1% based on cardanol) wasdissolved in 5 mL methanol. In a three-necked round-bottomed flask containing cardanol, with a mechanicalstirrer and distillation unit attached, furfural was addeddropwise through a dropping funnel along with thecatalyst solution. The formation of multinuclear card-anolfurfural resin (Scheme 2) might occur when thereaction mixture was heated under constant stirring at atemperature of 120C. The reaction mixture was with-drawn after every 45 min to determine the free form-aldehyde content (as per ASTM standard D1312-56)and free phenol content (as per ISO standard 9397) forchecking the completion of the reaction. The pH of thereaction mixture was found to be 2 at the end of thereaction. The final resinous product was collected anddried under vacuum at 60C overnight. Finally, the resinwas purified by column chromatography. A resinsolution prepared with n-hexane, charged to the silicagel column chromatographic purification, was adoptedmainly to remove the unreacted components, impuri-ties, etc., from the methylolated cardanol. Purificationwas accomplished by using the eluent mixture of ethylacetatebenzene (60:40).

Curing of cardanolfurfural-based novolac resin

A process mentioned elsewhere17 was adopted for curingof the cardanolfurfural-based novolac resin by usingHMTA. HMTA is the most widely used agent for curingprocesses of novolac resins.18,19 Novolac resins made fromcardanol and furfural at four different mole ratios, viz. 1:0.5,1:0.6, 1:0.7, and 1:0.8, were cured by the addition of 15%HMTA. The mixtures of novolac resin and curing agentwere taken in small glass vials and mixed uniformly with thehelp of a glass rod at room temperature. Thereafter, theglass vials were kept in a preheated air oven.

Coating of panels

The prepared samples of cardanolfurfural novolacresins were mixed with 15% HMTA and stirred well toget a homogenous coating mixture. For the mechanicalproperties of the films, the mild steel panels werecleaned well with mineral turpentine oil (MTO) anddetergent such as powdered soap and finally withmethanol, and dried in an oven at 100C for 20 min.Panels were then uniformly coated with the prepared

OH

(CH2)7(CH=CH)(CH2)5CH3

Structure of Cardanol

Scheme 1: Structure of cardanol


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homogenous mixture by using a Bird Film Applicator(M/s Sheen Instruments Ltd.). Resin-coated panelswere then subjected to the hot air oven for curing theapplied films. For chemical resistance of the films, glasspanels were used instead of mild steel panels. All of thecoating films were cured at 160C but at different timeintervals, as mentioned in Table 3.

EVALUATION OF MECHANICAL PROPERTIES OF FILMS: Allthe resin-coated panels were used for the evaluation ofcured film properties such as scratch hardness,adhesion, flexibility, gloss, and impact resistance.

EVALUATION OF CHEMICAL RESISTANCE PROPERTIES OF

FILMS: Each resin-coated panel was used for theevaluation of chemical resistance properties of the curedfilms such as acids, alkalis, deionized water, and solvents.

Characterization of cardanolfurfural basednovolac resin

Fourier-transform infrared (FTIR) spectroscopicanalysis

The purified resin was subjected to Fourier transforminfrared (FTIR) spectroscopic analysis to monitor theformation or disappearance of various functionalgroups using a Perkin-Elmer (Model 843) infraredspectrophotometer in the wavelength range of 5004000 cm1. Potassium bromide (KBr) pellets wereused to get the spectra of uncured material.

1H-NMR spectroscopic analysis

1H-NMR (nuclear magnetic resonance) of the purifiedcardanolfurfural-novolac resin was recorded using a Jeol-LA 500 NMR spectrophotometer. About 20 mg of thesample, in a 10 mm diameter sample tube, was dissolved inabout 5 mL of chloroform-d1 (CDCl3), which was used asolvent along with tetramethylsilane (TMS) as an internalstandard. Finally, the spectra were recorded on a computer.

Differential scanning calorimetry (DSC)

Differential scanning calorimetric (DSC) analysis of theprepared samples were carried out to investigate thecuring behavior of the cardanolfurfural novolac resins.Cure temperatures of the prepared samples wereobserved by taking a small amount of sample into ashallow aluminium pan sealed by the aluminium coverof a differential scanning calorimeter (TA instrument,USA; modulated DSC-2920). This was placed in asample cell of the instrument; the starting temperature,programmed rate, and final temperature were taken at aheating rate of 10C/min. Dynamic scans were obtainedwhich were used for assuming the cure temperature.

Mechanical properties of the prepared films

Scratch hardness tester

The scratch hardness of the films of cardanolfurfuralnovolac resins were checked by an automatic scratchhardness tester (M/s Sheen Instruments Ltd., UK).

Cardanol

Cardanolfurfural novolac resin

Cured by addition of 15% HMTA

(1 mol)

Oxalic acid(1% based on cardanol)

Furfural(0.5 mol)

Catalyst

120 C

160 C

Scheme 2: Synthesis of cardanolfurfural-based novolacresin

Table 1: Physical characteristics of cardanol

Properties Calculatedvalue

Literaturevalue

Viscosity (cP) 39.4 32.0Specific gravity (g/m3) 0.90 0.87Iodine value (Wijs) 278.8 279.8Moisture content at 100C (wt%) 2.91 2.6

Table 2: Sample designation and reaction conditionsfor synthesized novolac samples

S.no.

Cardanol(mol)

Furfural(mol)

Samplecodes ofnovolac

resin

Reactiontime(min)

Reactiontemperature

(C)

1 1.0 0.5 FFNR51 360 1202 1.0 0.6 FFNR61 360 1203 1.0 0.7 FFNR71 360 1204 1.0 0.8 FFNR81 360 120


305

Impact hardness tester

The impact hardness of the films of the preparednovolac resins were tested using a tubular impacthardness tester (M/s Khusboo Scientific, Mumbai).

Cylindrical mandrel

The adhesion and flexibility of the cured films ofcardanolfurfural resins were tested using a cylindricalmandrel (M/s Sheen Instruments Ltd., Model: 809),with the mandrel of the diameters 1/12 to 1.3 of aninch.

Gloss

Gloss was measured using a triglossometer (M/s SheenInstruments Ltd., UK). Watching the films from 60angles, it was observed that all the coating films hadgood gloss.

Chemical resistance of the prepared films

For chemical resistance testing, the panels wereprepared by applying the resin mixture to150 9 50 9 1.25 mm glass panels by using a Bird FilmApplicator (Sheen Instruments Ltd., UK). A dry filmthickness of about 100 lm was maintained throughouton all the panels.

Results and discussion

Analysis of cardanol

An analysis of cardanol is necessary to understand andcontrol the synthesis of phenolic resins. In this relation,the iodine value is required to determine the presenceof a degree of unsaturation in the cardanol molecule.Moreover, the viscosity and specific gravity is alsorequired for the synthesis of novolac resin. Theanalytical data of cardanol was compared with stan-dard technical CNSL. The lesser ash content andnonself-polymerized fractions were indicated by therelatively lesser viscosity (41.3 cP) of the cardanol, incomparison with that of standard technical CNSL (552cP). The specific gravity of cardanol (0.9 g/cm3) was

also relatively lower than standard CNSL (0.960g/cm3), due to lower ash content and self-polymerizedfraction. The degree of unsaturation in cardanol isdetermined experimentally by the iodine value, whichwas found to be 278.8 Wijs. Wijs is the standard unit ofiodine value. These observations provided evidencethat cardanol is a monoene metasubstituted phenol andits empirical formula is written as C21H34O. This wasalso given in our earlier studies20,21 for differentsystems. The structure of cardanol may be proposedas shown in Scheme 1.

Synthesis of cardanolfurfural-based novolac resin

The methylolation of cardanol was carried out withfurfural in the presence of dicarboxylic acid, viz.succinic acid using four different mole ratios. Thecompletion of the methylolation reaction was checkedby the periodic withdrawal of the reaction mixture toanalyze free formaldehyde content and free phenolcontent.

The polymerization of cardanol can be accom-plished in two ways: firstly, by the condensation offurfural, and secondly, through the unsaturation pres-ent in the side chain. The side chain of cardanolremained unaffected, because it is clear from themeasure of the iodine value.22 The iodine value ofcardanol before polymerization was 278.8 Wijs andafter polymerization the iodine value of the reactionproduct was found to be 278.2 Wijs. Therefore, it wasconcluded that the polymerization proceeded by thefirst way, i.e., by the complicated step-growth poly-merization reaction mechanism.23 The proposed mech-anism of the reaction between cardanol and furfuralwas based on the literature published earlier.24 Themechanism of formation of novolac oligomers in acidicmedia, using an excess of cardanol over furfural, mightproceed through the following steps. First, a furan-substituted methylene glycol is protonated by an acidfrom the reaction medium, which then releases waterto form a furan-substituted hydroxyl methylene carbo-nium ion. This ion acts as a hydroxyalkylating agent byreacting with the cardanol via electrophilic aromaticsubstitution. A pair of electrons from the benzene ringattacks the electrophilic element, forming a carbonanion intermediate, followed by deprotonation. Themethylol group of the hydroxylmethylolated cardanol,being unstable under acidic conditions, would losewater readily to form a benzylic carbonium ion. The

Table 3: Study of cure schedule

S. no. Samples Cardanol:furfural (mole ratio) Cure time (min) Cure temperature (C)

1 FFNR51 1.0:0.5 150 1602 FFNR61 1.0:0.6 120 1603 FFNR71 1.0:0.7 100 1604 FFNR81 1.0:0.8 90 160


306

products formed would react with another cardanolmolecule to form a methylene bridge in anotherelectrophilic aromatic substitution. This process wouldrepeat until all of the furfural has been exhausted.25

The related reactions have been represented inScheme 3.

Evaluation of coating films for their curingcharacteristics

The curing of all the prepared novolac resin samples(FFNR51, FFNR61, FFNR71, and FFNR81) on mildsteel panels was completed in an air oven using HMTAas the curing agent. The observations related to curingconditions are presented in Table 3. The curing char-acteristics of the resin films show that the resinFFNR81 prepared with mole ratio 1:0.8 has goodcuring characteristics, as the films were cured in90 min. However, the films of resins designated asFFNR71, FFNR61, and FFNR51 with mole ratios 1:0.7,1:0.6, and 1:0.5 were cured in 150, 120, and 100 min,respectively, at 160C.

Fourier-transform infrared (FTIR) spectroscopicanalysis

The FTIR spectra of sample FFNR81 (Fig. 1) arediscussed here. IR spectral analysis of cardanolfurfu-ral-based novolac resins reveals not only the conden-sation of methylolated cardanol, but also the degree ofortho- and para-substitution. The band observed at3472 cm1 might be due to the presence of thehydroxyl group in the methylolated cardanol. Thepeaks that appear near 3011 and 2926 cm1 in Fig. 1might be due to the presence of aromatic CH stretch-ing and aliphatic CH stretching, respectively, present inthe side chain of cardanol. The sharp band observed at2854 cm1 might be due to the CH structure in amethylene bridge. The methylene bridge might formdue to the condensation reaction between cardanol andfurfural. The stretching vibrations near 2926 and2854 cm1 and deformative vibrations near 14641486 cm1 indicate the presence of CH2 and CH3groups, respectively. The sharp peaks near 722 and884 cm1 represent the ortho- and para-substitution inbenzene nuclei, respectively. A peak near 1266 cm1

might correspond to phenol CO stretching. Thepreceding spectral data were found to be identical tothose given in the literature.25

1H-NMR spectroscopic analysis

Figure 2 shows the 1H-NMR spectrum of cardanolfurfural resins of samples FFNR81. The appearance ofa peak at 6.67.4 ppm is due to aromatic protons ofbenzene and the furan ring. The peak around theregion 6.6 ppm might be due to the presence of the

phenolic hydroxyl group. The peak at 4.75.4 ppmindicates the methylene (C=CH2) proton of a longalkyl side chain originally present in cardanol, and thepeak at 0.82.9 ppm is due to a long aliphatic sidechain. The peak at 0.9 ppm might be due to a terminalmethyl group of the chain. The strong peak at 1.3 ppmis attributed to the long chain (more than five meth-ylene groups) of the side chain. The peak at 2.8 ppmshows the methane proton of (C6H5)2CHC4H3O forthe bridge between two phenyl rings and one furanring. All these spectral data indicate that condensationof methylolated cardanol with furfural has been com-pleted under experimental conditions and was fullyconsistent with the proposed structure (Scheme 3) dueto the reaction mechanism as discussed in our previouspublication.23

Differential scanning calorimetric analysis forcuring of FFNR

The temperature of onset (Ti), peak temperature (Tp),and the temperature of completion of the exotherm(Tstop) are noted in Fig. 3 (sample FFNR81), and thedata related to the dynamic DSC scans of FFNR51,FFNR61, FFNR71, and FFNR81, respectively, aresummarized in Table 4. It is evident from the tablethat the initiation of the crosslinking reaction lies in therange of 64.1121C with peak maximum temperature129, 140, 146, and 153C for samples FFNR51,FFNR61, FFNR71, and FFNR81, respectively. Thecompletion of the exotherm was observed in the rangeof 185165C. The DH values related to the cureprocess were determined from the area of the exo-therm peak obtained from DSC analysis taken indynamic mode. The preceding data and results of theDSC scans were found to be in close agreement withthe values given in the literature for phenol formalde-hyde resin.26 The peak exotherm (Tp) is shifted to ahigher temperature due to the increased reaction ratewith the higher molar ratio of cardanol and furfural.Such a trend was observed by various authors duringthe studies of the curing of epoxy and phenolic resins.27

The resins prepared by cardanolfurfural resin werefound to show high thermal stability, unlike phenol orcardanolformaldehyde resins, which were thermallyless stable.16

Mechanical properties of the prepared films

The results on the mechanical properties of the curedfilms are tabulated in Table 5. The table indicates thatfilms of resin FFNR81 were the hardest of all the films,with a maximum value of 1500 g. The hardness of theresins was indicative of the C15 long side chain ofcardanol that induced softness in the films, resulting inan increase in flexibilty. Thus, it is clear now that all ofthe films were found to possess good flexibility, which


307

balances the rigid nature of the cured films byintroducing this chain in the crosslinked structure, thusincreasing the intermolecular spacing. Adhesion of thefilms was measured by a crosshatch tape test, and allthe fims showed 100% adhesion, i.e., no square waslifted by the crosshatch test. The presence of thehydroxyl groups (OH) in the cardanolfurfural resinmight be responsible for the adhesion property ofcardanolfurfural novolac resins and this could also beattributed to the high crosslink density and increasedcrystallinity due to the aromatic backbone of thefurfural moiety used. All of the films were found topossess good flexibility due to the presence of C15 longside chain in the cardanol, and they passed the 1/8-in.mandrel bend test successfully. All the cured films werefound to be smooth and uniform with good gloss.

Impact resistance of all the films was found to beexcellent. Overall, the mechanical properties of thecured films of the prepared novolac resins showedpromising results for nearly all the samples of novolacresin for application in surface coatings, as opposed tophenol or cardanolformaldehyde resins that werefound to have low flexiblity and weak impact resis-tance.16


Table 6 shows the comparative acids, alkalies, andsolvents resistance of the cured films of cardanolfurfural-based novolac resin. A quick perusal of Table 6clearly illustrates that the films of coatings prepared

OH OHSlow

CHR-OH++

C15H29

CHROH

C15H29

+

HOH

CHROH

C15H29+ H

Fast+

OH OHSlow

CHR-OH++

C15H29CHROH

C15H29

+

H

OH

CHROHC15H29

+ HFast

+

OH OHCHCH-R

+

+

C15H29 C15H29

OH

C15H29

+

OH

C15H29+ H

+

R

OH OH

RCH RCH+

C15H29 C15H29

OHOH

OH

C15H29

OH

OH

C15H29

OH

C15H29

C15H29

+ H+

CHR+ H2O

RCH OH2

C15H29

RCH

+ H+

+

OH

OH

OH

C15H29 C15H29

OH

CH

+ H2O

CHR H2OH2CC15H29

R

+ H+

+

OR

R+

HC

HC

OCH

R

R R

R R

R

O

CH CH

CH

CH CH CH

CH

CH

OH

OH OH

OH

OH

OHO

O

OO

O O

Structure of cardanol furfural resin

Scheme 3: Reactions involved during the synthesis of cardanolfurfural-based novolac resin


308

from resins FFNR71 and FFNR81 (i.e., mole ratios 1:0.7and 1:0.8) have offered maximum resistance towardsdifferent solvents, deionized water, and different con-centrations of alkalis and acids as compared to the filmsfrom other resin samples. The chemical resistance wasevaluated by solvents such as methyl ethyl ketone(MEK), xylene, and methanol, and showed no visibleeffect on cured films in all cases, irrespective of thehardener system employed. This could be due to theincreasing polarity of the cured backbone, as discussedabove. This was further supported by increasing thearomatic content from the furfural moiety and highlycrosslinked structure of prepared novolac resin, asopposed to phenolformaldehyde or cardanolformal-dehyde resin, which were found to exhibit weakchemical stability.16 The deionized water resistance ofthe cured films showed no effect, and maintained

homogeneity even after 6 months of dipping. This couldbe attributed to the hydrophobic nature of the novolacresin backbone, which resisted any possible interactionbetween the crosslinked backbone and water. Thenovolac resin backbone was further responsible forgiving excellent alkali (5% sodium carbonate) and weakacid (5% acetic acid) resistance. But the films immersedin strong acid (2% HCl) and strong base (2% NaOH)were affected to a large extent. These coated filmsshowed either dissolution or blistering during the first3 months and were further affected afterward. This wasevident from the fact that the resultant novolac resinstructure was found to be highly crosslinked, whichwould lead to increasing polarity of the system, which isone of the deciding parameters for adhesion of coatingon the metallic panels and its solvent compatibility.Thus, the prepared novolac resin system possessed poor

110

100

90

80

70

60

50

40

304000 3500 3000 2500 2000 1500 1000 500 0

Wavenumber (cm1)

Tra

nsm

ittan

ce (%

)

Fig. 1: FTIR spectrum of cardanolfurfural-based novolacresin FFNR81

11.0 10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0

Fig. 2: 1H-NMR spectrum of cardanolfurfural-based novolac resin FFNR81

0.2

0.0

0.2

0.4

0.6

0.8

1.0

Hea

t flo

w (W

/g)

40 60 80 100 120 140 160 180 200Temperature (C)

129.23 C

71.62 C

Fig. 3: Dynamic DSC scan of sample FFNR81


309

strong acid and strong base resistance, irrespective ofexcellent solvent, weak acid, alkali, and deionized waterresistance. Moreover, the cured film of FFNR81 wasfound to exhibit excellent and remarkable chemicalresistance properties compared to the other film sam-ples (see Table 6), except for the strong acid and thestrong base. The results obtained from chemical resis-tance after 6 months are given in Table 6.

Conclusions

The following conclusions seem to be warranted fromthe present findings of the study on the performanceproperties of cardanolfurfural-based novolac resinsand their films.

(1) The proposed research might prove to be amilestone in the field of resins based on renew-

able resources. The synthesized cardanolfurfu-ral-based novolac resin has the potential tominimize the use of phenol resin based onpetrochemical derivatives like phenolformalde-hyde resin because, unlike phenolformaldehyderesin, these cured cardanolfurfural resins havebetter mechanical properties, heat resistance, andespecially chemical resistance, particularly toalkalies, solvents, and water. Moreover, furfural,being a product of vegetable origin and availablein virtually unlimited quantities, is a much moreeconomical aldehyde than formaldehyde. In thesemany respects, cardanolfurfural resins are sim-ilar to, but superior to, phenolformaldehyderesins as well as cardanolformaldehyde resins.Hence, the work is novel. The mechanical andthermal properties of cardanolfurfural resinswere found to be better when compared withthe literature28,29 on phenolformaldehyde resins.

Table 4: Results obtained from dynamic DSC scan

S. no. Samples Ti (C)a Tp (C)b Tstop (C)c DH (J/g)

1 FFNR51 64.1 129 165 96.22 FFNR61 87.2 140 174 1073 FFNR71 111 146 181 1214 FFNR81 121 153 185 83.8

Ti represents temperature of onset, Tp peak temperature, Tstop temperature of completion of the exotherma Temperature of cure initiationb Temperature of cure maximumc Temperature of end of cure

Table 5: Mechanical properties of the cured films

S. no. Properties of films FFNR51 FFNR61 FFNR71 FFNR81

1. Adhesion (crosshatch test) (%) 100 100 100 1002. Flexibility (mandrel bend test) Pass Pass Pass Pass3. Scratch hardness (g) 900 1150 1400 15004. Gloss (60C angle) 80.9 86.8 92.5 94.95. Impact resistance (kg cm) 30 35 40 40

Table 6: Chemical resistance properties of the cured films after 6 months

S. no. Chemicals FFNR51 FFNR61 FFNR71 FFNR81

1. Deionized water 1 1 1 12. Methyl ethyl ketone 2 2 2 13. Xylene 1 1 1 14. Methanol 2 2 1 15. Sulfuric acid 2% 6 6 5 56. Acetic acid 5% 4 4 3 37. Sodium hydroxide 2% 3 3 2 28. Sodium carbonate 5% 4 3 2 1

1 unaffected, 2 loss in gloss, 3 softening observed, 4 slight loss in adhesion, 5 film partially removed, 6 film completelyremoved


310

(2) Utilization of the prepared cardanolfurfural-based novolac resin from renewable resources inthe green coatings can thus contribute to sustain-able development and will help in realizing theprinciples of green chemistry. Thus, the use ofcardanol and furfural in the synthesis of novolacresin is attractive in view of its low price andrenewable nature.

(3) The mechanical properties of the films of carda-nolfurfural novolac resin, such as adhesion,flexibility, gloss, and impact resistance, werefound to be good, though these films lacked inhardness.

(4) The chemical resistance properties of the films ofthe cardanolfurfural novolacs were found to beexcellent, except in resistance to acids, such assulfuric acid in particular.

(5) DSC results showed that the synthesized novolacresins showed high thermal stability.

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Mechanical, chemical, and curing characteristics of cardanol--furfural-based novolac resin for application in green coatingsAbstractIntroductionExperimentalMaterialsAnalysis of cardanolMethodsSynthesis of cardanol--furfural-based novolac resinCuring of cardanol--furfural-based novolac resinCoating of panelsEvaluation of mechanical properties of filmsEvaluation of chemical resistance properties of films

Characterization of cardanol--furfural based novolac resinFourier-transform infrared (FTIR) spectroscopic analysis1H-NMR spectroscopic analysisDifferential scanning calorimetry (DSC)Mechanical properties of the prepared filmsScratch hardness testerImpact hardness testerCylindrical mandrelGloss


Results and discussionAnalysis of cardanolSynthesis of cardanol--furfural-based novolac resinEvaluation of coating films for their curing characteristicsFourier-transform infrared (FTIR) spectroscopic analysis1H-NMR spectroscopic analysisDifferential scanning calorimetric analysis for curing of FFNRMechanical properties of the prepared filmsChemical resistance of the prepared films

ConclusionsReferences

Documents

Mechanical, Chemical, And Curing Characteristics of Cardanol–Furfural-based Novolac Resin for Application in Green Coatings