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Industrial Crops and Products 52 (2014) 38– 45
Contents lists available at ScienceDirect
Industrial Crops and Products
journa l h om epa ge: www.elsev ier .com/ locate / indcrop
ffect of organoclay on blends of individually plasticizedhermoplastic starch and polypropylene
illian H. Ferreira, Rachel R. Khalili, Mario J.M. Figueira Junior, Cristina T. Andrade ∗
nstituto de Macromoléculas Professora Eloisa Mano, Universidade Federal do Rio de Janeiro, Centro de Tecnologia, Bloco J, P.O. Box 68525, 21941-598 Rioe Janeiro, RJ, Brazil
r t i c l e i n f o
rticle history:eceived 17 July 2013eceived in revised form 6 October 2013ccepted 11 October 2013
eywords:mmiscible blendtarcholypropyleneodified montmorillonite
a b s t r a c t
Cornstarch and polypropylene (PP) blends were prepared by melt mixing at a constant 70:30 (mass/mass)ratio in a co-rotating twin-screw extruder. Both components were plasticized individually; glycerol andacetyl tributyl citrate (ATBC) were used as plasticizers for starch and PP, respectively. A commercialmaleated polypropylene (mPP) was added to the mixtures as a compatibilizing agent. A commercialorganoclay was also incorporated at increasing contents (1.0, 2.5 and 5.0 mass% over the total massof the blends). The extruded materials were pelletized, compression-molded, and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), dynamicmechanical analysis (DMA) and capillary rheometry. XRD results indicated that the addition of ATBCcontributed to the increase of PP crystallinity from 62% to 72%. The incorporation of the organoclay
olymer hybridhysical properties
caused alterations inside the PP-dispersed phase, particularly when its composition reached the amountof 5.0 mass%. SEM images revealed a coarse morphology for the blend prepared in the presence of mPPalone. XRD, SEM and DMA data revealed that improvements in the compatibility between the immisciblecomponents were achieved by the organoclay incorporation. The evolution of the XRD patterns for thehybrid materials submitted to aging at high humidity conditions for 120 days indicated that organoclayparticles were located preferentially in the starch matrix at the end of this experiment.
. Introduction
The development and use of biodegradable polymers were con-idered as an alternative to replace petroleum-based polymers ateast in some applications. Starch is a promising bio-based mate-ial, found worldwide from several crops at low prices (Shen et al.,010; Álvarez-Chávez et al., 2012). Starch occurs as semicrystallineranules constituted of two polysaccharides, amylose and amy-opectin, both formed by d-glucose repeating units. In its granularorm, starch found application as filler in polypropylene compos-tes (Roy et al., 2011). Submitted to thermomechanical treatmentn the presence of suitable plasticizers, starch can be transformednto a thermoplastic and essentially amorphous material, denotedhermoplastic starch (TPS). The highly hydrophilic character ofPS favors its biodegradability. However, this material has limitedpplications, mainly because of its mechanical properties, which
epend on ambient relative humidity (van Soest et al., 1996a; Yut al., 2006; Magalhães and Andrade, 2009; Li and Huneault, 2011).ecause of this drawback, the development of TPS blends with∗ Corresponding author. Tel.: +55 21 2562 7208; fax: +55 21 2270 1317.E-mail addresses: [email protected], [email protected]
C.T. Andrade).
926-6690/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.indcrop.2013.10.016
© 2013 Elsevier B.V. All rights reserved.
polyolefins has attracted the attention of many researchers. The aimwas to obtain low-cost materials with improved mechanical prop-erties, as well as to promote microorganism activity on discardedartifacts (Mir et al., 2013).
Although blending of two or more polymers has many advan-tages, only a few polymers are miscible with each other, a situationthat should be expected for noninteracting TPS and polyolefins. Toovercome the low interfacial adhesion between the blend com-ponents, some strategies were chosen by some authors. Starchderivatives, for example phthalate starch, were proposed as asubstitute to the natural material to be used in blends withpolyethylene (PE) (Thakore et al., 2001). Polypropylene (PP) wasmelt-processed with Mater-Bi, a commercial blend based onstarch; the thermal degradation and the biodegradation in soil ofthe resulting 50:50 blend were investigated to obtain informa-tion on possible ways of eliminating waste (Ramis et al., 2004;Cadenato et al., 2006). Other approaches, reactive processing andthe introduction of a third component as a compatibilizer, are com-monly used to modify the interface between incompatible polymerpairs.
Because of its low density, good thermal properties, and excel-lent processability, PP has found many applications in industry.Differently from PE/TPS blends, only a few studies were reportedon PP/TPS blends. To compatibilize TPS and PP, the addition of
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aleated polypropylene (mPP) to the neat blend turned out to be pragmatic option because of the commercial introduction of thismphiphilic product by some industries (DeLeo et al., 2010, 2011;uneault and Li, 2012). This chemically modified PP was used as
crosslinking agent to develop renewable elastomers based onotato starch (DeLeo et al., 2010). Two processing methods, whichiffered by adding starch in the dry-powder form (water and glyc-rol were added later into the extruder at a 1:10 ratio) or as alurry (50 mass% starch content and 25 mass% of both water andlycerol), were applied to prepare PP/TPS blends at a 75:25 com-osition in the presence of the mPP compatibilizer (Huneault andi, 2012). For the resulting materials, in which TPS was dispersedithin the PP matrix, the elongation at break values were severely
educed in relation to that found for PP alone, independently of theethod used. Slightly increased modulus and tensile strength val-
es were obtained for the materials prepared by the slurry method.ith higher contents of biodegradable glycerol-plasticized cas-
ava starch (higher than 45 mass%), some authors prepared TPS/PPlends. The mPP compatibilizer was introduced at 25 mass% con-ent based on the PP added mass. To improve properties, naturalnd organically modified layered silicates were also added to theixtures at a fixed 5 mass% concentration (DeLeo et al., 2011).The objective of this work was to prepare and characterize melt-
xtruded TPS/PP blends, compatibilized with a commercial mPP.o obtain materials with an inherent tendency to biodegradation,ornstarch was included at a high composition. Glycerol, the mainy-product from trans-esterification of oils in biodiesel manufac-uring process, often used as a plasticizer for starch (van Soestt al., 1996a; Magalhães and Andrade, 2009; Aouada et al., 2011;odríguez-Castellanos et al., 2013) was included together with the
ess polar acetyl tributyl citrate (ATBC). ATBC is a nontoxic ester,erived from naturally occurring citric acid, which was used to plas-icize other biopolymers (Ljungberg and Wesslén, 2002; Erceg et al.,005). The addition of ATBC aimed to prevent exudation of glycerolrom the extruded materials. A commercial organoclay, Cloisite®
0B, with polar substituents in the organic intercalant, was alsodded at different contents. The plasticized polymers, the mPP-ompatibilized blend and the hybrid blends were characterized by-ray diffraction, scanning electron microscopy, thermogravimet-ic and dynamic mechanical analysis, and by capillary rheometry.he aging process was investigated under high humidity condi-ions, and monitored by X-ray diffraction for 120 days.
. Experimental
.1. Materials
Regular cornstarch (CS) was supplied by Corn Products BrazilSão Paulo, SP, Brazil). According to the producer, this material isomposed of 26–30 mass% amylose and 74–70 mass% amylopectin,ith less than 0.5 mass% gluten. The gravimetric method was used
o determine the humidity content (10 mass%). Analytical gradelycerol and hexane were purchased from Vetec Química Fina (Rioe Janeiro, RJ, Brazil) and were used as received. PolypropylenePP, HP516M, with melt flow index of 8 g/10 min at 230 ◦C/2.16 kg)as supplied by Suzano Petroquimica (São Paulo, SP, Brazil). Maleic
nhydride-modified polypropylene (mPP, Polybond® 3200) (meltow index of 115 g/10 min at 190 ◦C/2.16 kg; 1 mass% of maleicnhydride, according to the producer) was supplied by Chemturaorporation (Philadelphia, PA, USA). Acetyl tributyl citrate (ATBC,candinol SP22) was supplied by Scandiflex do Brasil Indústrias
uímicas S.A. (Mauá, SP, Brazil) and was used as received. Cloisite®0B (C30B), a montmorillonite modified with dihydroxyethyl alkylethylammonium ions, was supplied by Southern Clay Products
Gonzales, TX, USA), and was used as received.
and Products 52 (2014) 38– 45 39
2.2. Preparation of samples
The mixture of CS and glycerol, added at 25 mass% based onstarch dry mass, was homogenized in a conventional mixer (IkaWorks, Wilmington, NC, USA) for 25 min, and maintained in tightlysealed polyethylene bags for 48 h at 4 ◦C before processing toobtain TPS, and before being used in blends. ATBC was used asa plasticizer at a composition of 15 mass% in relation to the PPmass. Polybond® 3200 (mPP) was added as a compatibilizer toprepare the 70/30 TPS/PP blend (hereafter denoted mPP blend)and the TPS/ATBC-plasticized PP/C30B hybrids. In these materials,30 mass% of PP + ATBC were substituted by mPP. To the TPS/ATBC-plasticized PP/C30B hybrids, the organoclay C30B was added at 1.0,2.5 and 5.0 mass% contents, over the total mass of the polymersand plasticizers. Before processing, glycerol-plasticized CS, ATBC-plasticized PP, the mPP blend and the three hybrid materials werealso homogenized in the conventional mixer.
2.3. Processing
One-step extrusion processings were carried out for the hybridmaterials in a Coperion ZSK 18 (Werner & Pfleiderer, Stuttgart,Germany) co-rotating twin-screw extruder, with a L/D ratio of 40,supplied with a circular die. TPS, PP alone, ATBC-plasticized PPsamples were also processed in the same extruder. To prepareTPS, the seven heating zones of the extruder were maintained at110, 110, 115, 115, 115, 110, 110 ◦C, and the screw speed wasset at 200 rpm. To prepare the other samples, the seven heatingzones of the extruder were maintained at 160, 160, 165, 165, 165,160, 160 ◦C, and the screw speed was set at 200 rpm. To preparespecimens for analyses, the extruded materials were pelletizedand compression-molded by heating at 150 ◦C under 68.9 MPa for10 min, and cooling for 5 min in a cold press. The resulting sheets,with 12 cm × 10 cm × 2 cm dimensions, were conditioned in desic-cators at ambient temperature.
2.4. X-ray diffraction (XRD)
XRD patterns were performed with a Miniflex diffractometer(Rigaku Corporation, Osaka, Japan) operating at the CuK� wave-length of 1.542 A, at 30 kV and 15 mA. The scattered radiation wasdetected at ambient temperature in the angular region 2◦ to 35◦
(2�) at 3◦ (2�)/min. The samples were also analyzed with a UltimaIV diffractometer (Rigaku Corporation) in the angular region 0.9 to10◦ (2�) at 3◦ (2�)/min, in reflection mode. The CuK�1 radiationwas generated at 40 kV and 20 mA. The samples were scanned at a0.01◦/s rate. The d-values were calculated by the Bragg’s Law (Eq.(1)).
n� = 2d sen� (1)
where n is an integer, � is the wavelength of incident wave(1.5418 A), d is the spacing between any two atomic planes in thecrystal lattice, and � is the angle of reflection.
Deconvolution of the XRD patterns was performed with the freesoftware Fityk, downloaded at http://www.unipress.waw.pl/fityk.
2.5. Phase morphology
The phase morphology of the samples was examined with a Jeolelectron microscope, model JSM-6460LV (Akishima-shi, Japan) at
the acceleration voltage of 20 kV. The samples were vacuum-coatedwith gold before measurements. Images were obtained before andafter PP selective extraction of the PP phase with hexane, underreflux for 12 h.
4 l Crops and Products 52 (2014) 38– 45
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II
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111130040
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Fig. 1. X-ray diffractograms in the 2� region of 2◦ to 35◦ for (a) TPS; (b) neat PP (trace
in the reflections observed for these materials in relation to thediffractogram obtained for the ATBC-plasticized PP sample. Thisresult suggested that a slight alteration of the local order occurredinside the crystalline lamellae of the PP phase in the mPP blend
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0 W.H. Ferreira et al. / Industria
.6. Thermogravimetric analysis (TGA)
Thermogravimetric analyses were performed in a Q500 TGAquipment from TA Instruments (New Castle, DE, USA) under nitro-en flow. Samples weighing approximately 15 mg were heatedrom 30 to 700 ◦C, at a heating rate of 20 ◦C/min.
.7. Dynamic mechanical analysis (DMA)
Dynamic mechanical analyses were performed in a Q800 DMAquipment from TA Instruments with compression-molded sam-les with 35 mm × 10 mm × 2 mm dimensions. The experimentsere carried out in bending mode from −100 to 150 ◦C, at a heat-
ng rate of 3 ◦C/min, at 1 Hz. Prior to analysis, the linear viscoelasticegion was determined by a strain sweep experiment.
.8. Off-line viscosity studies
A Göttffert capillary rheometer model Rheograph 25 (Buchen,ermany), equipped with a round-hole capillary of D = 1 mm
L/D = 30), was used to measure the materials flow properties. Allests were performed over a shear rate range of 50–3000 s−1, at80 ◦C. End corrections were not applied; thus, the viscosity val-es are reported as apparent viscosities. The setting of parametersnd evaluation of raw data, as well as the Rabinowitsch’s correc-ion, were performed with the software LabRheo, provided withhe equipment.
.9. Aging
Five replications of compressed-molded samples with5 mm × 25 mm × 1.0 mm dimensions were conditioned at 25 ◦Cnd 80% relative humidity (RH) in a climate-controlled chamber.S. Mistura, model MS 012 (Rio de Janeiro, RJ, Brazil), for 120
ays. Every 30 days, one replication of each sample was taken fromhe chamber and analyzed by XRD.
. Results and discussion
In previous experiments, glycerol was added as the only plas-icizer for TPS/PP blends compatibilized with mPP. The resulting
aterials were flexible, but a substance, most probably glycerol,xuded from the extruded strands soon after processing. Becausef this result, a new series of experiments were performed, inhich both glycerol and ATBC were used as plasticizers. In this case,o exudation was observed. Transparent and yellowish extrudatesith a smooth surface and cylindrical geometry were obtained for
ll samples. This result seemed to indicate that the better miscibil-ty of ATBC with PP hindered the migration of both plasticizers tohe surface.
XRD was used to investigate the crystallinity of the extrudedaterials in the 2–35◦ (2�) region (Fig. 1). For TPS alone, different
rystalline structures were observed (Fig. 1a). The reflections at 14◦
nd 21◦ (2�) were assigned to the VA-type crystallinity, attributedo processing-induced crystallinity of single helical amylose, foundn extruded and compression-molded TPS with less than 10 mass%f water. The reflections at ∼20◦ (2�) was assigned to the VH-typerystallinity, attributed to processing-induced crystallinity of singleelical amylose, found in processed starches with water contentsigher than 10 mass% (van Soest et al., 1996b). The reflection at24◦ (2�) was attributed to residual A-type crystallinity of granu-
ar starch, and revealed that a small fraction of the granules was notompletely ruptured during melt-extrusion. The unusual appear-nce of different crystal types may be attributed to the high speed athich this TPS sample was prepared (residual A-type crystallinity),
I) and ATBC-plasticized PP (trace II); (c) mPP blend (TPS/PP + mPP at 70:30 compo-sition) (trace I), mPP blend with addition of C30B at 1.0 mass% (trace II), 2.5 mass%(trace III) and 5.0 mass% (trace IV).
and also to the low-humidity conditioning in a desiccator (VA-typecrystallinity).
For PP and ATBC-plasticized PP (Fig. 1b), as well as for the mPPblend and hybrids (Fig. 1c), reflections were observed at ∼15◦, 18◦,20◦, 22.5◦ and 23◦ (2�), which correspond to the 1 1 0, 0 4 0, 1 3 0,1 1 1 and 1 3 1 + 0 4 1 lattice planes of monoclinic �-phase of PP,respectively (Thompson et al., 2011). Note that ATBC-plasticizedPP (Fig. 1b, trace II) has a much higher crystallinity (72%) than purePP (62%), which confirmed the plasticizing effect of ATBC.
No shifts in (2�) values of the PP phase were observed for themPP blend and the hybrids prepared with 1.0 and 2.5 mass% C30B.On the other hand, variations in intensity and width were observed
2θ (°)
Fig. 2. X-ray diffractograms in the 2� region of 0.6◦ to 10◦ for neat C30B (trace I),mPP blend (TPS/PP + mPP at 70:30 composition) (trace II), mPP blend with additionof C30B at 1.0 mass% (trace III), 2.5 mass% (trace IV) and 5.0 mass% (trace V).
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Fig. 1c, trace I) and in those hybrids (Fig. 1c, traces II and III, respec-ively). According to XRD results, with 1.0 and 2.5 mass% C30B, norystallinity was detected for the starch matrix, but the crystallinityf the PP-dispersed phase increased from 47% for the mPP blend,o 49% and 51% for those hybrids, respectively.
As observed in Fig. 1c (trace IV), for the hybrid with the addi-
ion of 5.0 mass% C30B, some reflections were wider and shiftedo lower (2�) values, and indicated a more pronounced alterationnside the less crystalline PP phase, with a reduced crystallinityig. 3. Scanning electron micrographs taken for the samples before and after extraction1), and for the mPP blend with addition of C30B at 1.0 mass% (b, b1), 2.5 mass% (c, c1) an
and Products 52 (2014) 38– 45 41
of 40%. The higher volume fraction of an amorphous phase in thehybrid prepared with 5.0 mass% C30B seemed to be related to a bet-ter compatibilization between the TPS matrix and the PP-dispersedphase.
Using a diffractometer with a higher resolution at low angles,the 0 0 1 reflection for the neat C30B (Fig. 2, trace I) was observed
at 2� = 4.6◦, and revealed a d0 0 1 value of 1.9 nm. For all theTPS/PP/C30B hybrids (Fig. 2, traces III–V), this reflection wasshifted to angles bellow 0.6◦ (2�). The disappearance of the basalof the PP phase, respectively; mPP blend (TPS/PP + mPP at 70:30 composition) (a,d 5.0 mass% (d, d1).
4 l Crops and Products 52 (2014) 38– 45
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0 100 20 0 300 40 0 500 60 0 7000
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Mas
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ss (%
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Tempera ture (° C)
7006005004003002001000Temperature (°C)
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/°C
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468°C301°C
469°C308°C
463°C310°C
458°C309°C
454°C
305°C b
Fig. 4. TG (a) and DTG (b) curves for TPS (�), PP (×), ATBC-plasticized PP (+), mPP
2 W.H. Ferreira et al. / Industria
eflection attributed to the organoclay in the diffractograms forhe hybrids should not be considered as a clear sign of exfoliation,nless supported by small-angle X-ray scattering (SAXS) and trans-ission electron microscopy (TEM). Anyway, the results indicated
hat these materials were highly intercalated between the silicateayers, leading to interlayer spaces higher than 11 nm.
The phase morphology of TPS/PP materials was investigatedy SEM before and after selective extraction of the PP dispersedhase (Fig. 3). As may be observed, PP was not fully extracted. Inoth images (Fig. 3a, a1), for the mPP blend, a coarse morphol-gy was visualized. This means that even with the incorporationf the maleated compatibilizer, the size of the phases and the lackf adhesion between the two phases evidenced immiscibility. Thisesult might be explained by the low content of the cyclic moi-ty introduced to the PP main chain of the commercial maleatedroduct (1 mass%). Also, the ineffectiveness of mPP as a compatibi-
izer may be attributed to some loss into the PP phase, as reportedreviously for other system (Papadopoulou and Kalfoglou, 2000).
With the addition of the organoclay (Fig. 3b–d), the micrographshowed improved compatibility between the phases and the typ-cal morphology of dispersed domains immersed in a continuous
atrix. Note that after the partial extraction of PP (Fig. 3b1–d1),oles of reduced size were visualized.
The barrier effect of organoclay platelets toward coalescence ofhe dispersed phase was observed previously for other syntheticolymers systems, and was attributed to the presence of clay min-ral platelets at the interface or in the continuous phase (Khatuat al., 2004; Si et al., 2006; Kelarakis et al., 2007; Vo and Giannelis,007; Filippone et al., 2010; Tiwari and Paul, 2011). This effect waslso observed for TPS/PHBV blends, in which the size of the PHBVispersed phase was reduced, increasing amounts of droplets werebserved, and improved interfacial adhesion was clearly visualizedy the addition of increasing contents of organoclay up to 10 mass%Magalhães et al., 2013). In this work, the addition of mPP and thencorporation of the organoclay up to 5 mass% led to finer droplets-n-matrix morphologies.
Well-dispersed layered silicates are expected to promotemprovements in the thermal stability of polymer/clay mineralanocomposites in relation to the corresponding neat polymers. Inhe case of polymer blend hybrids, their morphology and the loca-ion of the organoclay particles would certainly contribute to theirhermal properties. To verify the effect of blending TPS and PP, andlso the effect of the incorporation of C30B to the TPS/PP blend, ther-ogravimetric analyses were performed for the extruded samples
Fig. 4). For TPS (Fig. 4a), remaining water and glycerol evaporatedefore the initial degradation temperature of starch, and at 305 ◦Che maximum rate of mass loss was observed in the derivativehermogram (Fig. 4b). For PP, the initial thermal decompositionemperature (Tonset) was observed around 285 ◦C, and the temper-ture of maximum rate of mass loss (Tmax) was detected at 398 ◦CFig. 4b). After volatilization of the plasticizer, Tmax for the ATBC-lasticized PP was detected at 454 ◦C. The higher Tmax detected forTBC-plasticized PP is consistent with its higher crystallinity. Dif-
erently from TPS, which left a char residue of 10%, both PP andTBC-plasticized PP left no char residue at 700 ◦C. For the mPPlend, thermal decomposition began with the volatilization of thelasticizers, followed by two other degradation steps, with a slight
ncrease in both Tmax.It is worth observing in the DTG curves of Fig. 4b that the high-
st temperature (310 ◦C) reached for the maximum degradationate of the starch phase was detected for the hybrid with 1.0 mass%rganoclay. For the hybrids with higher organoclay contents, the
rst Tmax was observed at lower temperatures. In these cases, asbserved before for other hybrid systems (Ramos Filho et al., 2005;agalhães and Andrade, 2010), the catalytic effect of acidic sitesf inorganic montmorillonite, present within the starch matrix,
blend (TPS/PP + mPP at 70:30 composition) (�), mPP blend with addition of C30B at1.0 mass% (�), 2.5 mass% (�) and 5.0 mass% (♦).
might have caused its earlier thermal degradation. On the con-trary, an increase in Tmax was observed for the PP-dispersed phaseof the hybrids. This increase of 5–11 ◦C in Tmax for the PP phaseof the hybrids seemed not to depend on the crystallinity of thedispersed phase. According to XRD results, although the hybridswith the incorporation of 1.0 and 2.5 mass% C30B had a highercrystallinity than the mPP blend, the hybrid with the incorpora-tion of 5 mass% C30B had a reduced crystallinity. Since the Tmax forthe PP phase in this hybrid was also detected at a higher temper-ature (468 ◦C) than that for the neat PP, the loss of C30B particlesinto the PP phase should be considered. Indeed, enhancements inthe thermal stability of PP was observed with the incorporationof other less hydrophilic nanofillers (Sharma and Nayak, 2009; Heet al., 2013; Santos et al., 2013). The location of C30B in the PPphase was not expected because of the hydroxyethyl substituentsof its intercalant, which interact preferentially with the polar starchmatrix. In this case, the presence of some amount of mPP in thePP phase, probably justified by its low degree of maleic anhydridesubstitution, might have caused the migration of C30B.
The viscoelastic response to oscillatory deformation was evalu-ated for the extruded materials, and is shown in the DMA curvesof Fig. 5a and b. In Fig. 5a, a steep decrease in the storage modulusvalues (E′) may be visualized for TPS and for the mPP blend. Thistransition is associated with the maximum at −49 ◦C in the lossfactor (tan ı) versus temperature curve for TPS, and was attributedto a glycerol-rich phase (Forssell et al., 1997). Note that for thehybrid materials, this decrease in E′ was smoother, which mightindicate the effect of the organoclay in decreasing, at least slightly,the heterogeneity of the starch matrix. For the hybrids with 2.5and 5 mass% C30B, this transition occurred at higher temperatures,
−45 ◦C and −43 ◦C, respectively. For TPS alone, the mPP blend andthe hybrids with 2.5 and 5.0 mass% C30B, another relaxation wasdetected in Fig. 5b at higher temperatures (75 ◦C for TPS), and was
W.H. Ferreira et al. / Industrial Crops and Products 52 (2014) 38– 45 43
-100 -50 0 50 100 150
102
103
104
Temperature (°C)
Sto
rage
Mod
ulus
(MPa
)
a
-100 -5 0 0 50 10 0 15 00,00
0,05
0,10
0,15
0,20
0,25
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Tempe rature (°C)
b
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101 102 103 104
101
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App
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Fig. 6. Variation of apparent viscosity as a function of shear rate at 180 ◦C for TPS
aging experiment. The X-ray diffractograms taken on the 60th dayand on the 120th day are shown in Fig. 7. As expected, while nosignificant variation was observed for ATBC-plasticized PP, for TPS
0 5 10 15 20 25 30 352θ (° )
a
IVIII
II
I
0 5 10 15 20 25 30 35
b
2θ (° )
IV
IIIII
I
Fig. 7. X-ray diffractograms in the 2� region of 2◦ to 35◦ after aging at 80% relative
TBC-plasticized PP (�), mPP blend (TPS/PP + mPP at 70:30 composition) (�), mPPlend with addition of C30B at 1.0 mass% (�), 2.5 mass% (©) and 5.0 mass% (♦).
ttributed to a starch-rich phase (Forssell et al., 1997). The broad-ess and the unusual high temperature at which this relaxationas observed might be explained by the previous conditioning in
desiccator, which led to the elimination of a significant fractionf water from TPS and the other materials. Indeed, the humidityontents for TPS, mPP blend, and hybrids with 1.0, 2.5 and 5 mass%30B, measured by drying in an oven to constant mass, were 7.3,.4, 4.9, 3.5 and 3.4%, respectively.
The tan ı curve for ATBC-plasticized PP (Fig. 5b) exhibits a cleareak at 7 ◦C, which was attributed to the relaxation. Another tran-ition, at ∼85 ◦C, was clearly identified elsewhere, and attributed tohe diffusion of conformational defects in crystalline PP to the inter-hase between the crystalline and amorphous PP phases (Greint al., 2004). The peak at 7 ◦C corresponds to the glass transitionf ATBC-plasticized PP, below that determined for neat PP (resultot shown), and in accordance with literature data (Joseph et al.,003). Although this temperature decreased for the mPP blend,or the hybrids with 2.5 and 5.0 mass% C30B, the correspondingelaxations appeared at higher temperatures, around 11 ◦C and3 ◦C, respectively. Moreover, the broadness and higher intensityf this relaxation, in relation to the relaxation observed for theTBC-plasticized PP, seemed to indicate the effect of the organ-clay addition in compatibilizing, at least partially, the amorphoushases of the blends components. This result corroborates XRD databtained for the hybrid with 5.0 mass% C30B. Also, the presence of
fraction of C30B in the PP phase would contribute to the increasef the temperature of this relaxation. For the hybrid with 1 mass%30B, no clear maximum was visualized above −25 ◦C. On the otherand, for the hybrids with 2.5 and 5.0 mass% C30B, the increase inhe maxima corresponding to the starch-rich phase, at 82 ◦C and2 ◦C, respectively, might be explained as affected by the relaxationf PP and also by C30B well-dispersed particles.
Although in the glassy region the E′ values for ATBC-plasticizedP were lower than those observed for TPS, after the transition asso-iated with Tg, at 7 ◦C, the drop in E′ values was much smaller. For
he hybrids with 2.5 and 5.0 mass% C30B, even higher E′ values werebserved within a large temperature range, above −28 ◦C, whichere related to the higher stiffness of these hybrid materials.(�), PP (�), ATBC-plasticized PP (�), mPP blend (TPS/PP + mPP at 70:30 composition)(�), and mPP blend with addition of C30B at 1.0 mass% (�), 2.5 mass% (©), 5.0 mass%(♦) C30B.
The melt flow characteristics of the materials were investigatedby capillary rheometry, and are shown in Fig. 6 as apparent vis-cosity versus shear rate. All materials presented a shear thinningbehavior, with the mPP blend exhibiting the smallest viscosity overthe shear rate range. Addition of the organoclay at 1.0 mass% con-tent contributed to increase the viscosity of the blend in relationto the mPP blend. However, its viscosity was smaller than thatobserved for the ATBC-plasticized PP, and seemed to indicate thatsilicate layers and aggregates, added at a low content, were alignedwith the flow direction. The increase in C30B content led to higherviscosities, probably caused by a higher degree of organoclay aggre-gation or nonalignment of silicate layers with the flow of the meltedmaterials.
To investigate the effect of C30B on aging, the materials weremaintained at 80% relative humidity for a period of 120 days. Itis worth noting that the materials became clearer than before the
humidity for 60 days (a) and for 120 days (b), for the mPP blend (TPS/PP + mPPat 70:30 composition) (trace I) and for the mPP blend with addition of C30B at1.0 mass% (trace II), 2.5 mass% (trace III) and 5.0 mass% (trace IV).
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lone a new reflection at 17◦ (2�) appeared after 60 days of condi-ioning (results not shown), and increased in intensity with time.his reflection characterizes the formation of B-type crystallites,esulting from the aggregation of amylose and amylopectin dou-le helices (van Soest et al., 1996b; Hulleman et al., 1999), inducedy starch aging under humid atmospheres, and denoted retrogra-ation. No B-type crystallinity (Fig. 7a, trace I) was observed in theiffractogram for the mPP blend after 60 days of conditioning. How-ver, this type of crystallinity was visualized in the diffractogramaken for the mPP blend after 120 days of conditioning (Fig. 7b, trace). This result revealed that blending with the hydrophobic PP mayetard, but not prevent starch retrogradation. Similarly to TPS/PHBVanocomposites (Magalhães et al., 2013), this behavior was not
ollowed by the hybrids, to which no XRD reflection attributedo starch retrogradation was observed. On the other hand, theiffractograms taken for the hybrids showed that exposure to highumidity conditions caused a decrease in the intensity of PP crys-alline reflections along the period of the experiment (Fig. 7b, tracesI–IV). Since the barrier mechanism exerted by organoclay plateletsnd aggregates was effective on the 120th day for the starch matrixnly (traces II–IV), it seems reasonable to affirm that on this day,heir location was limited to the starch matrix. This result indicatedhat the prolonged aging at high humidity conditions facilitated the
igration of the amount of C30B particles located in the PP phaseo the starch matrix.
. Conclusions
Glycerol-plasticized CS and ATBC-plasticized PP were melt-lended in the presence of a commercial maleated polypropylenemPP). As a PP plasticizer, ATBC successfully avoided the exudationf glycerol from the materials, contributed to increase PP crys-allinity, and to decrease PP melt-viscosity and Tg. The results fromEM, XRD, DMA and capillary rheometry corroborated on the inef-ective role of the mPP sample to compatibilize the immisciblelend components, probably because of its low degree of maleicnhydride substitution. Additionally, results from XRD and TGAllowed the conclusion that at least a small fraction of the organ-clay was located within the PP-dispersed phase. The incorporationf an organoclay with polar hydroxyethyl groups in the intercalanted to materials with improved morphologies. The aging process atigh humidity conditions was monitored by XRD, and revealed theomplex dynamics of the system. Organoclay layers functioned as
barrier against the diffusion of humidity within the starch matrix,reventing retrogradation, but did not hinder the severe reductionf PP crystallinity. This latter result was attributed to migration ofP phase components to the starch matrix.
cknowledgements
The authors acknowledge Conselho Nacional de Desenvolvi-ento Científico e Tecnológico (CNPq), Fundac ão de Amparo à
esquisa do Estado do Rio de Janeiro (FAPERJ), and Coordenac ão deperfeic oamento de Pessoal de Nível Superior (CAPES) for financialupport.
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