LPTE #698685, VOL 51, ISS 12

Effects of Acetic Anhydride on the Propertiesof Polypropylene(PP)/Recycled AcrylonitrileButadiene(NBRr)/Rice Husk Powder(RHP) Composites

Santiagoo Ragunathan, H. Ismail, and K. Hussin

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Effects of Acetic Anhydride on the Properties of Polypropylene(PP)=Recycled Acrylonitrile Butadiene(NBRr)=Rice Husk Powder(RHP) Composites

Santiagoo Ragunathan, H. Ismail, and K. Hussin

Effects of Acetic Anhydride on the Propertiesof Polypropylene(PP)/Recycled AcrylonitrileButadiene(NBRr)/Rice Husk Powder(RHP) Composites

Santiagoo Ragunathan1, H. Ismail2, and K. Hussin2

51School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, Nibong Tebal,Penang, Malaysia2School of Environmental Engineering, Kompleks Pengajian Jejawi,Universiti Malaysia Perlis, Arau,Perlis, Malaysia

PP/NBRr/RHP composites were prepared by incorporation of10 rice husk powder at different loadings into PP/NBRr matrix with

an internal mixer at 180C for 9min and 50 rpm rotor speed. Theeffects of rice husk powder ller loading and acetic anhydride treat-ment on properties of PP/NBRr/RHP composites were investigatedfor processing torque, mechanical properties, water absorption,

15 swelling behavior, FTIR and SEM. Acetic anhydride-treatedRHP caused a signicant increase in mechanical properties, stabili-zation torque, water and oil resistance of the PP/NBRr/RHPcomposites. Results from FTIR and SEM observations indicatethat better adhesion was observed for all acetic anhydride-treated

20 composites.

Keywords Acetic anhydride; Morphology; Polypropylene;Recycled acrylonitrile butadiene rubber; Rice huskpowder; Tensile properties

25 INTRODUCTION

In recent years, the incorporation of lignocellulosicmaterials as reinforcing agents or as llers in polymer com-posites has received an increased attention. The addition ofllers has a high impact upon economics for thermoplas-

30 tics, while a general improvement in certain properties isalso achieved. Lignocellulosic materials exhibit a numberof attractive features including low density, low require-ments on processing equipment, less abrasion duringprocessing, abundance and certainly biodegradability[1,2].

35 The main advantage of lignocellulosic materials uponmineral llers is their environmental friendliness.

In general, polymer waste is disposed in large landllscausing serious problems on the environment, while biode-gradable materials are envisaged to be an excellent alterna-

40 tive to tackle this problem, by reducing the waste volume.

Considerable amount of studies have been carried out onutilisations natural llers such as sago, sisal, short silkbre, oil palm empty fruit bunch, rice husk ash, jute bre,rubber wood powder, jute, hemp, sisal, cotton stalk, kenaf,

45sugarcane banana bers and other cellulosic bres asreinforcement materials in various waste polymeric materi-als[3,4]. Consequently, it has not been surprising that the useof lignocellulosic materials in the production of compositeshas gained signicant importance in various manufacturing

50elds and industry[47].The main disadvantage encountered during the incor-

poration of natural lignocellulosic materials into polymersis the lack of good interfacial adhesion between the twocomponents, which results in poor properties of the nal

55material[8]. The polar hydroxyl groups on the surface ofthe lignocellulosic materials have difculty in forming awellbonded interface with a non-polar matrix, as thehydrogen bonds tend to prevent the wetting of the llersurfaces. Furthermore, the incorporation of lignocellulosic

60materials in a synthetic polymer is often associated withagglomerationas a result of insufcient dispersion, causedby the tendency of the llers to also form hydrogen bondswith each other. This incompatibility leads to poor mech-anical properties and high water absorption, especially

65when the matrix is hydrophilic.Thus, in order to develop composites with good proper-

ties, it is necessary to improve the interface between thematrix and the lignocellulosic material. There are variousmethods for promoting interfacial adhesion in systems

70where lignocellulosic[914], silane treatment[15,16], graftco-polymerization[17], use of compatibilizers[18]Q1 , plasmatreatment[19], and treatment with other chemicals[20]. Thesemethods are usually based on the use of reagents, whichcontain functional groups that are capable of bonding to

75the hydroxyl groups of the lignocellulosic material, whilemaintaining good compatibility with the matrix.

Q1

Address correspondence to H. Ismail, School of EnvironmentalEngineering, Kompleks Pengajian Jejawi 3, Universiti MalaysiaPerlis, 02600 Arau, Perlis, Malaysia. E-mail: hana@eng.usm.my

Polymer-Plastics Technology and Engineering, 51: 18, 2012

Copyright # Taylor & Francis Group, LLCISSN: 0360-2559 print=1525-6111 online

DOI: 10.1080/03602559.2012.698685

3b2 Version Number : 7.51c/W (Jun 11 2001)File path : P:/Santype/Journals/TandF_Production/LPTE/v51n12/LPTE698685/LPTE698685.3dDate and Time : 17/07/12 and 15:07

1

Interfacial compatibilization improves the stress transferbetween the two components and leads to the improvementof mechanical and physical properties of the produced

80 composites. Esterication by means of acetylation is thechemical modication procedure, which has been studiedthe most[914]. However, so far no work has been reportedon acetylation of RHP using acetic anhydride chemicaltreatment for the purpose manufacturing PP=NBRr=

85 RHP composites.The aim of the present work is to evaluate the effect of

acetic anhydride treatment on rice husk powder as ller inpolymer waste primarily on recycled acrylonitrile buta-diene rubber and polypropylene. Processing stabilization

90 torque, mechanical properties, water absorption, swellingbehavior, FTIR and morphological studies of PP=NBRr=RHP composites were also investigated.

EXPERIMENTAL

Materials

95 The materials used for the preparation of PP=NBRr=RHP composites are shown in Table 1. The rice husk pow-der were ground in a table typeQ2 pulverizing machine (RongTsong Precision Technology Co. Product Id: RT-34) withspeed of 2850 rpm, sieved at 300500 mm in particle size

100 and dried at 110C for 24 h in a vacuum oven to producerice husk powder of homogeneous fractions.

Acetic Anhydride Treatment

The bers were dipped in glacial acetic acid for 30min.The acid was drained, and the bers were dipped in 50%

105 acetic anhydride solution and stirred for 1 h, with ller tosolution ratio at 1:25. A few drops of concentrated sulfuricacid were also added as catalyze. The bers are nallywashed in distilled water for few times and then dried inthe vacuum oven at 80C for 24 h.

110 Processing/Sample Preparation

Polypropylene (PP) was mixed with recycled acryloni-trile butadiene rubber (NBRr) and rice husk powder

(RHP) at various loading (0, 10, 15, 20, 30) phr. Rice huskpowder was dried at 110C for 24 h in a vacuum oven prior

115to mixing. A constant PP and NBRr was used at 70 phr and30 phr, respectively. Table 2 shows the formulation of PP=NBRr=RHP composites.

The composites were prepared by melt mixing using aHaake Rheomix Polydrive R 600=610 Mixer at 180 C with

120the rotor speed of 50 rpm. PP was charged into the mixingchamber and melted for 4min before NBRr was added. At6min the RHP was added and the mixing was continued foranother 3min for a total mixing time of 9min. PP granulesand NBRr powder were dried for 24h at 80C under vacuum

125prior to melt mixing in an internal mixer. The compoundedsamples were compression-moulded in a Go-Tech com-pression moulding machine. A seven (7) min of preheatingat 180C, 2min of compression at 1000psi and another2min of cooling for sample fabrication. Moulded samples

130were cut into dumbbell with a Wallace die cutter S6=1=6.Aaccording to ASTM D638.

A period of 7-min preheating occurred at 180C, fol-lowed by 2min of compression at 1000 psi and another2min of cooling for sample fabrication. Moulded samples

135were cut into dumbbell shapes with a Wallace die cutterS6=1=6.A, according to ASTM D638.

Tensile Test

Tensile tests were carried out according to ASTM D 638using an Instron machine model 3366. The specimens with

1401mm thickness were cut from the molded sheets using aWallace die cutter S.A.6=1=6. Tensile modulus, tensilestrength and elongation at break were measured at across-head speed of 5mm=min and tests were performedat room temperature (25 3C).

145Absorption Studies

The specimens were dried for 4 h in a vacuum oven at100C until a constant weight was attained prior toimmersion in water in thermostated vessels at ambient tem-perature. Weight gains, after exposure, were recorded by

150removal of the specimen from the environment and by

TABLE 1Materials specication and description

Material Description Source

Polypropylene(PP) Homopolymer 6331: Code 3cm=g 0.9: Density Titan Pro Polymers (M)Sdn. Bhd. Johor,Malaysia

Recycled AcrylonitrileButadiene Rubber (NBRr)

Content: 33% of Acrylonitrile Density: 1.0153cm=g Juara One Resources Sdn.Bhd. Penang, Malaysia

Rice Husk Powder (RHP) Cellulose 35% Hemicellulose 25% Lignin 20% Ash17% Density :1.4702cm=g m 500-300: Size

Thye Heng Chan EnterpriseSdn. Bhd.

Treatment agent Acetic anhydride Alfa Aesar (M) Sdn Bhd

2 S. RAGUNATHAN ET AL.

weighing them periodically on a Stanton balance with aprecision of 1mg. The moisture content at any time t, Mtas a result of moisture absorption, was calculated by usingEquation (1).

Mt % Wo WdWo

100% 1

where by,Wd andW0 were, weight of dry material (i.e., theinitial weight of the material prior to exposure to theenvironment) and weight of moist material. The percentageequilibrium moisture absorption,Mm, was calculated as an

160 average value of several consecutive measurements thatshowed no appreciable additional absorption.

Swelling

ASTM Oil No. 3

Determination of the swelling percentage in ASTM oil165 No. 3 was carried out in accordance with ASTM D 471 test

method. The test pieces of dimension 30mm 5mm1mm were weighed and immersed in ASTM oil No.3 atroom temperature for 70 hours. As for toluene the test,samples were immersed for 48 hours at room temperature.

170 The swelling percentage of the samples for both ASTM oilNo. 3 and toluene was calculated using Equation. (2).

Swelling % swollen weight original weightoriginal weight

1002

Fourier Transform Infrared Spectroscopy Analysis

175 FTIR spectroscopic analysis of the composites was car-ried out using Perkin Elmer Spectrometer 2000 FTIR. TheATR (Attenuated Total Reectance) is applied. Scannedrange was 4004000 cm1. Both untreated and aceticanhydride-treated rice husk powder ller were character-

180 ized by FTIR to conrm the chemical reaction betweenthe acetic anhydride and the rice husk powder ller.

Fractography Studies

The failure mode of the fracture tensile specimens wasexamined using Field Emmision Scanning Electron

185Microscope FESEM Model ZEISS 36VP-24-54SUPRA.SEM micrographs were taken at various magnicationsfor fracture and other observations. Prior to the SEMobservations the fractured ends of the specimens weremounted on aluminium stubs and were sputter coated

190with a thin layer of gold to avoid electrical charging dur-ing examinations.

RESULTS AND DISCUSSION

Processing Properties

Figure 1 shows plot of stabilization torque at end of195mixing 9min for PP=NBRr=RHP composites. The stabili-

zation torque can be a direct measurement for evaluatingthe viscosity and processability of molten polymer com-posite systems. An increase in the torque value means anincrease in the viscosity of the molten polymer composite

200systems, whereas processability is decreased. It can be seenthat stabilization torque increases gradually with theincrease in ller loading. This is due to the presence ofmore rigid ller and interfacial interactions between llerand matrix, therefore reducing the polymer chains

205mobility[22,23].

FIG. 1. Stabilization torque at end of mixing 9min for PP=NBRr=RHP

composites.

TABLE 2Formulation for PP=NBRr=RHP composites

PP=NBRr =RHP composites (phr)

Composite Materials S1 S2 S3 S4 S5 S6 S7 S8 S9

PP 70 70 70 70 70 70 70 70 70NBRr 30 30 30 30 30 30 30 30 30Pure RHP 5 10 15 30 Acetic anhydride-treated RHP 5 10 15 30

EFFECTS OF ACETIC ANHYDRIDE ON PP=NBRr=RHP 3

At a similar ller loading, the composites with aceticanhydride-treated ller shows higher stabilization torqueas compared to the composites with untreated ller whichindicates more force is needed for each compounding to

210 be done. This is due to esterication process enhancesinteractions between ller and matrix and resulted in theincreases of viscosity of the molten materials for aceticanhydride-treated RHP. We have reported a similarobservation in our previous study on the PP=NBRr=RHP

215 with PPMAH(Polypropylene Maleic Anyhdride) compati-bilization[24], whereby higher stabilization torque resultedfor composites with good interfacial interactions betweenRHP and PP=NBRr matrixs.

Tensile Properties

220 Figure 2 shows plot of tensile strength versus ller load-ing of PP=NBRr=RHP composites. For composites withuntreated ller, tensile strength decreases with the increas-ing of ller loading. The reduction of this property may bebecause of the weak interaction between ller and matrix as

225 shown in SEM micrographs later in Figure 8. However, forcomposites with acetic anhydride-treated ller showshigher values of tensile strength at similar ller loading.This was due to the incorporation of non-reinforcingmaterial into the composites and the inability of RHP to

230 support stress transfer from the PP=NBRr matrices.The tensile properties of these composites depend on

how RHP is well dispersed in the PP=NBRr matrices.The tensile strengths at 5 phr and 10 phr RHP remainalmost the same as the tensile strength for the PP=NBRr

235 blends. However, acetic anhydride-treated PP=NBRr=RHP composites showed signicant increase in tensilestrength. The increases in tensile strength for 5 phr and10 phr of RHP loading as a result of modication withacetic anhydride were observed to be about 5.5MPa and

2404.1Mpa, respectively, compared to the PP=NBR=RHPcomposites. The ester bond between the hydroxyl groupfrom RHP and acetic anhydride may enhance the llermatrix interaction leading to good adhesion.

As mechanical properties of the composite highly245depend on ller dispersion and adhesion of ller in the

disperse matrix phase as shown in the morphologicalstudies latter. This again due to good stress transferbetween the PP=NBRr matrix and acetic anhydride-treatedRHP. The evidence of better interactions between matrix

250and ller can be seen from SEM micrographs shown inFigure 9.

Similar ndings were reported by Arbelaiz et al.[31],whereby improvement of stress transfer from the PP matrixto the ax bre bundle for maleic anhydride treated com-

255posites. Jebrane et al.[32] Q3in their research indicated thatthe acetylation of lignocelulisic material with acetic anhy-dride very found to be more readily to interact with lignin.Hence found to make good interaction with lignocellulosicmaterials beside vinyl acetate. Further addition of RHP l-

260ler exhibited a decreasing trend in the tensile strength forboth series acetic anhydride-modied and -unmodiedspecimen. This observation was attributed to particleagglomeration due to uneven distribution of llers at highller loading. Besides poor ability of RHP llers to absorb

265stress and distributing it the PP=NBRr matrix increasingthe stress-concentration points in the composites, whichcaused the tensile strength failure[21,26].

Figure 3 shows the elongation at break verses RHP llerloadings of PP=NBRr=RHP composites. Addition of RHP

270to the PP=NBRr=RHP composites exhibited a signicantdecrease in elongation of both acetic anhydride-modiedcomposites and -unmodied specimens. Elongation atbreak shows a decrease of 35% upon the addition of30 phr of RHP. The decrease in Eb caused by RHP indi-

275cates the lignocellulosic ber RHP may act as a hindrance

FIG. 3. Elongation at break versus ber loading of PP=NBRr=RHP

composites.

FIG. 2. Tensile strength versus ller loading of PP=NBRr=RHP

composites.

4 S. RAGUNATHAN ET AL.

for molecular mobility of the PP=NBRr matrixes. Thebrittle behaviour of RHP is also supported by the YoungModules results, which is discussed later.

However the acetic anhydride-modied composites have280 indicated a 15% increase in Eb at 5 phr of RHP. This is

resulted from formation of the ester bond (COO) and evi-denced by corresponding carbonyl groups (CO) relatedto the ester functions for acetic anhydride. Good matrixand ller interactions and resulted in higher elongation at

285 break. The presence of acetic anhydride act a linker tothe RHP ller resulting in greater support and increase instiffness. However at higher RHP content the brittle natureof RHP was exhibited with very small increment of 2% inEb at 30 phr of RHP. This due to RHP ller dominant state

290 in the PP=NBRr=RHP system.Figure 4 shows plot of tensile modulus versus ller load-

ing of PP=NBRr=RHP composites. Tensile modulusincreases with the increase of ller loading. This obser-vation indicates that the incorporation of RHP ller into

295 the matrix improves the stiffness of the composites. Theaddition of RHP ller into the PP=NBRr matrix reducesthe chains mobility, consequently producing more rigidcomposites. At a similar ller loading, tensile modulusfor composites with acetic anhydride-treated ller exhibited

300 higher tensile modulus compared to composites withuntreated ller. According to Bledzki et al.[26] an increasein tensile modulus was reported in treated natural veg-etable ber due to better interactions between matrix andller. Olsen et al.[30] also indicated that formation of cova-

305 lent bonds between OH groups of cellulose and anhydridegroup may be long enough to permit entanglements withthe PP in the interphase. This again supported results forhigher tensile modulus of PP=NBRr=RHP composited inacetic anhydride-treated RHP llers.

310Swelling Test

Figure 5 shows a plot of swelling percentage of PP=NBRr=RHP composites with and without acetic anhydridetreatment in ASTM oil No. 3 for 70 h. It was found thatswelling percentage increased with increasing of RHP con-

315tent in both acetic anhydride-treated and untreated PP=NBRr=RHP composites. This was due to the propertiesof natural ber RHP which absorb oil on its sur-face[3,4,22,23]. However, for the similar composites compo-sition, the treated composites exhibited lower swelling

320percentage due to better interaction of RHP particles inthe continuous PP=NBRr matrix, which limit the pen-etration of oil into the treated composites matrix. Thismight due to the ability of acetic anhydride to form betterinteraction and a protective layer at the interfacial zone to

325consequently prevent the direct diffusion of water and oilmolecules into the composites. We have reported similarobservation on polypropylene-maleic-anhydride (PPMAH)compatibilization to PP=NBRr=RHP composites in ourprevious work[24].

330FTIR Analysis and Reaction Scheme

Figure 6 shows FTIR spectra comparison of untreatedand acetic anhydride-treated ller in the region of4004000 cm1. The spectra were baseline corrected andnormalized at 1160 cm_1, the major absorbance peak

335reecting the C-C ring of the carbohydrate backbone ofcellulose. Rice husk is mostly composed of cellulose, hemi-cellulose, lignins and some pectins. The COH of the cellu-lose backbone (CO secondary and CO primary alcohols)corresponded to the 1056 cm1 and 1030 cm1 peaks,

340respectively. We also observed an increase of the band at1260 cm1 corresponding to the ester (COO) group for-mation and a vibration band at 1740 cm1 correspondingto the carbonyl groups (CO) related to the ester functionsfor acetic anhydride-treated RHP. Silmilar ndings were

FIG. 4. Tensile modulus versus ller loading of PP=NBRr=RHP

composites.

FIG. 5. Swelling percentage of PP=NBRr=RHP composites with and

without acetic anhydride treatment.

EFFECTS OF ACETIC ANHYDRIDE ON PP=NBRr=RHP 5

345 observed by Bessadok et al. on Alfa bers, modied bychemical treatmentsQ8 acetic anhydride[25].Q3

350 Water Absorption Properties

Figure 7 shows plot of water absorption of PP=NBRr=RHP composites with and without acetic anhydride treat-ment. Each data point represents the average of ve speci-mens. Water uptake increased with immersion time and

355 increasing ller loading as also reported by other research-ers[26,27]. However, in our previous research PP=NBRr=RHP were found to exhibit 2 stage absorption behavior[28]Q8 .The RHP in continues matrix absorb water much easiercompared to the RHP particles encapsulated by NBRr. It

360 can be seen in Figure 7 that ller content had a signicanteffect on water absorption properties of the composites.

It indicates that, the higher the ller content, the higherthe percentage of equilibrium water absorption[27]. This isdue to the fact that, the increases of ller content in com-

365posite will increase the number of free OH groups of ligno-cellulosic ber. Free OH groups come in contact with waterthrough hydrogen bonding which results in water uptakeand weight gain in the composites. At a similar ller loading,it can be seen that the composites with acetic anhydride-

370treated ller shows a lower water uptake compared to thecomposites with untreated ller. This result provides a clearindication that the RHP treatment with acetic anhydrideenhances the ller-matrix interactions at the interface, thusdecreasing the amount of equilibrium water uptake by the

375composites. Ismail et al.[23] reported similar ndings,whereby lower absorption in PP=NR=RHP is attributed tothe ability of the chemical to form a protective layer at theinterfacial zone to consequently prevent the direct diffusionof water molecules into silane-treated composites.

380SEM Micrographs

Figure 8(ab) shows SEM micrographs of fractured sur-face of PP=NBRr=RHP composites with 15 and 30phrRHP loading, respectively. The SEMmicrographs shows thatpoor adhesion of RHP to the PP=NBRr matrix is the main

385factor for the reduction of the tensile strength with an increas-ing of ller loading in the composites. The incorporation ofRHP ller into the PP=NBRr matrix increases the rigidityof the material thus reduces the ductility of the composites.Figure 8(a) shows some noticeable gaps between the ller

390and matrix, which is the evidence of poor adhesion betweenthe ller and matrix. Figure 8(b) shows that the RHP llerswere pulled out from the matrix, which are marked withthe white circles, exhibited more detachment of RHP llerfrom the matrix. This is due to the poor dispersion and poor

395wettability of the ller by the PP=NBRr matrix.Figures 9(ab) show SEM micrographs of fractured sur-

face of PP=NBRr=RHP composites with acetic anhydrideller at 15 phr and 30 phr ller loadings. It can be seen inFigures 9(ab) with 15 and 30 phr RHP loading,

400respectively, good ller and matrix and attachment anddispersion. Q4The adhesion between ller and matrix were

FIG. 6. FTIR spectra comparison of untreated and acetic

anhydride-treated RHP ller.

FIG. 7. Water absorption of PP=NBRr=RHP composites with and

without Acetic anhydride treatment.

FIG. 8. (a) SEMmicrograps of PP=NBRr=RHP composite without acetic

anhydride for 70=30=15 composition. (b). SEM micrograps of PP=NBRr=

RHP composite without acetic anhydride for 70=30=30 composition.

6 S. RAGUNATHAN ET AL.

enhanced with the usage of acetic anhydride. This explainswhy higher mechanical properties for PP=NBRr=RHPwere exhibited for acetic anhydride-treated RHP

405 composites. These ndings are supported by the ductilemorphology of the treated composites (Fig. 9b).

CONCLUSIONS

The following conclusions can be made, based on theresults presented in this work.

410 1. The processing torque and tensile modulus and swellingin oil increases with increasing RHP ller loading inuntreated composites. It is attributed to the brittlenature of RHP.

2. Acetic anhydride-treated composites exhibits higher415 processing stabilization torque, tensile modulus and

elongation at break compared to untreated compositesdue to strong interfacial bonding between RHP llerand PP=NBRr matrices.

3. The acetic anhydride treatment improved the mechan-420 ical properties of PP=NBRr=RHP composites. This is

due to the good adhesion between RHP ller and thePP=NBRr matrices, as shown in the SEM micrograps.

4. Acetic anhydride treatment is effective in reducing waterand oil absorption in PP=NBRr=RHP=composites. This

425 may due to the ability of acetic anhydride to form betterinteractions and a protective layer at the interfacial zoneto consequently prevent the direct diffusion of waterand oil molecules into the composites.

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FIG. 9. (a) SEM micrograps of PP=NBRr=RHP composite with acetic

anhydride treatment for 70=30=15 composition. (b). SEM micrograps of

PP=NBRr=RHP composite with acetic anhydride treatment for 70=30=

30 composition.

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