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Mechanical Properties of Recycled Polypropylene/SBR RubberCrumbs Blends Reinforced by Birch Wood FlourAdel Ramezani Ka kroo di^ Simon Leduc^, Rubn Gonzlez-Nez^, and Denis Rodrigue^*'Department of Chemical Engineering and CERM A, Universit Laval, Quebec City, Qc, G l V 0A6, C anada^Departamento de Ingenieria Qumica, Universidad d e Guadalajara, Guadalajara, Jalisco, 44430, M exicoReceived: 17 Novem ber 2010, Accepted: 3 October 2011

SUMMARYIn this work, recycled polypropylene (PP) and regenerated styrene butadiene rubber (SBR) ftom used tyres rubbercrumbs were combined to produce polymeric blends. The compounds were prepared via twin-screw extrusionto measure their mechanical behaviour for different SBR compositions (0 to 40%). Also, the addition of birchflour (0 to 40%) and coupling agent (0 to 5 phr) content were studied. The results showed that tensile strengthand modulus of the blends were substantially improved after incorporation of wood flour. The torsion modulusalso increased with birch content. However, the tensile strain at break of PP/birch wood composites decreasedwith both wood and coupling agent contents, showing a decrease in ductility of the composites. Adding theelastomer phase did not improve the properties. The results showed that adding a coupling agent was found tobe effective in improving the wood flour-PP interface, while less improvement was observed for the rubber-PPsurface adhesion. The tensile strength of PP/birch composites improved by more than 60% , while the torsionand tensile moduli of the composites improved by only 10% in some cases.Keywords: Recycled polypropylene. Mechanical properties,Birchw oodflour,Styreneb utadienem bber

1. INTRODUC TIONDuring the last decades, severalattempts have been dedicated top rov ide economica l ly ava i l ab lemethods to decrease the amount ofwastefromdifferent types of materials.Used plastics form a signif icantpart of municipal waste, while theirenvironmental impact is huge. Amongthese polymers, polypropylene (PP),polyethylene (PE ), poly(vinyl chloride)(PVC) and rubbers l ike styrene-butadiene rubber (SBR) are some ofthe most cormnonly used materials.This is the source of much attentionpaid to produce practical productsfrom recycled m aterials as a potentialway to reuse these huge amounts ofwaste plastics and rubbers. Thisfieldofinvestigation was the origin of researchworks in several industries especially

in composite fabrication'"^ Productionof low cost compo unds from recycledmaterials and easily producedfiUers sinteresting from both environmentaland economical points of view.Adding natural fibres to polymers, onthe other hand, have found severalapplications recently. This is due toimportant characteristics of naturalfibres like lower density, lower cost,renewability and less harsh processingconditions in mechanical equipmentw h e n c o m p a r e d t o t r a d i t i o n a lreinforceme nts like glassfibres.Today,special opportunities to create newhorizons in the comp osite industry arebeing developed*'''. This is why suchnatural fibres are excellent choicesfor applications like construction andvehicles interior parts (trunks and door

Corresponding author: D [email protected]

panels). Exam ples of naturalfibresusedare: silk, coir, sisal, flax, jute, bananaand wood. Thesefibreshave been usedas reinforcement in several polymercom posite formulations*"'".Nevertheless, natural f ibres havesome disadvantages. They are moreeasily thermally degraded than man-made reinforcements, and this is whypolyolefins like PE and PP, whichcan be processed under 200 C, havebeen used as matrices in most of theworks done in the field of naturalfibre composites. Natural fibres havesome drawbacks as reinforcing agentsin polymer-based composites, likelow processing temperature, highwater absorption and low fibre matrixinteraction due to hydrophilic natureof the fibres". Most natural fibrecomposites show low matrix-fibreinteraction due to high surface energydifference between highly polar fibresand nonpolar matrix. Good fibrematrix interfacial adhesion results


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Adel Ramezani K akroodi, Simon Leduc, Rubn G onzdlez-Nez, and Denis Rodrigue

fibres and increases the reinforcingeffect of fibres. This fibre matrixinteraction can be improved by severalmethods: 1) Surface modification withcoupling agents like maleic anhydrideand silane coupling agents. Severalresearch works have demon strated thatadding maleic anhydride or maleatedpolyolefins results in noticeableincreases in mechanical prop ertie s"" .2) Pre-impregnation of fibres bysoaking in dilute solution of thematrix to provide better wetting. 3)Alkalization of fibres to make voidsand increase thefibre-matrix nterface.A great deal of research work has bee ndone in thisfield,but most of these haveused simuar fibre treatment methods.Effect of fibre-matrix adhesion onthe mechanical properties of PEcomposites reinforced with henequnfibres was studied by Herrera-Francoet al. *. They used fibre treatment suchas alkali treatment, silane couplingagent and pre-impregnation of thefibres by soaking in dilute solutionof HDPE in xylene to investigatethe effect of fibre-matrix interaction.They reported that the interface shearstrength (IFSS), which is a criterionfor f ibre-matrix interaction, wasimproved significantly after fibretreatment. They co ncluded that fibreswith higher interface area, due toalkalization, highe r com patibility, dueto silane modification, and higher levelsof wetting, due to pre-impregnationin dilute PE solution, increasedinterfacial adhesion significantly. Theyalso observed that fibre treatment byboth silane coupling agent and alkalimodification improved the tensilestrength by up to 30%.Khalf et al." studied natural rubbert h e r m o p l a s t i c e l a s t o m e r ( T P E )composites made of rice husk asr e in fo rcemen t and LLDPE/SBR(50/50) as the matrix in the presenceof maleic anhydride (MA) couplingagent. They studied the effects ofdifferent concentrations of MA (0-

an increase in MA concentration upto 2.5 phr increased tensile p ropertiesof the composites significantly. FromSEM micrographs they concludedthat adding MA as coupling agentled to good interaction between thephases for the range of parametersstudied. Elongation at break of thestudied composites decreased afterincorporation of MA.Recycled rubber powder can alsobe used in thermoplastic elastomercomposites, butm ustb e devulcanizedor a t least sur face regeneratedbefore being added to the plasticmelt . Crosslinks density can bemodified by several methods likechemical, mechanical, thermal andultrasonic devulcanization, so thatfree rubber molecules can providebetter interaction with thermoplasticphase ' ' - " .The purpose of this work is to presentrecycled PP-Devulcanized Rubberblends as useable polymeric m aterialsand improve their properties byadding birch wood sawdust and byincorporating MAPP as a couplingagent.

2. EXPERIMENTALMETHODS2.1 MaterialsPost-industrial recycled polyprop ylene,PP-RP, was obtained from RECYC-RPM (Quebec , Canada) wi th amelt flow index of 19.8 g/10 min(ASTM-D1238). Birch wood flourwas obtained from local sawmillsas industrial residues. The materialwas sieved to keep only the particlesbetween 300 and 600 fim. Finally,styrene butadiene rubber was obtainedfrom used tyres and supplied byPhoenix Irmovations (Quebec, Cana da)with an average particle size of 40-60mesh (250-400 microns). This materialwas also used as received.The couplingagent used in this study was m aleated

2.2 Composite FabricationBirch wood reinforcements werefirst dried at 105 C for 24 h. Then,the dried fibres, recycled PP pellets,devulcanized rubber powder andcoupling agent were dry mixed firstto be blended in a twin-screw extruderto prepare well-dispersed compounds.The mixture prepared by extrusionwas next dried at 105 C for another24 hour period and injection-mouldedto fabricate the samples. Injectedsamples were prepared by a Nisseiinjection moulding machine with a62 ton clamping force, a screw diameterof 36 mm and an injection capacity of114 cm^ The barrel temperature profilewas fixed at 150,17 0,18 5 and 185 Cto minimize thermal degradation of thematerials. The samples were preparedat an injection speed of 109 cm^/swith a mould temperature of 60 C.Rectangular samples with dimensionsof 0.32 X 2.54 X 10.16 cm^ we reprepared for mechanical tests. Sampleswith different reinforcement and CA(MAPP Epolene PMG -3003) contentsare presented and coded in Table 1.2.3 Mechanical Test ingTensue properties of the compositeswere evaluated by an Instron model5565 universal testing machine with aload cefl of 500 N and a crosshead speedof 2 mm/min. A minimum of 5 sampleswere tested for each concentration.Testing samples were cut into desireddimensions by die cutting dog bonesamples with dime nsions of the narrowpart of the samples of 9.53 x 3 x 3 mm^(ASTMD638typeV).Torsiontestswereperformed using an ARES R heometerwith dynamic frequency sweeps at 1%strain (Hnear viscoelastic regime) andthe modulus was determined at 1 radsec. Three rectangular samples (75 x 11X 3 mm ') were cut to characterize eacconcentration.

3. RESULTS ANDDISCUSSION


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Mechanical Properties of Recycled PolypropylenelSBR R ubber Crum bs Blends Reinforced by Birch Wood Flour

Figu res 1-4 compared to PP sampleswithout any additives.Figure 1 presents the tensile strengthof PP/SBRAVoodfibrecompo sites withdifferent amounts of reinforcement,CA and rubber content compeired torecycled PP without any additives.Blends containing only PP and SBRshow lower tensile strength which isdue to low mechanical properties ofthe rubber compared to PP and lowcompatibility between PP and rubberpariicles. Adding birch w ood fiour tothe PP/rubber m ixtures did not lead toa noticeable increase in tensile strengthof the composites, which shows thatlow compatibil i ty between rubberparticles and the m atrix w a s controllingthe properties. But, an improvementin tensile strength is observed afterincorporation of high am ounts of woodpowder (sample 17).It is clear that for the composites,increasing the amount of wood did notimprove the mechanical properties ofPP itself, showing poor fibre-matrixinteraction in this case. In fact, addingwoodflourdecreased t h e continuity ofthe matrix phase. Incorporation of thecoupling agent produced a noticeablepositive effect on tensile properties ofall samples. This increase in tensilestrength was almost 30 % for PP/birchwood/rubber co mposites and got even

higher, over 60%, in the case of PP/Birch w ood composites. The EpolenePMG-3003 coupling agent used inthis study seems to be highly effectivehere, since Herrera-Franco et al.^'*reported that tensile strength was onlyimproved by 19% after silane surface

modification. They also reported thatthe most significant im proveme nt, 3 0 %increase in tensu e strength, happenedwhen henequn f ibres were f irsttreated by alkaline solution and thenwith silane coupling agent. Oksmanand de m on s'* also studied the effect

Table 1 . Blend composition and coding of different samplesSample code12345678910111213141516171819202122

P P ( w t . % )100808080606060606060606060606060808080606060

R u b b e r ( w t . % )0202020404040303030202020101010000000

W o o d ( wt .% )0000000101010202020303030202020404040

C A ( ph r)0035035035035035035035

Figure 1. Effect of blend composition on tensile strength

oil


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Adel Ram ezani Kakroodi, Simon Leduc, Rubn Gonzdlez-Nez, and Denis Rodrigue

Figure 2. Effect of blends comp osition on: (a) stress at break and (b) strain at break(a) 25.

CO

8 9 10 11121. 141516 171819 2021 22(b)

aICS

c

00ISJ

2 3 4 5 6 7 8 9 10 1112 13 1415 16 17 18 19 202122

of maleated polymers on the tensileproperties of PP based composites.They reported that tensile strength oftheir composites increased from 28 to32M Pa (only 14% improvement) afterincorporation of 2 wt.% maleated PP.The stress and strain at break resultsare presented in Figure 2. The datashow that stress at break changedwith composition in a similar way tostrength. Again an increase in rubbercontent led to lower stress at break,while adding woo d flour and couplingagent improved it significantly. Anincrease in reinforcement content is alsoobserved to cause higher dependence ofcomposites performance on coupling

powder (sample 17) increased thetensile strength by around 15%, whileincorporation of the same amount ofCA increased the tensile strength ofsample 20 (40% wood powder) by over60%. This indicates that the couplingagent used in this study increasedmechanical properties by directlyaffecting fibre-matrix adhesion, notby increasing the rubber/PP surfaceinteraction.It is also observed from Figure 2 thatthe strains at break of the com positesare much less than that of PP itself. Anincrease in CA content resulted inlowerstrain at break which could be due tohigher fibre-matrix interaction. As a

effect ofrigidfibreson the composite'sproperties. Figure 2 indicates that anincrease in fibre, coupling agent andeven rubber content decreases duc tilityof the blends.For samples com posed of only PP andSBR rubber, it is surprisingly observedthat an increase in rubber content notonly increases the strain at break, butalso decreases it noticeably wh ich canbe considered as a result of poor PP/rubber surface interaction. AlthoughEpolene PM G-3003 seems to be a goodcoupling agent to increase PP/woodflour surface interaction, it did notmodify the SBR/PP surface adhesion.


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Mechanical Properties of Recycled Polypropylene/SBR Rubber Crumbs Blends Reinforced by Birch Wood Flour

Figure 3. Effect of blend s composition on torsion m odulus

2 3 4 5 6 7 8 9 10 11 12 Li 14 l . 16 17 18 19 20 21 22

Figure 4. Effect of blends com position on tensile modulus

o -EI

2 3 4 5 6 7 8 9 10 1112 13 14 15 16 17 18 19 20 2122

respectively. These results show thatan increase in the proportion of birchwood reinforcement in the compositesincreased the torsional modulus, aswell as tensile properties. Torsionalmodulus of sample 20 (40% wood)is around 830 MPa compared to 580MPa for sample 17 (20% wood).Using a coupling agent also produceda positive effect on the fibre-matrixinterfacial adhesion and this effect ismore sensible for blends with higherfibre contents. As expected, tensileproperties of the composites declinedafter incorporation of rubber powderin the blends. For both wood our andrubber filled samples, an important

which is in agreement with the resultsreported by Lopez M anchado et al.^^.

4 . C O N C L U S I O NMechanical proper t ies of b lendsshowed that adding bi rch woodsawdust increased the tensile andtorsional modulus and tensile strengthof the composites. Such compositesalso achieved increased tensile andtorsional properties after inco rporationof MAPE as a coupling agent. Theeffect of the coupling ag ent used wasgreater for com posites with higher fibrecontent, which revealed a noticeable

of C A also increased the compatibilityof PP and rubber pow der slightly.Tensile strain at break m easurem ents,on the other hand, showed that anincrease in the proportions of the fibreand even the elastomer phase led toless ductile materials. In other words ,elastomer particles did not providegood interfacial adhesion with thethermoplastic matrix. Coupling agentaddition decreased the ductility of thecomp osites, which improved the effectof fibres on the composites p roperties.Production of compounds based on


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Adel Ram ezani Kakroodi, Simon Leduc, Rubn G onzdlez-Nez, and Denis R odrigue

the main objective of this work, wasattained. As an example, sample 22composed of recycled PP as the matrixand wood industry residue (Birchwoodflour)as reinforcement producedcomposites having good mechanicalproperties. Such compounds lead toa practical and economical recycledmaterial with less environmentalimpact.

ACKNOWLEDGEMENTSFinancial support from the NationalSciences and Engineering ResearchCouncil of Canada (NSERC) washighly appreciated. Technical supportfrom CQMF was very helpful in theexperimental work. SBR samplesfrom Phoenix Innovations, PP samplesfrom Recyc-RPM and MAPP samplesfrom Eastman Chemicals were alsohighly appreciated to perform theexperimental work.

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