IndianJournalof Engineering& MaterialsSciencesVol.5, October1998, pp. 324-328

High stress wear studies on addition of polycarbonate in red mud filledisotactic polypropylene

NavinChand& S A R HashmiRegionalResearchLaboratory(CSIR),NearHabibganjNaka,Bhopal462 026 India

Received26 September1997; accepted5 June 1998

Effect of addition of polycarbonate (PC) on abrasive wear resistance of red mud (RM) filled poly-propylene (PP) composites has been studied. Different volume fractions of PC have been incorporated inRM filled PP. Structural changes of samples were studied by using X-ray diffraction technique. Charac-teristic intensity peaks of PP have been reduced on addition of polycarbonate. Wear losses at differentloads have been evaluated for various blend compositions. Wear loss increased with the increase of PCcontents in PPIPCIRM composites up to 30 wt%, thereafter wear loss decreased due to morphologicalchanges in composites. Effect of load variation and sliding distance on wear characteristics of blendcomposites have been measured and discussed based on the observations of worn surfaces.

Heat distortion temperature of isotacticpolypropylene (PP) is inferior as compared to mostengineering plastics. This deficiency has restrictedits applications in many fields. Properties of PP aremodified by incorporation of various types ofparticulate fillers to achieve desired properties suchas high temperature stiffness, impact strength,dimensional stability toughness and creepresistance', Calcium carbonate is added to improvemodulus, heat stability', and dimensional stability',Similarly several other fillers such as talc" carbonblack', glass beads', mica" and red mud (RMf-1I

have been extensively added in thermoplastics toimprove their properties. RM is a new filler inthermoplastics as compared to talc, carbon black,calcium carbonate etc. It is a solid waste materialproduced by the alumina industries, following theBayer's process. Several studies related tocharacterization and utilization of RM, have beenreviewed by Thakur and Das 12. Addition of RMimproves the mechanical properties of PP and itsblend". Blending of high performance engineeringplastic improves the deficiencies inherent in PP. Ithas been reported by Liang and Williams13 thatflexural modulus increased with the addition ofpolycarbonate (PC) in PP. Heat distortiontemperature of polycarbonate (PC) at 1820 kPa isaround 140°C. Therefore, addition of PC isexpected to improve the heat resistance of PP. Inprevious paper it has been reported that thermalstability of RM particles filled PP was improved

with the addition of PC in the cornposite'". Thermalstability, heat deflection temperature, modulus etc.affect the wear properties of composites. Theseproperties are governed mainly by composition,morphology, interface and structure of elements ofcomposites. In one study wear properties have beenmodified by addition of particulate mixture of leadoxide. and graphite in poly tetra flouro ethylene(PTFE) filled poly phenylene sulfide (PPS) 15.

Some recent studies on RM particulate filledpolymers and polyblends have been reported inliterature 7-11. Mechanical properties of RM filledblends were improved by the addition of RMparticles 7-11. Increase in finness of RM particles,increased the modulus and tensile strength of theblend!', These studies show that addition of RMimproves modulus of PP and blending of RM filledPP with PC improves the thermal stability ofcomposite". It shall be interesting to observe thewear properties of PPIPCIRM composites. Inpresent investigation effect of addition of differentvolume fraction of PC to RM filled PP on highstress wear properties of PPfPCIRM compositeshave been determined and analyzed.

Materials and Methods

Materialslsotactic polypropylene (Koylene M0030)

having density 0.908 g/crrr' supplied by IPCL,India was used in this work. Commercial gradepolycarbonate (Makrolon AL 2643 of Bayer,

CHAND & HASHMI: EFFECT OF ADDITION OF PC ON ABRASIVE WEAR OF RED MUD 325

Germany) supplied by MIs Ennkay Polymers,Bhopal, India was used. RM particles of size lessthan 451lm were separated by wet sieving of RMsupplied by BALCO India. Major chemicalconstituents of RM particles are Si02 - 9.16%,Fe203 - 53.97%, Ah03 - 14.97%. The mineralphases present and structure of RM particles usedin this study have been reported earlier",

Compounding procedurePC, PP and RM particles were kept in air

circulating oven at 100°C for 24 h to dry thematerials. These materials werernixed on a20 mm single screw extruder having LID ratio as27.5. Temperatures of feed zone, compressivezone, metering zone and of the die was fixed at235, 245, 250 and 250°C respectively. Screwrotation per minute was kept at 15. Continuous

strands obtained from extruder were granulated to asize of 5 mm length.Molding process

The granules obtained by extruder werecompression moulded into 4 mm thick sheets attemperature 250°C for 1 min at 1.0 MPa pressure.Sheet was quenched immediately in the water at20°C.Measurements

X-ray diffraction patterns were obtained byusing philips diffractometer PW 1710 to study theeffect of addition of PC in RM filled PP oncrystallinity of PP which affect the wearproperties 16.

High stress abrasion tests were conducted on atwo-body Suga abrasion tester model NUSI(Japan). A rectangular specimen of size 35 mm x

I !tOo

o 90/10;~.261200

; 1000

au- 800>-t::...~ 600~~

C 60/40/5.26

400

OL- ~ ~~--------~~----------~10 20 :to /to 50

2"Fig. l-X-ray diffraction pattern ofPPIPCIRM composites

HOO

-aooo=.~!:: 1500

1000

2."

Fig. 2-X-ray diffraction pattern OJ 1"1"

Fig. 3-Micrograph of spheruntic crystal of PP at 160 magni-fication

326 INDIAN J. ENG. MATER. SCJ., OCTOBER 1998

40 mm x 4 mm was slide against a rotating wheelon which abrasive paper of 400 grit size wasmounted using double sided adhesive tapes. Theembedded hard SiC particles abraded thecomposite during the test. The weight lossmeasurements were taken for four set of cycles.Test was conducted for 100, 200, 300 and 400cycles, corresponding to the sliding distance of 6.4,12.8, 19.2 and 25.6 m at a constant sliding speed of2.56 m min". Three different loads such as 1 3, ,and 5 N were applied. Weight loss was measuredafter each set of 100 cycles. Fresh paper of thesame grit size was used for different loads.

Scanning electron microscope (SEM) JEOL35CF model was used to observe the surfaces ofcomposites. Leitz optical microscope was used toobserve the crystal of PP under polaroid light.

Results and DiscussionDiffraction pattern of PPIPCIRM composites of

90110/5 .26, 0/30/5.26 and 60/40/5.26 are shown ascurve a, band c respectively in Fig. 1. Loading of

Fig. 4--CryogenicaUy fractured surtace ot PP/PCIRM(a) 80/20/5.26, and (b) 60/40/5.26

RM particles is fixed at 5 part per hundred parts ofPP/PC blend by weight while PPIPC blendcomposition is varied. Content of PC in PP matrixincreased from 10 wt% to 40 wt%. On comparingthe X-ray diffraction pattern of PP (Fig. 2) andPPfPCfRM (Fig. I) it is noticed that latter exhibitsall reflections of PP. The main differences lie in theintensities of peaks, which reduced with theincrease of PC content in PP. Peak intensitiesobserved at 14.2, 17.1, 18.62 and 22.09 (2i) valuesreduced from 1500 to 1305 and 920, from 1410 to1303 and 855, from 1070 to 963 and 729 and from1211 to 1033 and 749 for compositions of90110/5.26, 70/30/5.26 and 60/30/5.26 respectively.Addition of polycarbonate in PP matrix reduced theintensity. Polypropylene is a highly crystallinepolymer producing spherulitic crystals whenallowed to crystallize from its melt as shown inmicrograph Fig. 3. The addition of polycarbonatewhich is present in solid globules form as dispersedand shown in micrograph (Fig. 4) restricts thegrowth of crystallites. These globules of PCbecome the centre of nucleation for PP crystalsbecause at crystallization temperature of PP, PP isin molten state whereas PC is in solid state due to

5""'

I 40-3

CJ>

",- 2'"E~

PP/PC/RML GAD :::: 1 Newton

~ 90/10/526~ 80/20/526~ 70/30/526~ 60/40/526

305 10 15 20Sliding distance, m

25

Fig. 5-Plot for the variation of weight loss with increasingsliding distance of PP/PC/RM polyblend composites subjectedto two body abrasion test at applied load of 1 N

PP/PC/RMlOAD,... .3 Newton

- 90/10/526- 80/20/526- 70/30/526- 60/40/526

10 15 20SI iding distance, m

25 30

Fig. 6--Plot for the variation of weight loss with increasingsliding distance of PP/PCIRM polyb1end composites subjectedto two body abrasion test at applied load of 3N

CHAND & HASHMI: EFFECT OF ADDITION OF PC ON ABRASIVE WEAR OF RED MUD 327

large difference in melting points of two polymers.Therefore, number of nucleate centres increased onaddition of PC in PP matrix and resulted inlowering the crystallinity.

Weight loss versus sliding distance curves forthe systems studied here, when subjected to high-stress abrasion are given in Figs 5-7. The variationin the weight loss with increasing sliding distanceexhibits a near linear relationship. The histogramgiven in Fig. 8 comparing the weight loss atdifferent applied loads reveals that there is a steadyincrease in weight loss with increasing load.

The effect of RM loading on the wear. behaviourof this system cannot be understood as the loadingof red mud particles has been kept constant.However, the fraction of constituent polymers PPand PC has quite significant effect on wearbehaviour of the entire system. This effect isillustrated in Fig. 9 in which weight loss is plottedagainst matrix composition. With the increase ofPC from 10 to 30% in the blend, the weight lossincreases. Thereafter on increasing PC content to40%, reduction in weight loss is observed. Theincrease in wear loss with the increase in weightper cent of PC upto a certain loading and a

Tr0 1610 14-x 12

100'

.,; 8II> 6.2

4~ 2

00 5

PP/PC/R ••LOAD = :. Newton

- 90/10/5.26- 80/20/,.26- 70/30/526- 60/40/5.26

10 15 20Sliding distance, m

25

Fig. 7-Plot for the variation of weight loss with increasingsliding distance of PP/PCIRM polyblend composites subjectedto two body abrasion test at applied load of 5N

12 PP/PC/RMr01

10 composition 90/10/5.26

S' • 1 N .3 N .5 Nx 80'

.,; 6II>.2

41:0'

2'4i~

6.4 12.8 19.2Sliding distance, m

25.6

Fig. 8-Histogram comparing weight loss of PPIPCIRM poly-blend composite at different sliding distance and differentapplied loads

subsequent decrease in wear loss thereafter can beexplained on the basis of morphology ofPPIPCIRM composites. PP and PC areincompatible polymers. In a PPIPC blend, PPforms the matrix and globules( domains) of PC aredispersed in PP as shown in Fig. 4. During abrasion

load

-+-: IN...•...: lH

'0 20 30 «) 50o~----+-----~----------------~

o% Composition of PC in PP/PC matrix

Fig. 9-Wear loss versus per cent composition of PC in PPIPCmatrix

301

Fig. 100Micrographs of worn surfaces of PPIPCIRJ(a) 90/10/5.26 and (b) 60/40/5.26

INDIAN 1. ENG. MATER. SCI., OCTOBER 1998

test, the isolated and unattached PC domains areremoved from the matrix leaving behind theircavities. The wear of PP occurs due to microcuttingand ploughing. On increasing PC content up to acomposition of 70/30/5.26, wear loss increaseswith the increase of PC. A similar observation wasmade in case of PC when compared with LDPE 3that PC showed less wear resistance as compared topolyolefin'". In present case, at high PC loading ofcomposition 60/40/5.26 (PPIPCIRM), the size ofdomains increased to a size larger than that ofabrasive particles as shown in Fig. 4b and hencewear loss decreased'Y.Increase in size of PCdomain at 40 wt% is attributed to coalition of smallPC domains on reduction of inter domain distances.For instant, on assuming average diameter of PCdomain as 10 urn, the distance between two PCdomains at PPIPCIRM, 90/10/5.26 compositionwould be 8.9J.lm which reduces to 1.6J.lm at60/40/5.26 composition. At this distance severalPC domains collapse with each other and form abig size domain as observed. It is evident from Fig.lOa that microcutting and microploughing is moresevere when the content of PC is around 10% in theblend but as its content increases up to 40% theseverity of abrasion reduced as shown in Fig. lOb.However, the one factor in weight loss is still theeffect of red mud particles. In case of 90/10combination of PPIPC, these particles remain inisolation embedded in either of the two polymers.During abrasion, when these particles encounterthe abrasives they get fractured and removed aswear debris.

Conclusions1 Crystallinity of PP decreased on addition of PC

due to hindrance offered by domains of PC inthe growth of crystals of PP.

2 .PC is dispersed in the matrix in the form ofsmall spherical domains of size less than 10 urnat 10 malo loading. Size as well as number ofdomains increased with the increase in PCcontent.

Wear loss increased with increased PC contentfrom 10 to 30% and then decreased at-40% ofPC in PPIPCIRM because size of domains of PCbecame larger than that of abrasive particles.

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