Behavior and melt viscosity of polycarbonate/low density polyethylene blend in capillary flow

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Interntionl Journl of Chemech Reserch CODEN( USA): IJCRGG ISSN : 0974-4290 Vol.6, No.

1 Interntionl Journl of Chemech Reserch CODEN( USA): IJCRGG ISSN : Vol.6, No.1, pp , Jn-Mrch 2014 Behvior nd melt viscosity of polycrbonte/low density polyethylene blend in cpillry flow Ahmd Flh Deprtment of chemistry-fculty of science, University of Dmscus, Dmscus Syri *Corres.uthor: wwillzoubi@yhoo.com Abstrct : A knowledge of the vrition of melt viscosity of thermoplstic polymers with both with both sher rte nd temperture is considerble importnce to plstics engineers s well s to polymer rheologist. he ctul mesurements of the melt viscosity t lrge number of the tempertures nd sher rtes re frequently tedious nd time-consuming tsk. A technique hs been developed, bsed upon the pplicbility of sher rte temperture superposition, for predicting the flow curves for PC/LDPE (50/50) blend t different tempertures for experimentl form dt obtined t one temperture for the mteril in question. he experimentl vlidity for superimposing flow curves t different tempertures long the log sher rte xis hs been estblished for PC/LDPE (50/50) blend. the temperture dependence of the resultnt shift fctors hs been determined for the system, nd the method of utilizing this informtion to predict viscosities s function of temperture nd sher rte is discussed. Keywords: Rheology, PC, LDPE, Shifting fctor, Activtion energy. Introduction A knowledge of the melt viscosity of thermoplstic polymers t vrious tempertures nd sher rtes is importnt to plstics engineers s well s to polymer rheologist who must design polymer processing equipment or who must specify the processing conditions for the fbriction plstics mterils, such informtion is eqully importnt to producers of polymeric mterils nd to the pplied polymer rheologist. While considerble dt my be found in the literture relting melt viscosity either to sher conditions or to temperture, it is frequently difficult or impossible to pply these dt to predicting the flow behvior of the specific resin polymers of interest to given engineers or rheologists. Moreover, the ctul mesurements of the melt viscosity t lrge number of the temperture nd sher rtes is normlly t tedious nd time consuming tsk. Becuse of its opticl clrity, excellent therml resistnce nd high impct strength, very useful engineering thermoplstic, polycrbonte (PC), is used in wide rnge of industrils such s utomotive nd trnsporttion, building nd construction, pckging, medicl, opticl nd ophthlmic, nd opticl medi [1-7]. Recently, it is in widespred use in the udio, video nd interctive softwre medi. he PC cpcities of the globl min mrkets in 2001, including North Americ, South Americ, Europe, nd Asi, ws incresed from

2 Ahmd Flh/Int.J. Chemech Res.2014,6(1), pp million m.t./yr in 1999 (Modern Plstics Interntionl, 2000) to 1.73 million m.t./yr (Chemicl Week, 2000). he world cpcity of PC is continuing to increse to 2.62 million m.t./yr in 2002 nd the cpcity is projected to grow to bout 3.1 million m.t./yr by 2007 (Chemicl Week, 2002). According to the sme report, the end uses of PC in 2001 were 1.1 billion lb, nd 20% of PC ws used in opticl medi whose proportion ws equl to utomotives nd window glzing. Form nother side, the higher price nd melt viscosity of PC limited its ppliction in some pplictions, such problems could be solved using polymer blending technique in the molten stte. he im of this work is to prepre PC/LDPE (50/50) in the molten stte using the extrusion process nd studying the rheologicl properties of this blend using cpillry rheometer (Melt indexer type) nd to generlize method of predicting the flow curves of PC/LDPE (50/50) blend t ny desired temperture from ny experimentl dt for this system. Experimentl Mterils Low density polyethylene (LDPE) (SABIC LDPE2308N00) [density = g/cm 3, MFI =7.5 g/10 min (190 C/2.16 Kg)] ws supplied by Sbic (KSA). Polycrbonte (PC) (Lexn OQ1026 resin CD producing grde) [density = 1.2 g/cm 3, MVFR = 11.0 cm 3 /10min (250 C/1.2 Kg)] ws supplied by Sbic (KSA). Blend preprtion Blends of PC/LDPE (50/50) ws compounded using lbortory scle single screw extruder (SSE) (D = 20 mm, L/D = 25). he screw speed ws set t 50 rpm in the blends preprtion, nd the extruder temperture profile long the brrel ws 180, 190, 200, 210 C (from feed zone to die). Melt rheology mesurements Rheologicl properties of the blends were studied using constnt pressure circulr cpillry rheometer. he melt is extruded by the use of ded weights (i.e. constnt pressure) rther thn constnt plunger speed. his instrument, populrly known s the Melt Flow Indexer (MFI), is very populr in the thermoplstics industry due to its ese of opertion nd low cost, which more thn compenstes for its lck of sophistiction. he prmeter mesured through the melt flow indexer contins mixed informtion of the elstic nd viscous effects of the polymer. he rheologicl experiments were crried out t 210, 215, 220, 225 nd 230 C, nd by using L/R = 15. he pprent sher rte ( ) is given by: where R is the cpillry rdius, nd Q is the volumetric flow rte. he pprent sher stress (τ ) is given by: where P is the pressure t the cpillry entrnce, nd L is the cpillry length. he pprent viscosity (η ) is given by: 4Q = (1) 3 πr RP τ = (2) 2L τ η = (3) he vlues of flow ctivtion energy t constnt sher stress (E τ ) were determined by using Arrhenius eqution form: Eτ R η = A. e (4) where A is the consistency relted to structure nd formultion nd R is the gs constnt (8.314 J/mol. K).

3 Ahmd Flh/Int.J. Chemech Res.2014,6(1), pp Results nd discussion Rheologicl curves Figure 1 represent the flow curves of the blend t the studied tempertures (210, 215, 220, 225, 230 C), these curves re very importnt in determining the processing conditions of the mteril in the different processing techniques such s injection, extrusion nd blow molding. Fig. 1 Flow curves of PC/LDPE (50/50) t vrious tempertures nd L/R=15 It cn be seen tht these curves pprently devite from liner reltionship inclining to the xis of sher rte, which mens tht the blend is pseudo plstic non-newton fluids similr to most polymeric melts [8], nd they obey the power lw: τ K. n = (5) where K is the consistency index nd n is the non-newtonin index, which cn be clculted from the slope of the lines in Fig. 1. d logτ n = (6) d log Figure 2 shows the viscosity curves of PC/LDPE (50/50) blend t vrious temperture nd sher rtes. It could be noted form Fig. 2, tht the melt viscosity of the blend decreses with incresing sher rte t the vrious tempertures; this behvior confirms the lst finding bout the pseudo plstic mnner of the blend.

4 Ahmd Flh/Int.J. Chemech Res.2014,6(1), pp Fig. 2 Viscosity curves of PC/LDPE (50/50) blend t vrious tempertures nd L/R=15 Shift fctor determintion he flow curves my be shifted long the sher rte xis, i. e. t constnt sher stress for ech point. he curve of superimpose on the single mster cure corresponding to n rbitrrily ws chosen s reference temperture. he rbitrry reference temperture used here for the blend ws 220 C. he horizontl shift fctor ( ) were obtined by choosing the sher stresses (14475, 27900, 38125, P). Flow curves nd shifting the corresponding points on the flow curves t the different tempertures were coincided t these sher stresses, the vlues of were clculted using the following eqution [9-12]: (220) = ( ) τ (7) where (220) is the reference sher rte (t 220 ºC), nd () is the sher rte t. vlues were clculted t ech sher stress. It could be noted tht the lst eqution my be rewritten s following: ( ) η ( ) = ( ) τ (8) η (220) where η (220) is the reference sher viscosity (t 220 ºC), nd η () is the sher viscosity t. he vlues of the shifted fctors re summrized in ble 1. In order to test the pplicbility of these sher rte-temperture superposition shift fctors. he vlues presented in tble 1 were used to contrst the mster flow curve t 220 ºC utilizing eqution (8).he resultnt mster curve shown in Fig. 3 clerly illustrtes the vlidity of the superposition method.

5 Ahmd Flh/Int.J. Chemech Res.2014,6(1), pp ble 1 Experimentl rheolgicl dt (ºC) τ (200) (P) (s -1 ) (s -1. η ) (s -1 ) (P.s) Fig. 3 he mster curve Moreover, it is not even necessry tht the known dt set be vilble t the reference temperture since, ssuming dt to be known t 1 nd desiring dt t 2, elimintion of (ref) from eqution 7 ( 2 ) 1 ( 1 ) / 2 = (9) he temperture dependence on the shift fctors ws next investigted together with simple exponentil or Arrhenius type eqution of the form:

6 Ahmd Flh/Int.J. Chemech Res.2014,6(1), pp E R. B. e = (10) Where is the bsolute temperture nd E is the shift fctor ctivtion energy nd R is the generl gs constnt. he lst eqution could be rewritten s following: his could be lso simplified s following: Where: E Log = LogB + (11) 2.303R. C Log = B' + (12) E C = (13) 2.303R Figure 4 shows the liner plots of Log versus 1/ t constnt sher stresses. he slop of these lines gives the shift fctor ctivtion energy. Fig. 4 shift fctor versus 1/ t constnt sher stresses he vlues of the shift fctor ctivtion energy t constnt sher stresses re listed in ble 2: ble 2 Shift fctor ctivtion energy t constnt sher stresses (E) Sher stress (P) E (kj/mol) Also, the flow ctivtion energy t constnt sher stresses from the pprent viscosity vlues (E τ ) ws clculted using Arrhenius form eqution (eqution 4), Fig 5 shows the plots of pprent viscosity versus 1/ t constnt sher stresses:

7 Ahmd Flh/Int.J. Chemech Res.2014,6(1), pp Fig. 5 Apprent sher viscosity versus 1/ t constnt sher stresses It could be seen from Fig. 5, tht the plots re liner nd they obey the Arrhenius type eqution (eqution 4), the flow ctivtion energy could be clculted from the slope of these line. he vlues of the flow ctivtion energy t constnt sher stresses (E τ ) re listed in ble 3: ble 3 Flow ctivtion energy t constnt sher stresses (E τ ) Sher stress (P) E τ (kj/mol) It is well known tht the vlue of flow ctivtion energy reflects the temperture-sensitivity of viscosity, so the more E τ ws the more sensitive the behvior of blends were to the temperture. It could be noted from bles 1 nd 2 tht both flow ctivtion energy (E τ ) nd shift fctor ctivtion energy (E) hs nerly the sme vlues, which confirms the used prediction method. Conclusion he generl vlidity of sher rte- temperture superposition of log sher stress VS log sher rte flow curves hve been demonstrted for PC/LDPE (50/50 wt%). he temperture dependent on the resultnt shift fctors hs been shown to be cpble of representtion by Arrhenius type eqution of the generic system. Moreover the technique of sher rte- temperture superposition nd the shift fctor temperture dependence to predict flow curve t vrious temperture llow us to determine the sher stress tht is necessry for desired temperture t sher rte constnt.

8 Ahmd Flh/Int.J. Chemech Res.2014,6(1), pp References 1. Surez H, Brlow JW, Pul DR (1984) Mechnicl properties of ABS/polycrbonte blends. J Appl Polym Sci 29: sdemir M (2004) Properties of crylonitrile butdiene- styrene/polycrbonte blends with styrene butdiene styrene block copolymer. J Appl Polym Sci 93: Wu JS, Shen SC, Chng FC (1993) Effect of polycrbonte moleculr weight on polymer blends of polycrbonte nd ABS. J Appl Polym Sci 50: Hung JC, Wng MS (1989) Recent dvnces in ABS/PC blends. Polm ech 9: Mishr SP, Venkidusmy P (1995) Structurl nd therml behvior of PC/PB blends. J Appl Polym Sci 58: Nthwt R, Vijy YK, Kumr P (2008) Physiclly nd chemiclly modified polycrbonte by metl ion implnttion. Adv.Polym.ech 27: Bhniwl S, Shrm A, Aggrwl S, Deshpnde S K, Shrm SK, Nir KG (2010) Chnges in structurl nd opticl properties of polycrbonte induced by Ag+ ion implnttion. J Mcrom Sci 49: Hu GS, Wng BB, Go FZ (2006) Investigtion on the rheologicl behvior of nylon 6/11. Mter Sci Eng 426: Mendelson RA (2004) Prediction of melt viscosity flow curves t vrious tempertures for some olefin polymers nd copolymers. Polym Eng Sci 8: Deri F (1994) Prediction of melt viscosity flow curves for polyproplene (PP). Dms univ. 11. Deri D, Kurdi M, Ibrhim B (1999) Prediction of Melt Viscosity Flow Curves for Polycrbonte(PC). Dms univ. 12. Shnchez P, Remiro PM, Nzbl J (1993) Physicl properties nd structure of unrected PC/PB blends. J Appl Polym Sci 50: *****

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