Keywords: Polypropylene, elastomers, polymer blends, compatibility, mechanical properties

Transcription

1 Key Engineering Materials Vol. 559 (2013 pp (2013 Trans Tech Publications, Switzerland doi: / Theral and echanical properties of unvulcanized polypropylene blends with different elastoers: ethylene-propylene-diene terpolyer, nitrile-butadiene copolyer and chlorinated polyethylene I. Reinholds 1, a, V. Kalkis 1,b, J. Zicans 2,c, R. Merijs-Meri 2,d, A. Grigalovica 2,e 1 Departent of Cheistry, University of Latvia, Riga, Latvia 2 Institute of Polyer Materials, Riga Technical University, Riga, Latvia a ingars.reinholds@lu.lv, b vkalkis@lu.lv, c zicans@ktf.rtu.lv, d reo.erijs-eri@rtu.lv, d grigalovica_a@inbox.lv (V. Kalkis Keywords: Polypropylene, elastoers, polyer blends, copatibility, echanical properties Abstract. In this work, coposites of isotactic polypropylene (PP with three unvulcanized elastoers terpolyer of ethylene-propylene-dicyclopentadiene (EPDM, chlorinated polyethylene (CPE and copolyer of acrylonitrile-butadiene (NBR have been investigated. The purpose of the investigation was to create PP/elastoer blend coposites of significantly different copositions (with an excess of PP, interediate ones, and with an excess of elastoer and to study the dependence of tensile behaviour and elastic properties on the blends with different coponent ratio. Tensile properties have been recognized fro the stress-strain curves. The changes of elastic odulus have been characterized with respect to the Hashin-Shtrikan upper and lower bounds and the Davies equation. Calorietric properties of PP blends with elastoers (crystallinity and elting behaviour of polypropylene phase have also been investigated with the ethod of differential scanning calorietry (DSC. Introduction Theroplastic elastoers (TPE based on polypropylene rubber blends have a great iportance in any engineering fields. Several effects of elastoers on iproveent of theral and echanical properties of polypropylene have been discussed in [1-2]. The ain benefit of incorporating elastoers in theroplastic atrices is iproveent of aterial toughness [3]. However, unodified blends are therodynaically incopatible that negatively affects properties of the aterial [2]. In this work, coposites of isotactic polypropylene with three unvulcanized elastoers chlorinated polyethylene, copolyer of acrylonitrile-butadiene and terpolyer of ethylenepropylene-dicyclopentadiene have been investigated. The blends at the wide PP/elastoer ratio were obtained. Tensile properties have been recognized fro the stress-strain curves at the rate of deforation equal to 50 /in to characterize deforability of the copositions. The dependence of elastic properties of PP/elastoer blends have been characterized coparing to the Hashin-Shtrikan upper and lower bounds calculated by Kerner equations [4]. The Davies equation useful for deterination of dual phase continuity in blends of theroplastic and elastoer coponents has also been applied in the research [5]. Theral properties of PP blends with different elastoers were investigated by differential scanning calorietry (DSC. Materials and investigation ethods. Materials. Isotactic polypropylene hoopolyer (PP of tradeark Moplen HP456 obtained fro LyondellBassel Cheical Co (density 0.90 g/c 3, elt flow index 3.4 g/10 in and Vicat softening teperature equal to 154 C, ethylene-propylene-diene terpolyer (EPDM of tradeark SKEPT- 40 with a content of PP 40 ol.% and dicyclopentadiene 0.9 ol.% (density 0.86 g/c 3 obtained fro JSC Ufaorgsintez (Russia, chlorinated polyethylene (CPE with a content of chlorine 36 All rights reserved. No part of contents of this paper ay be reproduced or transitted in any for or by any eans without the written perission of TTP, (ID: /05/13,19:30:34

2 94 Baltic Polyer Syposiu ol.% (density 1.17 g/c 3 obtained fro DOW Cheical Co and acrylonitrile-butadiene rubber (NBR of tradeark SKN-26 with a content of acrylonitrile 26 wt.% (density 0.96 g/c 3 obtained fro Voronezh Branch of FGUP NIISK (Russia have been used as coponents in coposites. Binary blends with PP/elastoer ratios equal to 100/0, 90/10, 80/20, 50/50 and 20/80 wt.-to-wt.% were obtained by theroplastic ixing of a total duration of 6 in. on a twin roll-ills at 190 C. Plates, obtained by copression oulding at 190 C and a pressure of 5 MPa, were cut in dog-bone speciens with a length of the working zone 15 and a transverse cross section Scientific ethods. Tensile properties of the coposites were deterined with Tinius Olsen H1- KS UTM at 20 С at a tension rate of 50 /in for stress-strain curves and at a tension rate of 1 /in for deterination of elastic odulus according to ISO Differential scanning calorietric easureents were carried out with Mettler Toledo DSC 1/200W under the nitrogen atosphere. DSC scans were perfored in a teperature range of 25 to 200 C at a constant heating rate of 10 C/in. The first heating cycle was used to eliinate the theral prehistory. The cooling and the second heating scans were analyzed. The average weight range of the saples was 10 g. Results of calorietric data were calculated by applied software METTLER Graph Ware TA72 PS. 5. Results and discussion Mechanical properties. The experiental values of elastic odulus E of PP/elastoer coposites expressed as a function of volue content of elastoer (EPDM, CPE, NBR are shown in Fig. 1. Expressed values are the average of five parallel test saples. We should pay attention to the dependence of elastic odulus on the coponent ratio. Often the experiental concentration dependence of elastic odulus of heterogeneous binary coposites has a for of S-shaped curve that is contributed to phase inversion phenoena [6-7]. The S-shaped dependence of lge has been observed in the case of heterogeneous ixtures of CPE with a low density polyethylene (LDPE, or with a polyvinylchloride (PVC [7]. The phase inversion proceeds gradually changing along with the foration of structures where both the coponents coexist in the for of continuous interpenetrating phases [7]. The experiental data of PP/elastoer coposites shown in Fig. 1 (dots partially agree with such a concept especially in the case of NBR as the disperse phase. The dependence of E(V elastoer changes practically linearly with increase of the voluetric content of the elastoer up to 0.19 that is equal to 20 wt.% of the elastoer. For the copositions with ediu concentration of the elastoer ( voluetric parts, the values of E decrease with the highest rate. At high elastoer contents (above 0.90 voluetric parts, however, the rate of E decrease is soewhat reduced. The experiental results were copared to the liiting values of the elastic odulus calculated by the well-known Kerner s equations [4], obtained by a self-consistent ethod for the voluetric K and shear G elastic odules of binary coposite systes with a well-defined atrix and disperse filler (Eq. 1. and Eq. 2.: K ( Kf K Vf K ; (1 Kf K 1 (1 Vf K 4 G 3 ( Gf G Vf G G, (2 6( K 2G 1 (1 Vf ( Gf G 5G (3K 4G where V f is the volue content of the filler, the subscript indexes and f are attributed to the characteristics of PP atrix and the filler (elastoer.

3 Key Engineering Materials Vol The values of K and G of the coponents of the PP/elastoer blend, necessary for calculations, were deterined fro the experiental values of E (E PP = 1200MPa, E EPDM = 2 MPa, E CPE = 8.8 MPa, E NBR = 2 MPa and assued Poison s ratios ( PP = 0.35, EPDM = CPE = NBR =0.49 as reported in [6-7] according to the known dependences for isotropic edia (Eq. 3. and Eq. 4.: E 3(1 2 K, (3 E 2(1 G (4 First, by the Equations 1, 2 and 3 the values of K and G for the investigated coposites with different coponent ratios were calculated. After that the values of elastic odulus E were deterined by the Eq. 5. E 9KG /(3K G. (5 a b c Fig.1. Elastic odulus as a function of the voluetric content of the elastoer (V elastoer of PP/EPDM (a, PP/CPE (b and PP/NBR (c blends. Dots experiental data, Curves upper (1 and lower (2 bounds, calculated fro the Kerner s equations, and theoretical curve of the Davies equation (3 and experiental curve (4 The results of calculation are shown in Fig. 1 as the lines of upper (1 and lower (2 boundaries of E. The upper lines are attributed to PP as the value of E for PP is about 136 ties greater than that of CPE and about 600 ties greater than those of EPDM and NBR copolyers; accordingly the lower boundaries are attributed to the elastoers as the atrices. For the coposites with voluetric content of the elastoer (corresponding to wt.%, experiental values of E alost coincide with the Hashin-Shtrikan upper bond. The experiental values of E of the coposites with a ratio of PP/EPDM, PP/CPE, PP/NBR 50/50 wt.% are by 43, 14 and 16% less than those of the upper liit and by 98, 93 and 98% higher than those of the lower liit respectively. Meanwhile the dependence shows a tendency of phase inversion at the content of elastoers 50 wt.% that reduces with the change of disperse phase fro NBR to EPDM, for which the inversion is not so obviously visible. This testifies about the fact that in the latter cases (EPDM and CPE as dispersed phase foration of the elastoer inclusions in the ore rigid PP atrix phase is prooted. The dependence of phase orphology on the elastic behaviour is also confired by coparing the experiental values of elastic odulus (Eq. 7 by the curves calculated by the Davies equation (Eq. 6.. The values of theoretical shear odulus of the coposites where taken fro the calculated data of G values of base coponents according to Kerner s equation (Eq. 4.. G 1/ 5 1/ 5 5 ( V G V G f f (6 E 2, 7G, (7

4 96 Baltic Polyer Syposiu The calculated curves (3, shown in Fig. 1, express relationship lge(v elastoer of the binary blend of plastic and elastoer with a dual phase continuity. The values of E of the investigated PP blends with 50 wt.% of EPDM, CPE and NBR are by 58, 50 and 67% higher respectively than those calculated by the Davies equation (curves (3 in Fig. 1. The typical stress-strain curves of PP blends with elastoers (PP/EPDM, PP/CPE, PP/NBR strained at 50 /in rate are copared in Fig. 2. As expected, neat PP has relatively high tensile properties (tensile strength, deforation at break and high toughness. However, the tensile behaviour of the investigated blends changes gradually fro plastic to elastoeric with increase of the content of elastoers in the blends. a b c Fig.2. Stress-strain curves of PP/EPDM (a, PP/CPE (b, PP/NBR (c blends with PP/elastoer wt.% ratio 100/0 (1, 90/10 (2, 80/20 (3, 50/50 (4, 20/80 (5, 10/90 (6 The values of yield stress decrease with increent of the content of elastoers in coposite blends. The PP/CPE blends with the content of CPE wt.% show a typical deforation character with a typical elastic-plastic transition siilar to neat PP with a change fro yielding to plastic deforation with a strain hardening up to the fracture (curves 2-3 in Fig. 2b., that indicate to the considerable influence of PP atrix on the tensile behaviour of the blends up the elastoer content of 50 wt.% In the case of PP/EPDM blends stress-strain behaviour at yield is not considerably changed until the elastoer content of 20 wt. % (curves 2-3 in Fig.2a, after that substantial drop of yield strength is observed. Most draatic changes in stress-strain behaviour are observed for PP/NBR blends. The blends with the content of NBR wt.% show a brittle behaviour with an iediate rupture at yielding (2-4 in Fig. 2c. It can be judged that PP affects echanical behaviour of PP/CPE blends ore than any other investigated blends. Besides this can indicate to an increased phase interaction of CPE and PP in coparison to those of PP with EPDM and especially PP with NBR. The values of PP blends with EPDM and NBR content wt.% show a character of typically unvulcanized blends, the properties of those ay be iproved by cheical vulcanisation or radiocheical cross-linking. Increased strength of PP/CPE blends with the content of CPE wt.% in coparison to the blends with EPDM and NBR is ost probably attributed to higher crystallinity of CPE. Theral properties (DSC. DSC therogras of the investigated blends are shown in Fig. 3. Changes in the crystallinity of the PP phase, calculated fro the experiental values of the fusion enthalpies, obtained fro the cooling scans, assuing the elting enthalpy of 100% crystalline PP H (100%PP equal to 207 J/g [8] as well as considering the ass content of PP in the blends, are copared in the Table 1.

5 Key Engineering Materials Vol a b c Fig.3. DSC curves of the 2 nd heating scan of PP/EPDM (a, PP/CPE (b and PP/NBR (c with wt.% ratios of the coponents in blends 100/0 (1, 90/10 (2, 80/20 (3, 50/50 (4, 20/80 (5, 10/90 (6 Table 1. Degree of crystallinity of PP/elastoer blends with different coponent ratios PP/elastoer c (PP, [%] ratio wt.% PP/EPDM PP/CPE PP/NBR 100/ / / / / / It is clearly seen that the change of the elting behaviour and the crystallinity of the investigated PP blends has a different character with the change of elastoer and the coponent ratio in the blends. The changes in theral properties confir the behaviour of elastic and tensile properties and also confir the changes of phase orphology with increase of different elastoer content in PP/elastoer blends discussed above. It is well seen that degree of crystalline phase of PP is affected by the incorporation of elastoers in PP atrix. Decrease of elting peak teperature of PP with increase of elastoer content ay be attributed to decrease of the arrangeent of crystallites. Certain increent of the elting peak teperatures with increase of the elastoer content up to wt.%, especially visible for NBR containing blends, is attributed to increent of the crystallite order in PP crystalline phase when the elastoer becoes as a atrix. (Fig. 3.. It is also interesting to note that crystallinity degrees of PP phase in NBR containing blends are coparatively highest (than in any other investigated blend. Apart fro incopatibility this could be additional factor deterining low echanical properties of PP/NBR blends. Conclusions Three unvulcanized binary blends of isotactic PP with different elastoers (EPDM, CPE, NBR with a wide ratio of coponents have been ade. The effect of the elastoer on echanical (elastic and tensile and theral properties have been researched. Mechanical properties of the investigated blends are especially affected at elastoer contents above 50 wt. %, especially for PP/NBR blends. Experiental data of E can be ost satisfactorily depicted by the Kerner equations at elastoer contents. up to 50 wt. %. The ost expressed phase inversion behaviour has been found in the case of PP/NBR blend. The further research should be done on iproveent the echanical behaviour of the coposite blends by the cheical or radiation induced copatibilization of the coposites. The changes in theral properties confir the behaviour of elastic and tensile properties as well as the changes of phase orphology with increase of elastoer content in the investigated blends.

6 98 Baltic Polyer Syposiu Acknowledgeents. This work has been supported by the European Social Fund with the project Support for Doctoral Studies at University of Latvia. References [1] N. R. J. Chouddhury, A. K. Bhowick, Strength of theroplastic elastoers fro rubberpolyolefin blends, Mater. Sci. 25 ( [2] R. Koningsveld, L. A. Kleintjens, H. M. Schoffeleers, Therodinaic aspects of polyer copatibility, Pure Appl. Che. 39 ( [3] F. Irananesh, F. Irananesh, B. M. Shafei, A review on echanical properties and applications of chlorinated polyethylene, Adv. Environent. Biol. 6 ( [4] E. H. Kerner, The elastic and thero-elastic properties of coposite edia, Proceedings of the Physical Society B 69 ( [5] W. E. A. Davies, The theory of coposite dielectrics, J. Phys. D: Appl. Phys. 4 ( [6] Z. Hashin, S. Shtrikan, A variational approach to the theory of the elastic behavior or ultiphase aterials, J. Mech. Phys. Solids 11 ( [7] T. Ivanova, J. Zicans, M. Kalnins, R. Maksiov, Z. Roja, Theroplastic ultiphase coposites: tensile and creep behavior. Mater. Sci. 42 ( [8] R. L., Blaine, Theral applications note. Polyer Heats of Fusion. PDF.