Selective crosslinking reaction in polymer blends. III. The effects of the crosslinking of dispersed EPDM particles on the impact behavior of PP/EPDM blends

The selective dynamic crosslinking reaction by means of the N,N'-m-phenylene–bismaleimide/poly-(2,2,4-trimethyl-1,2-dihydroquinoline) system was carried out on PP/EPDM blends and its effect on the Izod impact strength (IIS) was investigated. Three series of PP/EPDM combinations were adopted to establish different morphologies. In each series, the EPDM wt % varied from 5 to 30 at 5 wt % intervals. The system crosslinked the EPDM particles selectively without PP degradation and change of morphology. Following the crosslinking, the IIS at 23, ?10, and ?30°C increased in all blends, and the critical EPDM wt % at 23°C necessary to cause the dramatic IIS increase was lowered. The increase in interfacial adhesion is considered to be the most important factor necessary for the improvement. The nucleation effect of the crosslinked particles and the decrease of crystallinity of the EPDM were also considered to contribute to the improvement in the IIS. Impact fracture energy absorption can thus be changed by adjusting the magnitude of the interfacial adhesion by the dynamic crosslinking even at essentially the same morphology. © 1995 John Wiley & Sons, Inc.     

Selective crosslinking in polymer blends. II. Its effect on impact strength and other mechanical properties of polypropylene/unsaturated elastomer blends

The effect of selective crosslinking of the unsaturated elastomer particles in polypropylene (PP) matrix was investigated. The crosslink system comprised N,N′-m-phenylene-bismaleimide and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroqinoline or polymerized-(2,2,4-trimethyl-1,2-dihydroquinoline). The system, which produces only carbon radicals, crosslinks the elastomer particles selectively without causing excessive degradation of the PP matrix. The reaction was carried out under a dynamic crosslinking process using a twin extruder on PP/EPDM, PP/SBS, and PP/SIS blends, all of which comprised 80 wt % of PP and 20 wt % of the elastomer. After the crosslinking, the impact strength of the blends increased. Especially remarkable increase is obtained at 23°C where PP is above its T_g. The increase of interfacial adhesion caused by production of PP/elastomer graft copolymer at the interface is considered to be the most important factor in the improvement. It permits the interactions of the stress concentrate zone developed at the elastomer particles and causes shear yielding of the PP matrix. Impact fracture energy absorption can be thus changed by adjusting the degree of the interfacial adhesion even at essentially the same morphology. The crosslinked elastomer particles also play the role of a nucleation agent. The selective cross-linking of the elastomer particles in PP/elastomer blends is demonstrated to be an excellent technique to produce a high-impact, high-modulus PP. © 1994 John Wiley & Sons, Inc.     

PP／EPDM共混体系界面的研究

本文采用马来酸酐对三元乙丙橡胶（ＥＰＤＭ）进行熔融接枝改性,将性后的ＥＰＤＭ与聚丙烯（ＰＰ）共混,对ＰＰ／ＥＰＤＭ和ＰＰ／ＥＰＤＭ－ｇ－ＭＡＨ两种共混体系的界面状况进行了对比。运用Ｈｕｇｇｉｎｓ参数、界面张力参数对界面状况进行了表征;运用扫描电镜（ＳＥＭ）和偏光显微镜对共混物的冲击断口形貌以及结晶情况进行了观察与分析;探讨了界面状况与共混物力学性能以及流变性能间的关系。     

DSC法对动态硫化PP／EPDM中PP—EPDM共交联结构的研究

根据共交联ＰＰ分子与正常ＰＰ分子在结晶与熔融特征及其对外因素响应上的差异,采用ＤＳＣ分析方法,研究了动态硫化ＰＰ／ＥＰＤＭ中ＰＰ－ＥＰＤＭ共交联结构。结果显示在动态硫化ＰＰ－ＥＰＤＭ的熔融ＤＳＣ曲线上的１５０℃曲线上约１５０℃处出现一新的熔融峰,改变结晶速率或ＤＳＣ测试程序,可发现形成这一新峰的化学结构具有强烈的结晶滞后性,而简单共混ＰＰ／ＥＰＤＭ的ＤＳＣ曲线上始终未出现类似新峰。结合化学反应理论     

反应性聚丙烯/三元乙丙橡胶共混物的流变性能研究

采用高压毛细管流变仪 ,研究了EPDM含量、交联剂、交联助剂等因素对反应性PP/EPDM共混物性能的影响。结果表明 ,EPDM分散相浓度为 2 0～ 2 5phr,反应共混工艺对体系的消缠降粘效果显著 ;交联剂A的含量越高 ,体系表观粘度越小 ,但粘度对剪切的响应不敏感 ;交联剂B和并用交联剂S可抑制PP降解 ,进一步优化材料力学性能 ,并仍保持体系加工流动性高于简单共混PP/EPDM。     

Photoinduced crosslinking of polyolefine blends. I. Crosslinking of LDPE,PP, and LDPE/PP blends

Photocrosslinking of low-density polyethylene, (LDPE), polypropylene (PP) and their blends was investigated using xanthone and triallyl cyanurate as a photoinitiator and a coagent, respectively. The influence of the change of UV-irradiation conditions on the yield of photoinitiated processes was found to be very similar at any composition, while the crosslinking efficiency decreases with increase of PP content in the blend. The mechanism of the TAC action in photocrosslinking process was proposed and the effect of TAC reactions is discussed with regards to the effectivity of crosslinking of LDPE, PP, or the blends. © 1995 John Wiley & Sons, Inc.     

Dependence of impact strength on the fracture propagation direction in dynamic packing injection molded PP/EPDM blends

In order to further understand the brittle-ductile (B-D) transition in PP/EPDM blends, a shear stress field achieved via dynamic packing injection molding was used to control the rubber particles as elongated and orientated in the PP matrix. The impact strength of the blends was measured in three fracture directions, namely, along the shear flow direction, perpendicular to and oblique (45°) with the flow direction. A definite B-D transition of impact strength was found at 20 wt% of EPDM content along the shear flow direction. About 10 times increase of impact strength was observed at the B-D transition. However, a B-D transition and then a decrease of impact strength brittle-ductile-brittle (B-D-B) was found as increasing of EPDM content in the impact direction perpendicular to and oblique with the flow direction. One observes a big increase of impact strength at 20-30 wt% of EPDM content (B-D transition) from 10-20 to 70-80 kJ/m², then a sharp decrease of impact strength is seen when EPDM content reaches to 30-45 wt% (D-B transition) from 70-80 to 40-50 kJ/m². Correspondingly, there exists a change of rubber particles from roughly spherical shape to highly elongated and oriented shape at D-B transition. SEM shows a very smooth fractured surface when fracture propagation is along or oblique with the shear flow direction, but a lay-by-layer fracture behavior when fracture propagation is perpendicular to the shear flow direction. Our results suggest that the impact fracture direction with respect to the orientation direction play an important role to determine the impact strength. Wu's theory holds true as long as the rubber particles are roughly spherical when viewed in the same direction with fracture propagation direction, but no longer valid when dispersed rubber particles are elongated and oriented when viewed in the direction perpendicular to or oblique with the fracture propagation direction.     

Relationship between interfacial tension and dispersed‐phase particle size in polymer blends. I. PP/EPDM

Simple blends with different viscosity ratios of the components as well as compatibilized blends varying both in type and content of compatibilizers were used to study the relation between interfacial tension and dispersed‐phase particle size for PP/EPDM (80/20 wt %) blends in this work. Four compatibilizing systems, poly(ethylene‐co‐methacrylic acid) ionomers (EMA–I), dicumyl peroxide (DCP), DCP combined with EMA–I, and DCP in combination with trimethylol propane triacrylate (TMPTMA), were used. For blends prepared in an internal mixer, a power law relation was found between capillary number and torque ratio of the blends' components. This relation was used to estimate the interfacial tension for the compatibilized blends. The relation between steady‐state torque of the blends as a measure of viscosity and the estimated values of interfacial tension were also investigated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3148–3159, 2002     

Morphology/behavior relationship and recyclability of composites based on PP/EPDM blends and short aramid fibers

The effect of short aramid fibers on the mechanical behavior of polypropylene (PP) and ethylene‐propylene‐diene (EPDM) and their blends has been investigated by means of an experimental design. The results have shown that aramid fibers are very effective reinforcing agents for composites when the continuous phase of the matrix is constituted by PP, so sensible increments in tensile modulus and strength are obtained as fiber content in the composites increases. An optimal matrix composition and fiber content has been observed that produced high abrasion resistance compounds. However, the abrasion resistance of very rich EPDM matrices is hardly affected by fibers content. The addition of fibers to EPDM rich (>50%) matrices gives rise to a sensible decrease of the impact strength of this polymer. However, at PP contents above 50% in the polymer matrix, an increase of impact strength is observed at fiber percentages in the composites above 10%. The different behavior of the fibers depending on matrix type can be attributed to a better affinity of these fibers for PP matrix. Morphological studies of the composites have been carried out by scanning electron microscopy. Finally, the price and recyclability of these materials have been analyzed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2474–2484, 2002     

交联剂对动态硫化PP／EPDM中PP晶体及EPDM形态结构的影响

针对ＰＰ／ＥＰＤＭ动态硫化中有机过氧化物交联剂Ａ用量对试样拉伸,弯曲和冲击等性能所产生的较大的影响,采用偏光显微镜研究了不同交联剂Ａ用量下动态硫化ＰＰ／ＥＰＤＭ中连续相ＰＰ的晶体结构和分散相ＥＰＤＭ的形态结构特征。     

Effect of NR and EPDM on the rheology of HDPE/PP blends

Summary We studied melt-rheological properties of ternary blends of polypropylene and high-density polyethylene with an elastomer (natural rubber or ethylene-propylene-diene), at several blending ratios and shear rates. Measurements made on a cone-plate rheometer are presented and discussed as a function of blend composition. The effect of the shear rate on the viscosity and flow curve is discussed in terms of the exponent of the power low for a non-Newtonian liquid. The addition of an elastomer to the polyolefins blends changes the shape of the viscosity-composition curve; this change is discussed in terms of the possible morphology of the blend. Received: 25 September 1998/Revised version: 8 February 1999/Accepted: 9 February 1999     

Mercapto‐modified copolymers in elastomer blends. IV. The compatibilization of natural rubber/EPDM blends

Ethylene—propylene—diene functionalized with mercapto groups (EPDMSH) was employed as compatibilizing agent for natural rubber (NR)/EPDM blends, resulting in a substantial increase of the ultimate tensile strength of these blends without affecting the elongation at break. There is also a decrease of the curing time with the addition of as low as 2.5 phr of EPDMSH, mainly in NR/EPDM (70:30 wt %) blend, indicating the accelerator effect of this functionalized copolymer. This copolymer also increased the crosslink degree and the gel content. From dynamic mechanical analysis (DMTA), it was demonstrated that EPDMSH improves the covulcanization process. The reactive compatibilization of EPDMSH was demonstrated by the presence of insoluble material in nonvulcanized/compatibilized blends and by its thermogravimetric (TGA) analysis. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2892–2900, 2002; DOI 10.1002/app.10283     

动态硫化EPDM/PP共混物力学性能的研究

考察了硫黄用量和聚合物共混比对动态硫化ＥＰＤＭ／ＰＰ热塑性弹性体性能的影响。结果表明,随着硫黄用量增大,ＥＰＤＭ／Ｐ共混物的拉伸强度、１００％定伸应力和扯断伸长率先增大后减小、硬度有所增大,随着ＰＰ用量的增大,ＥＰＤＭ／ＰＰ共混物的拉伸强度、１００％定伸应力和硬度均有所增大,扯断伸长率也先大后减小。ＰＰ用量的变化对这些性能的影响更显。     

PP/EPDM共混物结晶及动态流变行为研究

以聚丙烯、EPDM为原料,采用熔融共混法制备了PP/EPDM复合材料。通过XRD、偏光显微镜和旋转流变仪等检测手段,研究EPDM含量对PP/EPDM共混物结晶及动态流变行为的影响。结果表明,EPDM显著提高了共混物的冲击强度,但拉伸强度与弯曲强度明显降低。其中,当EPDM质量分数为10%时,共混物的冲击强度为58.156kJ/m2,较PP提高了约20倍;随着EPDM含量的增加,共混物的球晶结构受到不同程度破坏,当EPDM质量分数为25%时,球晶结构破坏严重。同时,随着EPDM含量的增加,共混物的结晶温度降低。PP/EPDM熔体的复数黏度均随着角频率的增加而下降,表现为剪切变稀现象,材料为假塑性流体,EPDM的加入使得共混物的弹性模量和黏性模量增大。     

Mechanical properties,morphological structure,and thermal behavior of dynamically photocrosslinked PP/EPDM blends

A dynamically photocrosslinked polypropylene (PP)/ethylene–propylene–diene (EPDM) rubber thermoplastic elastomer was prepared by simultaneously exposing the elastomer to UV light while melt‐mixing in the presence of a photoinitiator as well as a crosslinking agent. The effects of dynamic photocrosslinking and blend composition on the mechanical properties, morphological structure, and thermal behavior of PP/EPDM blends were investigated. The results showed that after photocrosslinking, tensile strength, modulus of elasticity, and elongation at break were improved greatly. Moreover, the notched Izod impact strength was obviously enhanced compared with corresponding uncrosslinked blend. Scanning electron microscopy (SEM) morphological analysis showed that for uncrosslinked PP/EPDM blends, the cavitation of EPDM particles was the main toughening mechanism; whereas for dynamically photocrosslinked blends, shear yielding of matrix became the main energy absorption mechanism. The DSC curves showed that for each dynamically photocrosslinked PP/EPDM blend, there was a new smaller melting peak at about 152°C together with a main melting peak at about 166°C. Dynamic mechanical thermal analysis (DMTA) indicated that the compatibility between EPDM and PP was improved by dynamic photocrosslinking. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3371–3380, 2004     

降解PP/EPDM共混物的结晶性能研究

采用过氧化二异丙苯(DCP)降解聚丙烯(PP),熔融法制备了降解PP与三元乙丙橡胶(EPDM)共混物,采用差示扫描量热分析(DSC)及广角X射线衍射(WAXD)研究了降解PP/EPDM共混物的结晶行为,结果发现PP降解后β-PP晶型(300)消失 ;降解PP/EPDM共混物的非等温结晶过程是由成核控制的,并伴有明显的快速初级结晶和缓慢的次级结晶过程,降解PP以均相成核的三维球晶方式生长.     

EPDM与PP相容性研究的新发展

阐述了EPDM／PP共混型热塑性弹性体的发展历史，物料特性对相容性的影响、制备工艺对相容性的影响、增容研究、及研究展望。     

Brittle-ductile transition in PP/EPDM blends: effect of notch radius

The toughness of polypropylene (PP)/ethylene-propylene-diene monomer (EPDM) blends was studied over wide ranges of EPDM content and temperature. In order to study the effect of notch radius (R), the toughness of the samples with different notch radii was determined from Izod impact test. The results showed that both toughness and brittle-ductile transition (BDT) of the blends were a function of R, respectively. At test temperatures, the toughness tended to decrease with increasing 1/R for various PP/EPDM blends. Moreover, the brittle-ductile transition temperature (T_BT) increased with increasing 1/R, whereas the critical interparticle distance (ID_c) reduced with increasing 1/R. Finally, it was found that the different curves of ID_c versus test temperature (T) for different notches reduced down to a master curve if plotting ID_c versus T_BT^m-T, where T_BT^m was the T_BT of PP itself for a given notch, indicating that T_BT^m-T was a more universal parameter that determined the BDT of polymers. This conclusion was well in agreement with the theoretical prediction.     

Largely improved toughness of PP/EPDM blends by adding nano-SiO2 particles

As a part of long-term project aimed at super polyolefin blends, in this work, we report the toughness and phase morphology of polypropylene (PP)/EPDM/SiO₂ ternary composites. Two processing methods were employed to prepare PP/elastomer/filler ternary composites. One was called one-step processing method, in which the elastomer and the filler directly melt blended with PP matrix. Another one was called two-step processing method, in which the elastomer and the filler were mixed first, and then melt blended with pure PP. Two kinds of PP (grafted without or with maleic anhydride (PP-g-MA)) and SiO₂ (treated with or without coupling agent) were used to control the interfacial interaction among the components. The dependence of the phase morphology on interfacial interaction and processing method was investigated. It was found that the formation of filler-network structure could be a key for a simultaneous enhancement of toughness and modulus of PP and its formation seemed to be dependent on the work of adhesion (W_AB) and processing method. As the W_AB of PP/EPDM interface was much lower than that of PP/SiO₂ and EPDM/SiO₂, and the two-step processing method was used, the formation of filler-network structure was favorable. In this case, a super toughened PP ternary composite with the Izod impact strength 2-3 times higher than PP/EPDM binary blend and 15-20 times higher than pure PP could be achieved.