The orientation of the dispersed phase and crystals in an injection-molded impact polypropylene copolymer

The orientation of the dispersed phase and crystals in the injection-molded bar of an impact polypropylene copolymer (IPC) containing isotactic polypropylene (iPP), ethylene-propylene rubber (EPR) and a β-nucleating agent (β-NA) were studied simultaneously. In the IPC, iPP and EPR act as the matrix and dispersed phase, respectively. The EPR is amorphous and the iPP is crystallizable in α- and β-crystalline forms in the presence of the β-NA. The orientation and orientation distribution for both of the EPR phase and the iPP crystals, as well as the crystallization behavior of iPP, were investigated by two-dimensional wide-angle X-ray diffraction (2D-WAXD), two-dimensional small-angle X-ray scattering (2D-SAXS), scanning electron microscope (SEM) and differential scanning calorimetry (DSC). The results of the experiment show that orientation exists for both the EPR phase and the iPP crystals. But their orientation distribution manifests an opposite tendency. The EPR phase was observed to be highly oriented in the core layer but the orientation of the iPP crystals was weakened gradually from skin to core. The difference in the orientation behavior between the EPR phase and the iPP crystals reflects the distinct response of the micrometer-scale EPR particles and nanometer-scale iPP chains upon the flow field and temperature gradient in the mold. The diffraction geometry of the β-crystals has also been discussed in detail. The observations in this study may shed light on the study in the structure and property relationship for the IPC injection-molded products.     

橡胶相具有交联结构的新型抗冲聚丙烯合金

利用具有"颗粒反应器技术(RGT)"特征的Ziegler-Natta催化剂进行丙烯多相共聚(丙烯均聚+乙烯/丙烯无规共聚),通过在乙丙共聚阶段引入双烯烃单体1,9-癸二烯,使乙丙共聚物在聚合的同时实现交联,制备了新型抗冲聚丙烯合金.聚合反应结果表明,1,9-癸二烯可参与乙丙共聚,同时对聚合反应速率和共聚物组成影响较小;1,9-癸二烯使乙丙共聚物发生支化/部分交联,合金聚合物的熔体流动速率在引入1,9-癸二烯后显著降低,且凝胶含量随1,9-癸二烯用量的增加而增大.形态研究结果表明,乙丙共聚物的交联显著降低了其在聚丙烯基体中的分散尺度,提高了分散均匀性,分散相粒径随支化/交联程度提高而减小.力学性能测试结果表明,乙丙共聚物的交联使合金聚合物在保持较高韧性的同时显著提升了刚性,有利于实现抗冲聚丙烯合金的刚韧平衡.     

用Z-N催化剂分段聚合制备PP/EPR共混物的结构和形态特征

用Ziegler-Natta(Z-N)催化剂MgCl2/TiCl4/BMF-AlEt3(BMF代表内给电子体9,9-二甲氧基甲基芴),采用分段聚合的方法制备了PP/EPR原位共混物,通过改变乙丙共聚的时间调节聚合物中乙烯的含量.使用核磁共振(13C-NMR)、凝胶渗透色谱(GPC)、示差扫描量热分析法(DSC)、动态力学分析(DMA)、扫描电子显微镜(SEM)和偏光显微镜(PLM)等研究了聚合物的结构和形态特征.研究发现,分段聚合制备的PP/EPR共混物是一种包括丙烯均聚物、乙丙无规和嵌段共聚物在内的多组分混合物.动态力学的结果显示混合物中聚丙烯与乙丙无规共聚物的玻璃化转变峰出现了内移现象,说明两者呈现部分相容性.扫描电镜的照片表明了聚丙烯基体与乙丙无规共聚物分散相之间的相界面模糊,两相之间的相容性较好.随着聚合物中乙烯含量的增加,分散相出现明显的塑性变形,同时,聚丙烯的结晶形态也发生明显的变化,球晶的尺寸逐渐变小,同时球晶变得不完善.     

Microstructure, morphology, crystallization and rheological behavior of impact polypropylene copolymer

Impact polypropylene copolymer (IPC), named polypropylene catalloy, not only possesses excellent impact property, but also presents good rigidity. Its superior performances result from the complicated composition and microstructure. In the present article, recent progress in the studies on microstructure, morphology, crystallization and rheological behavior of IPC is summarized, and findings of the authors and their collaborators are reported. In general, IPC is divided into three components, i.e., ethylene-propylene random copolymer (EPR), a series of different segment lengths ethylene-propylene copolymer (EbP) and propylene homopolymer. The reasonable macromolecular structures of EbP and a multilayered core-shell model of dispersed phase structure in IPC were proposed, in which the dispersed phase consists of an outer EbP shell, an inner EPR layer and an EbP core. It is found that the annealing at melt-state may lead to an abnormal phase inversion, and the phase inversion disappears when temperature cools down to room temperature. The cause of phase inversion is ascribed to the existence of EbP component, which results in the stronger activity of the dispersed phase. The crystalline structure and morphologic results confirm the formation of β-iPP in IPC. Furthermore, it is found that the ethylene content in IPC and cooling rate of the samples have an important influence on the formation of β-iPP. Based on the crystallization kinetics analyzed by Lauritzen-Hoffman theory, crystallization behavior of different IPC samples is discussed and it is proposed that the dilution effect of ethylene propylene copolymer has a more remarkable influence on surface nucleation than on crystal growth. In addition, annealing at high temperature can result in the changes of chain structure for IPC, and this instability is ascribed to the oxidative degradation and crosslink reaction mainly in iPP component.     

Structure and morphology of polypropylene/poly(ethylene-co-propylene) in situ blends synthesized by spherical Ziegler-Natta catalyst

Polypropylene/poly(ethylene-co-propylene) (iPP/EPR) in situ blends of different composition were synthesized by spherical Ziegler-Natta catalyst, and were fractionated into three portions: the random copolymer (EPR), the block copolymer, and the iPP matrix. The EPR fraction was characterized by ¹³C NMR, and the block copolymer fraction was characterized by crystalline segregation and differential scanning calorimetry analysis. The blends showed bi-phase structure with EPR existing in the dispersed phase. Increasing EPR in the blends resulted in increase of the number and diameter of the EPR particles, but there is an upper limit for the particle number. There were only highly irregular spherulites or tiny crystallites in the isothermal crystallized blends. The morphology of the impact fracture surfaces of the blends clearly showed that they were fractured in ductile fashion. There was strong dependence of impact strength of the blends on their morphology, and the sequence distributions of the EPR and segmented copolymer fractions also markedly influenced the mechanical properties.     

Effects of composition on microstructure and crystallization behavior for impact polypropylene copolymer investigated by restructuring the complex core-shell dispersed particles in ternary blends

A series of ternary blends of polypropylene/ethylene-propylene random copolymer/ethylene-propylene segmented copolymer(HPP/EPR/Eb P) whose microstructures are similar to those of impact polypropylene copolymer(IPC) were prepared in order to systematically investigate the effects of composition on microstructure and crystallization behavior of IPC. The observation of primary phase morphology reveals that the dispersed phase with core-shell structure could be rebuilt in certain composition and excessive EPR leads to a bicontinuous phase structure in ternary blends. After undergoing same quiescent crystallization including isothermal and non-isothermal crystallization, these blend samples exhibit special composition-dependent melting behavior, i.e., the melting point increases markedly with the increase of EPR content until it turns down at a critical content(about 30 wt%). The crystallization behavior is mainly ascribed to the different nucleation abilities. It is suggested that although the compatibility between EPR and HPP components becomes worse with the increase of EPR content due to the increased interfacial area and the decreased concentration of Eb P, higher EPR content in the blend facilitates to heterogeneous nucleation except for the appearance of obvious bicontinuous phase structure.     

聚丙烯“催化合金”组成对结晶行为的影响

用示差扫描量热仪(DSC)和偏光显微镜(POM)研究了聚丙烯“催化合金”(PP-cats)组成对等温结晶行为与动力学的影响,并与等规聚丙烯(iPP)进行比较.结果表明,与纯PP相比较,PP-cats的平衡熔融温度明显下降,表明PP-cats中作为主要组分的丙烯均聚物和乙丙无规共聚物之间存在较强的相互作用.PP-cats的结晶初期动力学可用Avrami模型很好地描述,结晶过程均为预先成核和三维生长方式.PP-cats的结晶速率随体系中乙丙共聚物含量的增加而增大,而PP-cats的晶体生长速率随体系中乙丙共聚物含量的增加而减小.由于PP-cats熔体的粘度远高于纯PP,使得PP-cats中PP分子链运动能力降低,导致了PP-cats较低的晶体生长速率.此外,与纯PP相比,PP-cats的成核密度大幅度提高,被认为是PP-cats具有快的结晶速率的主要原因.     

Poly(ethylene-co-propylene)-g-polystyrene through macromer polymerization: Preparation,morphology, and structure–properties relationships

Graft copolymers with ethylene-propylene (EPR) backbone and polystyrene (PS) grafts, EPR-g-PS, were prepared by terpolymerization of a PS macromer with ethylene and propylene using a vanadium catalyst, with graft efficiency of up to 80% and PS content in the copolymer 5–45%. Such polymerization parameters as molecular weight and dosage of the macromer, catalyst concentration, and reaction temperature which affect the mobility and hence polymerizability of the macromer may have a marked influence on the polymerization and the structure of the products. The molecular architecture of the copolymers was characterized by osmometry, UV, NMR, and GPC methods. TEM and torsional pendulum studies revealed that EPR-g-PS possessed a phase separation morphology with PS domains evenly dispersed in the EPR matrix. The PS content and average number of grafts strongly influence the tensile properties of the copolymers. EPR-g-PS graft copolymers prepared by macromer copolymerization exhibit the mechanical properties of a typical thermoplastic elastomer having two or more branches of a certain length.     

等规聚丙烯/二元乙丙橡胶合金相分离对结晶动力学的影响

用小角激光光散射(SALLS)、相差显微镜(PCM)、示差扫描量热仪(DSC)和偏光显微镜(POM)研究了聚丙烯/二元乙丙橡胶(iPP/EPR)共混体系的相分离行为和等温结晶行为.发现iPP/EPR(50/50,W/W)发生的液-液相分离遵循spinodal机理.通过Cahn-Hilliard方程求得了不同实验温度下iPP/EPR的表观扩散系数(Dapp)以及spinodal温度(Ts).考察了不同相分离程度的iPP/EPR体系结晶动力学,发现延长相分离时间(tps)或提高相分离温度(Tps)均会导致半结晶时间(t1/2)增大,即结晶速率降低.这被归于EPR成核作用的降低.动力学分析结果表明Avrami模型适用于描述该体系的等温结晶过程,其结晶机理基本不受相分离程度的影响,结晶均以瞬时成核和三维生长为主.     

Phase morphology of iPP/aPS/SEP blends

Supermolecular structure and phase morphology of the ternary isotactic polypropylene/atactic polystyrene/poly(styrene-b-ethylene-co-propylene) (iPP/aPS/SEP) compression molded blends with 100/0, 90/10, 70/30, and 50/50 iPP/aPS weight ratios and with different amounts of added SEP compatibilizer were studied by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD). SEP significantly reduced the size of dispersed aPS particles that enabled better spherulitization in the iPP matrix. Furthermore, iPP spherulites in ternary blends with 90/10 iPP/aPS weight ratio became larger in comparison with the pure iPP. TEM revealed that the SEP formed continuous interface layer around the dispersed aPS particles even when only 2.5 wt.% of SEP was added. Particle size distribution was distinctly bimodal. When the SEP content was increased to 10 wt.%, joining together smaller and bigger aPS and SEP particles formed dispersed aggregates. Additionally, both amorphous components (aPS and SEP) influenced crystallization process of iPP matrix and so modified, to some extent, its final supermolecular structure. SEP compatibilizer did not significantly affect crystallite orientation. The increase of crystallite sizes, which was more affected by the addition of aPS than by the addition of SEP, seemed to be influenced by the solidification effect rather than by the phase morphology of the blends.     

Recent key developments in isotactic polypropylene in-reactor alloy and in-reactor nanocomposite technology

Alloying and nanocompositing are two most effective techniques by which isotactic polypropylene (iPP), one of the most promising polymers of the 21st century, can be endowed with high performance for ever-demanding high-end applications. Thanks to the continuous advancement of catalyst technology, the technological trend for iPP alloy and nanocomposite fabrication has been projected to be in-reactor synthesis, the performance and economic advantages of which are beyond doubt. In this paper, we review two recent key developments in the iPP in-reactor alloy and in-reactor nanocomposite technology in our laboratory that will have profound influence on the continuing development of the prestigious iPP modification art. The first is the simultaneous EPR (ethylene-propylene random copolymer) cross-linking chemistry for controlling its physical growth pattern during in-reactor alloying, which helps to remove the compositional cap on EPR that so far greatly limits the iPP in-reactor alloying technique. The second is the nanofiller support fabrication strategy for simultaneously controlling both the phase morphology of the nanofiller dispersion and the polymer particle granule morphology of synthesized nanocomposites, which resolves the critical scale-up issue surrounding the iPP in-reactor nanocompositing technique. Based on these new developments, new advancements of iPP materials are envisaged.     

制备方法对聚合物共混物相分离与黏弹弛豫的影响

采用小角激光光散射(SALLS)和动态流变方法研究了通过不同制备方法得到的等规聚丙烯/乙丙橡胶共混物(iPP/EPR)的相分离行为与黏弹行为.依据Cahn-Hilliard-Cook理论分析了熔融共混和溶液共混法制备的质量比为60/40和40/60的iPP/EPR共混物在恒温相分离早期的动力学,发现熔融共混iPP/EPR具有更大的表观扩散系数(Dapp).相分离中后期的实验结果表明,当相区尺寸增长程度相同时,熔融共混试样所用时间更短.表明熔融共混iPP/EPR试样具有更快的相分离速率.动态流变测试结果表明,与溶液共混相比,熔融共混试样具有更快的松弛速率.考虑到相分离过程实质是由高分子链的运动与扩散所控制,两种方法制备的iPP/EPR共混物相分离速率的差异应归于其分子链运动能力的不同.     

Stress-Whitening of High-Impact Poly(propylene): Characterization and Analysis

Summary: High-impact isotactic polypropylene (hiPP) is a multiphase material and hiPP is susceptible to stress-whitening (or blushing) when exposed to impact, tension etc. Stress-whitening will influence the quality of the products. The object of this work is to find the factors influencing the resistance of stress whitening. Five reactor-alloy hiPP samples were used. Stress whitening was characterized by Gardner-type impact apparatus. Automated PP viscometer and xylence solubles analyzer (CrystEX), tapping mode atomic force microscopy (TMAFM), Fourier transform infrared spectroscopy (FTIR), dynamic mechanical analysis (DMA), wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) were used to characterize the samples. The stress-whitening was found to be related with the following factors: 1.particle size of the dispersion phase (rubber phase), 2.composition of the dispersion phase, 3.crystallization in in the dispersion phase, 4.crystalline form of the matrix (iPP).     

Phase morphology, crystallisation behaviour and mechanical properties of isotactic polypropylene/high density polyethylene blends

The phase morphology, crystallisation behaviour and mechanical properties of isotactic polypropylene (iPP)/high density polyethylene (HDPE) blends were investigated. It was found that the properties are intimately related to each other. The morphology of the blends showed a two phase structure in which the minor phase was dispersed as domains in the major continuous matrix phase. The domain size of the dispersed phase increased with increasing concentration of that phase due to coalescence. It was also found that the domain size of the dispersed phase depends on the viscosity difference between the two phases. For a given HDPE/iPP blend, where HDPE is the matrix and iPP is the dispersed phase, the iPP domains were smaller than HDPE domains of the corresponding iPP/HDPE blend where iPP is the matrix and HDPE is the dispersed phase. A co-continuous morphology was observed at 50/50 PP/HDPE composition. Crystallinity studies revealed that blending has not much effect on the crystalline melting point of polypropylene and high density polyethylene. The crystallisation enthalpy and heat of fusion values of HDPE and PP in the blend were decreased as the amount of the other component increased. The variation in percent crystallinity of HDPE and PP in the blend was found to depend on the morphology of the blend. All the mechanical properties except Young's modulus and hardness showed negative deviation from the additivity line. This is due to the incompatibility of these blends.     

Morphology and properties of isotactic polypropylene/poly(ethylene terephthalate) in situ microfibrillar reinforced blends: Influence of viscosity ratio

In situ microfibrillar reinforced blends based on blends of isotactic polypropylene (iPP) and poly(ethylene terephthalate) (PET) were successfully prepared by a “slit extrusion-hot stretching-quenching” process. Four types of iPP with different apparent viscosity were utilized to investigate the effect of viscosity ratio on the morphology and mechanical properties of PET/iPP microfibrillar blend. The morphological observation shows that the viscosity ratio is closely associated to the size of dispersed phase droplets in the original blends, and accordingly greatly affects the microfibrillation of PET. Lower viscosity ratio is favorable to formation of smaller and more uniform dispersed phase particles, thus leading to finer microfibrils with narrower diameter distribution. Addition of a compatibilizer, poly propylene-grafted-glycidyl methacrylate (PP-g-GMA), can increase the viscosity ratio and decrease the interfacial tension between PET and iPP, which tends to decrease the size of PET phase in the unstretched blends. After stretched, the aspect ratio of PET microfibrils in the compatibilized blends is considerably reduced compared to the uncompatibilized ones. The lower viscosity ratio brought out higher mechanical properties of the microfibrillar blends. Compared to the uncompatibilized microfibrillar blends, the tensile, flexural strength and impact toughness of the compatibilized ones are all improved.     

i-PP/EPR REACTOR ALLOY PREPARED THROUGH ETHYLENE/PROPYLENE SLURRY COPOLYMERIZATION CATALYZED BY METALLOCENE SUPPORTED iPP PARTICLES

i-PP/m-EPR reactor alloy were prepared through ethylene/propylene slurry copolymerization catalyzed by metallocene(rac-Et(Ind)_2ZrCl_2)supported on porous iPP particles.Polar monomer(dihydromyrcene alcohol)treated with triethyaluminum was added in the preparation of porous iPP particles to introduce hydroxyl groups and thus enhance the ability for chemically supporting the metallocene catalyst.The effects of MAO/Zr ratio and monomer composition in feed on the reaction activity and property of polymer wer...     

Crystallization,melting and structure of polypropylene/poly(vinylidene-fluoride) blends

Blends were prepared from isotactic polypropylene (iPP) along with its b-nucleated form and poly(vinylidene-fluoride) (PVDF). Melting, and crystallization characteristics as well as structure of the blends were studied by polarized light microscopy (PLM) and differential scanning calorimetry. According to PLM studies, the phase structure of these blends is heterogeneous in the molten state. The temperature range of crystallization of PVDF during cooling is higher than that of iPP. PVDF has a strong α-nucleating effect on iPP. The crystallization of iPP starts on the surface of dispersed PVDF droplets and an α-transcrystalline layer forms on the surface of the crystalline PVDF phase. The iPP matrix crystallizes predominantly in a-form in spite of the presence of a highly active b-nucleating agent. This revised version was published online in August 2006 with corrections to the Cover Date.     

乙丙嵌段共聚物的X-射线衍射研究

用大角X-射线衍射(WAXD)方法对按嵌段聚合程序合成的聚丙烯(PP)和乙丙共聚物(EPR)的嵌段共聚物PP-EPR和PP-EPR-PP,以及相应的混合物进行对比研究.乙丙共聚物及其共混物均发现在2θ=20°处存在由EPR中PP链段引起的γ-晶型衍射峰.通过诠释X-射线衍射图,计算结晶度,微晶尺寸和晶格参数等表明,用δ-TiCl_3-Et_2AlCl催化剂获得了嵌段共聚物结构.     

EPR-g-PS热塑弹性体结构与性能的关系

通过聚苯乙烯大分子单体与乙烯、丙烯共聚得到的乙丙橡胶(EPR)为主干、聚苯乙烯(PS)为支链的接枝共聚物EPR-g-PS,在无化学交联的情况下,模压样品具有与三元乙丙硫化胶可比拟的强度(PS=37.5％,M_(300％)=113公斤/厘米~2,抗张强度=198公斤/厘米~2,伸长率=705％)。聚苯乙烯含量、平均支链数目和成型条件是影响接枝共聚物力学性能的主要因素。聚苯乙烯微区除了以热塑交联网络起到物理交联作用外,在应力作用下本身还发生非弹性形变,起到补强填料的作用,使EPR-g-PS表现出热塑弹性体的性质。