Influence of a nucleating agent on the crystallization behaviour of isotactic polypropylene and elastomer blends

The influence of a nucleating agent on the crystallization behaviour of isotactic polypropylene (iPP), in their blends with poly(styrene-b-ethylene butylene-b-styrene) (SEBS), and a metallocenic ethylene-octene copolymer (EO) was investigated by DSC, optical microscopy and real-time small and wide angle X-ray scattering (SAXS and WAXS) experiments using synchrotron radiation. In non-nucleated iPP/SEBS blends, the crystallization of the iPP matrix occurred in the presence of the styrenic domains which induced a nucleating effect on the process, as observed in the synchrotron experiments. The metallocenic elastomer did not affect the crystallization behaviour of iPP in the iPP/EO blends in non-isothermal experiments, however, the development of crystallinity in the elastomer was restricted. In the nucleated isotactic polypropylene/elastomer blends a significant increase in the crystallinity and the crystallization rate of the iPP matrix was observed due to the presence of the nucleating agent. However, the nucleating efficiency of the additive was strongly affected by the nature and content of the elastomeric component. The nucleating agent efficiency was higher in the presence of the ethylene-octene component than the styrenic elastomer.     

Toughening effects of nucleating agent on impact polypropylene copolymer

In this study, the impact polypropylene copolymer (IPC) blended with the sorbitol‐based nucleating agent (NA) NX8000 was prepared and then characterized using a wide range of instrumentations. The results showed that the NA formed a fibril network which resulted in the increased viscosity of system and the decreased size of ethylene–propylene random copolymer (EPR) phase. The results of mechanical tests revealed “the brittle–ductile transition (BDT)” occurred while the ethylene content was between 3.5 wt % and 6 wt % and indicated that the impact strength of IPC was greatly improved by the addition of NX8000 when the EPR content was right over the critical value of BDT. The investigations provided valuable information for the further development of IPC materials and boarded its potential industrial applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40705.     

The effect of conditions of mixing of polypropylene/ethylene-propylene elastomer blends on their morphological structure and impact strength

The dependence of morphological structure and notch impact strength of polypropylene/ethylene-propylene elastomer blends on conditions of mixing was investigated. Two types of polypropylene and two types of ethylene-propylene elastomer having different viscosities were used. At low rates and short times of mixing the samples contain both regions showing fine dispersion and regions showing large elastomeric inclusions surrounded with pure polypropylene. With increasing rate and time of mixing the large inclusions gradually disappear. The conditions of mixing which are necessary for reaching a homogeneous structure of the blends depend on viscosities of the components. The independence of particle size of the rate of mixing in homogeneous samples is discussed on the basis of a dynamic equilibrium between the break up and coalescence of droplets. The notch impact strength of the individual samples of the same blend is determined by the size and number of inhomogeneities (large inclusions) in the given sample.     

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.     

Photodegradation of polypropylene containing a nucleating agent

The effect of including 0.5 wt % talc on the photodegradation behavior of polypropylene (PP) was investigated in injection-molded samples exposed to ultraviolet radiation (UV) in the laboratory for periods of up to 24 weeks. The structure of the talc-nucleated samples was characterized by X-ray diffraction and light microscopy and compared with that of nonnucleated PP, and the information was used to explain the differences in their photodegradation behavior. Measurements of the extent of chemical degradation were made by Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC), and they showed that there is no significant effect of a nucleating agent on the kinetics of photooxidation. PP bars containing a nucleating agent showed a larger reduction in mechanical properties with UV exposure and a partial recovery in properties after prolonged exposure was observed with both types of samples. An increase in crystallinity during UV exposure (chemicrystallization) was detected by X-ray diffraction and differential scanning calorimetry (DSC) and the dependence with exposure time was similar in nucleated and nonnucleated samples. DSC was also used to determine the melting behavior and transition temperatures of the specimens during exposure and after recrystallization from the melt. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2505–2517, 1997     

聚丙烯/聚烯烃弹性体共混物的制备与性能研究

通过熔融共混法制备了一系列聚丙烯(PP)/聚烯烃弹性体(POE)共混物,采用热重分析、示差扫描量热分析和拉伸测试对所得样品进行了热性能及力学性能的表征。结果表明,随着POE含量的增加,PP的抗拉强度和断裂伸长率均呈现先增加后减小的趋势。而当POE的含量低于5%时,样品的熔融温度明显低于纯PP的熔融温度;而当其含量超过5%时,样品的熔融温度与纯样基本一致。另外,POE的引入导致PP的热降解温度降低。     

低收缩率成核剂在抗冲共聚聚丙烯EP5010C中的应用

通过对抗冲共聚聚丙烯EP5010C与国内外同类产品的力学性能和收缩率的比较与分析,研究了EP5010C收缩率较大和翘曲变形的原因.结果表明:将EP5010C配方中的苯甲酸钠成核剂替换为低收缩率成核剂B,对EP5010C力学性能影响较小,明显降低了EP5010C的横向和纵向收缩率,解决了EP5010C收缩率大和易翘曲变形...     

助交联剂对动态硫化聚烯烃弹性体/聚丙烯共混物性能的影响

以纯度为40%的双叔丁基过氧化二异丙基苯为交联剂、异氰尿酸三烯丙酯为助交联剂,研究了动态硫化的温度和转速对于聚烯烃弹性体/聚丙烯(POE/PP)共混物的性能以及异氰尿酸三烯丙酯的用量对于POE/PP共混物的性能和转矩的影响。结果表明,POE/PP共混物的拉伸强度、扯断伸长率和300%定伸应力都随动态硫化温度的升高而先增大后减小,撕裂强度随动态硫化温度的升高而减小,动态硫化温度为180℃时的总体力学性能较好;随着动态硫化转速的提高,POE/PP共混物的拉伸强度和300%定伸应力都先增大后减小,扯断伸长率减小,撕裂强度则增大,动态硫化的转速为50 r/min时共混物的总体力学性能较好。助交联剂异氰尿酸三烯丙酯的加入明显提高了POE/PP共混物动态硫化时的转矩,其用量以1份(质量)为宜。     

Rheological study of polypropylene copolymer/polyolefinic elastomer blends

Blends of polypropylene copolymer (PP‐cp) and a polyolefinic elastomer (POE) were prepared by a melt‐blending process at 210°C and 60 rpm using a counterrotating twin‐screw extruder. The POE content was varied up to 25%. The shear viscosity over a wide range of shear rate was measured. All blend compositions showed well‐defined zero shear viscosity and shear thinning behavior. The melt viscosity values were between those of the principal components in all cases. Rheology of blends shows different behavior up to concentrations of POE corresponding to the tough–brittle transition. The linear viscoelastic properties (G′, G″, η*, η′, η″) were used to check the miscibility of the two components in the melt state. All blend compositions showed a good degree of miscibility over the range of POE concentrations studied. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 665–671, 2002; DOI 10.1002/app.10376     

Morphology and rheological properties of polypropylene/reactive elastomer blends

The relation of morphology to the linear viscoelastic properties for polymer blends consisting of an inert polypropylene and an elastomeric dispersed phase, made of two miscible copolymers, EVA and EMA, was investigated. The rheological properties of the elastomeric phase were modified by crosslinking in presence of an organometallic catalyst. The activation energy for the transesterification reaction taking place between EVA and EMA has been determined by following the increases of the complex viscosity with time and temperature. The Palierne model has been used to describe the linear viscoelastic behavior of the blends, and to estimate the interfacial tension between the immiscible components. The model was shown to describe relatively well the linear viscoelastic properties of reactive and nonreactive blends containing 30% or less elastomer. In parallel, the morphology of reactive and nonreactive blends (i.e. without catalyst in the elastomeric phase), before and after rheological experiments, has been determined using scanning electron microscopy. The size of the dispersed elastomeric particles for reactive blends prepared using an internal mixer was found to be, in most cases, much smaller than that for nonreactive blends.     

Linear low-density polyethylene addition to polypropylene/elastomer blends: Phase structure and impact properties

Morphology features and effects of particle size and composition of the disperse phase on the impact properties have been studied for the blends of isotactic polypropylene (PP)/ethylene-propylene-diene terpolymer and (EPDM)/linear low-density polyethylene (LLDPE). The blend components were mixed in a twin-screw extruder, press molded, and analyzed by scanning electron microscopy, SEM (fractured and toluene etched samples), and by transmission electron microscopy, TEM (RuO₄ stained samples). TEM was most effective for the identification of component distribution and particle size measurement. An increasing degree of LLDPE and EPDM interpenetration was observed with the PE content. Not one case of a neat component separation was detected. LLDPE addition improves the EPDM dispersability, affecting mainly the larger particles. The impact properties at room temperature were especially dependent on the rubber content, whereas at low temperature the particle diameter appears to be the controlling parameter. The affect of LLDPE on blend toughness is more evident in the latter case.     

Effects of compatibility on foaming behavior of polypropylene/polyolefin elastomer blends prepared using a chemical blowing agent

Polypropylene (PP) exhibits poor foaming property because of its low melt strength arising from its linear chains and relatively narrow molecular weight distribution. To fabricate a PP foam without crosslinking, PP should be blended with polyolefin elastomers (POEs) using chemical blowing agents. In this study, the effects of POE types and contents in a PP matrix were studied by analyzing the melt flow index, morphology, and thermal and dynamic viscoelastic properties. Furthermore, the POE type/content and foaming conditions (i.e., foaming temperature and oven residence time) were optimized by investigating the volume expansion ratio (VER), cross‐sectional morphology, and hardness of the PP/POE foams. We focused on how the foaming behavior and foaming conditions were affected by the compatibility and POE content in the PP/POE blend. The results demonstrated that the optimal VER of ～9 was obtained at 30 wt % POE and foaming conditions of 220 °C for 9 min. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45201.     

Dynamic mechanical properties and morphology of polypropylene block copolymers and polypropylene/elastomer blends

The relation between the dynamic mechanical properties and the morphology of polypropylene (PP) block copolymers and polypropylene/elastomer blends was studied by dynamic mechanical analysis (DMA), light- and electron microscopy. The latter techniques contributed to an improvement in assignments of relaxation transitions in the DMA spectra. It was established that PP block copolymers had multiphase structure since the ethylene/propylene rubber phase (EPR) formed in the copolymerization contained polyethylene (PE) domains. An identical morphology was found in the case of PP/polyolefin thermoplastic rubber (TPO) blends. Impact modification of PP by styrene/butadiene block copolymers led to a multiphase structure, too, due to the polystyrene (PS) domains aggregated in the soft rubbery polybutadiene phase. In the semicrystalline polyolefinic and in the amorphous styrene/butadienebased thermoplastic rubbers, PE crystallites and PS do mains acted as nodes of the physical network structure, respectively. PP/EPDM/TPO ternary blends developed for replacing high-density PE showed very high dispersion of the modifiers as compared to that of PP block copolymers. This fine dispersion of the impact modifier is a basic regulating factor of impact energy dissipation in the form of shear yielding and crazing.     

Optimizing the balance between viscosity/modulus and impact in particulate composites

The objective of this study was to develop some new concepts of importance when trying to optimize the viscosity/modulus and impact relative to the particle‐size distribution in suspensions and particulate composites. The results of this study appear to indicate that, conceptually, it is possible to significantly improve the viscosity versus the impact balance for material formulations by optimizing the particle‐size distribution. For binary particle‐size distributions, the influence of the preferred particle‐size distribution, as determined using a square‐root distribution, did not yield the most desirable particle‐size distribution if the particle‐to‐particle component of the interaction coefficient was high. However, if three or more particles were utilized in the distribution, then the optimum particle‐size distribution utilized can apparently be characterized using the square‐root distribution even when the particle–particle component, σ_pc, of the interaction coefficient, σ, was found to be quite high. In addition, this same square‐root particle‐size distribution can also satisfactorily predict a probability of impact that can remain consistently high as long as the particles utilized are well chosen and not too close in size. Thus, this preferred particle‐size distribution can be utilized to predict at least one of the preferred distributions to optimize the balance of properties between impact and the viscosity/modulus. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 291–304, 2002     

Relationship between cell morphology and impact strength of microcellular foamed high‐density polyethylene/polypropylene blends

Polymer blends, such as those resulting from recycling postconsumer plastics, often have poor mechanical properties. Microcellular foams have been shown to have the potential to improve properties, and permit higher‐value uses of mixed polymer streams. In this study, the effects of microcellular batch processing conditions (foaming time and temperature) and HDPE/PP blend compositions on the cell morphology (the average cell size and cell‐population density) and impact strength were studied. Optical microscopy was used to investigate the miscibility and crystalline morphology of the HDPE/PP blends. Pure HDPE and PP did not foam well at any processing conditions. Blending facilitated the formation of microcellular structures in polyolefins because of the poorly bonded interfaces of immiscible HDPE/PP blends, which favored cell nucleation. The experimental results indicated that well‐developed microcellular structures are produced in HDPE/PP blends at ratios of 50:50 and 30:70. The cell morphology had a strong relationship with the impact strength of foamed samples. Improvement in impact strength was associated with well‐developed microcellular morphology. Polym. Eng. Sci. 44:1551–1560, 2004. © 2004 Society of Plastics Engineers.     

Microstructures and mechanical properties of polypropylene/polyamide 6/polyethelene-octene elastomer blends

A series of polymer blends were designed and manufactured. They are composed of three phases: polypropylene (PP), polyamide-6 (PA6) and polyethylene-octene elastomer (POE) grafted with maleic anhydride. The weight fraction of PA6 was adjusted from 0 to 40% by increments of 10%, and the weight fraction of POE was systematically half that of PA6. The morphology, essentially made of PA6 particles dispersed in the PP matrix, was characterised by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In the extruded plates prepared with the blends, the shape of the dispersed PA6 particles showed an elongated ellipsoidal shape, whose aspect ratio increased somehow with alloying content. The POE modifier was observed both as a thin interlayer (less than 100 nm thickness) at the PP/PA6 interface, and as a few isolated particles. The elastic modulus and yield stress in tension are nearly constant for PP and blends. By contrast, the notched Izod impact strength increases very much with alloying content. This remarkable effect is interpreted in terms of POE interphase cavitation, enhanced plastic shear deformation and resistance of PA6 particles to crack propagation.     

Enhancement of drawdown force in polypropylene containing nucleating agent

The effect of the nucleation efficiency of three commercial nucleating agents, such as 1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (DMDBS), sodium 2,2′-methylene-bis-(4,6-di-tert-butylphenyl)phosphate (SMBP), and magnesium silicate (talc), on the melt-stretching performance of isotactic polypropylene (PP) is studied. It is found that the addition of 0.5 wt % of a nucleating agent enhances the crystallization temperature and that effect is pronounced for DMDBS and SMBP. Furthermore, DMDBS is more efficient than the other tested nucleating agents in enhancing the drawdown force, defined as a force required for stretching a molten strand. Nanofibers of DMDBS, which show significant alignment in the flow direction, are responsible for the rapid crystallization of PP in the flow field leading to an increase of drawdown force. The stretched strand shows a highly oriented structure in which the α-form crystals orient to the flow direction. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47295.     

Effect of nanosilica on the co-continuous morphology of polypropylene/polyolefin elastomer blends

This paper reports the effect of nanosilica (SiO₂) on the morphology of co-continuous immiscible polypropylene (PP)/polyolefin elastomer (POE) blends. The unfilled blends display phase inversion and a co-continuous structure at a ratio of 50/50 PP/POE by weight. Upon addition of SiO₂ in the presence of maleated PP compatibilizer a finer structure, consisting of elongated POE particles dispersed within the PP phase is obtained. This transformation is associated to the presence of finely dispersed SiO₂ particles that are localized exclusively within the PP matrix. The impact properties, flexural and Young's moduli of the blends increase significantly, pointing to a synergistic effect arising from the presence of the reinforced PP phase, containing high amounts of the finely dispersed elastomeric phase.     

成核剂对聚丙烯性能的影响

研究了各种α晶型成核剂和β晶型成核剂对聚丙烯性能的影响,发现用α晶型成核剂NA-11和用N催化剂生产的高等规指数聚丙烯组合,可制成透明型高强度、高耐热聚丙烯。这种高性能聚丙烯在家电、汽车等方面具有极为广泛的应用前景。