Polymer blends based on the β-modification of polypropylene

iPP/sPP, iPP/rPP, iPP/PVDF and iPP/PA-6 blends, and their β-nucleated forms were prepared in the present study. The components of iPP/sPP and iPP/rPP blends are compatible in the molten state. The phase structure of the melt of iPP/PVDF and iPP/PA-6 blends is heterogeneous. The melting and crystallisation characteristics as well as the structure and polymorphic composition of these blends were studied by polarised light microscopy (PLM) and differential scanning calorimetry (DSC). When semicrystalline polymers are added to iPP, the most important factor of the formation a blend with β-crystalline phase is the α-nucleation effect of the second polymer. In the case of polymers with an α-nucleating effect, the temperature range of their crystallisation should be lower than that of β-iPP. β-nucleated iPP/PVDF and iPP/PA-6 blends are extreme examples showing that completely β-iPP matrix can not form even in the presence of a highly effective β-nucleant, because of the strong α-nucleating ability and higher crystallisation temperature range of PVDF and PA-6. We found that the β-crystallisation tendency of random propylene copolymers can be enhanced by adding an iPP homopolymer.     

半晶聚合物复合材料中的横晶

半晶聚合物复合材料,尤其是纤维增强的半晶聚合物复合材料,在其界面区常有横晶结构生成。本文综述了横晶自发现至今的研究情况,对横晶的形成和生长机理进行了描述,对影响横晶生成和性质的因素进行了分析,着重介绍了几种典型半晶聚合物复合材料体系的横晶形态,并讨论了横晶对界面特性和复合材料性能的影响。     

AFM imaging of interfacial morphologies in carbon-fiber reinforced isotactic polypropylene

 The morphology of high-modulus carbon-fiber (HM-CF) reinforced isotactic polypropylene (iPP) was investigated for the first time by atomic force microscopy (AFM) using chemically etched specimens. The images exhibited α-transcrystalline morphology for samples crystallized from quiescent melts, nucleated by HM-CF. In melts sheared by fiber pulling, αβ-cylindritic columnar morphology was observed in agreement with earlier thermo-optical studies. AFM images in the interfacial region of the β-cylindrites unveiled fine morphological details of α-row nuclei. Based on the observations, we concluded that in β-cylindrites, the lamellar growth in α-row nuclei occurs during epitaxial crystallization on bundles of extended iPP chains which form during shearing of the polymer matrix by fiber pull. Received: 25 June 1996 Accepted: 17 October 1996     

Transcrystallization of PTFE fiber/PP composites (I) crystallization kinetics and morphology

Transcrystallization of polypropylene (PP) on the polytetrafluoroethylene (PTFE) fiber was investigated. Both nucleation rate and crystal growth rate were determined by a polarized optical microscope. Based on the theory of heterogeneous nucleation, it has been found that the induction time can correlate well with the nucleation rate in determining the interfacial free energy difference function Δσ. The ratio of Δσ in the bulk matrix to that at the interface is 1.63 which implies the transcrystalline growth is favorable from a thermodynamic point of view. No difference in crystal growth rate of PP has been found in either spherulites or transcrystalline layers. On the basis of regime theory, a transition between regimes II and III was observed at ΔT = 48K. From the morphology studies, it has been found that the thickness of the transcrystalline layer increases with crystallization temperature, from 30 to 120 μm in the temperature range of 110–140°C. The growth of transcrystalline layer is hindered by the spherulites nucleated in the bulk. Moreover, the radius of spherulites adjacent to the transcrystalline layer is much smaller than that distant to the fiber. No significant increase in nucleation density at fiber ends is observed. Effect of internal stresses of fibers on the fiber's nucleating ability is not pronounced. © 1996 John Wiley & Sons, Inc.     

碳纤维-尼龙1010界面形态的研究

通过偏光显微镜,研究了碳纤维-尼龙1010的界面形态,发现石墨、高模量碳纤维(M40)诱发尼龙1010形成横晶的能力大于高强度、中强度碳纤维;界面横晶形态强烈地依赖于结晶温度。     

Transcrystalline interphases in natural fiber-PP composites: effect of coupling agent

The interest in lignocellulosic fiber composites has been growing in recent years because of their high specific properties. In this work, a new technique was used to prepare specimen to observe the transcrystalline zones in kenaf fiber-polypropylene composites. A maleated polypropylene (MAPP) coupling agent was used to improve the stress-transfer efficiency in the composites. Transcrystallinity was observed for both the uncoupled and coupled composites, although the rate of growth was higher for the coupled composites. Dynamic mechanical spectroscopy was used to observe the relaxations of the composites. The peak temperature of the β-relaxation, associated with the glass-rubber transition of the amorphous molecules, of the coupled composites was higher than that of the uncoupled composites. Restricted molecular mobility due to covalent interactions between the MAPP and the lignocellulosic surface may account for the shift to higher temperatures. It appears that during compounding the extractives sheared from the fiber surface is an important factor in determining the β-relaxation of these composites. The intensities of the α-transition, related to molecular mobility associated with the presence of crystals, is proportional to the fiber volume fraction. Thus it is possible that the molecules responsible for the α-transition are predominantly in the transcrystalline zone. These 'rigid' amorphous molecules in the transcrystalline zone do play a role in composite behavior and need to be considered when tailoring interphases.     

纤维增强树脂基复合材料中的横穿结晶研究

在以结晶性聚合物为基体树脂的纤维或织物增强复合材料中,经常出现横穿结晶(横晶)界面相。本文综述了近年来对纤维增强树脂基复合材料中横穿结晶的研究,内容包括横晶的概念,纤维表面诱导成核的机理,纤维诱导成核的能力和条件,横晶的生长和终止以及横晶的力学效应等。在不同的树脂/纤维复合材料体系中,由于其横穿结晶本身和本体球晶在尺寸和数目比例等方面呈现各不相同的复杂局面,横晶对复合材料性能的影响显得复杂。通过各种手段调控横晶的形态、尺寸及数量,使横晶的存在有利于复合材料整体性能的提高,是进行纤维增强结晶性聚合物基复合材料设计时应该遵循的一个基本原则。     

Transcrystallinity phenomena in PET and PAN fibres/polyhydroxybutyrate matrix systems

The interface in polyhydroxybutyrate/ PAN- and polyhydroxybutyrate/ PET fibres model composites has been investigated by polarizing optical and scanning electron microscopy. Under certain melting/cooling conditions in PAN fibre system a transcrystalline interphase is clearly observed, whereas in PET/PHB model composites the transcrystallization phenomenon occurs only when fibres with significant surface roughness are used.