STUDY OF ACOUSTIC EMISSION DURING NON-ISOTHERMAL CRYSTALLIZATION OF POLYPROPYLENE

In this paper we have presented the results of acoustic emission (AE) during non-isothemal crystallization of polypropylene (PP) melt with mean cooling rate 4℃/min, and discussed the effects of molecular weight (MW) on AE activity. It is shown that the amount of AE ring-down counts during whole crystallization of PP depends on the MW strongly.The copious AE bursts have been observed at the late stage of PPcrystallization. AE bursts are caused by cracking, crazing and cavitation between spherulites and inside spherulites.     

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.     

Determination of low levels of polymer additives migrating from polypropylene to food simulated liquids by capillary SFC and solvent venting injection

Summary Methods for the determination of specific migration of polymer additives from polypropylene to aqueous acetic acid and isooctane have been studied. The migrants were extracted from aqueous acetic acid and characterized by supercritical fluid chromatography (SFC) with flame ionization detection (FID) and mass spectrometry (MS). The isooctane simulant was concentrated and injected directly into the SFC. Injection of extracts after incubation, using the solvent venting injection technique in the SFC, enabled additive concentrations as low as 10 ppb in 150 ml simulant to be determined, corresponding to a specific migration level of approximately 1 g additive/dm² polymer.     

聚丙烯中硫酯类抗氧剂的质谱分析

采用齐格勒-钠塔催化剂使丙烯催化聚合得到聚丙烯。聚丙烯树脂本身具有优良的性能,如机械强度好,易加工成型,质量轻,成本低等,但也存在一些缺陷,如由于聚丙烯结构中存在叔碳原子,在造粒加工、贮存和使用过程中,易受热、光、氧等的作用而降解,导致材料的性能降低。为了抑制和延缓聚丙烯的氧化降解,需要在造粒阶段加入抗氧剂。本文以一种聚丙烯树脂样品为研究对象,采用溶剂抽提法提取有机添加剂,并用柱层析法对添加剂进行了分离;利用EI-MS分析了添加剂的组成,其中通过谱图解析,鉴定出添加剂中含有硫酯类抗氧剂-硫代二丙酸二(十四)酯(DMTP),并用此类常用化合物进行了验证,分析结果对树脂牌号的开发具有指导意义。     

Blends of propylene-ran-ethylene and propylene-ran-(1-butene) copolymers: Crystal superstructure and mechanical properties

Blends of isotactic propylene-ran-ethylene (EP) and propylene-ran-(1-butene) (BP) copolymers with various comonomer content (2-3.1 wt.% ethylene, 9.9 wt.% 1-butene), were prepared in Brabender internal mixer at various compositions (25/75, 50/50, 75/25). Static, impact and dynamic mechanical behavior of copolymers and their blends was investigated. The crystalline structure was studied by DSC and SAXS analysis. For all copolymers the lamellar thickness, crystallinity degree and glass transition temperature are lower than those of iPP homopolymer, depending on the comonomer content. It was found that the copolymers exhibit improved impact strength as compared to plain iPP, due to lower crystallinity and higher mobility of chains within amorphous component. Moreover, the elastic modulus as well as the yield behavior of the examined samples resulted to depend primarily on the amount of the crystalline phase and the thickness of the lamellar crystals, respectively. A linear dependence of yield stress on the logarithm of reciprocal lamellar thickness was observed for blends and copolymers, supporting the concept of thermal nucleation of dislocations which control the crystallographic slip processes initiated at the yield point. The blends of BPS with either EPS or EP2 display complete miscibility in the entire range of composition and their mechanical properties are intermediate between those of plain components, changing gradually with the composition.     

负载型催化剂制备的聚丙烯等规度分布

负载型Ziesler－Natta催化剂中存在许多活性中心［'3，为了解其本质，需对其各自产生的聚合物进行分离，以往采用的溶剂抽提法［'－'j只能将聚合物大致分级．最近，升温淋洗分级法（TREF）已被运用于聚丙烯的分级卜，'，其原理是根据聚合物的结晶度分级D'，影响聚丙烯结晶性的主要因素是等规度，而分子量到达一定程度后其影响较小，故通过TREF分级可得到聚丙烯的等规度分布．TREF法的淋洗温度可控，故分级效果较好．该法在分级前需对样品进行等温结晶处理，以消除抽提法由于样品未必充分结晶而带来的误差．本文用TREF法对不同催化…     

Molecular fractionation in isotactic polypropylene during isothermal crystallization

The nucleation frequency of isotactic polypropylene shows for certain molecular weight distributions during isothermal crystallization a “stepwise” development of the nuclei as a function of time. The resulting curve can be fitted by a superposition of exponential functions assuming a separate nucleation density for each nucleation step. The multimodal nucleation is discussed as a consequence of molecular fractionation effects during crystallization. Received: 23 October 1997 Accepted: 12 May 1998     

聚丙烯-聚乙烯嵌段共聚物的分子结构及性能的研究

本工作用核磁共振(~(13)C-NMR)、示差扫描量热(DSC)、动态力学分析(DMA)和扫描电子显微镜(SEM)等技术研究了将丙烯、乙烯单体两步分段共聚、预期为聚丙烯-聚乙烯嵌段共聚物的合成物(简称为聚丙烯-聚乙烯嵌段共聚物或嵌段共聚物)。结果表明,在嵌段共聚物中含有一定量的、能为正庚烷抽提出来的乙丙无规共聚物(EPR);分段共聚的产物并非预想的PP-b-PE两嵌段共聚物,而是含有多种组分的共混物;形态表征的结果表明了嵌段共聚物为多相体系,EPR和PE形成分散相以球形无规分布于PP基体中。     

Fabrication of a novel Li<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MoO<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> film modified electrode and its application as an electrochemical sensor of iodate

A novel organic gel film modified electrode was simply and conveniently fabricated by casting Li_xMoO_y and polypropylene carbonate (PPC) onto the surface of a gold electrode. The cyclic voltammetry and amperometry studies demonstrated that the Li_xMoO_y film modified electrode has a high stability and a good electrocatalytic activity for the reduction of iodate. In amperometry, a good linear relationship between the steady current and the concentration of iodate was obtained in the range from 3×10^–7 to 1×10^–4 mol L^–1 with a correlation coefficient of 0.9997 and a detection limit of 1×10^–7 mol L^–1.     

从聚丙烯流动曲线估算分子量分布

聚丙烯的控制降解技术由于能够带来很好的经济效益，国内外都在进行研究．其中分子量分布是一个重要数据，它对于聚丙烯的注塑、纺丝、薄膜等加工过程都有重要的影响．分子量分布一般用重均分子量Mw和数均分子量Mn之比D=Mw/Mn来表征，称为分子量分布指数．它可以