聚丙烯多单体接枝共聚物的结晶行为

通过固相接枝法制备聚丙烯(PP)与马来酸酐、甲基丙烯酸甲酯和丙烯酸丁酯的多单体接枝共聚物(PPTM)。采用差示扫描量热法、X射线衍射和偏光显微镜等研究接枝支链对接枝共聚物结晶行为的影响,并计算接枝共聚物的晶胞参数。接枝支链能诱导PPTM的异相成核,形成β晶型,也能阻碍结晶的进行。接枝支链诱导PPTM形成β晶型需要合适的支链长度。PPTM的微晶尺寸和晶胞参数都受到接枝支链的影响。PPTM的c轴(晶体生长方向)的晶胞参数比PP的稍大。     

聚丙烯固相接枝苯乙烯

研究了聚丙烯（ＰＰ）固相接枝苯乙烯（Ｓｔ），讨论了反应温度，反应时间，引发剂（ＢＰＯ）浓度，Ｓｔ浓度，溶胀时间对接枝率的影响，结果表明，在反应时间为４ｈ，反应温度为９０℃，ＢＰＯ用量为１．０％，Ｓｔ：ＰＰ的质量比为０．２５：１溶胀时间４ｈ时，可获得最大接枝率（１７．５％）。     

聚丙烯悬浮法接枝苯乙烯的研究

研究了聚丙烯悬浮法接枝苯乙烯,考察了聚丙烯(PP)型号、溶胀时间、反应温度、反应时间、苯乙烯(St)及过氧化苯甲酰(BPO)的浓度对St接枝率和接枝效率的影响。较佳的实验条件为:PP:St=1:1,BPO 1％,60℃溶胀2h,反应温度85～90℃,反应时间6～7h。St接枝率可达10％以上。     

乙烯基硅烷/苯乙烯接枝聚丙烯的结晶和力学性能

研究了乙烯基硅烷（VS）和苯乙烯（St）双单体接枝聚丙烯（PP-g-VS/St）的结晶性能和力学性能。结果表明,长支链的引入使PP-g-VS/St的结晶峰值温度和熔融峰值温度相对于线形等规聚丙烯（iPP）分别提高了10、2 ℃,且球晶得到了细化; PP-g-VS/St在10 ℃/min的降温速率下结晶产生的晶型为α晶型与少量γ晶型的混合物;在注塑条件下结晶产生的晶型为α晶型与β晶型的混合物; 利用莫志深法研究PP-g-VS/St的非等温结晶动力学过程发现,在结晶的早期和后期,长支链对PP-g-VS/St的结晶分别起到了加速成核和阻碍生长两种相反的作用;相对于iPP,PP-g-VS/St的拉伸强度、弯曲模量和冲击强度分别提高了29 %、40 %和453 %。     

端氨基聚氨酯接枝聚丙烯的结晶行为

通过反应挤出法将端氨基聚氨酯(ATPU)接枝到聚丙烯(PP)上,提纯后产物的傅里叶变换红外光谱上出现氨基甲酸酯的C=O和N-H的特征吸收峰。使用光学解偏振仪、差示扫描量热法和广角X射线衍射等研究试样中ATPU含量对结晶行为的影响。结果表明,功能化基团的加入起到类似成核剂的作用,能加快PP的结晶速率;随着功能化基团含量的增加,PP结晶度呈现先上升后下降的变化。     

苯乙烯接枝改性聚丙烯制备及其性能

以过氧化苯甲酰为引发剂,采用反应挤出法将苯乙烯(St)接枝到等规聚丙烯(iPP)上,并考察了St浓度对接枝PP结晶性能、流变性能和发泡性能的影响。由FTIR、GPC和MFR表征结果表明St成功接到PP上;DSC结果表明,接枝PP结晶峰值温度与iPP相比最大提高了15.4℃;由剪切流变测试结果,在低频区,接枝PP的G'值增大,出现明显的剪切变稀现象,tan δ-ω曲线中出现平台,说明接枝PP中有长支链结构的存在;由于接枝PP的熔融流动速率降低即熔体强度提高,使得接枝PP的泡孔更规则。     

马来酸酐及苯乙烯同时接枝聚丙烯的研究

用过氧化二异丙苯(DCP)作为引发剂，采用双螺杆反应挤出的苯乙烯、马来酸酐2种单体同时接枝聚丙烯．研究了单体总浓度、单体比例、引发剂浓度对PP的接枝率、接枝效率和熔体流动速率的影响。通过实验发现苯乙烯的加入使接枝率和接枝效率比单独的马来酸酐接枝都有很大的提高。     

聚丙烯纤维接枝苯乙烯的研究

采用化学接枝法以苯乙烯(St)为接枝单体、过氧化苯甲酰(BPO)为引发剂,1,2-二乙烯苯(DVB)为交联剂、甲醇和正辛醇为溶剂,对聚丙烯(PP)纤维进行接枝改性。研究了原料配比和反应条件对其接枝的影响。结果表明,PP纤维上接枝St,适宜的原料配比和操作条件为:St质量与PP体积比(St/PP)为4,BPO质量与St体积比(BPO/St)为0.025,DVB与St体积比(DVB/St)为0.025,溶剂与St体积比为5,浸渍24～30h,在85℃恒温水浴中反应6～8h。在较佳条件下可得到导入率为110%-160%的接枝纤维。     

马来酸酐苯乙烯双单体接枝聚丙烯的研究

研究了聚丙烯（ＰＰ）采用熔融法接枝马来酸酐（ＭＡＨ）聚乙烯（Ｓｔ）双单体。实验表明,马来酸酐接枝率随其加入量增加而提高;添加两种单体时,马来酸酐添加量保持不变,马来酸酐接枝率随苯乙烯添加量增加而提高。经转矩流变,红外,热失重和差示扫描量热分析表明：马来酸酐,苯乙烯均与聚丙烯发生接枝反应,且有交联网络出现,因此推断出苯乙烯和马来酸酐预先发生交替共聚,共聚物与聚丙烯反应生成最终接枝物。接枝物应用于ＰＰ     

Crystallization behaviors of polypropylene and functional polypropylene

The crystallization behaviors of polypropylene (PP) homopolymer and its blends with 0–15% functional polypropylene (FPP), the backbones of which were grafted with guanidine and diamide polymer chains, were investigated with differential scanning calorimetry and wide‐angle X‐ray scattering. The crystallization kinetics were studied with spectral depolarization. The results revealed that the presence of FPP reduced the crystallinity and crystallite size of PP. Meanwhile, FPP increased the crystallization rate. Compared with that of the PP homopolymer, the crystallization temperature of PP/FPP blends was increased by more than 10°C. During isothermal crystallization, the relative crystallinity, developed as a function of time, was described by the Avrami equation. The half‐time of crystallization for PP/FPP blends was much shorter than that for the PP homopolymer. The half‐time of crystallization of PP/FPP blends depended much less on the crystallization temperature than that of the PP homopolymer. Therefore, FPP accelerated the crystallization rate of PP in a manner similar to that of a nucleator. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 872–877, 2003     

Crystallization behaviors of polypropylene/montmorillonite nanocomposites

The isothermal crystallization kinetics of polypropylene/montmorillonite (PP/MMT) nanocomposites synthesized via intercalation polymerization were investigated by using differential scanning calorimeter and polarizing optical microscope (POM). The crystallinity of the nanocomposites decreased with the increase of the montmorillonite content, indicating that the MMT layers dispersed in the PP matrices confined the PP chains and hindered the crystallization of the PP chains. The POM photographs showed that the spherulites of the PP/MMT nanocomposites were greatly decreased in size as MMT was introduced. On the other hand, the crystallization rate increased dramatically with the increasing of MMT content. The interfacial free‐energy per unit area perpendicular to PP chains in PP/MMT nanocomposites decreased with increasing MMT content, suggesting that the MMT layers acted as heterogeneous nuclei in the nucleation of crystallization. The nucleus density increased with the increasing of MMT content, leading to a positive effect on the crystallization. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1978–1985, 2002     

Crystallization behavior of polypropylene/ethylene butene copolymer blends

One polypropylene (PP) was mixed with two ethylene butene copolymers (EBM). EBM1 had 12.5 mol % of butene and was immiscible with the PP. EBM2 had 51.6 mol % of butene and was miscible with the PP. The dispersed PP in EBM1 showed fractionalized crystallization behavior with a crystallization temperature at around 45°C and a much slower isothermal crystallization rate comparing to the neat PP. The PP did not exhibit fractionalized crystallization behavior in EBM2. EBM1 did not decrease both the crystallization and melting temperatures of the continuous PP. However, EBM2 could decrease both the two temperatures. It was found that EBM2 could largely suppress the epitaxial lamellar branching of the PP. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Crystallization behaviors and foaming properties of diatomite-filled polypropylene composites

The non-isothermal crystallization kinetics and foaming properties of polypropylene (PP) filled with various contents of diatomite were investigated. The results showed that the diatomite had strong effects on the PP crystallization kinetics, which significantly increased the crystallization temperature and reduced crystallite size. These were attributed to the nucleation effect of the diatomite particles and the complex interface properties between the PP chains and diatomite particles. Non-isothermal crystallization can be well described by the Mo’s method. The non-isothermal crystallization activation energy calculated by the Kissinger’s method increased with increased content of diatomite. The foamed PP composites, in particular, the PP composites filled with 10 wt% diatomite had better cell morphology ascribed to the facilitated crystallization and increased polymer melt strength compared with the foamed pure PP.     

Crystallization behaviors in the isotactic polypropylene/graphene composites

Crystallization behaviors and kinetics of iPP in an in-situ prepared isotactic polypropylene/graphene (iPP/G) composites were studied in this paper. In samples used in this study, the graphene fillers were well dispersed, and the interfacial adhesion exhibited enhanced features between graphene and iPP components. The thermal stability of the composites was improved by about 100 °C compared to the pristine iPP. It was found that the crystallization morphology, crystallization rate and kinetics of the iPP/G composites were significantly influenced by the presence of graphene. The nucleation and epitaxial growth of iPP on the graphene surface were observed and studied in detail. It was observed that the nucleation of iPP favored to occur at the wrinkles and edges due to the good match of the lattice parameters and the weak spatial hindrance compared to the smooth surface. Numerous nuclei epitaxially formed and the size of the crystals was very small. The schematic diagram was also proposed for the nucleation and growth process of iPP on the graphene surface in the iPP/G composites. Meanwhile, the overall crystallization kinetics and crystals growth were analyzed through Avrami equation. The obtained Avrami index n decreased with the graphene loadings and was close to 2 for the iPP/G composites, which implied that the growth of iPP in the composites was in two-dimension. And this was caused by the structure of graphene and the spatial confinement effect of graphene platelets in the iPP/G composites.     

Crystallization characteristics of polypropylene and low ethylene content polypropylene copolymer with and without nucleating agents

In this paper, the crystallization characteristics of polypropylene and low ethylene content polypropylene copolymers with and without nucleating agents were studied by differential scanning calorimetry (DSC) and polarized light microscopy (PLM). In order to determine the nonisothermal crystallization rate of these materials, a new estimation method was introduced. Comparing with the crystallization rate coefficient (CRC), which was proposed by Khanna, we found the new approach is more reasonable. From the analysis of results of DSC and PLM, it can be concluded that nucleating agent is more efficient than it is in PP homopolymer. © 1994 John Wiley & Sons, Inc.     

Space charge behaviors of low-density polyethylene blended with polypropylene copolymer

In this study, the space charge behaviors of the blend polymers of low-density polyethylene (LDPE) and polypropylene copolymer were investigated by the pulsed electro-acoustic method (PEA) with the electrode system of aluminium/specimen/semiconductive layer. The blend specimen composed by 90 wt% LDPE and 10 wt% polypropylene copolymer (B10) showed a larger amount of space charge than pure LDPE (PE) under a DC field of 50 MV m⁻¹ at both 30 and 60 °C. Positive carriers moved more slowly in B10 than in PE under a positive DC voltage applied to the semiconductive electrode at 30 °C. DC currents were also measured under the same experimental condition as the space charge measurement. The DC current of B10 was lower than that of PE at 30 °C, but higher at 60 °C. The experimental results were explained by the introduction of traps by blending.     

Crystallization in blends of isotactic polypropylene with polyethylene-b-poly(ethylene-co-butylene)-b-polyethylene block copolymer

In this study, isothermal crystallization in blends of isotactic polypropylene (i-PP) with polyethylene-b-poly(ethylene-co-butylene)-b-polyethylene block copolymer (CEBC) was investigated using a polarized photometer, polarized microscope and differential scanning calorimeter. Half time of crystallizaiton (τ_1/2) is increasing with increasing CEBC content in i-PP/CEBC blends. Avrami index and rate constant of crystal growth decrease with increasing CEBC content in i-PP/CEBC blends. On the contrary, heat of fusion of i-PP crystal in the blends is almost constant against the variation of CEBC content in i-PP/CEBC blends. Hence, it is pointed out that blending i-PP with CEBC caused only retardation of rate of crystalline growth and change in mechanism of crystalline growth from three dimensional to two dimensional growth. Received: 19 May 1999/Revised version: 15 July 1999/Accepted: 19 July 1999     

聚丙烯基复合材料的结晶行为

综述了3类聚丙烯(PP)基复合材料体系包括PP/无机物体系、PP/有机物体系和PP／聚合物体系的结晶行为。阐述了PP基体的结晶结构以及结晶动力学特征,包括添加物对PP的结晶温度、结晶速率及结晶度等的影响;分析了结晶行为对复合材料力学性能的影响。复合材料界面对基体聚合物取向结晶形态及结晶行为的影响等还需进一步研究。