升温淋洗分级研究聚丙烯流延膜专用料的微观结构及热学表征

采用升温淋洗分级技术分离了2种聚丙烯流延膜(CPP)专用料(CPP1、CPP2),通过红外光谱仪、差示扫描量热仪和高温凝胶色谱对2种样品的链结构、熔融和结晶行为进行了表征,确定了产品各级分的分子结构信息.结果表明,对于低温(<100℃)级分,CPP1样品中其含量为9.29％(质量分数,下同),CPP2样品中其含量为26...     

Studies of the comonomer distributions in low density polyethylenes using temperature rising elution fractionation and stepwise crystallization by DSC

The comonomer distributions of commercial linear low density polyethylenes (LLDPE) and linear very low density polyethylenes (VLDPE) produced with traditional high activity Ziegler–Natta (Z–N) catalysts were characterized by temperature rising elution fractionation (TREF). In order to develop faster characterization methods the polymers were also characterized using a segregation fractionation technique (SFT) based on a stepwise crystallization by differential scanning calorimetry (DSC). Comparative studies of SFT and TREF demonstrated that SFT provides an alternative tool for the relative qualitative analysis of the chemical composition distribution (CCD) and the technique is useful to characterize the heterogeneity in comonomer unit distribution. Lamellar thickness distributions can be calculated from the DSC endo-therms by applying the Thomson–Gibbs equation. The SFT technique was also applied to commercial single-site (metaliocene) LLDPE and VLDPE polymers. In spite of their more homogeneous structure compared with the Z–N copolymers, which contain many active sites, these single site copolymers also gave thermograms resolved into several peaks.     

Structural evaluation of copolymers of ethylene and 1‐octadecene by using the temperature rising elution fractionation technique

Three samples of ethylene‐octadecene copolymers having different quantitative composition were analyzed structurally and in terms of their thermal behavior. The samples were fractionated by temperature rising elution fractionation, presenting different chemical composition distributions (CCD) that are essentially the result of the proportion of incorporated octadecene. The CCD profiles were relatively wide for samples generated by metallocene catalysts. The analyses of the fractions showed that the melting and crystallization temperatures decrease with increasing comonomer incorporation, but this relation is affected by the average molecular weight of the chains. The melting thermograms of those fractions having higher proportions of octadecene may be divided into two characteristic regions: the first one, at a higher temperature, originates from the melting of the least modified chains, which crystallize more perfectly. The second one is formed by the melting of chains having a high degree of comonomer incorporation, which melt in a diffuse manner over a wide range of temperatures. It is probable that the morphology of the crystals formed in this region does not follow the folded chain model, and are better represented by a model involving the alignment of chain segments (bundling). © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 221–227, 2001     

Carbon‐13 NMR,GPC, and DSC study on a propylene‐1‐butene copolymer fractionated by temperature rising elution fractionation

A random copolymer of propylene with small amounts of 1‐butene comonomer, synthesized with a Ziegler–Natta catalyst, was fractionated by temperature rising elution fractionation (TREF) to systemically investigate the fraction samples' molecular microstructure, as well as their relationship to the melting and crystallization behavior. First, TREF was employed to fractionate the sample, and then crystallization analysis fractionation (Crystaf) was used to check the effect of the TREF experiment. In the characterization of the molecular microstructure, carbon‐13 NMR spectroscopy (¹³C NMR) and gel permeation chromatography (GPC) experiments gave the following results: the fraction samples have relatively uniform molecular microstructure; with an increase in elution temperature, the 1‐butene content in the fraction samples decreases, but the molecular weight (M_n) and number average sequence length of propylene (n?_P) increase. In the study on melting and crystallization behavior, differential scanning calorimetry (DSC) experimental results show that the melting temperature increasingly decreases with an increase in 1‐butene content; however, dependence of the melting temperature on molecular weight becomes weaker and weaker with an increase in the number average molecular weight in the range of number average molecular weight below 1.82 × 10⁵ g/mol. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 845–851, 2006     

Microstructural characterization of propylene–butene-1 copolymer using temperature rising elution fractionation

Propylene–butene-1 copolymer (PBC) prepared with a titanium catalyst system was fractionated by temperature rising elution fractionation (TREF) over a temperature range of 5–80°C. PBC was shown to have a wide composition distribution ranging between 12–47 mol % of butene-1. Most of the fractions showed nearly the same crystallinity regardless of the butene-1 content. However, the solubility of the crystalline parts, which turned out to be the driving force for the fractionation, varied over the butene-1 content. Evidence that PBC shows isomorphism was obtained by the analysis of fractionated polymers, using ¹³C nuclear magnetic resonance spectrometry, X-ray diffraction, differential scanning calorimetry, and gel permeation chromatography. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1493–1501, 1998     

Influence of the short‐chain branch length on the calibration of temperature rising elution fractionation systems

The effects of short‐chain branch (SCB) length on the calibration of temperature rising elution fractionation (TREF) were examined. Samples of ethylene–hexene, ethylene–octene, and a novel polyolefin produced using Eastman Chemical Company's Gavilan catalyst technology were used to prepare TREF calibration curves. Preparative TREF was used to collect fractions of the materials based on their crystallizability, and the branching frequencies of the fractions were determined by NMR. Calibration curves were generated by plotting the branching frequency as a function of the TREF elution temperature. The results indicate that the calibration curves shift to lower TREF elution temperatures as the length of the SCB increases from methyl to butyl to hexyl. Other factors that may contribute to this shift include chain microstructural differences from variations in catalyst structure and process conditions. The shift can be decreased by plotting the data in “number of branches per 1000 backbone carbons” versus TREF elution temperature instead of the more traditional “number of branches per 1000 total carbons.” These data indicate that the branch type must be known a priori to calculate SCB averages and SCB distributions and that unique calibration curves exist for copolymers made using different α‐olefin comonomers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 722–728, 2003     

Study on thermal behavior of impact polypropylene copolymer and its fractions

An impact polypropylene copolymer (IPC) was fractionated into three fractions using n‐octane as solvent by means of temperature‐gradient extraction fractionation. The glass transitions, melting, and crystallization behavior of these three fractions were studied by modulated differential scanning calorimeter (MDSC) and wide‐angle X‐ray diffraction (WAXD). In addition, successive self‐nucleation and annealing (SSA) technique was adopted to further examine the heterogeneity and the structure of its fractions. The results reveal that the 50°C fraction (F₅₀) mainly consists of ethylene‐propylene random copolymer and the molecular chains may contain a few of short but crystallizable propylene and/or ethylene unit sequences; moreover, the lamellae thicknesses of the resulting crystals are extremely low. Furthermore, 100°C fraction (F₁₀₀) mainly consist of some branched polyethylene and various ethylene‐propylene block copolymers in which some ethylene and propylene units also randomly arrange in certain segments, and some polypropylene segments can form crystals with various lamellae thickness. An obvious thermal fractionation effect for F₁₀₀ samples after being treated by SSA process is ascribed to the irregular and nonuniform arrangement of ethylene and propylene segments. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

国外抗冲共聚聚丙烯结构的研究

利用升温淋洗分级柱、核磁共振波谱仪、差示扫描量热仪、凝胶渗透色谱仪和扫描电子显微镜等研究了国外抗冲共聚聚丙烯(PP)的组成、序列结构、相对分子质量及其分布、热转变、相态结构和宏观性能.结果表明,该抗冲共聚PP由均聚PP、乙丙橡胶和可结晶的乙丙共聚物组成,具有优良的机械性能;均聚PP为抗冲共聚物提供刚性,乙丙橡胶可提高抗冲共聚物的韧性;抗冲共聚物的相对分子质量呈多分散性,其分布较宽;乙丙橡胶的相对分子质量较大,以直径为1～2μm的微粒均匀分布在PP基体中,有利于提高抗冲共聚物的冲击强度;抗冲共聚物的熔点较高,耐热性好.     

抗冲共聚聚丙烯J842的开发

通过设计合理的生产控制方案,成功开发出高性能抗冲共聚聚丙烯J842产品,并分析了产品的力学性能.J842产品综合性能优良,抗冲击性能好,刚性稍有不足.建议通过改变催化剂体系、适当提高均聚聚丙烯粉料的熔体流动速率、优化改性剂添加配方等来改进J842产品的质量.     

Combined effect of β‐nucleating agent and processing melt temperature on the toughness of impact polypropylene copolymer

The phase morphology and toughening behavior of impact polypropylene copolymer (IPC) with and without nucleating agent (NA), prepared at different processing melt temperatures (T_p), were investigated. Interestingly, three different structures can be formed in the IPC samples by adding NA or tuning T_p. A well‐defined core–shell structure is obtained in samples with α‐NA or without NA prepared at all T_p. A developing multilayered structure is mainly formed at high T_p with added β‐NA, while an incomplete phase separation structure with interpenetrating chains is the dominant structure for IPC samples prepared at low T_p with added β‐NA. In this case, because of the synergistic effect between phase morphology and relatively high β‐form crystal content, the chain interaction among the components and chain mobility of the amorphous portion of IPC are distinctly improved, resulting in a largely improved toughness under 0 °C. This improvement in toughness is very important for applications. © 2012 Society of Chemical Industry     

Structure and properties of impact copolymer polypropylene. I. Chain structure

In this work, impact copolymer polypropylene (ICPP) was fractionated into 4 fractions. ICPP and the 4 fractions were studied using Fourier transform infrared and ¹³C nuclear magnetic resonance analysis. The results demonstrate that fraction A is ethylene–propylene rubber, fraction B is ethylene–propylene (EP) segmented copolymer, fraction C is ethylene–propylene block copolymer, and fraction D is polypropylene with a few ethylene monomers in the chain. The differences in properties between different impact copolymer polypropylenes should be due to their fractions' differences in composition and chain sequence structure. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 93–101, 1999     

Comprehensive branching analysis of polyethylene by combined fractionation and thermal analysis

Linear low density polyethylene (LLDPE) and low density polyethylene (LDPE) differ significantly in their branching types and branching distributions. For a comprehensive analysis, preparative temperature rising elution fractionation and/or preparative molar mass fractionation are used to fractionate typical LLDPE and LDPE bulk resins into narrowly distributed fractions. The chain structures of the bulk resins and their fractions are further analysed using SEC, crystallization analysis fractionation, DSC and high‐temperature HPLC to provide detailed information on short chain branching in LLDPE and long chain branching in LDPE. For LDPE it is shown that the multiple fractionation approach is a powerful source of sample libraries that may have similar molar masses and different branching structures or alternatively similar branching but different molar masses. The analysis of these library samples by thermal analysis provides a much deeper insight into the molecular heterogeneity of the samples compared to bulk sample analysis. © 2018 Society of Chemical Industry     

两性纤维素接枝共聚物CGAD热降解行为的研究

本文用热失重分析法研究了两性纤维素接枝共聚物CGAD的热分解特征，用三种不同方法进行实验得到了热降解反应的动力学参数，取得了比较—致的结果，时对接枝共聚物的热降解机理进行了初步探讨。     

聚丙烯的热降解和燃烧行为

采用热重分析法对聚丙烯(PP)的热降解行为进行了表征,测定了不同升温速率下PP的热降解过程,得出其热降解活化能为239.58 kJ/mol;用锥形量热仪研究了PP的燃烧行为,随着辐射强度增加,PP的热释放速率增加,质量损失速率加快且分解起始时间提前,热释放总量保持恒定;试样厚度对表征材料的燃烧行为有一定影响。     

Effect of unsaturated chain end‐group on thermal oxidative behavior of polypropylene

In order to clarify the influences of unsaturated chain end‐groups on the oxidative degradation of isotactic polypropylene (iPP), values of activation energy (ΔE) for the oxidative degradation reactions of Ziegler‐catalyzed iPP (ZiPP) and metallocene‐catalyzed iPP (MiPP) having similar tacticity were evaluated by the temperature dependence of the oxidation induction time as determined by thermogravimetric analysis over the range 130–145 °C. The correlation between the content of unsaturated chain end‐groups and the change of ΔE was also studied. The results obtained indicated that the unsaturated chain end‐groups strongly influenced the rate of iPP degradation. Moreover, on addition of oligomer‐like MiPP having unsaturated chain end‐groups, the ΔE value of ZiPP became lower, suggesting that iPP having unsaturated chain end‐groups served as an infectious agent of the degradation. Copyright © 2007 Society of Chemical Industry     

Influence of molten-state annealing on the phase structure and crystallization behaviour of high impact polypropylene copolymer

The phase structure evolution of high impact polypropylene copolymer (IPC) during molten-state annealing and its influence on crystallization behaviour were studied. An entirely different architecture of the IPC melt was observed after being annealed, and this architecture resulted in variations of the crystallization behaviour. In addition, it was found that the core-shell structure of the dispersed phase was completely destroyed and the sizes of the dispersed domains increased sharply after being annealed at 200 °C for 200 min. Through examination of the coarseness of the phase morphology using phase contrast microscopy (PCM), it was found that a co-continuous structure and an abnormal ‘sea-island’ structure generally appeared with an increase in annealing time. The original matrix PP component appeared as a dispersed phase, whereas the copolymer components formed a continuous ‘sea-island’ structure. This change is ascribed to the large tension induced by solidification at the phase interface and the great content difference between the components. When the temperature was reduced the structure reverted to its original form. With increasing annealing time, the spherulite profiles became more defined and the spherulite birefringence changed from vague to clear. Overall crystallization rates and nucleation densities decreased, but the spherulite radial growth rates remained almost constant, indicating that molten-state annealing mainly affects the nucleation ability of IPC, due to a coarsened microstructure and decreased interface area.     

Kinetic study of polypropylene nanocomposite thermo‐oxidative degradation

Polypropylene (PP) has wide acceptance for use in many application areas. However, low thermal resistance complicates its general practice. The new approach in thermal stabilization of PP is based on the synthesis of PP nanocomposites. This paper discusses new advances in the study of the thermo‐oxidative degradation of PP nanocomposite. The observed results are interpreted by a proposed kinetic model, and the predominant role of the one‐dimensional diffusion type reaction. According to the kinetic analysis, PP nanocomposites had superior thermal and fireproof behaviour compared with neat PP. Copyright © 2005 Society of Chemical Industry     

Structure and properties of a β‐nucleated polypropylene impact copolymer

The effect of a β‐nucleating agent (β‐NA) on the properties and structure of a commercial impact polypropylene copolymer (IPC) was investigated. The effect of selected β‐NAs on the impact resistance, stress and strain behaviour of the IPC is reported. In addition, the IPC was fractionated according to crystallinity by preparative temperature rising elution fractionation. Fractions with varying chemical composition and crystallinity were treated with a two‐component β‐NA to investigate the effect of the β‐NA on the various fractions. The results indicate that the efficacy of the β‐NA is dependent on the chemical composition of the polymer that crystallises, more specifically on the sequence length of crystallisable propylene units. The effect of the addition of β‐NAs on the overall morphology of the IPC was also investigated, and in particular the size and distribution of the rubbery particles in these complex reactor blends were probed. © 2014 Society of Chemical Industry     

Tailoring toughness of injection molded bar of polypropylene random copolymer through processing melt temperature

In this study, a facile route to realize the superior toughness of injection molded polypropylene random copolymer (PPR) is reported. The toughness of PPR is increased about twofold when the processing melt temperature increases from 180 to 250 °C. Systematic and detailed structural characterizations have been carried out to establish the structure–property relationships by using polarized light microscopy, scanning electron microscopy, infrared microscopy and dynamic mechanical analysis. It is found that increasing the melt temperature is beneficial for the coalescence of rubbery domains and enhanced molecular mobility which are mainly responsible for the improvement in toughness. Other factors, such as molecular orientation, crystallinity and so on, seem to have little effect. The vital role of enhanced molecular mobility in improving toughness is further demonstrated by the annealing of injection molded samples at elevated temperature, i.e. 110 °C. Copyright © 2011 Society of Chemical Industry     

Influence of nucleation on the brittle‐ductile transition temperature of impact‐resistant polypropylene copolymer: From the sight of phase morphology

Influence of α‐ and β‐nucleation on brittle‐ductile transition temperature (BDTT) of impact‐resistant polypropylene copolymers (IPCs) and their phase morphologies were comparatively investigated. Impact test showed that the BDTT of β‐nucleated IPC (β‐IPC) is ～ 24°C lower than that of α‐nucleated one (α‐IPC). Structural characterizations including atomic force and scanning electron microscopic observations, small angle X‐ray scattering examination, and dynamical mechanical analysis revealed that dispersion of the ethylene‐propylene random copolymer‐rich (EPR‐rich) phase was finer in β‐IPC in comparison with that in α‐IPC. For the reason of looser lamellar arrangement, the portion of EPR‐rich components included in the interlamellar region of β‐IPC was higher than those of α‐IPC, which led to improved mobility for the amorphous polypropylene chains. It was proposed that the finer distribution of EPR‐rich phase, which might result from faster growth rate of the β‐crystal and looser lamellar arrangement of β‐spherulite, should be responsible for the improved impact‐resistance and lower BDTT in β‐IPC samples. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012