Relationship between Structure and Mechanical Properties of Melt Processable PTFE: Influence of Molecular Weight and Comonomer Content

The influence of molecular weight and comonomer content on the mechanical properties of several melt‐processable polytetrafluoroethylene (MP PTFE) materials is studied. Additionally, a comparison of mechanical properties including tensile properties and their dependence on environment as well as fatigue life of PTFE, MP PTFE and perfluoroalkoxy copolymer (PFA) is made. PTFE homopolymer and PTFE copolymers exhibit considerably different mechanical properties. The small strain deformation behaviour up to yielding correlates with the degree of crystallinity and comonomer content, whereas the large strain deformation was found to depend on intercrystalline connections, such as tie molecules and chain entanglements. The special role of these elements in determining the fatigue life and sensitivity to environmental stress cracking is also demonstrated.

     

Effects of vacuum ultraviolet on the structure and optical properties of poly(tetrafluoroethylene) films

The effects of vacuum ultraviolet (VUV) at wavelengths of 5–200 nm on the microscopic structure and optical properties of poly(tetrafluoroethylene) (PTFE) films were investigated. X‐ray photoelectron spectroscopy analysis showed that the C_1s spectra changed from a single peak at 292.8 eV to multiplex peaks with binding energies of 284.6, 286.6, 288.6, 290.5, and 293.0 eV after VUV irradiation at 680 esh. With an increasing irradiation dose, the C_1s peaks at 290.5 and 293.0 eV disappeared. After the PTFE film specimens irradiated at 1600 esh were sputtered with argon ions for 3 min, the C_1s peaks at 290.5 and 293.0 eV appeared again, and the height of the peaks at 286.6 and 288.6 eV increased. The content of fluorine decreased after VUV irradiation. The content of fluorine in the film surface layer decreased significantly with the increase in the VUV intensity, but it did not change with the irradiation dose. Fourier transform infrared (FTIR) analysis results indicated that some conjugated bonds, such as ? FC?CF? , were formed during VUV irradiation, but no CH absorption bands were observed in the FTIR spectra; this indicated that the increase in the height of the C_1s peak at 284.6 eV arose mainly from the carbon–carbon bonds, that is, from carbonification. The spectral transmittance of the PTFE film decreased gradually with an increasing VUV irradiation dose, and at a given dose, the lower the intensity was of the VUV irradiation, the greater the change was in the spectral transmittance. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 115–121, 2003     

聚丙烯树脂分子量测试的核磁共振研究

采用低分辨率脉冲核磁共振法测定聚丙烯树脂分子量及分子量分布，应用自旋回波(CPMG)法测定疋，由此获得T2-MwT2-Mn线性关系，实践应用证明，该技术成熟可行，可以应用于科研开发和生产控制中。     

The Influence of the Irradiation Temperature on the Ratio of Chain Scission to Branching Reactions in Electron Beam Irradiated Polytetrafluoroethylene (PTFE)

Polytetrafluoroethylene (PTFE) films have been irradiated by electron beam in vacuum at various temperatures ranging from room temperature up to temperatures far above the melting temperature. Changes of the chemical structure have been analyzed by ¹⁹F solid‐state NMR and IR spectroscopy. The concentration of several structures generated by irradiation increases with increasing irradiation temperature up to the beginning of the thermal degradation. The molar ratio of >CF? branching points to ? CF₃ end groups changes with crossing of the melting temperature. The generation of >CF? branching points is accelerated if the PTFE is irradiated in the molten state, where branching reactions become more important.

     

超高相对分子质量聚乙烯的相对分子质量及其分布的测试方法

介绍了超高相对分子质量聚乙烯（PE-UHMW）的相对分子质量及分布的测试方法,主要有黏度法、流变法和凝胶渗透色谱法（GPC）。黏度法是目前应用最广泛的一种测试方法,主要采用高温乌氏黏度计,按照聚烯烃稀溶液的黏度测试方法进行,并通过经验公式计算得到PE-UHMW的相对分子质量。流变法是一种有效的测试PE-UHMW相对分子质量及其分布的方法,但目前该方法仍需改进。采用GPC法测试PE-UHMW的相对分子质量及其分布在技术上存在局限性。     

聚合工艺条件对PS分子量的影响

分析了影响ＰＳ产品平均分子量的主要影响因素,提出了提高产品分子量,改善其机械性能的措施。     

关于聚苯乙烯的摩尔质量分布与性能

对国内外聚苯乙烯瓣摩尔质量分布的渗透色谱法测定结果,结合有关性能进行了分析和讨论,表明了熔融指数不仅随重均摩尔质量的增高而变小,而且和摩尔质量分布有关。国内某些厂（批）的聚苯乙烯性脆问题与低聚物含量较多有关。     

Preparation of grafted polytetrafluoroethylene fibers and adsorption of bilirubin

BACKGROUND: A successful hemoperfusion technique requires that the adsorbent for bilirubin should have a high specificity, adsorption capacity and adsorption rate, blood compatibility and no toxicity. Compared with polymer microbeads, polytetrafluoroethylene (PTFE) fibers have many advantages. The aim of the work reported here was to prepare a new polytetrafluoroethylene‐graft‐poly(glycidyl methacrylate)‐block‐polyethyleneimine (PTFE‐g‐PGMA‐b‐PEI) adsorbent for bilirubin based on PTFE fibers by the ⁶⁰Co radiation‐induced graft polymerization of GMA followed by the chemical modification of the epoxy groups on the PTFE‐g‐PGMA fibers with PEI. In addition, the adsorption properties of this novel adsorbent for bilirubin were examined. RESULTS: The highest content of amino groups obtained on the PTFE‐g‐PGMA‐b‐PEI fibers was 1.87 mmol g^?1. The maximum adsorption capacity of the grafted fibers was 9.6 mg g^?1 at pH = 6.5. Bilirubin adsorption on these fibers obeyed the Langmuir model. Also, these fibers possessed the ability to selectively adsorb bilirubin in the presence of bovine serum albumin. CONCLUSION: The PTFE‐g‐PGMA‐b‐PEI fibers have a high adsorption capacity for bilirubin and excellent adsorption properties. In addition, this new adsorbent is inexpensive, easy to prepare and has no toxicity. So the PTFE‐g‐PGMA‐b‐PEI fibers as a biomedical adsorbent are promising for the removal of bilirubin through the hemoperfusion technique. Copyright © 2009 Society of Chemical Industry     

Mechanism of filler action in reducing the wear of PTFE polymer by differential scanning calorimetry

Two types of representative nanometer materials, i.e., fibroid nanometer attapulgite and approximate spherical ultrafine diamond, were selected as fillers of polytetrafluoroethylene (PTFE) to study the mechanism of the wear‐reducing actions of the fillers in PTFE composites. The friction and wear tests were performed on a block‐on‐ring wear tester under dry sliding conditions. Differential scanning calorimetry (DSC) was used to investigate material microstructure and to examine modes of failure. No significant change in coefficient of friction was found, but the wear rate of PTFE composites was orders of magnitude less than that of pure PTFE. DSC analysis revealed that nanometer attapulgite and ultrafine diamond played a heterogeneous nucleation role in PTFE matrix and consequently resulted in increasing the crystallinity of PTFE composites. Moreover, the PTFE composite with higher heat absorption capacity and crystallinity exhibited improved wear resistance. A propositional “sea‐frusta” frictional model explained the wear mechanism of filler action in reducing the wear of PTFE polymer, i.e., fillers in the PTFE matrix effectively reduced the size of frictional broken units for PTFE composites and restrained the flowability of the units, as well as supporting the applied load. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

An analysis of the changes in the structure and tensile properties of polytetrafluoroethylene films under vacuum ultraviolet irradiation

The effect of 5–200 nm of vacuum ultraviolet (VUV) irradiation on the structure and tensile properties of polytetrafluoroethylene (PTFE) films was investigated. The change in structure before and after VUV irradiation was evaluated with differential scanning calorimetry (DSC) and electron spin resonance (ESR) analysis. DSC analysis results showed that the melting point, melting enthalpy, and crystallization enthalpy increased and the maximum crystallization temperature decreased a little with increasing VUV dose. It was deduced from the DSC data that the molecular weight of the PTFE films decreased and the destruction of the crystal structure took place under VUV irradiation. The ESR results showed that the radicals formed under VUV irradiation were chain‐end radicals and peroxy radicals, which may have been formed due to the scission of carbon‐to‐carbon bonds. The tensile fracture strength and elongation decreased with increasing VUV irradiation dose. Under the same irradiation dose, the tensile properties were more sensitive to the lower VUV intensity. The decrease in the molecular weight and the destruction of crystal structure might have been the major reasons for the deterioration of the tensile properties. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1494–1497, 2004     

一种快速测定多聚羟基烷酸分子量的方法

以氯仿作溶剂，用黏度法测定了多聚羟基烷酸的分子量．摸索了检测的最佳温度与溶液浓度．比较了黏度外推法与黏度单点法测验结果，建立了黏度法测定多聚羟基烷酸平均分子量的操作方法。该法具有溶剂毒性小、溶解性好、准确度高和操作简便等优点．适用于生产过程和成品检验中的多聚羟基烷酸分子量的测定。     

凝胶色谱法测定高聚物的平均分子量及分子量分布

介绍了用凝胶色谱法测定高聚物的平均分子量及分子量分布。     

醇醚型表面活性剂疏水基和分子量的测定

用＾１３Ｃ－ＮＭＲ技术测定了醇醚型表面活性剂基Ｒ的平均碳数、环氧乙烷平均合数和平均分子量,并用实例说明了测量方法与步骤。最后列出了不同试样的分析结果,并与以谱联合 Ｈ－ＮＭ法测得的结果进行了比较,得到了满意的结果。     

Tailoring the Degree of Polymerization of Low Molecular Weight Cellulose

The degradation of cellulose to lmw samples with $\overline {DP} _{{\rm w}} $ varying from 15 to 130 is investigated. Cellulose samples prepared from the hydrolysis of regenerated cellulose fibers in dilute HCl possess $\overline {DP} _{{\rm w}} $ = 50. Applying homogenous degradation of microcrystalline cellulose in H₃PO₄ at RT for 3 weeks, samples with $\overline {DP} _{{\rm w}} $ = 35 and a PDI of 1.58 are obtained. Decreasing the hydrolysis temperature to 8 °C results in lmw cellulose with $\overline {DP} _{{\rm w}} $ > 70. Fractionation in DMA/LiCl provides samples with $\overline {DP} _{{\rm w}} $ = 12 to 130, together with a narrow molecular weight distribution. Detailed structural analysis by 2D NMR spectroscopy reveals that the prepared lmw celluloses are suitable as mimics for cellulose.

     

不同相对分子质量壳聚糖絮凝性能

壳聚糖作为天然高分子絮凝剂具有无毒、不存在2次污染、使用方便等优点;但生产和应用成本高,具有一定限制。而相对分子质量是壳聚糖的一个重要分子参数,不同相对分子质量的壳聚糖性质差异很大,研究了不同相对分子质量的壳聚糖对生活污水的絮凝性能,结果表明：高相对分子质量壳聚糖的絮凝效果较好,且随着壳聚糖用量的增加絮凝性能也随之增加,但是5×10^-6后絮凝下降,其在pH值为6.5时絮凝效果最佳。     

Study on Immobilized Metallocene and Single-Site Catalysts for the Preparation of Ultra-High Molecular Weight Polyethylene at Various Polymerization Conditions

Ultra-high molecular weight polyethylene (UHMWPE) possesses advantages over conventional polyolefins such as excellent mechanical properties. Recent progresses in transition-metal complexes have led to the discovery of highly active catalysts for the preparation of UHMWPE. In this study, Ti with bis(phenoxy-imine) ligand (FI catalyst) and Me₂Si(C₅Me₄)(N-tBu)TiCl₂ (CGC) were immobilized on silica and tested for the preparation of UHMWPE. Results revealed that soluble FI catalyst and CGC can produce polyethylene having relatively high molecular weight above 10⁶ g/mol, which also can be successfully immobilized on carriers for better adaptability to production processes.     

聚丙烯酰胺分子量算图

根据ＧＢ１２００５．１和ＧＢ／Ｔ１２００５．１０，制作了聚丙烯酰胺的分子量算图，由一已知浓度和测得的相对粘度方便地读出特性粘数和分子量。     

苯乙烯改性醇酸树脂分子质量的影响因素

用ＧＰＣ测试苯乙烯改性醇酸树脂的分子质量及其分布,并测试苯乙烯改性醇酸树脂及其快干醇酸漆的性能,讨论了影响苯乙烯改性醇酸树脂的分子质量及其分布的因素。     

明胶氧化产物的分子量分布

用改进的SDS-PAGE凝胶电泳法对明胶氧化产物的分子量分布进行了测定。结果表明:当氧化时间小于24h,H_2O_2用量低于60mmol/g胶时,分子量各组分的分布没有太大的变化。这是H_2O_2氧化明胶的临界条件。     

新型相对分子质量调节剂在聚合物多元醇合成中的应用

采用连续法以新型相对分子质量调节剂合成聚合物聚醚多元醇(POP),研究其用量对POP产品性能的影响,并与硫醇为相对分子质量调节剂合成的POP进行对比。结果表明,用新型相对分子质量调节剂合成产品的固含量、粘度、过滤性都优于硫醇合成的POP,且POP颗粒圆滑,平均粒径相对较小;用其POP产品制备的聚氨酯泡沫的力学性能不低于硫醇合成的POP产品。