共查询到18条相似文献,搜索用时 125 毫秒
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用X射线法测定了不同熔体流上聚丙烯材料的结晶度。结果表明,材料熔体流动性的变化将会影响其结晶行为,随熔体流动速率降低,结晶度越低,拉伸强度下降,断裂伸长率增大。熔体流 性对冲击强度的影响较为复杂,发现存在一极大值,该极值的出现预示可能与分子量和分子量分布的变化有关。 相似文献
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采用X射线衍射法测定了聚丙烯树脂的结晶度,考察了制样方法、测试条件以及计算方法等因素对测试结果的影响.通过精密度试验考察了方法的精密度.结果表明,95%置信水平时,在重复性试验条件下,两次测定结果绝对差不大于3.5%;在再现性试验条件下,两次测定结果绝对差不大于5.0%.方法具有较好的重复性和再现性,可以满足聚丙烯树脂... 相似文献
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介绍了利用复配外给电子体技术在洛阳石化HYPOL工艺聚丙烯装置开发高性能PPH(均聚聚丙烯)管材专用树脂的实施方案,同时阐述了在Ziegler-Natta催化剂体系中外给电子体的作用及原理,并且对环己基甲基二甲氧基硅烷(CHMMS,C-Donor)和二环戊基二甲氧基硅烷(DCPMS,D-Donor)对主催化剂催化活性、立体定向性及氢调敏感性的影响及原理进行了比较分析。通过外给电子体的非对称加入和两反应器的加氢调整,以实现产品宽相对分子质量分布及小分子部分高等规度、大分子部分低等规度,使材料具有良好的机械加工性能和力学性能。 相似文献
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In the cast film process a polymer melt is extruded through a slit die, stretched in air, and cooled on a chill roll. During the path in air the melt cools while being stretched. Film casting experiments were carried out with an isotactic polypropylene resin. The temperature and width distributions were measured along the draw direction. Further, the crystallinity and Hermans orientation factor were measured on the final film. The process was described by a simple thermomechanical model derived elsewhere. The evolution of the molecular orientation parameters was calculated on the basis of a dumbbell model coupled with velocity and temperature distributions provided by the thermomechanical model. The experimental crystalline orientations of the final films collapsed into a single step‐shaped curve (from low to high orientation) if plotted versus the stress calculated by the model at the frozen line. The experimental values of the crystallinity and Hermans orientation factors are discussed on the basis of predictions of the dumbbell model for melt orientation at the frozen line and the crystallinity data obtained in quiescent conditions under the same cooling rate. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1981–1992, 2002; DOI 10.1002/app.10422 相似文献
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Jiquan Li Zhou Zhu Taidong Li Xiang Peng Shaofei Jiang Lih-Sheng Turng 《应用聚合物科学杂志》2020,137(16):48581
In this study, the mechanical properties of isotactic polypropylene (iPP) materials with different crystallinities at room and elevated temperatures were investigated. In order to obtain samples with a certain range of crystallinity, and to ensure a uniform microstructure of these samples, the iPP samples obtained by injection molding required melt compression molding and controlled annealing. In the macromechanical studies, the experimental results showed that the storage modulus and Young's modulus of polypropylene were sensitive to the service temperature. The crystallinity also had a great influence on this relationship. A function was proposed to evaluate the dependence of the Young's modulus of polypropylene on initial crystallinity and service temperature, and tested based on experimental data. The Young's modulus of iPP is reduced by about 90% when the service temperature rises from 25 to 125 °C. Moreover, the reduced value in Young's modulus between polypropylene having the highest and lowest crystallinity was reduced from 214.55 to 56.75 MPa. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48581. 相似文献
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The well known occurrence of different crystalline forms in polypropylene and their easy recognition in the polarising microscope has provided a method of analysing the behaviour of this material during the production of hot plate welds. The different thermal behaviour of the α- and the β-forms of crystalline polypropylene allows estimation of the thermal history of the polymer in the region of the weld. In particular it is possible to estimate the amount of material actually melted by contact with the hot plate. The effect of the original crystalline microstructure of the components being welded on the microstructure of the recrystallised material forming the weld bond has also been explored. It is possible to characterise the general crystalline texture in the weld bead in terms of the shear and thermal history of the material. The influence of pre- and post-welding annealing of the polypropylene has been investigated and a difficulty is encountered in explaining an apparent ‘memory’ of β-form crystallisation which conflicts with established x-ray diffraction results. 相似文献
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Elinor L. Bedia Marissa A. Paglicawan Cynthia V. Bernas Severino T. Bernardo Masatoshi Tosaka Shinzo Kohjiya 《应用聚合物科学杂志》2003,87(6):931-938
Natural weathering of isotactic polypropylene (PP) plates (2 mm in thickness) was conducted for 15 months in the Philippines. Optical microscopy, scanning electron microscopy, and atomic force microscopy revealed that the surface layer (200–300 nm in thickness) was affected in the first month, and cracks are formed toward the deeper layer. On the basis of the microscopic observations along with FTIR, DSC, GPC, and tensile strength measurements, the following degradation mechanism of PP was proposed. At first, through oxygen introduced into the PP, only the surface layer seems to be affected. Gradually, the surface layer may be removed, exposing the inner layer. Then, molecular chains of the inner layer start to be degraded, accompanying a significant loss of tensile properties. Part of the degraded materials seems to be eroded, leading to the formation of cracks on the surface of the uncovered inner layer. Finally, the original surface layer may be totally eroded, making the structure of the inner layer (which should reflect the spherulitic texture) evident. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 931–938, 2003 相似文献