【作者】 程蓉；

【导师】 张九渊； 钱欣；

【作者基本信息】 浙江工业大学 ， 材料学， 2003， 硕士

【摘要】 本文主要研究了聚丙烯（PP）的成核改性和交联改性。两种方法都是通过改变PP的微观结构从而改变其宏观性能。其中前者的改性效果是由于PP球晶形态的变化，而后者则是由于交联网络的生成。另外，本文也对PP收缩率的控制研究作了一些初步的探讨。 在成核改性的研究中，主要采用差示扫描量热法、偏光显微镜和广角X衍射详细表征了成核PP的结晶结构及其对力学性能的影响。结果表明：α和β两种成核剂的加入均使结晶向高温方向偏移，结晶速度加快。α成核剂的加入主要是细化了球晶尺寸，结晶规整均匀，从而使结晶度增大，刚性增加，冲击强度总体呈下降趋势；β成核剂的加入则诱导了相当部分的α晶型向β晶型转变，β晶独特的束状晶片聚集结构是其具有较高韧性的主要原因，束状结构在受力时产生银纹带，从而使拉伸强度和拉伸模量下降，而韧性大大增加。在β成核剂质量分数为0.6％时，β晶相对含量最高，简支梁缺口冲击强度和断裂伸长率达到最大值，皆为纯PP的2倍多。 通过对β成核PP热处理的研究发现，随着热处理温度的升高，材料的结晶度增大，结晶形态由β晶型逐渐转变为α晶型。当热处理温度为142℃时，材料完全转化为α晶型，其拉伸强度及弯曲强度增大，而悬臂梁缺口冲击强度和断裂伸长率却降至最低，由韧性材料转变为刚性材料。 在交联改性的研究中，采用过氧化物引发剂和多官能团助交联剂对共聚PP进行交联改性。研究了加工工艺、引发剂及助交联剂对改性效果的影响。结果表明，随着引发剂A₁及助交联剂B₁用量的增大，改性PP的交联程度逐渐增大，强度及韧性都显著增强。当A₁用量为0.05％、B₁用量为1.0％时，在双螺杆挤出机上进行反应挤出，制得了高抗冲PP材料。在保持其它力学性能良好的前提下，它的悬臂梁缺口冲击强度高达360.73J／m，为纯共聚PP的3倍多。聚丙烯成核及交联改性的研究摘要 收缩率的研究表明，控制PP的结晶度是控制PP收缩率的关键所在。在注射工艺中，熔体温度的提高会增大收缩率;注射压力的提高可明显减小收缩率;适当延长保压时间也可减小收缩率。成核改性PP由于结晶度的增大，收缩率也相应增大。更多还原

【Abstract】 This paper mainly discussed the nucleation and crosslinking modification of polypropylene (PP). These two methods both change the macroscopic properties of PP by change its microstructure. The former method put emphasis on the change of spherulite morphology, but the latter method stresses the formation of crosslinking network. Also, the control of shrinkage of PP was studied.During the study of nucleation modification, the influence of two different nucleating agents on the mechanical properties of PP was studied, which corresponded to the change of crystallization behavior reveled by differential scanning calorimetry (DSC) -, polarized optical microscopy (POM) and wide angle X-ray diffraction (WAXD). Compared with pure PP, nucleated PP showed a higher crystallization temperature and a faster crystallization rate. With the addition of a nucleating agent, the spherulites became so small and even that the crystalline degree of nucleated PP increased, which resulted in higher rigidity and lower impact strength than those of pure PP. While the addition of β nucleating agent, induced a large part of a crystalline form to converted to β crystalline form. The special sheaf-like structure of β crystalline form accounted for its high toughness. Craze strip was formed when external force was exerted on β nucleated PP, which resulted in decrease of tensile strength and tensile modulus of β nucleated PP, but an increase of toughness. When 0.6% β nucleating agent was added, the relative β crystalline fraction was the highest, so the Charpy notched impact strength and the elongation at break came up to the highest level, being more than two times of that of pure PP.The influence of thermal treatment on the properties of β nucleated PP was studied. The results showed that with the increase of the thermal treatment temperature, the crystalline degree increased and the initial β crystalline form converted to a crystalline form gradually. When the material was totally composed of a crystalline form at 142癈, the tensile strength and flexural strength were both very high, and the elongation at break and the notched impact strength were the lowest, which meant the tough material had turned to be brittle.During the study of crosslinking modification, copolymerization PP was modified by peroxide initiator and multifunctional assistant crosslinker. The influence of the machining technology , initiator and assistant crosslinker on the mechanical properties of modified PP was studied. The results showed that with increasing initiator and assistant crosslinker concentration, the crosslinking degree increased, followed by increased strength and toughness. When 0.05% initiator A1 and 1.0% assistant crosslinker B1 were added, high-impact PP was prepared by twin-screw extruder. The modified PP had good mechanical properties. Its Izod notched impact strength was particularly high to 360.73J/m, as over three times as that of pure PP.The study of the shrinkage of PP showed that the control of crystalline degree was the key factor. During the molding technology, the increase of the molding temperature would increase the shrinkage, and the shrinkage could be decreased by increasing the molding pressure or prolonging the holding time. Nucleated PP has higher shrinkage because of its higher crystalline degree.更多还原