【作者】 罗鹏；

【导师】 敬波；

【作者基本信息】 湘潭大学 ， 材料工程， 2014， 硕士

【摘要】 聚甲醛（POM）作为第三大工程塑料，其工业应用很大程度受制于其缺口敏感性，对于其增韧改性一直以来是研究热点，但其增韧产品的工业化应用停留在理论阶段。本文重点研究了共聚甲醛（CPOM）的增韧改性方法，分别采用三种增韧改性剂，粉末丁腈橡胶（PNBR）、均聚甲醛（HPOM）以及超高分子量聚乙烯（UHMWPE）对共聚甲醛进行增韧改性，通过熔融共混法制备了一系列增韧复合材料，分别探讨了各增韧剂对共聚甲醛性能的影响。实验综合应用了差示扫描量热仪（DSC）、热失重分析仪（TGA）、偏光显微镜（PLM）、简支梁冲击试验机、万能试验机、扫描电镜（SEM）等检测方法，对复合材料各项性能进行了表征和分析。研究表明，从加工性能、力学性能等方面来比较，已硫化粉末丁腈橡胶（PNBR-A）较未硫化粉末丁腈橡胶（PNBR-B）而言，CPOM/PNBR-A复合材料综合性能更加优异；且较热塑性聚氨酯（TPU）而言，在同等增韧剂含量下，PNBR-A增韧效果远远优于TPU。当弹性体含量达到10%时，粉末丁腈以橡胶带形式存在于基体中，TPU仍以粒子形式存在，其增韧机理存在差异。PNBR-A的加入可能会限制CPOM分子链的运动，使得分子链段在小范围内有序排列，形成更多尺寸较小的球晶，使得CPOM结晶度提高，熔融峰向高温方向移动；且加入5%PNBR-A和热稳定剂后，T5%提高了约36℃，Tp提高了约69℃，显著提高了材料的热分解温度。对于CPOM/UHMWPE复合体系，当UHMWPE含量为1%时，复合材料缺口冲击强度达到最大值，提高了约24%，且拉伸强度为52.8MPa，刚性和韧性均保持在较高的水平。分别采用Avrami，Ozawa和莫志深理论分析了材料的结晶行为，研究发现，UHMWPE的加入能显著影响材料的结晶过程，减慢了CPOM的结晶速率，改变了CPOM球晶的成核和生长方式。UHMWPE在较高温度下部分熔融，阻碍CPOM分子链段的运动，随着温度的降低又起到异相成核的作用，显著降低了CPOM的结晶活化能。对于CPOM/HPOM复合材料，均聚甲醛的加入能显著提高复合材料的综合性能。当配比为50/50时，复合材料的缺口冲击强度提高了约1.5倍，且拉伸强度为54.8MPa，较共聚甲醛二次加工后有了较高幅度的提高。但随着均聚甲醛添加量的逐渐增大，复合材料的热分解温度出现一定的下降趋势，其有效的热稳定体系值得进一步探索。更多还原

【Abstract】 Polyoxymethylene (POM) is a kind of important industrial material and becomethe third largest engineering plastic. However, the poor notched impact strength ofPOM restrains its applications. Its toughening modification is a focus topic, but theindustrial application of toughening products remains in the theoretical stage. Thispaper focuses on toughening method of acetal copolymer. Elastomers (PNBR, TPU),ultra-high molecular weight polyethylene (UHMWPE) and acetal homopolymer(HPOM) were used for toughening agents respectively. A series of CPOM compositematerials were prepared by melt blending. The effects of properties of acetalcopolymer on three modification agents were discussed. The properties of compositematerials were characterized and analysed by differential scanning calorimetry (DSC),polarized light microscopy (PLM), thermal gravimetric analyzer (TGA), charpyimpact testing machine, universal testing machine, scanning electron microscopy(SEM) etc.By comparing processing properties and mechanical properties, vulcanizedpowder nitrile rubber (PNBR-A) has a better toughening effect than uncured powdernitrile rubber (PNBR-B). Moreover, under the same content of toughening agent,PNBR-A was far superior to thermoplastic polyurethane (TPU) by comparing withCPOM/TPU. There were differences in toughening machanism between PNBR-A andTPU. Powder nitrile rubber existed in the form of rubber belt in matrix and TPU wasstill in the form of particles when the content was more than10%.It was showed by DSC and TG analysis that PNBR-A can restrain the movementof molecular chain segments, so that the molecular chains arranged orderly in a smallscale. Therefore, the crystallinity of CPOM was improved and melting peak shifted toa higher temperature. Moreover, adding powder nitrile rubber can increase thedecomposition temperature of the materials significantly. T5%and Tpincreased byabout36℃and69℃respectively.UHMWPE was used as impact and nucleation modifier to prepare blends by meltextrusion. When the content of UHMWPE was1wt%, the notched impact strength ofthe material was1.24folds that of neat CPOM and the tensile strength of material was52.8MPa. The comprehensive properties of material stay at a high level. Avrami,Ozawa, and Mo’s theories were performed to analyze the nonisothermalcrystallization kinetics of CPOM and CPOM/UHMWPE (100/1) blend. The result showed that two parts of UHMWPE affected the blend melts. One part had highentanglements with the molecular chains of CPOM, which hindered the movement ofthe molecular chains of CPOM. The other part existed as a form of solid particles andthis one induced heterogeneous nucleation. UHMWPE can slow down thecrystallization rate of composite material, prolong the time of the crystallization andimprove the crystallization of CPOM. Activation energy was calculated by theKissinger method. Addition of1wt%UHMWPE decreased the activation energy ofCPOM significantly.For CPOM/HPOM composites, polyoxymethylene homopolymer improved theoverall performance of materials. When the ratio was50/50, the notched impactstrength of material increased by1.5times and the tensile strength was54.8MPa.However, thermal decomposition temperature of the composite materials appeared anobvious downtrend. Therefore, the effective system of thermal stability is worthfurther exploration.更多还原