【作者】 张纯；

【导师】 周国治； 于杰；

【作者基本信息】 上海大学 ， 钢铁冶金， 2009， 博士

【摘要】 聚合物的微发泡技术对于获得综合性能较为理想的微孔聚合物材料,提高其使用性能,满足某种特殊的需要,降低生产成本,均具有非常重要的意义。聚烯烃作为应用最为广泛的聚合物材料,通过微发泡技术在聚烯烃内部引入大量的微孔及微孔作为第二相均匀的分散在聚烯烃内部的微孔聚烯烃材料,既可以保持原有聚烯烃材料某些优良的性能,又可以改进本身性能的不足,兼顾了降低成本又能保持较好的力学性能,是一种新型的高性能复合材料。微孔聚烯烃材料的结构与形态很大程度上依赖于加工过程中的成型工艺、树脂特性,研究其成型工艺、树脂特性与结构形态和性能的关系及变形断裂机制,对于调控和优化材料性能具有重要理论价值和应用指导意义。本文系统的研究了化学发泡注塑成型工艺、聚烯烃本征特性(不同凝胶含量聚乙烯、不同流体流动速率聚丙烯)、纳米无机粒子对制备发泡聚烯烃材料发泡行为的影响规律和机理,制备出高质量的微孔发泡聚烯烃材料;对微孔发泡聚烯烃材料变形与断裂行为进行了深入探讨,阐明各种影响因数,提出微孔对聚烯烃增韧机理的新见解,并建立了相应的物理数学模型。论文研究取得了以下主要成果:首先,注塑工艺参数中注塑温度对聚烯烃发泡材料的泡孔平均直径、泡孔尺寸分布、泡孔密度影响最大,其次为注塑压力。注塑温度的影响与其对发泡剂分解速度、产气量、熔体强度的影响而导致泡孔的形核和长大(并泡)过程有关。而注塑压力的影响与发泡剂分解产生的气体在外压下的压强平衡有关。通过优化工艺,获得了泡孔平均直径为21μm、泡孔密度3.2×107个/cm3,泡孔尺寸分布均匀的高品质聚烯烃微孔发泡材料样品。其次,聚烯烃本征特性对发泡聚烯烃材料泡孔平均直径、泡孔尺寸分布、泡孔密度以及工艺的影响表现为熔体强度的影响。在相同的注塑工艺条件下,熔体强度高导致泡孔临界形核半径较大,熔体强度低易导致泡孔长大(并泡),从而要获得高品质发泡聚烯烃材料,熔体强度应在一定范围内;不同工艺条件下不同的熔体强度聚烯烃可以获得高品质发泡材料。再次,纳米无机粒子对化学发泡注塑成型制备其微孔发泡材料的泡孔平均直径、泡孔尺寸分布、泡孔密度以及成型工艺的影响,一方面,纳米有机蒙脱土的添加将引起泡孔形核率和聚烯烃熔体粘度的提高,从而制备出泡孔平均直径19.49μm,泡孔尺寸分布均匀,泡孔密度为3.8×107个/cm3的更高发泡品质聚烯烃/纳米有机蒙脱土复合微孔发泡材料;另一方面,聚烯烃中引入均匀分布的插层形式纳米有机蒙脱土,起到“钉扎”和应变强化作用,导致其在发泡过程中具有更稳定的发泡工艺及更宽的注塑温度,实验表明,注塑温度在170℃～195℃范围内,聚丙烯/纳米蒙脱土复合发泡材料的泡孔平均直径、泡孔尺寸分布、泡孔密度变化不大,注塑温度高于195℃后,才有较大的变化。最后,首次提出了微孔对聚烯烃材料冲击断裂韧性作用与聚烯烃材料的本征韧性有关。微孔发泡聚烯烃材料在外加冲击力场作用下变形断裂过程和机理的研究结果表明了,微孔的存在导致聚烯烃材料变形断裂机制发生了变化,微孔的引入一方面减小了试样(材料)的有效承载面积,另一方面导致聚烯烃试样芯部基体材料易松弛裂纹尖端应力集中阻止裂纹扩展,并会诱使主裂纹分解成次生裂纹,使裂纹扩展的方向和方式都发生变化,表现为裂纹扩展的阻力,其综合作用结果导致了微孔的增韧作用随聚烯烃材料本征冲击强度(αk0)的不同存在差异,当裂纹扩展断面的有效截面积减小将导致聚烯烃材料冲击强度下降的值(αk1)小于微孔的存在松弛了裂纹尖端的应力,或改变应力分布形成不同方向的次生裂纹增加裂纹扩展功提高聚烯烃材料冲击强度的值(αk2)时,微孔表现为增韧的作用,反之,微孔的存在则降低材料的韧性。从而得出微孔发泡聚聚烯烃的冲击强度(αk)的物理数学表达式为: a k = a k 0 ? a k 1 + ak2。更多还原

【Abstract】 To obtain microcellular polymer material with better performance, to meet particular needs, to reduce production costs, the research on polymer micro-foaming technology is of great significance. Microcellular polyolefin materials with a large number of microcells dispersing uniformly, obtained through micro-foaming, are a series of new high-performance composite materials. These materials can maintain the original good mechanical performance and meanwhile low cost. The structure of microcellular polyolefin depends mostly on the processing technology in the process of molding, resin characteristics. Therefore, it’s important theoretically and empirically for the control and optimization of material properties to study the molding process, resin characteristics and the structure of the relationship between morphology and properties of fracture and deformation mechanisms.In this thesis, the effect of the chemical foam injection molding processes, intrinsic properties of polyolefin (different gel content of polyethylene, polypropylene of different fluid flow rates), nano-particles of inorganic materials on foaming behavior and mechanism of polyolefin was studied systematically, which aim to prepare high-quality microcellular polyolefin . Deformation and fracture behavior of microcellular polyolefin was detailedly investigated to clarify the effect of various factors and toughening mechanism of the new opinion, and set up a mathematical model of physics. Research paper made the following main results:First, the effect of injection temperature on cell size, cell density and cell size distribution of foamed HDPE is foremost, which lead to different decomposing rate, gas amount of foaming agent, melt-viscosity of HDPE and injection pressure. The effect of injection pressure is related to balance pressure. The average cell diameter of 21μm, cell density of 3.2×107 (cells. cm-3), the cell size uniform distribution of high-quality microcellular polyolefin samples were produced By optimizing the process conditions.Second, the effect of intrinsic properties of polyolefin and processing parameters on the average cell diameter, cell size distribution, cell density and the melt strength of polyolefin was studied. In the same processing conditions, the high melt strength leaded to larger bubble nucleation radius of the critical hole, while the low-melt-strength enhanced bubbling. Thus to obtain high-quality polyolefin foam materials, the melt intensity should be within a certain range. The polyolefin foam materials with different melt strength can be obtained under different processing conditions. Furthermore, the effect of nano-inorganic particles on the average cell diameter, cell size distribution, cell density was studied. On the one hand, the addition of Nano-OMMT leaded to higher cell nucleation rate and melt viscosity. The microcellular polyolefin / Nano–OMMT composite foam material with average cell diameter of 19.49μm, cell size uniform distribution, cell density of 3.8×107 cell.cm-3 was obtained. On the other hand, the introduction of intercalated Nano-OMMT dispersing uniformly played the role of "pinning" and strain-hardening, resulting in foam with more stable injection molding process and a broader temperature range. The experiment showed that the injection temperature of 170℃~ 195℃range of polypropylene / nano- montmorillonite composite foam materials. The average cell diameter, cell size distribution, the cell density changed inconsiderably, while there could be a large change when injection temperature is higher than 195℃.Finally, the relationship between the impact fracture toughness of polyolefin material and intrinsic toughness of polyolefin was introduced for the first time. Mechanism of fraction and deformation of microcellular polyolefin material indicated that the existence of microcells leaded to a change in fracture mechanism. The existence of microcells may reduce the actual section area of samples under impact test, meanwhile, cause easily the cell sample polyolefin matrix material to relax the crack tip stress concentration to prevent crack propagation. The main cracks were broken down to secondary ones, so the direction of crack propagation changed. The resistance performance to crack growth is related with intrinsic impact strength (αk0). If the crack growth in the actual section area of polyolefin materials reduced, the decreased value of impact strength (αk1) was less than the existence of microcells relaxation of crack tip stress. And the microcells toughening property were enhanced provided that the value of impact strength (αk2) were improved, which arised from extended function of the secondary cracks in different directions by means of varying stress distribution. Otherwise, the existence of microcells reduced the toughness of polyolefin materials. And we drew a conclusion that the impact strength (αk) of these microcellular polyolefin materials can be expressed by the following physical mathematical expression: a k = a k 0 ? a k 1 + ak2.更多还原