Building a phenomenological chain-level understanding of mechanics of semicrystalline polymers: 2. Conceptual
Building a phenomenological chain-level understanding of mechanics of semicrystalline polymers: 2. Conceptual
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DOI：
10.1016/j.polymer.2023.125877
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发表时间：
2023-04
期刊：
影响因子：
4.6
通讯作者：
Gengxin Liu;T. Smith;C. Gupta;A. Siavoshani
中科院分区：
文献类型：
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作者：
Gengxin Liu;T. Smith;C. Gupta;A. Siavoshani
为了合理化论文 1（本卷，第 125878 页）中的综合现象学，我们通过综合对玻璃态和半结晶聚合物机械特性的先前理解，对半结晶聚合物 (SCP) 的机械行为进行了定性描述。基于将SCP视为结晶链网络（CCN）的中心思想，其中测试链可以具有结晶和非晶链，我们强调几个关键概念：（a）结晶决定了CCN的结构，其通常弱于由链间不可交叉性形成的熔融状态下的预结晶链网络，（b）SCP的延展性由足够坚固的CCN提供，以及（c）SCP的屈服和塑性变形需要成功的结构转变涉及通过从结晶相中明显的链拉出来改变结晶相的形状，而不破坏CCN。换句话说，正是 CCN 驱动延性 SCP 通过大量拉出承载线（LBS）（即系带和缠结线）而发生屈服和随后的大变形。脆性断裂和缺乏可拉伸性发生在那些 CCN 太弱（由于 LBS 数量稀疏）而无法引起晶相充分熔化的 SCP 中：没有足够的 LBS 来进行屈服和晶体转变所需的拉拔。基于这些概念，我们可以通过演示结晶或熔融状态下的预变形如何产生更有利的结构来获得更强的机械特性，从而探索加工-结构-性能 (P-S-P) 关系。
To rationalize the comprehensive phenomenology in Paper 1 (this volume, p. 125878), we present a qualitative description for the mechanical behavior of semicrystalline polymers (SCPs) through a synthesis of prior understandings about the mechanical characteristics of glassy and semicrystalline polymers. Based on the central idea to regard an SCP as a crystalline chain network (CCN), in which a test chain can have crystalline and amorphous strands, we emphasize several key concepts: (a) crystallization determines the structure of the CCN, which is generally weaker than the pre-crystallization chain network in the molten state formed by interchain uncrossability, (b) ductility in SCPs is afforded by a sufficiently robust CCN, and (c) yielding and plastic deformation of SCPs require a successful structural transformation involving shape-change of crystalline phases through appreciable chain pull-out from the crystalline phases without breakdown of the CCN. In other words, it is the CCN that drives ductile SCPs to undergo yielding and subsequent large deformation through massive pull-out of load bearing strands (LBSs), which are the tie and entangling strands. Brittle fracture and lack of drawability occur in those SCPs where the CCN is too weak (due to a sparse population of LBSs) to cause sufficient meltdown of crystalline phases: There are not enough LBSs to undergo pull-out that is necessary for yielding and crystal transformation. Based on these concepts we can explore the processing-structure-property (P–S–P) relationship by demonstrating how pre-deformation in either crystalline or molten state produces more favorable structures for stronger mechanical characteristics.