PDF(Pubmed)
Abstract：
Mechanical recycling is the most efficient way to reduce plastic pollution due to its ability to maintain the intrinsic properties of plastics as well as provide economic benefits involved in other types of recycling. On the other hand, molecular dynamics (MD) simulations provide key insights into structural deformation, lamellar crystalline axis (c-axis) orientations, and reorganization, which are essential for understanding plastic behavior during structural deformations. To simulate the influence of structural deformations in high-density polyethylene (HDPE) during mechanical recycling while paying attention to obtaining an alternate lamellar orientation, the authors examine a specific way of preparing stacked lamella-oriented HDPE united atom (UA) models, starting from a single 1000 UA (C1000) chain of crystalline conformations and then packing such chain conformations into 2-chain, 10-chain, 15-chain, and 20-chain semi-crystalline models. The 2-chain, 10-chain, and 15-chain models yielded HDPE microstructures with the desired alternating lamellar orientations and entangled amorphous segments. On the other hand, the 20-chain model displayed multi-nucleus crystal growth instead of the lamellar-stack orientation. Structural characterization using a one-dimensional density profile and local order parameter {P2(r)} analyses demonstrated lamellar-stack orientation formation. All semi-crystalline models displayed the total density (ρ) and degree of crystallinity (χ) range of 0.90-0.94 g/cm-3 and ≥42-45%, respectively. A notable stress yield (σ_yield) ≈ 100-120 MPa and a superior elongation at break (ε_break) ~250% was observed under uniaxial strain deformation along the lamellar-stack orientation. Similarly, during the MD simulations, the microstructure phase change represented the average number of entanglements per chain (). From the present study, it can be recommended that the 10-chain alternate lamellar-stack orientation model is the most reliable miniature model for HDPE that can mimic industrially relevant plastic behavior in various conditions.
摘要：
机械回收是减少塑料污染的最有效方法，因为它能够保持塑料的固有特性，并提供其他类型回收的经济效益。另一方面,分子动力学(MD)模拟提供了对结构变形的关键见解，层状结晶轴(c轴)取向，和重组，这对于理解结构变形过程中的塑性行为至关重要。为了模拟机械回收过程中高密度聚乙烯（HDPE）结构变形的影响，同时注意获得交替的层状取向，作者研究了一种制备堆叠的层状取向HDPE联合原子(UA)模型的特定方法，从晶体构象的单个1000UA（C1000）链开始，然后将这些链构象包装成2链，10链，15链，和20链半结晶模型。2链，10链，和15链模型产生的HDPE微结构具有所需的交替层状取向和缠结的无定形片段。另一方面,20链模型显示多核晶体生长，而不是层状堆叠取向。使用一维密度分布和局部有序参数{P2（r）}分析的结构表征证明了层状堆叠取向的形成。所有半结晶模型显示的总密度（ρ）和结晶度（χ）范围为0.90-0.94g/cm-3和≥42-45％，分别。在沿层状堆叠取向的单轴应变变形下，观察到显着的应力屈服（σ_屈服）≈100-120MPa和优异的断裂伸长率（ε_断裂）〜250％。同样，在MD模拟期间，微观结构相变表示每个链的平均缠结数()。从目前的研究来看,可以推荐的是，10链交替层状堆叠取向模型是HDPE最可靠的微型模型，可以在各种条件下模仿工业相关的塑料行为。
