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首页> 外文期刊>Journal of Applied Polymer Science >Physical and mechanical properties of polyethylene for pipes in relation to molecular architecture. II. Short-term creep of isotropic and drawn materials
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Physical and mechanical properties of polyethylene for pipes in relation to molecular architecture. II. Short-term creep of isotropic and drawn materials

机译：与分子结构有关的管道用聚乙烯的物理和机械性能。二。各向同性和拉制材料的短期蠕变

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Tensile drawing and short-term creep of ethylene/alpha-olefin copolymers having bimodal (BM) molar weight distribution are studied in comparison with unimodal (UM) copolymers of similar crystallinity. The natural draw ratio and viscoelastic recovery upon unloading strongly suggest that BM copolymers have more tie chains and chain entanglements than corresponding UTV copolymers. The incorporation of co-units in the longest chains of BM copolymers is ascribed a major role on these topological changes. Creep of isotropic materials shows lower compliance for BM copolymers in parallel with higher-durability grades. This is attributed to a better "macromolecular network efficiency." The creep behavior of strain-hardened samples, which is assumed to simulate the mechanical behavior of craze fibrils at the tip of a propagating crack, reveals similar trends. The better fibril strength in BM copolymers is again ascribed to a better network efficiency. Necked samples display an odd behavior of higher compliance at low stress and lower compliance at high stress for BM copolymers compared with the behavior of UM counterparts. This is associated with the exhaustion of viscoelastic capabilities with increasing draw ratio and stress. The phenomenon is discussed in relation to cavitation. A short-term creep test is proposed for comparative prediction of long-term behavior. (C) 2002 Wiley Periodicals, Inc. [References: 23]
机译：与具有相似结晶度的单峰（UM）共聚物相比，研究了具有双峰（BM）摩尔分布的乙烯/α-烯烃共聚物的拉伸强度和短期蠕变。卸载时的自然拉伸比和粘弹性恢复强烈表明，BM共聚物比相应的UTV共聚物具有更多的键链和链缠结。在这些拓扑变化中，将主要单元归因于在BM共聚物的最长链中引入共单元。各向同性材料的蠕变表明BM共聚物的顺应性较低，而耐久性等级更高。这归因于更好的“大分子网络效率”。假定为模拟正在传播的裂纹尖端处的裂纹原纤维的机械行为，应变硬化样品的蠕变行为也显示出类似的趋势。 BM共聚物中更好的原纤维强度再次归因于更好的网络效率。与UM对应物的行为相比，颈缩样品在BM共聚物的低应力下表现出较高的顺应性，在高应力下表现出较低的顺应性。随着拉伸比和应力的增加，这与粘弹性能力的耗尽有关。讨论了与气蚀有关的现象。提出了短期蠕变测试，用于长期行为的比较预测。 （C）2002 Wiley Periodicals，Inc. [参考：23]

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