Hierarchical structure of injection-molded bars of HDPE/MWCNTs composites with novel nanohybrid shish–kebab
Hierarchical structure of injection-molded bars of HDPE/MWCNTs composites with novel nanohybrid shish–kebab
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DOI：
10.1016/j.polymer.2009.11.059
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发表时间：
2010-02
期刊：
影响因子：
4.6
通讯作者：
Jinghui Yang;Ke Wang;H. Deng;Feng Chen;Q. Fu
中科院分区：
文献类型：
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作者：
Jinghui Yang;Ke Wang;H. Deng;Feng Chen;Q. Fu
由于剪切梯度和温度梯度的存在，注塑制品通常呈现从表皮到芯层的分层结构。研究其层次结构有助于更好地理解注塑样品的结构与性能之间的关系，这对设计和制备高性能聚合物制品具有重要意义。采用扫描电镜（SEM）、差示扫描量热仪（DSC）和二维广角X射线衍射仪（2D-WAXS）研究了高密度聚乙烯（HDPE）/多壁碳纳米管（MWCNTs）复合材料注塑棒材沿着试样厚度方向逐层的微观结构和晶体形态，探讨了复合材料注塑棒材的层次结构。为了增强剪切效应，使用所谓的动态填充注射成型（DPIM）技术来制备具有高取向水平的模塑棒。有趣的是，SEM显示，在皮肤和核心区，聚乙烯的层状随机锚定在MWCNTs的表面上，而明确的纳米杂化串（NHSK）实体，其中纳米碳纳米管（CNTs）作为shish而HDPE层状作为kebab，存在于取向区。NHSK晶体结构沿着厚度方向的变化被认为是由于注塑过程中的剪切梯度和热梯度。并根据实验观察，讨论了剪切作用下原位形成NHSK的根本原因。
Injection-molded products usually show hierarchical structure from skin to core due to the existence of shear gradient and temperature gradient. Investigating the hierarchical structure is helpful to better understand the structure-property relationship of injection-molded sample, which is important for design and preparation of polymer products with high performance. In this work, the hierarchical structures of injection-molded bars of high-density polyethylene (HDPE)/multi-walled carbon nanotubes (MWCNTs) composite were explored by examining the microstructure and crystal morphology, layer by layer, along the sample thickness, using SEM, DSC and 2D-WAXS. To enhance the shear effect, a so-called dynamic packing injection molding (DPIM) technique was used to prepare the molded bar with high orientation level. Interestingly, SEM revealed that in the skin and core zones, the lamellae of PE anchored randomly on the surface of MWCNTs, while well-defined nanohybrid shish–kebab (NHSK) entities, in which fibrillous carbon nanotubes (CNTs) act as shish while HDPE lamellae act as kebab, exist in the oriented zone. The changed NHSK crystal structure along the thickness direction of molded bar is considered as due to the shear gradient and thermal gradient in injection molding. And the underlying origin of in situ formation of NHSK under shear effects is discussed based on experimental observations.