芯棒与口模反向旋转挤出聚乙烯管结构与性能的研究

采用自行研制的新型旋转挤出装置,通过芯棒与口模同时反向旋转挤出制备聚乙烯(PE)管.结果表明,在口模与芯棒反向旋转挤出过程中,管道内外壁除受到轴向应力作用外,还受到芯棒和口模旋转所施加的环向应力,其合力方向不再是沿管道轴向而是与其有一定的角度.因此,分子链的取向方向和以此链为初级成核点形成的串晶偏离轴向,增强了管道抵抗...     

旋转挤出加工制备高性能聚合物管

聚合物管主要用于流体压力输送,要求环向强度高,耐应力开裂性能好,使用寿命长。我们借鉴天然管竹子因竹纤维轴向排列使其轴向破裂易,横向破裂难的结构特点,提出形成偏离轴向的增强相结构可以显著提高聚合物管的性能,自行设计研制了新型的聚合物管旋转挤出装置,通过芯棒和口模独立可调的旋转运动与轴向速度可调的挤出/牵引运动的不同组合,形成与常规挤出不同的应力场,并通过管内外壁双冷技术调控聚合物管中温度场,从而在聚合物管中形成和定构不同层次的偏离轴向排列的增强相结构(如取向分子、串晶、原位成纤诱导形成串晶、外加纤维等),大幅度提高聚合物管的环向强度和耐应力开裂性能,如旋转挤出聚乙烯管形成偏离轴向串晶结构,使其环向拉伸强度和裂纹引发时间分别比常规挤出聚乙烯管提高78%和544%。我们还从理论上分析了旋转挤出中聚合物的流变行为,得到其流动速率数学表达式,阐明旋转挤出形成偏离轴向增强相结构的机理。旋转挤出加工为制备高性能聚合物管提供新设备、新技术、新理论。本文简要总结了我们通过旋转挤出制备高性能聚合物管的一些研究工作。     

聚合所得初生聚乙烯的晶型

聚合所得初生聚乙烯的晶型伍青，张启兴，卢泽俭，王海华，欧阳巍，林尚安，张光华（中山大学高分子研究所，广州，５１０２７５）（中国科学院广州化学研究所）关键词聚乙烯，结晶，单斜晶，颗粒形态热力学稳定的聚乙烯晶型为正交晶系［１］．当聚乙烯受一定应力作用时如...     

聚苯乙烯/聚乙烯的反应性挤出共混

多官能团单体;聚苯乙烯/聚乙烯的反应性挤出共混     

溶液结晶制备聚乙烯/碳纳米管串晶结构

通过等温以及非等温溶液结晶法制备了聚乙烯/碳纳米管复合串晶(shish-kebab)结构.电镜结果显示,等温结晶1 h得到的聚乙烯/碳纳米管串晶(shish-kebab)结构kebab长度为30~140 nm,kebab间间距为35~80 nm.使用非等温结晶法得到的产物kebab长度为40~180 nm,kebab间距与等温结晶过程得到的相同.此外实验发现聚乙烯/碳纳米管shish-kebab结构生长过程中,kebab的生长与新的kebab形成是同步发生,直至结晶结束.将得到的聚乙烯/碳纳米管shish-kebab结构在对二甲苯中静置3个月,光学图像显示仍能保持良好的分散性.使用沸腾对二甲苯冲洗聚乙烯/碳纳米管shish-kebab结构以验证其稳定性,发现冲洗过程中虽然部分聚乙烯链溶解,但仍有部分聚乙烯链吸附于碳纳米管上,并在降温过程中重新生成shish-kebab结构.     

新型旋转挤出流变仪

聚合物加工是决定塑料制品最终结构性能的中心环节,其重要的理论基础是聚合物流变学,研究聚合物流变行为的关键仪器是流变仪.但现有流变仪大多基于简化的流动模型,与实际复杂加工条件不符,难有效揭示聚合物在复杂应力场/温度场作用下的流变行为.我们基于前期发明的聚合物管旋转挤出加工技术和装备,研制了新型旋转挤出流变仪,可实现挤出/旋转的不同组合和管内外壁双冷,实施和调控旋转挤出中多种运动模式和应力场及温度场,实时检测挤出/旋转速度、应力、温度场,显示记录有关数据,既可用于研究实际加工复杂条件下聚合物加工流变行为,也可用于制备高性能多功能聚合物微导管.本文综述了新型旋转挤出流变仪的结构特点和原理及其在流变测试与聚合物微导管制备方面的应用.     

超高分子量聚乙烯凝胶膜超高取向过程的几个不同阶段

通过Ｘ射线衍射、平板照相、扫描电镜等方法观测超高分子量聚乙烯凝胶／结晶膜取向过程中的结构形态变化，并根据ＰＥ片晶分子动力学模拟结果，提出ＵＨＭＷＰＥ凝胶膜在热拉伸取向过程中明显存在３个不同阶段，即：初期片晶转动或滑移，ｂ轴优先垂直于拉伸方向取向；随着拉伸比增大，片晶的ｃ轴平等于伸方向，同时，分子链的解折叠开始，部分非晶链也进入伸直链区取向，当拉伸比达到极限倍率时，分子链已经接近完全伸展成为比较刚直     

超声辐照下聚乙烯熔体挤出流变特性的研究

研究了超声辐照作用下HDPE和LLDPE的挤出流变特性。结果表明,超声辐照可以促进聚乙烯分子链段的运动,降低熔体的挤出口模压力和表观粘度,明显提高聚乙烯熔体的流动性,使挤出物外观质量明显提高,为改善聚乙烯的加工性能及制品质量提供了新途径。     

自增强高密度聚乙烯的结构与性能

<正> 高分子材料的自增强与外增强不同,它是充分利用材料本身的潜力,改变其内部的聚态结构,形成内在的增强相,达到增强的目的。由于自增强材料的增强相和基体相具有完全相同的分子结构,因此增强相与基体相之间不存在外增强材料中普遍存在的界面问题,表现出整体结构的优异的比强度和比刚度,而且具有较高的冲击韧性和耐化学稳定性,热     

含少量共聚组分聚乙烯熔体拉伸薄膜的形态结构

利用透射电子显微学(TEM)和示差扫描量热学(DSC)等方法研究了含少量丁烯-1组分(摩尔分数为0.64%)的聚乙烯共聚物(PE100)熔体拉伸高取向薄膜的形态结构. 结果表明, 在PE100熔体拉伸薄膜中, 除存在高取向片晶结构外, 还含有大量的纤维晶, 纤维晶平行于拉伸方向, 穿过几个片晶区, 平均直径约为12 nm. 模拟实验结果表明, 纤维晶的生成源于聚乙烯共聚物中的超高分子量组分, 但不同于传统意义上的伸直链纤维晶, 其形态特征应为晶桥结构. 由此提出了晶桥结构纤维晶模型, 该模型不但有助于深入理解和认识聚合物取向结晶机理, 同时也为该材料的高性能化提供了理论依据.     

Free Radical Grafting of Polyethylene with Vinyl Monomers by Reactive Extrusion

The free radical grafting of polyethylene with vinyl monomers by reactive extrusion was studied numerically. Numerical computation expressions of key variables, such as the concentrations of the initiator and polymer, grafting degree, average molecular weight and apparent viscosity, were deduced. The evolutions of the above variables were predicted by means of an uncoupled semi‐implicit iterative algorithm. The monomer conversion monotonically increases with decreasing throughput or increasing initial initiator concentration; with increasing barrel temperature, the monomer conversion first increases then decreases. The simulated results are nearly in good agreement with the experimental results.

     

Preparation of Exfoliated Low-density Polyethylene/Montmorillonite Nanocomposites Through Melt Extrusion

Introduction Polymer layeredsilicatenanocompositesexhibit somesuperiorcharacteristics,suchasthermal,me chanicalandbarrierproperties,incomparisonwiththe polymermatrixes[1—3].Intercalationpolymerization[4],polymersolutionintercalation[5]andpolymermeltinter…     

Crystallization behavior of polylactide on highly oriented polyethylene thin films

The crystalline structure and morphology of the PLA crystallized isothermally from the glassy state on highly oriented PE substrates at 130℃were investigated by means of optical microscopy,AFM and X-ray diffraction.The results indicate that the PE substrate influences the crystallization behavior of PLA remarkably,which leads to the growth of PLA crystals on PE substrate always in edge-on form rather than the twisted lamellar crystals from edge-on to flat-on when crystallizing the PLA on glass surface under the same condition.The edge-on PLA lamellae on the PE substrate are preferentially arranged with their long axes in the chain direction of the PE substrate crystals.It is further demonstrated that except for the different crystal orientation,the PE does not influence the crystalline modification and crystallinity of the PLA.     

Polyethylene blends: A correlation study between morphology and environmental resistance

HDPE is widely used in outdoor applications in which dielectric, mechanical and thermal behaviors combined with high environmental resistance are a major concern. Unfortunately, the required processing conditions of the material often result in residual stresses that in connection with environmental exposure are responsible for premature failure. In an attempt to combine good durability with more facile processing conditions for HDPE based components, blends of this polymer with LDPE and LLDPE were studied, as a function of the blend composition ratio. Measurements of crystallinity and dynamical mechanical studies were conducted which established a quantitative relationship between morphological features and composition. The optimal results of performance were obtained with HDPE/LLDPE blends which are discussed here in terms of their morphology and mobility of the amorphous phase.     

The influence of chitin nanocrystals on structural evolution of ultra-high molecular weight polyethylene/chitin nanocrystal fibers in hot-drawing process

Ultra-high molecular weight polyethylene (UHMWPE)/chitin nanocrystal (CNC) fibers were prepared. Compared with the pure UHMWPE fibers, the ultimate tensile strength and Young’s modulus of UHMWPE/CNC fibers are improved by 15.7% and 49.6%, respectively, with the addition of chitin nanocrystals (CNCs) of 1 wt%. The melting temperature (T _m) of UHMWPE/CNC fibers was higher than that of pure UHMWPE fibers. Pure UHMWPE fibers and UHMWPE/CNC fibers were characterized with respect to crystallinity, orientation and kebab structure by wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS) and scanning electron microscopy (SEM). It is found that the CNCs act as the shish structure in UHMWPE/CNC fibers and the kebab crystals are grown around the CNCs. There was almost no difference between pure UHMWPE fibers and UHMWPE/CNC fibers in orientation. But the degree of crystallinity of various stages of UHMWPE/CNC fibers was respectively higher than the corresponding stage of pure UHMWPE fibers. Moreover, the addition of 1 wt% CNCs improved the thickness of kebab crystals and accelerated the transformation of kebab to shish.     

左旋聚乳酸/聚(ε-己内酯)共混物在取向聚乙烯基底上的附生结晶行为

利用电子显微镜结合电子衍射研究了左旋聚乳酸/聚(ε-己内酯)(PLLA/PCL)共混物在取向聚乙烯(PE)基底上的结晶行为.纯PLLA在取向PE基底上能够附生结晶,主要形成分子链相互垂直的片晶结构.PCL在PE基质上也能发生附生结晶,导致两者分子链平行.PLLA/PCL共混物在取向PE基底上结晶的形态结构依赖于共混组成.在PLLA含量大于95 wt%时,PCL不影响PLLA与PE的附生结晶行为.当PCL含量增加至10 wt%时,PLLA在PE上的附生结晶行为受到了一定程度的影响.当PCL含量超过40 wt%时,PLLA在PE上的附生结晶被抑制,取而代之是PCL在PE取向基质上附生结晶,产生两者分子链平行的取向片晶.另外,在PLLA含量在50 wt%~30 wt%之间时,体系产生明显的微相分离,微相分离并不影响PCL与PE的附生结晶,在PCL的富集区仍然发生平行链附生结晶,而PLLA的富集区结构变得模糊.当PLLA含量少于20 wt%时,微相分离不明显,少量PLLA应该分散在PCL片晶间的非晶区.     

新型塑料管材加工方法研究进展

塑料管材综合性能优异,广泛应用于城乡建设的各个领域.随着管材行业的发展,对管材性能的要求也越来越高,塑料管材加工方式也在不断发展.本文说明了塑料管材应用领域,介绍了管材的挤出成型生产方法,概括了塑料管材行业现状,探讨了传统管材加工方式存在的不足,阐明了开发新型管材生产工艺的必要性和重要性,从定义、原理、结构、管材性能等...