碳纳米纤维增强聚甲醛复合材料制备及性能

摘要：通过纳米碳纤维(CNFs)在聚甲醛(POM)基体中的均匀分散以及取向,制备了具有优异力学性能和热性能的POM/CNFs复合材料。利用扫描电子显微镜、透射电子显微镜、拉伸性能测试、热重分析、动态热机械分析测试表征了POM/CNFs复合材料的结构和力学、热学性能。结果表明,CNFs与POM分子链形成氢键相互作用,促进了CNFs在POM基体内分散,同时使POM/CNFs复合材料的结晶度显著提高。随着CNFs含量增加,POM/CNFs复合材料的拉伸强度、储能模量和损耗模量均得到提高。当添加0.5%的CNFs时,拉伸强度、储能模量及损耗模量分别提高了20.5%,127%和58%。进一步研究了高温拉伸对POM/CNFs复合材料性能的影响。结果表明,CNFs沿拉伸方向定向排列,同时复合材料拉伸后结晶度提高,拉伸强度显著增加。     

高分子材料导热性能影响因素研究进展

介绍了高分子材料导热性能影响因素研究进展,重点阐释了聚合物基体的结构特性(链结构、分子间相互作用、取向、结晶度等)、导热填料(种类、含量、形态、尺寸等)以及制备方法等对高分子材料导热性能的影响.     

防晒剂在乳化体系中结晶规律及其抑制机制的研究进展

随着经济水平的发展和人民生活质量的提高,防晒产品已经成为人们日常生活中不可或缺的部分,而防晒剂结晶析出作为防晒产品的主要失稳现象越来越引起人们的重视.目前,国内对于乳液体系中防晒剂结晶现象的研究主要集中在如何开发新型包覆载体技术或优化配方体系以避免结晶的出现,而对防晒剂在乳液体系中结晶机制的研究报道十分匮乏.该文概述了...     

Early stages of polymer crystallization—a dielectric study

The existence and the formation of pre-ordered structures as the initial step during the complex process of polymer crystallization are discussed controversially. Most of the findings and interpretations are based on scattering experiments, which test small density differences between the assumed precursors of the crystals and the surrounding melt. Because of the low contrast the interpretation of experimental results become often speculative. In contrast relaxation experiments are probing motions in the sample and are therefore independent on density contrast. During crystallization, material is transformed from the liquid to the solid state. Consequently, motions typical for a liquid become impossible and do not longer contribute to the measured signal. For pre-ordered structures we expect some changes in mobility too because of the changes in conformation on pre-ordering.We performed dielectric relaxation experiments during isothermal crystallization of PCL. Pronounced effects in ?′ are observed long before changes in crystallinity can be detected. The observations strongly support the idea of pre-order in the polymer melt before the formation of crystals.     

Microbiological, physicochemical and sensory quality of maple syrup aseptically packaged in paper-based laminate

Quality of maple syrup packaged in paper-based laminate at 82°C or room temperature (25°C) was evaluated and compared to a reference syrup packaged in glass bottles stored at 4°C. to prevent microbial growth and blown containers, maple syrup must be heated at 82°C before packaging. Significant pH decrease related to storage temperature was similar to the observation of other authors for glass bottles and cans. Syrup in laminate cartons stored at 4°C, had higher transmittance measurements with time, but at higher storage temperatures, browning effect related to caramelization of sugars balances this transmittance increase. Changes in invert sugar level were significant only in syrup packaged in laminate at 25°C and stored at 23°C and 37°C and were related to the microbial growth. Physicochemical changes were not large enough to affect the overall quality of the product. 'Burnt sugar' off-flavour was detected for samples stored at 37°C. Packaging maple syrup in paper-based laminate at 82°C is an economic alternative to glass bottles, while maintaining a good quality product.     

氯化铵法制取活性氧化锌的工艺研究

介绍了用氯化铵浸取法制备活性氧化锌的新工艺，产品各项技术经济指标均达到部标准，适应性强，工艺简单，锌回收率８７．１％以上。     

On the triple melting behaviour of poly(ethylene succinate)

The morphology of melt-crystallized poly(ethylene succinate) (PES) was investigated by optical microscopy and scanning electron microscopy, and the melting behaviour of PES was studied by differential scanning calorimetry (DSC). At low crystallization temperature imperfect crystals were formed which could melt and recrystallize during the DSC scan. Triple melting peaks were observed, and the melting behaviour was strongly dependent on crystallization time and scan rate. It was observed that crystallization at high temperature perfected the crystals (dominant and subsidiary lamellae in the spherulitic structure). Increasing the scan rate reduced the chance for reorganization. However, at high crystallization temperature two melting peaks were observed. The material formed was much more perfect, so that the melting process was not dominated by recrystallization. Accordingly, the cause of dual melting is the existence of two kinds of crystal perfection.     

Reversible secondary crystallization during cooling of polypropylene

Ultra-violet microscopy has been used to follow the distribution of fluorescent additives during the isothermal crystallization and cooling of polypropylene. During cooling from the crystallization temperature there is a flow of additives away from the spherulite centres and into the spherulite boundaries. This demonstrates a marked densification at the centre of the spherulites with less within the bulk and only a small increase at the boundary. This change reverses when the sample is reheated to the crystallization temperature. Thus spherulites which appear to be quite uniform in crystallinity at high temperatures become non-uniform on cooling. The spherulites also become fibrous in appearance when cool. These effects are explained in terms of non-uniform concentrations of poorly crystallizable polymeric species which retard secondary crystallization.     

Ni－P合金由晶态向非晶态转变的电结晶机理

在阴极极化电流下叠加一恒电流小幅度对称方波、测定被扰动的体系的交流信息──电位随时间变化曲线．研究证明Ｎｉ－Ｐ合金由晶态向非晶态转变时过电位脉冲幅由生核步骤迟缓造成．电极过电位，表面能和镀层Ｐ含量对镀层晶粒尺寸有不同的影响．