CNT-MF/硅橡胶泡沫复合材料的制备及介电性能

以碳纳米管(CNT)作为核,密胺树脂(MF)作为壳,苯乙烯马来酸酐共聚物(SMA)为乳化剂,原位聚合制备微胶囊化碳纳米管(CNT-MF),并将包覆后的碳纳米管作为填料添加到硅橡胶泡沫中,制备了CNT-MF/硅橡胶泡沫复合材料。探讨了核/壳质量比对微胶囊化碳纳米管的包覆效果的影响,同时研究了微胶囊化碳纳米管用量对硅橡胶泡沫泡孔结构和介电性能的影响。结果表明,微胶囊化碳纳米管的加入有利于提高复合材料的泡孔结构,大泡孔的存在和泡孔面积有利于材料介电性能的提高。当核/壳质量比为1∶10的微胶囊化碳纳米管添加量为15 phr时,复合材料介电性能表现最佳,此时复合材料在1 kHz的介电常数为26.34,介电损耗仅为0.013 6。     

Improving the functional properties of soy glycinin by enzymatic treatment. Adsorption and foaming characteristics

In this contribution we have determined the effect of limited enzymatic hydrolysis on the interfacial (dynamics of adsorption and surface dilatational properties) and foaming (foam formation and stabilization) characteristics of a soy globulin (glycinin, fraction 11S). The degree of hydrolysis (DH=0%, 2%, and 6%), the pH of the aqueous solution (pH=5 and 7), and the protein concentration in solution (at 0.1, 0.5 and 1 wt%) were the variables studied. The temperature and the ionic strength were maintained constant at 20 °C and 0.05 M, respectively. The rate of adsorption and surface dilatational properties (surface dilatational modulus, E, and loss angle) of glycinin at the air–water interface depend on the pH and DH. The adsorption decreased drastically at pH 5.0, close to the isoelectric point of glycinin, because of the existence of a lag period and a low rate of diffusion. The interfacial characteristics of glycinin are much improved by enzymatic treatment, especially in the case of acidic aqueous solutions. Hydrolysates with a low DH have improved functional properties (mainly foaming capacity and foam stability), especially at pH close to the isoelectric point (pI), because the native protein is more difficult to convert into a film at fluid interfaces at pH≈pI. The foam capacity depends on the rate of diffusion of protein to the interface and is much improved by the enzymatic treatment. Foam stability correlates with surface pressure and, to a minor extent, with surface dilatational modulus at long-term adsorption with few exceptions.     

聚氨酯预聚体技术及其应用

对聚氨酯预聚体的制备技术及其在胶粘剂、涂料、弹性体、软硬泡、纤维等方面的应用作了综述 ,并对与预聚体技术有关的聚氨酯研究、开发和生产技术进展作了简要介绍。     

Acidified sodium caseinate emulsion foams containing liquid fat: A comparison with whipped cream

Aeration properties of acidified casein-stabilized emulsions containing liquid oil droplets have been compared to the whipping of dairy cream. The foam systems were characterized in terms of overrun, microstructure, drainage stability, and rheology. With acidification using glucono-δ-lactone, the casein-stabilized emulsions could be aerated to give foams of far higher overrun (>600%) than whipped cream (∼120%). The development of foam volume, stability and rheology in the aerated casein-stabilized emulsion systems was found to be strongly dependent on the pH and the concentration of added calcium ions. Whereas whipped cream is stabilized by partially coalesced fat globules, the casein emulsion foams are stabilized by aggregation (gelation) of the protein coat surrounding the oil droplets. Casein emulsion foams formed at low pH were found to be more stable than whipped cream, whilst those formed at high pH were predominantly liquid-like and unstable. Instability arose in the acidified casein emulsion foams mainly through gel syneresis. We conclude that there are substantial textural differences between whipped cream and acidified casein emulsion foams, especially in terms of the small-deformation rheology and the extent of the linear viscoelastic regime.     

Effect of ultraviolet processing on selected properties of egg white

The effect of ultraviolet processing (10.6 and 63.7 kJ m(-2)) on selected properties of egg white (absorbance, particle size, protein fractions, free sulfhydryl content, immunoreactivity, viscosity, gelling and foaming properties) was investigated. Ultraviolet exposure induced the development of browning, the formation of large protein aggregates by disulfide exchange, and protein backbone cleavage. However, egg white proteins were differently sensitive to UV radiation. No changes in immunoreactivity, gelling temperature and gel firmness were observed. Independently on the UV dose, light treated egg white produced foams with higher stability. This effect was attributed to protein aggregates jamming in the fluid interstices between bubbles and/or to the higher viscosity of the aqueous phase. The latter was also associated to higher foam volume.     

蜂窝材料增强聚氨酯硬泡

介绍了蜂窝增强聚氨酯硬泡复合材料的制备工艺,并讨论了其影响因素,说明了这一材料的用途及发展前景。     

泡沫化指数在冶金熔体中适用性的探讨

通过理论推导及对有关文献中实验事实的分析,认为现在普遍采用的描述冶金熔体发泡能力的泡沫化指数表征的是熔体发泡能力与泡沫衰减能力的比例关系,在物理意义和数值大小上都不等同于泡沫寿命;泡沫化指数受外界几何条件的影响,并非熔体的本征物理化学性质;影响冶金熔体泡沫化的许多内禀因素没有被泡沫化指数涵盖,因此用其作为冶金熔体发泡能力的可靠判据,仍缺乏充分的理论和实验依据．     

聚氨酯/乙烯基酯树脂互穿聚合物网络结构与性能的研究

通过同步法制备了一系列聚氨酯／乙烯基酯树脂互穿聚合物（ＰＵ／ＶＥＲ－ＩＰＮ）,研究了ＰＵ／ＶＥＲＩＰＮ性能的影响因素。结果表明：随着ＰＵ含量的增加,ＩＰＮ的热稳定性能有一定程度的提高;而ＶＥＲ的含量增加,ＰＵ／ＶＥＲ－ＩＰＮ的剪切强度提高。实验还发现：当ＰＵ／ＶＥＲ－ＩＰＮ为部分相容的多相微区结构时,对增加ＩＰＮ的力学损耗更有利     

成核剂CaCO_3对聚丙烯开孔发泡性能影响的研究

将高熔体强度聚丙烯(HMSPP)、线型低密度聚乙烯(LLDPE)、成核剂CaCO3共混后在自制超临界CO2动态发泡模拟机上发泡制备了聚丙烯开孔泡沫材料,研究了CaCO3的粒径和含量对聚丙烯开孔发泡性能的影响。结果表明:2 500目CaCO3在HMSPP/LLDPE共混体系中的分散效果比5 000目CaCO3的好。添加2 500目和5 000目CaCO3后,发泡样品的发泡倍率减小,泡孔密度增大,泡孔直径减小,泡孔形貌变得规则,泡孔直径分布变窄,泡孔均匀性增加。添加3%的2 500目和5 000目CaCO3时发泡性能最好。在共混体系中添加成核剂CaCO3能够提高发泡样品的开孔性能。     

塑料网套专用LDPE树脂结构与性能的研究

分析了发泡工艺过程及其对原料的要求,对发泡网套用低密度聚乙烯(LDPE)2420H的结构性能、流变性能进行了分析研究,并与进口产品进行了对比。结果表明:2420H的重均分子量较小,分子量分布较窄,支化度低于对比样,使得2420H的熔体强度较低,熔体黏度较小,导致制品回弹性损失过快,需适当提高2420H的支化度以增加熔体强度。