Comparative Study of the Effect of Addition of Silica and Silicate Nanofillers on the Properties of Epoxy Coatings

The effect of adding different amounts (0.5–3 wt%) of nanosilica (NS) and organomodified montmorillonite (MMT) to diglycidyl ether bisphenol A (DGEBA) cured with isophorone diamine at different temperature on the viscoelastic, topographical and gelation properties of epoxy resin was studied. Gel time measurements revealed that both NS and MMT accelerated the curing reaction of DGEBA with IPDA. Both nanofillers were adequately dispersed in DGEBA. The particle size distribution depended on the amount of nanofiller. A broader distribution for NS than for MMT filled epoxy was obtained. On the other hand, an increase in the curing temperature was required to obtain the intercalation of the epoxy into the MMT tactoids. At room temperature, the addition of NS increased both the stiffness (high storage modulus) and the toughness (an increase in the area and height of the tan δ curve) of epoxy, but no significant differences were found by curing at higher temperature. Epoxy/MMT composites showed higher storage modulus in the rubbery region. The improved properties imparted by NS can be ascribed to the interactions between the silanol moieties on the nanosilica surface and the polar groups in the epoxy, whereas the improvement imparted by MMT organoclay was related to tactoid intercalation within the epoxy matrix.     

Effect of chemical treatment on dynamic mechanical properties of sisal fiber-reinforced polyester composites fabricated by resin transfer molding

The dynamic mechanical properties of treated sisal fiber-reinforced polyester composites fabricated by resin transfer molding (RTM) have been studied with reference to fiber surface modifications, frequency and temperature. The sisal fibers have been subjected to various chemical and physical treatments like mercerization, heating at 100°C, permanganate, benzoylation and vinyl tris(2-ethoxymethoxy) silane to improve the interfacial bonding with isophthalic polyester resin. Results indicated that treatment changed the storage modulus (E′), loss modulus (E″) and damping factor (tan δ) drastically at a wide range of temperature. The E′ value increased for every treatment, and is maximum for the composites fabricated by benzoylated-treated fibers. The T _g value obtained from the E″value showed an increase as compared to untreated fiber-reinforced composites. The alkali-treated fiber-reinforced composites showed lower tan δ value. Using Arrhenius' equation the activation energy was calculated and found maximum for the composites fabricated by alkali-treated fiber, which shows good fiber/matrix interactions.     

Epoxy-silica hybrid materials synthesized via sol-gel process

We have successfully utilized the sol-gel method to synthesize epoxy-silica hybrid material at nanoscale. Using the sol-gel process we could overcome many disadvantages of conventional composite materials. In this research, two different methods are recommended — a one-step process and a two-step process — to synthesize epoxy-silica hybrid materials. The coupling agent, γ-glycidoxypropyl-methyldiethoxysilane (KBE-402), was utilized to modify the surface properties of the silica via the sol-gel process. The role of the coupling agent is to provide covalent bonding between the epoxy resin and silica. This method could reinforce the interfacial force of the hybrid material and promote the thermal properties of the materials. The thermal properties of the epoxy-silica materials were characterized by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). From these results, we noted that the best reaction time in the one-step process is 2 days and the addition of the inorganic component enhanced the thermal stability of the hybrid materials. On the other hand, the two-step process led to a phase separation phenomenon after mixing epoxy resin and precursor without coupling agent. The coupling agent could avoid the phase separation problem of hybrid materials and enhance the thermal stability of the materials through this process. At the same time, the T _g of the materials increased proportionally to the content of silica from 80°C to 113°C.     

Dimensional changes of carbon fiber fabrics reinforced phenolic resin-based carbon/carbon composites during pyrolysis

The dimensional changes of two-dimensional phenolic resin-based carbon/carbon composites during pyrolysis were investigated. The carbon/carbon composites were obtained by pyrolyzing the carbon fiber/phenolic resin composites that were fabricated using a vacuum bag hot pressing technique. Length, width and thickness of the rectangular composite samples were measured carefully before and after pyrolysis. The effects of heat treatment temperature and fiber pre-heat treatment on the dimensional changes of carbon/carbon composites were investigated. The measurement results indicated that different behavior in dimensional changes could be obtained for carbon/carbon composites with different fiber–matrix bonding in the interface.     

聚氨酯与接枝乙烯基酯树脂互穿网络研究: 自由基共聚 单体的影响

通过分子设计技术合成了两种侧链种类和长度可能控制的接枝乙烯基酯树脂(VER),并用它们与聚氨酯(PU)形成了同步互穿网络(SIN)。通过DSC,SEM,TEM,FTIR等考察了接枝VER的共聚单体对VERSIN的形态结构与力学性能的影响。研究结果表明,用甲基丙烯酸甲酯(MMA)为共聚单体的接枝VER网络中的MMA链段与PU网络中的硬段有较好的相容性,导致这类PU/接枝VERSIN中两个网络间的相容性和互穿程度好于由苯乙烯为共聚单体时合成4SIN。因此,在这两类共聚单体合成的SIN中,由MMA形成的接枝VER网络增强PU网络的效果更为显著。     

金的离子交换与吸附化学 I: 酰胺/膦酸酯型树脂483C1-Au(III), Au(I)-HCl系统

研究了酰胺/膦酸酯型树脂483C1[CONHCH2CH2P(O)(OR)2]从盐酸中吸金的化学问题,结果表明平衡服从Freundlich吸附等温式, AuCl4^-以缔合机制吸着; 测得了AuCl4^-的内扩散系数以及HCl-硫脲为解吸剂时的有关动力学参数; 还研究了AuCl4^-的柱穿透曲线.