Preparation Of OBSH/MMT Nanocomposite Foaming Agent Via Colloid-Modified Process And Its Foaming Properties

Microcellular foams (MCF) have a light weight and can provide a higher mechanical strength, better thermal insulation and acoustic properties compared with conventional polymer foams due to their ultra small cell size and high cell density. Therefore, microcellular polymer materials have attracted much attention because of their scientific interest and potential applications as packaging, construction, auto part and thermal insulation materials. The supercritical fluid (SCF) foaming agents were mainly used to prepare MCF so far in which the high pressure and/or high temperature were usually used. Now we proposed a mechanism to obtain MCF by use of a novel nanocomposite foaming agent, which may lead to the fine dispersion of chemical foaming agent and reduce the local gas. The microcellular foams have been extensively studied mainly focus on the preparation from thermoplastic polymers. However, in the field of thermosets, microcellular foams had seldom been reported to be obtained, especially for epoxy foams. In this work, nanocomposite foaming agent was prepared via a colloid-modified process. The nanocomposite foaming agent was applied to producing microcellular epoxy foams.(1) The montmorillonite (MMT) was hydrated, acidized and exfoliated with ultrasound. Exfoliation of the layered material in formamide solution yielded colloidal suspensions of nanosheets with lateral dimensions of about 100-300 nm and thicknesses down to 1 nm, ascertained by TEM and AFM. Integration of The MMT nanosheets with 4,4’-oxybis(benzenesulfonyl hydrazide) (OBSH) in the formamide solution yielded the nanocomposite foaming agent. The intercalation of OBSH in MMT was confirmed by characterizations with XRD, NMR and FT-IR. Thermal decomposition behaviour of OBSH embedded in the confined space of MMT was also different.(2) Through the investigations of the reaction temperature, concentration and time, it’s found that there was a competitive equilibrium relationship between OBSH and DMF when they were intercalated into the reassembling montmorillonite layers. The interaction between inner surface OH and C=O of DMF is stronger than OBSH. Then increasing reaction temperature and time were in favor of the intercalation of DMF into the reassembling layers. When the reaction temperature was too high, the OBSH may be deintercalated from the layers. In addition, increasing reaction concentration was conductive to the intercalation of DMF into the reassembling layers.(3) The morphology of the composite foaming agent may be influenced by the different washing methods.Washing with the mixed solution of DMF and methanol could slow down the precipitation of OBSH and resulted in the OBSH molecules dispersing in the interlayer of MMT uniformly. Methanol as a solvent with small interfacial tension could prevent the aggregation of MMT. The mixed solution saturated with OBSH could avoid deintercalation of OBSH in the washing process. Therefore, the highly dispersed nanocomposite foaming agent was produced. The loading of OBSH was 20 wt% and the particle size was about 5μm.(4) The OBSH/MMT nanocomposite foaming agent was applied to producing epoxy foams. The microcellular epoxy foams with average cell size as small as 27μm and a cell density up to 106 cells/cm3 were obtained through the investigations of the foaming conditions. Compared with the epoxy foams produced by pure OBSH, the foams quality was obvious improved.Moreover, the epoxy foams obtained from nanocomposite foaming agent were better than that produced by the physical mixture of foaming agent and fillers.