Preparation And Modification Of NBR-based Water-swellable Elastomers

Water-swellable elastomer or water-swellable rubber (WSR) is a new kind of functional elastomer with elastic sealing and water-swelling properties. It can be used widely as caulking, sealing of gaps and waterproof materials. WSR is normally prepared through multicomponent mechanical blending of a elastic matrix, a super water-absorbent resin and other additives. Due to the hydrophilic polar nature of water-absorbent resin and the hydrophobic nonpolar nature of the rubber matrix, the aggregation and poor dispersion of water-absorbent resin inside the rubber often lead to the instability and degradation of water-swelling ability, mechanical properties, long-term water retention and so on, which limits the practical application of WSR. So how to improve the miscibility of water-absorbent resin and elastic matrix is a challenging task to extend its industrial applications.In this research, WSR were prepared by blending crosslinked sodium polyacrylate (CSP), nitrile butadiene rubber (NBR), inorganic fillers and other additives using the physical mixing and vulcanization process. The effects of WSR composition on mechanical properties, morphologies and water-swelling behavior were investigated by means of soaking in the medium, mechanical testing, thermal gravimetric analysis, temperature aging test, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The main contents are as follows:1. Inorganic fillers, as a necessary component of rubber products, has a key role in the mechanical properties of rubber products. In this paper, OMMT or nano-silica, as the reinforcing phase, was added to CSP/NBR composites, and the effects of two kinds of inorganic fillers with different structures on the mechanical properties and water-swelling behavior of CSP/NBR were compared and analyzed. The studies showed that the addition of OMMT or nano-silica increased the mechanical properties of WSR before and after water swelling, water absorption capacity, aging resistance and structural stability of CSP/NBR, and also improved the dispersion of water absorbent resin in the NBR. Compared with nano-silica, the addition of OMMT displayed higher mechanical properties of CSP/NBR after water absorption, and better the aging resistance.2. The effects of swelling media on the absorption behavior of WSR were investigated by soaking the prepared OMMT/CSP/NBR (30/100/100) in different temperature, salt concentration and pH solution. The results showed that with an increase of temperature of deionized water below 40?, the swelling ratio of blend increased; however the swelling ratio of blend decreased with an increase of temperature above 40? due to migration of CSP particles from WSR to water phase, which was not conducive to the sustained increase of water absorption. The increase of the salt concentration of the solution can significantly reduce the water absorption and water absorption rate of WSR. Even in the high temperature salt solution at 80?, the water absorption rate of WSR remained low, and the water absorption rate was less than 100%. The increase of the acidity or alkalinity of the solution reduced the water absorption of WSR. When the pH value was equal to 7, the swelling ratio of WSR reached the maximun value.3. In order to improve the poor compatibility between the rubber matrix and the water-absorbent resin, acrylamides and nitrile rubber graft copolymer (P(NBR-g-AM)) as compatibilizer between the NBR and CSP was prepared, and compatibilization of P(NBR-g-AM) in WSR with different contents of P(NBR-g-AM) was investigated by morphology, mechanical measurement, and water-swelling tests. The results showed that adding P(NBR-g-AM) improved the compatibility of the WSR between components, and reduced mass loss rate after absorbing water, resulting in the increase of mechanical properties and water absorption, especially for the blends of 30% P(NBR-g-AM) with better comprehensive performance. In addition, adding P(NBR-g-AM) with amide groups improved the water absorption capacity of WSR in different swelling media (temperature, pH value, saline solution).