| As a novel functional material, the water-absorbing rubber composite can stop water not only through elastic sealing but also by swelling in water, possessing wide applications in sealing materials, soil-improving agents, water sensors and biomedical materials, receiving more and more attention in recent years.This paper aims to explore the methods of preparing rubber/starch/ sodium acrylate (NaAA) composites with high performance and to investigate the factors affecting properties. Main research aspects are as follows:1. Effects of addition processing of starch and NaAA on the properties of NBR/starch/NaAA composites were investigated. Starch was added through direct addition and co-coagulation methods; NaAA by direct blending and in situ methods. To obtain better mechanical and water-absorbing properties, the process of pasting starch paste and direct adding NaAA is recommendatory. The effect of dicumyl peroxide (DCP) contents, soaking temperature, and soaking time on the water-absorbing property of NBR/starch/NaAA composites prepared by co-coagulation method were also investigated. The results indicated that water-absorbing property decreased with increasing the DCP loading; for the composite with direct adding NaAA, the water-absorbing ratio increased with increasing the soaking time and temperature, while for the composite containing NaAA in situ, the water-absorbing ratio increased first and then decreased as the soaking time extended and the temperature rose. From FT-IR analysis and SEM observation, the extraction of sodium polyacrylate resulted in decrease in water-absorbing capacity. Compared with the co-coagulation method, the spray drying method is time-consuming. Generally speaking, the water-absorbing property and elongation at break need to be further increased.2. For the chloroprene rubber (CR) system, the possible reaction between starch and CR was clarified by measuring the vulcanizing behavior and thermal transitions, and observing the microscopic morphology of cut surface after curing. Later the effects of the different amounts of starch, NaAA and DCP on the properties of CR/starch/NaAA composites prepared by melting method were investigated. The results showed that the addition of starch improved the mechanical properties, decreased the water-absorbing capacity of the composite. Comparing with CR/clay/NaAA composites, the mechanical and water-absorbing properties of CR/starch/NaAA composites were better. The as-prepared composite demonstrated higher water-absorbing capacity, resulting from the incorporation of NaAA. The mechanical properties decreased with increasing the DCP loading, and the water-absorbing ratio is the maximum at 1.0 phr DCP. The tensile strength of the composite decreased significantly after water immersion, due to the plasticization effect of absorbed water. The morphology of the composites before and after water immersion was observed by optical transmission microscopy (OTM). The results indicated that the starch exhibits a good dispersion state, and the water-absorbing capacity results primarily from sodium polyacrylate.3. The effect of crystallinity of CR-A90, CR-210 and CR-3211 with the gradually declining crystallization ability, and the preparation method on the CR/starch/NaAA composites were studied. CR-A90 and CR-210 composites were prepared by the melting method, and CR-3211 composite by co-coagulation processing. The results showed that mechanical properties are CR3211 latex> CRA90> CR210; water-absorbing capacity is CR210 (599%) > CR3211 latex (349%)> CRA90 (301%) and the mass loss ratio CR3211 latex< CRA90< CR210. To balance the two properties, the composite prepared by co-coagulation is optimum, exhibiting a smooth surface after immersion and a better water-swellable uniformity, and its reusing performance is best.4. To further improve the water-absorbing capacity of CR/starch/NaAA composites by co-coagulation method, the amount of NaAA was increased to 30 phr, and effect of DCP content on the properties was discussed. With the increase of the DCP content, the crosslinking density increased, and curing time reduced, and the mechanical performance decreased, while the water-absorbing property increased, and the mass loss ratio gradually decreased. To compromise mechanical and water-absorbing properties, the optimum DCP amount is 1.5 phr and the volume expansion ratio is up to 615%. Moreover, the surface is flat, indicating the composties possessing a better water-swellable uniformity. The microstructure before and after absorbing water observed by OTM showed that starch particles had little agglomeration. The water-absorbing capacity was the highest (703%) at 2.25 phr DCP.
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