Abstract
Graft copolymers, deproteinized natural rubber-graft-polystyrene (DPNR-g-PS) and deproteinized natural rubber-graft-polyacrylonitrile (DPNR-g-PAN), were prepared by the grafting of styrene (St) or acrylonitrile (AN) monomers onto DPNR latex via emulsion copolymerization. Then, ultrafine fully vulcanized powdered natural rubbers (UFPNRs) were produced by electron beam irradiation of the graft copolymers in the presence of di-trimethylolpropane tetra-acrylate (DTMPTA) as a crosslinking agent and, subsequently, a fast spray drying process. The effects of St or AN monomer contents and the radiation doses on the chemical structure, thermal stability, and physical properties of the graft copolymers and UFPNRs were investigated. The results showed that solvent resistance and grafting efficiency of DPNR-g-PS and DPNR-g-PAN were enhanced with increasing monomer content. SEM morphology of the UFPNRs showed separated and much less agglomerated particles with an average size about 6 μm. Therefore, it is possible that the developed UFPNRs grafted copolymers with good solvent resistance and rather high thermal stability can be used easily as toughening modifiers for polymers and their composites.
Highlights
Ultrafine fully vulcanized powdered natural rubbers (UFPNRs) have been developed and demonstrated high potential as a toughening filler in a polymer matrix [1,2] with competitive performance compared to ultrafine fully vulcanized powdered rubbers (UFPRs) based on synthetic rubbers, such as styrene-butadiene (UFPSBR) [3,4], nitrilebutadiene (UFPNBR) [5,6] and polybutadiene rubber (UFPBR) [7].UFPRs were prepared by irradiation of rubber latex in the presence of crosslinking agent and subsequently a fast spray drying process
The increasing monomer content up to 15 phr provided the highest grafting efficiency of graft copolymers, in consequence, thermal stability, swelling ratio, and crosslink density of the graft copolymers were significantly enhanced. They could not be used for the production of powdered natural rubber after spray drying due to their insufficient crosslink density
The deproteinized natural rubber (DPNR)-gPS and the DPNR-g-PAN were irradiated by electron beam to produce the practical ultrafine fully vulcanized powdered natural rubbers (UFPNRs)-g-PS and UFPNR-g-PAN through spray drying
Summary
Ultrafine fully vulcanized powdered natural rubbers (UFPNRs) have been developed and demonstrated high potential as a toughening filler in a polymer matrix [1,2] with competitive performance compared to ultrafine fully vulcanized powdered rubbers (UFPRs) based on synthetic rubbers, such as styrene-butadiene (UFPSBR) [3,4], nitrilebutadiene (UFPNBR) [5,6] and polybutadiene rubber (UFPBR) [7].UFPRs were prepared by irradiation of rubber latex (by gamma rays or electron beam) in the presence of crosslinking agent and subsequently a fast spray drying process. Compared with conventional rubber blends in a latex form, the UFPRs would provide some advantages for polymer blends, such as, for example, low energy consumed and time efficiency during the mixing process This is because the interactions between crosslinked rubber particles are much lower than the cohesion of uncrosslinked rubber particles. All compositions could only be mixed into a continuous matrix phase because of the crosslinking of dispersed rubber that keeps an elastic state [10] These characteristics have been reported in epoxy systems; a good dispersion between powdered rubber and epoxy resin leads to an improvement in the impact strength of epoxy resin being higher than that observed in an epoxy toughened with rubber latex [11]. The dynamic mechanical, mechanical and thermal properties were improved by adding a small quantity of UFPRs in polymer blends [11,12,13,14,17]
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