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ABSTRACT:The surface modification of sulfur-prevulcanized natural rubber (SPNR) sheets by the polyethyleneimine-functionalized-poly(methyl methacrylate) (PMMA/ PEI) nanoparticles was successfully performed via a simple dipping method. The percentage of surface coverage (C s ) of the nanoparticles on SPNR sheets was found to be affected by a variation of nanoparticle latex concentrations and immersion times. The adsorption isotherm of PMMA/PEI nanoparticles on SPNR sheets was analyzed and found to fit well to the Freundlich model. After coating, it can be observed that the presence of PMMA/PEI nanoparticles on SPNR surface had no effects over the SPNR mechanical properties e.g., tensile strength, elongation at break, and hardness. On the other hand, the coated SPNR sheets showed a reduction of surface friction coefficients and interfacial adhesion up to 45 and 59%, respectively. Furthermore, PMMA/PEI nanoparticles adsorbed on the SPNR surface was subjected to stretching and wearing conditions, and found to be stable for at least seven stretching and wearing cycles.

Core-shell hydrogel latexes, composed of a poly(2-hydroxyethyl methacrylate) (PHEMA) core chemically coated with chitosan (CS) shell, were synthesized via an emulsifier-free emulsion polymerization, free radically initiated by a redox couple of tertbutyl hydroperoxide and amine groups on CS itself. The variation of some polymerization parameters [e.g., polymerization time, CS/ 2-hydroxyethyl methacrylate (HEMA) weight ratio, and content of crosslinker] was systematically investigated in this study. We found that the weight ratios between CS and the HEMA monomer influenced the course of polymerization, which was traced by the change in percentage monomer conversions, and the colloidal stability of the PHEMA-CS hydrogel latexes obtained. Moreover, the polymerization time affected their particle sizes and surface charges. For the colloidally stable PHEMA-CS hydrogel latexes, their sizes and charges ranged from 600 to 689 nm and from 32 to 51 mV, respectively. N,N 0 -Methylene bisacrylamide was used as a crosslinking agent for the core component; this was found to be able to enhance the hydrogels' thermal stability and water uptake. Moreover, the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay showed that 100% cell viability was achieved during the treatment of the PHEMA-CS latex (0.2-2.5 mg/mL) with Caco-2 cells.