Thesis (M.Sc.)--Chulalongkorn University, 2009

The poly(methyl methacrylate) (PMMA) or acrylic sheets containing graft copolymer of PMMA on deproteinized natural rubber (DPNR) (GDPNR) were prepared by bulk polymerization using benzoyl peroxide and azo-compounds as initiators. GDPNR and graft copolymer of PMMA on concentrated natural rubber latex (GNR) were produced via emulsion copolymerization. The effect of reaction time was the important factor to study for preparation of graft copolymer step. It was found that the reaction time at 3 h gave the maximum value of grafting efficiency for production of GDPNR; while the preparation of GNR presented the lower grafting efficiency. The influence of type and content of graft rubbers on the mechanical and physical properties of the modified acrylic sheets before and after ageing with heat and ultraviolet was also investigated. The results showed that mechanical properties of the modified acrylic sheet were a function of amount of grafted rubbers. The impact resistance of the acrylic sheet containing GDPNR increased with increasing GDPNR content. The highest impact strength of the modified acrylic sheet was ca. 150 kJ/m² at 10 wt% GDPNR content. However, the addition of GNR into the acrylic sheet was limited due to the lower level of grafting efficiency compared to GDPNR and the higher molecular weight of NR which caused the difficulty to be dissolved in methyl methacrylate monomer during preparation of PMMA sheet. Moreover, the heat and UV stability of the GDPNR-modified acrylic sheet was higher than that of the acrylic sheet containing DPNR. Silica was used as a thermal and UV stabilizer for acrylic sheets. The results indicated that the increase in the silica content improved the thermal and UV stability of the modified acrylic sheets.