Thesis (M.Sc.)-- Chulalongkorn University, 2010

The preparation of natural fabric/castor oil polyurethane sandwich composites and laminated sheet was investigated aiming for synthetic fabric replacement. The natural fabric gave the reinforcement of sandwich composites which the castor oil polyurethane was required as an adhesive. In this work, the natural fiber/castor oil polyurethane sandwich composites were prepared by hand-lay up technique of various combination of hemp and cellulose layers. Mechanical properties, flexural strength of biocomposites under sea-water effect and the dynamic mechanical analysis were investigated. From the immersion of sandwich composites and laminate sheets in seawater, it was found that the biocomposites reinforced with 100 wt% cellulose fabric had maximum absorption while the natural fabric and the synthetic fabric at 50/50 wt% reinforced composite had minimum absorption. Comparison with the nontreatement biocomposites, the treated hemp by 5 %wt NaOH reinforced composite showed the decreasing percentage absorption while the mechanical properties increased. From the dynamic mechanical analysis, the storage modulus and loss modulus of the treated hemp fabric composite laminate sheet increased. Glass transition temperature was also increased from 49.7 °C to 57.2 °C.