Thermoplastic nanocomposites filled with wheat straw cellulose whiskers .2. Effect of processing and modeling

The reinforcing effect of cellulose microcrystals, or whiskers, dispersed in a thermoplastic matrix is analyzed. in Part I [Polym. Compos., 17, 604 (1996)], the preparation and the characterization of cellulose whiskers obtained from wheat straw were detailed. Composite films were processed by freeze-drying and molding a mixture of aqueous suspension of these microcrystals and a film forming latex of poly(Styrene-co-ButylAcrylate). Using the same filler and latex, materials were processed by casting and evaporating the mixture of aqueous suspensions. It was found that the reinforcing effect is greater in the latter case. This behavior is ascribed to the sedimentation of die filler during evaporation, evidenced by scanning electron microscopy, wide angle X-rag scattering, and dynamic mechanical analysts, and to the formation of a network of whiskers governed by a percolation mechanism. The behavior of the composite is modeled by subdividing the sample into layers with different whisker contents lying parallel to the film surface.