Structure and mechanical properties of starch/ styrene-butadiene latex composites

The structure of the starch/styrene-butadiene latex composites was characterized using Scanning Electron Microscopy (SEM). In order to get a better contrast between starch and latex, OsO₄ were used to stain latex. Ion-beam cutting and liquid nitrogen cracking were employed to fabricate qualified cross-sections for SEM characterization. During drying, starch and latex migrate, creating non-uniform structure with latex dominated in the lower surface (next to the substrate) and starch in the upper surface (open to the air). The film formation of latex is slower than the starch/latex film forming. Phase separation occurs with starch granules embedded in the latex-starch matrix, reinforcing the composites. The analysis of composite structure and use of Perera approach indicate that good adhesion is present between latex phase and starch phase, starch granules and latex-starch matrix. When the latex is substituted by starch, the elastic modulus and tensile strength increase whilst the elongation at break decreases. When the volume fraction of starch is higher than 41.7 %, increasing starch content, the increase of ultimate tensile strength and elastic modulus accelerate, whereas the elongation at break decreases slower, which may arise from the phase co-continuity of starch.