(7c) Mechanical, Structural and Thermal Properties of Polymer Composites Containing Short Ragweed Pollen Grains

Pollen grains are ubiquitous biological particles possessing a high-strength outer shell with remarkable chemical stability. In addition, the unique ?spiny' ornamentations on many pollens offers intriguing possibilities for bio-based polymer composites with enhanced matrix-filler adhesion. In this work, the effect of the incorporation of short ragweed pollen grains on the mechanical, interfacial and thermal properties of pollen/polymer (PCL: poly(ε-caprolactone) or PS: polystyrene) composites cast by different solvents (THF and chloroform) was investigated under different annealing conditions. The addition of pollen grains resulted in the reduction in both the tensile strength and elongation, while the modulus of PCL composites unchanged. Pollen/PCL composites exhibited detwetted interfaces with interfacial voids due to poor compatibility between the pollen and the PCL matrix. Casting solvents have an influence on the morphological (crystalline density), mechanical and interfacial properties of semicrystalline PCL films. Less ordered structures, with lower crystalline density achieved by THF casting and sub-melting temperature (Tm) annealing, showed reduced interfacial defects. This led to less reduction in the elongation properties by the incorporation of pollens. Thermal characterization revealed that the presence of pollens could narrow the crystallization behavior of the PCL matrix without changing the melting and crystallization temperature. For amorphous PS polymer, the elongation properties of composites were maximized at low pollen loading, whereas the tensile strength decreased continuously with pollen content. Together with an increase in the glass transition temperature of PS composites by incorporation of pollens, the reduced defect formation at pollen-PS interfaces indicates better affinity of the pollen surface with the PS matrix compared to those of PCL composites.