Great efforts are being made at Brunel University, UK in attempt to develop natural fiber composites with desired structure and good overall properties for construction. This work focuses on the mechanical and morphological characterization of the pultruded composite rods made from hemp and wool fiber reinforcements. The results showed that the composite using polyurethane resin system has higher specific tensile and compressive strength as well as the Young's and compressive moduli compared with the polyester and vinyl ester composites, while the polyester composite exhibits better flexural strength. The SEM observation of the cross section and layered polyester and polyurethane composites has found defects on the interface of fibers and resin matrix. It is also revealed that fibers are not evenly distributed in the composites and more resin aggregates in areas close to rod surface. Meanwhile, voids have been noticed existing in both composites, but more of them are found in the polyurethane-matrix rod, which correlated to the higher water absorption for this composite.
Extruded pellets from starch-based materials have been heated and foamed under microwave radiation. The foaming mechanisms and effects of some additives on the dielectric properties of the materials have been investigated using a microwave calorimeter. A rapid increase in dielectric loss factor (ɛ″) has been found for all the tested materials foamable under microwave heating and the onset of the ɛ″ increase is considered to be correlated to glass transition. It has been found that extruded starch materials can be foamed at 15℃/min but the expansion level reduced compared with that of the same material foamed at higher heating rate. The incorporation of organic additives in starch-based materials generally led to significant decrease of their microwave foamability when glycerol and polyvinyl alcohol are used as the additives in the extruded pellets.
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