Heat Barrier Properties of Green Composites

Thermal insulation characteristics of natural fiber reinforced green composites are examined. The green composites were composed of epoxy resin and two kinds of natural fibers, namely abaca fiber and bamboo fiber. The natural fiber was unidirectionally aligned in the composites in order to preserve the hollow internal microstructure which is called lumen. Several kinds of green composite samples with different fiber contents were fabricated by a resin transfer molding technique and then their thermal conductivity was evaluated by using a steady-state method. The thermal conductivity and density of the green composites reinforced by abaca fiber having large lumen, decrease with increasing fiber content. On the other hand, in the case of bamboo fiber with small lumen, the thermal conductivity and density increase in a similar manner to that of glass fiber reinforced plastics (GFRP). In addition, thermal conductivity of all the samples has a good correlation with density; i.e., the thermal conductivity is proportional to the density. This unique fiber content dependence on thermal conductivity is related to the lumen size of the natural fiber.