Relationship Between the Shape of Giant Reed-Based Fillers and Thermal Properties of Polyethylene Composites: Structural Related Thermal Expansion and Diffusivity Studies

Abstract

This paper describes the effect of two different fillers derived from giant reed (Arundo donax L.), namely fibers and shredded aerial parts of the plant, on the thermal properties of polyethylene-based composites, as the analysis of dimensional stability of lignocellulose-based composites, and its relationship with their thermal diffusivity, has not yet been assessed in the literature. It has been found that the introduction of such materials resulted in a significant reduction of the coefficient of thermal expansion, particularly more important in the case of fibers, due to their higher aspect ratio; in particular, this coefficient is reduced to less than half for fibrous composites (from 1.6·10− 4 K− 1 to 6.1·10− 5 K− 1 or 3.5·10− 5 K− 1 for 20 and 40% loadings). This parameter also influences the thermal diffusivity of the final parts; the diffusivity of composites increases with the ratio of lignocellulosic filler used, particularly when using fibers, due to a better orientation of these fibers than the shredded material, which does not exhibit a fibrous shape. Composites with 20% share of the filler exhibited a thermal diffusivity increased by about 15% compared to neat polyethylene, while 40% loadings resulted in a 25% and 60% increase for ground and fibrous materials, respectively. These results provide additional features to lignocellulose-composites characterization, providing properties not usually mentioned in the literature to expand the knowledge about such composite materials beyond mechanical properties, providing a broader range of properties to offer a wider application area of such composites.