Arundo Donax particles as reinforcement for PLA based composites

Abstract

Poly(lactic acid) (PLA) is a suitable alternative to conventional petroleum-based polymers in several common applications [1]. Nevertheless, PLA is often modified in many ways to improve its properties, e.g. by the introduction of fillers or fibers, especially for structural applications. Combining PLA with lignocellulosic fibers results in decreased price and increased stiffness, while maintaining the environmental advantage, i.e. compostability [2]. There is a wide range of different natural fibres that are used as fillers of polymeric composites: i.e., obtained from plants grown for their fibre content and from agricultural wastes or by-products. Nevertheless, there are some others that can be potentially used as reinforcements for thermoplastic matrices but not yet investigated, e.g. Arundo donax. A. donax is a perennial rhizomatous grass that grows plenty and naturally in all the temperate areas of Europe. This species shows very high growth rate, it is invasive and aggressive but with almost no economic value and, moreover, difficult to be disposed. Aim of this work was to use particles obtained by grinding the culms of Arundo Donax used as reinforcement for PLA based composites. The influence of the content (10 wt% and 20 wt%) and size (150-300 μm and 300-500 μm) of Arundo Donax filler (ADF) on the morphology and on the properties of PLA-ADF composites was evaluated. The composites were prepared by melt compounding the PLA with ADF using a co-rotating modular twin screw extruder. For comparison, neat PLA was processed under the same conditions. Both the neat PLA and the composites were characterized by SEM, DSC, tensile and flexural measurements. The melt compounding of PLA and ADF with a co-rotating twin screw extruder allowed easily obtaining a biocomposite with a good level of filler dispersion, although the extrusion decreases the dimensions, and the l/d distribution of ADF. The addition of ADF significantly influenced all the investigated properties. In particular, by increasing the ADF content, both the tensile and flexural moduli greatly increased whereas the ADF size did not influence significantly the composite stiffness. On the contrary, both the tensile strength and the flexural strength of the filled materials decreased if compared with the neat PLA (Fig. 1).