Sustainable Biocomposites Based on Invasive Rugulopteryx okamurae Seaweed and Cassava Starch

Abstract

The development of plastic materials based on cassava reduces the dependence on non-biodegradable petroplastics, and enhances the sustainability of the cassava value chain. In this sense, cassava starch (CS) is used as a reinforcer of biocomposites that also contain brown seaweed Rugulopteryx okamurae (RO). RO is an invasive species whose accumulation poses a strong environmental burden in the strait of Gibraltar. Because it can be used as a biopolymer, its use in the plastics industry would promote a healthy ecosystem. Thus, RO/CS mixtures with different RO/CS ratios (from 100/0 to 30/70) were processed through injection moulding at 140 °C. The thermal properties of plastic samples have been analysed through calorimetric, thermogravimetric and rheological techniques. Moreover, the mechanical properties, hydrophilicity, and microstructure of samples have also been studied. Thus, biopolymer degradation of the composites seems to happen at 213–303 °C, as revealed by thermal gravimetric analysis (TGA) of the samples, whereas an exothermic peak observed in DSC at 350–500 °C would be related to the degradation of organic compounds in anaerobic conditions. Rheological tests evidenced a softening of the RO/CS biocomposites when CS content increased in the formulation, so that elastic moduli dropped from 23.72 MPa in the 70/30 to 5.69 MPa for 30/70. However, RO/CS biocomposites became more resistant and deformable as CS content increased: maximum stress and strain at break increased from 78.2 kPa and 0.14% (70/30 system) to 580 kPa and 25.2% (30/70), respectively. Finally, no important differences were observed in their water uptake capacities or microstructures when increasing CS ratio in the mixture. As cassava starch can be extracted from agro-industrial wastes (i.e., cassava peel and bagasse), its use in biocomposites could be of great use for a more sustainable approach for plastic materials.