Accelerated aging effect in physical and thermo-mechanical properties of maize starch biocomposites reinforced with agave salmiana fibers from different leaf ages

Abstract

In this study, lignocellulosic fibers from Agave salmiana –an important socio-economical species endemic to Mexico– were used to reinforce thermoplastic maize starch (TPS). Fibers from young raw leaves (YRL) and old roasted leaves (ORL) were obtained according to the traditional methods used by small producers. The formulations of biocomposites were obtained varying the content of both types of fiber and processed by extrusion and injection molding. Morphological, structural, mechanical, thermal, and thermomechanical properties of biocomposites were evaluated. To use the hydrophilicity of these materials as an advantage in unexplored applications, biocomposites behavior under degradative tests such as accelerated aging and salt water immersion was evaluated. The processes of heating the old leaves partially removed the lignin and hemicellulose layer from the fibers, which led to a better interaction fiber-matrix, as confirmed by FESEM, ATR FTIR, and TGA. Biocomposites with 30 wt% of YRL fiber reported the highest values of tensile strength and Young’s modulus when compared to ORL biocomposites and with TPS. Accelerated aging exposure affected mainly the thermomechanical properties of TPS and confirmed the reinforcing effect of the fibers due to the thermal and mechanical stability they provided to the matrix, especially when 20 wt% of fiber was added. This was also observed when biocomposites were immersed in salt water solution. Using Agave salmiana fiber obtained from different leaf ages by traditional methods in the production of biocomposites promotes the complete harnessing of this species and represents a possibility to small producers in Mexico to introduce circular economy in their communities.