Sustainable automotive composites: A systematic review of dispersion methods for cotton fibers in poly(lactic acid) matrix

Composite materials are created by combining two or more different materials, such as a filler or fibrous reinforcement dispersed in a polymer matrix to improve the properties that surpass those of the individual components while reducing weight, making them ideal for the sustainable development of the automotive industry. Poly(lactic acid) (PLA) has emerged as a promising polymer matrix for composites due to its ecological and biodegradable nature and good mechanical properties (tensile strength and modulus of elasticity) but limited when compared to engineering polymers such as Acrylonitrile Butadiene Styrene (ABS) and Acrylonitrile Styrene Acrylate (ASA). Cotton fibers (CF) have gained visibility as filler or reinforcement in PLA/CF composites due to their low cost, renewable sources and relatively abundance. Although, to ensure mechanical enhancement, fiber dispersion in PLA matrix is of paramount importance, often being neglected. This article aims to study how to achieve a uniform distribution and strong chemical interaction between the PLA matrix and CF. This study employed PRISMA protocol to conduct a systematic review of articles retrieved from four databases: ScienceDirect, Web of Science, Scopus and Engineering Village. The search query combined the following keywords: “PLA” AND “composite” AND “cotton”. The analysis of the research articles suggests that twin-screw extrusion is the preferred method for post-dispersion mixing due to its ability to control the process and optimization capabilities, resulting in homogeneous composite materials. Pre-dispersion techniques, including masterbatch, hydraulic presses or rheometers, produce concentrated mixtures of additive and polymer, effectively reducing fiber agglomeration during subsequent mixing. The use of solvent casting becomes an unfavorable option on an industrial scale due to the time required for production. However, it is still necessary for the validation and characterization of the material in laboratory scale, so that, in the future, an optimal formulation can be scaled up industrially with more robust machinery.