Biological pretreatments of lignocellulosic fibers and their effects on biocomposites performance

Over the last decade, the use of natural fibers as reinforcement in composite materials has received an increased attention from both academia and industry scientists. Due to their benefits, such as biodegradability, reduced energy consumption during production or positive impact on CO 2 emissions, lignocellulosic fibers have a great market potential for different applications where lightweight and environmental performance are key issues. However, some disadvantages related to the fiber's moisture absorption, dimensional and thermal stability or fiber-matrix poor compatibility require specific treatments in order to improve their performance. Favored by the current trend in research to tackle the environmental issues associated to the industrial production, the biological methods to modify the surface of natural fibers intended for high performance composites registered a fast and specific development given their advantages (use of nontoxic chemicals, low energy requirements and clean production technology, etc). Their selectivity and hydrolysis rate need further investigation and control for enhancing the quality of the final product and the process reproducibility. This chapter discusses the key principles of lignocellulose enzymatic hydrolyzing processes with a comprehensive summary of the various lignocellulolytic enzymes. The evaluation will be focused on the surface modification of the cellulose (mainly, in the presence of fungal and bacterial cellulases), as well as on the performance of the biocomposites reinforced with modified lignocellulosic fibers. The review also covers research challenges for the current best practice in materials, processes, characterization and applications.