Effect of lignin removal on the properties of coconut coir fiber/wheat gluten biocomposite

The effect of fiber lignin content on biocomposite properties was investigated. Coconut fiber was treated with 0.7% sodium chlorite to selectively decrease amounts of lignin. The fiber lignin content was then reduced from 42 to 21 wt.%. The composition and mechanical properties of the individual modified fibers were characterized. Gluten-based materials reinforced with modified fibers were prepared by compression molding. Then, the mechanical properties, water sensibility, matrix glass transition and infrared spectra of biocomposites prepared with fibers containing various amounts of lignin were evaluated. This study showed that the addition of coconut coir fiber significantly improved properties of wheat gluten biomaterials. In addition, the variation of lignin content in the fibers, in the investigated range, had no significant effect neither on matrix deplasticization nor fiber/matrix adhesion, suggesting that a partial lignin removal is not an efficient way to improve the properties of natural fiber/plasticized protein biocomposites.