Alkaline pretreatment and steam explosion process on coffee silverskin and incorporation of cellulose fibers in poly(butylene adipate-co-terephthalate)

Abstract

In this work, coffee silverskin (CSS) fibers were subjected to alkali pretreatment (ALK-CSS) and alkali pretreatment, followed by a 4-bar steam explosion process (SEW4). Both treated fibers presented a higher degree of crystallinity, enhanced thermal resistance and also cleaner, rough, and defibrillated surface due to the removal of noncellulosic components, as was shown in scanning electron microscopy, thermogravimetric analysis, Fourier-transform infrared spectra, and x-ray diffraction (XRD) results. The SEW4 fibers were incorporated into the poly(butylene adipate-co-terephthalate) (PBAT) matrix in contents up to 5% wt. through melt processing. PBAT/SEW4 composites were evaluated by their microstructure, thermal properties, degree of crystallinity, and hydrophilic behavior. XRD results showed PBAT/SEW4 composites with higher degrees of crystallinity and contact angle tests revealed increased composite hydrophobicity with the increase of SEW4 content in the PBAT matrix. This work describes the importance of recovering coffee lignocellulosic waste and producing value-added by-products, especially in packaging manufacturing.