Thermo-Compressed Films of Poly(butylene succinate) Reinforced with Cellulose Fibers Obtained from Rice Straw by Green Extraction Methods

In this study, two green extraction methods are explored to valorize rice straw into cellulose fibers (CFs), namely subcritical water extraction (SWE) and combined ultrasound-heating treatment (USHT). The resultant fibers are, thereafter, successfully pretreated with (3-glycidyloxypropyl) trimethoxysilane (GPS) and incorporated at 3% wt into poly(butylene succinate) (PBS) by melt-mixing. The green composites are shaped into films by thermo-compression and characterized in terms of their performance for food packaging applications. The chemical analysis of the fibers reveals that SWE is more effective to selectively remove hemicelluloses than USHT, whereas silanization promotes the removal of lignin in both fiber types. Fiber incorporation, more notably in the case of the silanized fibers, restricts the movement of the PBS chains, indicating good interaction with the biopolyester matrix. In particular, CFs act as antinucleating agents in PBS, delaying both glass transition and crystallization from the melt phenomena and hindering crystal formation. Furthermore, the fibers mechanically reinforce and improve the oxygen barrier of the PBS films. The highest barrier enhancement is obtained for the thermo-compressed composite film with silanized fibers obtained by SWE, yielding a decrease of nearly 20% in the permeability to oxygen versus the unfilled PBS film.