This review discusses the extrusion process parameters and their impact on the mechanical properties of composites reinforced with lignocellulosic fibers.

Poly(3-hydroxybutyrate), PHB, has gathered a lot of attention for its promising properties—in particular its biobased nature and high biodegradability. Although PHB is prime candidate for the packaging industry, the applications are still limited by a narrow processing window and thermal degradation during melt processing. In this work, three novel additives based on ferulic acid esterified with butanediol, pentanediol, and glycerol (BDF, PDF, and GTF, respectively) were used as plasticizers and antioxidative additives to improve mechanical properties of PHB. Elongation at break up to 270% was obtained in presence of BDF and the processing window was improved nearly 10-fold. The Pawley method was used to identify the monoclinic space group P2 of the BDF. The estimated crystallite size (71 nm) agrees with a crystalline additive. With PHB₇₀BDF₃₀ blends, even higher elongations at break were obtained though dwindled with time. However, these properties could be recovered after thermal treatment. The high thermal stability of this additive leads to an increase in the fire retardancy property of the material, and the phenolic structure induced antioxidant properties to the samples as demonstrated by radical scavenging tests, further highlighting the possibilities of the PHB/additive blends for packaging applications.

A new class of biobased composites with tailorable mechanical properties made of natural fibers, polylactic acid, and ferulic acid derivatives (FAD) is studied. FAD was used to develop composites with elastomeric properties like improved elongation at break and highly reversible deformation upon elongation. Composites were prepared using raw and enzymatically treated hemp fibers. The fibers were defibrillated due to the enzymatic treatment increasing their aspect ratio. The composites were characterized by their mechanical properties and their reaction to fire. No significant change in the dispersion of the fibers in the composites was reported. Homogenously dispersed crystallites of FAD were observed by scanning electron microscopy in the PLA matrix and at the interface between the PLA and the fibers, where they are suspected to increase the free volume in correlation with a decrease in mechanical properties following the increase in the aspect ratio of the fibers. FAD also degraded the reaction to fire of the material with an increase in 10% of the peak of Heat Release Rate (pHRR) in comparison to neat PLA. It also increased the charring residue up to 3 wt.%. A synergistic effect between FAD and the lignin increasing the charring residue is also reported. GRAPHICAL ABSTRACT