Effect of Cowpea Lignocellulosic Fibers as a Low-Value Reinforcing Filler on the Properties of Poly(butylene succinate-co-adipate) Bio-Composite Foams

Herein, fully bio-based and biodegradable bio-composite foams are produced from poly(butylene succinate-co-adipate) (PBSA), reinforced with low-value cowpea lignocellulosic fibers, and azodicarbonamide as a chemical blowing agent. These are produced by melt extrusion followed by compression molding. Fiber addition increases the melt viscosity and melt strength, this restricts uncontrolled bubble growth during foaming to decrease the bubble size. The bio-composite foam containing 15% fibers has the largest decrease in bubble size from 209 µm in the unfilled PBSA foam to 95 µm in the foam containing 15% fibers. Fiber addition significantly increases the bubble density, from ≈1.05 × 10⁹ cells cm⁻³ in the unfilled PBSA foam to 5.13 × 10⁹ cells cm⁻³ in bio-composite foam containing 15% fibers, due to heterogeneous bubble nucleation induced by the fibers. The stiffness of the bio-composite foams increases with fiber addition, with the bio-composite foam containing 15% showing the largest increase relative to the unfilled PBSA foam as revealed by dynamic mechanical analysis. In conclusion, the fibers not only induce heterogeneous bubble nucleation to increase bubble density and decrease bubble size during the foaming of PBSA, but also act as reinforcement to increase the stiffness of the bio-composite foams. These bio-composite foams have potential applications in packaging and agriculture.