Understanding novel biocomposites comprising of short cellulose fibres in a hybrid cellulose/silk fibroin matrix

Biopolymer blends offer a promising route to tunable, high-performance biomaterials, yet their potential in reinforced composites remains underexplored. This study investigates biocomposites produced by reinforcing a hybrid biopolymer matrix (90:10 cellulose:silk fibroin) with randomly oriented short cotton fibres and varying the reinforcement weight percentage. A pure cellulose matrix was tested for comparison. The composites were characterised using X-ray diffraction (XRD), density analysis, tensile testing, optical microscopy, scanning electron microscopy (SEM), and acoustic insulation analysis. Optimal hybrid composites with 50 vol% reinforcement exhibited superior performance to pure cellulose, achieving a Young’s modulus of 3.3 ± 0.3 GPa, strain at failure of 1.4 ± 0.2%, and maximum tensile strength of 42 ± 6 MPa. These enhancements were attributed to the hybrid matrix’s reduced viscosity and improved solvation capacity allowing higher fibre loading and stronger interfacial adhesion. In addition, the hybrid matrix’s greater extensibility enabled more efficient stress transfer to the fibres, maximising mechanical performance. Fibre content was identified as the primary driver of material modulus, underscoring the critical role of reinforcement. Flock content was then shown to correlate with improved acoustic insulation performance which led to a maximum average acoustic transmission loss of 47 ± 7 dB in hybrid samples compared to 29 ± 4 dB in cellulose samples. This work demonstrates the viability of hybrid biopolymer blends for creating low-density, high-performance materials from short-fibre textile waste with sustainable applications in insulative structural engineering.