Preparation of energy-efficient, environmentally friendly and high-strength biocomposites from wood fibre ultramicro self-composite cellulose matrices

Abstract

Considering the diminishing forest as a natural resource, the efficient use of small-diameter shrubs is crucial for global sustainable development. This approach has significant potential to prevent wasting forest resources and reduce carbon emissions. However, small-diameter timber has inherent drawbacks, such as the looseness of this material, susceptibility to cracking and deformation, and low strength, all of which significantly impact its range of applications. In this study, an efficient, green method was developed to prepare adhesive-free biocomposites from discarded small-diameter shrubs via ultrasonic pretreatment and thermoforming. After the ultrasonic pretreatment, the flexural and tensile strengths of the biocomposites increased by 145% and 132%, respectively. Ultrasonic pretreatment separated and destroyed chemical bonds among the lignocellulosic biomass macromolecules through high-speed shear and microjets. This process significantly increased the amount of binding sites on the cellulose fibres, and further densified the cell walls through hot pressing. Moreover, the ultrasonic pretreatment may remove components of the wood flour that act as fillers or density enhancers, resulting in a reduction in the density of the biocomposite. Simultaneously, lignin acted as a binder and improved fibre bonding through both physical and chemical cross-linking, resulting in a dense cellulose structure with a three-dimensional lattice structure and a less hydrophilic surface, as evidenced by a water contact angle of 81.72°. In addition, the high-quality, binder-free biocomposites did not emit harmful gases such as formaldehyde. Hence, they are expected to become sustainable materials for building decoration and furniture applications in the future.