Polyimine-modified lignocellulose nanofibers and their use for enhancing mechanical properties of recycled mixed plastics

Abstract

The mechanical performance of recycled thermoplastics is often limited by deteriorated material properties and the formation of immiscible polymer blends. In this study, lignocellulose nanofiber (LCNF)–reinforced nanocomposites were developed to enhance the mechanical properties of recycled plastics. The matrix consisted of unpurified blends of low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), and polyethylene terephthalate (PET) (35/35/20/10 wt%), to characterize the heterogeneous plastic waste streams. LCNFs were polyimine surface–modified to improve the interfacial adhesion with the hydrophobic matrix, and several properties of these fibers were investigated to determine their suitability for polymer composites. The nanocomposites were melt-compounded with varying LCNF loadings (1, 2.5, and 5 wt%) and characterized for their mechanical, morphological, and structural properties. Scanning electron microscopy (SEM) analysis suggested that modified LCNFs promoted network formation within the polymer matrix. Tensile testing further demonstrated modest improvements in stiffness and strength, with the elastic modulus increasing by up to 14.2%. X-ray computed tomography scans confirmed the fracture mechanism of these composites, indicating that matrix-related defects limited further improvements in tensile properties. Overall, the study demonstrated the potential of cellulose nanomaterials to valorize recycled plastics by enhancing their mechanical performance, even in complex, unpurified polymer blends.