Thermal and Mechanical Characterization of Recycled LDPE/Sida acuta Fiber/Paper Pulp Composites for Sustainable Wall Panels

Plastic waste, especially low-density polyethylene (LDPE), poses a serious environmental challenge. This work develops wall panel composites by reinforcing recycled LDPE with Sida acuta (wire weed) fibers and recycled paper pulp. Panels were fabricated by melt mixing and compression molding (150–160 °C), with S. acuta fiber at 0–45 wt% and 5 wt% constant paper pulp (except the neat sample). Mechanical tests (tensile, flexural, impact, Rockwell hardness) and dynamic mechanical thermal analysis (DMTA) were conducted. Results show tensile strength of neat LDPE (33 MPa) declined with fiber addition to 21 MPa at 45 wt% fiber, while tensile modulus rose from 0.31 to 0.61 GPa (0-45 wt%). Flexural strength peaked at low fiber content (225 MPa at 5 wt%, vs. 209 MPa for neat) and then decreased to 189 MPa (45 wt%). In contrast, flexural stiffness roughly doubled (modulus 0.247-0.534 GPa at 45 wt%). Impact toughness and surface hardness improved continuously: impact energy increased with fiber (3.2 kJ/m² at 45 wt%), and hardness rose from 14.6 to 69.2 HRB (0-45 wt%). DMA showed that all composites retain dimensional stability up to 240 °C, with reinforced samples exhibiting lower damping (tan δ) and higher effective Tg than neat LDPE, indicating restricted polymer mobility. These findings demonstrate that valorizing LDPE waste with Sida acuta fiber and paper pulp yields composites with enhanced stiffness, toughness, and thermal stability. The composites' performance especially increased modulus and impact resistance suggests they show potential for non-load-bearing interior partition applications in indoor partitions.