Upcycling end-of-life high-density polyethylene shampoo bottles and jute caddies into multilayer composite panels for sound insulation and multifunctional applications

With the increasing need for sustainable solutions to tackle both environmental waste and urban noise pollution, acoustic materials made from recycled resources have gained notable attention. In this study, multilayer composite panels were fabricated using recycled high-density polyethylene (RHDPE) from end-of-life shampoo bottles and waste jute fibers (WJF) from jute caddies. Four configurations: M0 (RHDPE only), M1 (one WJF interlayer), M2 (two WJF interlayers), and M3 (three WJF interlayers) were fabricated via compression molding and characterized for physicochemical, thermal, mechanical, vibrational, and acoustic properties. The fabricated multilayer composites demonstrated enhanced mechanical properties, with maximum tensile strength, flexural strength, Shore hardness, and impact strength in the M3 configuration. Water absorption increased from 2.2 % in the M0 configuration to 17.7 % in the M3 configuration over 52 weeks, while the RHDPE surface exhibited hydrophobic and oleophilic behavior with contact angles of 89.3° (DI water) and 13.1° (diesel), respectively. Thermogravimetric analysis revealed high degradation resistance, with a two-step degradation and maximum thermal stability retained up to approximately 495 °C; additionally, thermal conductivity decreased from 0.309 W.m −1 .K −1 (M0 configuration) to 0.247 W.m −1 .K −1 (M3 configuration), indicating improved thermal insulation. Vibration-damping tests showed damping ratios of up to 2.52 % (M2, Mode 1), validating enhanced vibrational energy dissipation with WJF interlayers. Acoustic characterization confirmed that the M3 configuration achieved an average sound transmission loss of 30.25 dB under normal incidence, comparable to commercial materials, such as polycarbonate (32.73 dB) and polymethyl methacrylate (PMMA) (32.58 dB), though not too mild steel (49.04 dB) due to its much higher surface density. The fabricated panels hold strong potential for implementation in infrastructure and transport-related applications such as highway noise barriers, generator enclosures, and office partitions, offering a sustainable alternative with demonstrated multifunctionality. • Upcycling HDPE shampoo bottles and jute caddies into multilayer composite panels. • Fabricated panels with 0, 1, 2, and 3 jute fiber interlayers. • Flame-retardant coated panels met HB and V2 flammability classifications. • Transmission loss (up to 30.25 dB), and thermal conductivity (down to 0.233 W/m·K). • Suitable for highway barriers, generator enclosures, and office cabin partitions.