Sustainable Acoustic Bio-Nanocomposites from Recycled HDPE and Modified Rice Straw Nanofillers: Performance and Biodegradability

The valorization of agricultural residues and post-consumer plastics is critical for achieving a circular economy. This study presents a sustainable pathway to fabricate eco-friendly acoustic panels by melt-blending recycled high-density polyethylene (rHDPE) with 10–50 wt% rice straw waste-derived nanofillers. Multi-stage chemical refinement (10% NaOH mercerization and H2O2 bleaching) before ball milling isolated nanofibrils under 50 nm. XRD analysis showed a crystallinity index increase from 37.0% (untreated) to 67.2% (bleached), confirming amorphous phase removal. FTIR and SEM verified successful delignification and excellent interfacial wetting. Consequently, the 50 wt% bleached cellulose composite exhibited the highest reinforcement, increasing flexural strength by 126% and flexural modulus by 132.6% over neat rHDPE. The hydrophilic framework enhanced environmental biodegradability, yielding a 15.18% maximum weight loss after a 90-day soil burial test, providing a viable end-of-life alternative to persistent synthetics. To optimize acoustic utility, a 1.76% geometric micro-perforation ratio was engineered into the panels. Backed by a 6 cm air cavity, the 50 wt% untreated composite achieved an outstanding peak sound absorption coefficient of 0.98 at a low frequency of 400 Hz. These findings establish these high-filler bio-nanocomposites as high-performance, low-carbon alternatives for noise control in construction and automotive infrastructure.