Engineered hybrid fibre reinforced composites for sound absorption building applications

The sound absorption was investigated in a series of 21 isotropic Hybrid Fibre Reinforced Composite (HFRC) prototypes, using the impedance tube method. The composite blends were engineered targeting the recovery of highly-available natural and synthetic fibrous polymeric materials -thermoplastic, ligno-cellulose, keratin, alginate bio-polymer-sourced locally from the post-consumer and end-of-life waste streams. Two major environmental pollution problems are discussed, such as urban noise and waste fibres, and how to transfer this waste into building materials, targeting a two-fold solution with environmental, economic, and social benefits. The diversion of valuable fibrous resources from landfill disposal is pursued, promoting multi-stage cascading use of raw materials as local industrial feedstock, through the development of high-end non-toxic products, for acoustic building applications. The noise absorption properties of the HFRCs is the focus of the study, since urban noise is considered by the World Health Organization amongst the major sources of anthropogenic environmental pollution of global industrialized urban settlements. The experimental results indicated low absorption coefficient at mid-frequencies (500 Hz-2.5 kHz) and a higher absorption (2.5-6.4 kHz) coefficient at higher frequency ranges. Peak sound absorption values of +/- 0.78 were achieved by the low-density prototypes with minimal filler-matrix interfacial voids and in which the filler phase was constituted by natural fibres with intricate hierarchical intraparticle microstructure. These series of innovative low-carbon materials from wastes introduce a sustainable alternative to traditional commercial synthetic products, for the improvement of the indoor quality by a significant noise reduction, particularly targeting dwellings in densified urban zones.