SEM for PLA-UTDPWF (a and b), PLA-SA (c), and PLA-SE (d).Journal of Cleaner Production 346 (2022) 131242
Climate change4 and the global crisis in energy costs are driving scientists to come up with thermal insulation solutions for buildings that are cost-effective, sustainably produced and biodegradable. While conventional thermal insulator materials such as mineral wool, expanded polystyrene or polyurethane foam work well, they are often derived from petroleum and are hazardous to health if inhaled.
Date palm wood fibre (DPWF) is a promising biodegradable alternative given its natural insulating properties and its abundance: 200,000 tonnes are generated every year due to wastage from the date palm industry. But it absorbs water easily and is hard to combine with a suitable matrix material. Now, Hyder Al Abdallah, Basim Abu-Jdayil and Muhammad Iqbal from United Arab Emirates University’s Department of Chemical and Petroleum Engineering have come up with a way of addressing the problem. The researchers found that combining DPWF with a biopolymer of poly-lactic-acid (PLA) and applying a silane treatment of either acetone-water or ethanol-water can significantly improve the water resistance and mechanical properties of the DPWF-PLA bicomposite, making it potentially suitable as an insulation material.
“The treatment forms a hydrophobic layer on the surface of the natural fibre. This hydrophobic layer of polysiloxane solves the issues associated with bio-composites of high water absorption and low compatibility to a high extent,” explains Abu-Jdayil. “The water retention is reduced significantly and the improvements in mechanical properties are sufficient for the composite to be used as a heat insulation material.”
The team used a variety of analysis techniques such as scanning electron microscopy, fourier-transform infrared spectroscopy and tensile testing to assess the materials before and after the silane treatment. They found that the ethanol-water treatment showed the best results. While the thermal conductivity remained largely unchanged after the treatment, the tensile strength improved by as much as a factor of two and the cold/hot water retention dropped significantly. The resulting insulation offered a tensile strength of 25–30 MPa, a low thermal conductance of ~0.0085 W/(m.K) and 2% water retention after 48-hour immersion in hot water.
The team is hoping to explore the use of other coating treatments with a view to making further improvements to water resistance and fire risk. “Other future possible treatment could be peroxide chemicals, coating the fibres with a protective layer to further reduce water retention and adding fire retardant materials to enhance flame resistance,” Abu-Jdayil adds.