Cairo, Egypt – Flexible polyurethane foam materials have found widespread use in noise reduction applications, with highly interconnected pores an important factor in its ability to dissipate sound waves. The cavity size and pore architecture can be optimised by careful selection of the quantities of catalyst, stabilisers and blowing agent. The addition of fillers can also improve performance.
Now, scientists at Ain Shams University and the Egyptian Petroleum Research Institute in Cairo have investigated the potential of using biochar made from eggshell. The shells – predominantly calcium carbonate – are typically disposed of in landfill without proper treatment. What if they could be upcycled into biochar as a filler for noise-reducing PU foam instead?
Biochar is a porous carbonaceous material made by pyrolysis in a nitrogen-rich environment at temperatures between about 450°C and 550°C, with the temperature affecting its properties, and can be used as an alternative to costly fillers such as graphene and carbon nanotubes in sound-reducing foam. Hydroxyl, carboxyl and carbonyl groups on the surface enhance physical crosslinking with the polymer matrix, and treating it with silane coupling agents can give better dispersion, further improving its acoustic properties.
Chicken eggshells sourced from domestic waste were used to make the biochar for their experiments. The shells were washed to remove pollutants, dried, shredded and crushed before calcination at 550°C to eliminate excess biological material and release the calcium carbonate. The powder was then subjected to pyrolysis under nitrogen at 500°C in a tube furnace, followed by milling and modified with the (3-aminopropyl)trimethoxysilane (APTMS) coupling agent.
The biochar was then used as a filler in a PU foam made using a polyether polyol and TDI, using a one-shot free-rise polymerisation with DABCO and distilled water as the blowing agent. The best acoustic performance was achieved with 0.7% by weight of the biochar. APTMS modification further enhanced its noise-blocking capabilities, and smaller particles gave better results than larger ones.
The work has been published in the journal Scientific Reports.
