Co-authors​ :

 Xue Yang GOH (SINGAPORE), Kaiting GUO (SINGAPORE), Luon Tan LUON NGUYEN TAN (SINGAPORE), Ren Hong ONG , Tianliang BAI (SINGAPORE), Xinying DENG (SINGAPORE), Wern Sze TEO , Hai Minh DUONG  

Environmental issues brought about by waste polyethylene terephthalate (PET) calls for the urgent need for an alternate recycling solution. For the first time, PET aerogel (PA) made from waste plastic bottles is proposed as an integrative radiative cooler and a thermal insulator. The hydrogel of recycled PET fibres and polyvinyl alcohol (PVA) are first frozen and then freeze-dried to create the PA. Due to the highly emissive nature of the developed PA within the sky window (8 – 14 µm), and its highly insulative properties enables the PA to passively cool an object directly underneath. Despite the unfavourable conditions of a warm Singapore night sky with high downwelling of 420 W/m2, the PA can still cool an object below the ambient temperature, by more than 2 C, providing 12 W/m2 of cooling power. Without the need for electricity, the PA offers an environmentally friendly thermal management solution that can also be used in conjunction with conventional compressor-based cooling systems to further improve energy efficiency. However, one major drawback of PAs is its relatively soft and flexible nature. The lack of structural rigidity makes PA susceptible to severe deformation. The densification of the material, and its pores, negates its usefulness as a thermal insulator and negatively affect its performance as a radiative cooler. One way to circumvent this issue is to incorporate a honeycomb structure within the PA to create the PET aerogel composite (PAC). The proposed method aims to preserve the pores within the aerogel under loaded conditions. The effects of various honeycomb cell size (1 – 2 cm), PET-PVA ratios (5-1, 10-1, and 20-1), on the 3-dimensional mechanical properties, and thermal properties of the PACs are extensively investigated. The developed PAC achieves the ultra-low density of 0.042 – 0.072 g/cm3 and low thermal conductivity values of 0.033 – 0.038 W/mK. The compressive modulus of the PAC with 1-cm cell size exhibits the compressive modulus of 15.30 MPa in the out-of-plane direction, and 0.070 – 0.128 MPa in the other in-plane directions. The stiffness of the PAC is up to 2,550x greater than that of the PA. As a result, the PACs can withstand high loads without the severe deformation of PA within the cell, maintaining its insulative structure and potential cooling capabilities. Aside from the radiative cooling potential, the added functionality also allows the PACs to be used as a conventional thermal insulator. The PAC is comparable to commercial Styrofoams and offers a promising alternative as an eco-friendly solution to such materials.