Subcritical water for recycling of plastic waste (polyurethane)

Abstract

Polyurethane (PU) represents more than 7 % of global plastic production and is widely used in our daily life such as in sofa and mattress cushion, insulation, packaging, and many more applications. The proper end-of-life handling or disposal of the PU waste has become increasingly important considering the environmental impact of plastic waste. PU foam represents about 65% of the total PU, which is one huge PU type that needs to be handled properly to ensure sustainability of the resources and environment.

In this FYP project, subcritical water process has been used for treating ether and ester PU foam. This is done by using (i) high pressure reactor with heating and stirring function with the high pressure generated autogenously and (ii) hydrothermal Autoclave. The breakdown of the PU foam can be one way to minimize the large volume of the low-density PU foam, and at the same time potentially producing suitable products for subsequent reuse.

Different parameters have been used in studying the effectiveness of subcritical water treatment for handling PU foam waste within 200 to 275 ℃. For instance, the N–H bonds within solid PU Ether were broken down and more effective degradation of solid PU Ether took place once the reaction temperatures were higher than 225 °C. The subcritical water process can be effective to a certain extent in breaking down both ether and ester PU foam, with much better effectiveness for ether PU foam. Further optimisation of the subcritical water process parameters could further improve the breakdown of PU foam.