Minute Rebond: A simple method for making lab scale rebonded foam and its application as a novel soilless growing media

Polyurethane foams (PUF) utilised in the comfort industry generate substantial trim waste volumes requiring end-of-life management. Rebonding, one form of mechanical recycling, is a technique involving the mechanical breakdown and subse-quent adhesion of PUF using polyurethane prepolymers yielding a recycled material. However, the limited investigation into the properties of rebond PUF constrains its potential for novel alternative uses, such as soilless plant growing media, and new materials will need to be utilised to keep up with growing demand. Virgin PUF has been demonstrated to work as a growing media, so the recycling of current PUF waste into rebonds presents an opportunity to develop customisable up-valued materials for plant cultivation. A laboratory-scale rebond production method has been developed, and a series of re-bond PUF produced to evaluate the influence of crumb size, density, prepolymer chemistry and prepolymer loading on the properties of the rebond PUF and their suitability as growing media. Results indicated that higher quality rebonds were ob-tained with larger crumb sizes (mixed or > 7 mm), moderate amounts of prepolymer (4.5 to 7.5 % by mass) and higher den-sities. Density directly influenced plant growth-related properties, including airflow (which decreased with higher density), water uptake through wicking (which increased with density), and water retention through drainage (which increased with both density and larger crumb sizes [>7 mm]). These findings underscore density as a critical factor in the application of re-bonds as growing media. Eruca sativa plants were grown in three different rebonds at low, medium, and high density along-side a mineral wool control. Low density rebonds exhibited comparable growth (leaf length, leaf width and shoot fresh weight) to mineral wool, whereas medium and high density rebonds showed reduced growth. This study demonstrates the potential of rebond PUF foams as a viable growing media, which can be optimised using a laboratory-scale technique.