Flexible waterborne polyurethane nanocomposite foams incorporated with halloysites as fresh-keeping packaging inserts for fresh fruits

Food losses due to the deterioration of fresh fruits and related economic problems can be prevented by the use of active food packaging materials. Here, waterborne polyurethane (WPU)/halloysite nanotube (HNT) nanocomposite foams with ethylene and moisture absorption properties are presented, which can be inserted into existing food packages as fresh-keeping packaging materials for the improvement of the shelf life of fruits. WPU with moisture absorption properties has been utilized as a carrier for HNTs, which have a large capacity to absorb ethylene gas, the plant hormone responsible for the ripening of climacteric fruits. HNTs were incorporated into WPUs during a foaming process, resulting in open-cell foams with average pore sizes of 316 µm and a density of 0.136 g/cc. The resulting WPU-HNT foams were shown to absorb moisture by 7 % when they were incubated in a closed container of 100 % relative humidity for 14 days. The WPU-HNT foams were also demonstrated to absorb 2.5 ppm of ethylene gas per gram of foam when kept in a sealed container injected with 90 ppm ethylene gas for 3 days. Tomatoes stored together with the nanocomposite foams in plastic boxes at 4 °C for 14 days presented significantly higher firmness values than the tomatoes stored without the foams. Similarly, bananas stored in polyethylene bags containing the nanocomposite foam remained firmer and free of brown spots for at least 2 days longer than the bananas stored without the nanocomposite foam. The WPU-HNT foams have a strong potential as low-cost, environmentally friendly food packaging inserts that can prevent spoilage of fruits.