Technological watch

Multilayer materials are frequently used in food and beverage packaging, delivering favourable properties for storage and protection. However, their complex construction, consisting of several layers of plastics, aluminium and paperboard (i.e., beverage cartons) makes them difficult for complete material recycling. Currently, the common treatment process used is hydropulping, resulting in partial recovery of the paperboard only. The so-called beverage carton reject fraction, consisting of plastics, aluminium, and some fibres, is incinerated for energy recovery, leading to the loss of secondary resources. Here a novel recycling procedure based on enzymatic hydrolysis of cellulose, followed by bioleaching of aluminium finally allowing recovery of pure polyethylene is presented. Application of a cellulase cocktail resulted in the release of 15 mM glucose within 24 h, followed by over 95% aluminium bio-extraction within 3–7 days using bacterially produced sulfuric acid. Dissolved aluminium could afterwards be completely recovered by selective precipitation at pH 6.4, resulting in the formation of aluminium hydroxide. Pure polyethylene at the end of the process was used in re-processing and film production, showing comparable results to commercially available materials. Additionally, scaling up in a 1 L stirred tank reactor proofed the feasibility of the process in reject recycling. With this innovative, environmentally friendly recycling method, maximum material recovery could be achieved, leaving a minimum of impurities for incineration (