Biodegradable barrier coating on paperboard:Effects on biodegradation, recycling and incineration

Environmental demands set new pressure to packaging materials. Biodegradable coating is an alternative for polyethylene in barrier boards. In this experimental study boards with biodegradable coatings were compared with uncoated and LDPE coated board by evaluating their biodegradation potential and also considering their potential in waste reduction through recycling and incineration processes. The biodegradation potential was studied in a soil burial test. The results demonstrate that under tropical conditions uncoated paperboard samples degrade fast (in less than two months) when there is a good contact with the soil that contains nutrients, organic material and has a suitable pH. It was found that the biodegradable coating materials degrade but at a considerably slower rate than the fibrous base board. The degradation of the coating layer take place very locally, possibly initiating at some local grooves, pores or cracks in the coating. When the microorganisms reach the base board then the degradation proceeds in the base board at an accelerated pace. The biodegradability of coating materials gives an additional option in waste management. However, the high water vapor transmission values of these materials mean that thicker coating layers are needed, and this - together with the higher price of biodegradable polymers - may escalate the production costs. The barrier coated boards, without exception, were found to be recyclable; and after recycling the fiber and paper quality properties were comparable with those of the uncoated sample. But the heat value of the polyethylene coating was much higher (more than double) than heat values of the biodegradable barrier coatings. These facts imply that in short term the biodegradable coatings will have difficulties to find profitable applications in paperboard packages, especially if legislation is emphasizing the recycling and incineration options in waste treatment. However, developments in biopolymer science and in barrier coating formulations during the last years together with the increasing oil price promise more effective coating structures and better price competitiveness in the future for the barrier coatings