According to IKV, the market potential of PP and PLA is restricted in the beverage packaging sector due to high oxygen and carbon dioxide permeability. So the institute has initiated a research project to investigate transfer of existing plasma barrier coating technologies used for PET to these alternative materials.

There are great demands on the plasma coating process due to the different surface properties of PP and PLA, meaning achieving successful results requires good pre-treatment and an understanding of suitable bottle geometry, says IKV.

IKV has already carried out some initial trials on half-liter PET, PP and PLA bottles supplied by Coca-Cola Co., Milliken Chemical and SIG Plasmax. Effective barriers were obtained using both hydrocarbon and inorganic silica-based plasma coatings, with IKV citing oxygen barrier improvements by a factor of 12 with PP and 4 with PLA.

These first evaluations show that it is possible to raise the barrier performance of PP and PLA bottles to match the levels obtained with uncoated monolayer PET types.

The institute says that plasma-coated PP and PLA bottles could substitute at least some of the PET bottles currently in use, although further research work is required to determine an efficient means of production.

Plasma coating is not new to IKV. The instituteā€™s researchers presented a machine concept for a stretch blow moulding vacuum coating module for outer coating of PET bottles using microwave-excited plasma polymerisation back in 2006. Tests at that time had shown that carbon dioxide barrier properties could be improved by a factor of 3.3.

IKV has also developed the use of optical emission spectroscopy as an online quality assurance tool for the plasma coating barrier process. It had maintained that lack of suitable systems to monitor plasma technology had prevented it from reaching its full potential.