A Study on Lignin or Zein Based Hydrophobic Coatings

Abstract: The two by-products lignin, from the paper industry, and zein, from starch production, have shown potential as hydrophobic barriers. Therefore, this study has aimed to produce and in-vestigate the hydrophobicity of lignin or zein dispersions coated on paper. The lignin coatings were made from softwood (spruce) and hardwood (birch) lignin that was extracted using hy-drotropic extraction (HEX) and milled wood lignin (MWL) extraction. The lignin was then dissolved in acetone and spray coated onto paper. In the zein dispersions, zein was dissolved in either ethanol (EtOH) or acetic acid (AcOH). In two of the zein coatings, glycerol was add-ed as a plasticiser. For the lignin coatings, no difference in hydrophobicity was found between softwood lignin and hardwood lignin. The MWL coatings gave the highest contact angle (CA), birch 107° and spruce 106°, and the lowest cobb value of around 37 g/m2. However, none of the lignin coat-ings showed potential as a water vapour barriers as all the coatings had high water vapour transmission rate (WVTR) values of around 1300 g/(m2 day). The paper that the coatings were applied to had high water CA and low moisture uptake. This makes the success of the MWL more difficult to establish. The zein coatings did not give hydrophobic CA except for the dispersion containing 15wt% zein in EtOH (the highest value being 90°). However, it was found that some zein dispersions had a better water vapour barrier compared to the lignin dispersions and 10wt% zein in AcOH plasticised with glycerol had a WVTR value of 89 g/(m2 day) and 10wt% zein in EtOH had WVTR value of 710 g/(m2 day).