Technical lignins and their utilization in the surface sizing of paperboard

Technical lignins, which are the coproducts of the pulping industry, have a high potential for use in surface sizing of paperboard. We investigated the use of kraft lignin and lignosulfonate in surface sizing of paperboard with the target of understanding the influence of lignins on the development of strength and hydrophobicity. Prior to surface sizing, the lignins are purified by ultrafiltration and precipitation respectively. Strength properties and hydrophobicity of lignin-sized paperboard were measured and compared with references as well as with unsized paper. An increase in the strength properties of lignin-sized samples was observed, which was in the same range as references and at least 10% higher compared to unsized paperboard. Moreover, air permeability, hydrophobicity, and water absorptiveness were affected, and depending on the lignin art, an improvement was achieved. These results encourage partial or total substitution of conventional surface-sizing chemicals by technical lignins.