Chemical Modification
Advanced barrier performance in specialty packaging papers often requires the selective activation of cellulose fibres before applying protective coatings. Through epoxidation pretreatment, manufacturers introduce highly reactive oxirane rings onto the polysaccharide backbone of the pulp. This chemical alteration provides active sites for subsequent grafting of water-resistant polymers and bio-based barrier materials.
Processing mills use this step to enhance the affinity between hydrophilic wood fibres and hydrophobic barrier coatings.
Reaction Mechanism
The chemical process involves reacting cellulose with an epoxidizing agent under controlled temperature and pH conditions. Typically, hydrogen peroxide and an organic acid are mixed with the pulp slurry to generate peroxy acids in situ. These reactive intermediates attack the hydroxyl groups of the cellulose, converting them into functional epoxide groups.
The reaction must be monitored carefully to prevent excessive degradation of the fibre length, which would reduce the tensile strength of the paper. Neutralization and thorough washing follow to remove any remaining chemical residues.
Substrate Performance
Modified fibres demonstrate superior barrier adhesion and wet-strength properties in the finished paperboard. This enhanced bonding prevents the delamination of barrier films when exposed to high humidity. It also increases the grease resistance of the paper, making it suitable for food wrap.
Converting lines can run at higher speeds due to the improved surface uniformity.
