Creating bulky papers with hydroxypropyl methylcellulose.

High bulk papers are attractive because they use less pulp but achieve properties suitable for applications in tissue, filters, and lightweight packaging. This study explores using hydroxypropyl methylcellulose (HPMC), a low-cost and renewably-sourced cellulose derivative, as a surface modifier for mechanical pulps to enhance paper properties. Two application methods were investigated: (1) pre-treatment by adding HPMC to the pulp dispersion and (2) post-treatment by spraying HPMC solution onto paper. Both pre- and post-treated handsheets exhibited improved tensile index and bulk concurrently, which is rarely observed. HPMC adsorbed to the fibre surface spontaneously improving fibre–fibre bonds through polymer entanglement, which led to higher tensile properties. Higher bulk values resulted from preventing fibre collapse during drying (i.e., maintaining open fibre lumens), attributed to the surface activity of HPMC and reinforcement of the fibre cell wall (supported by reduced kinks and curl index upon HPMC adsorption). X-ray tomography showed non-collapsed fibres and symmetric structures in handsheets from fibres pre-treated with HPMC, also suggesting improved cell wall strength and fibres that resisted pressure gradients. These findings indicate that HPMC as a paper additive is a practical and sustainable approach to reinforcing paper products, offering an alternative to high energy refining and oxidizing agents. This approach challenges the traditional trade-off between tensile index and bulk in pulp refining, emphasizing the potential of HPMC as a "green" surface modifier to enhance the strength of bulky papers. [ABSTRACT FROM AUTHOR]