Inhibition of hornification in simao pine fibers and recycled paper with different beating degrees by microwave expansion treatment

Abstract Pulp and paper industry, though vital, strains forest resources, highlighting the importance of alternative materials and waste paper recycling. This study explores how beating degree and microwave expansion affect Simao pine fibers and recycled paper. Beating damages fiber cell walls, enhancing water-related and fibrillation abilities, increasing fine fiber content and water retention, and boosting paper tensile strength (from 11.5 kN/m at 13°SR to 48.45 kN/m at 62°SR), but over-beating weakens fibers. More recycling cycles reduce mechanical strength (except tear index). Microwave expansion improves fiber water retention and fine fiber content; 13°SR un-beaten fibers see 49.34 % more fiber-fiber bonds. Recycled paper with microwave-expanded fibers has stronger bonds. For example, 24°SR microwave-expanded paper after three cycles has 39.83 % higher tensile strength than conventional paper, and secondary expansion makes 13°SR paper after three cycles 51.82 % stronger. The study, by reducing hornification via microwave puffing and improving fiber water retention, provides theoretical and technical support for better waste paper recycling efficiency.