Harnessing total chemical-free paper and packaging materials barrier properties by mechanical modification of cellulosic fibers for food security and environmental sustainability

Surging interest in finding sustainable alternatives for single-use plastics has galvanized research into cellulosic fiber-based paper and packaging materials. This investigation examines mechanical (refining & calendering) approaches to enhance paper's barrier properties comprising Southern bleached hardwood kraft (SBHK) and Southern bleached softwood kraft (SBSK) fibers. With increased refining intensity followed by calendering, paper thickness decreases while the apparent density increases. The refining process also generates more fibrils and fines, as reflected by reduced pulp freeness. Air resistance increases significantly due to denser fiber networks and reduced porosity. Refining also improves the water vapor transmission rate (WVTR) and oil & grease resistance (OGR). A 48 % reduction in WVTR and a Kit "9″ rating for OGR were observed in SBHK paper sheets refined at 16000 revolution. Notably, refining modifies cellulose fiber morphology, promoting 59 % and 94 % external fibrillation in SBSK and SBHK fibers, respectively. This change facilitates a more compact fiber arrangement, enhancing barrier properties. XRD patterns show an initial increase in cellulose crystallinity with refining, decreasing at a higher revolution of refining. SEM analysis reveals decreased surface roughness and pore fraction post-calendering, enhancing air and OGR. In a relative sense, hardwood fibers showed higher barrier performance than softwood fibers. Our work demonstrates mechanical modifications of fibers and paper web can effectively tune paper barrier performance such as WVTR, OGR, and air/oxygen resistance.