Investigation of holocellulose, lignin, and plasticizer interactions and their effect on the thermoformability of plasticized kraft pulp studied by ssNMR, O-PTIR and SAXS/WAXS

Journal article, 2026

Plasticization-enhanced thermoformability in pulp materials could enable the replacement of fossil-based thermoplastics, but the process is still in its infancy, with many knowledge gaps. One such gap is how plasticizers of varying chemical structures distribute themselves within the pulp cell wall and what components - cellulose, hemicellulose, or lignin - they preferentially interact with. This gap has hindered a full understanding of how these compounds affect the thermoformability of the cell wall - a key factor in pulp molding. In this work, unbleached softwood kraft pulp was plasticized with glycerol and triacetin. Solid-state spin-transfer and relaxation NMR and optical photothermal infrared spectroscopy (O-PTIR) revealed differences in the molecular dispersion of the two plasticizers within the cell wall. Dynamic mechanical analysis (DMA) showed that the softening temperature of the pulp - the T-g of lignin - was reduced from 235 degrees C to similar to 120 degrees C with both plasticizers, allowing for thermal processing at non-degrading temperatures. X-ray scattering of pulp hot-pressed above and below the T-g revealed increased cellulose aggregation, but only with plasticizers was this observed without reduction in crystallinity. This indicates that deformation mechanism under hot-pressing was more plastic when plasticized and operated above the T-g of lignin.