Mechanical and thermal stability improvement of cellulosic fiber products derived from waste poplar boards under UV irradiation via lignin retention

As a derivative of agriculture crops and forestry cultivated plants, cellulosic fiber product (CFP) is of much industrial interest deemed a promising alternative to wooden composites and plastics owing to the low environmental impact. The high-performance CFP was fabricated via a facile molding and hot-pressing process without using adhesives. The UV aging test was carried out to evaluate the physical and mechanical stability before and after delignification. The tensile strength was increased from 41.3 MPa to 53.7 MPa, and the flexural strength was increased from 72.3 MPa to 85.4 MPa as the lignin was removed from 11.7% to 3.0%. The holocellulose content and crystallinity of fibers were increased, and the fiber dimensions were correspondingly decreased after delignification. However, the delignified specimens exhibited a faster reduction in mechanical strength than that of lignin-rich products (e.g., 0.074 vs 0.041 in the slope rate of fitting curves) throughout the UV irradiation, and the thermal stability was also decreased from 317.2 ℃ to 311.3 ℃ in onset decomposition temperature due to the delignification. Moreover, the lignin-rich CFP was superior to that of typical plastics (e.g., PP and epoxy resin) and wooden composites (e.g., WF/PP) in mechanical and thermal stability under UV irradiation through the comparison.