Recycling without Fiber Degradation-Strong Paper Structures for 3D Forming Based on Nanostructurally Tailored Wood Holocellulose Fibers

摘要

Cellulosic paper products based on sustainable resources are of interest as a replacement for petroleum-based plastics, for example, in packaging applications. Improvements are desired for mechanical performance, recyclability, and possibilities to shape fiber networks into complex geometries. Commercial bleached wood fibers from the kraft process have insufficient mechanical properties for many applications, even with beating and additives. In addition, mechanical properties of paper structures are significantly reduced after recycling. Here, recycling and 3D shaping performance of holocellulose fibers are compared with kraft fibers and investigated in the context of wood fiber tailoring for eco-friendly materials. Holocellulose fibers from wood are prepared by mild peracetic acid delignification for well-preserved nanostructures and hemicellulose content (28 wt %). Paper structures of about 50% porosity are prepared from both types of fibers by vacuum filtration and drying. Mechanical tensile tests are performed, and fracture surfaces are investigated. The effects of recycling on the fiber structure (chemical composition, morphology, and crystallite size in fibers) and mechanical paper properties are reported. 3D-shaping performance is studied using compression molding with a double-curved mold. Holocellulose paper structures showed much better mechanical properties than kraft fiber paper (Young's modulus 10 GPa, ultimate tensile strength 100 MPa), as well as better recycling performance (only 26% decrease in strength after 5 cycles) and 3D formability. The well-preserved cellulose and hemicellulose components are important, as well as the homogeneity of the fiber cell wall nanostructure. This preserves the intrinsic mechanical properties of fibers, reduces hornification effects, and provides strong interfiber adhesion. Furthermore, the water-soluble hemicelluloses present at the cellulose-cellulose interface are able to facilitate recycling and 3D forming.