High-density short aspen fiber networks have similar tensile properties as networks from longer spruce fibers

• Peracetic acid produces aspen holocellulose fibers preserving hemicellulose in 5 h. • Short aspen fibers match spruce strength in high-density holocellulose networks. • Critical fiber length explains fiber dimension insignificance in dense networks. • High interfiber shear strength causes fiber fractures, not pull-out at failure. • Holocellulose networks offer potential for recyclability with minimal fiber degradation. Mechanical behavior of high-density oriented spruce and aspen fiber networks from mildly delignified holocellulose fibers is investigated. Such recyclable, eco-friendly fiber networks are of interest for molded fiber materials and biocomposites. The aspen holocellulose fiber network showed excellent mechanical properties comparable to spruce despite much shorter fiber length. This contrasts with lower density “paper” structures from short fibers which show lower strength than spruce fiber networks. Present results are explained by improved interfiber shear strength and reduced critical fiber length. Microstructures and damage mechanisms were analyzed for materials design purposes using FE-SEM, wide-angle X-ray scattering (WAXS) and tensile testing with strain-field measurements using Digital Image Correlation (DIC).