Cellulose sandwich composites with tube-reinforced foam cores

Lightweight porous cellulose materials, in particular pulp fibre foams, face challenges in achieving suitable mechanical efficiency while maintaining sustainability. Porous cellulose structures were developed by inserting high-density pulp fibre cylinders into the pre-perforated pulp fibre foam to form a sandwich structure with kraft liner paper deck sheets using a simple and scalable manufacturing process. The resulting porous cellulose composite structures, with densities ranging from 80 kg/m 3 to 177 kg/m 3 , were mechanically characterised under compression, three-point bending, and double lap shear loading. We demonstrate that tube-reinforced configurations outperformed perforated pulp fibre foams in stiffness and strength, showing a significant improvement of 10,300% in compressive, 1500% in flexural, and 350% in shear modulus compared to perforated pulp fibre foams. We showed that the mechanical performance of pulp-based materials can be controlled by structural design rather than material modification, providing a viable strategy to overcome mechanical limitations of cellulose fibre foams.