A sandwich panel with a high ratio of strength to weight is commonly used in aerospace, construction, packaging and other fields. Using a renewable material such as wood to make sandwich panels can achieve a perfect unity of material and structure. In view of the lack of systematic analyses of wood-based sandwich panels, this work reviewed the development of wood-based sandwich panels. Based on the core structure, these panels can be divided into hollow-core structures and solid-core structures. With the emergence of new materials and new technologies, new wood-based sandwich products had been created. However, the current research only focused on the manufacturing, and the related novel design was still lacking. This work put forward a research idea of bionic design based on the integration of structure and function and pointed out the research direction for wood-based sandwich panels.
In this paper, the art-of-the-state of heat-induced inkless eco-printing (HIEP) technology in recent years was summarized and prospected, mainly from the printing effect, degree of carbonization, environmental impact and feasibility. The main results were as following: (1) The paper used in HIEP is predominantly yellow in color, which enables a practical printing effect. (2) After HIEP, the paper exhibits no significant carbonized microstructure and keeps its high strength. (3) HIEP is an ecologically and environmentally preferable technology. Only a small amount of toxic products is generated, and no carcinogens are emitted. (4) No significant damage to the paper is evident following HIEP, as the degree of heat experienced during HIEP is far below that experienced during a thermogravimetric (TG) experiment. Additionally, the evaporated water has a buffering effect. Based on the previous research results, this paper finally pointed out the possible research direction in terms of discoloration mechanism and printing effect, environmental impact improvement, paper damage mechanism and strength during HIEP, high-temperature printing head installation and relevant techniques, optimization of printing process parameters.
To explore the feasibility of hem-fir for CLT products, this work addressed the exploratory and pilot plant studies of hem-fir cross-laminated timber (CLT) products through mechanical tests. The hem-fir lumber was procured and then stress-graded based on dynamic modulus of elasticity (MOE). The resulted 5-ply prototype CLT products were then tested non-destructively and 3-ply pilot plant hem-fir CLT was tested destructively. The results showed that bending performance of hem-fir CLT panel can be predicted. Considering cost-competitiveness and end applications of hem-fir CLT products, the panel structure can be optimized based on the stress-graded data of hem-fir lumber.