Design, Fabrication And Performances Of Lightweight And Strong Artificial Wood Via Directional Freezing

The development and progress of human civilization is closely related to our recognition and utilization of materials.Mankind has increased the research and utilization of functional materials with the development and progress of modern science and technology,but we have never slowed down the study of structural materials.In the process of exploring and utilizing structural materials,we noticed that under the same mechanical condition,the lightweight structural materials can more effectively reduce the cost and energy consumption,and this is the most important significance.Wood,which is made up with oriented channel,is the most representative of lightweight materials with high strength in nature.The unique anisotropic structure on the one hand reduces the apparent density and thereby improves the specific strength;on the other hand,it endows the excellent thermal insulation capacity in the direction perpendicular to the channels and so woods have always been widely used as building materials until today.This natural lightweight and strong material has always attracted the attention of scientists.In order to imitate the structure of natural wood,scientists have developed a variety of new technologies,such as unidirectional freeze casting and so on.In this dissertation,we will focus on the development of wood-like structure.Firstly,preparation and assembly methods of lightweight and high-strength materials including unidirectional freeze casting technology are reviewed.Secondly,the control theory and method of ice-templated technology are mainly discussed.Finally,on this basis,we developed a method for the preparation of resin-based artificial wood by using unidirectional freeze casting technology.Results of the study are as follows:1.A new technique of unidirectional freeze-casting for polymer sol system was developed,and a new artificial wood material was designed and fabricated.We used two resins,water-soluble thermosetting phenolic resin and commercial water-soluble melamine resin as the matrix,chitosan sol was used as framework.Freeze-casting and freeze-drying processes were successively applied to the homogeneous solution of resin and chitosan sol to obtain the resin cryogel.After curing process,we successfully prepared the resin-based artificial wood material.The oriented channels are retained perfectly due to the strong electrostatic interaction between resin and chitosan sol.Meanwhile,we systematically studied the effects of various parameters such as resin content,freezing initiation temperature,freezing and cooling rate and curing temperature on the structure and mechanical properties of the prepared artificial wood materials.It also provides detailed technical guidance for the preparation of other polymer-based artificial wood material with aligned channel structure.2.The comprehensive performances of the novel artificial wood materials were systematically tested and analyzed.The results of the mechanical performance test of the resin-based artificial wood with different densities showed that the mechanical properties of the lightweight and high-strength materials prepared by unidirectional freeze casting method are much higher than those of the ceramic materials prepared by the same method,and the performance is comparable to that of the general wood.In addition,through the vertical combustion test,limit oxygen index test,thermal conductivity test and water resistance test,we found that the resin-based artificial woods display a more excellent thermal insulation performance and water resistance performance compared to natural wood.