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The imbalance between timber supply and demand is a prominent issue in the interior decoration and furniture industries, including wood products. In 2016, the output value of China's furniture industry, including large-scale enterprises, reached 856 billion yuan, of which wooden furniture accounted for approximately 64%. Annual demand for timber from the wood products industry alone exceeds 100 million cubic meters. However, my country's current dependence on imported timber is approaching 50%, exceeding the critical threshold. With increasing global attention to environmental protection, more precious tropical species will be listed under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), and imports of high-quality timber will become increasingly scarce. Therefore, developing new technologies for the processing and utilization of softwoods, addressing the challenges of using plantation timber for interior decoration, furniture, and other wood products, and replacing high-quality and precious timber with plantation timber, is an important approach to resolving this imbalance in timber supply and demand.
Plantation timber grows rapidly, but it suffers from shortcomings such as softness, low density, high variability, poor dimensional stability, and poor surface finish. These drawbacks significantly limit its application, particularly in solid wood furniture production. Therefore, softwood modification and enhancement techniques have become a key research topic in plantation timber processing and utilization.
Solid wood compression densification technology can significantly improve the physical and mechanical properties of wood and is an effective method for physical modification of wood. Traditional compression densification methods soften low-density wood as a whole and then increase its density by compressing it with a press plate. This involves compressing and densifying the solid wood or board as a whole. This method's most prominent drawback is the significant loss of wood volume.
The solid wood layered compression described in this article is a new type of wood physical modification technology, which can also be called solid wood layered compression enhancement technology under hydrothermal control. Using this new technology, the parts that need to be strengthened can be compressed and enhanced selectively, while the remaining parts can still basically maintain the inherent natural properties of the wood. This achieves precise controlled compression of the wood, greatly reduces the loss of wood volume, and opens up new directions for the utilization of low-density wood.
1. Research and Development Progress of Solid Wood Layered Compression Reinforcement Technology
Research on layered compression reinforcement technology for solid wood began with an accidental discovery during experiments in 2010: compressed, densified wood obtained under specific experimental conditions exhibited a distinct high-density layer, formed in the center layer of the solid wood board. Repeated experiments and verification confirmed the repeatability of this phenomenon. Theoretically, if a compression layer can appear in the center layer, it should be able to appear at any level through the thickness. Following this basic idea, the research team conducted systematic research on the formation mechanism of layered compression, the density distribution of layered compressed wood, color changes, surface hardness, wood hardness, bending strength, elastic modulus and other physical and mechanical properties, as well as dimensional changes in the hygroscopic state, and the fixed parameters of compression deformation under normal pressure heat treatment and pressurized heat treatment, thus forming a complete theoretical system for layered compression reinforcement.
Building on fundamental theoretical research, the company further developed pilot trials, large-scale production trials, and the development of large-scale product processing technologies. This established a system for layered compression technology for a variety of low-density, fast-growing timbers, including both softwood and hardwood. The company then collaborated with businesses to develop products such as solid wood flooring, office furniture, and home furniture. Laboratory and pilot trials were conducted at the Experimental Center of the Wood Industry Research Institute, Chinese Academy of Forestry. Large-scale production trials with an annual output of 100,000 to 400,000 square meters and the processing of layered compressed wood products were completed at six companies, including Jiusheng Flooring Co., Ltd. A dedicated exhibition area was established at Jiusheng Flooring Co., Ltd.'s exhibition hall.
So far, 9 patents have been applied for, of which 2 invention patents and 1 utility model patent have been authorized, 2 invention patents have entered the substantive examination stage, 3 new invention patents and 1 utility model patent have been applied for, 1 achievement has been recognized by the State Forestry Administration, 1 second prize of the Liang Xi Science and Technology Award has been won, and many graduate students have been trained.
2. Technical characteristics and product performance of solid wood layered compression
After more than seven years of continuous research and exploration, we have achieved innovative breakthroughs in the formation of the compression layer, precise control of the position of the compression layer, precise control of the thickness of the compression layer, fixation of compression deformation, development of production equipment and continuous production methods of layered compressed wood.
Solid wood layered compression reinforcement technology and its products have the following characteristics:
1. Low compression rate and minimal volume loss. For low-density plantation wood (less than 0.5g/cm³), traditional overall compression methods for densification and reinforcement require compression rates of 50% or higher to meet the requirements for use in solid wood furniture, flooring, and other materials. This high compression rate and high cost are problematic. Solid wood layered compression reinforcement technology compresses only the areas requiring reinforcement, leaving the rest largely uncompressed. While maintaining performance that meets product requirements, the compression rate can be reduced to below 20%, only 40% of that achieved with traditional overall compression methods, effectively reducing volume loss.
3. The processing and products are environmentally friendly. Layered compression is a physical modification of wood. The process is completed under hydrothermal control without the addition of any chemicals. It is pollution-free and emission-free, and basically maintains the original natural properties of wood. Compared with other wood composite materials, it is environmentally friendly.
6. Low processing costs. The production process for laminated compressed wood is simple, with processing costs primarily consisting of wood compression loss (which can be controlled below 20%), energy costs for heating and cooling the press, and labor costs (on an automated production line, only one person is required per press plus material transport personnel). The trial production costs for a laminated compressed wood production line with an annual output of 300,000 m2 include 10 yuan/m2 of heat source consumption during compression and 15 yuan/m2 of drying and pressurized heat treatment costs. Compared to currently popular and relatively inexpensive solid wood panels such as mangosteen, birch, and oak, laminated compressed reinforced wood offers significant price advantages (Table 1).
Table 1 Cost analysis and comparison between laminated compression reinforced wood and common solid wood flooring materials
7. Wide range of applications. Layered compression reinforced wood offers high dimensional stability and surface hardness, requiring no special painting processes, and its performance is nearly equivalent to that of high-quality hardwood. It can be directly used in the production of solid wood flooring, antique-style flooring, and floor heating systems. After sanding, it has a texture similar to precious hardwood and can be processed into exquisite, high-quality solid wood furniture. When processed into cross-jointed boards, it can replace fiberboard and particleboard without the need for veneer and can be used directly in the production of panel furniture. After shaping, it can be directly used to produce cabinet bodies and doors for pure solid wood cabinets.
3. Social, Economic and Environmental Significance
In his report to the 19th National Congress of the Communist Party of China, General Secretary Xi Jinping proposed establishing and improving a green, low-carbon, circular economic system, building a market-oriented green technology innovation system, and fostering a spatial pattern, industrial structure, production methods, and lifestyle that conserves resources and protects the environment. The development approach for solid wood layered compression technology is highly consistent with the green environmental protection philosophy put forward at the 19th National Congress of the Communist Party of China. This is specifically reflected in the coordinated development of resource conservation and environmental protection achieved through the application of high-quality physical modification technology for plantation wood, the environmental friendliness of the modification technology and products, and the need for industrial upgrading.
Planted forest timber is renewable and multifunctional, carrying enormous potential for ecological industries and a recyclable forest products industry. According to the results of the Eighth National Forest Resources Inventory, my country's planted forest area reached nearly 69.33 million hectares, ranking first in the world. By fully utilizing my country's abundant planted forest timber resources and through technological innovation, we can improve the quality of planted timber and reduce timber processing costs to meet the growing market demand for solid wood furniture and other wood products, while also promoting the development, transformation, and upgrading of my country's wood product processing industry.
Solid wood layered compression reinforcement technology is applicable to all low-density woods. After modification, the material's performance is enhanced, transforming woods previously characterized by low density, soft texture, and poor dimensional stability into excellent processing and usability, allowing them to be directly used in wood product manufacturing. This technology provides a technical platform for using low-quality plantation wood in solid wood furniture manufacturing, increasing the added value of low-quality plantation wood by over 50%. This can effectively alleviate the shortage of high-quality hardwood lumber in my country and reduce dependence on imported wood. Upon completion, the project will establish a comprehensive intellectual property system encompassing technologies, patents, and standards, which will enhance the market competitiveness of my country's furniture industry and promote industrial upgrading and product upgrades for furniture companies.
During the implementation of the project, we will cooperate with leading companies in the industry to carry out productive demonstration, promotion and radiation, so that the research results can be effectively applied as soon as possible, and provide technical support for the transformation and upgrading of the furniture industry.
The promotion and application of this technology has broad social, economic and environmental significance.
1. It will help address timber resource shortages. The latest appendix to the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), which came into effect on January 2, 2017, increased the number of endangered wild tree species prohibited from import and export to over 260. This includes many high-density, valuable hardwoods closely related to the wood products industry, leading to a further shortage of wood for solid wood flooring and furniture. Furthermore, the complete logging ban on natural forests in China has further reduced the availability of domestically produced wood for flooring and furniture. Leveraging my country's abundant plantation timber resources and physically modifying it through solid wood layered compression reinforcement technology to achieve performance levels that meet the requirements for manufacturing high-quality solid wood furniture, flooring, and other wood products is an effective way to address resource shortages for solid wood flooring and furniture.
2. It helps meet market demand for wood products. With the continuous development of the economy and society and the improvement of people's living standards, the market demand for solid wood products is growing, and the requirements for the environmental performance of materials are becoming increasingly stringent. Solid wood layered compression reinforcement technology uses a physical modification method without any chemical additives during the processing process, completely solving the formaldehyde emission problem of traditional wood composite materials. Layered compressed wood has high dimensional stability, effectively overcoming the deformation problem of solid wood floor heating, and has a positive impact on the development of the floor heating floor industry.
3. It will promote plantation cultivation and increase forest farmers' income. Low-density wood can be directly used for furniture and flooring, providing a new avenue for the utilization of fast-growing timber. This will stimulate market demand for large-diameter plantation timber, thereby promoting the cultivation of timber plantations and increasing forest farmers' income. This will play a positive role in targeted poverty alleviation, achieving a moderately prosperous society in all respects.
Author profile: Huang Rongfeng, researcher at the Institute of Wood Industry, Chinese Academy of Forestry.