**2.2 Plywood**

Plywood is generally made of rotary cut veneer or planed thin wood to adjacent layers of veneer fiber direction perpendicular to the group of blanks by the adhesive gluing into a multi-layer wood-based composite material, with a small

**Figure 4.** *Physical photograph of plywood.*

coefficient of deformation, excellent mechanical properties, etc. are widely used in construction, packaging, furniture, flooring, car, and shipbuilding industries, the physical photograph of plywood is shown as **Figure 4**. Over the years, plywood has been one of the leading products in China's wood-based panel industry. With the technological progress and industrial restructuring, the development of plywood industry has entered the key stage of transformation and upgrading, and valueadded function has become one of the important ways to increase the added value of plywood, expand its application areas, and enhance the competitiveness of plywood products.

The flammability of ordinary plywood has limited its application in many fields. At present, flame retardant plywood production methods are mainly immersion method, veneer lamination composite method, and surface coating method. Among them, flame retardant plywood is most commonly prepared by veneer impregnation process (**Figure 5**), which is mainly to impregnate veneer or plywood with flame retardant components by pressurized (or atmospheric pressure) method. The current research mainly focuses on the development of new environmentally friendly flame retardant with high impregnation efficiency, good flame retardant effect, small impact on mechanical properties and not easy to precipitate. In addition, in order to meet the more demanding practical application environment, the development of flame retardant multifunctional (aldehyde reduction, low smoke, mold, moisture,

**Figure 5.** *Preparation of flame retardant plywood by impregnation method.*

*Introductory Chapter: Engineering Wood Review DOI: http://dx.doi.org/10.5772/intechopen.112866*

**Figure 6.** *Preparation of electromagnetic shielding plywood.*

antibacterial, etc.) plywood is of great significance [9]. Using ammonium dicyanide, phosphoric acid, magnesium sulfate, boric acid (BX), and other compound treatment of plywood, heat release is significantly reduced by 91.9%, and smoke release is reduced by 76.8%. It has a certain anticorrosive and anti-mold function, while the formaldehyde release of the plywood was reduced by 82.3%.

In addition, electromagnetic shielding plywood is a veneer and electromagnetic shielding materials with electromagnetic shielding material using stacking, mixing, and flexible pressurization and other methods of preparation with the electromagnetic shielding effect of wood-based composite materials. Copper powder, nickel powder, graphite powder, and other conductive powder and iron fiber, copper fiber and other metal conductive fibers added to the adhesive can be used to prepare electromagnetic shielding plywood (**Figure 6**). The metallic copper fibers within a certain size range can effectively improve the electromagnetic shielding effect by increasing the amount of fiber coating and glue coating, which has some practical value. Increasing the amount of conductive material coating can improve the electromagnetic shielding efficiency but is not conducive to the strength of the glue. Metal conductive fiber is more conducive to improving electromagnetic shielding performance than conductive powder under the same amount of conductive material.

Ordinary plywood is susceptible to insect and fungal attack and decay, and its service life and scene are limited. After anticorrosive and anti-insect treatment, plywood has certain anticorrosive, anti-insect, and anti-mold effects, which in turn extends the service life of plywood. The use of impregnation method of horsetail pine and poplar veneer preservative treatment with ammolysis alkylamine copper, borate and different additives compound as preservative, after phenolic or urea-formaldehyde glue gluing can be obtained after a good anticorrosive effect of plywood. It was found that the average drug loading capacity of sound brewing ammonia-soluble alkyl turned horsetail pine and poplar wood preservation plywood was the highest, reaching 7.80 and 9.10 kg/m3, respectively, the average drug loading capacity of adhesive ammonia-soluble copper vanillylamine horsetail pine and poplar wood preservation plywood was 4.21 and 4.53 kg/ m3 , respectively, and that of UF adhesive BX poplar wood preservation plywood was 4.96 kg/m3 , respectively. The average boron retention rate of the phenolic adhesive glyoxal/propanetriol and BX compounded horsetail pine plywood and the phenolic adhesive glyoxal/propanetriol and borax (BA) compounded poplar preservative plywood were 45.52% and 49.38%, respectively, and the preservative plywood produced under the most favorable conditions could reach the strong corrosion-resistant grade.

#### **2.3 Fiberboard**

Fiberboard is an artificial panel made from wood fibers or other vegetal fibers, cured by hot pressing under the bonding action of adhesives; the physical photograph of the fiberboard is shown in **Figure 7**. Fiberboard has excellent comprehensive performance and is an important part of packaging, indoor furniture, and decorative materials. However, it is easy to burn and produces smoke and toxic gases when burning, which may lead to fire, and the toxic smoke will cause secondary injury to the human body in the fire, which will bring serious harm to people's living environment as well as personal health and property safety. Therefore, it is necessary to choose safe and harmless green flame retardant to modify fiberboard.

Inorganic flame retardants have the advantages of wide source, low price, environmental protection and safety, good flame retardant performance, and small toxic side effects when they play a flame retardant role, etc. They are the most widely used flame retardants at present and gradually become a hot spot of flame retardant research. Inorganic flame retardants mainly include boron flame retardants, phosphorus and nitrogen flame retardants, metal hydroxide flame retardants, and metal oxide flame retardants. Two borates such as BX and BA are the most commonly used flame retardants in the boron family of flame retardants, which have the advantages of low toxicity to humans and environmental friendliness [10]. Borates are widely used in fire protection because they reduce flame propagation [11]. In addition, the combined use of BX and BA has a synergistic flame-retardant effect [12]. However, inorganic flame retardants use the process of moisture absorption and loss and other shortcomings, and a single inorganic flame retardant is difficult to meet the application requirements, the use of the process is often used in a variety of composite, to obtain excellent performance of the flame retardant smoke suppressant.

In order to overcome the shortcomings of inorganic flame retardants, such as moisture absorption and loss, researchers have developed organic flame retardants on the basis of inorganic flame retardants. Organic flame retardants have good compatibility with the base material fiber and excellent anti-loss performance. Organic flame retardants mainly include organophosphorus and nitrogen, organophosphorus and boron, organophosphorus and nitrogen and boron. Due to the high production cost and unstable performance of organic flame retardants and other shortcomings affecting its application, the application of organic flame retardants in fiberboard research

**Figure 7.** *Physical photograph of fiberboard.*

has rarely been reported, and more organic flame retardants and inorganic flame retardants composite, the preparation of better performance of the flame retardant.

### **2.4 Oriented strand board**

OSB is a kind of wood structural board made from small diameter timber, mesquite timber, wood core, and other raw materials, after slicing, drying, gluing, oriented paving, hot press molding, and other processes, with high strength, high bending strength, good nail grip, less glue, less formaldehyde emission, anticorrosive, anti-moth-eaten, anti-deformation, heat insulation, sound insulation properties, etc. The physical photograph of OSB is shown in **Figure 8**. OSB can be used to replace structural plywood in applications. OSB can replace structural plywood in applications, but compared with structural plywood, the process of obtaining structural units through the planing process makes it less demanding on raw materials, so the raw material sources are more extensive. At the same time, in the OSB manufacturing process, the wood utilization rate is high, up to more than 80%, which can efficiently utilize the wood and achieve the purpose of "inferior wood, better use". With its excellent overall performance, OSB is used as a building panel in Europe and the United States for flooring, wall panels and structural support materials, and is now also used in the wood packaging sector, mainly for packaging pallets and container floors. In China, OSB is mainly used for furniture and interior decoration, commonly used as door frames, shelves, and interior wall panels.

The main research focuses on the theoretical and experimental studies of various processes in the OSB preparation process, including the influence of particle lay-up on the mechanical properties of the boards, the study of OSB lay-up structure and sectional density, the theory of bonding interface between particles and adhesive in OSB, the modeling study of OSB processing and expansion, and the influence of adhesive and its dosage on the overall performance of OSB [13, 14]. In addition, it also includes the modification of OSB by adding borate, the improvement and optimization of hot pressing process parameters, the optimization of directional paving process, the research and development of OSB adhesive for broadleaf timber, and the improvement of particle production process, etc.

Comprehensive analysis of the current research situation can be found; the current OSB research has achieved great results. Researchers on OSB manufacturing

**Figure 8.** *Physical photograph of OSB.*

process of raw materials and basic process parameters for a more in-depth study; but at the same time should also be noted that, compared with other wood-based panel products, OSB research is still somewhat insufficient but also need to continue to strengthen the research on the theoretical and practical aspects of the two.
