The quality of raw materials required for the production of particle board is one of the key factors that determine the quality of particle board products.
Influence of raw material types
Generally speaking, compared with non-wood plant raw materials, wood raw materials have high content of fibroblasts, good morphology, low content of extractions and ash, no pulp core and waxy layer, and commonly used wood adhesives can achieve good gluing. It is used to make particle board. The physical and mechanical properties are better than that of non-wood plant fiber-based particle board.
Using wood from a single tree species as raw material, it is easier to master the control of flower quality, drying process and hot pressing process. Therefore, the performance of particle board manufactured is usually better than that of particle board products made from mixed tree species.
The scraps in the production of small-scale logs and plywood can prepare high-quality shavings. Compared with branch wood and sheet wood, the bark content is low, and compared with factory shavings and sawdust, the shavings have good shape and long fibers. Therefore, the quality of the particle board manufactured by it is better.
Influence of chemical composition of raw materials
The most important thing in the chemical composition of raw materials is the content of cellulose .Cellulose is the skeleton that makes up various fibers and determines the mechanical strength of various fibers .The high cellulose content of the raw material means that the product has good water resistance and high mechanical strength.
Hemicellulose has a low degree of polymerization, low strength and high hygroscopicity .Hemicellulose hydrolyzes to produce monosaccharides, which are easily coked by heat during hot pressing, resulting in a sticky plate phenomenon, which degrades the quality of the plate.
The strength of lignin itself is not high, but lignin has good water resistance, high heat resistance and good plasticity .Lignin can undergo a condensation reaction, and when it is hot pressed, it can act as a glue like an adhesive.2.3.3 Wood
Effects of density and intensity
The density of wood directly affects the quality of the board .In the case of the same quality of particle board, low-density wood is larger than high-density wood .In the case of the same glue type and amount of glue, when the same hot pressing process is used to make boards of the same density, the compression ratio of low-density wood is greater than that of high-density wood, which increases the contact area between the shavings. Therefore, boards made of low-density wood have higher strength .However, in the above cases, low-density wood is tightly compressed and has a large potential deformation capacity. When the board absorbs water or moisture, its expansion and deformation will be relatively large.
The strength of the wood itself has a great impact on the strength of the sheet .In the process of using the board, in most cases it is subjected to static bending/bending force, which is basically manifested as tensile and compressive deformation. In addition to the factors of adhesive and plate structure, under the same density, the board made of high-strength wood has high strength.
The structure of the wood also has a certain influence on the strength of the board .Generally under the same process conditions, finely constructed wood can be processed to produce smooth and flat shavings, which can distribute the adhesive to a greater extent on the surface of the shavings; however, wood with coarse structure can often only obtain rough and porous shavings, so that too much adhesive penetrates into the inside of the shavings, reducing the gluing strength.
Effect of extract and pH
Under the action of water and heat, some extracts from the wood will appear on the surface of the shavings. Some of the ingredients can improve the water resistance of the product, but some ingredients will affect the gluing, thereby affecting the quality of the product .For example: extracts such as resins, gums, triterpenoids, waxes, etc. will reduce the adhesion and adhesion of the adhesive, resulting in reduced mechanical properties of the product, but will improve its water resistance; Ligninphenol can improve the product’s corrosion resistance, insect resistance and mildew resistance; volatile oils can easily cause the product to bubble during hot pressing.
The pH of wood has little effect on the performance of the product, but it has a significant impact on the curing speed of urea-formaldehyde resin glue .When the pH value of the raw material changes greatly, if the fixed amount of curing agent and the hot pressing process conditions are still used, the quality of the particle board will be directly affected, and waste products may even appear.