1、 Determination of bleach for bleached poplar face veneer:
Because wood bleaching is achieved through oxidation and reduction reaction, the compounds with oxidation or reduction have bleaching effect. Reducing bleaching agents mainly include nitrogen containing compounds, inorganic sulfur containing compounds, organic sulfur containing compounds, acids, etc. This type of bleaching agent is less used to bleach poplar face veneer. Therefore, the most commonly used method of poplar face veneer bleaching is still the oxidation bleaching method with oxidants. At present, the most commonly used chemical agent for poplar face veneer bleaching is hydrogen peroxide.
2、 Bleaching mechanism of bleached poplar face veneer:
Peroxide hydrogen ions produced by hydrogen peroxide dissociation have strong oxidation capacity, which can make some colored genes in lignin, such as opposite brewing and adjacent brewing, oxidized and cracked to become colorless genes, thus improving the whiteness of poplar face veneer. The latest quotation for poplar bleached flour is today.
3、 Bleaching process of bleached poplar face veneer:
1. Alkali treatment of bleached poplar face veneer
Pretreatment with alkali liquor is the first stage of poplar face veneer bleaching process, which mainly plays the following roles:
First, it can purify veneer and eliminate stain and stain on wood surface;
Second, a considerable part of resin and soluble colored substances in wood can be extracted in alkaline solution, which is conducive to reducing the consumption of bleach in the main bleaching process;
Third, increase the permeability of monopoles by swelling cellulose and hemicellulose. The concentration of lye can be determined by the degree of dirt on the veneer surface and the level of wood content.
2. Bleached poplar face veneer washed and dried
In the process of alkali treatment, other impurities such as resin and organic acid dissolved in alkali liquor should be washed away repeatedly with a large amount of clean water, which can not only save bleaching agent, but also prevent the ineffective decomposition of hydrogen peroxide caused by some impurities on the surface of poplar face veneer.
3. Main bleaching of bleached poplar face veneer
The main bleaching is the most important stage in the bleaching process of poplar primary color skin. In this stage, through the oxidation of hydrogen peroxide, the conjugated double bonds on the side chain of lignin are broken, the chromophore group is broken, and the absorption spectrum moves to the ultraviolet light region, leading to the white or light color of poplar skin, so as to achieve the purpose of poplar skin bleaching.
4. Post treatment of bleached poplar face veneer
As the bleached poplar face veneer still retains unreacted hydrogen peroxide, other lye and additives, which affect the normal dyeing of poplar face veneer, a large amount of water must be used to thoroughly clean the poplar face veneer to neutral and then filter it dry. The latest quotation of poplar bleached dough today is between 2.5 yuan and 6 yuan per piece.
5. Drying of bleached poplar face veneer
For the convenience of use, the bleached poplar face veneer needs to be pasted with adhesive tape to prevent cracking and dried. The moisture content is generally controlled within 16% according to the use situation.
