Detailed explanation of poplar veneer bleaching method!
Introduction: Because wood bleaching is achieved through oxidation and reduction reaction, compounds with oxidation or reduction have bleaching effect.
1、 Determination of bleach
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 wood. Therefore, the most commonly used method of wood bleaching is still the oxidation bleaching method with oxidants. At present, the most commonly used chemical agent for wood veneer bleaching is hydrogen peroxide.
Detailed explanation of poplar veneer bleaching method!
2、 Bleaching mechanism
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 split to become colorless genes, thus improving the wood whiteness.
3、 Bleaching process
- Alkali treatment
Alkali pretreatment is the first stage of the bleaching process of the dough (veneer). It mainly plays the following roles: First, it can purify the veneer and eliminate the stain and stain on the wood surface; Secondly, 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, through the expansion of cellulose and hemicellulose, increase the permeability of monopole The concentration of lye can be determined by the degree of dirt on the veneer surface and the level of wood content.
- Wash and filter dry
During alkali treatment, other impurities such as resin and organic acid dissolved in alkali liquor shall 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 veneer surface.
- Main drift
The main bleaching is the most important stage in the bleaching process of poplar primary color skin (veneer). In this stage, through the oxidation of hydrogen peroxide, the conjugated double bonds on the side chains of lignin are broken, the chromophore group is broken, and the absorption spectrum moves to the ultraviolet light region, leading to the veneer becoming white or light, so as to achieve the purpose of veneer bleaching.
Detailed explanation of poplar veneer bleaching method!
- Post processing
The bleached veneer still contains unreacted hydrogen peroxide, other lyes and additives, which affect the normal dyeing of the veneer. Therefore, a large amount of clean water must be used to thoroughly clean the veneer to neutral and then filter it dry.
- Drying
For the convenience of use, the bleached poplar 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.
