With the gradual improvement of living standards, people's health awareness of indoor ambient air quality has gradually increased, and the demand for environment-friendly plywood and green home has increased, which has driven the development and production of low formaldehyde and formaldehyde free products in the industry, formaldehyde removal methods and products such as formaldehyde adsorbents and capture agents.

At present, according to the aldehyde removal methods and the plywood process stage, the aldehyde reduction or aldehyde removal methods of plywood and its products can be roughly divided into three categories, namely, source control, process control and finished product post-treatment, which are classified in this paper for industry reference.

01  Plywood Source control aldehyde removal

Source control formaldehyde removal is to solve the problem of formaldehyde release from plywood in terms of raw and auxiliary materials such as adhesives, additives, decorative paper, etc. used in plywood production, mainly including the research and development and application of formaldehyde free additive adhesives (hereinafter referred to as formaldehyde free adhesives), adhesives with low free formaldehyde content, non aldehyde additives, low free formaldehyde impregnated adhesive film paper, etc.

01-1 aldehyde free adhesive

The research and development and technological innovation of formaldehyde free adhesives are the research focus of plywood industry. At present, formaldehyde free adhesives that have been put into industrial use mainly include isocyanate adhesives, soy protein adhesives, starch adhesives, lignin adhesives and thermoplastic resin adhesives. Among them, isocyanate adhesive is the most mature and widely used formaldehyde free additive adhesive in plywood production.

01-2 Research and development of formaldehyde free decorative paper

At present, the research direction of formaldehyde free decorative paper is mainly to impregnate decorative paper with formaldehyde free adhesive, that is, to impregnate decorative paper with formaldehyde free adhesive (such as inorganic adhesive or thermosetting resin) instead of traditional aldehyde adhesive. The commonly used formaldehyde free adhesive includes waterborne polyurethane and acrylic resin.

However, the physical properties such as scratch resistance and cigarette burning resistance of the formaldehyde free paper pressed plywood surface have not yet reached the ideal effect, and the improvement method is still being sought.

There are two kinds of pre coated paper: pre impregnated paper and post impregnated paper. The former is made by adding resin in the papermaking stage, and finally by pattern printing and surface coating; The latter is prepared by dipping and coating printed decorative paper with good absorbency without dipping in a specific adhesive.

The production cost of pre painted paper is lower than that of melamine resin impregnated paper. There is no need for hot pressing when pasting, and the process is simple. But at the same time, there is a problem of poor scratch resistance and water vapor resistance on the product surface, which is only applicable to surfaces with low requirements for wear resistance.

01-3 Process control aldehyde removal

Formaldehyde removal by process control is a method to reduce or remove free formaldehyde emission from plywood by optimizing process parameters during plywood production process.

At present, the process control formaldehyde removal mainly includes two aspects: one is to change the surface curing degree of decorative paper and reduce free formaldehyde by adjusting the pressing parameters - hot pressing time, temperature and pressure during the pressing process;

The second is to treat the finished plywood or change the curing conditions of plywood, such as vacuum and high-pressure treatment of plywood to reduce the formaldehyde emission of plywood.

02 Plywood Formaldehyde adsorption method for plywood

02-1 Reactive adsorption

Formaldehyde adsorption by plywood is also a commonly used method at present. Adsorption of formaldehyde can be divided into reactive adsorption and physical adsorption. Reactive adsorption is to convert formaldehyde into other nonvolatile or harmless stable substances through chemical reaction.

At present, there are two common methods in the research. One is to spray formaldehyde remover on the plywood surface to remove formaldehyde emitted from the plywood surface and free formaldehyde in the environment; The other is to add formaldehyde remover to impregnated paper or plywood substrate to reduce formaldehyde released by plywood.

The main components of aldehyde remover mainly include chitin, photocatalyst TiO2, tea tree extract, imidazole derivatives and oxidation-reduction agent, etc. In addition, tea tree stems are directly used as raw materials for plywood substrate.

Removal of formaldehyde by adsorption is a research focus of formaldehyde treatment. Spray type and additive type have their own advantages and disadvantages. The disadvantages of spraying type are usually that they will affect the touch and appearance of furniture in use, and they need to be sprayed regularly, while the disadvantages of additive type are that it is difficult to ensure the formaldehyde removal effect and durability.

02-2 Physical adsorption

The principle of physical adsorption of formaldehyde is to use intermolecular force to adsorb free formaldehyde in the environment into porous materials to achieve the effect of removing formaldehyde. The most common method for removing formaldehyde by physical adsorption is to use porous materials such as activated carbon and mineral crystal to adsorb free formaldehyde in the environment.

However, there is an upper limit for physical adsorption, and the adsorption carrier needs to be replaced regularly. In practical application, physical adsorption and reactive adsorption are used together to obtain better results. This method often uses porous materials as carriers and carries materials that can react with formaldehyde and convert it into a stable state, giving full play to the advantages of both.

03 Write at the end

Source control, process control and formaldehyde removal by adsorption of finished products are the main methods for formaldehyde removal of plywood and its products at present. In terms of source control, formaldehyde free adhesive has been applied and promoted in plywood production in recent years, and formaldehyde free paper with good performance has yet to be explored and developed.

The formaldehyde removal by process control has a certain effect, but because of its high requirements for equipment and processing steps, it faces the problem of high cost and difficult to promote. The research direction of adsorption formaldehyde removal is relatively broad. At present, there are several kinds of formaldehyde removers that have been proved to be useful. How to solve the problem of stability, efficiency and durability of aldehyde removal efficiency of the formaldehyde removers is an urgent problem.