Commonly used adhesives and auxiliary agents for OSB boards

Abstract: This paper briefly introduces the commonly used adhesives and auxiliary agents as well as the adhesive mixing system in the production of oriented strand board. It also briefly compares the application, advantages and disadvantages of two adhesive mixers used in the production of oriented strand board.

In Europe and the United States, oriented strand board (OSB), with its uniform texture, high strength, and dimensional stability, is gradually replacing other wood-based panels like plywood and fiberboard. It is widely used in construction, decoration, and packaging. In my country, with the rapid development of the particleboard industry in recent years and the commissioning of numerous OSB production lines, the product, performance, and application areas of OSB are becoming increasingly recognized, and the industry holds promising prospects. Because OSB differs from conventional particleboard in terms of particle size, installation method, and primary application areas, the adhesives, adjuvants, and mixing systems used are also different. This article briefly introduces commonly used adhesives and adjuvants for OSB, as well as their mixing systems, for reference in OSB production.

Commonly used adhesives

Common adhesives used in the production of oriented strand board include urea-formaldehyde (UF) or melamine-modified urea-formaldehyde (MUF), phenol-formaldehyde (PF), and polyisocyanate (PMDI). The main physical and chemical properties of each adhesive are as follows.

1) UF is a resin solution made by the reaction of urea and formaldehyde aqueous solution. UF is an acid-curing thermosetting adhesive. The quality indicators of commonly used UF adhesives are shown in Table 1.

2) MUF is UF modified with melamine. Its physical and chemical properties are similar to those of UF, but the moisture resistance and strength of the boards made from it are better than those made with UF adhesive.

PF is a resin solution prepared by reacting phenol and formaldehyde in aqueous solution. It is an alkali-cured thermosetting adhesive with a high curing temperature and long curing time, but its weather resistance is superior to all adhesives used in oriented strand board. While working at Hebei Saibo Board Industry, Zheng Fengshan, with the help of Professor Lu Renshu, jointly developed a fast-curing PF with Northeast Forestry University. Its curing time is reduced by one-third to one-half compared to traditional PF.

4) PMDI is a non-aldehyde thermosetting adhesive that has seen rapid growth in usage in recent years. Its main component is polymethylene polyphenyl polyisocyanate (PMDI) containing a certain proportion of 4,4′-diphenylmethane diisocyanate. PMDI performance varies across brands and types, as shown in Table 2.

Figure 1 is a PMDI temperature-viscosity relationship curve that I made in 2003 when I was working at Shanghai Guling Board Industry Co., Ltd.

Commonly used adjuvants

In the production of oriented strand board, it is usually necessary to add the following types of auxiliary agents according to the requirements of adhesive curing and board performance:

1) Waterproofing agent. To improve the moisture-proof/waterproof performance of OSB boards, a waterproofing agent in a certain proportion of dry wood chips needs to be added during the glue mixing process. Commonly used waterproofing agents include molten 56-60# paraffin wax and paraffin wax emulsion.

2) Curing agent. During the hot pressing process, a certain proportion of curing agent must be added during the adhesive mixing process to reduce the hot pressing temperature, shorten the curing time, and improve production efficiency. The type and amount of curing agent used vary depending on the adhesive type. For example, the curing agent used in UF or MUF adhesives is NH4Cl, (NH4)2SO4, or a composite curing agent or latent curing agent supplemented with an acid.

3) Dye. To distinguish the types of boards produced, different colored dyes need to be added during the glue mixing process. Moisture-proof boards are marked green, waterproof boards are iron gray or black, and flame-retardant boards are red.

4) Process water. To ensure a gradient distribution of moisture content from high to low in the surface and core layers of the slab, and to increase the heat transfer rate, it is usually necessary to spray a certain amount of water on the surface to increase the moisture content of the surface layer.

5) Reserved items: These are used to deal with a metering system failure or to add a certain auxiliary agent when producing a special type of board.