Common adhesives and additives for OSB boards

Abstract: This paper briefly introduces the commonly used adhesives and additives in the production of oriented strand board (OSB) and the adhesive mixing system, and briefly compares the application and advantages and disadvantages of two types of adhesive mixers used in OSB production.

In Europe and America, oriented strand board (OSB) has gradually replaced plywood, fiberboard, and other engineered wood products due to its uniform texture, high strength, and dimensional stability, and is widely used in construction, decoration, and packaging. In my country, with the rapid development of the particleboard industry and the commissioning of multiple OSB production lines in recent years, the products, performance, and application areas of OSB have become increasingly recognized, indicating a promising future for the industry. Because the particle specifications, laying methods, and main application areas of OSB differ from those of ordinary particleboard, the adhesives, additives, and mixing systems used also differ. This article briefly introduces commonly used adhesives and additives for OSB and their mixing systems for reference in OSB production.

Common adhesives

In the production of oriented strand board (OSB), commonly used adhesives include urea-formaldehyde (UF) or melamine-modified urea-formaldehyde (MUF), phenolic resin (PF), and polyisocyanate (PMDI). The main physicochemical properties of these adhesives are as follows.

1) UF is a resin solution prepared by reacting 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 a melamine-modified UF. Its physical and chemical properties are similar to those of UF, but the moisture resistance and strength of the boards made from it are superior to those made from UF adhesive boards.

3) PF is a resin solution prepared by reacting phenol and formaldehyde aqueous solution. It belongs to alkali-curing thermosetting adhesives, with high curing temperature and long curing time, but it is superior to all adhesives for oriented strand board in terms of weather resistance. During his work at Hebei Cyber ​​Board Industry, Zheng Fengshan, with the help of Professor Lu Renshu, jointly developed a fast-curing PF with Northeast Forestry University, which shortened the curing time by 1/3 to 1/2 compared with traditional PF.

4) PMDI is a non-aldehyde thermosetting adhesive whose usage has grown rapidly in recent years. The main component of PMDI is polymethylene polyphenyl polyisocyanate containing a certain proportion of 4,4′-diphenylmethane diisocyanate. The properties of PMDI vary among different brands and models, as shown in Table 2.

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

Commonly used adjuvants

In the production of oriented strand board (OSB), the following types of auxiliary agents are usually added depending on the requirements of adhesive curing and board performance:

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

2) Curing agent. During hot pressing, a certain proportion of curing agent needs to be added during adhesive preparation to reduce the hot pressing temperature, shorten the curing time, and improve production efficiency. Different types of adhesives require different types and amounts of curing agents. For example, UF or MUF adhesives use NH4Cl, (NH4)2SO4, or composite curing agents composed of certain acids, or latent curing agents, as curing agents.

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

4) Process water. To ensure a gradient distribution of moisture content from high to low in the surface and core layers of the slab, thereby improving the heat transfer rate, a certain amount of water is usually sprayed onto the surface to increase its moisture content.

5) Reserved items. These are for use in case of a malfunction in a metering system or when a certain auxiliary agent is needed to produce a special type of sheet material.