Isocyanates wood adhesives

ISOCyanatGS. Polymeric diphenylmethane diisocyanate (pMDI) is the most commonly used isocyanate wood adhesive mainly because of its lower volatility and toxicity when compared to other isocyanates such as toluene diisocyanate and dicylcohexylmethane diisocyanate. Some of the advantages enjoyed by pMDI include the fact that it is a liquid polymer, and so it does not require a solvent carrier for application, it is free of formaldehyde, and also it does not require acidic (the case with UF) or alkaline catalysts (the case with PF). It is an effective wood adhesive because the high reactivity of the isocyanate (—N=C=0) groups allows the resin to cure rapidly, and it has the potential to covalently bond directly to the wood by reacting with the hydroxyl groups on the wood surface (Fig. 5) (7,18-20). 

Weaver, E. W., Owen, N. L. (1995). Isocyanate-wood adhesive bond. Applied Spectroscopy Reviews, 49(2), 171-176. 

Surface oxidation processes have also been used as pretreatments for improving the bonding strength of adhesives. Brink et al. [9] reported that the wet bonding strength of plywoods or particleboards manufactured using phenol formaldehyde increased after pretreatment of wood with nitric acid. Mari et al. [10] also reported that nitric acid oxidation reduced the amount of isocyanate resin adhesive required to manufacture particleboard and improved the mechanical properties and biological resistance of boards. 

A wood-based composite can be defined as a composite material mainly composed of wood elements. These wood elements are usually bonded together by a thermosetting adhesive (wood truss products could also be regarded as wood-based composites, but connected by metal connectors). The commonly used adhesives include urea-based adhesive (such as urea formaldehyde resin), phenolic-based adhesive (including phenol resorcinol adhesives), isocyanate-based adhesive, and adhesives from renewable resources (like soybean, lignin etc). The wood elements in wood composites can be in many different forms such as ... 

Emulsion Polymer Isocyanates as Wood Adhesive A Review... 

EPI, Emulsion Polymer Isocyanate, MDI, pMDI, wood adhesives, solid wood panel, parquet, window frame, furniture, plywood, finger joint, glulam beam, I-betim, cross-laminated timber... 

Water-based Polymer Isocyanate (JIS name [7]) or Emulsion Polymer Isocyanate (EPI) adhesives were developed in Japan by Kuraray Co., Ltd, Koyo Sango Co., Ltd and Asahi Plywood Co., Ltd in the early 1970 s [8]. The driving forces were to establish new markets for poly(vinyl alcohol) (PVA) and to develop alternatives to formaldehyde-based wood adhesives. The technology was patented [9], and thereafter licensed to different companies worldwide [8]. The licenses led to introduction of EPI adhesives into Europe, North America and Oceania. Since the EPI adhesives are of Japanese origin, their popularity is naturally concentrated in the Asian markets. Non-Asian consumption is growing, but the market for this adhesive type is still limited. 

For the first time wood adhesives in which no fortification with synthetic resins, such as the isocyanates or phenol-formaldehyde resins used in the past, is necessary to obtain results satisfying relevant standards were developed. 

As discussed in the Introduction, in addition to hot-melt adhesives, one of the most important forms of adhesives for the future is the waterborne system. In general, an advantage of the waterborne system is that it is free from the solvent-pollution problem. For this reason, we shall describe several new waterborne systems in detail acrylics, modified ethylene-vinyl acetate, polyurethanes, phenolics, epoxies, isocyanates, and tackifiers. Applications of these systems range from PSA s contact adhesives, and laminating adhesives to wood adhesives. 

As wood adhesives, isocyanates have found applications as binders for composition board (100). The advantages of isocyanates are many high adhesive and cohesive strengths, flexibility in formulation, versatility of various cure temperatures and curing rates, excellent structural properties, ability to bond with material having moisture content, and lack of formaldehyde emission. The most important advantage is their ability to form waterborne adhesives. 

Emulsion-polymer isocyanates (EPI s) were introduced by Ashland Chemical Co. as better performing wood adhesives (101). EPI s are equivalent to phenol-resorcinol and cross-linkable polyvinyl acetate adhesives. EPI s are more advantageous than others because they have shorter press times, no chalking temperature, a low-temperature curing, no formaldehyde emission, better resistance to high temperatures and accelerated aging, environmental attractiveness, an ability to determine performance by adjusting hardener level, and more tolerance to variations in process conditions. 

Isocyanate A Durable, Water-based Wood Adhesives," Adhesives Age, No. 10, 34 (1981). 

Related articles include Wood adhesives - hot melts, Wood adhesives - isocyanates/ urethanes, Wood adhesives - phenolics and Wood composites - adhesives. 

C. E. Frazier, Isocyanate wood binders, in Handbook of Adhesive Technology, 2nd edn, A. Pizzi and K. L. Mittal, Eds., Dekker, New York, 2003, Chap 33. 

Wood adhesives - isocyanates/urethanes A PIZZI Bonding to damp wood... 

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