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低甲醛和无甲醛胶粘剂

来源：林中祥胶粘剂技术信息网2011年07月18日

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Low-formaldehyde and Formaldehyde-free Adhesives

Introduction

Much has been made of recent, more severe changes in formaldehyde regulations as they apply to adhesives. These have been well-covered in previous SpecialChem articles and editorials. However, the alternatives to "formaldehyde challenged" products are not as clear. The industry is developing "low-formaldehyde" adhesive products as well as "formaldehyde-free" products. Unfortunately, these initiatives are still in the relatively early stages and some consider them to be suspect because of higher costs and / or lower performance properties.

This article will review several of the more significant developments in this goal to reduce formaldehyde emission. It will describe the potential advantages and disadvantages of each and attempt to shed light on their probability of commercial success. The focus will be on newly developed and developing adhesive products and not on regulations or health effects which have been previously published.^1,2

There are several challenges to developing low- or formaldehyde-free adhesives. One, of course, is the cost involved (manufacturing and development). Another is developing alternatives that have physical properties (viscosity, durability, reactivity, etc.) and other characteristics similar to the conventional adhesives. Also, the formulator needs to be certain that the newly developed product employs sustainable or "green" principles and that the new product or its production processes are less environmentally damaging than current practices.

However, the potential for a product with lower formaldehyde emissions is large. Adhesives or binders are widely used for binding wood, wood fibers, glass fibers, sand, and/or cellulose in the building and construction industry. Adhesives used to make only plywood, particleboard and other manufactured wood products account for 64% of the total 24 million metric tons of formaldehyde consumed worldwide each year.³

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Background

Although wood is a natural material, bonded wood products have caused environmental concern. There are several problem areas, but the foremost area of concern has been formaldehyde emissions. The most commonly used adhesives in the wood composite and laminate industry have been phenol formaldehyde (PF) and urea formaldehyde (UF) adhesives.

Other formaldehyde derivatives include diisocyanates used in polyurethane and additives that are commonly used as biocides and to improve moisture resistance of other adhesive types. The largest concern has historically been particleboard, due to the large volume of indoor usages and the high level of adhesive that is used in manufacturing the product. Plywood, wood composites, fiberglass insulation, roofing shingles, and other composites are also of concern.

The formaldehyde problem can arise from both unreacted and generated formaldehyde. Unreacted formaldehyde is a problem during the adhesive formulation, application and bonding operations and in freshly produced wood products. The rate of unreacted formaldehyde emissions is initially high, but slowly decreased due to reactivity and diffusion limitations. On the other hand, formaldehyde can be generated by the decomposition of some formaldehyde based adhesive such as those based on urea-formaldehyde. These adhesive bonds are prone to hydrolysis which generates free-formaldehyde.

Development Goals

Adhesive products that are developed as alternatives to todays conventional formaldehyde containing adhesives must meet several challenging performance targets. The successful technology will be required to:

Replace formaldehyde adhesives in wood products and other building products
Be moisture resistant after cure (preferably acceptable for outdoor weather exposure)
Cure at moderate temperatures and pressures that are commonly used in manufacturing todays wood products
Not compromise and possibly improve applications and performance properties of current products
Have an environmental life cycle analysis that represents an improvement over todays products and, preferably, be based on renewable raw materials
Be appropriately priced with respect to its overall value proposition.

The strategy to attacking this problem has taken two paths: INSERT INTO [lzx].[dbo].[tb_new]([id],[type],[title],[source],[personal],[image],[contents],[time],[number]) VALUES (1) reducing formaldehyde levels in current products and INSERT INTO [lzx].[dbo].[tb_new]([id],[type],[title],[source],[personal],[image],[contents],[time],[number]) VALUES (2) developing alternatives to formaldehyde containing or producing raw materials. Development of alternative approaches has included dispersions, emulsions, aqueous solutions and high solids polymeric resins. It is difficult to determine to weigh all of the development activ