Formaldehyde release bonded wood products

Formaldehyde release from UF-bonded wood products has decreased by a factor of more than ten over the past 15 years. Today 90% of the entire U.S. production is capable of meeting the 0.4 ppm standard for manufactured housing at the time of sale. Since 1979 European products have been classified into three categories. 

Formaldehyde release from UF-bonded wood products depends on the resin formulation and on curing conditions. The basic chemistry of... 

Formaldehyde Release from Wood Panel Products Bonded with Phenol Formaldehyde Adhesives... 

Even though formaldehyde release from UF-bonded wood products has been studied for more than 25 years, only very little Is known about how formaldehyde Is stored In UF-bonded wood products. In fact. It is not even known whether storage of formaldehyde is a physical or a chemical process. Formaldehyde is gaseous at room temperature, but it can polymerize forming para-formaldehyde, and it readily dissolves In water forming methyIenegIycoI (2). The most likely physical storage process is absorption by moisture. Water is present in wood in two forms free water In the cell cavities In form of liquid... 

Due to its affinity for water, formaldehyde will concentrate in wood products in their water reservoirs. Since wood collects water in Its S-2 secondary wall on the surface of wood cellulose, formaldehyde will come into contact with wood cellulose. This work shows that formaldehyde can be expected to react with wood cellulose forming hemiacetals. Since this reaction is reversible, these hemiacetaIs constitute a temporary reservoir for formaldehyde within wood. This fact may explain the complex formaldehyde release and absorption properties of UF-bonded wood products. 

Formaldehyde emission from particleboard has been studied at our laboratory for over 15 years. We search for an answer to the following question Given the fact that amino-resin bonded wood products have the ability to release formaldehyde into indoor air when they are in use, what simple and rapid analysis method can be used at the time of manufacture to predict formaldehyde release under use conditions as quantitatively as possible Obviously, the chosen method needs to be applicable for all types of boards that are available on the market. 

In the last three decades a special problem arose when large quantities of UF-bonded wood products were used in confined areas that were poorly ventilated. In these applications, several different types of products are often used jointly. Originally, most freshly manufactured UF-bonded products released noticeable quantities of formaldehyde, but emission levels have been reduced by a factor of more than ten (3), and today only defective products, or improperly used products, emit large enough quantities to cause problems. However, the volume of these products has become so large that even a small percenage of complaints can cause a substantial number of complaints. For example. In the U.S. alone, the entire... 

HIS BOOK SUMMARIZES OUR CURRENT UNDERSTANDING of many problems related to measuring, abating, and understanding formaldehyde emission from wood products bonded with formaldehyde-based adhesive resins. It contains expanded and updated versions of selected papers presented at an ACS symposium, Formaldehyde Release from Cellulose in Wood Products and Textiles. In addition, three chapters from participants who could not attend the meeting were added. 

C-NMR spectra of water soluble cellulose model compounds indicate that formaldehyde is capable of reacting with wood cellulose functions under hot press conditions as well as at room temperature yielding hemiacetals. The formation of hemiacetals is reversible, and thus constitutes a reservoir for formaldehyde storage. Due to its affinity for water, formaldehyde released during the manufacture of UF-resin bonded products will be retained in the aqueous phase of wood. Wood contains about 9 wt% of moisture. Most of this is in the S-2 secondary cell walls that consist mainly of wood cel IuIose. 

There are many chemical processes leading to emissions of phenol and its derivatives into urban air. Phenolic compounds are present in exhaust gases of motor vehicles and in waste gases of other combustion processes. In the indoor environment phenols are released from phenol-formaldehyde bonded wood-based products. 

Plywood and particleboard, affordable building materials, have been used in many facets of exhibition case design and storage. Unfortunately, these wood products are often bonded together with formaldehyde resins. As the resin cures over time, it will release formaldehyde vapors into the environment. In the presence of moisture, atmospheric formaldehyde will be converted to corrosive formic acid (36). In an attempt to diminish the acidifying effects of wood, coating and varnishes have been applied on the... 

Applications. UFs are the primary commodity binder in caul and caulless particleboard processes and medium density fiberboard (MDF). They can be formulated to develop tack and generally are used as a neat liquid. Acid catalysts are frequently used unless the wood species is acidic such as southern pine or oak. Products manufactured with UFs are rated for interior application. Use of MUFs or MFs increases bond durability and imparts water resistance to the bond, speeds cure rate, and reduces potential formaldehyde release. 

In 1993, worldwide consumption of phenoHc resins exceeded 3 x 10 t slightly less than half of the total volume was produced in the United States (73). The largest-volume appHcation is in plywood adhesives, an area that accounts for ca 49% of U.S. consumption (Table 11). During the early 1980s, the volume of this apphcation more than doubled as mills converted from urea—formaldehyde (UF) to phenol—formaldehyde adhesives because of the release of formaldehyde from UF products. Other wood bonding applications account for another 15% of the volume. The next largest-volume application is insulation material at 12%. 

The major disadvantage associated with urea-formaldehyde adhesives as compared with the other thermosetting wood adhesives, such as phenol-formaldehyde and polymeric diisocyanates, is their lack of resistance to moist conditions, especially in combination with heat. These conditions lead to a reversal of the bond-forming reactions and the release of formaldehyde, so these resins are usually used for the manufacture of products intended for interior use only. However, even when used for interior purposes, the slow release of formaldehyde (a suspected carcinogen) from products bonded with urea-formaldehyde adhesives is observed. 

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