Phenolic panels formaldehyde emissions

A third reason for predicting very low emissions of formaldehyde from phenolic panels is that the cured resin is extremely stable and does not break down to release additional formaldehyde, even under extremely harsh environmental conditions ( ). The high resistance of phenolic resins to deterioration under severe service conditions is, of course, a principal reason they are used so widely in making exterior types of wood panel products. Because of their chemical stability the U.S. Environmental Protection Agency has declared that phenol formaldehyde resins represent a consumptive use of formaldehyde, meaning that formaldehyde is irreversibly consumed in its reaction with phenol so that the formaldehyde loses its chemical identity (3). 

The earliest wood adhesive for mass produetion of panels was phenol formaldehyde (PF). This is widely used for products designed to perform in severe weathering eonditions and dominates the exterior plywood market. Resorcinol formaldehyde is a somewhat similar resin system that cures at ambient temperatures, but the cost is much higher, limiting its use in high-volume applications. These systems, although formaldehyde-based, do not have the continuing formaldehyde emission problem that is associated with other formaldehyde-based systems. 

Particleboard and other products made with isocyanates emit only little formaldehyde (IJ, but these adhesives are expensive and require expensive manufacturing procedures. In contrast, phenolic soft wood plywood is a well established product that is predominantly used for exter i or appIi cat i ons. It conta i ns forma Idehyde i n chemically strongly bonded form and also emits little formaldehyde, as shown in a later chapter in this book. In fact, under almost all common use conditions this type of board contributes not much more formaldehyde than is already present in ambient air in many urban areas. The same is true for waferboard, which has recently become popular for replacing plywood. Likewise, phenolic particleboard emits little forma Idehyde, unIess the phenoIi c res in is bIended w i th UFR. Normally, the products with highest potential for formaldehyde emission are those bonded with UFR. During the past year, approximately 300,000 metric tons of UFR have been used for panel manufacturing in the U.S. 

Lines of demarcation between hardwood plywood, softwood plywood and certain other wood based panel products have become less distinct in recent years. One of the most important distinctions in respect to formaldehyde emission potential is that softwood plywood is typically bonded with phenol-formaldehyde while hardwood plywood is typically bonded with urea-formaldehyde. Phenol-formaldehyde adhesives are more stable and have less tendency to emit formaldehyde than do urea-formaldehyde adhesives. Some important features of hardwood plywood ... 

Because phenolic panels have not presented formaldehyde-related problems in the marketplace, there has not been much need to develop information on formaldehyde emissions from these products. 

Any formaldehyde that might be present initially in fresh phenolic panels, would be expected to diminish through time, since additional formaldehyde is not released from a breakdown of the resin. Thus, barring contamination from other sources, formaldehyde emissions associated with thoroughly aged phenolic panels should be nil. 

Nestler ( ) thoroughly reviewed the worldwide literature on formaldehyde emissions from wood products published through January, 1977. According to Blomquist ( .)> Nestler s literature review includes only three citations which even mention phenolic adhesives, and none of these citations made specific mention of any problems associated with the use of phenolic panels. 

Since Nestler s review was published, some additional information on formaldehyde emissions from phenolic panels has appeared in the literature. Information obtained using dynamic test chambers is summarized in Table I. Perforator and two-hour desiccator data are summarized in Table II. 

It is important to note here that higher temperatures probably increase emissions from phenolic panels simply by accelerating the release of that small amount of residual formaldehyde that originates from the adhesive and subsequently becomes adsorbed to the wood substance and water in the wood. Because phenolic resins are very stable chemically, any temperature-related increase in emissions would not be expected to be associated with resin degradation. Consequently, temperature would be expected to exert much less influence on emissions from panels which have been aired out than from fresh panels. Indeed, this trend is shown by the data, as discussed below. 

Much of the information pertaining to formaldehyde emissions from phenolic panels has been obtained by manufacturers of these products but has not been published previously in the open literature. This information has been obtained primarily to form a basis for answering consumer inquiries. 

Formaldehyde as a pollutant in the indoor air is usually connected with the use of formaldehyde based resins in e.g. building materials and in furniture. This article presents measurements of the formaldehyde emission from various products containing urea-formaldehyde (UF) or phenol-formaldehyde (PF) resins. The emission from all test objects have been measured in a ventilated test chamber at the standardized testing atmosphere 23 C, 50 % RH according to the International Organization for Standardization (ISO). The emission from woodbased panels and other materials have been measured at a loading factor of 1.0 m /m and at an air change rate of 1.0 h . ... 

The main parameter for the application of tannins as adhesives for wood-based panels is the content of reactive polyphenols and the reactivity of these components towards formaldehyde. Tannins can be used as adhesives alone (with a formaldehyde component as crosslinker) or in combination with aminoplastic or phenolic resins. These resins can react chemically with the tannin component in a polycondensation reaction, form only two interpenetrating networks, or both. The simplest adhesive mix formulation consists of the tannin solution and powdered paraformaldehyde as crosslinker [283]. The addition of paraformaldehyde can cause in the short term a relatively high level of formaldehyde emission. Glue mixes using paraformaldehyde for the production of particleboards with low formaldehyde emission are described and used industrially [284]. In the literature a large number of papers describe the combinations of tannins with synthetic resins (Table 14). 

Emission of volatile noxious chemicals from wood-based panels during their production can be caused by chemicals inherent to wood itself, like terpenes or free acids, as well as by volatile compounds and residual monomers of the adhesive. The emission of formaldehyde as well as free phenol effluents is a matter of concern. 

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