Wood panel products

It is worthwhile to review the U.S. market size for the four principal resins currently used in wood-panel products today (4 )- These are phenol-formaldehyde (PF), urea-formaldehyde (UF), melamine-formaldehyde (MF), and resorcinol-formaldehyde (RF) (Table III). When these production figures are compared to the quantities of lignin potentially available (Table II), it is immediately obvious that all wood adhesives could be replaced by only a very small fraction of the lignin produced annually during chemical woodpulping processes. 

Panel volume data is available from several sources. While the FAO yearbooks provide some data, industry publications offer a more up to date perspective. The data are not always consistent or comprehensive. FAO data include OSB within the particleboard classification. Further FAO data cover world wood-panel production volumes whereas industry surveys (Wadsworth, 2005) are based on plant capacity of all operational units in each region. The difference between these two numbers reflects capacity utilization which varies as demand rises and falls. The volumes in this analysis are used to indicate trends rather than absolute levels (Table 12.1). 

During the past forty years wood panel products bonded with... 

The most widely used wood panel products are particleboard, softwood plywood, hardwood plywood, medium density fiberboard (MDF) and waferboard. The most common adhesive is urea-formaldehyde resin (UFR). Phenol-formaldehyde resins (PFR) are second in volume and melamine-formaldehyde resins (MFR) are a distant third. Recently,... 

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

Virtually all wood panel products such as plywood and particleboard are manufactured using either urea formaldehyde or phenol formaldehyde adhesives. Urea formaldehyde adhesives are used in hardwood plywood and in certain types of particleboards. These adhesives are not waterproof, and products made with them are normally used indoors for paneling, furniture, shelving and floor underlayment. 

Phenol formaldehyde, on the the other hand, is used to make the waterproof adhesives that are used in structural wood panel products such as softwood plywood, oriented strand board, waferboard and exterior (phenolic) particleboard. These products are commonly used for roof, floor and wall sheathings, exterior sidings, concrete forms and in pallets and numerous other products. 

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 formaldehyde emitting potential of wood panel products can be evaluated in numerous ways, including the use of dynamic chamber tests (tests involving chambers which are ventilated and simulate real-world conditions) static (unventilated) tests, such as... 

The higher formaldehyde levels associated with the first two studies summarized in Table I can probably be attributed primarily to the relatively high temperatures employed. Numerous investigations have shown that formaldehyde levels increase exponentially with temperature ( 2 Several studies have shown that formaldehyde levels associated with wood panel products can increase by more than a factor of 3 as the temperature increases from 25°C to 40 C ( ). 

EMERY Wood Panel Products Bonded w ith Phenol Formaldehyde Adhesives 31... 

The first three chapters deal with particleboard, medium density fiberboard, hardwood plywood, and softwood plywood, the four most widely used wood panel products. Chapter four compares these products with other consumer products. Chapters five through seven explain the basic chemistry of formaldehyde with cellulose and wood components and provide a current understanding of the nature of liquid urea-formaldehyde adhesive resins. The next two chapters present new analytical methods that might become useful in the future. Chapters eight and eleven through sixteen explain the complex nature of the latent formaldehyde present in the products and its correlation to formaldehyde emission from wood products. Chapters fifteen and sixteen describe currently popular formaldehyde reduction methods. The last two chapters discuss the problems involved in reducing formaldehyde emission by regulating air levels or source emissions. 

Exactly the same type of approach can be used for the formulation of other polycondensation adhesives. For example, the formulation of melamine urea formaldehyde adhesive resins for wood panel products can also be successfully approached in the same way as has been shown above for the cold-setting PRF adhesives. 

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