Formaldehyde emission various

Table III. Regulation of Formaldehyde Emission Various European Countries...

These ratios then are correlated to various properties of the wood-based panels, e.g., internal bond strength or subsequent formaldehyde emission. Various papers in the literature describe examples of such correlations and present workable predictive equations. For UF resins Ferg [30], Ferg et al. [99,100] for MF resins Mercer and Pizzi [101] for MUF resins Mercer and Pizzi [102], Panamgama and Pizzi [103]. 

However, it has to be considered that it is neither the content of free formaldehyde itself nor the molar ratio which eventually should be taken as the decisive and the only criterion for the classification of a resin concerning the subsequent formaldehyde emission from the finished board. In reality, the composition of the glue mix as well as the various process parameters during the board production also determine both performance and formaldehyde emission. Depending on the type of board and the manufacturing process, it is sometimes recommended to use a UF-resin with a low molar ratio F/U (e.g. F/U = 1.03), hence low content of free formaldehyde, while sometimes the use of a resin with a higher molar ratio (e.g. F/U = 1.10) and the addition of a formaldehyde catcher/depressant will give better results [17]. Which of these two, or other possible approaches, is the better one in practice can only be decided in each case by trial and error. 

Only a small amount of work has been done up to now concerning the prediction of bond strengths and other properties based on the results of the analysis of the resin. Ferg et al. [59] worked out correlation equations evaluating the chemical structures in various UF-resins with different F/U molar ratios and different types of preparation on the one hand and the achievable internal bond as well as the subsequent formaldehyde emission on the other hand. These equations are valid only for well defined series of resins. The basic aim of such experiments is the prediction of the properties of the wood-based panels based on the composition and the properties of the resins used. For this purpose various structural components are determined by means of - C NMR and their ratios related to board results. Various papers in the chemical literature describe examples of such correlations, in particular for UF, MF, MUF and PF resins [59-62]. For example one type of equation correlating the dry internal bond (IB) strength (tensile strength perpendicular to the plane of the panel) of a particleboard bonded with PF adhesive resins is as follows [17]... 

MUF resin is widely used as an adhesive in wood industries, coating technology, paper industries and a main material in kitchenware production. In various applications, different resin properties are needed to suit its application. Important resin properties are for example higher resin solubility, low curing period with lower temperature and catalyst amount, good stability for longer shelf life, and lower free formaldehyde emission, as formaldehyde is very toxic, and can cause cancer [1]. One of the factors that affecting the MUF resin properties is the mole composition. The mole composition is a ratio of formaldehyde to amino compoimd... 

However, on an empirical basis, the range of potential emission behavior is reasonably well known, and the correlation between emission measurements on product samples under standard conditions can now be related well to the expected range of indoor air levels under various user conditions. This subject is discussed in two separate chapters. Thus, quality control depends on formaldehyde emission measurements. This can be done by determination of the formaldehyde content of the finished product, or by measuring air levels around the product. 

Plotting 1/Cg against n/a, gives a straight line, from which both concerned board properties are gathered. Graphs show that independent of the size of the apparatus, this statement is backed up quite well. Various examples that influence both those parameters illustrate the use of this formaldehyde emission method. 

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 . ... 

Furnishing. The formaldehyde level in a room at actual conditions depends on several factors, and is not an arithmetical sum of various sources (10), (11). In order to estimate the contribution of formaldehyde emission from single pieces of furniture the test objects have been exposed in area to air volume proportions to which they can be found in a small room or a kitchen. The assumption that the formaldehyde level in the chamber and in the actual room is the same, is based on a theoretical model originally developed for particle boards (4). At constant climate the emission from a test object is determined of the relation between the loading factor and the air change rate. 

After a discussion of mechanisms for the liberation and subsequent emission of formaldehyde from particleboard, methods to assess the extent of these processes are described. Data are presented for the formaldehyde emission from particleboard with various surface treatments. These data were obtained by a laboratory method and by large climate chamber measurements and show that some of the surface treatments studied constitute very efficient diffusion barriers and considerably reduce the formaldehyde emission rate. 

Not much work has been done up to now concerning the prediction of bond strengths and other board properties based on the results of the analysis of the adhesive resin in its liquid state. What has been investigated and derived up to now are correlation equations that correlate the chemical structures in various UF resins having dilferent molar ratios F/U and dilferent types of preparations with the achievable internal bond strengths of the boards as well as the formaldehyde emission measured after resin hardening. 

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. 

Melamine-fortified resins with a melamine content of up to approximately 10% based on liquid resin are used for various applications where straight UF resins cannot provide the desired combination of processing tolerance, formaldehyde emission, and specific board properties such as a low thickness swelling. MUF resins with higher content of melamine (up to 30% based on liquid resin) find applications in enhanced performance grade boards for use in hiunid conditions (moisture-resistant application). 

Only a few investigations have been done concerning the prediction of adhesive bond strengths and other properties based on the composition of the resin. Equations for evaluating a possible correlation between the chemical structures in various MUF resins with different molar ratios [F/(NH2)2l and different types of preparation and the achievable internal bond together with the subsequent formaldehyde emission have been investigated. For this purpose, various structural components have been determined by means of NMR, and several ratios of the amounts of the various structural components have been calculated, eg,... 

Finally, formaldehyde emissions are frequently raised as an issue of particular environmental importance for methanol vehicles on two counts first, there is concern for formaldehyde as an air toxic, and second, there is its role as a highly reactive ozone precursor. Formaldehyde is a gas that is naturally present at low concentrations in the atmosphere, originating as an intermediate in the slow photooxidation of various organic compounds released into the environment from a variety of sources. As a low-level constituent of engine exhaust, it is also emitted directly into the air by both diesel and gasoline vehicles. 

Unbumed Hydrocarbons Various unburned hydrocarbon species may be emitted from hydrocarbon flames. In general, there are two classes of unburned hydrocarbons (1) small molecules that are the intermediate products of combustion (for example, formaldehyde) and (2) larger molecules that are formed by pyro-synthesis in hot, fuel-rich zones within flames, e.g., benzene, toluene, xylene, and various polycyclic aromatic hydrocarbons (PAHs). Many of these species are listed as Hazardous Air Pollutants (HAPs) in Title III of the Clean Air Act Amendment of 1990 and are therefore of particular concern. In a well-adjusted combustion system, emission or HAPs is extremely low (typically, parts per trillion to parts per billion). However, emission of certain HAPs may be of concern in poorly designed or maladjusted systems. 

The development of new models for the prediction of chemical effects in the environment has improved. An Eulerian photochemical air quality model for the prediction of the atmospheric transport and chemical reactions of gas-phase toxic organic air pollutants has been published. The organic compounds were drawn from a list of 189 species selected for control as hazardous air pollutants in the Clean Air Act Amendments of 1990. The species considered include benzene, various alkylbenzenes, phenol, cresols, 1,3-butadiene, acrolein, formaldehyde, acetaldehyde, and perchloroethyl-ene, among others. The finding that photochemical production can be a major contributor to the total concentrations of some toxic organic species implies that control programs for those species must consider more than just direct emissions (Harley and Cass, 1994). This further corroborates the present weakness in many atmospheric models. 

An infrared chemiluminescence study [501] of the reaction 0(3P) + CH3 shows that it is direct with the formaldehyde product being highly vibrationally excited. A lower limit of (Fv) > 0.43 has been placed on this excitation. The high pressure reactions of 0(3P) atoms with various hydrocarbons show emission of vibrationally excited OH(d < 14) radicals which is attributed to the reaction [ 502]... 

In contrast to this anti-maser action in formaldehyde, H20 and OH are observed in maser emission. Collisional or radiative pumping is thought to maintain the population inversion between the two levels. As photons pass through the cloud, they are amplified by stimulated emission of radiation. The maser emission of H20 is possibly the most unusual of the observed anomalies, both from an astrophysical and a spectroscopic point of view. This is not the place to discuss details of the various models suggested, we would refer to concentrate on some of the general features observed in the maser emission spectra. 

This is the most explosive of the nitrate esters. Not only will it bum in an atmosphere of oxygen, nitric oxide or nitrogen dioxide, but also it can support a stationary decomposition flame which can be stabilized on a burner [122]. At low pressures the various zones of the decomposition flame are clearly separated and the early stages show strong formaldehyde bands in emission. 

Another reason for predicting low emissions is that the small amount of residual formaldehyde that might be present in the prepared resin is diminished even farther by reactions which occur when the resin cures. Phenolic resins are cured under heat and pressure in a hot-press, usually under highly alkaline conditions. Curing temperatures are usually in the range of 130-220 C. Under these conditions, unreacted formaldehyde continues to react with phenol to form larger phenol formaldehyde polymers. Also, some formaldehyde reacts with various chemical constituents in the wood. Moreover, some formaldehyde is probably converted to methyl alcohol and formic acid by way of the Cannizzaro reaction (J ). ... 

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