Particleboard formaldehyde liberation

To shed additional light on the emission mechanism and the contribution of resin hydrolysis to formaldehyde emission, my recent experiments have examined the liberation or extraction of formaldehyde from particleboards, from wood containing sorbed formaldehyde, and from cured resins. Here, I present results from particleboard and formaldehyde-sorbed wood experiments in which rates of formaldehyde removal were measured by three different procedures (see Appendix 1 for experimental details). 

Figure 7. Formaldehyde liberation from particleboards and CH20-sorbed wood at 27°C and 33 percent relative humidity (RH) weighing bottle test with -80 mesh materials (o Southern pine impregnated with pH 2 tartaric acid and vapor-equilibrated with CH20/salt solution at pet RH O as before except heated 4 min. 16O°C after CH2O sorption 0 urea-formaldehyde particle board (b) phenol-formaldehyde particleboard, values approximate P = Perforator value at indicated moisture content (MC)).

Interpretation for Comminuted Systems. The similarities and differences noted for the kinetics of formaldehyde removal from UF and PF particleboards and from formaldehyde-sorbed wood are brought out more clearly by plotting relative formaldehyde losses versus time. Loss ratios, i.e., formaldehyde loss by any material divided by the UF board loss at the same time, are shown in Figures 10 and 11 included in Figure 10 are analogous ratios for resin data from formaldehyde liberation (weighing bottle test) and formaldehyde elution by toluene experiments (10). Examination of the data leads to the following additional comments ... 

Figure 9. Formaldehyde liberation in water at 25 C and pH 3 from particleboard and CH20-sorbed wood all materials -80 mesh. (Sodium azide in water at 100 mg/L as preservative symbols and abbreviations as in Figure 7.) (ML85 5436)...

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. 

Figure 10. Formaldehyde loss ratios at 20 percent relative humidity for various materials. (Formaldehyde removed from a material divided by that removed from urea-formaldehyde particleboard. Board elution by nitrogen. Resin liberation by weighing bottle test. PF = phenol-formaldehyde) (ML85 5437)...

Figure 11. Formaldehyde loss ratios at 80 percent relative humidity (RH) and in water. (Loss ratio = CH2O liberated relative to that from urea-formaldehyde particleboard in same test.

Formaldehyde is liberated during the condensation reactions that take place when the urea formaldehyde resin binder in particleboard is cured by hot pressing. Some of this formaldehyde is retained in the board and is available for subsequent emission to the surroundings. 

If the mass transfer coefficient is sufficiently low, the emission will be so slow that the ventilation can manage to remove the formaldehyde at almost the same rate as it is liberated, resulting in a very low formaldehyde concentration in the air. This presentation deals with what can be achieved in terms of reduced mass transfer coefficient and emission rate by applying some sort of diffusion barrier to the surface of the particleboard. The diffusion barriers studied comprise overlays or surface finishes commonly applied when particleboard is used as a building material, such as wall paper, painting and floor covering, but even overlays that are used by the furniture and joinery industries, such as veneers, melamine facing and resin saturated paper foils (finish foils). 

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