First, the adhesive itself containing free formaldehyde. With "unstable" group in the lower PH value, high tide, high humidity will be broken chain, isolated from formaldehyde.
① resin synthesis remaining unreacted free formaldehyde;
② resin synthesis involved the reaction of an unstable group of formaldehyde, in the hot pressing process to be released;
③ In the resin synthesis has been around the colloidal particles adsorbed on the protonated formaldehyde molecule, under the influence of the electrolyte will be released.
Second, the impact of raw materials. Perforated timber is 1-3mg/100g, when the timber in a dry part of the decomposition, generating acetic acid and formic acid, at least half-long fiber solution, lignin methoxy-chain scission in the release of formaldehyde; oak plywood formaldehyde release lower than the amount of pine plywood; to pine, for example, the formaldehyde emission of wood 2.65mg/100g, wood shavings was 3.69mg/100g, increased by 40%; the formaldehyde emission of wood ash 3.39mg / 100g; fir wood formaldehyde emissions degree 1.32mg/100g; willow wood released formaldehyde is 1.60mg/100g; formaldehyde emissions than wood bark; trees and wood shavings form a greater impact, such as spruce will increase formaldehyde emission, while the oak opposite; sawdust formaldehyde release is about 10 times higher than particle board; with low density of trees made of particleboard, the formaldehyde distribution capacity than species with high-density particleboard made. The form of wood shavings, the smaller the size (ie, greater surface area), the stronger the ability of formaldehyde distribution.
Third, the impact of the system board technology. Board core layer higher formaldehyde potential distribution due to core layer is cured "weak zone", a lower temperature, high moisture content, PH value is lower, the degree of cure is poor, easy hydrolysis and production of formaldehyde; with sizing After a decline in raw material moisture content, production and product formaldehyde emission decreases, the product of some other properties are not conducive to low lung heat transfer, but will make products of formaldehyde emission increases; with sizing increases, wood-based panels used in the formaldehyde emission of hot and straight up; shavings after sizing, moisture content doubled, when the hot formaldehyde emission also increased 3-fold, into the board formaldehyde emission also increased 2-fold. With the hot temperature, the hot plate when the formaldehyde emission lines increase, due to the increase in synthetic rubber plate cross-linking degree, which feed the formaldehyde emission (but the temperature should not exceed 220 ℃); extension of time will be hot the release of formaldehyde feed plate, but the economy of the starting, this method is not desirable to reduce temporary high pressure hot plate of formaldehyde emission, but the board density. Rational use of curing agent (type and amount applied) and "catch aldehyde agent" (urea, paraffin wax emulsion + urea, thioamide, ammonium carbonate, ammonia), can reduce formaldehyde emission, hot plate after the weak binding that exist within formaldehyde than the board.
Fourth, the structural degradation of formaldehyde release. After curing at 100 ℃ heating UF unchanged after 14d, but in 85 ℃ water, UF solubility reached 5%, PH value of 6.9 when the time is 72 times PH value of 2.21, indicating strong acid can be used curing of UF hydrolysis. In order to achieve solubility of 50%, 95 ℃ time required for 1400min, 100 ℃ time required for 550min; used for a long time after the distribution of the amount of formaldehyde plywood and just after the same hot plate is almost the same amount of formaldehyde distributed and sometimes even increased. Temperature, humidity, pH, weathering, sunlight and other environmental conditions that are not one hundred percent original plate curing resin degradation and the release of formaldehyde. Complete cure of the resin due course of time the formaldehyde distribution harsh conditions. Water and acids (especially the water under certain temperature and chemical corrosion material) sheet structure of the dangers of even more. Plate at 80 ℃ than 50 ℃, the formaldehyde emission increase of 10% humidity from 35% to 80%, emissions increased by 50%. The release of formaldehyde in plywood is durable.
