Development of melamine modified urea formaldehyde resins based o nstrong acidic pH catalyzed urea formaldehyde polymer
To upgrade the performance of urea-formaldehyde (UF) resin bonded particleboards, melamine modified urea-formaldehyde (MUF) resins based on strong acidic pH catalyzed UF polymers were investigated. The study was conducted in a series of two experiments: 1) formulation of MUF resins based on a UF polymer catalyzed with strong acidic pH and 2) determination of the effects of increased melamine content and melamine reaction pH on performance of MUF resins. Formaldehyde emission, internal bond (IB) strength, and thickness swell (TS) of the panels made with the formulated MUF resins were evaluated. UF polymer as backbone structure prepared by strong acidic pH had a significant effect on the overall performance of the MUF resin system. Strong acidic pH was the single most important factor effecting the formaldehyde emission of the panels. Melamine content and melamine reaction pH were evaluated in the final 24 MUF resins prepared in the study. The effects of increased melamine content were significant only for IB strength, but changes in melamine reaction pH in resin preparation resulted in a resin system that had a significant effect on the overall performance of the panels. IB strength increased, formaldehyde emission decreased, and TS decreased as melamine reaction pH decreased from 6.0 to 4.5. These results indicated that the changes in molecular species and resin structure in resin preparation as effected by melamine reaction pH were the most important factors in upgrading the performance of MUF resins. A low melamine content MUF resin was fabricated with formaldehyde (F)/urea (U)/melamine (M) molar ratios of 1.38F/1U/0.055M (melamine content of 6.4%) and reacted under melamine reaction pH of 4.5. This resin produced panels that satisfied the required performance standards of both formaldehyde emission (National Particleboard Association 2-h-desicator test) and IB strength (American National Standard Institute’s IB strength for industrial boards).