Estimating thermal behavior and analyzing evolved species of adhesives through thermogravimetric analysis combined with spectrometric techniques

Abstract

Four types of commercial adhesives, urea formaldehyde resin adhesives (UF), melamine-urea formaldehyde copolymer resin adhesives (MUF), phenol formaldehyde resin adhesives (PF) and diphenylmethane diisocyanate adhesives (MDI) were studied, by first using thermogravimetric analysis (TGA) alone, and then by using thermogravimetric analysis with infrared spectrometry (TGA-IR). Results obtained from the TGA tests found that MDI exhibited the highest initial decomposition at a temperature of 297°C and better overall thermo-stability than the other types of adhesives. PF and MDI provided a better yield of char at about 24.88 and 20.61 wt%, respectively, at 850°C. This showed that their thermal behavior was better than that of UF (5.40 wt%) or MUF (6.99 wt%). The IR response of all adhesives in the TGA-IR tests showed that the absorbance of UF, MUF and MDI was higher than that of PF; this indicated that the concentration of evolved species of PF was less than that of MDI, and less than that of the urea copolymer series adhesives, UF and MUF. It has been suggested that PF is the most environmentally friendly adhesive, because it has the least environmental impact when used in many industrial and domestic applications, such as for structural members in furniture or architecture. These results, when compared to the molecular structures of the adhesives, enabled us to point out the kinds of evolved species (functional bases or the change in molecular structures) for referencing the thermo-degradation processes of the adhesives. Using TGA-IR, to analyze the thermal behavior of 4 types of adhesives, in combination with TGA analysis, has led to useful results, involving the identification of pyrolysis products.