Page 635 - Handbook of Thermal Analysis of Construction Materials

602 Chapter 14 - Sealants and Adhesives

and physical characteristics of different hot melt systems. From the results,
it was concluded that modern thermoanalytical techniques, individually or
combined, can be invaluable tools in quantifying the total energy aspects of
hot melt adhesives and sealant compositions. The author also reported that
the effect of crystalline content of the different components on both
properties and performance characteristics can be better understood by use
of DSC. Furthermore, thermomechanical analysis (TMA) offers a repro-
ducible, quantitative means to study the deformation characteristics, either
expansive or compressive, of components of a fully formulated system
during controlled thermal conditions. Also, it is ideally suited to character-
ize the heat resistance properties of hot melt adhesives. On the other hand,
TG offers many ways to better understand the effects of components on
thermal stability, particularly when combined with infrared spectroscopy.
In another study, Lu, et al., [41] used DSC and TG to investigate the
thermal characteristics of the Larch (Larix gmelini) tannin-phenol-formal-
dehyde adhesive, and its application in plywood and hardboard manufactur-
ing. From their investigation, it was concluded that Larch tannin extracted
from Larix gmelini bark is suitable to partially replace the phenolic
component in adhesives for plywood and hardboard applications. Moreover,
they concluded that both the TG and DSC methods can be utilized to directly
study the thermal curing reaction of the Larch. Thermogravimetric analysis
has also been used to investigate the degradation of holt melt adhesive
materials used in disposable diapers. [42]
Thermomechanical analysis (TMA) was used to investigate the
curing behavior of resorcinol-formaldehyde (RF) and phenol-resorcinol-
formaldheyde (PRF) adhesive resins used for structural glued laminated
timber and veneer lumber. [43] Samples were heated from room temperature
to 200°C and the storage modulus of the adhesive was measured. The TMA
results showed a rapid increase in the storage modulus of the commercial
RF between 60° and 80°C and remain stable above 85°C, the same as the
synthetic PRF adhesives. Furthermore, RF and PRF curing periods at room
temperature conditions required more than thirty days.
The thermal curing behavior of phenol-formaldehyde (PF) adhe-
sives was also studied by DSC [44] using three different scanning methods
(single-heating, multi-heating rates, and isothermal methods). The results
showed that the single-heating rate method is fairly rapid and produces
abundant reaction kinetic parameters, which are useful for comparison
of different PF resins. However, it produced greater activation energy
compared to the multi-heating rate method. This method was applied