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Differential scanning calorimetry and dynamic mechanical analysis of amine‐modified urea–formaldehyde adhesives
Author(s) -
Ebewele R. O.
Publication year - 1995
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1995.070581005
Subject(s) - differential scanning calorimetry , adhesive , urea formaldehyde , materials science , curing (chemistry) , dynamic mechanical analysis , formaldehyde , composite material , hexamethylenediamine , polymer chemistry , chemistry , polymer , organic chemistry , physics , layer (electronics) , thermodynamics , polyamide
Urea–formaldehyde (UF) resins are susceptible to stress rupture and hydrolytic degradation, particularly under cyclic moisture or warm, humid conditions. Modification of UF resins with flexible di‐ and trifunctional amines reduces this problem. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were used to study the thermal behavior of modified and unmodified adhesives to identify the physical and morphological factors responsible for the improved performance. A UF resin modified by incorporating urea–capped poly(propyleneoxidetriamine) during resin synthesis exhibited a higher cure rate and greater cure exotherm than the unmodified resin. Resins cured with a hexamethylenediamine hydrochloride curing agent had slower cure rates than those cured with NH 4 Cl. DMA behavior indicated that modified adhesives were more fully cured and had a more homogeneous crosslink density than unmodified adhesives. DMA behavior changed with storage of specimens at 23°C and 50% relative humidity, after previous heating for approximately 20 min at 105°C to 110°C. The initial changes were postulated to occur because of physical aging (increase in density) and continued cure. These were followed by physical breakdown (microcracking) and possibly cure reversion. © 1995 John Wiley & Sons, Inc.