Abstract
At present, the disadvantage of powder epoxy adhesive is the limited application area. In order to widen the application range of powder epoxy adhesive from heat-resistant substrates (such as metals) to heat-sensitive substrates (such as plastic products, cardboard and wood), it is necessary to decrease the curing temperature. In this article, a series of fast-curing powder epoxy adhesives were prepared by the melt blending method with bisphenol A epoxy resin (E-20), hexamethylenetetramine (HMTA) as a curing agent and 2-methylimidazole (2-MI) as an accelerant. The structure and properties of the E-20/HMTA/2-MI systems were characterized by Fourier transform infrared, thermogravimetric analysis, dynamic mechanical analyser and differential scanning calorimetry (DSC). 2-MI added into the E-20/HMTA systems can simultaneously enhance toughness, tensile strength, glass transition temperature (Tg) and thermal stability in comparison with the E-20/HMTA systems. The best mechanical properties were obtained at 100/8/0.6 weight ratio of the E-20/HMTA/2-MI systems. DSC experiments revealed that the exothermic peak of the E-20/HMTA/2-MI system was about 55°C lower than that of the E-20/HMTA system. The activation energy of the cure reaction was determined by both Kissinger's and Ozawa's methods at any heating rates. The activation energy and pre-exponential factor were about 100.3 kJ mol−1 and 3.57 × 1011 s−1, respectively. According to the KAS method, the curing time of the E-20/HMTA/2-MI systems was predicted by evaluating the relationship between temperature and curing time.
Highlights
Bisphenol A epoxy resins (DGEBAs) are a unique class of thermoset polymers, which have been gaining ground since their commercial debut in the 1940s [1]
We have successfully synthesized a series of fast-curing powder epoxy adhesives
The structure and properties of the E-20/HMTA/2-MI systems were characterized by FTIR, Thermogravimetric analysis (TGA), dynamic mechanical analyser (DMA) and differential scanning calorimetry (DSC)
Summary
Bisphenol A epoxy resins (DGEBAs) are a unique class of thermoset polymers, which have been gaining ground since their commercial debut in the 1940s [1]. Epoxy resins have found a myriad of applications as in coatings, adhesives, construction and electrical engineering for decades [2], owing to their superior mechanical and chemical properties, such as high tensile, good chemical and solvent resistance, and high heat distortion temperatures [3,4,5]. A novel kind of epoxy resins without any solvent, have recently received considerable attention because of the imposition of increased legislative restrictions on the emission of organic solvents to the atmosphere [6]. Epoxy adhesives that cure fast at mild temperatures are needed because excessive heat cannot be applied to the peripheral components and adherend [7]. In consideration of energy saving and consumption reduction, a fast-curing powder epoxy system deserves to be explored
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