Preparation and properties of epoxy‐modified tung oil waterborne insulation varnish

Abstract

This work aimed to develop a novel epoxy-modified tung oil waterborne insulation varnish with blocked hexamethylene diisocyanate as a curing agent. The Diels-Alder reaction between tung oil and maleic anhydride, and the ring-opening esterification reaction of epoxy resin were confirmed. The conversion rate of epoxy was explored as a function of reaction time and temperature. The effects of epoxy resin content on the thermal stability, water absorption and insulation properties (insulation strength, volume resistivity, and surface resistivity) of films were investigated, and the resistances of films to salted water were evaluated. The increase in epoxy resin contents could improve the thermal stability and insulation properties of films, and decreased the water adsorption of films, but when the epoxy resin content reached 30% and above, the water solubility of resin became poor. After being immersed in 3.5 wt % NaCl solution, the electrical insulation strength of films were lower than that in dry state, and decreased as the immersed time prolonged. In particular, the electrical insulation strength loss of films increased significantly for epoxy resin content at 15% and below. Furthermore, the increase of epoxy resin content could improve the hardness and adhesion of films, but the flexibility of films became worse. On the basis of experimental, the epoxy resin content at 25% was appropriate to prepare waterborne epoxy-modified tung oil resin. The resulting varnish may have potential as an immersing insulation varnish for the spindle of electric motor. V C 2015Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42755.

Synthesis and Properties of Thermosets from Tung Oil and Furfuryl Methacrylate

“…These peaks for furan rings remained intact in polymers, which explained that the furan ring itself did not take part in free radical polymerisation due to its stable aromatic ring structure. Small -C-H stretching vibration at 3012 cm −1 , associated with C=C in TO, was also absent from all powder and film samples [6,21]. Since both the raw materials, FMA and TO, are hydrophobic in nature, there is little possibility of moisture absorption in the developed polymer product.…”

“…Soybean oil, castor oil and linseed oil (among others) have widely been used for polymer synthesis [3][4][5]. Compared to other vegetable oils, tung oil (TO), which is obtained from seeds of the tung tree, has remained relatively underexplored as a thermoset precursor [6,7]. This oil is mostly used in paint and varnish formulations because of its fast drying property [8].…”

Self-emulsified waterborne epoxy hardener without acid neutralizers and its emulsifying and curing properties

“…The introduction of hydrophilic groups may have an unfavorable effect on the water-resistant properties of films, for example, reduction of insulation level, corrosion of circuit module and deterioration of mechanical properties (Hu et al , 2015; Cao et al , 2015). Therefore, the water absorption plays an important influence on the application of waterborne coatings.…”

Polar migration behavior of phosphonate groups in phosphonate esterified acrylic grafted epoxy ester composites and their role in substrate protection

“…However, good water compatibility of the coating material is not achieved, which may be due to the hydrophobicity of the vegetable oil chain segments. Cao et al (16) adopted waterborne epoxy to modify tung oil waterborne insulation varnish. Based on the D-A addition reaction of tung oil and maleic anhydride and the ring-opening esterification reaction of epoxy resin, the development of new epoxy-modified tung oil waterborne insulating varnish.…”