Abstract
The manufacture and properties of waterborne UV-cured coatings (WUV coatings) by acetone process based on urushiol for wood finishing were investigated. Firstly, epoxide urushiol (EU) was prepared by reacting urushiol with epichlorohydrin. Secondly, the EU was reacted with acrylic acid to obtain acrylic epoxide urushiol (AEU). Next, the prepolymers were synthesized by the reaction of AEU, 2,2-Bis(hydroxymethyl)propionic acid (DMPA), and isophorone diisocyanate (IPDI) and hexamethylene diisocyanate (HDI), respectively, using acetone as a solvent. The prepolymers were further neutralized by triethylamine (TEA) to obtain ionomers and dispersed in the water. After removing the acetone by vacuum distillation, the polyurethane dispersions (PUDs) were obtained. Finally, the WUV coatings were performed by adding a photoinitiator (Irgacure 2959). The products in the synthesized processes and the properties of the WUV coatings were examined. The results showed that the EU, AEU, prepolymers, and ionomers could be synthesized stably. The PUDs synthesized by the IPDI and HDI had a similar solid content of 25.2% and 26.2%, and similar pH values of 7.8 and 7.6. However, the IPDI-containing PUD displayed lower viscosity, smaller particle size, and a more even polydispersity index. The IPDI-containing WUV film displayed a higher hardness, gloss, and lightfastness. The HDI-containing WUV film possessed superior impact resistance. Both IPDI-containing and HDI-containing WUV films showed excellent adhesion, bending resistance, and mass retention, and demonstrated a potential for wood finishing.
Highlights
In recent decades, excessive reliance on petrochemicals has resulted in irreversible environmental pollution problems, including the greenhouse effect, air pollution, unrecyclable garbage, etc., and these forms of pollution have directly or indirectly caused risks to human health
To further confirm the synthetic products, the Fourier-transform infrared spectroscopy (FTIR) analyses were used to detect the changes in the functional groups among the urushiol, epoxide urushiol (EU), and acrylic epoxide urushiol (AEU)
The results showed that when the dispersion reached the phase inversion point, the hexamethylene diisocyanate (HDI)-containing ionomer dispersion demonstrated a higher viscosity than the isophorone diisocyanate (IPDI)-containing ionomer dispersion
Summary
Excessive reliance on petrochemicals has resulted in irreversible environmental pollution problems, including the greenhouse effect, air pollution, unrecyclable garbage, etc., and these forms of pollution have directly or indirectly caused risks to human health. High costs and carbon emissions trading promoted the partial or complete substitution of petrochemicals with renewable biomass [1,2,3,4]. Raw oriental lacquer is a natural and renewable polymeric material with water in oil (W/O) emulsion sap, which is obtained by tapping Rhus trees in Southeast Asia [5,6,7]. The global lacquer sap output is over 3800 ton in the year 2014, and the lacquer tree cultivation area in Asia increases every year. In Vietnam alone, the lacquer sap output had increased from 46 tons in the year 2000 to 350 tons in the year 2015. Its film possesses a wax-like gloss, an elegant appearance, and high durability compared to synthetic coatings and is widely used for wood furniture and handicrafts finishing
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