| Summary: | 博士 === 國立中興大學 === 森林學系所 === 102 === For solving the defect of VOCs in traditional solvent-borne coatings, the synthesis, coating properties and film performance of three vegetable oil based waterborne wood coatings including 2-package waterborne polyurethane (WPU) coating, waterborne UV curing (WUV) coating and waterborne dual curing coating were examined. The effects of four kinds of hardener on the properties of castor oil based 2-package WPU coatings were evaluated. Castor oil glyceride (COG) was first prepared by transesterification of glycerin and castor oil (CO) at the molar ratio of 2.0. The waterborne polyurethane dispersed polyols (PUDp) was first synthesized from COG, dimethylol propionic acid (DMPA) and isophorone diisocyanate (IPDI) by the acetone process to provide a prepolymer with a carboxyl and hydroxyl groups. Then the prepolymer was neutralized by triethylamine (TEA) to obtain an ionomer and was dispersed into water. After vacuum distillation to remove acetone, the PUDp was obtained and then mixed with four different hardeners: IPDI, hexamethylene diisocyanate (HDI), polyethylene glycol (PEG) modified PIPDI (polymeric IPDI), named PEG-PIPDI and PEG-modified PHDI (polymeric HDI), named PEG-PHDI. The NCO/OH molar ratio of 1.5 was used and a 2-package WPU coating was obtained. The results showed that the film of the 2- package coatings obtained from IPDI hardener had excellent hardness and gloss. On the contrary, the film containing PEG-PHDI had low hardness but had high tensile strength, elongation at break, abrasion resistance and impact resistance. The film containing HDI hardener showed the best tensile strength, superior water resistance, and higher elongation at break and hardness, however it had the worst gloss among four WPU coatings. The film with PEG-PIPDI hardener had the best heat resistance, high gloss and optimal hardness and tensile strength, and it was suitable for wood coatings among four WPU coatings.
The WUV coating for wood finishing was investigated. First, urethane acrylate prepolymers were synthesized from COG, DMPA, 2-hydroxyethyl methacrylate (2- HEMA) and HDI. And then the prepolymer was neutralized with TEA and dispersed in water. A waterborne acrylated polyurethane dispersion (APUD) was obtained after removing the acetone. The WUV coatings were formulated by mixing the APUD with 1, 3, or 5 wt.% photoinitiator Irgacure 2959 or Irgacure 184, repectively, and were cured by different UV light sources including mercury lamp (H), halogen lamp (C) and both of C+H lamps. The results indicated that the coating containing 3wt.% Irgacure 2959 photoinitiator and cured by mercury lamp for 18 sec showed the best tensile strength and glass transition temperature (Tg), but it had the lowest hardness. The WUV coatings synthesized by IPDI and pentaerythritol triacrylate (PETA) showed hard and brittle film, and was not suitable for wood finishing. For improving the poor hardness which containing HDI alone, the HDI was partially replaced by IPDI. The results showed that a WUV coating with an HDI/IPDI molar ratio of 3/1 had superior film hardness, elongation at break, and adhesion, and it would be suitable for wood finishing.
In the chapter Ⅴ, the synthesis of linseed oil based WUV dispersion as a dual curing wood coatings using different curing processes, as well as their coating and film properties were examined. The prepolymer was synthesized first from linseed oil glyceride (LOG), DMPA, IPDI, HDI and HEMA using an acetone process to prepare a solvent-borne prepolymer with double bonds derived from methacrylic acid and fatty acids. The prepolymer was subsequently neutralized with TEA and dispersed in water. After removing acetone, WUV dispersion was obtained. Wood coatings were formulated by mixing WUV dispersion with photoinitiator (Irgacure 2959) for UV curing alone, named UV or by mixing WUV dispersion with metal driers for air drying alone, named Air or by combining WUV dispersion with the two formulations as UV/Air and Air/UV dual curing systems. The results showed that the durability and the colo of films prepared using the UV/Air dual curing process (i.e., first UV curing, followed by air drying) were better than those of the coatings cured using UV alone. Furthermore, the poor adhesion of the films cured using UV alone was significantly improved through the use of the UV/Air dual curing system. In conclusion, the linseed oil based waterborne UV/Air dual curing coatings possess the potential to provide high- efficiency, high-performances and environmentally friendly coatings for wood furniture finishing.
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