The Effects of Adding Different HALS on the Curing Process, Film Properties and Lightfastness of Refined Oriental Lacquer.

Chia-Wei Chang,Kun-Tsung Lu,Jia-Jhen Lee

doi:10.3390/polym12040990

Abstract

Oriental lacquer is a natural polymeric coating with a satiny texture and excellent characteristics, such as chemical resistance and durability. However, the poor lightfastness resulted in the natural aromatic structures of the urushiol structures limited its suitability for outdoor application. This study aimed at the improvement of the lightfastness by adding the different hindered amine light stafbilizers (HALS) with 2 phr addition as well as the effects on the coating and film property of the refined oriental lacquers (RL). The Cryptomeria japonica plate, glass sheets, and the other substrates were used for finishing. The results showed that the lightfastness of RL film was obviously improved by adding 2 phr HALS of Bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate (H90) containing -NH group and Bis (1,2,2,6,6-pentamethyl-4-piperidinyl)-[[3,5-bis(1,1-dimethyl ethyl) -4-hydroxyphenyl] methyl] butylmalonate (H60) containing -NCH3 groups. The HALS additions increased the pH value of RL and improved the activities of laccase-catalyzed reaction. Meanwhile, the oxidative polymerization of the side chains of RL was inhibited, caused by a radical scavenging ability of HALS. The changes in the drying process affected not only the curing time, but also the film properties. Among the 2 phr additions of different HALS, the film containing H90 had the best lightfastness. Meanwhile, it kept the most similar properties with RL and shortened the drying time of RL, and it was selected as the best HALS addition under 2 phr in this study.

Highlights

With the consumption of petrochemical raw materials, the use of natural and renewable resources as raw materials combines the principles of environmental protection and sustainable development, leads to cost reductions, and promotes the creation of a comfortable, safe, and healthy environment for humans
Different hindered amine light stabilizers (HALS), including H90, H60, H93, H95 with 2 phr were mixed with refined oriental lacquers (RL), and Table 1 lists their coating properties
The results showed the RL had the lowest pH value of 3.3, while the RL contained HALS were 3.6–4.8

Summary

Introduction

With the consumption of petrochemical raw materials, the use of natural and renewable resources as raw materials combines the principles of environmental protection and sustainable development, leads to cost reductions, and promotes the creation of a comfortable, safe, and healthy environment for humans. Oriental lacquer (OL), which is a natural polymeric material from Rhus trees, is regarded as a renewable resource because it can be cultivated [1]. The main component in OL, urushiol, is a catechol derivative with a long unsaturated hydrocarbon side chain, and the chemical structure imparts various properties to the coatings [1,3,4,5,6]. The laccase acts as a catalyst and promotes the oxidative polymerization of the urushiols [7,8]. The oxidative reaction of the catechol moiety of urushiol to form oligomers is the first step of OL curing. The urushiols transform into less-antioxidative quinones through the laccase-catalyzed polymerization [9]. The unsaturated double bonds, the side chains of urushiols, undergo autoxidative polymerization to form

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