Comparisons of chemical characteristic variations for photodegraded softwood and hardwood with/without polyurethane clear coatings

For better understanding of the differences between softwood and hardwood in the photodegradation process, hinoki (Chamaecyparis sp.) and maple (Acer sp.) were used in this study. The variations in chemical characteristics on their surfaces were analyzed by diffuse reflectance FTIR. The results revealed that in softwood lignin photodegradation, the phenolic hydrogen abstraction reacted faster than the beta-aryl ether linkage cleavage. In addition, the guaiacyl structure in hardwood degraded faster than the syringyl unit. More nonconjugated carbonyl compounds were produced on the softwood surfaces than that on the hardwood surfaces. The cellulose crystallinity decreased to some extent in both the softwood and the hardwood. The protection effect of the hardwood surface by a polyurethane free film is better than that of the softwood surface. The guaiacyl unit was more degradable in the lightfastness test than the syringyl unit under the same filtering effect of the clear coatings. (C) 2002 Elsevier Science Ltd. All rights reserved.