Enhancing exterior performance of clear coatings through photostabilization of wooden surfaces. Part 1: Treatment and characterization |
| |
Authors: | Bernard S W Dawson Adya P Singh Hank W Kroese Michael A Schwitzer Suzanne Gallagher Stephen J Riddiough Shuhong Wu |
| |
Affiliation: | (1) Ensis (A Joint Venture of CSIRO & Scion), PB Bag 3020, Rotorua, New Zealand;(2) School of Agricultural & Forest Sciences, University of Wales, Bangor, Wales, UK;(3) Research Institute of Wood Industry, Chinese Academy of Forestry, Wan Shou Shan, Beijing, 100091-25, China |
| |
Abstract: | The aim of this work was to produce a less photodegradation-prone substrate for clear coating by partially delignifying the
surface cells of Pinus radiata boards to a depth of 2–3 mm while maintaining the integrity of the wood surface tissues in the delignified zone. To achieve
this, several surface oxidative delignification treatments were trialled in the method development process and peracetic acid
was chosen as the method for refinement and deployment. The treatment method was optimized to yield a significant degree of
delignification compatible with the aim of producing a photostabilized yet intact wooden surface. A preweathering technique
was also used as a second delignification method for producing photostabilized boards. Microscopic and chemical techniques
were used to characterize the effects of chemical and preweathering treatments, which produced delignified surface envelopes
2–3 mm and 100 μm deep, respectively. Acetyl bromide lignin analyses, infrared spectroscopic analyses, and density changes
of 30-μm-thick sections of peracetic-acid-treated samples, as a function of depth from the wood surface, suggested that a
partial delignification had occurred that diminished with depth. Light and transmission electron microscopy provided evidence
of delignification at the cellular level. In the surface layers of peracetic-acid-treated boards, all cell wall regions were
delignified, with the middle lamella being the most severely affected. Lignin appeared to be completely removed from the cell
corner middle lamella regions, but tracheids were still joined in other parts of the middle lamella. The S1, S2, and S3 walls were also delignified. In subsurface layers, cell walls were only partially delignified and the tissues held their
integrity. In contrast, in the preweathered boards, cell walls in the outermost layers were completely separated at the middle
lamella from photodegradation. Preferential lignin removal over that of hemicelluloses was achieved via oxidative treatment
of solid wood. The outcome of this was the successful fulfillment of our aim to produce partially delignified wooden surfaces
that retained sufficient strength and aesthetic appearance and were suitable for application in wooden structures, provided
that the necessary protection measures were carried out. Due to the narrow surface zone produced, machining of such surfaces
would not be recommended as the most delignified zone would be removed first. In Part 2 of this series, the photostability
of treated boards, which had been clear coated and weathered, will be considered. |
| |
Keywords: | Peracetic acid treatment Delignification Photostabilization Preweathering treatment Pinus radiata |
本文献已被 SpringerLink 等数据库收录! |
|