WOOD RESEARCH Volume 67, Number 4, 2022
Song Xiaozhou, Liu Guorui, Feng Xuechun, and Zhang Li

Preparation and properties of agglomerated cork panels bound with chitosan binder

In this paper, acidified chitosan was used as an adhesive to prepare aldehyde-free, environmentally-friendly agglomerated cork panels by hot-pressing. After preparation, the physical, mechanical, and the finishing properties of the chitosan-glued agglomerated cork panels were investigated. The optimal mass ratio of acetic acid solution (1 wt.%) to chitosan was determined to be 30:1. The resulting hot-pressed agglomerated cork panels, which featured a density of 0.55 g.cm-3 and a thickness of 4 mm, exhibited a tensile strength of 1.70 MPa and a thermal conductivity of 0.11 W.m-1•K-1. The agglomerated cork panels coated with the oil-based polyurethane and water-based, acrylic-modified polyurethane paints exhibited significantly lower lightness and higher glossiness. The total color differences (ΔE*) of both agglomerated cork panels increased before and after finishing. The oil-based polyurethane paint coating exhibited high adhesion of paint film, reaching a level-0 adhesion, while the water-based, acrylic-modified polyurethane paint coating achieved a level-1 adhesion. The abrasion resistance results showed that the substrates of cork agglomerates coated two types of paint did not expose after undergoing abrasion for 100 revolutions at the turntable speed of 60 rpm.

WOOD RESEARCH Volume 62, Number 6, 2017
Song Xiaozhou, Zhu Lingyan, Wu Shiqian, and Lei Yafang

Structural and mechanical properties of cork cell walls from quercus variabilis blume (Fagaceae)

The properties of cork are strongly dependent on its cell wall properties. Thus, it is very important to characterize the cork cell walls in order to understand structure-property relationships. The reproduction cork tissue from Quercus variabilis Blume was examined with field-emission scanning electron microscopy to detect the structural characteristics of the cell walls. Several noteworthy anatomical features were present in the cells of Quercus variabilis cork. In most instances, the inner wall of cork cells was not smooth and showed an irregular surface. Solid deposits of various shapes were observed in the inner surfaces of the cell walls. Cell walls of cork tissue had severe corrugations in transverse and radial sections. Trabeculae were found for the first time in the cork tissue of Quercus variabilis Blume. They extended across a few cells, with a rod-like form. Nanoindentation techniques provide a new view of the mechanical properties of the cork cell walls. The hardness of cell walls of untreated and boiled reproduction cork from Quercus variabilis was 0.54 GPa and 0.51 GPa. The elastic modulus was 11.47 GPa and 11.81 GPa, respectively. Boiling treatment of cork could improve mechanical properties of cell walls.

WOOD RESEARCH Volume 63, Number 6, 2018
Wu Shiqian, Song Xiaozhou, Lei Yafang, and Zhu Mingqiang

Characterizations and properties of torrefied Quercus variabilis cork

The energy properties and physicochemical structure of torrefied Quercus variabilis cork were investigated with torrefaction between 150°C and 300°C in a tubular furnace. The mass yield, energy yield, and physicochemical properties of torrefied cork were characterized via proximate analysis, elemental analysis, colour analysis, and scanning electron microscope. The results showed that volatiles, moisture content, and the ratios of oxygen to carbon and hydrogen to carbon decreased with increasing torrefaction temperature. Ash content and fixed carbon content increased with increasing temperature, and the enhanced fixed carbon content resulted in the increase of high heating value (HHV) of cork. The HHV compared to untreated cork increased by around 16% after torrefaction at 300°C for 1h. With increasing torrefaction temperature, the cell cavity increased in size, the corrugation was less deformed, and less sediment appeared on cell walls. In conclusion, torrefaction improved both the energy and physicochemical properties of cork. In addition, FTIR and CP/MAS 13C NMR spectra analysis showed that polysaccharide degraded at 200°C, and lignin degraded between 250 and 300°C. Although suberin had better thermal resistance, its NMR signal intensity decreased after torrefaction at 300°C.

WOOD RESEARCH Volume 64, Number 2, 2019
Shangguan Weiwei, Wang Qingguo, Yuan Yidan, Song Xiaozhou, and Zhu Mingqiang

Alkaline solvent cooking treatment of cork and component analysis of filtrates

This study aimed to determine the effects of alkaline solvent treatment on the physical properties of cork, and to analysis the filtrate components of cork after cooking treatment. Potassium hydroxide (KOH), alkaline hydrogen peroxide (AHP), and ammonium hydroxide (AOH) were used as solvents. The properties of treated cork including color, volume, hardness, compression resilience ratio, and filtrate components of different solvent treatments were investigated. The results showed an increase in the cork’s volume, changes in color, and decrease in lightness after three solvent treatments. Hardness and compression resilience decreased after three solvents cooking, and the difference in the compression resilience ratio between 15 min and 24 h was at a minimum when cork was cooked in KOH solvent. The analyses of filtrate components after KOH and AHP cooking treatments indicated that the hemicelluloses content was generally higher than lignin content. Moreover, water-soluble lignin, obtained from the three solvent filtrates, consisted of a small amount of monosaccharides, such as arabinan, galactan, glucan, and xylan. Nuclear magnetism (NMR) spectra analysis demonstrated that the lignin in KOH and AOH filtrates consisted of G units and H units, while S units only appeared in KOHimmersed lignin. This study shows that solvent treatment changes cork’s physical and chemical properties based on the solvent type and concentration.