Kwei-Nam Law

Influence of TEMPO-mediated oxidation on the lignin of thermomechanical pulp.

The influences of various factors in 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation on delignification, lignin aromatic ring and side chain structures of thermomechanical pulp (TMP) were investigated. The results indicate neither TEMPO nor NaBr alone can provoke changes in lignin content or lignin structure under weakly alkaline conditions. However, NaClO and NaClO-NaBr were able to remove lignin effectively, causing remarkable changes in lignin structure. Delignification was promoted when TEMPO was used with NaBr and NaClO. In contrast to NaClO alone, an additional 15% lignin was removed when TEMPO-mediated oxidation system was used, but it did not induce further changes on lignin structure. Increased doses of oxidizing agent and reaction time also improved the oxidation of cellulose and delignification, but they did not have a significant impact on lignin aromatic and side chain structures.

Torsional-Shear Stress of Wood at Various Temperatures

SummaryThe maximum torsional-shear stress of 5 softwoods and 4 hardwoods were tested in the radial and tangential planes. These tests were carried out in glycerin which was preheated to different temperatures between 22°C and 150°C, inclusively.The dense hardwoods possess 2.4 times higher shear stress than softwoods at 22°C. However, at elevated temperatures, the same degree of shear stress reduction (77 %) is obtained for hardwoods and softwoods in both radial and tangential failure. Thus, the reduction in shear stress is independent of physical and structural wood variables.

The role of nanoclay formations and wood fiber levels on central composite designed polyethylene composites

Central composite designed experiments are conducted to study the independent effects of maleated polyethylene, dicumyl peroxide and nanoclay in the forms of natural (Cloisite® Na+) and masterbatch (Nanoblend™ concentrates MB2001) on the mechanical properties of fiber reinforced PE composites with different fiber levels. The optimum values are predicted on the results of designed experiments and there are linear regressions between fiber content and their mechanical properties. The deposition and formation of nanoclay particles in PE composites are ascertained by scanning electron microscope and transmission electron microscope observations. Both natural nanoclay and MB2001 can be delaminated and even exfoliated in polarized PE matrix. As wood fiber is introduced, natural nanoclay particles (nanoclay-natural) are deposited on fiber surface even loaded in fiber lumens, but the nanoclay particles of MB2001 (nanoclay-concentrate) are mostly dispersed in the matrix. In addition, the different reinforcements between nanoclay-natural and nanoclay-concentrates are also investigated to find out the influence of particle formation on the quality of composite materials.

The breakdown mechanism of earlywood and latewood in refining

The principal objective of this research project is to study the breakdown mechanism of Jack pine (Pinus banksiana) earlywood (EW) and latewood (LW) in thermomechanical pulping by means of microscopic observations. Characteristics such as fiber splitting, shortening, delamination (internal fibrillation), external fibrillation, etc. are evaluated. Physical changes in the EW and LW fibers are qualified and quantified with the aid of light microscopy as well as scanning electron microscopy. The impacts of the observed changes on pulp and paper properties are assessed to establish possible interrelation between the fiber characteristics and paper properties.