Lignocellulosic materials modification

Nakano, T. (1996). Characterization of chemically modified wood. In Chemical Modification of Lignocellulosic Materials, Hon, D.N.S. (Ed.). Marcel Dekker, New York, USA, pp. 247-275. 

Most research on chemical modification of lignocellulosic materials has focused on improving either the dimensional stability or the biological resistance of wood. This paper reviews the research on these properties for wood and other lignocellulosic composites and describes opportunities to improve fire retardancy and resistance to ultraviolet degradation. 

Meshitsuka, G, and Isogai, A. 1996. Chemical structure of cellulose, hemicellulose, and lignin. In Hon, D. N.-S. (Ed.), Chemical modification of lignocellulosic materials (pp. 11-34). New York Marcel Dekker. 

Extraction of lignocellulosic materials with dioxane has been used for quite some time as a method for lignin isolation at atmospheric pressure (1) or, as recently reported, at high pressure and with supercritical C02 mixtures (2-5). In this case, it was possible to extract from wood lignin oligomers with a low degree of chemical modification, hemicelluloses were also depolymerized and extracted, but cellulose remained without significant mass losses. 

Many products with industrial value are manufactured from wood and lignocellulosic materials. The optimum conditions for the reactions have been established by scientists from academia or industry. Hence, to utilize this basic chemistry to redesign wood products or lignocellulosic materials with superior properties will be the main issue of the chemical modification of... 

Based on the materials highlighted by the authors of this book, it is clear that scientists throughout the world have worked diligently to improve the properties, performance, and utility of wood and other lignocellulosic materials. High-level chemical modification research activities have been developed and continuing. 

Chemical modification specifically tailored for macromolecular structures of lignocellulosic materials is a fascinating scientific endeavor in its own right as well as a useful art for the creation of specialty polymeric materials for technological applications. By utilizing suitable chemical reactions, new products with hybrid properties of nature and synthesis will take an important position with regard to utilization in the competitive world. 

Lignocellulosic research today is poised on the threshold of a new era of research breakthroughs. It has enabled the use of a wide variety of lignocellulosic materials, low-quality wood species and sawdust, and low-value lignin products. Lignocellulosic and cellulosic research efforts are under way to produce novel products for construction, transportation, plastics, fiber, packaging, and medical applications. Some of the major activities in chemical modifications of wood, cellulose, and lignins are the main features of this book. 

Chemical modification reactions continue to play a dominant role in improving the overall utilization of lignocellulosic materials [1,2]. The nature of modification may vary from mild pretreatment of wood with alkali or sulfite as used in the production of mechanical pulp fibers [3] to a variety of etherification, esterification, or copolymerization processes applied in the preparation of wood- [4], cellulose- [5] or lignin- [6] based materials. Since the modification of wood polymers is generally conducted in a heterogeneous system, the apparent reactivity would be influenced by both the chemical and the physical nature of the substrate as well as of the reactant molecules involved. 

Figure 1 Model for the chemical treatment of wood. (A) Cellular level. (l)-(3) Untreated cell wall, (4)-(6) treated cell wall (1) untreated (4) no chemical deposits in lumen (2) and (5) deposits on cell wall surface (3) and (6) filling of lumen. (B) Modification of lignocellulosic material at molecular level, (o) Hydroxyl group available for hydrogen bonding ( ) substitution of hydroxyl group ( ) bulking agent.

M. Takahashi, Y. Imamura, and M. Tanahashi, Int. Chem. Congress of Pacific Basin Societies, Agrochemistry, Sub-symposium on Chemical Modification of Lignocellulosic Materials-Chemical Reactions, Hawaii, 1989. 

Chemical modification of lignocellulosic materials / edited by David N.-S. Hon. 

Moreover, wood has limited thermoplasticity. Although it can be bent under steam and chemical treatment, wood normally bums before it melts or becomes sufficiently plastic for heat molding or extrusion. These two techniques are important ways of shaping materials in high-speed composite production and are therefore keys to the cost-efficient penetration of lignocellulosic materials into the composites market. Chemical modification of wood offers a means of improving its thermoplasticity. 

In addition to wood, other lignocellulosic materials of commercial value, such as bamboo, kenaf, and rice straw, also lend themselves to chemical modification for use in composites. 

A useful characterization of these modified lignocellulosic materials would be that of the size or of the size distribution of the water-filled submicroscopic pockets and of the additional internal surface area in the water-swollen condition created by the various modifications. Characterization such as this based on adsorption measurements has been made by Stone and Scallon (34). Additional characterizations based on x-ray-scattering measurements are being carried out at the U. S. Forest Products Laboratory. 

Meshitsuka G., Isogai A. Chemical structure, hemicellulose and lignin. In Hon D.N.S. (ed.) Chemical Modification of Lignocellulosic Materials, pp. 11-34. Marcel Dekker Inc., New York (1996)... 

Hon DNS (1996b) Chemical modification of lignocellulosic material. Marcel Dekker, New York Inada A, Nakanishi T, Tokuda H, Sharma OP (1997) Antitumor activities of lantadenes on mouse skin tumors and mouse hepatic tumras. Planta Med 63 476-478 Jayakumar R, Mahadevappa M, Joshi S, Prasad TG (1989) Dormancy studies in Cassia sericea seeds. Seed Res 17(2) 118-121... 

Hon DNS (1988) Cellulose a wonder material with promising future. Polym News 13 34-140 Hon DNS (1992) Chemical modification of lignocellulosic materials old chemistry, new... 

The effect of flax fiber modification and the effect on the presence of TCL were also studied by Arbelaiz et al. [17]. In his studies, fibers were subjected to maleic anhydride, vinyltrimetoxy silane, and aUcali with addition of MAPP-grafted polypropylene. All applied modifications produced improvement in the thermal stability of lignocellulosic material. Analysis of the crystalline structure showed the increase of crystallinity as a result of fiUer addition. Nucleation density around unmodified fibers was higher than around fibers modified with maleic anhydride. Surfaces of unmodified fibers had the surface active for initialization of transcrystaUization, which, in the case of modified fibers, did not occur. Son et al. [32] explained this phenomenon as... 

---