Composition of Wood:
1. Cellulose
2. Lignin
3. Hemicelluloses
4. Extractives
5. Ash Producing Minerals
Wood is a linear polymer having a high molecular weight. The main building block of cellulose is sugar-glucose. As the tree grows, linear cellulose molecules arrange themselves into highly ordered strands, called fibrils. These ordered strands form the large structural elements that compose the cells walls of wood fibers.
Lignin: Accounts for 23% to 33% of softwood and 16% to 25% of hardwood by weight. It is mostly an intercellular material. Chemically lignin is an intractable, insoluble, material that is loosely bonded to the cellulose. It is the glue that holds the tubular cells together. It’s bonds affect the shear strength of wood.
Hemicelluloses: Are polymeric units made from sugar molecules. Differs from cellulose in that it has several sugars tied up in its cellular structure. Hardwood contains 20% to 30% hemicellulose and softwood averages 15% to 20%. The main sugar units include xylose and monnose.
Extractives: Compose 5% to 30% of the wood substance. Included in this group are tannins and other polphenolics, coloring matters, essential oils, fats, resins, waxes, gums, starches, and simple metabolic intermediates. These materials can be removes with inert neutral solvents (water, alcohol, acetone, and benzene).
Ash-Forming Materials: Account for 0.1% to 3% of the wood material and include calcium, potassium, phosphate and silica.
No comments:
Post a Comment