Wood biomass is composed primarily of three complex polymers: cellulose, hemicellulose, and lignin. While traditional uses focus on lumber and paper, modern industrial chemistry modifies these components to create advanced products. By breaking down wood’s cell wall structure, scientists transform these natural polymers into new materials, including semi-synthetic fibers, functional additives, and liquid fuels. This transformation leads to high-tech textiles, pharmaceuticals, and sustainable energy sources.
Cellulose-Based Fibers and Films
Wood-derived synthetic products often involve processing purified wood pulp, which is nearly pure cellulose, to create textile fibers and flexible films. These products are termed “regenerated” or “semi-synthetic” because the chemical process dissolves the cellulose structure and then reforms it into a new physical shape. The most common example is Viscose Rayon, a textile fiber produced by treating wood cellulose with sodium hydroxide and carbon disulfide to form cellulose xanthate. This solution is then extruded into an acid bath, which regenerates the cellulose into continuous filaments.
Cellophane, a transparent packaging film, uses a nearly identical Viscose process, but the solution is extruded through a narrow slit to form a sheet. The resulting film has high transparency and is a good barrier to gases, though it is permeable to water vapor. Another derivative is Cellulose Acetate, a thermoplastic created by reacting cellulose with acetic anhydride and a catalyst. This process replaces the hydroxyl groups on the cellulose chain with acetyl groups, changing the polymer’s solubility and melting point. Cellulose Acetate is used in fibers for cigarette filters and textiles, or cast into films for specialized optical applications.
Functional Additives and Specialty Cellulose Products
Synthetic products are also created for the unique chemical function they provide when incorporated into other materials. Carboxymethyl Cellulose (CMC) is produced by reacting alkali cellulose with chloroacetic acid, which introduces carboxymethyl groups onto the polymer backbone. This modification makes the cellulose highly water-soluble, allowing it to function as an effective thickener, binder, and stabilizer. CMC is used in products ranging from ice cream and baked goods to drilling muds; its viscosity is customized based on the degree of substitution.
Hydroxypropyl Methylcellulose (HPMC) is a similar derivative created by reacting alkali cellulose with methyl chloride and propylene oxide. This allows HPMC to dissolve in cold water and form a gel upon heating, a thermoreversible property. This property is exploited in pharmaceuticals for controlled-release drug delivery tablets, where the HPMC hydrates to form a gel layer that slowly erodes. A more reactive derivative is Nitrocellulose, formed by treating wood pulp with nitric and sulfuric acids, replacing hydroxyl groups with nitrate groups. Low-nitrated versions are soluble in organic solvents and used as a fast-drying film-former in lacquers and nail polish, while highly-nitrated versions, known as guncotton, are powerful explosives and propellants.
Lignin and Hemicellulose Derivatives
Lignin is the second most abundant wood polymer and is being explored as a precursor for high-value carbon-based products. Since lignin is rich in carbon and aromatic, it can be used to create advanced materials like carbon fibers, which are conventionally made from petroleum-based materials. The industrial process often uses lignosulfonate, a byproduct of sulfite pulping, which is spun into precursor fibers before being stabilized and carbonized.
Lignin’s aromatic rings are also chemically fractured through oxidative depolymerization, breaking the large polymer into smaller, valuable aromatic chemicals. The most notable example is the synthesis of vanillin, which is industrially produced by oxidizing lignin.
Hemicellulose Derivatives
Hemicellulose is a shorter, more branched polymer that is easier to break down than cellulose and contains various sugar units, including xylose. The industrial focus is converting xylose into the sugar alcohol Xylitol, a low-calorie sweetener used in chewing gum and diabetic foods. This process involves hydrolyzing the hemicellulose found in wood waste, typically with acid, to release the xylose monomers. The purified xylose solution is then subjected to catalytic hydrogenation, converting the sugar into the stable, crystalline Xylitol.
Wood-Derived Fuels and Solvents
The complete chemical breakdown of wood biomass yields liquid fuels and solvents. Bioethanol, a gasoline additive, is produced through a biochemical conversion platform. This requires pretreatment of the wood to separate the cellulose and hemicellulose from the lignin matrix. The carbohydrate polymers are then hydrolyzed to release sugar monomers, such as glucose and xylose. These wood sugars are subsequently fermented by specialized yeasts or bacteria, which metabolize the sugars into ethanol.
Methanol, historically known as “wood alcohol,” is primarily produced through a high-temperature thermochemical process called gasification. Wood is exposed to high heat and controlled amounts of oxygen or steam, breaking down the polymers into a synthesis gas, or syngas, composed primarily of hydrogen and carbon monoxide. This syngas is cleaned and conditioned to the precise ratio necessary for catalytic synthesis. The cleaned syngas is then passed over a catalyst, where the molecules recombine to form liquid methanol.