Cellulose and cellulose derivatives are important commercial products for plastics, textiles, packaging, films, laquers, and explosives. More recently, cellulose derivatives which are soluble in water or dilute alkali have been developed. Researchers are finding ways to use these derivatives as finishing and sizing agents for textiles, as absorbable surgical gauze, protective colloids, adhesives, thickening agents for foods, creams, ointments and pastes, and in pharmaceutical, printing, paper, and other industries.
Wood cellulose is the principal raw material for cellulose derivative products, and several million tons are produced each year. The second source of cellulose for cellulose derivatives is cotton linters (chemical cotton). Cotton linters find preferred use in certain products such as in cellulose acetate for plastics or high-tenacity rayon. For other applications cellulose acetate is more often made from wood cellulose.
Cellulose acetate is the major ester derivative and is prepared by reacting cellulose with acetic anhydride. An acetate group is placed on one of the available hydroxyls, with the percentage of hydroxyls derivatized depending on the amount of acetic anhydride used. Each monomer of glucose in cellulose has three available hydroxyls. Complete substitution would put three acetate groups on the monomer and the material would be said to have a degree of substitution of 3. Uses include:
Properties of cellulose esters. Properties of a cellulose derivative depend on the DP and DS
As the DP decreases
For cellulose acetate, as DS increases
An alkylation reaction will produce cellulose ethers. Most are water soluble and are used extensively in water based formulations for:
The properties of cellulose ethers are controlled by DP and DS. Products include:
Sodium carboxymethyl cellulose (CMC). The most widely used ether, prepared by the reaction of chloroacetic acid and cellulose.
Methylcellulose and ethyl cellulose
The Viscose Process. The viscose process is responsible for the production of rayon, cellophane, and hawaiian shirts. Rayon and cellophane are regenerated cellulose products The formation of the xanthate is an intermediate step in the process. A xanthate is a thioester which is prepared by first treating cellulose with NaOH to give alkali cellulose, which is allowed to ripen (i.e. the DP is slowly lowered to 200-400 by base hydrolysis). Alkali cellulose is then reacted with carbon disulfide to generate sodium cellulose xanthate (the DP will be 0.5-0.6). Cellulose xanthate (viscose) is allowed the age for several days. During the ageing process the DP is slowly lowered. The regeneration step is done in an acid precipitation bath containing zinc sulfate, in which the xanthate is decomposed and coagulated to regenerate the cellulose. The crystallinity of the regenerated cellulose can be varied by putting the regenerated fibers under tension as they are precipitated. For the chemical reactions see the Auburn University Wood Chem Pages.
The spent sulfite liquor from the acid sulfite process produces a sulfonated lignin that can be used for several industrial applications. Although they are all relatively inexpensive applications (Borregaard/Lignotech) this is currently a growth industry.
Tall oils are a mixture of rosin acids, fatty acids, and a small amount of unsaponifiable substances. Crude tall oil is produced by splitting with sulfuric acid, the sodium salts of the rosin and fatty acid produced when pine wood is pulped by the kraft process. Tall oils produced from various places in the world yield oils of various composition:
* Fatty acids - 30-35% -oleic 45-50% -lineolic 45-50% -palmitic 5-7% * Rosin acids - 35-60% -abietic 30-40% -neoabietic 10-20% *Unsaponifiables - 5-10% -beta-sitosterol 25-30%
To achieve the composition desired for a specific application, crude
tall oil must be processed. A wide ratio of fatty acids to resin acids can
be obtained, ranging from pure fatty acids to pure rosin acids. The only
restriction on the amount produced is that one ton of pulp yields only about
70 pounds of crude oil. Tall oils are in high demand in the industrial arena
due to their low cost and accessibility. Whole tall oil is the lowest priced
organic acid in the world. The components of tall oil have many uses:
1) Fatty Acids react in the typical chemical fashion. They react to form water-soluble soaps when reacted with alkali, ammonia, amines, and form oil soluble soaps when reacted with the salts of heavy metals.
2) Rosin Acids- Although many of the reactions of Rosin acids are the same as those of fatts acids, a few others should be mentioned. The reaction with lime or zinc oxide produce a high melting oil that is used in varnishes and printing inks.
3) Unsaponifiables- There is interest in a small fraction of the beta-sitosterol. It has been used to synthesize sex hormones and other compounds such as cortical steroids or cortisone. Beta sitosterol is the source of Benecol, the cholesterol-reducing substance Westvaco (in cooperation with the Finnish firm Raiso) will begin to market in the near future.
Terpenes are organic solvents that are derived from citrus or pine oil. There are many different types of terpenes, but the two more common are beta-limonene and alpha-pinene. Terpenes generally have a strong odor, even at low concentrations thus they are easy to recognize. Terpenes are not very reactive towards metals and most polymers lead to their use as industrial cleaners. Many are used to clean off heavy petroleum based greases as well as being used to clean printed circuit boards.
A good overview of wood chemical derivatives can be found in Union Camp's chemical products page.