Re: Cellulose has many hydroxyl groups. What does this allow cellulose to do?

Function of hydroxyl group in cellulose

Over half of the total organic carbon in the earth's biosphere is in cellulose. Cotton fibres are essentially pure cellulose, and the wood of bushes and trees is about 50% cellulose. As a polymer of glucose, cellulose has the formula (C6H10O5)n where n ranges from 500 to 5,000, depending on the source of the polymer. In the cellulose chain, the glucose units are in 6-membered rings, called pyranoses. They are joined by single oxygen atoms (acetal linkages) between the C-1 of one pyranose ring and the C-4 of the next ring.

In order to expand the ways in which cellulose can be put to practical use,chemists have devised techniques for preparing solutions of cellulose derivatives that can be spun into fibers, spread into a film or cast in various solid forms. A key factor in these transformations are the three free hydroxyl groups on each glucose unit in the cellulose chain, --[C6H7O(OH)3]n--. Esterification of these functions leads to polymeric products having very different properties compared with cellulose itself. Synthetic fibers such as rayon and acetate rayon in which the free hydroxyl groups of the glucose units in cellulose are chemically modified are prepared from Cellulose. I.e. In acetate rayon all free -OH groups are acetylated.

1. Cellulose Nitrate: It is prepared by treating cellulose with nitric acid and is the earliest synthetic polymer generally used. The fully nitrated compound, --[C6H7O(ONO2)3]n--, called guncotton, is explosively flammable and is a component of smokeless powder. Partially nitrated cellulose is called pyroxylin. Pyroxylin is soluble in ether and at one time was used for photographic film and lacquers. The high flammability of pyroxylin caused many tragic cinema fires during its period of use. Furthermore, slow hydrolysis of pyroxylin yields nitric acid.

2. Cellulose Acetate: --[C6H7O(OAc)3]n--, is less flammable than pyroxylin, and has replaced it in most applications. It is prepared by reaction of cellulose with acetic anhydride and an acid catalyst. The properties of the product vary with the degree of acetylation. An acetone solution of cellulose acetate may be forced through a spinnerette to generate filaments, called acetate rayon that can be woven into fabrics.

3. Viscose Rayon: is prepared by formation of an alkali soluble xanthate derivative that can be spun into a fiber that reforms the cellulose polymer by acid quenching. The product fiber is called viscose rayon.

A few of the reactions involving hydroxyl groups are:

Etherification: The simple methyl and ethyl ethers to more complex materials, such as carboxymethyl celluloses are made by reaction of cellulose with chloroacetic acid. Reaction of cellulose with ethylene oxide, or other epoxides, yields hydroxyethyl cellulose, or other hydroxyalkyl derivatives, which can have a number of useful properties, depending on DS and the length of the hydroxyalkyl side chains. Cellulose hydroxyls can also be made to add across activated double bonds, as in the formation of cyanoethyl cellulose from reaction with acrylonitrile.

Acetal Formation: the hydroxyl group of cellulose reacts with aldehydes and hemiacetals to form acetals. Reaction with formaldehyde and formaldehyde derivatives (most commonly urea-formaldehyde resins) imparts dimensional stability to cellulosic textiles such as cottons and rayons.

Oxidative Degradation: oxidation of cellulose hydroxyls forms the expected aldehyde and ketone, and carboxyl groups. However, unlike their simple carbonyl analogs, the oxidation products of cellulose (termed oxycelluloses) are significantly less stable in the presence of alkali.

Because the individual cellulose polymer molecules can line up, with extensive hydrogen bonding to their neighbors, cellulose is insoluble. [This seems like it might be the most apropos answer to your son's question, "Form extensive hydrogen bonds." -- Moderator]

Cellulose has many uses as an anti-cake agent, emulsifier, stabilizer, dispersing agent, thickener, and gelling agent, also as alternate fuel for ethanol production etc.

References:

 
http://www.fibersource.com/f-tutor/cellulose.htm#chemistry
 
http://www.cem.msu.edu/~reusch/VirtualText/carbhyd.htm
 
http://www.mansfield.ohio-state.edu/~sabedon/campbl05.htm
 
http://instruct.uwo.ca/chemistry/223b-98/carbos.htm
 
http://www.lsbu.ac.uk/water/hycel.html

Best Regards,

Devendra