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Naturally Occurring Polymers—Plants 291

shear. Dilute solutions approach being Newtonian in their flow properties even under a wide range

of shear rates.
HEC is used as a protective colloid in latex coatings and pharmaceutical emulsions; as a fi lm
former for fabric fi nishes, fibrous glass, and in aerosol starches; thickener for adhesives, latex coat-

ings, toothpaste, shampoos and hair dressings, cosmetic creams and lotions, inks, and joint cements;
lubricant for wallpaper adhesives and in pharmaceutical gels; and as a water binding for cements,
plastics, texture coatings, ceramic glazes, and in printing inks.
Sodium carboxymethylcellulose is formed by the reaction of sodium chloroacetate with basic
cellulose solutions. The sodium form of carboxymethylcellulose is known as CMC or as a food
grade product as cellulose gum. It is soluble in both hot and cold water.

Cellulose–OH, NaOH + Cl–CH COONa → Cellulose–O–CH –COONa (9.12)
2 2
Sodium carboxymethylcellulose
The most widely used cellulose gums have DS values about 0.65–1.0. CMCs are used as thick-
ening, binding, stabilizing, and fi lm-forming agents.
Carboxymethylhydroxyethylcellulose, CMHEC, is synthesized from the reaction of hydroxeth-
ylcellulose with sodium chloroacetate. The product is a mixed ether. It has properties similar to
both CMC and HEC. Like CMC it exhibits a high water binding ability and good fl occulating
action on suspended solids but it is more compatible than CMC with salts. It forms ionic cross-
links in the presence of salt solutions containing multivalent cations, allowing its viscosity to be
greatly increased by the presence of such cations. Solutions can be gelled by addition of solutions
of aluminum and iron. It is a water-soluble material used in oil recovery and in hydraulic fractur-
ing fl uids.
Methyl and hydroxyalkylmethylcelluloses are nonionic polymers soluble in cool water.
Methylcellulose (MC), hydroxyethylmethylcellulose (HEMC), and hydroxypropylmethylcellulose
(HPMC) do not interact with cations forming insoluble salts, but electrolytes that compete with MC
for water can cause precipitation.
Hydroxylpropylcellulose (HPC) is a thermoplastic nonionic cellulose ester that is soluble in both
water and a number of organic liquids. It is synthesized through reaction of the basic cellulose slur-
ried with propylene oxide.
O
/ \
Cellulose − OH, NaOH + H C − CH − CH 2 Cellulose−( − O − CH − CH(CH ) − ) − OH (9.13)
n
3
2
3
Hydroxypropylcellulose
Methylcellulose is formed from basic cellulose and its reaction with chloromethane.
Cellulose–OH, NaOH + CH Cl → Cellulose–O–CH 3 (9.14)
3
Methylcellulose

Methylcellulose is used as an adhesive; in ceramics to provide water retention and lubricity; in
cosmetics to control rheological properties and in the stabilization of foams; in foods as a binder,
emulsifier, stabilizer, thickener, and suspending agent; in paints, paper products, plywood as a rhe-

ology control for the adhesive; in inks, and in textiles as a binder, and for coatings.
Ethylhydroxyethylcellulose (EHEC) is a nonionic mixed ether available in a wide variety of
substitutions with corresponding variations in aqueous and organic liquid solubilities. It is compati-
ble with many oils, resins, and plasticizers along with other polymers such as nitrocellulose. EHEC
is synthesized through a two-step process, beginning with the formation of the HEC-like product
through reaction between the basic cellulose and ethylene oxide. The second step involves further
reaction with ethyl chloride.

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