Modification of the properties of cellulose by means of grafting

Abstract

Owing to a combining of the original polymer properties, greatly widening the field of their application, graft copolymers of cellulose are of considerable interest. The graft copolymers may be obtained by chemical action on the initial polymer molecules or by activation of the macromolecules with the aid of physical methods, such as γ‐rays, ultraviolet rays, mechanical rupture of the molecular chains, etc. We have employed both chemical methods and γ‐radiation (Co60). Cotton cellulose was used as starting material. Acrylonitrile and styrene were the monomers employed. Chemical treatment of cellulose was accomplished by the action of ozone‐oxygen mixtures to obtain polyperoxide cellulose compounds. The latter decompose upon heating, with formation in given regions of the cellulose molecule active of macroradicale capable of reacting with monomers to produce the graft copolymers. The grafting of the monomers onto the activated cellulose was carried out in high vacuum at 100°C. In this way graft copolymers of cotton cellulose with acrylonitrile and viscose cord with styrene containing 40% (by weight) of the graftings were obtained. A study of the graft copolymer properties showed the acrylonitrile‐containing compound to dye much better and to be more resistant to microbial action and sun rays than the original material. After grafting polystyrene to viscose cord its adhesion to rubber increased by 75%. Acrylonitrile‐cellulose graft copolymers were also obtained by irradiating mixtures of cellulose and acrylonitrile solutions in various solvents over a wide range of radiation doses and monomer concentrations. The optimal dose for synthesis of graft copolymers was 100,000 r. Preliminary experiments showed that separate irradiation of cellulose with subsequent treatment with the monomer did not lead to the formation of graft copolymers. The formation of cellulose‐acrylonitrile graft copolymers takes place only when the acrylonitrile solvent wets the cellulose well and is sorbed by the latter, thus facilitating the penetration of the former into the intermolecular spaces of the cellulose molecules. This process is not associated with formation of cellulose peroxides, but with another mechanism of activation. In order to demonstrate the formation of graft copolymers under the conditions described, and not simply of cellulose derivatives with the acrylonitrile and styrene groups uniformly distributed over the chain units, we have developed a method for determining the degree of polymerization of the grafted sections. This consisted of hydrolysis of the cellulose graft copolymers in acid media. The graft copolymer, of which the cellulose had broken down to the monosugar, was washed with water and the degree of polymerization of the polystyrene or polyacrylonitrile graftings was determined viscometrically. The degree of polymerization of the grafting was found to vary within the range of 20 to 100.

Photoinitiator‐free UV grafting of styrene, a weak donor, with various electron‐poor vinyl monomers to polypropylene film

“…Styrene is a common monomer used mainly in the production of polystyrene. However, styrene displays good grafting properties and it has been successfully grafted to various polymers, such as cellulose,8–10 modified celluloses,11 polyolefins,12, 13 poly(vinyl chloride), nylon 66 and poly(ethylene terephthalate),14 by various grafting methods with the ionising radiation method being the predominant one. Furthermore, styrene has been found to induce grafting of other vinyl monomers, such as acrylonitrile (AN)14 and methyl methacrylate (MMA),13, 15 onto polypropylene (PP) as well as cellulose substrates.…”