Cellulose grafted

Following the findings of Mino and Kaizerman [51] that ceric ion can form a redox system with cellulose, grafting onto various natural polymers has been carried out by the ceric ion method. In the case of cellulose, the reaction between ceric ion and cellulose occurs to produce active sites on cellulose in the following manner ... 

Improvement in the solvent and oil resistance of rubbers can be achieved via grafting of acrylonitrile onto rubber [140-142] and rubber blends [143]. The careful control of the degree of grafting allows vulcanized rubber with high-mechanical properties compared with ungrafted vulcanized rubber to be obtained. Also, acid resistance [144] and resistance to microbiological attack [145,146] was improved for cellulose grafted with acrylonitrile, and increases in base resistance were also noted for MMA and a mixture of MMA and ethyl acrylate [13],... 

Condensation of an acrylic acid-cellulose graft copolymer with 5-amino-l,10-phe-nanthroline (233) has been utilized to provide polymer (234 Scheme 113) with the phenanthroline ligand oriented optimally for complexation (77MI11110). The polymer was described as exhibiting a strong sorption capacity for Co2+ and Cu2+ ions. 

Proof of grafting was presented through comparison of the solubilities of their saponified vinyl acetate and cellulose grafts and of the physical mixtures of the corresponding homopolymers. While from a cupriethyl-enediamin solution of the physical mixture pure cellulose is precipitated on acidification, the precipitate from the graft solution always contains constant amounts of polyvinyl alcohol, as proven by infrared spectroscopy. 

The first application of the ferrous ion-hydrogen peroxide initiation for polymerizing vinyl monomers on and into cellulose fibers has been reported by Landeias and Whewell (41) in three successive papers. They are apparently the first who applied the "anchored catalyst technique, which other people have termed "in situ polymerization to cellulose grafting. The authors internally deposited methyl methacrylate, acrylonitrile, styrene, methyl vinyl ketone and methacrylamide in amounts between 10 and 80%. No attempt had been made to determine if actual grafting had occurred. In 1961 Richards (42) studied this question in great detail. Products obtained by polymerization of acrylonitrile and of styrene in viscose rayon were acetylated. Fractionation of... 

Kamogawa, and Sekiya (54) studied the graft polymerization of acrylamide onto cotton fabric using ceric ammonium nitrate as the catalyst. Similarly to Kulkarni et al. (35) the authors performed subsequent cross-linking with formaldehyde amd methylol compounds. From precipitation studies by acidification of cuprammonium solutions on mixtures of polyacrylamide and cellulose on the one hand and polyacrylamide-cellulose grafts on the other the authors conclude that chemical bonds must exist between the two polymers in the grafted product. 

The acrylonitrile cellulose grafts were examined by differential thermal analysis, solvent extraction and solubility studies. They conclude from their data that the unextractable portion is present mainly in grafted form. 

The properties of cellulosic graft copolymers have been studied to a considerable extent but mainly in the form of grafted fibers or films of ill-defined composition. However, a few properties have been measured on well defined grafts (147). It was found that solutions of cellulose acetate-polystyrene grafts in dimethyl formamide are less tolerant to the addition of polystyrene than cellulose acetate itself. This result was attributed to the greater coil expansion in the case of the graft copolymer. On the other hand, the tolerance of the grafts to each homo-... 

Yasuda, H J. A. Wray, and V. Stannett Preparation and characterization of some cellulose graft copolymers. Part I. J. Polymer Sci. C2, 387 (1963). 

Table VII. Properties of Textile Fabrics Containing Cellulose Graft Copolymers...

A similar evaluation was made for the other series of CA-g-PHAs to establish a general relationship between their molecular architecture and thermal transition behavior [24]. Of particular interest is the finding that the composition dependence of the Tg of the cellulosic graft copolymers was represented well in terms of a formulation based on a comb-like polymer model [29], when CAs of acetyl DS 2 were employed as a trunk polymer. 

Heinze et al. found that DMSO in combination with tetrabutylammonium fluoride trihydrate dissolved cellulose (degree of polymerization < 650) within 15 min at room temperature [38]. They also demonstrated that homogeneous esterification of cellulose is possible in this solvent system. The applicability of this new solvent system to cellulose grafting has recently been proved by adoption of cyclic compounds such as lactones and N-carboxy a-amino acid anhydrides (NCAs) [39]. e-Caprolactone was facilely graft-polymerized on cellulose at a graft rate of 65% (per trunk weight of 100), and NCAs at over 100%, in the respective homogeneous reaction systems at < 60 °C. 

In spite of these enormous efforts, there is still no large-scale commercial application of cellulose graft copolymers. The reasons for this situation and the challenge it represents to cellulose and polymer scientists and engineers will be the subject of this introductory paper. It is convenient to break down such a discussion into the following areas, synthesis, characterization, properties and, finally, applications. The discussion will be mainly devoted to cellulose itself, although grafting to cellulose derivatives has also been actively pursued. 

There are some formidable challenges facing those engaged in the synthetic aspects of cellulose grafting if viable commercial processes are to be developed. The most important of these may be enumerated as follows ... 

In the field of true cellulose grafting, there have been numerous attempts at commercialization in the cellulose fiber field. Some have reached pilot stage proportions, others have been full commercial processes such as the Deering-Millikan durable process now apparently in abeyance. Most of these developments have been in the field of textiles. 

UV light induced grafting onto wood cellulose is reported for several vinyl monomers. The reaction is initiated by free radical initiators such as phenylace-tophenone and benzophenone derivatives. Percent grafting-time conversion curves are determined as a function of the initiators, monomers, pulps and additives. Additional typical results obtained in IR spectroscopy, GPC and thermal analysis are reported. A discussion about the use of a photochemical procedure in obtaining cellulose graft copolymers is presented. 

Sodium bisulfite-china clay proved to be an efficient initiator for homopolymerization and graft polymerization of methyl methacrylate onto cellulose. Grafting reactions using ceric ammonium sulfate, sodium bisulfite-soda lime glass or -china clay are inhibited or retarded on adding soda lignin to the grafting medium. 

Although an appreciable thermoplasticization was realized by the decrystallization treatment, the treatment did not give cellulose graft products which melt upon heating. This lack of melting was confirmed by microscopic observations of films prepared with the decrystallized composites. 

Teramoto Y., Nishio Y. Structural designing and functionalization of biodegradable cellulosic graft copolymers. Cellulose Communications 77 115-120 (2004). 

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