Cellulosic fibers, graft

Figure 17.12 Evolution of the adsorption capacity vs. the acylation degree for Cell-C12 and Cell-C16 solute 2-Naphthol, pH 6.5 -7 (Cell-C12 and Cell-C16 refers to cellulose fibers grafted with dodecycl and hexadecyclanhydride acid respectively). ...

As in the case of ceric and vanadium ions, the reaction of organic compounds with Co(III) proceeds via formation of an intermediate complex. Such a complex decomposes and produces free radicals capable of initiating vinyl polymerization. However, only a few reports on Co(IIl) ion-initiated grafting onto cellulose fibers are available [38]. 

Graft copolymerization can be initiated by physical or chemical processes. This paper describes methods for chemical initiation of grafting onto cellulosic fibers with special emphasis on recent developments, i.e. studies from the last 10-15 years. The initiation reactions may be free radical or ionic processes. The grafting reaction may also be a condensation or addition process. 

Cellulosic fibers contain a partly crystalline cellulose phase as the main constituent. The grafting reactions can usually occur only with the amorphous or disordered cellulose. Only highly swollen cellulose with an expanded lattice may react throughout the ordered regions. 

A few examples of recently developed grafting reactions applied to cellulosic fibers are described to illustrate typical processes and discuss the mechanisms involved. 

The hydroxyl radicals formed may abstract hydrogen from the cellulose fiber substrate which gives grafting sites and subsequently grafted polymer with monomer present. The HO- radicals may also initiate homopolymerization. This means that reaction (17) is not specific for initiation of grafting. Another disadvantage is that the Fe + ions formed - if not carefully removed -may cause discoloration of the resulting product. 

Peracetic acid, formed in situ from acetic acid and hydrogen peroxide in acid aqueous solution, was found to initiate graft copolymerization of vinyl monomers, e.g. methyl methacrylate and 4-vinyl pyridine, onto wood and cellulosic fibers at a good rate (1-3 h time) at 60°C2. The initiati on reaction is not specific for grafting and considerable amounts of homopolymer is formed. 

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... 

Korshak, Mozgova, Shkolina, Uzina, and Ionova (70) obtained graft copolymers of vinyl monomers on cellulose fibers by activation of... 

Armstrong, and Rutherford have reported extensive studies on the vapor phase grafting of vinyl monomers to cellulosic fibers both mutual and pre-irradiation methods have been used (97, 120). Again, water or another swelling agent was found to be necessary for effective grafting to rayon and cotton for all the monomers studied. In the case of cellulose acetate water was helpful but not necessary except for styrene. Acetic acid and methanol vapors were also found to be effective promotors of vapor phase grafting to cotton and cellulose acetate fibers. 

Schwab, E., V. Stannett, and J. J. Hermans Grafting onto cellulose and cellulose fibers. Tappi 44, 251 (1961). 

Okamura, S., T. Iwasaki, Y. Kobayashi, and K. Hayashi Gamma-ray initiated graft copolymerization on the surface of nylon fibers and in the inner layers of cellulosic fibers. Large Radiation Sources in Ind., Proc. Conf., Warsaw, 1959, 1, 459. 

The elastomers exhibited rubber-like behavior. From an examination of electron photomicrographs of cross sections of the elastomers, the fibrillar structure of the cellulose fibers apparently formed a network, and poly (ethyl acrylate) was distributed uniformly among the fibrils. The rigid crystalline regions of the cellulose fibers apparently stabilized the amorphous, grafted poly (ethyl acrylate) to determine the mechanical properties of the elastomers (43, 44). For example, typical elastic recovery properties for these elastomers are shown in Table X. 

The properties of grafted cellulose fibers, films, powders, pulp and paper have been well described in a number of reviews and will not be discussed per se further in this paper. 

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. 

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