Cellulose graft copolymers selection

The morphology of the fibrous cellulose graft copolymers depended on the method of initiation of free radical formation, experimental conditions during the copolymerization, chemical modification of the cellulose before reaction, and the type of monomer used (60). Variations in the shape of the fibrous cross section, in layering effects in the fiber, and in the location and distribution of the grafted copolymer in the fiber were observed by electron microscopy (61). Cotton cellulose—poly (acrylonitrile) copolymer was selected to show the possible variations in location and distribution of the grafted copolymer in the fiber. 

Isolation of graft copolymers from homopolymers and unreacted cellulose nitrate was conducted by using selective solvent extraction technique. 

A significant number of works are concerned with the development of new membranes for the separation of mixtures of aromatic/alicyclic hydrocarbons [10,11,77-109]. For example, the following works can be mentioned. A mixture of cellulose ester and polyphosphonate ester (50 wt%) was used for benzene/cyclohexane separation [113]. High values of the separation factor and flux were achieved (up to 2 kg/m h). In order to achieve better fluxes and separation factors the attention was shifted to the modification of polymers by grafting technique. Grafted membranes were made of polyvinylidene fluoride with 4-vinyl pyridine or acrylic acid by irradiation [83]. 2-Hydroxy-3-(diethyl-amino) propyl methacrylate-styrene copolymer membranes with cyanuric chloride were prepared, which exhibited a superior separation factor /3p= 190 for a feed aromatic component concentration of 20 wt%. Graft copolymer membranes based on 2-hydroxyethyl methylacrylate-methylacrylate with thickness 10 pm were prepared [85]. The membranes yielded a flux of 0.7 kg/m h (for feed with 50 wt% of benzene) and excellent selectivity. Benzene concentration in permeate was about 100 wt%. A membrane based on polyvinyl alcohol and polyallyl amine was prepared [87]. For a feed containing 10 wt% of benzene the blend membrane yielded a flux of 1-3 kg/m h and a separation factor of 62. 

To prepare the graft copolymer, a PO (MW = 50 to 1,000 kg/mol) was either dissolved or swollen in an inert hydrocarbon, monomers (>80 wt% of a methacrylic ester, CH2=C(CH3)COOR) and an initiator was added to the heated mixture while stirring. As a result, acrylic branches of a relatively high molecular weight (MW = 20 to 200 kg/mol) were grafted onto the PO macromolecules. The graft copolymer could be used as a compatibilizer-cwm-impact modifier in a variety of polymers selected from between PO, acrylic polymers, SAN, EVAc, PA, PEST, PC, POM, PAr, PVC, ABS, PVDC, cellulosics, polyester-polyether block copolymers, PEA, PEEK, PEI, PES, CPVC, PVDF, PPE, PPS, PSF, TPU, PAI, PCL, polyglutarimide, blends of PEST with PC or PVC [Ilendra et al., 1992, 1993]. 

The apparent distributions of grafted copolymers in fibrous cellulose are indicated in Figures 18 and 19. Differential solubility tests have been made on electron-microphotograph cross-sections to define these distributions more clearly. Covalently linked cellulose and polymer are less soluble in selected solvents than in either solvents for cellulose or polymer. ... 

An effective method of NVF chemical modification is graft copolymerization [34,35]. This reaction is initiated by free radicals of the cellulose molecule. The cellulose is treated with an aqueous solution with selected ions and is exposed to a high-energy radiation. Then, the cellulose molecule cracks and radicals are formed. Afterwards, the radical sites of the cellulose are treated with a suitable solution (compatible with the polymer matrix), for example vinyl monomer [35] acrylonitrile [34], methyl methacrylate [47], polystyrene [41]. The resulting copolymer possesses properties characteristic of both fibrous cellulose and grafted polymer. 

The selective oxidation of cellulose to dialdehyde by sodium periodate is well known. It has been postulated by Criegee (74) and by Waters (73) that this reaction proceeds by a free radical mechanism. Toda (76) and Morimoto, Okada, Okada, and Nakagawa (77) have concluded that sodium periodate oxidation should initiate graft polymerization. They succeeded in grafting methyl methacrylate and acrylonitrile onto cellulose substrates, such as rayon and paper. A similar procedure is recommended in a patent of Chemische Werke Huels (78) to graft vinyl monomers onto cotton, polyethylene oxide, copolymers of vinyl chloride-vinyl acetate, and others. 

---