Irradiation of Cellulose

Table I. Trapped Radical Yield on Irradiation of Cellulose"...

In a Soviet study23,24 the mobility of cellulose macromolecular fragments was investigated by means of the paramagnetic label technique. Cellulose macroradicals serving as paramagnetic centres were obtained by irradiation of cellulose at —120° to —140 °C. The mobility of their fragments was found to increase sharply with the water content in the sample to reach a maximum at 10% water. It is this increase which appears to be responsible for the rapid decomposition of macroradicals in moist cellulose. 

There are many data about the nature of free-radical particles, being formed at irradiation of cellulose by ultraviolet light. Since, being formed products of phototransformation are... 

By gamma ray irradiation of cellulose fibers, it was noticed that a separation of a gas mixture (25-30% H 13-18% CO 45-58% CO and 2-3% CH ) occurs due to the dehydrogenation, depolymerization and glucoside chain destruction. By analyzing the molar mass and polydispersity of the irradiated cellulose fibers with gel permeation chromatography technique, it was concluded that cellulose destruction by high energy radiation profoundly affects the molecular structure on both a primary and supramo-lecular level [34]. 

The y-irradiation of cellulose in the atmosphere associates oxidation and degradation mechanisms, as one would expect from the particularly high energy involved. A recent investigation has also shown that this type of treatment favours some cellulose crosslinking [86, 87], as well as a decrease in crystallinity accompanied by thermal degradation, whose extent increases with increasing irradiation doses [88]. 

Furthermore, the ambient pressure also influences the impulse transfer to the target [35]. An increase in the peak pressure of the shock wave in the target, with increase of the ambient pressure between 0.1 - 1 atmosphere, is observed after laser irradiation of cellulose acetate targets. Too high a pressure may reduce the peak pressure in the target due to decomposed material redeposited onto the surface of the explosive. An ambient pressure of about I atmosphere is used in the experiments described below. 

The decay of radicals produced by photo-irradiation of cellulose at room temperature, and the characteristics of photo-irradiated cellulose for the initiation of graft copolymerization with methyl methacrylate have been investigated. The e.s.r. spectra of irradiated samples of untreated, swollen, oximated, or ferric-ion-sensitized celluloses were examined. The decay of radicals was accelerated by solvents (water — methanol > acetone > p-dioxan) and was retarded by methacrylic acid > methyl methacrylate styrene. Graft copolymerization of methyl methacrylate with photo-irradiated cellulose was effectively initiated by water or methanol, but not by either acetone or p-dioxan. It appears that initiation of the graft copolymerization onto pre-irradiated cellulose is promoted by radicals exhibiting a singlet in the e.s.r. spectrum. 

The effects of photosensitizers on the formation of free radicals on u.v.-irradiation of cellulose at 77 K have been investigated. Samples of cellulose treated with benzoyl peroxide, hydrogen peroxide, benzophenone, riboflavin, Cr + ions, or Ni + ions exhibited single-line e.s.r. spectra, whereas those treated with Pb + or Fe + ions exhibited three- and five-line e.s.r. spectra, respectively. Studies of the decay of radicals in photo-irradiated cellulose at low temperatures indicated that at least six types of radical are formed. Changes in the radicals with the reaction conditions were carefully examined. 

Table 4,8 ESR spectra of free radicals formed during UV irradiation of cellulose... 

Fig. 6. The CP/MAS spectra of cellulose acetate-butyrate (CAB) and of cellulose acetate (CA, degree of substitution = 1.97), 20. The observation frequency was 50.1 MHz and the irradiation frequency 199.5 MHz. The pulse repetition time was 5 s and the contact time 2 ms. For CAB 400 scans and for CA 60 scans were collected...

Two commercial disazo disperse dyes of relatively simple structure were selected for a recent study of photolytic mechanisms [180]. Both dyes were found to undergo photoisomerism in dimethyl phthalate solution and in films cast from a mixture of dye and cellulose acetate. Light-induced isomerisation did not occur in polyester film dyed with the two products, however. The prolonged irradiation of Cl Disperse Yellow 23 (3.161 X = Y = H) either in solution or in the polymer matrix yielded azobenzene and various monosubstituted azobenzenes. Under similar conditions the important derivative Orange 29 (3.161 X = N02, Y = OCH3) was degraded to a mixture of p-nitroaniline and partially reduced disubstituted azobenzenes. 

Keqiang [43] has successfully produced block copolymers, based upon cellulose, while Henglein has been able to produce both graft and block copolymers using polystyrene and polymethyl methacrylate. Price [68] has shovm that the irradiation of mixtures of polystyrene and poly(cis-butadiene) and separately polystyrene and... 

The dose distribution in the materials is given as a depth-dose curve. An example of the curve is illustrated in Fig. 4 obtained with the irradiation of electron from 0.5 to 1.0 MeV using cellulose triacetate (CTA) film dosimeter [12]. The existence of the maximum dose is an important characteristic of the depth-dose curve. Irradiation from two opposite sides by using two accelerators was proposed in order to give better uniformity in water [13]. The uniform irradiation is also important for flue gas treatment. Better efficiency of NO removal was proved with both-side irradiation by using three accelerators for coal-fired flue gas than single-side irradiation at the same dose [14]. 

Polymer solids also work as a carrier of photochemical reaction components. The irradiation of a cellulose paper after adsorbing EDTA, Ru(bpy)3 and MV2+ induced rapid formation of MV4 in the solid phase (Table 2) 45,48). The quenching experiments showed that a photoinduced electron relay of EDTA Ru(bpy)2 - —> MV2+occurs in the solid phase just like in the solution. In this reaction the main path for the MV4 formation is through Ru(bpy)2, and the rate of direct reduction of MV2 by cellulose molecule is very small. Such an electron relay occurred also in a gelatine film 47). 

The inherent viscosity values of cellulose triacetate samples are summarized in Table II. In all the irradiated samples insoluble materials were also obtained. 

Thus in the instance of 1% solution exposed for an interval of 4 hr to the action of light the decrease in viscosity is 0.3-0.7%. With 10-20% solutions, on the other hand, the reduction in viscosity during the same period is 25.0-34.2%. Mine s experiments showed that in solutions of low viscosity the reduction of viscosity could remain unobserved. Claesson and Wettermark [92a] investigated the irradiation of solutions of cellulose nitrate with light of wave-length 253 rafi. The depolymerization was followed viscosimetrically and the chain breakage was found to obey the course predicted theoretically for a random process with a quantum yield of 0.01-0.02. 

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. 

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