Celluloses radiolysis

Photochemistry within a glass gas chromatographic column Photodecomposition of sulfonamides and tetracyclines Photoreduction of methylviologen adsorbed on cellulose Radiolysis of D,L-tryptophan Photolysis of dichlorofluanid... 

For radiolysis studies of the grafting solutions without cellulose, i.e. homopolymer runs, tubes were either lightly stoppered or sealed off at 10-J Torr after three freeze-thaw cycles. For the molecular weight determinations on the homopolymers, oligomer solution was poured into excess methanol, the precipitated polystyrene collected, dried and analysed by g.p.c. on a Waters Associates Model ALG/GPS201 instrument. 

Singlet 1,6 mT wide being observed at photolysis and radiolysis of cellulose and its derivatives is attributed to radicals with the chain of conjugation these are alkyl and polyenyl radicals [148]. 

In this report, focusing to carboxymethyl chitin/chitosan and carboxymethyl cellulose, we studied the reactivity of water radiolysis products with polymer chains using the pulse radiolysis method as the first step to clarify early gelation process of polymer radicals related to crosslinking. 

Figure 3 is the result of pulse radiolysis experiment about the reaction of hydrated electron with polymer chains(0 or 30 mM carboxymethyl chitosan solution with 0.3 M terf-butanol under Ar saturation), and shows the decay of the absorbance as a function of time. This absorbance was measured at wavelength 720 nm, which is the absorption peak of hydrated electron. As seen in Figure 3, the absorbance increases immediately after the irradiation, and attenuates afterwards. This means that hydrated electron is generated immediately after irradiation and diminishes gradually by some reactions of hydrated electron. Compared the absorbance decay of polymer solution with the decay of solution without polymer, the decay of polymer solution is faster than without polymer, so it is obvious that hydrated electron reacts with polymer chains. The decay curve can be fitted by pseudo first-order decay. The pseudo first-order decay is shown by equation (8). From estimating the slope of the pseudo first-order decay rate of the absorbance at 720 nm against polymer concentration, the rate constant of the reaction of hydrated electron with polymer chains can be calculated Figure 4). The rate constants of the reaction of hydrated electron with CM-chitin and CM-chitosan was determined as l.lxlO7 and MxlO M V1]. These values are almost the same with the value of carboxymethyl cellulose(2< ).

A considerable amount of work has been devoted to the action of ionizing radiation on polymeric carbohydrates in the solid state, in particular with regard to its effect on the mechanical properties even though some chemical effects have also emerged. For a recent review see [99]. Of these polymers, cellulose has been the most studied (c/. [99, 100]). Native cellulose is locally crystalline. Determination of chain breakage by radiolysis has usually been done after dissolution through complexation, e.g. as the copper-ammine complex (Schweizer s reagent), or the cadmium-ethylenediamine complex. 

When cellulose is irradiated in vacuo G(H2) = 3, G(C02) = 6 and G(CO) == 1 x 10 mol J have been observed [99]. The gaseous products CO and CO2 are ascribed to the decay of highly excited states (excited radical cations). It is noted that CO formation is also of some importance in the radiolysis of alcohols in the liquid and frozen state [102, 103]. However, for CO2 and CO, a free-radical pathway starting with the P-fragmentation of the oxyl radical 80 [reaction (59)] is also conceivable, as one expects the radicals in the solid to have a long lifetime due to a reduced mobility, which could selectively permit reactions (60) - (64) to occur. 

The acetone result is particularly important since it indicates that further parameters, in addition to those already proposed,are needed to adequately define the conditions required to explain gel effects in these reactions. It is therefore suggested that the radiation chemistry of the system, particularly that of the monomer and solvent as proposed originally for the cellulose work also needs to be considered in any mechanistic discussion of the radiation grafting to polyolefins. In this respect, it is significant that all of the above solvents have one common property, namely, under radiolysis conditions, they produce finite yields of H atoms. An analysis of such G(H) data from these solvents (Table 1) suggests that there is a relationship between these hydrogen yields and both the yield and Trommsdorff effect in radiation grafting. 

Radiation-induced main-chain degradation renders polysaccharides soluble, or at least increases their solubility, and therefore technical interests have focused on the radiation-induced main-chain degradation of certain biopolymers, such as cellulose, chitin and chitosan [96,104-107]. In being the main component of plants, cellulose is a widespread biopolymer. In technical processes, high-energy radiation treatment is applied to increase the solubility and to alleviate the hydrolysis of the constituent cellulose of plant-based raw materials. The G-values of the main radiolysis products, as reported by Ershov,... 

Table S.6 Co-7-ray-induced radiolysis of cellulose at room temperature in the absence of O2. Data given are lOOeVyields (G-values) of products [96].

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