The chracteristics of wood radicals formed by γ-ray irradiation are discussed on the basis of spectra and the kinetics of decay of radical concentration.
It was previously confirmed by ESR measurements that PMMA propagating radicals are formed during the reaction of MMA with wood radicals. The factors influencing formation of PMMA radicals during reaction of MMA with wood components were studied. The reaction of MMA with delignified wood and cotton linters were studied on reaction to radical concentration and apparent grafting.
The results obtained are as follows :
(1) The ESR spectra of mixtures of isolated wood components of the same proportions as found in wood are similar to those of the original. However,ΔH_<msl> of this mixture is larger than that of wood. This shows that the procedures of isolation have rescilted in a shortening of the spin-spen relaxation time. The concentration of wood radicals decreases because of bimolecular kinetics in the range of 333゜K to 353゜K.
(2) The reactivity of monomer with respect to wood radicals is probably affected by the swelling efficiency of the monomer.
(3) PMMA radical concentration during reaction of MMA with irradiated delignified wood increases with increasing degree of delignification. PMMA radicals are not formed by the reaction of MMA with preirradiated cotton linters. This result suggests that MMA does not diffuse into the cellulose radical site. However, PMMA radicals are formed in solutions of MMA and methanol. In this reaction system the cellulose radical reacts with MMA monomer during initial polymerization. Therefore the main reaction is that of MMA with PMMA radical. The diffusion velosity of MMA into cotton linters is considered as the rate-determining factor.