Chemical and radiation-chemical radical reactions in lignocellulose materials

Abstract Chemical and radiation-chemical radical reactions in lignocellulose materials were explored by 3-cm and 2-mm ESR spectroscopy. Background (intrinsic) singlet signals at g =2.003 from wood pulp and lignin and those arising during reaction of lignocellulose materials with acids and chlorine were attributed to radicals with conjugated CC bonds. The 2-mm ESR signal with 3D anisotropy of g -factor from o -semiquinone radical ions formed in reaction of lignin with NaOH was recorded for the first time. The singlet signals derived from cellulose γ-irradiated at 77 K and marked out during post-thermal reactions were assigned to radicals with conjugated bonds. In wetted cellulose, a triplet signal with α β H ≅2.7 mT and imposed quadruplet structure (0.5–0.7 mT) from three γ-protons was detected at 300 K and attributed to С 4 -radicals. The triplet signals derived from С 2 - and С 3 -radicals in pyranose cycles of cellulose exhibited higher values of α β H (3.0–3.2 mT) and lower thermal stability (up to 250 K). In radiolyzed cotton pulp, detected were ESR signals derived from formyl radicals formed upon rupture of the С 5 С 6 bond in pyranose cycles. Heating up irradiated samples under О 2 was accompanied by formation of peroxide radicals. Photoinduced recombination of trapped electrons with С 1 -radicals was found to proceed as a chain reaction with a kinetic length of about 25 units. Photolysis ( λ ≥360 nm) of radiolyzed cellulose enhanced the disclosure of pyranose cycles and, as a result, the evolution of CO 2 by a factor of 2–2.5.