Physico-chemical and thermal characterization of lignins from Caligonum monogoliacum and Tamarix spp.

Caligonum monogoliacum and Tamarix spp. were pre-treated with ethanol-H2O ( 60/40,v/v) under acid catalyst (0.2 N HCl) at 70 degreesC for 4 h and then post-treatment with 2% H2O2 at pH 11.5 for 16 h at 45 degreesC, respectivel y. Alkaline peroxide post-treatment released a higher amount of lignin (10. 6% from Caligonum monogoliacum and 12.1% from Tamarix spp.) as compared to acidic organosolv pre-treatment (5.5% from Caligonum monogoliacum and 6.4% from Tamarix spp.). The two-stage treatments together solubilized or degrad ed 84.3 and 90.2% of the original lignins from Caligonum monogoliacum and T amarix spp., respectively. Analyses of the acid-insoluble lignin fractions revealed that alkaline peroxide post-treatment resulted in a substantial ox idation of the isolated lignins as they are enriched in carbonyl and carbox yl groups. In comparison, the isolated four acid-insoluble lignin samples w ere further characterized by both degraded methods such as alkaline nitrobe nzene oxidation and thermal analysis, and non-degradation techniques such a s ultraviolet (UV), Fourier transform infrared (FT-IR), and carbon-13 magne tic resonance spectroscopy (C-13-NMR) as well as gel permeation chromatogra phy (GPC), and their results are reported. (C) 2001 Elsevier Science Ltd. A ll rights reserved.