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, respectively. 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 degraded 84.3 and 90.2% of the original lignins from Caligonum monogoliacum and Tamarix spp., respectively. Analyses of the acid-insoluble lignin fractions revealed that alkaline peroxide post-treatment resulted in a substantial oxidation of the isolated lignins as they are enriched in carbonyl and carboxyl groups. In comparison, the isolated four acid-insoluble lignin samples were further characterized by both degraded methods such as alkaline nitrobenzene oxidation and thermal analysis, and non-degradation techniques such as ultraviolet (UV), Fourier transform infrared (FT-IR), and carbon-13 magnetic resonance spectroscopy (C-13-NMR) as well as gel permeation chromatography (GPC), and their results are reported. (C) 2001 Elsevier Science Ltd. All rights reserved.