Iran Polym J DOI 10.1007/s13726-015-0380-x 1 3 ORIGINAL PAPER Gelation and isoconversional kinetic analysis of synthesis of lignin–resorcinol–glyoxal resin curing Mohamed Ammar 1 · Ramzi Khiari 2,3,4 · Mohamed Naceur Belgacem 3,4 · Elimame Elaloui 1 Received: 13 April 2015 / Accepted: 6 August 2015 © Iran Polymer and Petrochemical Institute 2015 and 72 %, for LRFR and LRGR, respectively. These values were compared to those calculated from Flory and Stock- mayer equation and found to be close to each other. Keywords Lignin–resorcinol–glyoxal resins · Lignin–resorcinol–formaldehyde resins · Kinetics · DSC · Rheology · Gelation · Curing Introduction Recent environmental and sustainability concerns, dealing with the tendency of saving fossil resources, led to increas- ing use of bio-based raw materials for the production of bio- fuels, bioenergy, biomolecules, and several other products [1, 2]. Lignin is a bio-based by-product arising from pulp and papermaking industries. It is usually burned as fuel in the recovery boilers of pulps mills. Although the organo- solv lignin has been extensively studied [3–5], its chemical potential, needed to expand its industrialization process, is not still well explored. The lignin structure contains aliphatic and aromatic groups, with several substituted phenol–pro- pane units linked to each other by different types of chemical bonds, such as carbon–carbon or ether linkages [6, 7]. The main lignin units, guaiacyl (G), syringyl (S), and p-hydroxy- phenyl (H), differ by the presence or the absence of ortho- methoxyl group substitutions in the aromatic rings. Lignin is the main source of aromatic rings-bearing molecules in vegetal biomass raw material. These moieties can substitute (totally or partially) phenol to prepare phenolic resins, which present both environmentally and economically interesting alternatives to phenol–formaldehyde binders [8]. Recently, there has been considerable industrial inter- est in the development of natural, or green, wood adhe- sives, namely, the use of soy protein-, tannin and vegetable Abstract Two resins were prepared from Stipa tenacis- sima L. and their physical and chemical behaviors were evaluated. The resins were produced by modification of extracted lignin from the S. tenacissima L. using phe- nolation reaction (resorcinol). Glyoxal and formalde- hyde as cross-linking agents were employed to produce lignin–glyoxal resin and lignin–resorcinol–formaldehyde resins (LRFR), respectively. The curing process of two lignin-based resins (lignin–resorcinol–glyoxal, LRGR, and lignin–resorcinol–formaldehyde, LRFR) was studied by rheological measurements and differential scanning calorimetry (DSC) techniques, which showed that the gel formation obeys an isoconversional principle. In fact, an analysis on curing kinetics was performed by processing its non-isothermal DSC data using Ozawa’s isoconversional methods and found that good fittings could be obtained. This method allowed the determination of activation energy and the pre-exponential factor dependencies on the degree of curing. In kinetics method, the variation in activation energy, evaluated at different curing degrees, revealed that the mechanism of phenolic resins is based on two reac- tions: methylolation followed by condensation. Finally, the gel points of these systems were found to be around 63 * Ramzi Khiari khiari_ramzi2000@yahoo.fr 1 Materials, Environment and Energy Laboratory, Faculty of Sciences of Gafsa, University of Gafsa, Gafsa, Tunisia 2 University of Monastir, Faculty of Sciences, UR13ES63-Research Unity of Applied Chemistry & Environment, 5000 Monastir, Tunisia 3 Université Grenoble Alpes, LGP2, 38000 Grenoble, France 4 CNRS, LGP2, 38000 Grenoble, France