Abstract
Lignin-based polyols (LBPs) with controlled microstructure were obtained by cationic ring opening polymerization (CROP) of oxiranes in an organosolv lignin (OL) tetrahydrofuran (THF) solution. The control on the microstructure and consequently on the properties of the LBPs such as hydroxyl number, average molecular weight, melting, crystallization and decomposition temperatures, are crucial to determine the performance and application of the derived-products. The influence of key parameters, for example, molar ratio between the oxirane and the hydroxyl groups content in OLO, initial OL concentration in THF, temperature, specific flow rate and oxirane nature has been investigated. LBPs with hydroxyl numbers from 35 to 217 mg KOH/g, apparent average Mw between 5517 and 52,900 g/mol and melting temperatures from −8.4 to 18.4 °C were obtained. The CROP procedure allows obtaining of tailor-made LBPs for specific applications in a very simple way, opening the way to introduce LBPs as a solid alternative to substitute currently used fossil-based polyols.
Highlights
Diminishing fossil fuel reserves and degradation of the environment are highly important concerns nowadays
We reported the synthesis of Lignin-based polyols (LBPs) by cationic ring opening polymerization (CROP) of oxiranes in an organosolv lignin (OL) THF solution and the investigation on how key reaction parameters such as, oxirane/–OH-lignin-groups molar ratio, initial OL concentration, temperature, oxirane specific addition flow rate (Qs ) and oxirane nature influence the physicochemical properties of the obtained LBPs
LBPs were synthesized by CROP of oxiranes and THF in the presence of a OL source using a Lewis acid catalyst (BF3 ·OEt2 ) (Scheme 1) being both the THF comonomer and solvent as previously discussed
Summary
Diminishing fossil fuel reserves and degradation of the environment are highly important concerns nowadays. Lignin, which is obtained in huge amounts as by-products in the pulp industry [8,9], is probably one of the most interesting and abundant bioresources for the synthesis of industrially useful bio-based polyols [10,11] In this sense, our research group has recently reported a new, greener and economic route to obtain lignin-based polyols (LBPs) under very mild reaction conditions by cationic ring opening polymerization (CROP), substantially improving the more traditional routes to obtain LBPs such as either lignin fragmentation [12,13,14], lignin oxypropylation, or both, in basic media [15,16], which are carried out under harsher reaction conditions [17,18]. We reported the synthesis of LBPs by CROP of oxiranes in an organosolv lignin (OL) THF solution and the investigation on how key reaction parameters such as, oxirane/–OH-lignin-groups (oxirane/OH–OL) molar ratio, initial OL concentration, temperature, oxirane specific addition flow rate (Qs ) and oxirane nature influence the physicochemical properties of the obtained LBPs
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