Chemorheological analysis and model-free kinetics of acid catalysed furfuryl alcohol polymerization

Abstract

The complete curing of furfuryl alcohol (FA), was studied by chemorheological analysis and model-free kinetics under isothermal and non-isothermal modes. Polymerization of FA under acidic catalysis involves complex reactions, with several steps (such as condensations and Diels-Alder cycloadditions). To account for the polymerization complexity, kinetic analysis of DSC data was performed with a model-free isoconversional method. The obtained E(alpha)-dependencies were closely-correlated with the variation of complex viscosity during curing. Linear condensations are predominant during the early curing stage and are followed by two distinct stages of branching cycloadditions. Gelation and vitrification, identified by rheometric measurements, were associated with a decrease of the overall reaction rate that becomes controlled by diffusion of small oligomers. Before vitrification, the rate of crosslinking is limited by the mobility of longer polymer chains and diffusion encounters a large energy barrier due to the cooperative nature of the motions, leading to higher E(alpha) values.

Evolution of glassy carbon under heat treatment: correlation structure–mechanical properties

“…The structure is allowed to eliminate them in the non-equilibrium conditions by the formation of polygons such as pentagons or heptagons or highermembered rings resulting in the folding of carbon layers. It should be noted that the pentagon rings are also originally present in the initial structure of the furfuryl alcohol polymer [22,26] and they can partly survive at the later stages of heat treatment, as confirmed by Tondi et al [27], causing out-of-plane ripples. In parallel, the curvature is created by the carbon layers which branch out or link together by forming the specific tubular caps, marked in Fig.…”

Wood modification with furfuryl alcohol and furfurylated wood durability in water

“…On the other hand, FA has a five member heterocyclic system with increased π-electron density that might lead to π-electron donor-acceptor complex formation between MA and FA. Such complex is precursor of Diels-Alder cycloadditions [18]. Formation of such more voluminous complex as well as furfuryl hydrogen maleate formation by anhydride reaction with FA will decrease probability of its penetration into the wood cell wall that is necessary for wood protection against interaction with water.…”

The FA Polymerization Disruption by Protic Polar Solvent

“…A similar increase is observed for the water system, but at lower temperature and in a wider temperature interval (107-136°C). This final re-increase was attributed to the cross-links formation in the gelled state due to Diels-Alder cycloadditions [40]. Thus, addition of water, allows for the reactivation of chemical reactions at lower temperature, probably because of the higher mobility of the system.…”

“…The three systems exhibit decreasing Eα values at the initial stages of the reaction (for α values until to 0.10 for reference and water systems, 0.20 for IPA system) that can be attributed to an autocatalytic step [41]. This initial step corresponds to the formation of an active furfuryl carbenium for the reference system is correlated with the high viscosity increase due to the formation of crosslinks [40]. This phenomenon is not visible for FA/MA/water due to the presence of water, which still induces a lower viscosity at same extent of conversion.…”

“…This is mainly due to an increase of the viscosity of the system, which reduces the chemical reactions rates and leads to a decrease of Eα [41]. This decrease is observed for both systems and is characteristic of a transition from kinetic to diffusion regime [40]. Diffusion control generally become rate limiting when the characteristic relaxation time of the reaction medium exceeds markedly the characteristic time of the reaction itself [29].…”