The kinetics of curing of diglycidyl ether of bisphenol A (DGEBA) with m‐phenylenediamine (m‐PDA) has been studied by using DSC under isothermal and nonisothermal conditions. An advanced isoconversional method has been applied to the data in order to evaluate a dependence of the effective activation energy on the extent of conversion. The method has been applied to the stoichiometric system as well as to the system with an excess of the amine. The nonstoichiometric system demonstrates an effective activation energy that is practically independent of the extent of conversion. The resulting value (≈55 kJ · mol−1) provides an estimate for the curing reaction of the primary amine. The stoichiometric system demonstrates a decreasing activation energy for both isothermal and nonisothermal cures. The value varies from ≈55 kJ · mol−1 to as low as ≈20 kJ · mol−1. The decrease is explained by shifting the rate determining step from a kinetic to a diffusion regime. The diffusion control is associated with the processes of gelation and vitrification that occur on curing and cause a dramatic decrease in molecular mobility. Dynamic rheometry and temperature modulated DSC have been employed to study these processes.

No 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.

A challenge of today’s industry is to transform low-value side products into more value-added materials. Humins, a byproduct derived from sugar conversion processes, can be transformed into high value-added products. Thermosetting furanic composites were elaborated with cellulose filters. Large quantities of humins were included into a polyfuranic thermosetting network. Comparisons were made with composites generated with polyfurfuryl alcohol (PFA) and with PFA/lignin. It was concluded that new chemical interactions were created between the side-chain oxygen groups of the humins and the PFA network. Analysis of the fracture surface of the composites containing humins lead to the conclusion that higher interfacial bonding and more efficient stress transfer between the matrix and the fibers is present. The higher ductility of the humins-based matrix allows for a two-fold higher tensile strength in comparison with other composites tested. Incorporation of humins decreases the brittleness of the furanic composites, which is one major drawback of the pure PFA composites.