Epoxy–Amine Based Nanocomposites Reinforced by Silica Nanoparticles. Relationships between Morphologic Aspects, Cure Kinetics, and Thermal Properties

In general, the incorporation of nanoparticles into polymers shows an increase of the materials performances, but the effect of the nanosized objects is still not well understood. In this study, we have investigated the impact of incorporation of silica nanoparticles in an epoxy/amine (DGEBA/<i>m</i>PDA) system. Naked silica nanoparticles (SiNP) were synthesized via a sol–gel technique. To evaluate the interfacial effect on properties of nanocomposites, the surface of the nanoparticles was modified by substituting silanol groups into epoxide functions (SiNPEp). A new method was elaborated for obtaining different organic–inorganic nanocomposites with a very good dispersion without any aggregation according to transmission electron microscopy (TEM) analyses. The influence of the different silica nanoparticles (SiNP or SiNPEp) on the mechanisms of the reaction between epoxy and amine groups is highlighted. Important new inputs on the cure kinetics of the epoxy/amine mixture are given. The glass transition temperatures and thermal properties of nanocomposites have been examined, and relationships have been established

Cross-Linking Mechanisms of a Rigid Plant Oil-Based Thermoset from Furfural-Derived Cyclobutane

cis-Cyclobutane-1,2-dicarbocylic acid (CBDA-2) was synthesized and used as a biobased hardener to cross-link epoxidized linseed oil to produce a fully biobased thermoset. The polymerization mechanism was studied by means of real-time attenuated total reflection-Fourier transform infrared (ATR-FTIR), differential scanning calorimetry (DSC), stochastically modulated temperature DSC, and rheometry. The study highlights the importance of hydrogen bonding of CBDA-2 and catalytic effect of hydroxyl groups created during the reaction. Evolution of reactive functions with temperature and time, variation of activation energy, and pre-exponential factor was correlated to macroscopic changes, such as heat capacity variations and chemorheology. A macrokinetic model was proposed to describe the complete polymerization mechanism. It is shown that the obtained parameters accurately describe the polymerization using parameters with a real physical meaning

Radical Oxidation of Itaconic Acid-Derived Unsaturated Polyesters under Thermal Curing Conditions

Itaconic acid has attracted a lot of interest as a green and low-cost building block toward the synthesis of biobased polyesters and polyurethanes with a wide range of applications in the UV-curing field. However, the thermal curing of itaconic acid-derived polyesters has been not extensively investigated. To gain deeper insight into the thermally induced crosslinking process, the curing of poly(hexylene itaconate) was investigated by advanced isoconversional analysis performed under isothermal and non-isothermal conditions. Rheology and thermal analysis pointed out a three-step mechanism (initiation, propagation, and termination) typical of free-radical polymerization associated with the double bond conversion. Moreover, due to the comprehensive information obtained by different analytical techniques such as isothermal DSC, ATR-FTIR, and DMTA, we speculate that thermo-oxidative mechanisms occur under thermal curing conditions of poly(hexylene itaconate). Thus, β-scissions of poly(hexylene itaconate) chains might lead to the formation of anhydride and oligomeric radicals, which can recombine to a highly branched and crosslinked poly(hexylene itaconate) resin

Effects of Incorporation of Organically Modified Montmorillonite on the Reaction Mechanism of Epoxy/Amine Cure

The aim of this study is to understand the effect of nonmodified or different organically modified montmorillonites on the reaction mechanism of epoxy/amine cure. The reference material consists of diglycidyl ether of bisphenol A (DGEBA) and 1,3-phenylene diamine (<i>m</i>PDA) in stoichiometric proportions. The reaction with various organically modified montmorillonites (I28E, I34TCN, and MMTm) is compared to highlight the catalytic effect of MMT water content and of the alkylammonium cations on the epoxy/amine reaction mechanism. In the absence of <i>m</i>PDA curing agent, DGEBA develops homopolymerization reactions with I28E, I34TCN, and MMTm. Chemorheological kinetics and advanced isoconversional analysis of epoxy cure are studied by rheometrical measurements and differential scanning calorimetry (DSC). Molecular mobility of the system under curing is modified in the presence of montmorillonites. Finally, the study underlines the role of montmorillonites and the influence of the change in reaction mechanisms on glass transition of the nanocomposites

Valorization of Biorefinery Side-Stream Products: Combination of Humins with Polyfurfuryl Alcohol for Composite Elaboration

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