Alice Mija

Hybrid Nanocomposites: Advanced Nonlinear Method for Calculating Key Kinetic Parameters of Complex Cure Kinetics

Complex cure kinetics involved in the elaboration of organic/inorganic hybrid silicate nanocomposites based on diglycidyl ether of bisphenol A (DGEBA), 1,3-phenylenediamine (m-PDA), and modified montmorillonite (MMTm) clay have been studied. An advanced isoconversional method has been applied to nonisothermal data in order to evaluate cure kinetic parameters. A new method based on nonlinear optimization was proposed to compute nonisothermal kinetic parameters avoiding complex optimization techniques. The objective is to obtain kinetic parameters rather than modeling values in order to give more insight into the elucidation of complex cure mechanisms. Key kinetic parameters of cure have been computed according to this method. It appears that the reaction mechanism changes if MMTm is added to the curing system. The results reveal an increase of the efficiency of collisions in presence of MMTm at the beginning of the cure and an increase of the frequency of diffusion jumps at the later stage of the reaction.

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 (mPDA) 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 mPDA 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.

Complex Kinetic Pathway of Furfuryl Alcohol Polymerization Catalyzed by Green Montmorillonite Clays

Furfuryl alcohol (FA) which is derived from lignocellulosic biomass polymerizes into poly(furfuryl alcohol) (PFA) under acidic catalysis. A greener and more sustainable catalytic route was proposed in order to replace hazardous acidic catalysts. Organically modified montmorillonite (Org-MMT) and, in comparison, sodium MMT (Na-MMT) are used to evaluate the catalytic effect on the FA polymerization. X-ray diffraction (XRD) and transmission electronic microscopy (TEM) show that clay layers have been exfoliated during polymerization. Additional FTIR spectroscopy measurements confirm that furanic oligomers have intercalated between clay layers by cation exchange. An original combination between chemorheological and model-free kinetic analysis allows highlighting the influence of MMT on the overall polymerization pathway. The octadecyl ammonium cation (ODA) was also used as homogeneous acidic catalyst to highlight the specific role of this interlayer cation present in Org-MMT. Interestingly, FA/Org-MMT polymerizes more rapidly than FA/ODA but initiation of polymerization is slightly shifted to higher temperature due to initial intercalation between MMT layers. Then, the dual acidic character (Lewis + Brönsted) of Org-MMT leads to gelation at early stage of polymerization. The results clearly show that exfoliation of MMT layers increases the efficiency of collisions.

Synthesis and characterization of some epoxy resins bearing azomethine groups

Abstract New epoxy resins bearing azomethine groups were synthesized by the reaction between the diglycidyl ether of bisphenol-A (DGEBA) and some aromatic azomethines, in the presence of n-butylamine as catalyst. The azomethines were obtained through the condensation reaction of aromatic diamines with 2-hydroxybenzaldehyde. The epoxides synthesized at 100 °C were characterized by i.r., u.v. and 1H-NMR spectral techniques, as well as by DSC and TG thermoanalytical methods. Some other properties of the resins are presented, such as epoxy equivalent, melting points and nitrogen content. The epoxy resins containing azomethine groups show an apparent higher thermal stability than that of crude DGEBA epoxy resin, and some of them show a pronounced tendency towards crystallization.

Auto-Crosslinked Rigid Foams Derived from Biorefinery Byproducts

Abstract A new macroporous foam‐like material is presented based on autocross‐linking humins, an industrial biorefinery byproduct. Humins foams are obtained by a simple heating process, without any pretreatment and with high control of morphology, porosity, and carbon content. Untreated humins have been characterized by GC, ultra‐performance liquid chromatography (UPLC), elemental analysis, and FTIR, whereas the mechanism of foaming was elucidated by a combination of thermal and rheological analyses. A preliminary screening of conditions was conducted to identify the parameters controlling this foaming process. A foam was produced in a controlled way with open and/or closed cells with cell diameters between 0.2 and 3.5 mm. Humins foams were characterized by Raman spectroscopy, FTIR, SEM, nitrogen adsorption, pycnometry, and mechanical tests. The results show that, based on humins, it is possible to obtain porous materials with controlled architectures and a range of parameters that can be tailored, depending on the foreseen applications.