5 research outputs found
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