Pere Colomer

Thermal degradation kinetics of epoxy–anhydride resins: I.: Influence of a silica filler

Abstract Thermal degradation kinetics of epoxy–anhydride resins has been studied by thermogravimetry in both, isothermal and non-isothermal conditions. It was found that the kinetics of thermal degradation can be fairly described by a simple reaction-order model. The calculated kinetic parameters, Ea and n, are considerably lower for pure resin than for resin containing silica filler. Therefore, the addition of silica filler increases thermal degradation rate of the resin. A difference was also observed between the set of kinetic parameters obtained by kinetic analysis of isothermal and non-isothermal data, particularly with respect to the activation energy.

Vitrification and dielectric relaxation during the isothermal curing of an epoxy–amine resin

Abstract The isothermal curing of an epoxy resin based on diglycidyl ether of bisphenol A (DGEBA) with a diamine based on 4,4′-diamino-3,3′-dimethyldicyclohexylmethane (3DCM) was analysed by dielectric relaxation spectroscopy (DRS), conventional differential scanning calorimetry (DSC) and temperature modulated DSC (TMDSC). The chemical kinetics corresponds to an autocatalytic model with an apparent activation energy of 58xa0kJxa0mol −1 . The vitrification was analysed by TMDSC, between 40 and 140xa0°C, using the modulus of the complex heat capacity, |C p ∗ |. A mobility factor based on the evolution of |C p ∗ | was used to study the reaction step controlled by diffusion. The permittivity and loss factor were measured by DRS as a function of time in the frequency range between 10xa0Hz and 100xa0kHz. The dipolar relaxation, analysed by the peak of the maximum loss factor, was correlated with the vitrification determined by TMDSC. The analysis of the logarithm of the frequency against the conversion degree allows the characterisation of the molecular dynamics of the crosslinking reaction up until the vitrification of the system.

Thermal degradation kinetics of epoxy-anhydride resins: II. Influence of a reactive diluent

The effect of reactive diluent on the thermal degradation kinetics of epoxy-anhydride resins has been studied by thermogravimetry in both isothermal and non-isothermal conditions. It was found that the kinetics of thermal degradation can be described well by a simple reaction order model. The addition of reactive diluent increases the apparent activation energy and the kinetic exponent. A difference was also observed between the set of kinetic parameters obtained by kinetic analysis of isothermal and non-isothermal data. Such behavior indicates a more complex mechanism of thermal degradation of epoxy resin.

STUDY OF THE CRYSTALLIZATION AND MELTING REGION OF PET AND PEN AND THEIR BLENDS BY TMDSC

The cold crystallization and melting of poly(ethylene therephthalate) (PET), poly(ethylene 2,6-naphthalene dicarboxylate) (PEN) and their blends were studied using temperature modulated differential scanning calorimetry (TMDSC) at underlying heating rates of between 1 and 3 K min-1 and periods ranging from 30 to 90 s. The amplitude of modulation was selected in order to give an instantaneous heating rate β≥0. Heat flow is analyzed by the total heat flow signal o, which is equivalent to the conventional DSC signal, and the reversing heat flow oREV, which only detects the glass transition and the melting processes. The dependence of the melting region in the reversing heat flow on the frequency of modulation is analyzed. The use of the so-called non-reversing heat flow oNREV (=o-oREV)) and the effect of frequency and amplitude on the complex heat capacity are also studied. The results show the complexity of these magnitudes.

Molecular Mobility in Hyperbranched Polymers and Their Interaction with an Epoxy Matrix

The molecular mobility related to the glass transition and secondary relaxations in a hyperbranched polyethyleneimine, HBPEI, and its relaxation behaviour when incorporated into an epoxy resin matrix are investigated by dielectric relaxation spectroscopy (DRS) and dynamic mechanical analysis (DMA). Three systems are analysed: HBPEI, epoxy and an epoxy/HBPEI mixture, denoted ELP. The DRS behaviour is monitored in the ELP system in three stages: prior to curing, during curing, and in the fully cured system. In the stage prior to curing, DRS measurements show three dipolar relaxations: γ, β and α, for all systems (HBPEI, epoxy and ELP). The α-relaxation for the ELP system deviates significantly from that for HBPEI, but superposes on that for the epoxy resin. The fully cured thermoset displays both β- and α-relaxations. In DMA measurements, both α- and β-relaxations are observed in all systems and in both the uncured and fully cured systems, similar to the behaviour identified by DRS.

Study of the molecular dynamics of multiarm star polymers with a poly(ethyleneimine) core and poly(lactide) multiarms

Multiarm star polymers, denoted PEIx-PLAy and containing a hyperbranched poly(ethyleneimine) (PEI) core of different molecular weights x and poly(lactide) (PLA) arms with y ratio of lactide repeat units to N links were used in this work. Samples were preconditioned to remove the moisture content and then characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dielectric relaxation spectroscopy (DRS). The glass transition temperature, Tg, is between 48 and 50 °C for all the PEIx-PLAy samples. The dielectric curves show four dipolar relaxations: γ, β, α, and α′ in order of increasing temperature. The temperatures at which these relaxations appear, together with their dependence on the frequency, allows relaxation maps to be drawn, from which the activation energies of the sub-Tg γ- and β-relaxations and the Vogel–Fulcher–Tammann parameters of the α-relaxation glass transition are obtained. The dependence of the characteristic features of these relaxations on the molecular weight of the PEI core and on the ratio of lactide repeat units to N links permits the assignation of molecular motions to each relaxation. The γ-relaxation is associated with local motions of the –OH groups of the poly(lactide) chains, the β-relaxation with motions of the main chain of poly(lactide), the α-relaxation with global motions of the complete assembly of PEI core and PLA arms, and the α′-relaxation is related to the normal mode relaxation due to fluctuations of the end-to-end vector in the PLA arms, without excluding the possibility that it could be a Maxwell–Wagner–Sillars type ionic peak because the material may have nano-regions of different conductivity.

Study of hyperbranched poly(ethyleneimine) polymers of different molecular weight and their interaction with epoxy resin

Two different commercial hyperbranched poly(ethyleneimine)s (HBPEI), with molecular weights (MW) of 800 and 25,000 g/mol, and denoted as PEI800 and PEI25000, respectively, as well as the mixtures with a Diglycidyl Ether of Bisphenol-A (DGEBA) epoxy resin, have been studied using thermal analysis techniques (DSC, TGA), dielectric relaxation spectroscopy (DRS), and dynamic mechanical analysis (DMA). Only a single glass transition is observed in these mixtures by DSC. DRS of the HBPEIs shows three dipolar relaxations: γ, β, and α. The average activation energy for the γ-relaxation is similar for all HBPEIs and is associated with the motion of the terminal groups. The β-relaxation has the same average activation energy for both PEI800 and PEI25000; this relaxation is attributed to the mobility of the branches. The α-relaxation peak for all the HBPEIs is an asymmetric peak with a shoulder on the high temperature side. This shoulder suggests the existence of ionic charge trapped in the PEI. For the mixtures, the γ- and β-relaxations follow the behaviour of the epoxy resin alone, indicating that the epoxy resin dominates the molecular mobility. The α-relaxation by DRS is observed only as a shoulder, as a consequence of an overlap with conductivity effects, whereas by DMA, it is a clear peak.