C. Salom

Polymer viscoelasticity : stress and strain in practice

Structure of polymers crystalline and amorphous states in polymers rubber elasticity stress-strain relations for ideal solids and ideal liquids linear viscoelasticity - viscoelastic functions dynamic viscoelastic functions experimental determination of viscoelastic properties viscoelastic behaviour of polymers above the glass-transition retardation and relaxation spectra viscoelastic models molecular models of the viscoelastic polymers viscoelasticity of glassy and semicrystalline polymers flow behaviour of polymer melts and solutions yield crazing and fracture reinforced polymers multiaxial analysis of linear viscoelastic stress flexion and torsion of viscoelastic rods.

Thermal properties and interactions in blends of poly(ε-caprolactone) with unsaturated polyester resins

Blends of two linear unsaturated polyester (LUP, commercially named AL-100 and 6603) with poly(e-caprolactone) (PCL) were prepared by the casting method. Differential scanning calorimetry (DSC) has been used to study the miscibility, melting behaviour and crystallinity of 6603+PCL and AL-100+PCL blends. Two different heat treatments (Method 1 and Method 2), were carried out, in both systems. Only by following Method 2 a crystallization temperature (Tc) was selected before monitoring the glass transition and melting behaviour of the blends. When samples were scanned under Method 1, a unique Tg intermediate between the Tg’s of the pure polymers in all the blends studied was found. It indicates that the PCL is miscible with both unsaturated resins in the whole composition range. Nevertheless, when samples were scanned following Method 2 the Tg–composition dependence exhibited an asymmetric behaviour that could indicate a certain lack of homogeneity in the blends at intermediate compositions.

Dielectric study of poly(methylacrylate) plus poly(4-hydroxystyrene) or plus poly(4 hydroxystyrene-co-4-methoxystyrene) blends near the glass transition

The dynamics of blends of poly(methylacrylate) (PMA)+poly(4-hydroxystyrene) (P4HS) and poly(4- hydroxystyrene-co-4-methoxystyrene) (MP4HS) have been studied by dielectric relaxation in the frequency range 20 < ω/Hz < 105. The results have been analysed in terms of the Havriliak-Negami function plus a conductivity contribution. The time-temperature superposition principle breaks down for the blends, while it seems to be valid for PMA. The width of the relaxation region increases with the content of P4HS or MP4HS, in accordance with previous dynamic mechanical relaxation data. For a given composition, the data of the blends follow the scaling curve proposed by P. W. Dixon (Phys. Rev. Lett., 1990, 42, 8179), however in the low frequency region each sample follows a different scaling curve, which slope is related to the α parameter of the Havriliak-Negami function. The increase of the width of the relaxation curves with decreasing the PMA content can be well correlated by the coupling model when a gaussian distribution of coupling parameters is taken into account.

Influence of Different Organoclays on the Curing, Morphology, and Dynamic Mechanical Properties of an Epoxy Adhesive

The thermal, mechanical, and adhesive properties of nanoclay-modified adhesives were investigated. Two organically modified montmorillonites: Cloisite 93A (C93A) and Nanomer I.30E (I.30E) were used as reinforcement of an epoxy adhesive. C93A and I.30E are modified with tertiary and primary alkyl ammonium cations, respectively. The aim was to study the influence of the organoclays on the curing, and on the mechanical and adhesive properties of the nanocomposites. A specific goal was to compare their behavior with that of Cloisite30B/epoxy and Cloisite15A/epoxy nanocomposites that we have previously studied. Both C30B and C15A are modified with quaternary alkyl ammonium cations. Differential scanning calorimetry results showed that the clays accelerate the curing reaction, an effect that is related to the chemical structure of the ammonium cations. The three Cloisite/nanocomposites showed intercalated clay structures, the interlayer distance was independent of the clay content. The I.30E/epoxy nanocomposites presented exfoliated structure due to the catalytic effect of the organic modifier. Clay-epoxy nanocomposites showed lower glass transition temperature (T g ) and higher values of storage modulus than neat epoxy thermoset, with no significant differences between exfoliated or intercalated nanocomposites. The shear strength of aluminum joints using clay/epoxy adhesives was lower than with the neat epoxy adhesive. The water aging was less damaging for joints with I.30E/epoxy adhesive.

Thermal behaviour of unsaturated polyester resins + poly(3-octylthiophene) blends

Abstract Blends of poly(3-octylthiophene) (POT) with unsaturated polyester (UP) resin have been investigated. Two glass transition temperatures, T g , were detected by differential scanning calorimetry (DSC) in blends of POT+uncured polyester resins, which indicate the partial immiscibility of these systems. It has been demonstrated that the miscibility behaviour of these blends depends up to a point on the solvent used in sample preparation. Also POT was found to be immiscible with crosslinked polyester resins which was concluded from the results of thermal analysis. The influence of the presence of POT on the crosslinking reaction, the miscibility of the crosslinked system and finally the melting behaviour of POT were analysed. The results obtained have been compared in the crosslinked and uncrosslinked blends.