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During the past decades there has been a great accumulation of important data on the diffusion of water molecules in polymeric solids and its effect on the mechanical and viscoelastic behavior of polymers. It has become apparent that in many cases diffusion in polymers as well as its effect exhibits features that cannot be expected from classical theories and that such departures are related to the molecular structure characteristics of polymers. In the present investigation, the mechanical and viscoelastic behavior of an epoxy resin system is studied as a function of absorbed water, temperature, and time of immersion. Water sorption was achieved by immersing the material in distilled water at constant temperature of 60°C and 80°C for 2,5,8,13, 32, 74, 128, 266, 512, 1024, and 1536 h. Subsequently the specimens were tested in static and dynamic three-point bending tests to study their mechanical and viscoelastic behavior. The variation of T g , tan ␦, bending modulus, and strength was measured as a function of exposure time and respective percentage of water uptake for both temperatures. Some anomalies in their behavior due to water absorption were observed, and a model for the description of the experimentally observed mechanical behavior due to hygrothermal aging is proposed. The results show that the model predictions are in good agreement with experimental findings.

Abstract. This work presents an insight into the effect of preparation procedure and the filler content on both electrical and mechanical properties of a nanocomposite system. For the preparation of the nanocomposites diglycidyl ether of bisphenol A (DGEBA) was used with triethylenetetramine (TETA) as a curing agent. As fillers carbon black (CB) nanoparticles with size from 25 to 75 nm were used. The characterization was done using Dynamic Mechanical Analysis (DMA), Dielectric Relaxation Spectroscopy (DRS), Differential Scanning Calorimetry (DSC), Wide Angle X-ray Diffraction (WAXD) and electrical conductivity measurements. The dependence of the dynamic mechanical and dielectric parameters (E′, E″, tanδ, ε′, ε″, σ and Tg) is associated with the filler content and is controlled by the employed curing conditions. An increase in electrical conductivity, which is observed at about 1% w/w of carbon black, indicates the creation of conducting paths and is associated with the Maxwell Wagner Sillars (MWS) relaxation, probably due to the formation of aggregated microstructures in the bulk composite.

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Thermoplastic apparent interpenetrating polymer networks (thermoplastic‐AIPNs) were prepared at several compositions by melting and pressing of crystallizable polyurethane (CPU), based on butylene adipate glycol (BAG), and styrene/acrylic acid random copolymer (S/AA). Structure‐property relationships in the thermoplastic‐AIPNs were investigated by means of wide‐angle and small‐angle X‐ray scattering (WAXS, SAXS), differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), thermally stimulated depolarization currents (TSDC) techniques, dielectric relaxation spectroscopy (DRS) and several physico‐mechanical characterization techniques. The results obtained by the various techniques were critically compared to each other. They suggest that the two components show weak affinity to each other and that the thermoplastic‐AIPNs can be classified into two groups with high and low contents of CPU, showing essentially the behavior of CPU and S/AA, respectively. However, deviations from additivity and significant changes for several properties on addition of small amounts of either of the components suggest partial miscibility. Most of the results are explained by physical interactions of COOH‐groups of AA in S/AA with the ester groups of the flexible CPU blocks, which promote microphase separation in both the CPU and the S/AA components.