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This work aims at producing and characterizing unidirectional carbon/epoxy composites containing different fractions of paraffin microcapsules (MC) for thermal management applications. The viscosity of the epoxy/MC mixtures increases with the MC content, thereby increasing the final matrix weight and volume fraction and reducing that of the fibers. This is at the basis of the decrease in mechanical properties of the laminates with high MC concentration (the elastic modulus decreases up to 53% and the flexural strength up to 67%), but the application of theoretical models shows that this decrease is only due to the lower fiber volume fraction, and not to a change in the properties of the constituents or the fiber/matrix interaction. The MC phase is preferentially distributed in the interlaminar zone, which leads to a thickening of this region and a decrease in matrix-related properties, such as the interlaminar shear strength, which decreases of up to 70%. However, a modest MC fraction causes an increase in the mode I interlaminar fracture toughness of 48%, due to the introduction of new toughening mechanisms. On the other hand, an excessive MC content lets the crack propagating through the matrix and not at the fiber/matrix interface, thereby reducing the toughening mechanism provided by fiber bridging. For the thermal properties, the phase change enthalpy increases with the MC fraction up to 48.7 J/g, and this is reflected in better thermal management performance, as proven by thermal imaging tests. These results are promising for the development of multifunctional polymer composites with thermal energy storage and thermal management properties, and future works will be focused on a deeper study of the micromechanical properties of PCM microcapsules and on the improvement of the capsule/matrix adhesion.

Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) nanocomposite films containing 0.25 wt % of Graphene Oxide (GO) nanoparticles were prepared by solution-casting and characterized by Differential Scanning Calorimetry (DSC), X-Rays Diffraction (XRD) and Positron Annihilation Lifetime Spectroscopy (PALS). Gas transport properties were analyzed in the 295–343 K interval using CO2, N2, D2 and He. Neat PHBH films showed a semi-crystalline structure with lamellar crystalline domains of 30 ± 1 and 5 ± 1 nm size in the (020) and (002) direction, respectively. GO dispersion increases the PHBH crystalline fraction from 0.28 to 0.60 wt. % without changing the size of crystalline domains and the structure of the PHBH free volume. Nanocomposite films show mechanical properties similar to those of the neat PHBH film but improved gas barrier properties as consequence of the larger number density the of gas- impermeable crystalline domains.

Electrically conducting fibers based on coconut fibers (CF) and polyaniline (PANI) were prepared through in situ oxidative polymerization of aniline (ANI) in the presence of CF using iron (III) chloride hexahydrate (FeCl 3. 6H 2 O) or ammonium persulfate (APS) as an oxidant. The PANI-coated coconut fibers (CF-PANI) displayed various morphologies, electrical conductivities and percentages of PANI on the CF surface. For both systems, a PANI conductive layer was present on the CF surface, which was responsible for an electrical conductivity of around 1.5 × 10 −1 and 1.9 × 10 −2 S cm −1 for composites prepared with FeCl 3 .6H 2 O and APS, respectively; values that are similar to that of pure PANI. In order to modify the structure and properties of polyurethane derived from castor oil (PU) both CF-PANI and pure PANI were used as conductive additives. The PU/CF-PANI composites exhibited higher electrical conductivity than pure PU and PU/PANI blends. Additionally, the PU/CF-PANI composites showed a variation in electrical resistivity according to the compressive stress applied, indicating that these materials could be applied for pressure-sensitive applications.

Effects of nanofiller concentration and surface treatment on the morphology, thermal, viscoelastic and mechanical behavior of polypropylene copolymer (PP)/boehmite alumina (BA) nanocomposites were investigated. Both untreated BA particles and those treated with octylsilane (OS) or sulphonic acid compound (OS2) were added at up to 10 wt% to produce nanocomposites by melt mixing followed by film blow molding and hot pressing. Dispersion of BA was studied by scanning electron microscopy. Differential scanning calorimetry and wide-angle X-ray scattering were adopted to detect changes in the crystalline structure of PP. Thermooxidative degradation of the nanocomposites was assessed by thermogravimetrical analysis. Dynamic mechanical analysis served for studying the viscoelastic properties, whereas quasi-static tensile, creep and Elmendorf tear tests were used to detect changes in the mechanical performance. BA nanoparticles were finely dispersed in PP up to 10 wt%, even when they were not surface modified. The resistance to thermal degradation was markedly improved by BA nanomodification. Since the crystalline characteristics of the PP matrix did not practically change with BA modification, changes observed in the mechanical properties were attributed to BA dispersion, filler/ matrix interactions and related effects.

The Boltzmann superposition principle (BSP) valid for “standard linear solids” is presented in all textbooks on viscoelasticity. In practice, the BSP is not applicable to viscoelastic polymers because (i) the apparent limit (if any) of the stress–strain linearity is very low, (ii) real deformations (stresses) are not infinitesimal, and (iii) tensile deformations give rise to additional free volume, which affects all currently running deformation processes. Consistent application of the free volume approach, including the strain-induced free volume, allowed us to derive and verify a new type of the internal time–tensile strain superposition for a series of single-step nonlinear creeps [J. Kolařik, A. Pegoretti, Nonlinear tensile creep of polypropylene: time–strain superposition and creep prediction, Polymer 47 (1) (2006) 346]. The Boltzmann-like superposition principle for multistep nonlinear tensile creep, proposed in this paper, consists of (i) the separation of individual creeps, (ii) their reconstruction for the initial free volume by introducing a specific internal time, and (iii) the superposition of the reconstructed creeps. The procedure is demonstrated using creep data for three types of commercial polypropylene.

A DGEBA-based epoxy matrix was loaded with 10, 20 and 30 phr of fumed silica particles. Single edge notched bend (SENB) specimens were prepared and deformed to failure in three-point bending configuration. Their fracture surfaces were examined by atomic force acoustic microscopy (AFaM) in order to obtain information about the local elastic modulus of the surface at high spatial resolution. The collected information was correlated to the bulk thermo-mechanical properties of the composites. In particular, the decrease in thermo-mechanical properties like tensile modulus, yield strength, stress at break and glass transition temperature, observed for samples filled with 10 and 20 phr with respect to the unfilled matrix was found to correspond to highly heterogeneous fracture surfaces presenting a broad distribution of elastic modulus values. The AFaM data were interpreted as representative of different degrees of filler exposure on fracture surfaces and also of localized cavitation effects involved in crack propagation, both phenomena accounting for the effective plasticizing effect macroscopically observed at silica amounts of 10 and 20 phr. A substantial reduction in the exposure probability of silica particles on fracture surfaces was found for the sample filled with 30 phr of silica, which also displayed an improvement of the mechanical and thermal properties. This latter evidence was tentatively explained by supposing a physical immobilization of polymer chains at the polymer-matrix interface.

The indentation of a sphere into a flat support under a constant load provides information on the resistance of polymeric materials to pressure, which may be of basic importance in various applications. The existing theoretical background for indentation creep in an elastic–plastic regime is reviewed briefly. The indentation creep was measured over the interval 0.1–100 min; in addition, five auxiliary measurements lasting 0.4, 1, 4, 10 and 40 min were performed with the same load. After a recovery period 10 times longer than the creep time, the irreversible part of the indentation depth was read off. The acquired experimental data were fitted with a suitable function in order to calculate irreversible deformation for any time in the interval 0.1–100 min. An essential part (up to 50%) of the indentation depth was found to be irreversible; plastic deformation grew with the creep time somewhat faster than total deformation. Indentation mainly proceeded in short periods after the initiation of loading, while a further increase in penetration depth was much slower; however, no “break” was observed in the time dependencies of measured properties. The acting pressure was linearly decreasing with the logarithm of time due to the rising penetration depth and contact area in the course of individual measurements. The penetration depth/sphere radius ratio was in all cases smaller than 0.10. The logarithm of compliance, which was proportional to the fraction of impact modifiers, was for all samples a linear function of the logarithm of creep time. Although the slope of these dependencies was rather small, it increased with the modifier content, thus indicating the rising creep rate. The effects of two types of impact modifiers on the indentation creep of PET were virtually identical.

In the present work, a test method to characterize the dynamic behaviour of rubber compounds by electrodynamic shaker (ES) in the frequency range of 10–1000 Hz was developed. Data of dynamic moduli of two different rubber compounds were determined through the analysis of the transmissibility of a suitably designed test system. The results were compared with those of dynamic moduli master curves obtained through frequency–temperature reduction of data measured by a commercial dynamic mechanical thermal analyser (DMTA), by scanning temperature at various frequencies in the range 0.3–30 Hz. Very good agreement of the data obtained by the two different aproaches were found, in spite of the different range of frequency explored by the two instruments, ES and DMTA, respectively. For one of the material examined, non-linear effects at low strain amplitudes were investigated by the two experimental methods considered.