Search results for "Thermal"
showing 10 items of 3576 documents
Epoxy resins as a matrix material in advanced fiber-reinforced polymer (FRP) composites
2013
Abstract: This chapter discusses the epoxy resins which, thanks to their good and versatile properties, can be considered nowadays the most important class of thermosetting polymers. In particular the chapter first reviews both the epoxy resins commonly available on the market, including a new class of bio-derived epoxy resins, and the most-used curing agents. it then describes the principal characteristics of the epoxy resins and how it is possible to enhance them by adding several fillers to the epoxy system. Finally, the chapter analyzes the main engineering fields in which epoxy resins find application today and their possible future utilization.
Low-temperature specific heat of orientational glasses
1992
This review summarizes specific heat data measured at low temperatures (T<1 K) on orientational glasses. Three species of mixed molecular crystals exhibiting orientational disorder are considered, namely (KBr)1−x (KCN) x , (NaCN)1−x (KCN) x (Rb)1−x (NH4) x H2PO4. For intermediate concentrations of the anisotropic components, glass-like excitations have been observed. It is demonstrated that with respect to thermal properties, orientational disorder leads to the same “universal” behaviours than for structural disorder, i.e. a specific heat which varies below 1 K and for times 10−4 s–10 s as:C p(T,t)∞T 1×ln(t). The variation of the glass-like anomaly with compositional disorder is also discus…
Thermal and viscoelastic properties of entangled supramolecular polymer networks as a powerful tool for prediction of their microstructure
2018
Abstract Thermal and viscoelastic properties of entangled supramolecular polymer networks, SPNs, depend strongly on binary and collective assembly of associative groups. The collective assemblies can phase separate from polymer matrix chains and form domains with different sizes and shapes, which have different melting point transitions. By increasing content of associative groups along the polymer chains, their high-order association leads to formation of domains, which have higher melting temperatures than other ones. We prepared a SPN system that contains three networks. All networks have similar precursor polymer backbone, but different content of ureidopyrimidinone, UPy, moiety as stro…
Hydrothermal ageing of radiation cured epoxy resin-polyether sulfone blends as matrices for structural composites
2010
Abstract The hydrothermal ageing of epoxy–thermoplastic blends, used as matrices for carbon fibre composites, cured by electron beam, has been studied. Two different thermoplastic percentages have been adopted. A suitable choice of both curing process and formulation parameters allows to carry out irradiation at mild temperature with several advantages, coming from a “non thermal” process, for both the final properties of the materials and the environment. Nevertheless the occurring of vitrification phenomena needs the use of a short thermal treatment after irradiation on the already solid materials, in order to complete the cure reactions. Radiation cured epoxy based matrices have been sub…
Interactions between aroma and edible films. 1. Permeability Of methylcellulose and low-density polyethylene films to methyl ketones.
1998
This work contributes to the study of aroma transfers through edible and plastic packaging films. Permeability, sorption, and diffusivity of three methyl ketones (2-heptanone, 2-octanone, and 2-nonanone) in and through low-density polyethylene and methylcellulose-based edible films have been determined. Permeability was measured using a dynamic method coupled with a gas chromatograph. The methyl ketone permeability of polyethylene films mainly depends on diffusivity of the penetrant in the polymer. In the case of 2-heptanone, a saturation of the polymer network is observed at high vapor concentrations. The formation of clusters could take place when concentrations are higher in the vapor ph…
Combined thermal evaporated and solution processed organic light emitting diodes
2011
Abstract Highly efficient, partly solution processed phosphorescent red, green and white organic light emitting diodes with small molecular weight host materials are prepared from commercially available starting compounds. Starting from an evaporated reference device, layers are stepwise replaced by solution processed layers. Replacing the evaporated hole transport layer by a solution processed polymer interlayer does not affect the performance and allows spincoating of the emissive layer after annealing of the polymer. Devices with, next to the spincoated hole injection and transport layer, a solution processed emission layer show similar characteristics and efficiencies as the reference d…
Thermal diffusivity measurements for Mg-Mn ferrites
1992
Abstract The thermal diffusivity of Mg-Mn ferrites is studied through a modified scheme of the photothermal deflection method able to derive the diffusivity of low-diffusivity samples and to avoid any influence of the vertical offset parameter. The examined samples have been realized under different preparation conditions producing different grain dimensions, and a negligible influence of the grain dimensions is found on the thermal properties.
3D Metamaterials with Negative Thermal Expansion and Negative Effective Compressibility
2018
Materials with negative thermal expansion are desired for controlling thermal stresses, but unusual in nature. With two-component metamaterials it is possible to tune the thermal expansion from positive over zero to negative values, even if both components have positive thermal expansion. Using gray-tone laser lithography we fabricate three-dimensional two-component polymer microlattices, exhibiting zero or negative thermal expansion [1].
Non-Isothermal Effects in the Elongational Flow of Polymer Melts
1980
Non-isothermal histories occur in almost all polymer processing, and however only a few experimental and theoretical studies have been devoted to the rheological response of the polymeric fluids under non-isothermal conditions. A systematic study, which cannot however be considered exhaustive, has been recently carried out in this field by Bogue and coworkers1–3.
Use of transmission electron microscopy to obtain quantitative information about polymers
2005
In the polymer field the electron microscope is frequently used as a tool for obtaining purely qualitative data, but only rarely to obtain quantitative information. In order to discuss the potential of this instrument for the latter purpose it is convenient to separate the discussion into the following sub-sections.