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Abstract: Although aluminate phosphors have attracted great interest for applications in lamps, cathode ray tubes and plasma display panels, there still remain issues affecting operational parameters such as luminescence efficiency, stability against temperature, high color purity and perfect decay time. In addition, issues involving important aspects of the monoclinic↔hexagonal phase transition temperature still exist. In this work, SrAl x O y :Eu2+,Dy3+ phosphor powders were prepared by the sol–gel method. X-ray diffraction (XRD) has shown that both crystallinity and crystallite sizes increased as the temperature increased. Both SrAl2O4 and Sr2Al3O6 phases were observed. Photoluminescence (PL) characterization shows temperature-dependence, which indicates emission at low and high annealing temperatures originating from Eu2+ and Eu3+ ions. Thermoluminescence glow and decay measurements provided useful insight on the influence of traps on luminescence behavior. Differential scanning calorimetry (DSC) and thermogravimetric studies (TGA) on composites of the phosphor in low density polyethylene (LDPE) demonstrated the varied influence of annealing temperature on some luminescence and thermal properties. [Copyright &y& Elsevier]

Abstract: The performance of nanophase luminophors is usually compromised by environmentally induced degradation. In this study, composites of low density polyethylene (LDPE) with various concentrations of the blue-emitting europium and dysprosium co-doped strontium aluminate (SrAl2O4:Eu2+,Dy3+) phosphor were investigated. The blue long-lasting phosphorescence of the composites was observed in the dark after removal of the excitation light. X-ray diffraction analysis revealed the presence of the SrAl2O4 phase in the composites. PL spectra of the composites have two sets of peaks, major broad bands peaking at about 4855Å and minor ones at wavelengths between 4115 and 4175Å, attributed to the 4f–5d transition of Eu2+. DSC and TGA results show that the introduction of the phosphor in LDPE matrix caused a slight reduction in the crystallinity of LDPE but a significant increase in the stability of the composites. [Copyright &y& Elsevier]

Abstract: Nanostructured wollastonite was synthesized by a sol–gel method and then used as a filler for polypropylene (PP). The obtained wollastonite particles were investigated using XRD, TEM and FTIR techniques. Non-isothermal crystallization measurements revealed that the wollastonite filler reduced the crystallization temperature of the matrix. TGA analyses showed improved thermal stability of the nanocomposite with respect to that of the pure polypropylene. From the DMA tan δ curves, it was concluded that the introduction of the filler into the PP matrix induced a slight shift of the β-transition (glass transition) towards higher temperature. The measurements of storage moduli showed that the nanocomposites have higher stiffness than the pure PP over the whole range of test temperature. An increase in stiffness was also confirmed by tensile measurements. [Copyright &y& Elsevier]

Abstract: Two waxes, a soft petroleum wax and a hard Fischer–Tropsch paraffin wax, have been investigated to find the reasons for multiple endothermic peaks observed during heating in a DSC. DSC curves, molar mass distribution curves, and variable-temperature XRD results were compared, and it was confirmed that the first endothermic peak for the soft petroleum wax was due to a solid–solid transition, while the second endothermic peak was due to melting. However, for the hard Fischer–Tropsch paraffin wax there was no evidence of a solid–solid transition, and it was concluded that the multiple endothermic peaks in this case were due to melting of different molar mass fractions. [Copyright &y& Elsevier]

Abstract: The influence of sisal fibre content, peroxide cross-linking, and wax addition on the thermal properties of LDPE–sisal composites was investigated using differential scanning calorimetry and thermogravimetric analysis. It was found that the presence of wax and sisal fibre, as well as peroxide treatment, has an effect on the LDPE crystallinity. In the presence of sisal, the melting temperature of peroxide treated samples decreases substantially, and this decrease becomes more pronounced with increasing sisal content. The presence of wax reduces the extent to which the melting temperature decreases. It was further found that the presence of wax and sisal fibre, as well as peroxide treatment, has an effect on the thermal stability of the composites. [Copyright &y& Elsevier]

Abstract: Phase change materials, based on low-density polyethylene blended with soft and hard paraffin waxes respectively, were studied in this paper. DSC, DMA, TGA and SEM were employed to determine the structure and properties of the blends. The blends were able to absorb large amounts of heat energy due to melting of paraffin wax, whereas the LDPE matrix kept the material in a compact shape on macroscopic level. The hard paraffin wax was, however, much more miscible with LDPE because of co-crystallization than the soft paraffin wax. LDPE blended with hard paraffin wax degrades in just one step, while blends containing soft paraffin wax degrade in two distinguishable steps. SEM showed completely different morphology for the two paraffin waxes and confirmed the lower miscibility of LDPE and soft paraffin wax. DMA analyses demonstrated the toughening effect of the waxes on the polymer matrix. This technique was also used to follow the thermal expansion as well as the dimensional stability of the samples during thermal cycling. The most visible expansion could be seen in the first cycle, probably due to a totally different thermal history of the sample. With further cycling the dimensions stabilized after two and four cycles for soft and hard paraffin wax, respectively. Controlled force ramp testing on DMA confirmed poor material strength of the blends containing soft wax, especially at temperatures above wax melting. [Copyright &y& Elsevier]

Abstract: Phase change materials, based on isotactic polypropylene (PP) blended with soft and hard Fischer−Tropsch paraffin wax respectively, were studied in this paper. DSC, DMA, TGA and SEM were used to determine the structure and properties of the blends. While paraffin waxes in the blend changed state from solid to liquid, the PP matrix kept the material in a compact shape. Strong phase separation was observed in both cases, which was more pronounced in the case of soft paraffin wax. Despite the fact that both grades of paraffin wax are not miscible with PP due to different crystalline structures, it was shown that the hard Fischer−Tropsch paraffin wax is more compatible with PP than the soft one. Both waxes plasticized the PP matrix. TGA showed that PP blended with the hard Fischer−Tropsch wax degrades in just one step, whereas blends containing soft paraffin wax degrade in two distinguishable steps. SEM exposed a completely different morphology for the two paraffin waxes and confirmed the lower compatibility of PP and soft paraffin wax. The soft and hard characters of the waxes were manifested in the viscoelastic properties, where the blends containing soft paraffin wax exhibited a lower elastic modulus than pure polypropylene, whereas the hard Fisher−Tropsch paraffin wax solidified the matrix. However, both kinds of blends were able to sustain the dynamic forces applied by the DMA within five cycle runs implying good shape stability. [Copyright &y& Elsevier]

The influence of the wax content and different concentrations of the crosslinking agent on the thermal and mechanical properties of linear low-density polyethylene–wax blends has been investigated. It was found that an increase in wax content induces an increase in elastic modulus and yield stress of the blends. This is a consequence of the higher crystallinity of the blends in the presence of a higher amount of wax. The average tie chain concentration in the blends is estimated in order to explain detrimental effects of the wax on the ultimate properties. A significant correlation was found between stress and strain at break and the concentration of tie chains. Cross-linking improves the ultimate properties of the blends and pure polyethylene. On the other hand, because of its low molecular weight, thermal stability decreases with an increase in wax content and this trend remains unchanged after crosslinking. [Copyright &y& Elsevier]