Materials Science Forum Vols. 587-588

Abstract: There are many manufacturing techniques to form metallic particles with certain size and properties. The laser heating method has been successfully applied to generate metallic particles when a supersonic gas flow is assisting this process. The metallic target is heated, melted and vaporised and micro-particles are carried away by a gas flow stream. The high-velocity gas is used to solidificate molten particles and to condensate the metallic vapour resulting in the formation of fine particles. Several attempts were carried out for the production of metallic particles by laser supersonic heating method, obtaining spherical micro-particles (1- 50 "m) of copper, steel, or aluminium. This work presents the application of this method to generate particles from fish bone, in order to obtain a material with a composition close to the inorganic part of the bones. A pulsed Nd:YAG laser has been used to obtain calcium phosphate micro- and nanoparticles. Microparticles size ranges from 10 to 100"m, whereas the nanoparticles have diameters as small as 2 nm. High resolution transmission electron microscopy (HRTEM) allowed us to identify the nanoparticles as whitlockite.

Abstract: A prototype modular single screw extruder fitted with a screw extracting device is used to monitor melting of an immiscible polymer blend (PP/PA6, with different weight ratios) in this widely used processing equipment. As anticipated, the phenomena observed are much more complex than those involved in extruding PP or PA6, when the well known Maddock/Tadmor mechanism is valid. Consequently a hybrid melting mechanism, involving Maddock/Tadmor and Dispersive melting sequences, is proposed.

Abstract: This work is focused on the first step of the extrusion blow moulding process as part of a global optimisation process encompassing several steps: optimisation of the part thickness, optimisation of the parison thickness that will guarantee the specified thickness profile and optimisation of the extrusion conditions (namely, the sequence of the die mandrel movements) required to obtain the optimal parison thickness distribution. A high density polyethylene (HDPE) extrusion blow moulded tamper evident container was studied using a finite element based analysis (FEA) in order to determine the optimized thickness distribution required for the blown part, considering its mechanical specifications. Several tests corresponding to the requirements for UN homologation for dangerous substances transportation were performed using a commercial software. Non-linear models were used to better describe the mechanical part behaviour. The results obtained at this stage were used to redesign the blown part. In future work this optimised design will be used as an input for optimising the subsequent stages.

Abstract: The objective of this study is to manufacture and investigate novel nanostructured polymer composites (NPC) based on oriented blends of high-density polyethylene (HDPE) and polyamide 6 (PA6). Conventional polymer processing techniques are used for this purpose including extrusion blending, cold drawing and compression molding. Thus, various polymer blends are prepared comprising 10 and 20 wt% of PA6 and 0-10 wt% of a copolymeric compatibilizer. These blends are cold-drawn to high draw ratios and the oriented strands so produced are further compression molded at various temperatures between the melting points of HDPE and PA6. All NPC obtained are characterized by microscopy techniques, solid state NMR, mechanical tests and wide- and small-angle X-ray scattering from synchrotron. The mechanical and structural data of NPCs are discussed with relation with the polyamide fibrils’ orientation, as well as with the effect of compatibilizer at the matrix-fibrils interface.

Abstract: This work aimed to prepare biodegradable polymeric materials based on blends of a synthetic high density polyethylene (HDPE) and biodegradable polymers such as polylactic acid (PCL) and poly(caprolactone) (PLA), in a co-rotating twin-screw extruder. A polyethylene modified with maleic anhydride was used as compatibiliser. The mechanical results showed that the addition of PLA improves the blends stiffness while the addition of PCL leads to materials with a greater elongation at break and a lower Young modulus. This feature is related with the mechanical properties of each material as well as the adhesion between them. Concerning the biodegradability tests, it was found that HDPE/PCL blend presents the highest degree of biodegradability.

Abstract: The logistic mixture model was successfully studied previously in the separation of overlapping steps in some polymeric systems by the authors. In the present work, this method is applied to a polyesther-polyurethane degradation under air and inert atmospheres at several heat rates (5, 10, 15, 20 and 25 °C/min) in dynamic TGA. Every logistic component is fitted by reaction order, Johnson-Mehl-Avrami and Sestak-Berggren kinetics equations in order to calculate its kinetic parameters (activation energy, frequency factor and exponents). The reaction order model gives a good fitting and reproduces accurtelly the experimental curves. Johnson-Mehl-Avrami and Sestak- Berggren equations resulted to be not suitables because of the activation energy values obtained.

Abstract: This work deals with an experimental investigation of the strain-induced crystalline microstructure that develops under uniaxial elongation of amorphous poly(ethylene terephthalate), PET, above its glass transition temperature, as an approach for industrial stretch-blow moulding processes. The present study aims at: a) defining the most relevant processing parameters which govern and are of significance for the induced morphology, and b) establishing of relationships between processing and morphology. Compression moulded amorphous PET was uniaxial stretched with variations of following stretching parameters: stretching temperature, Tst, stretching velocity, Vst, and stretching ratio, λst, that were varied in two levels according to a L8 Taguchi orthogonal array. The developed morphologies were characterized by differential scanning calorimetry (DSC) and birefringence measurements. Obtained results were analyzed by ANOVA statistical tool. The glass transition temperature, Tg, is influenced mainly by the stretching ratio. The cold crystallization temperature, Tcc, is determined by complex influence of all stretching variables and the interaction Tstxλst. The degree of crystallinity, χc, mainly depends upon Vst and Tstxλst interaction. The birefringence,
n, is essentially determined by λst and the interaction Vstxλst. The distinct morphological parameters are then related with the purpose of understand the structure development upon polymer stretching.

Abstract: The kinetics of the isothermal crystallization of the γ-phase Poly(vinylidene fluoride) has been investigated. Samples were prepared from the melt at different crystallisation temperatures and the variation of the microstructure of the samples was monitored with time by optical microscopy. Raman and Infrared transmission spectroscopies also show the appearance of the γ-phase for higher crystallisation temperatures. Two types of γ-phase spherulites have been identified. These spherulites represents different ways to obtain the γ-phase and show different thermal stability. The correlation between microstructure and kinetic parameters allows the tailoring of the microstructure by choosing the crystallisation conditions of the samples.

Abstract: Mono-substituted and sandwich-type copper substituted polyoxoanions ([PW11CuO39]5− and [Cu4(H2O)2(PW9O34)2]10−) were studied as catalysts for the epoxidation of cyclooctene and geraniol, using the green oxidant H2O2, with the results suggesting good efficiency at room temperature. High selectivity and reasonable conversion data were found after the first minutes of reaction. The copper centre may be responsible for this performance and our on-going research focuses in the preparation of new materials incorporating copper into polyoxometalates (POMs). In this context, we have also isolated a new crystalline dimeric sandwich-type polyoxocoppertungstate {H7.05[Cu3WO(H2O)(CuW9O34)(Cu0.6W9O34)]}7.75−. This compound was isolated as potassium salt and structurally characterized by FTIR and single-crystal X-ray diffraction (XRD). The polyoxoanion is composed by the [CuW9O34]12− and [Cu0.6W9O34]12.8− anionic fragments, joined together by a rhomb-like arrangement of three Cu2+ and one W6+ metallic centres, all exhibiting octahedral coordination geometries.

Abstract: In this work, commercial poly(vinylidene fluoride) PVDF, in its β phase was analysed before and after the samples were exposed to UV radiation using a xenon lamp, for ten weeks. Changes in chemical structures, crystallinity, dielectric and piezoelectric response were investigated. From the present study it can be concluded that PVDF shows high stability towards photodegradation and can be used for outdoor applications without interference in its performance.