Papers by Author: Olga S. Carneiro

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 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 effect of different dispersion states on the rheological and AC conductivity properties of carbon nanofibre/epoxy suspensions was investigated. Both rheological and electrical properties revealed to be good indicators of the fillers’ dispersion state, as confirmed by optical microscopy. It was shown that imposing a low shear deformation to poorly dispersed suspensions leads to agglomerate rearrangement resulting in a worse dispersion quality and, consequently, lower electrical conductivity. On the other hand, the imposition of a high shear deformation improves the original dispersion, resulting in better electrical conductivity. Rheological observations confirm the trends observed.

Abstract: A 3D numerical code, based on the finite volume method, able to model the cooling stage of an extrusion line is presented and validated. For this purpose, an analytical solution of a simple heat transfer multi domain problem was developed, the result obtained being compared with the predictions given by the numerical code. A prior study performed with the above mentioned code showed that in general when a reduction of the profile average temperature is imparted, lower temperature homogeneity is also obtained, being the only exceptions the reduction of the extrusion velocity and splitting the calibrator into several units, separated by annealing zones. Therefore, the only way to improve the cooling efficiency without compromising the production rate is to divide the total cooling length into several independent units. In this work that investigation is further extended to study the influence of the individual cooling units and annealing zones lengths distributions on the global cooling efficiency.

Abstract: The effect of the dispersion state of carbon nanotubes in polycarbonate on the rheological, mechanical and electrical properties of melt-extruded compounds is presented. The dispersion state was monitored by means of grey values distribution histograms of optical micrographs of the composites. Increasing the processing residence time, and hence the deformation induced by the surrounding polymer, increased the level of dispersion of CNTs in the matrix. This, in turn, resulted in a large improvement of the CNTs reinforcement effect and decreased composite electrical resistivity. Rheological behaviour is in agreement with these observations.

Abstract: In this work, a rectangular polypropylene profile was produced with several different extrusion conditions, in order to identify the most relevant processing variables determining its morphology and mechanical properties and to establish relationships between them. A Taguchi Design of Experiments (DOE) technique considering two levels for each variable (extrusion temperature, extrusion throughput, drawdown ratio and distance between the die and the cooling bath) defined the set of extrusions runs carried out. The resulting plastic profiles were characterized in terms of their microstructure and mechanical properties. It was concluded that the most significant processing variable determining the mechanical properties of the profiles is the extrusion temperature and that the drawdown ratio controls the degree of molecular orientation of the profile and, therefore, the extension of its shrinkage after heatiing.