11 documents found, page 1 of 2
In-process assessment of clay dispersion in PLA during melt compounding: Effect...
Teixeira, P. F.; Covas, J. A.; Hilliou, L.Shear viscosity, clay particle size and volume fraction are measured in-situ during the extrusion of PLA-clay nanocomposites. These in-process measurements are particularly adequate to assess the dispersion of fillers in thermo-mechanically sensitive systems, as the additional degradation associated with sample preparation for off-line characterization is readily avoided. Overall, results point towards the impa...
Assessing temporary speed restrictions and associated unavailability costs in r...
Andrade, A. R.; Teixeira, P. F.This paper analyses the occurrence of temporary speed restrictions in railway infrastructure associated with railway track geometry degradation. A negative binomial regression model is put forward to estimate the expected number of temporary speed restrictions, controlling for the main quality indicators of railway track geometry degradation and for the maintenance and renewal actions/decisions. The prediction ...
Exploring different alert limit strategies in the maintenance of railway track ...
Andrade, A. R.; Teixeira, P. F.This paper explores a quantitative model with different maintenance strategies to control railway track geometry degradation in Portugal. The alert limits put forward by the international standards are assessed regarding the planned and unplanned impacts associated with those limits, namely preventive maintenance and renewal costs, corrective maintenance costs, planned infrastructure delays due to changes in th...
Effects of residues on the degradation of PHA produced from mixed microbial cul...
Hilliou, L.; Teixeira, P. F.; Machado, Diogo Silva; Covas, J. A.; Oliveira, Catarina S. S.; Gouveia, Ana; Reis, Maria A. M.Thermal degradation upon melting is one of the major drawbacks reported for polyhydroxyalkanoates (PHA). However, the role of residues originating from the fermentation and the extraction steps on the thermal stability of this class of biopolymers still needs to be clarified. In the particular case of PHA produced from mixed microbial cultures (MMC), this topic is even less documented in the literature. Here, t...
Rheo-optical characterization of liquid crystalline acetoxypropylcellulose melt...
Teixeira, P. F.; Fernandes, Susete N.; Canejo, João; Godinho, Maria Helena; Covas, J. A.; Leal, Catarina Rosa; Hilliou, L.The rheological and structural characteristics of acetoxypropylcellulose (APC) nematic melt are studied at shear rates ranging from 10 s 1 to 1000 s 1 which are relevant to extrusion based processes. APC shows a monotonic shear thinning behavior over the range of shear rates tested. The negative extrudate-swell shows a minimum when a critical shear rate g_ c is reached. For shear rates smaller than g_ c, the fl...
In-line particle size assessment of polymer suspensions during processing
Teixeira, P. F.; Maia, J. M.; Covas, J. A.; Hilliou, L.The validation and the operating window of an in-line rheo-optical slit die coupled to a prototype single/twin-screw mini-extrusion system are reported. This experimental set-up is able to perform in-situ rheological measurements, together with Small Angle Light Scattering (SALS) and Polarized Optical Microscopy (POM), thus enabling the structural characterization of materials during extrusion. The optical vali...
Assessing the practical utility of the hole-pressure method for the in-line rhe...
Teixeira, P. F.; Hilliou, L.; Covas, J. A.; Maia, J. M.The most promising method capable of providing accurate measurements of the first and second normal-stress differences in shear flows at shear rates typical of polymer processing is the so-called hole-pressure method, but its use has not been as widespread as would be expected, namely due to the experimental difficulties associated with performing such experiments accurately. In this work, we use a small-scale ...
When liquid crystalline cellulose flows and relaxes
Teixeira, P. F.; Fernandes, Susete N.; Canejo, João; Godinho, Maria Helena; Leal, Catarina Rosa; Hilliou, L.Cellulose-based liquid crystalline materials can generate stimuli-responsive fibbers and films [1,2]. Changes in orientational order, which can be affected by variation of temperature and UV irradiation as well as by the presence of solvent vapours, give rise to stresses, which result in strains and modifications in sample shape. The processing conditions of the liquid crystalline material are crucial for fibbe...
In-line optical characterization during extrusion of polymer blends
Teixeira, P. F.; Hilliou, L.; Covas, J. A.; Maia, J. M.The assessment of morphological development during the extrusion of small amounts of high-valued polymer-based systems is critical for understanding the processability of new plastics and for monitoring the extrusion of complex formulations. However, reports on the structural development during the extrusion of industrial plastics, measured by means of in-line optical techniques, are still scarce. In this contr...
In-line rheo-optical characterisation of polymeric systems
Teixeira, P. F.; Hilliou, L.; Covas, J. A.; Maia, J. M.As increasingly more sophisticated polymer systems are being developed, it is important to rapidly estimate their processability, morphology after processing and performance under service conditions, if possible using small amounts of materials. In order to accomplish this, a single I twin-screw mini-extrusion system of modular construction, with well-controlled outputs in the range 30-300 g/h, was coupled to a...