Materials Science Forum Vols. 587-588

Abstract: “Sargaço” is the name given to a mixture of dead seaweeds collected on Portuguese beaches. “Sargaço” is composed of algae containing biopolymers such as carrageenan, alginate and agar which are extensively used in food and pharmaceutical industries as gelling and stabilizing agents. The objective of this work was the biopolymers extraction from “Sargaço”, collected at Leça da Palmeira-Portugal, for production of biodegradable films and subsequent application in edible coatings for food. A mixture of biopolymers was hot-extracted from alkali treated “Sargaço”. Films were made from an optimized extract, using the knife coating technique. Films physical properties were characterized and results show that biodegradable films from “Sargaço” are more hygroscopic, less elastic, more deformable, and more permeable to water than films obtained from a commercial alginate and a domestic κ/ ι-hybrid carrageenan developed during previous studies. As such, this mixture of biopolymers is an interesting cheap alternative to produce biodegradable materials and a potential application to fresh fruit preservation has been tested.

Abstract: This investigation aims at establishing the relationships between the thermomechanical conditions and the mechanical properties of a direct injection moulded polypropylene/polycarbonate blend (70/30wt composition). Rectangular plates (2 mm thick) were injection moulded by systematic variations of the processing conditions. The moulding programme was based on a design of experiments (DOE) approach, being considered variations in two levels of the melt (240 and 280°C) and the mould (5 and 80°C) temperatures and the injection flow rate (3.8 and 38 cm3/s). For comparison purposes, neat polypropylene was also moulded under the same set of processing conditions. In both cases the thermomechanical environment was characterised by computer simulations of the mould filling phase using commercially available codes (Moldflow). Tensile specimens were cut from the injected plates. The microstructure of the mouldings was characterized by polarized light microscopy, PLM. The mechanical characterization encompass the assessment of the tensile (at 5 mm/min at 23 °C) and impact toughness (unnotched Charpy test). The results are analysed by ANOVA. The presence of PC particles affects the crystallization of PP, this being revealed on the mouldings microstructures observed by PLM that are distinct for the neat and PP/PC blends. The mechanical properties are determined differently by the processing variables.

Abstract: During the injection moulding process, the material is subjected to successive transformations, being submitted to a thermo-mechanical environment that determines the final dimensions of the part. This environment is characterized by several parameters which are related to material properties, the mould design, equipment and process variables. As a result, deviations of the dimensions of the moulded parts from the dimensions of the cavity cannot be avoided. If differences on shrinkage occur, caused for example by anisotropies of the material or non-uniform cooling, distortions will happen. In order to predict this two effects on the injection cycles is require one strategy to monitoring and control the process variables. The aim is to achieve highest quality control of all manufacture parts. This paper presents the effect of different holding pressures and mould temperatures on shrinkage and warpage in two different materials, one amorphous (PC) and another semi crystalline (PP). An instrumented mould was manufactured. During the injection moulding process sensors signals were continuously monitored by a Data Acquisition System. The experimental results were compared with predictions made by commercial software.

Abstract: The rising of consumers’ demands and an ever increasing pressure of international markets imposed a deep change in the product development process to respond to an increasing product complexity and higher quality, as well to the need to promptly introduce products into the market. Stereolithography plays an important role on this new product development context. This technology produces models for thermosetting resins through a polymerisation process that transforms liquid resins into solid materials. In this work, a new route to produce metallic parts through stereolithography is explored. The curing analysis of hybrid reinforced polymeric systems, polymerised through radicalar or/and cationic mechanisms, is investigated. The rheological behaviour of these polymeric systems is also evaluated due to its importance for recoating. The influence of other processing and material characteristics like light intensity, initiator concentration, low powder size of metallic powders, degree of dilution, etc. is also investigated.

Abstract: A polyethylenterephthalate-hydrotalcite (PET-HT) composite was prepared by in situ polymerisation, using polyethylenterephthalate (PET) and different amounts of a hydrotalcite with dodecylsulphate in the interlayer space (DS-HT). The resulting material has been characterised by powder X-ray diffraction (PXRD) and thermogravimetric (TG) analysis. The thermal stability of PET is not greatly enhanced upon incorporation of the inorganic component, despite PXRD shows that the HT is exfoliated in the composite. Thus with 2-10% shows a complete dispersion of the layered component in the polymeric matrix, while if the inorganic loading is between 20-50 % (larger loadings were not tested) no complete dispersion is achieved and PXRD-detectable agglomerates are formed.

Abstract: Polymer crystalline regions can be characterized by wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS). The in-situ study of isotactic polypropylene with measurement of wide angle and small angle X-ray scattering (WAXS and SAXS), at varying distances from the exit of the extruder have been successfully completed using an X-ray system with a standard X-ray source. The processing conditions, used were: 50, 100, 200 and 400m.min-1 for the take up speed, 0.3, 0.6, and 1.2 cm3min-1hole-1 for the melt flow rates, and a spinning temperature of 220°C. These experimental conditions produced draw down ratios ranging from 33 up to 1058. The X-ray characterization was carried in-situ at 15, 30, 45 and 60 cm from the exit of the spinneret and also ex-situ. The results obtained show the crystallinity index and the crystalline orientation to increase for the higher draw down rates, as expected under draw induced crystallization conditions, and a logarithmic relationship was observed within the experimental conditions used in this work. This communication reports the relationship between the crystallinity, crystalline orientation and lamellar long period and draw down ratio along the spin line.

Abstract: The mechanical behaviour of single lap adhesive joints was characterized, using two commercial acrylic adhesives. For this purpose the surfaces were cleaned and abraded using fine grit abrasives. The effect of temperature and moisture in the mechanical strength was, also, evaluated. For this characterization, mechanical tests were carried out according procedure and geometry foreseen by ASTM D3163-01 [1] and ASTM D4501-01 [2] standards. The results show that it is possible to get good strengths without great surface preparation. The temperature and moisture effect observed don’t seem to be relevant for the mechanical behaviour.

Abstract: Polymerisation of urea-nitryle-urethanes performed in electric heating devices. It was suggested to manufacture these materials using microwave radiation as the heat source. As a part of this research project urea urethanes were fabricated using various strength of microwave radiation. The structure and properties of manufactured materials were investigated.

Abstract: This work reports on research being carried out in the area of functional knitted fabrics with a special structure incorporating hydrophobic fibres near to the skin and suction channels of hydrophilic fibres to suck moisture from the skin on the hydrophilic layer away from the skin; in this way, comfort is maximised in active wear as the fabric does not feel wet near to the skin.

Abstract: This paper describes experimental and numerical studies on the application of the End Notched Flexure (ENF) and End Loaded Split (ELS) tests to mode II wood fracture characterization. In this context, ENF and ELS specimens were used to determine GIIc of a clear Pinus pinaster wood in the RL system, which is the most relevant for structural design. In mode II fracture tests the crack faces are in contact, thus hindering a rigorous visualization of the crack tip. This makes classic methodologies based on crack length measurement during experimental tests inadequate, since they induce significant errors on the mode II fracture properties. To overcome this experimental problem a Compliance Based Beam Method (CBBM) is used. This new data reduction scheme does not require crack length monitoring and includes the effect of the Fracture Process Zone (FPZ) ahead of crack tip. Furthermore, the clamped cross-section rotation of the ELS specimen is also taken into account. In the present work a numerical analysis considering a cohesive damage model was performed with a cohesive damage model in order to validate the application of the CBBM to the experimental results. The results confirmed the adequacy of the CBBM and the applicability of the ENF and ELS tests for mode II wood fracture characterization.