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Polymer-cork composite for the fabrication of wine closures by injection model : effects of paraffin wax on the mechanical and thermal properties

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URI: http://hdl.handle.net/10016/10165
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2009-12
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2009
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In a previous work composites polymer/cork for the production of wine closures by injection moulding were developed. This new material exhibited good flow behaviour during moulding and suitable mechanical properties. However some critical aspects such as dark coloration of final product, porosity and hardness should be improved. For these reasons the aim of this work was to study the causes of dark coloration in cork composite and to improve hardness without to lose too much of the tensile strength. First, to study thermal degradation of cork and composite thermal treatment was carried out by differential scanning calorimetric (DSC), thermo gravimetrical analyses (TGA) and conventional furnaces. Then blends were prepared in a twin screw extruder. Cork content was 40 vol%. The matrix consisted in 55 vol% of LDPE/PW in volume relation of 90/10, 70/30 and 50/50. 5 vol% of Stearic acid was coated onto cork surface to improve flow behaviour and the interaction between cork and polymer. Injection stage was carried out and parameters such as temperature, injection volume and speed were optimized. Mechanical properties of final parts were tested. Tensile strength of samples ranged between3.21 and 7.4 MPa. On the other hand hardness ranged between 40 and 50 Shore D been these values better than composites without paraffin wax. Finally it was concluded that PW has a positive effect on thermal characteristics of blends allowing processing the mixtures at lower temperature avoiding thermal degradation of cork. Besides wax also proved to enhance flow behaviour of mixtures and to lower the harness of final parts what is desirable for final application.
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Materiales compuestos, Polímeros, Polímero-corcho, Moldeo por inyección
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