Estudio de la fractura de materiales compuestos por una matriz de plástico

Se estudia el comportamiento a fractura de materiales, compuestos por una matriz de plástico en la que se ha dispersado una segunda fase en forma de partículas elastoméricas. Como matriz se han utilizado dos materiales diferentes: una resina de poliéster insaturada y poliestireno. Se estudia la morfología de los materiales compuestos preparados, se determinan los parámetros de fractura y otras propiedades mecánicas, se realiza el estudio fractográfico y finalmente se analizan los resultados e identifican los mecanismos de refuerzo que han actuado en cada caso.Se demuestra que la modificación con partículas elastoméricas tanto del poliéster insaturado como del poliestireno produce una mejora de la tenacidad a la fractura.El mecanismo de refuerzo de la tenacidad para el caso de matriz termoestable es el de "crack pinning-bowing" y para el caso de matriz termoplástica es el de múltiple "crazing"

Disseny d'una peça de plàstic reciclat: Metodologia i aplicació

El disseny d'una peça de plàstic és un procés complex que implica el coneixement de les característiques mecàniques, elèctriques i físiques de la peça, i també dels processos de transformació. La principal tasca del dissenyador és traduir una sèrie de requeriments i idees prèvies en les dimensions i formes finals de la peça. Per aconseguir-ho de manera òptima, el dissenyador ha de fer ús, a banda de l'experiència i els coneixements propis, d'una metodologia de disseny adquada. L'objectiu d'aquest article és posar de manifest els passos a seguir quan s'aborda un disseny i la seva aplicació a una peça de plàstic fabricada en material reciclat

Diseño de una pieza de plástico reciclado: Metodología y aplicación

El mecanismo por el que se diseña una pieza de plástico es un proceso complejo que implica el conocimiento de las características mecánicas, eléctricas y físicas de la pieza y también de los procesos de transformación. La principal tarea del diseñador es traducir una serie de requerimientos e ideas previas en las direcciones y formas finales que tendrá la pieza. Para conseguirlo de forma optimizada el diseñador debe hacer uso de su experiencia, conocimientos y de una metodología de diseño adecuada. El objeto de este trabajo es poner de manifiesto los pasos a seguir cuando se aborda un diseño y la aplicación a una pieza de plástico fabricada en material reciclad

PLA and P3HB-3HH-based bio-composites made with cotton fabric

Composite panels were produced using film stacking procedure: a dry layer of fabric and two layers of matrix were piled up alternately and compression molded. The matrices used were PLA or PHB and the fabric was a cotton twill fabric without any chemical pre-treatment or treated with an epoxy functional oligomeric acrylic polymer (J). The PLA-based composite had clearly better mechanical properties than the pure matrix, namely +75%, +39% and +45% for elastic modulus, elongation at break and tensile strength, respectively. The PHB gave dramatic results reaching increases of +103%, +83%,+104% of the same three parameters. The J additive employed in the PLA gave no substantial changes but reduced the elongation at break. The same J additive in the PHB-based composite apparently increased the adeshion between matrix and fabric, showing an modulus and strenght increase with a reduction of elongation at break

Essential Work of Fracture of Bio-Polyamides and Clay Composites

Fully (PA10.10) and partially (PA6.10) bio-based polyamides were extruded in a film casting machine. A modified montmorillonite (Cloisite 30B) was also added to the bio-PAs in a preliminary extrusion step to increase the thermal, mechanical and barrier properties. Despite the materials are interesting for a possible industrial development in the packaging field, data concerning mechanical performances are rare in the literature. Thus, tensile tests were carried out on extruded films. The modified clay increased the rigidity, yield strength and decreased the deformation at break. To better understand this behavior, the Essential Work of Fracture (EWF) protocol was applied to the films. The ligament length was in the range from 5 to 22 mm. The specific work of fracture (wf) was obtained as well as the essential (we) and non-essential (wp) work of fracture were extrapolated. Clay did not significantly affect the work required for the onset of crack propagation (we) in PA6.10 while it was decreased in PA10.10. The plastic item (β·wp) of both PAs was increased with clay. The clay particles acted as stress concentration points, which promoted cavitations and thus induced relatively large local deformation. Consequently, the mechanical work content necessary to generate the plastic flow was increased, leading to a higher wp value

Design of a recycled plastic part: Methdology and application

The process of design is a complex procedure wich often involves the knowledge of different concepts such as mechanical, electrical and also transformation rules and processes, that are necessary to take into account in order to fullfill the part requirements. The designer task is to transform previous requirements and ideas into dimensions and final real shapes. However, many times, requirements are totally or partially unknown and suppositions have to be done, to accomplish that, the designer has only its skills and the use of a design methodology. The aim of this paper is to describe a design methodology and its application to a component made with recycled plastic

Influence of topographical features on the surface appearance measurement of injection moulded components

Adding textures to surfaces is known to improve the external appearance of injection moulded components. However, when high surface quality is required, normally a paint coating is applied on top of the moulded textured surface. In this work, an alternative to painting for obtaining high quality surfaces is proposed, following an environmental-friendly process and having low production cost. Three different surface textures obtained by injection moulding have been characterized and compared with a painted one. Alternative topographical parameters such as the absolute functional height (AFH), the functional height distribution (FHD), texture slope (TS) or texture aperture angle (TAA) besides to the traditional roughness parameters such as the arithmetical mean height (Sa) and the root mean square height (Sq) have been utilized to characterize the random surface textures. The relationships between these parameters and the surface quality appearance represented by gloss and reflectivity contrast have been established using a new total appearance measurement (TAM) apparatus. It was found that by applying secondary operation on the textured mould cavity, such as adding micro roughness features or coatings, equal apparent quality to the ones obtained by painting can be reached

Effect of the viscosity ratio on the PLA/PA10.10 bioblends morphology and mechanical properties

PLA bio-blends with a predominantly biosourced PA10.10 in the composition range 10–50 wt% were prepared by melt blending in order to overcome the advanced brittleness of PLA. Due to the inherent immiscibility of the blends, 30 wt% of PA was needed to achieve a brittle-to-ductile transition and a co-continuous morphology was predicted at 58 wt% of PA. The initial enhancement of the PLA rheological behaviour through the environmentally friendly reactive extrusion process yielded a finer and more homogeneous microstructure and hence enhanced the mechanical properties of the bioblends at much lower PA contents. The brittle-to-ductile transition could be achieved with only 10 wt% and co-continuity was observed already at 44 wt% of PA. Results indicate the significant potential of modifying PLA flow behaviour as a promising green manufacturing method toward expanding PLA-based bio-blends applications

Ductile-brittle transition behaviour of PLA/o-MMT films during the physical aging process

The ductile-brittle transition behaviour of organo modified montmorillonite-based Poly(lactic acid) films (PLA/o-MMT) was analysed using the Essential Work of Fracture (EWF) methodology, Small Punch Tests (SPT) and Enthalpy relaxation analysis. While the EWF methodology could only be applied successfully to de-aged samples, small punch test (SPT) was revealed as more effective for a mechanical characterization during the transient behaviour from ductile to brittle. According to differential scanning calorimetry (DSC) results, physical aging at 30°C of PLA/o-MMT samples exhibited slower enthalpy relaxation kinetics as compared to the pristine polymer. Although all samples exhibited an equivalent thermodynamic state after being stored one week at 30°C, significant differences were observed in the mechanical performances. These changes could be attributed to the toughening mechanisms promoted by o-MMT