Obtención de curvas esfuerzo-deformación verdaderas del PP y copolímeros en bloque a velocidad de deformación constante aplicando correlación de imágenes digitales

El presente trabajo tiene por objetivo investigar y comparar el comportamiento mecánico verdadero a tracción, macroscópico y en tiempo real, de un polipropileno homopolímero (PP060) y cuatro copolímeros bifásicos propileno-etileno (PB110, PB150, PB170 y PB171), con diferencias en el porcentaje de etileno y el peso molecular, bajo dos controles distintos de solicitación: velocidad de mordaza constante (VMC) y velocidad de deformación constante (VDC). En el primer caso se utilizó una única velocidad de desplazamiento fijada en 30 [mm/min] hasta la ruptura del la probeta, mientras que en el segundo caso, se programó un perfil de velocidades a fin de mantener constante la tasa de variación de la deformación con el tiempo. El estudio se realizó a través del análisis óptico de deformación basado en la técnica de correlación de imágenes digitales (DIC, por sus siglas en ingles) en tres dimensiones. Dicha técnica consta de dos stereo cámaras tipo 2M de alta resolución acopladas una máquina servo-hidráulica de ensayos universales que permiten la adquisición de datos desde pequeñas hasta grandes deformaciones. Los ensayos se llevaron a cabo en probetas con geometría halterio tipo 1A modificada, de sección transversal prismática, bajo las especificaciones que establece la norma ISO 527-2:2012 fabricadas mediante el proceso de inyección y un posterior procedimiento de recocido. Como resultado de este procedimiento fue posible evaluar, cuantitativamente, la influencia que tiene control de solicitación en la respuesta mecánica de los distintos materiales, con base las características químicas y morfológicas que cada uno presenta, a través de las curvas esfuerzo verdadero-deformación verdadera (σ true vs ε) y deformación volumétrica (εv). Ligeras diferencias en la zona elástica de las curvas esfuerzo verdadero-deformación verdadera fueron observadas en todos los materiales. Fenómenos como ablandamiento por deformación y endurecimiento por deformación fueron registrados una vez superado el esfuerzo de cedencia. El primer fenómeno se dio en el PP060 sin el posterior endurecimiento, por otro lado, la presencia de una segunda fase en el material motivó el desarrollo de endurecimiento sin ablandamiento en el PB110. Materiales como el PB150 y PB170 mostraron evoluciones similares en las curvas σ true vs ε durante la propagación del cuello, no así en el endurecimiento por deformación. Respecto a los daños volumétricos, en los copolímeros bifásicos PB110 y PB171 se presentó una fluctuación en el desarrollo de la deformación volumétrica a bajas deformaciones como consecuencia de dos características morfológicas: cristalinidad y polidispersidad. En el régimen plástico, mecanismos de daño tuvieron lugar a una deformación correspondiente al instante del inicio de endurecimiento por deformación

Extruded-calendered sheets of fully recycled pp/opaque pet blends: Mechanical and fracture behaviour

This work presents the experimental results of the mechanical and fracture behaviour of three polymeric blends prepared from two recycled plastics, namely polypropylene and opaque poly (ethylene terephthalate), where the second one acted as a reinforcement phase. The raw materials were two commercial degrees of recycled post-consumer waste, i.e., rPP and rPET-O. Sheets were manufactured by a semi-industrial extrusion-calendering process. The mechanical and fracture behaviours of manufactured sheets were analyzed via tensile tests and the essential work of fracture approach. SEM micrographics of cryofractured sheets revelated the development of in situ rPP/rPET-O microfibrillar composites when 30 wt.% of rPET-O was added. It was observed that the yield stress was not affected with the addition of rPET-O. However, the microfibrillar structure increased the Young’s modulus by more than a third compared with rPP, fulfilling the longitudinal value predicted by the additive rule of mixtures. Regarding the EWF analysis, the resistance to crack initiation was highly influenced by the resistance to its propagation owing to morphology-related instabilities during tearing. To analyze the initiation stage, a partition energy method was successfully applied by splitting the total work of fracture into two specific energetic contributions, namely initiation and propagation. The results revelated that the specific essential initiation-related work of fracture was mainly affected by rPET-O phase. Remarkably, its value was significantly improved by a factor of three with the microfibrillar structure of rPET-O phase. The results allowed the exploration of the potential ability of manufacturing in situ MFCs without a “precursor” morphology, providing an economical way to promote the recycling rate of PET-O, as this material is being discarded from current recycling processes.Peer ReviewedPostprint (published version

The effect of titanium dioxide surface modification on the dispersion, morphology, and mechanical properties of recycled PP/PET/TiO2 PBNANOs

Titanium dioxide (TiO2) nanoparticles have recently appeared in PET waste because of the introduction of opaque PET bottles. We prepare polymer blend nanocomposites (PBNANOs) by adding hydrophilic (hphi), hydrophobic (hpho), and hydrophobically modified (hphoM) titanium dioxide (TiO2) nanoparticles to 80rPP/20rPET recycled blends. Contact angle measurements show that the degree of hydrophilicity of TiO2 decreases in the order hphi > hpho > hphoM. A reduction of rPET droplet size occurs with the addition of TiO2 nanoparticles. The hydrophilic/hydrophobic balance controls the nanoparticles location. Transmission electron microscopy (TEM_ shows that hphi TiO2 preferentially locates inside the PET droplets and hpho at both the interface and PP matrix. HphoM also locates within the PP matrix and at the interface, but large loadings (12%) can completely cover the surfaces of the droplets forming a physical barrier that avoids coalescence, leading to the formation of smaller droplets. A good correlation is found between the crystallization rate of PET (determined by DSC) and nanoparticles location, where hphi TiO2 induces the highest PET crystallization rate. PET lamellar morphology (revealed by TEM) is also dependent on particle location. The mechanical behavior improves in the elastic regime with TiO2 addition, but the plastic deformation of the material is limited and strongly depends on the type of TiO2 employed

REPORTAJE CARMELO ARTILES BOLAÑOS. PRESIDENTE DEL CABILDO DE GC [Material gráfico]

Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte, 201

Diseño y manufactura de un carro de arrastre para una máquina de extrusión

Diseño y manufactura de un carro de arrastre para una máquina de extrusió

Impact of titanium dioxide in the mechanical recycling of post-consumer polyethylene terephthalate bottle waste: tensile and fracture behavior

This work provides an experimental analysis regarding the fracture behavior of recycled opaque PET (rPET-O) containing titanium dioxide (TiO2) under plane stress conditions. For this purpose, a commercially post-consumer transparent colored/opaque PET flakes mix was processed using a semi-industrial extrusion calendering process. The manufactured rPET-O sheets had a TiO2 content of 1.45 wt.%. The mechanical and fracture properties of unaged and physically aged (1 year) samples were determined through uniaxial tensile experiments and the Essential Work of Fracture (EWF) methodology, respectively, and were compared to those of recycled transparent PET (rPET-T). Under tensile loading, independently of the aging time, rPET-O samples exhibited similar mechanical behavior as rPET-T up to the yield point. The main differences remained in the post-yielding region. The presence of TiO2 particles allowed reducing the strain energy density up to neck formation in aged samples. Regarding the EWF analysis, it is argued that the energy consumed up to the onset of crack propagation (we) for rPET-T was mainly dependent of the molecular mobility. That is, the we value decreased by 26% when rPET-T was physically aged. Interestingly, we values remained independent of the aging time for rPET-O. In fact, it was highlighted that before crack propagation, the EWF response was principally governed by matrix cavitation ahead of the crack tip, which allowed a significant release of the triaxial stress state independently of the molecular mobility. This property enabled rPET-O to exhibit a resistance to crack initiation 17% higher as compared to rPET-T when the material was physically aged. Finally, independently of the aging time, rPET-O exhibited a resistance to crack growth approximately 21% larger than rPET-T due to matrix fibrillation in large scale deformation.Peer ReviewedPostprint (published version

The effect of titanium dioxide surface modification on the dispersion, morphology, and mechanical properties of recycled PP/PET/TiO2 PBNANOs

Titanium dioxide (TiO2) nanoparticles have recently appeared in PET waste because of the introduction of opaque PET bottles. We prepare polymer blend nanocomposites (PBNANOs) by adding hydrophilic (hphi), hydrophobic (hpho), and hydrophobically modified (hphoM) titanium dioxide (TiO2) nanoparticles to 80rPP/20rPET recycled blends. Contact angle measurements show that the degree of hydrophilicity of TiO2 decreases in the order hphi > hpho > hphoM. A reduction of rPET droplet size occurs with the addition of TiO2 nanoparticles. The hydrophilic/hydrophobic balance controls the nanoparticles location. Transmission electron microscopy (TEM_ shows that hphi TiO2 preferentially locates inside the PET droplets and hpho at both the interface and PP matrix. HphoM also locates within the PP matrix and at the interface, but large loadings (12%) can completely cover the surfaces of the droplets forming a physical barrier that avoids coalescence, leading to the formation of smaller droplets. A good correlation is found between the crystallization rate of PET (determined by DSC) and nanoparticles location, where hphi TiO2 induces the highest PET crystallization rate. PET lamellar morphology (revealed by TEM) is also dependent on particle location. The mechanical behavior improves in the elastic regime with TiO2 addition, but the plastic deformation of the material is limited and strongly depends on the type of TiO2 employed.Peer Reviewe

PLA/BIOPA bioblends for FDM: Mechanica and fracture behavior

The fracture behaviour of PLA/PA bioblends has been investigated in order to extend its processing through fused deposition modeling printing by pellets supply (FDM-p). The viability of the processing technique in creating in situ microfibrillated composites (MFCs) through the microfibrillation of the PA dispersed phase has been evaluated as a way to strengthen and toughen PLA. The mechanical behaviour was assessed through uniaxial tensile tests performed at room temperature (22oC) using type 1BA dumbbell tensile test specimens (ISO527-2) featuring an unidirectional infill pattern fully oriented in the longitudinal direction of the samples. The fracture behaviour was assessed through the determination of the CTOD value just before the crack propagation onset in single-edge-notched tension (SENT) test geometry featuring a multi-axial multilayer infill pattern. For all the samples, a nominal filling density of 100 % was predefined. Morphological observations revealed that the 3D printing conditions used in this study allowed the manufacturing of in- situ MFCs with an average diameter of the PA microfibrils as low as 320 nm. The developed morphology led to a significant increase in the structural integrity of the parts manufactured through FDM-p, as clearly evidenced by the 206% increase in the CTOD values as compared to samples obtained through conventional compression-moulding using the same raw pellets.Postprint (published version