Infiltración de suelos yesosos tras quemas controladas en laboratorio

El fuego es un factor natural de la evolución paisajística de los ecosistemas Mediterráneos. Debido a los cambios sociales y económicos, los incendios forestales han causado cambios hidrológicos y geomorfológicos aún más pronunciados, provocando una mayor erosión del suelo. Este proceso se agudiza en sectores con suelos poco desarrollados y sobre yesos, con una vegetación fundamentalmente arbustiva y en entornos semiáridos. Este experimento pretende reproducir la perturbación hidrológica que supone el efecto de un fuego a lo largo de una ladera, mediante la quema de bloques inalterados. Para cuantificar las modificaciones experimentadas por estos suelos yesosos, se emplea el Infiltrómetro de mini disco (MDI) de Decagon, para medir la conductividad hidráulica del suelo y la hidrofobicidad o repelencia al agua del suelo (SWR), obteniéndose mayores tasas de conductividad hidráulica y de hidrofobicidad en los bloques que han sido sometidos a la quema. Fire is a natural factor of landscape evolution of Mediterranean ecosystems. Due to social and economic changes, forest fires have caused even more pronounced hydrological and geomorphological changes, causing increased soil erosion. This process is exacerbated in areas with underdeveloped soils and over gypsum soils, mainly with shrub and semiarid environments. This experiment aims to reproduce the hydrological disturbance involving the effect of a fire along a hillside, by burning unchanged blocks. To quantify the changes experienced by these gypseous soils, employ the Mini Disk Infiltrometer (MDI) of Decagon, to measure the hydraulic conductivity of the soil and hydrophobicity or soil water repellency (SWR), obtaining higher hydraulic conductivity and hydrophobicity in the blocks that have been subjected to burning

Creative Project-based learning to boost technology innovation

This paper shows the results of the application of a project-based learning methodology that blended flipped classroom and face-to-face sessions, along with creativity and lateral thinking techniques, to integrate the expected concepts and procedures of technology innovation and boost entrepreneurship among students of Master?s degree in chemical engineering. The constructive alignment between the expected learning outcomes and skills with the proposed activities and assessment methods was decisive in the design of the methodology, which tractor activity was the creation of an innovation project. The use of techniques of creativity promoted lateral thinking and originality in the definition of projects. Active methodologies provoked team engagement and collaborative learning, enhanced participation and stimulated intrinsic motivation. The grades obtained by all groups in their projects, given by external evaluators, were relevant, thus pointing out the quality and impact of their proposals. There was a general satisfaction on students, with special emphasis of the transcendence at a professional level, thus showing the potential of this methodology to boost entrepreneurship in technology innovation

Long-term properties and end-of-life of polymers from renewable resources

The long-term properties and end-of-life of polymers are not antagonist issues. They actually are inherently linked by the duality between durability and degradation. The control of the service-todisposal pathway at useful performance, along with low-impact disposal represents an added-value. Therefore, the routes of design, production, and discarding of bio-based polymers must be carefully strategized. In this sense, the combination of proper valorisation techniques, i.e. material, energetic and/ or biological at the most appropriate stage should be targeted. Thus, the consideration of the end-of-life of a material for a specific application, instead of the end-of-life of a material should be the fundamental focus. This review covers the key aspects of lab-scale techniques to infer the potential of performance and valorisation of polymers from renewable resources as a key gear for sustainability

Suitability of Blends from Virgin and Reprocessed Polylactide: Performance and Energy Valorization Kinetics

A blending strategy of virgin and reprocessed polylactide may be postulated as an alternative to reduce the material cost at industrial level, and as a valorization route to plastic waste management of production scraps. The performance of blends prepared from virgin polylactide and polylactide mechanically reprocessed up to two cycles (PLA-V/R) was assessed in terms of thermo-oxidative stability, morphology, viscoelasticity and thermal kinetics for energetic valorization. PLA-V/R blends showed appropriate thermo-oxidative stability. The amorphous nature of polylactide was preserved after blending. The viscoelastic properties showed an increment of the mechanical blend effectiveness, which suggested the feasibility of using PLA-V/R blends under similar mechanical conditions to those of virgin PLA goods. Finally, it was shown that the energetic valorization of PLA-V/R blends would result in a more feasible process, due to the lower required activation energy, thus highlighting the advantages of the energetic demand for the process. In conclusion, PLA-V/R blends showed similar processability, service performance and valorization routes as virgin PLA and therefore could be relevant in the sustainable circular industry of bioplastics

Thermal analysis as a quality tool for assessing the influence of thermo-mechanical degradation on recycled poly(ethylene terephthalate)

Mechanical recycling of poly(ethylene terephthalate) (PET) was simulated by multiple processing to assess the effects of thermo-mechanical degradation, and characterized using rheological and thermal analysis techniques. Thermo-mechanical degradation under repeated extrusion induces chain scission reactions in PET, which result in a dramatic loss in the deformation capabilities and an increase in the fluidity of the polymer under reprocessing, reducing its recycling possibilities after four extrusion cycles. Multiple reprocessing severely affects the storage modulus and the microstructure of recycled PET, both in the amorphous and crystalline regions. Multimodal melting behavior is observed for reprocessed PET, indicating heterogeneous and segregated crystalline regions. A deconvolution procedure has been applied to individually characterize each crystalline population in terms of lamellar thickness distribution and partial crystallinity. Thermal analysis techniques such as differential scanning calorimetry (DSC) and dynamic-mechanical analysis (DMA) have proved to be suitable techniques for the quality assessment of recycled PET, giving unequivocal information about its degree of degradation compared to the common technological measurements of melt-mass flow rate (MFR) or oxidative stability (TOx)

Material valorisation of amorphous polylactide. Influence of thermo-mechanical degradation on the morphology, segmental dynamics, thermal and mechanical performance

This paper reports the effects of multiple mechanical recycling on the structure and properties of amorphous polylactide (PLA). The influence of the thermo-mechanical degradation induced by means of five successive injection cycles was initially addressed in terms of macroscopic mechanical properties and surface modification. A deeper inspection on the structure and morphology of PLA was associated to the thermal properties and viscoelastic behaviour. Although FT-IR analysis did not show significant changes in functional groups, a remarkable reduction in molar mass was found by viscometry. PLA remained amorphous throughout the reprocessing cycles, but the occurrence of a cold-crystallization during DSC and DMTA measurements, which enthalpy increased with each reprocessing step, suggested chain scission due to thermo-mechanical degradation. The effect of chain shortening on the glass-rubber relaxation studied by DMTA showed an increase in free volume affecting the segmental dynamics of PLA, particularly after the application of the second reprocessing step, in connection to the overall loss of performance showed by the remaining properties

Thermal analysis applied to the characterization of degradation in soil of polylactide: I. Calorimetric and viscoelastic analyses

An accelerated soil burial test has been performed on a commercial polylactide (PLA) for simulating non-controlled disposal. Degradation in soil promotes physical and chemical changes in polylactide properties, which can be characterized by Thermal Analysis techniques. Physical changes occurred in polylactide due to the degradation in soil were evaluated by correlating their calorimetric and viscoelastic properties. It is highly remarkable that each calorimetric scan offers specific and enlightening information. Degradation in soil affects the polylactide chains reorganization. A multimodal melting behavior is observed for buried PLA, degradation in soil also promotes the enlarging the lamellar thickness distribution of the population with bigger average size. Morphological changes due to degradation in soil lead to an increase in the free volume of the polylactide chains in the amorphous phase that highly affected the bulk properties. Thermal Analysis techniques provide reliable indicators of the degradation stage of polylactide induced by degradation in soil, as corroborated by molecular weight analysis

Performance of polyester-based electrospun scaffolds under in vitro hydrolytic conditions: From short-term to long-term applications

The evaluation of the performance of polyesters under in vitro physiologic conditions is essential to design scaffolds with an adequate lifespan for a given application. In this line, the degradation-durability patterns of poly(lactide-co-glycolide) (PLGA), polydioxanone (PDO), polycaprolactone (PCL) and polyhydroxybutyrate (PHB) scaffolds were monitored and compared giving, as a result, a basis for the specific design of scaffolds from short-term to long-term applications. For this purpose, they were immersed in ultra-pure water and phosphate buffer solution (PBS) at 37 °C. The scaffolds for short-time applications were PLGA and PDO, in which the molar mass diminished down to 20% in a 20-30 days lifespan. While PDO developed crystallinity that prevented the geometry of the fibres, those of PLGA coalesced and collapsed. The scaffolds for long-term applications were PCL and PHB, in which the molar mass followed a progressive decrease, reaching values of 10% for PCL and almost 50% for PHB after 650 days of immersion. This resistant pattern was mainly ascribed to the stability of the crystalline domains of the fibres, in which the diameters remained almost unaffected. From the perspective of an adequate balance between the durability and degradation, this study may serve technologists as a reference point to design polyester-based scaffolds for biomedical applications

Thermal analysis applied to the characterization of degradation in soil of polylactide: II. On the thermal stability and thermal decomposition kinetics

The disposal stage of polylactide (PLA) was assessed by burying it in active soil following an international standard. Degradation in soil promotes physical and chemical changes in the polylactide properties. The characterization of the extent of degradation underwent by PLA was carried out by using Thermal Analysis techniques. In this paper, studies on the thermal stability and the thermal decomposition kinetics were performed in order to assess the degradation process of a commercial PLA submitted to an accelerated soil burial test by means of multi-linear-non-isothermal thermogravimetric analyses. Results have been correlated to changes in molecular weight, showing the same evolution as that described by the parameters of thermal stability temperatures and apparent activation energies. The decomposition reactions can be described by two competitive different mechanisms: Nucleation model (A2) and Reaction Contracting Volume model (R3). The changes in the kinetic parameters and kinetic models are in agreement with the calorimetric and dynamic-mechanical-thermal results, presented in the Part I of the study

Thermal and thermo-oxidative stability of reprocessed poly(ethylene terephthalate)

An exhaustive assessment of the behaviour of virgin and mechanically reprocessed poly(ethylene terephthalate) (PET) facing thermal and thermo-oxidative decomposition processes is presented in this work, as an approach for the energetic valorisation of post-consumer PET goods. Multi-rate linear-non-isothermal thermogravimetric (TGA) experiments under inert (Ar) and reactive (O2) conditions were performed to virgin PET and its recyclates in order to simulate the thermal behaviour of the materials facing pyrolysis and combustion processes. The release of gases was monitored by evolved gas analysis of the fumes of the TGA experiment, by in-line Fourier-transform infrared (IR) analysis, with the aid of 2D-correlation IR characterisation. A kinetic analysis methodology, consisting in the combination of six different methods (namely Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, Vyazovkin, Master-Curves and Perez-Maqueda criterion along with Coats-Redfern equation) was applied. Its validity for being used for both constant and variable kinetic parameters was discussed. The kinetic model that described both thermal and thermo-oxidative decompositions of PET and its recyclates was of the type An: nucleation and growth of gas bubbles in the melt. Novel parameters and functions were proposed to characterise the thermal stability along the reprocessing cycles, as well as the variation of the activation energy and the pre-exponential factor during thermal and thermo-oxidative decompositions. The reliability of a simplified kinetic triplet with constant activation parameters was suitable only under thermal decomposition. The usability of PET after reprocessing showed a threshold in the thermal performance from the second recyclate on. During thermal and thermo-oxidative processes, reprocessed PET behaved similarly to virgin PET, and thus current energetic valorisation technologies could be assimilable for all materials