Examinando por Autor "Paredes, Beatriz"

Mostrando 1 - 8 de 8

Assessing the circularity of post-consumer HDPE milk bottles through open-loop recycling and their environmental impact
(Elsevier, 2024-06) Blanco, Aymara; Juan, Rafael; Istrate, Robert; Paredes, Beatriz; Martín-Gamboa, Mario; Domínguez, Carlos; Dufour, Javier; García-Muñoz, Rafael A.
Plastics are key in the packaging sector, but their widespread use contributes significantly to environmental challenges, such as the short life and high daily production of HDPE milk bottles. This study therefore aims to find a solution to this plastic waste, focusing on mechanical recycling. A comprehensive characterization of this post-consumer recycled HDPE reveals significant PP contamination, which poses a significant barrier due to polyolefin incompatibility, a common challenge in mixed plastics recycling. To mitigate this, blending with virgin HDPE and the use of various compatibilizers were investigated to improve the recyclability of the material. Several extrusion cycles were performed to analyse the thermo-mechanical degradation and to measure the performance and stability of the blends. The environmental impact of incorporating recycled HDPE into new bottles was also evaluated. Comparative evaluations with virgin bottles show that incorporating 25% or 50% recycled HDPE in the bottle yields carbon footprint reductions of 3% and 14%, respectively. These benefits could amplify with a wind-powered supply chain and a 100% recycled content. The findings lay the foundation for future plastic recycling scenarios, including dedicated sorting for this waste stream, providing a pathway to address the environmental impact of HDPE milk bottle disposal through recycling practices
Challenges and opportunities for recycled polyethylene fishing nets: towards a circular economy
(MDPI, 2021-09) Juan, Rafael; Domínguez, Carlos; Robledo, Nuria; Paredes, Beatriz; Galera, Sara; García-Muñoz, Rafael A.
Plastic waste generation has become an important problem that critically affects marine and oceans environments. Fishing nets gear usually have a relatively short lifespan, and are abandoned, discarded and lost, what makes them one of the largest generators of ocean plastic waste. Recycled polyolefin resins from fishing nets (rFN), especially from polyethylene (PE), have poor properties due to the presence of contaminants and/or excessive degradation after its lifetime. These reasons limit the use of these recycled resins. This work aims to study the incorporation of recycled fishing nets PE-made to different grades of virgin PE, in order to evaluate the potential use of these rFN in the development of new products. The recovered fishing nets have been fully characterized to evaluate its properties after the collection and recycling process. Then, different PE virgin resins have been mechanically blended with the recovered fishing nets at different recycling contents to study its feasibility for fishing nets or packaging applications. Critical mechanical properties for these applications, as the elongation at break, impact strength or environmental stress cracking resistance have been deeply evaluated. Results show important limitations for the manufacture of fibers from recycled PE fishing nets due to the presence of inorganic particles from the marine environment, which restricts the use of rFN for its original application. However, it is proved that a proper selection of PE raw resins, to be used in the blending process, allows other possible applications, such as non-food contact bottles, which open up new ways for using the fishing nets recyclates, in line with the objectives pursued by the Circular Economy of Plastics.
Chromium oxide/metallocene binary catalysts for bimodal polyethylene: hydrogen effects.
(Elsevier, 2012-12) Paredes, Beatriz; Grieken, Rafael van; Carrero, Alicia; Moreno, Jovita; Moral, Alberto
Bimodal resins came up to meet application requirements: low molecular weight for good processability and high molecular weight for mechanical properties. For obtaining this bimodality there are several strategies: physical melt mixing of the two components produced separately, a single catalyst in two different serial reactors and a single reactor technology employing a tailor made catalyst and/or switching conditions. This last method has many advantages such as lower investment costs, less process complexity and intimate mixing of high and low molecular weight components (improved product quality). By means of this single reactor technology, bimodal polyethylene was synthesized using a mesostructured catalyst based on Al-SBA-15 where two active centers, chromium and metallocene, were incorporated. Ethylene polymerizations were carried out over binary catalysts (hybrid and mixed Crmetallocene) and the polyethylenes obtained were compared with those obtained with individual catalysts in order to determine the contribution of each active centre. As well, the effect on polymer properties of the partial pressure of hydrogen in the reactor was evaluated. Results indicate that the hybrid catalyst (metallocene supported over Cr-Al- SBA-15) and physical mixture (Cr-Al-SBA-15 mixed with met-Al-SBA-15) lead to bimodal polyethylenes which combine high molecular weight, crystallinity and melting point with good processability (high melt index).
Enhancing the recyclability of ELV plastic bumpers: Characterization of molecular, morphological, rheological, mechanical properties and ageing degradation
(Elsevier, 2024-12) Juan, Rafael; Expósito, M. Teresa; Paredes, Beatriz; Lechuga, Daniel; Martínez, Cristina; Cardil, Andres; Aguilera-Villegas, Lola; Ramos, Javier; Domínguez, Carlos; Vega, Juan F.; Grieken, Rafael Van; García-Muñoz, Rafael A.
While the automotive industry has traditionally prioritized metal recycling, the increasing use of plastics in vehicles underlines the need for sustainable management of these materials. Recycling rates of plastics from end-of-life vehicles (ELVs) in Europe are low, but recent EU legislation requires 25 % of the plastics in new vehicles to be recycled, forcing innovative designs and strategies to enhance the recovery and quality of recycled resins. This study focuses on post-consumer bumpers, a significant recoverable component of ELVs, by assessing their molecular, morphological, rheological, and mechanical properties to investigate their homogeneity and quality from various sources to assess their suitability for recycling. Since the aging of these materials, caused by thermo-oxidative and thermo-mechanical degradation processes, can compromise the quality of recycled bumpers, we propose a blend of recycled PP from different bumper cars with virgin resin, representing a realistic scenario where the post-consumer ELV bumpers are collected. Interestingly, this blend, which can replace up to 50 % of the virgin resin without additional compatibilizers or additives, mitigates the degradation effects. Furthermore, the study evaluates the degradation resistance of these blends through multiple extrusion cycles and accelerated weathering tests in a temperature-controlled UV chamber to ascertain the number of cycles the material can tolerate without significant quality degradation, and to determine its suitability for long-term applications. Our results not only support the feasibility of using recycled PP for automotive components but also contribute to meeting the EU's recycling targets. This research highlights the potential for significant advances in the circularity of automotive plastics, providing a sustainable pathway for integrating recycled materials into new vehicle production
Evaluation of bimodal polyethylene from chromium oxide/metallocene hybrid catalysts for high resistance applications
(Wiley, 2020-08) Paredes, Beatriz; Moreno, Jovita; Carrero, Alicia; van Grieken, Rafael
An interesting alternative to the industrial two-stage cascade process for the production of bimodal polyethylene, used for high resistance applications such as pressure pipes, has been developed. The key point is a binary catalytic system with chromium and metallocene sites incorporated together on AlSBA-15 mesostructured material. This hybrid catalyst is able to produce bimodal polyethylene in a single reactor. In the present work, it is shown that, in the presence of hydrogen and comonomer (1-butene or 1-hexene) in the reaction medium, the obtained polyethylenes exhibit appropriate mechanical properties for pipes manufacture, such as resistance to rapid crack propagation (RCP) and low crack growth (SCG), reaching standards for PE100 and even for PE100RC grades.
Incorporation of recycled high-density polyethylene to polyethylene pipe grade resins to increase close-loop recycling and Underpin the circular economy
(Elsevier, 2020-12) Juan, Rafael; Domínguez, Carlos; Robledo, Nuria; Paredes, Beatriz; García-Muñoz, Rafael A.
High-density polyethylene (HDPE) is one of the most used and demanded plastic, not only for packaging, but also for construction and within this application especially for non-pressure and pressure pipes, which makes this material the most abundant in the municipal waste stream. On the basis of the Circular Economy and the sustainable life that promotes, it is important to explore new applications for recycled HDPE (rHDPE) to increase the polymer recycled uptake. However, recycled HDPE is not currently being used in pressure pipes, mainly due to the high structural and loading requirements that must be met. The present study evaluates the potential use of post-consumer rHDPE from different origins in the manufacture of polyethylene pressure pipes. Different rHDPE sources are blended in different ratios with raw HDPE with PE100 grade quality. Blends are fully characterized to determine their feasibility to be used for pipe applications. Properties such as tensile strength at yield, elongation at break and flexural modulus for all blends yield values above the minimum required for PE100 grades. Furthermore, two important mechanical properties of polyethylene pipes, Slow Crack Growth (SCG) and Rapid Crack Propagation (RCP) resistances, are deeply evaluated. Remarkably, a dual correlation of SCG and RCP with the content of recycled PE in blends was established, allowing to develop predictive capabilities that guarantee the requirements and specifications for pressure pipe applications. Finally, through the evaluation of different waste streams, it can be concluded that handling, sorting, separation and selection of polyethylene’s waste is critical to achieve the required pipe specifications, and to increase the percentage of post-consumer rHDPE into the final product. This investigation is in line with the sustainability objective and the commitment to boost the circular economy by replacing part of the conventional HDPE raw material with recycled HDPE to increase close-loop recycling on PE for pipe application, and the basis for the recycling of rHDPE from pipe at its end-life, after 50 years in service.
Quantification of PP contamination in recycled PE by TREF analysis for improved the quality and circularity of plastics
(Elsevier, 2021-06) Juan, Rafael; Paredes, Beatriz; García-Muñoz, Rafael A.; Domínguez, Carlos
Polyethylene constitutes more than one-third of the world’s plastic and is one of the main components in municipal waste streams. Unfortunately, varying imounts of polypropylene (PP) are usually found in recycled high-density polyethylene (rHDPE), which erodes their mechanical properties and reduces the quality of these recyclates and their possible reuse in the industry. Differential Scanning Calorimetry (DSC) is the technique commonly used to detect and determine the presence of PP in these blends, but intrinsic limitations of this method lead to inaccurate results. Thus, alternative techniques must be employed to solve these drawbacks and help to estimate more accurately the levels of the PP impurities in rHDPE. In this work, crystallization techniques, such as Temperature Rising Elution Fractionation (TREF) is used to fractionate PE and PP blends into their components to obtain quantitative information. Municipal waste samples of HDPE contaminated with different amounts of PP have been characterized by DSC and TREF. Comparative results of both techniques show an underestimation of PP values when DSC is used as analytical technique. Results prove that TREF analysis irrespective of the crystallization rate used is valid for the identification and quantification of PP impurities in rHDPE samples, even at low PP percentages in the blend lower than 2 wt. %, which could help to control the quality of rHDPE and achieve the priority of reusing and recycling adopted by the European Union for a Circular Economy of Plastics.
Strain hardening test on the limits of the Slow Crack Growth evaluation in high resistance polyethylene resins: Effect of comonomer type
(Elsevier, 2020-01) Domínguez, Carlos; Robledo, Nuria; Paredes, Beatriz; García-Muñoz, Rafael A.
Long term performance assessment of polyethylene pipes is an issue that has greatly increased in importance in recent years due to the incorporation in the market of high resistance to crack polyethylene grades (PE100RC), where established Slow Crack Growth (SCG) evaluation using traditional tests such as Full Notch Creep Test (FNCT) or Pennsylvania Notch Tensile (PENT) Test is insufficient. The development in recent years of fast evaluation techniques such as Strain Hardening (SH) modulus has opened an important alternative for quick SCG evaluation since it correlates well with other conventional tests such as FNCT and PENT. In this work, a large number of commercial and experimental polyethylene pipe resins with different comonomer types were evaluated in order to define their SH values to rank the resins as PE100 or PE100RC. A relationship is proposed that utilizes SH test results to estimate the SCG resistance of PE pipes. 1-Butene copolymer resins display threshold SH values of 38 and 53 MPa that have been assigned to PE100 and 100RC grades, respectively. Moreover, dependence of the SH values on comonomer type used has been demonstrated. The experimental results show that 1-hexene copolymer resins exhibit higher SH values than 1-butene comonomer based resins.