Search

[EN] This work aims to study the effect of immersion in a ethanolic food simulant in mechanically recycled poly(lactic acid) (PLAR) and its nanocomposites reinforced with halloysite nanotubes (HNT). PLAR was obtained by subjecting PLA to an accelerated ageing process, which includes photochemical, thermal and hydrothermal ageing steps, followed by a final demanding washing step. PLAR was further reinforced with 4 %wt. HNT to improve the properties of the PLAR films. The materials were melt compounded by melt extrusion and processed into films by compression molding. The resulting films were exposed to food simulant D1 (50 %vol. ethanol solution) for 10 days at 40 °C. The intrinsic viscosity, crystallization behavior, thermal stability as well as the mechanical performance were analyzed before and after the contact with the food simulant. The swelling, plasticizing and hydrolyzing effect of the food simulant led to an important decrease of the intrinsic viscosity of all the samples, along with a significant increase of the crystallinity. Thermal stability was negatively affected by the decrease of the molecular weight, while the high crystallinity values resulted in materials with higher Vickers hardness values after the immersion in the food simulant., This work was supported by European Union’s Horizon 2020 research and innovation program [grant agreement No. 860407 BIO-PLASTICS EUROPE], by MINECO-Spain [project CTM2017-88989-P] as well as Universidad Politécnica de Madrid [project UPM RP 160543006].

The oxidation and thermal stability of low-density polyethylene (LDPE) films (stabilized and unstabilized) used as greenhouse covering have been investigated. A mixture of kaolin, UV absorber, hindered amine light stabilizers (HALS) and heavy metals was used to stabilize LDPE films; these films were also compared with unstabilized LDPE films. Both films were exposed to natural weathering in Laghouat, Algeria. The oxidation resistance of unstabilized specimens for different ageing periods was determined by measuring the oxidation induction time (OIT) at 180 °C. It has been found that the highest OIT value was obtained for the unaged film and the values decline with ageing time. On the other hand, the stabilized specimens showed a significant stability under the conditions of OIT determination experiments. Furthermore, the oxidation resistance of these samples was evaluated by measuring the oxidation onset temperature (OOT). The results obtained showed that the OOT of the stabilized films ranges from 219 to 236 °C. Finally, a comparative analysis of the thermal stability results of both films was conducted. The activation energy of the photodegradation process of the both films was calculated by using TGA thermograms following the isoconversional approach. The results revealed that the stability of the stabilized specimens diminishes with ageing time and that the stabilizer additives improve the thermal stability of LDPE films. The influence of the photooxidation on the degree of crystallinity (based on DSC and WAXS techniques) of both films was also reported. Generally, there is a strong correlation between TGA, OIT, OOT, UV and FTIR results.

A genetic search algorithm in conjunction with density functional theory calculations was used to determine the lowest-energy minima of the pure B22 cluster and thereby to evaluate the capacity of its isomers to form endohedrally doped cages with two transition metal atoms M (M = Sc and Ti). An important charge transfer from metal atoms M to the boron cage takes place, stabilizing the endohedral compounds, as predicted with the genetic algorithm implemented. High-level coupled-cluster theory CCSD(T) calculations were carried out to confirm that the structures found are the lowest-energy isomers. For a deeper understanding of the doping effects and related charge transfer, the best structural motif of the B22 isomers was also determined when the bare cages are in anionic states, such as B222- and B224-. It was found that B22 has an appropriate size, geometric shape and electronic state to host the chosen metal atoms and, consequently, to form stable endohedrally doped compounds Ti@B22 (C2v, 4-Ti) and Sc@B22 (C2v, 5-Sc). The chemical bonding was analyzed in order to understand the molecular orbitals that these novel systems form. The cage aromaticity was evaluated by means of the nuclear independent chemical shift (NICS(0)iso) indices, the isochemical shielding surface (ICSSzz), the anisotropy of the current induced density (ACID) maps, and the magnetic ring current Gauge-Including Magnetically Induced Current (GIMIC) method, indicating that aromaticity plays a crucial role in the stabilization of endohedrally doped boron clusters. Finally, the thermodynamic stability of the latter, using parameters derived from density functional theory (DFT), was evaluated. Ab initio molecular dynamics (AIMD) simulations were performed to elucidate the stability, at high temperature, of the most stable endohedrally doped boron clusters 4-Ti and 5-Sc.

The main objective of the present research is to study the effect of the incorporation of low amounts of silk fibroin nanoparticles (SFNs) and yerba mate nanoparticles (YMNs) on the migration phenomenon into ethanolic food simulants as well as on the disintegrability under composting conditions of mechanically recycled polylactic acid (PLA). Recycled PLA was obtained under simulated recycling conditions by melt processing virgin PLA into films and further subjecting them to an accelerated aging process, which involved photochemical, thermal, and hydrothermal aging steps followed by an intense washing step. SFNs were extracted from Bombyx mori cocoons and YMNs from yerba mate waste. Then, recycled PLA was melted, reprocessed, and reinforced with either 1%wt. of SFNs or YMNs, by melt extrusion, and further processed into films by compression molding. The obtained nanocomposites were exposed to ethanolic food simulants (ethanol 10% v/v, simulant A and ethanol 50% v/v, simulant D1) and the structural, thermal, and mechanical properties were studied before and after the exposure to the food simulants. The migration levels in both food simulants were below the overall migration limits required for food contact materials. The materials were disintegrated under simulated composting conditions at the laboratory scale level and it was observed that the nanoparticles delayed the disintegration rate of the recycled PLA matrix, but nanocomposites were fully disintegrated in less than one month.

From an environmental point of view, mechanical recycling is, in general, a good end-of-life option for poly(lactic acid) (PLA), one of the most important biobased polymers. However, the degradation of PLA during the service life and, especially, during the mechanical recycling process, leads to a decrease in the properties of PLA, thus reducing the applications of the recycled plastic. The main aim of this work was to study the addition of small amounts of halloysite nanotubes, during the recycling step, as the basis of a cost-effective method for improving the properties of the recycled PLA. Raw halloysite was modified with an aminosilane, and 2% by weight of both raw and modified halloysite were melt compounded with PLA previously subjected to accelerated ageing. The addition of the nanotubes led to recycled materials with improved properties because halloysite reduces the degradation of PLA by blocking the carboxyl groups, generated during the ageing and washing steps, which catalyze the degradation during the recycling process. This effect was more intense in the silanized nanotubes, because the carboxyl groups were effectively blocked by acid–base interactions with the amino groups of the chemical modification. The properties of the recycled plastic with only 2 wt% of silanized halloysite were very close to those of the virgin plastic., The authors would like to thank the Centro Nacional de Microscopía Electrónica of the Universidad Complutense de Madrid (Spain), for the collaboration in the TEM measurements. This work was supported by MINECO-Spain (Grant Number CTM2017-88989-P) and Universidad Politécnica de Madrid (project UPM RP 160543006).

Vortex state and magnetic response in a disk with an array of weakly-superconducting (or normal regions) created in the sample increasing the temperature T locally by using a continuous wave laser (CWL) that emits a beam with a controlled heat output, beam duration and intensity are studied. The time-dependent Ginzburg–Landau theory is used to describe the interaction of the light with the superconductor, where the defects are include through the spatially-dependent temperature. Vortices penetrating into the weak-superconducting regions which are generated considering that T > Tc (Tc is the critical temperature of the sample) where the CWL is pointing. Qualitative changes are observed in the dynamics of the superconducting condensate in the presence of pinning with different shapes and sizes which are possible to be modified in the same superconducting sample without any structural changes that could include metals, permanent magnets and implantation of heavy ions.

A theoretical study has been performed for deposited AumAgn (m + n = 1–6) clusters. The combined use of the Mexican Enhanced Genetic Algorithm (MEGA) and Density Functional Theory (DFT) calculations allows us to explore the potential energy surface and therefore, find the global minimum configuration for each composition. We have performed calculations of clusters deposited on defects (oxygen vacancies) known as F centers on MgO (100) surfaces. Our results show interesting differences in the geometries of the clusters upon deposition and as a consequence in their electronic properties. The combination of two metals with different electronegativities creates an inhomogeneous charge distribution on their exposed surface producing good conditions for a catalytic process to take place.

A comparative theoretical study has been performed on AumRhn (6 ⩽ m + n ⩽ 10) clusters in the gas phase. The combined use of Density Functional Theory (DFT) calculations and the Mexican Enhanced Genetic Algorithm (MEGA) has been employed to efficiently explore the potential energy surface. Our results show interesting structural changes, such as the 2D-3D transformation on varying the Au:Rh composition. New structures of high stability are obtained when compared with either gold or rhodium pure clusters. The results show that the cluster properties exhibit different kind of dependencies on both the Au:Rh ratio and the cluster size.

In recent years, a great effort has been devoted to the development of new automated identification and sorting methods for post-consumer plastics in the waste streams that reach the recycling processes, as the final properties of the recycled materials largely depend on the purity of the plastic residue. This work explores the use of fluorescence spectroscopy as a complementary technique to address the limitations of the current technologies. Specifically, the use of fluorescent markers for the removing, for technical or safety related issues, of selected high density polyethylene containers from the waste stream has been studied. The results indicate that identification by extrinsic fluorescence can be easily achieved even with small proportion of markers (10−3 wt%) without significant change of the polymer structure. The effect of thermal, hygrothermal and photochemical degradation on the fluorescence emission has been analyzed. Although the signal intensity decreases during the accelerated degradation, distinguishable fluorescent emission was recorded even after sample exposure to aggressive conditions, thus enabling the correct identification of the marked plastics.

The aim of the current study is to explore the structural evolution of neutral and negatively charged gas-phase gold clusters in the size range of 27–30 atoms. We conducted an improved Genetic Algorithm global search combined with the density functional theory study, which we present and explain. New and lower energy structures are reported; these new structures are found to exhibit core–shell structures with the number of core atoms increasing with cluster size. Important discrepancies were observed in the energy ranking and energy differences of the obtained geometries when two different functionals (TPSS and PBE) are used. In general terms Au27– and Au28– clusters form nanotube-like structures, whereas that geometry changes into cage-like structures for Au29– and Au30–. On the contrary, structures related to a fcc fragment were found to own lower energies for the neutral systems for Au27, Au28, and Au29, while for Au30 a nonsymmetric cage with one core atom was the lowest-energy isomer. The obtained st...

Recently, the use of natural materials has grown in the plastics industry. In this study, novel bio-nanocomposites were developed from poly(lactic acid)/poly(ε-caprolactone) (PLA/PCL) blends and silk fibroin nanoparticles (SFNP). SFNP were successfully synthesized from silk fibroin (SF) and analyzed by Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The obtained results revealed that the well-ordered structures in SF were changed to the amorphous structures in SFNP. Then (PLA/PCL) blends containing 10–30% of PCL were prepared and characterized. According to the obtained results, the PLA/PCL (70/30) blend was selected as the optimized sample for further studies. The scanning electron microscopy results illustrated that the addition of 1% of SFNP into this blend improved the compatibility between PLA and PCL and reduced the PCL droplet sizes from 1.170 ± 92 to 794 ± 46 nm. The results from TGA analysis indicated that the presence of SFNP enhanced the thermal stability of materials at high temperatures. The crystallization kinetics results revealed that while SFNP promoted the crystallization of neat PLA, the crystallization rate of PLA/PCL blend was decreased upon the incorporation of nanofiller. Furthermore, the PLA/PCL/SFNP exhibited higher microhardness and barrier properties than the neat blend. The results suggest that the developed bio-nanocomposites are promising materials for demanding applications such as food packaging., The authors thank Perstorp Co. Ltd., Sweden, for supplying the PCL Capa™ 6800, MINECO-Spain (Project CTM2017- 88989-P) and Universidad Politécnica de Madrid (Project UPM RP 160543006). This project has received funding from the European Union’s Horizon 2020 research and innovation program under Grant Agreement No. 860407 BIO-PLASTICS EUROPE

In this work, yerba mate nanoparticles (YMNs) were extracted from Ilex paraguairiencis yerba mate wastes and further used to improve the overall performance of mechanically recycled PLA (PLAR). Recycled PLA was obtained by melt reprocessing PLA subjected to an accelerated ageing process, which involved photochemical, thermal and hydrothermal ageing steps, as well as a final demanding washing step. YMNs (1 and 3 wt. %) were added to the PLAR during the melt reprocessing step and further processed into films. The main goal of the development of PLAR-YMNs bionanocomposites was to increase the barrier properties of recycled PLA, while showing good overall performance for food packaging applications. Thus, optical, structural, thermal, mechanical and barrier properties were evaluated. The incorporation of YMNs led to transparent greenish PLAR-based films with an effective blockage of harmful UV radiation. From the backbone FTIR stretching region (bands at 955 and 920 cm&minus, 1), it seems that YMNs favor the formation of crystalline domains acting as nucleating agents for PLAR. The morphological investigations revealed the good dispersion of YMNs in PLAR when they are used in the lowest amount of 1 wt. %, leading to bionanocomposites with improved mechanical performance. Although the addition of high hydrophilic YMNs increased the water vapor transmission, the addition of 1 wt. % of YMNs enhanced the oxygen barrier performance of the produced bionanocomposite films. These results show that the synergistic revalorization of post-consumer PLA and nanoparticles obtained from agri-food waste is a potential way for the production of promising packaging materials that meet with the principles of the circular economy.

The influence of nanoclays on the structural changes of hydrated poly(l-lactic acid) (PLLA) was investigated at two temperatures, above and below its Tg. Samples of a commercial PLLA and nanocomposites with 2 wt% of an organically modified montmorillonite and an unmodified halloysite were kept in a phosphate buffered solution for different times at 37 and 58 °C and then characterized. The crystallinity degrees and the nature of the crystalline structures developed were determined by differential scanning calorimetry, X-Ray Diffraction and Fourier Transform infrared spectroscopy. While in the cold crystallization of PLLA in dry conditions the α form is obtained only above 100 °C, different mixtures of α and α′ forms were obtained in water at 58 °C, depending on the clay used. The hydrolytic degradation of PLLA played a main role in the structural transformations found at long immersion times, since the short chains formed allowed greater crystallinity degrees and leaded to more perfect crystals. PLLA structure is changed by clays because of its ability as nucleating agents but also due to its effect on the hydrolytic degradation. The unmodified tubular halloysite inhibited degradation, so that lower degrees of crystallinity were obtained in the halloysite based nanocomposite. On the other hand, the modified montmorillonite acted as catalyst of degradation, which explained the appearance of crystalline structures in the nanocomposite with montmorillonite after 84 days of immersion at 37 °C.

The growing production of poly(lactic acid) (PLA) has increased the interest for the mechanical recycling of this polymer. The main objective of this work is to study the effect of different mechanical recycling processes on the hydrolytic degradation of PLA. A commercial grade of PLA was subjected to two different recycling processes, one of them comprising an accelerated thermal and photochemical aging and a second melt compounding and compression molding step, and other including a demanding washing step after the accelerated aging process. The accelerated aging and, especially, the washing step had a significant effect on degradation during recycling. Samples of virgin and recycled plastic immersed in a phosphate buffered solution at 37 or 58 °C were removed at selected times and then characterized by gravimetric analysis, IR and UV spectroscopy, thermal analysis, x-ray diffraction and microhardness and viscosity measurements. The water absorption process, at both temperatures, can be modeled using a Fickian model only when the immersion times were short. The different recycling processes caused an increase of the diffusion coefficient of PLA at 37 °C, while at 58 °C the differences were smaller. DSC results pointed out that mechanical recycling promotes a slight crystallization of PLA at 37 °C that explains the increasing of the hardness during the hydrolysis.

Poly(lactic acid) (PLA) is a biobased polymer that represents one of the most interesting alternatives to fossil-fuel based polymers in food packaging applications. Most of the PLA used in food packaging is used only once and then discarded, even though the PLA types used in packaging have good properties and stability. Therefore, it seems reasonable to consider the possibility of recycling the used polymer through a mechanical recycling process. The main aims of this work are to study the effect of the mechanical recycling on the properties of PLA and the usefulness of different upgrading methods to obtain recycled PLA with improved properties. A commercial type of PLA was subjected to accelerated thermal, photochemical and hydrolytic aging and then reprocessed. During reprocessing, aged PLA was blended with virgin PLA and a commercial chain extender was added. Results point out that recycling causes the degradation of PLA, and negatively affects the thermal stability and mechanical properties. However, addition of virgin PLA, and the chain extender, led to an increase of up to 9% in the intrinsic viscosity and 8% in the Vickers hardness of the recycled material. These results suggest that mechanically recycled PLA with improved performance can be obtained, a fact which might improve the recyclability of PLA and thus the environmental impact of this material.

The aim of this work is to study the effects of different simulated mechanical recycling processes on the structure and properties of PLA. A commercial grade of PLA was melt compounded and compression molded, then subjected to two different recycling processes. The first recycling process consisted of an accelerated ageing and a second melt processing step, while the other recycling process included an accelerated ageing, a demanding washing process and a second melt processing step. The intrinsic viscosity measurements indicate that both recycling processes produce a degradation in PLA, which is more pronounced in the sample subjected to the washing process. DSC results suggest an increase in the mobility of the polymer chains in the recycled materials; however the degree of crystallinity of PLA seems unchanged. The optical, mechanical and gas barrier properties of PLA do not seem to be largely affected by the degradation suffered during the different recycling processes. These results suggest that, despite the degradation of PLA, the impact of the different simulated mechanical recycling processes on the final properties is limited. Thus, the potential use of recycled PLA in packaging applications is not jeopardized.

A comparative theoretical study has been performed of the gas phase and deposited AumRhn (4 ≤ m + n ≤ 6) clusters. The combined use of a genetic algorithm and Density Functional Theory (DFT) calculations allows us to explore the potential energy surface and, therefore, find efficiently and automatically the global minimum configuration for each composition. Our results show interesting effects on the geometries of the clusters on deposition. This occurs because the rhodium atoms (electronically) prefer to be in contact with the MgO surface, sometimes promoting planar clusters to become three-dimensional when deposited, and three-dimensional clusters in the gas phase to become two-dimensional. Together with the change in geometries, the magnetic moment is reduced from the gas phase, as the electrons rearrange themselves when the cluster interacts with the substrate.

Theoretical evidence is presented for the molecular and dissociative adsorption of O2 on free Au n Rh neutral, anionic and cationic clusters with 1 to 5 gold atoms, indicating that the stabilization of the activated di-oxygen species is a key factor for the unusual catalytic activities of Au-based catalysts. The structure, stability, for both molecular and dissociative O2 adsorption on Au n Rh n = 1–5 clusters has been investigated using density-functional theory. To find the transition states, the minimum energy paths have been explored for a few clusters. In general, lower values for the activation energy have been found when compared with the barriers that occur on pure Au n based clusters. The higher binding energies in the AuRh mix favor oxygen dissociation among any other possible reaction paths. The anionic clusters being the most reactive of all. The molecular bonding mechanism to these complexes involves charge transfer to the oxygen molecule with a concomitant activation of the O-O bond to a superoxo-like state. The characteristic planar structures of both pure gold and AuRh clusters prevail for most of the cases here studied. The odd-even characteristic catalytic activation of pure gold clusters is not observed once even a single rhodium atom has been added to the cluster.

Cyclindrical structures of nematics give rise to several opto-optical effects related to molecular reorientation. One of these effects is the formation of diffraction ring patterns similar to the ones observed in planar cells, but differing in shape. Another effect has been observed, namely a quasi-chaotic motion of rings with a very large angular spread; this motion can be obtained using a cw laser and high power densities. The phenomenon could be attributed to thermal motion, however, there are some features that cannot be explained by a purely thermal effect, e.g., a wavelength dependence of the threshold and the frequencies of the ring motion.

3D printing PLA wastes were recovered from a well-known reference grade and from different sources. The recovered wastes were subjected to an energic washing step and then reprocessed into films by melt-extrusion, followed by compression molding to simulate the industrial processing conditions. The obtained materials were characterized and the optical, structural, thermal and crystallization behavior are reported. The mechanical recycling process leads to an increase of the crystallinity and a decrease of the intrinsic viscosity of the formulations, particularly in the sample based on blends of different 3D-PLA wastes. Moreover, the obtained films were disintegrated under composting conditions in less than one month and it was observed that recycled materials degrade somewhat faster than the starting 3D-PLA filament, as a consequence of the presence of shorter polymer chains. Finally, to increase the molecular weight of the recycled materials, the 3D-PLA wastes were submitted to a solid-state polymerization process at 110, 120, and 130 °C, observing that the recycled 3D-wastes materials based on a well-known reference grade experiences an improvement of the intrinsic viscosity, while that coming from different sources showed no significant changes. Thus, the results show that 3D printing PLA products provides an ideal environment for the implementation of distributed recycling program, in which wastes coming from well-known PLA grades can successfully be processed in films with good overall performance.