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In the present work, fiber mats of poly(lactic acid), PLA, plasticized by different amounts of oligomer lactic acid, OLA, were obtained by electrospinning in order to investigate their long term hydrolytic degradation. This was performed in a simulated body fluid for up to 352 days, until the complete degradation of the samples is reached. The evolution of the plasticized electrospun mats was followed in terms of morphological, thermal, chemical and crystalline changes. Mass variation and water uptake of PLA-based electrospun mats, together with pH stability of the immersion media, were also studied during the in vitro test. The results showed that the addition of OLA increases the hydrolytic degradation rate of PLA electrospun fiber mats. Moreover, by adding different amounts of OLA, the time of degradation of the electrospun fiber mats can be modulated over the course of a year. Effectively, by increasing the amount of OLA, the diameter of the electrospun fibers decreases more rapidly during degradation. On the other hand, the degree of crystallinity and the dimension of the α crystals of the electrospun fiber mats are highly affected not only by the presence but also by the amount of OLA during the whole process.

In the last few decades, the development of new electrospun materials with different morphologies and advanced multifunctional properties are strongly consolidated. There are several reviews that describe the processing, use and characterization of electrospun nanocomposites, however, based on our knowledge, no review on electrospun nanocomposites reinforced with nanoparticles (NPs) based on magnesium, Mg-based NPs, are reported. Therefore, in the present review, we focus attention on the fabrication of these promising electrospun materials and their potential applications. Firstly, the electrospinning technique and its main processing window-parameters are described, as well as some post-processing methods used to obtain Mg-based materials. Then, the applications of Mg-based electrospun nanocomposites in different fields are pointed out, thus taking into account the current trend in developing inorganic-organic nanocomposites to gradually satisfy the challenges that the industry generates. Mg-based electrospun nanocomposites are becoming an attractive field of research for environmental remediation (waste-water cleaning and air filtration) as well as for novel technical textiles. However, the mayor application of Mg-based electrospun materials is in the biomedical field, as pointed out. Therefore, this review aims to clarify the tendency in using electrospinning technique and Mg-based nanoparticles to huge development at industrial level in the near future.

In this study, copolymer/clay nanocomposites were prepared by two different methodologies, the in-situ method and solution blending method. Comparative analyses of mechanical and thermal properties of the nanocomposites fabricated by the two different methods were performed. The solution blending method was found to be an efficient technique to obtain nanocomposites with uniform dispersion of the organoclay loading of up to 10 wt%, simple and fast. On the other hand, the in-situ method produced nanocomposites with good exfoliation and high thermal stability, whereas solution blending method produced materials with good mechanical properties compounds in the nano/clay intercalation and high thermal stability.

Different blends based on polysulfone (PSU), polyethersulfone (PES) and polyimide (PI) were prepared and characterized by Fourier transform IR spectroscopy, differential scanning calorimetry, dynamic-mechanical analysis, and microhardness. Subsequently, polysulfone and polyethersulfone homopolymers were sulfonated by treatment with chlorosulfonic acid. Then, analogous blends to the non-sulfonated ones were obtained and studied through the analysis of their glass transition temperature, microhardness, and electrical behaviour. In addition, a statistical method, suitable for the design of systems with optimized behaviour, has been applied to study these polymer blends and to predict the compositions with the best properties.

This paper reports a study on the structural characterization, thermal stability, and thermal degradation kinetics of urea-formaldehyde cellulose (UFC) composites filled with zinc particles. Structural characterization of UFC/Zn composites carried out by SEM, XRD and FTIR analyses reveals that the composites are fairly homogenous, and the interactions between UFC and zinc in the composites are physical in nature. Afterwards, measurements of inherent thermal stabilities, probing reaction complexity, and thermal degradation kinetics of UFC/Zn composites have been carried out. The integral procedure decompositions temperature elucidates significantly higher thermal stabilities of UFC/Zn composites. Isoconversional kinetic analysis suggests multi-step reaction pathways of UFC/Zn composites in terms of the substantial variations in their activation energies with the reaction advancement. Advanced reaction model determination methodology with the help of an innovative kinetic function F(α, T) reveals that the thermal degradation of UFC goes to completion by following complicated multi-step nucleation/growth mechanisms. A detailed account of the mechanistic information regarding to the thermal degradation processes taking place in UFC/Zn composites is given and discussed in the present study.

To modulate the properties of degradable implants from outside of the human body represents a major challenge in the field of biomaterials. Polylactic acid is one of the most used polymers in biomedical applications, but it tends to lose its mechanical properties too quickly during degradation. In the present study, a way to reinforce poly-L lactic acid (PLLA) with magnetic nanoparticles (MNPs) that have the capacity to heat under radiofrequency electromagnetic fields (EMF) is proposed. As mechanical and degradation properties are related to the crystallinity of PLLA, the aim of the work was to explore the possibility of modifying the structure of the polymer through the heating of the reinforcing MNPs by EMF within the biological limit range f·H < 5·× 109 Am−1·s−1. Composites were prepared by dispersing MNPs under sonication in a solution of PLLA. The heat released by the MNPs was monitored by an infrared camera and changes in the polymer were analyzed with differential scanning calorimetry and nanoindentation techniques. The crystallinity, hardness, and elastic modulus of nanocomposites increase with EMF treatment.

Several composites were prepared based on a polypropylene random copolymer (PPR) and different amounts of date stone flour (DSF). This cellulosic fiber was silanized beforehand in order to reduce its hydrophilicity and improve the interfacial adhesion with the polymer. Other composites were also obtained, including a sorbitol derivative as an effective nucleant. Films made from these composites were prepared using two different thermal treatments, involving slow crystallization and rapid cooling from the melt. Scanning electron microscopy was used to evaluate the morphological features and the DSF particle dispersion within the PPR matrix. X-ray diffraction experiments and differential scanning calorimetry tests were employed to assess the crystalline characteristics and for the phase transitions, paying especial attention to the effects of the DSF and nucleating agent on PPR crystallization. An important nucleation ability was found for DSF, and evidently for the sorbitol derivative. The peak crystallization temperature upon cooling was considerably increased by the incorporation of either the nucleant or DSF. Additionally, a much higher proportion of orthorhombic crystals developed in relation to the monoclinic ones. Moreover, the mechanical responses were estimated from the microhardness experiments and significant improvements were found with increasing DSF contents. All of these findings indicate that the use of silanized DSF is a fairly good approach for the preparation of polymeric eco-composites, taking advantage of the widespread availability of this lignocellulosic material, which is otherwise wasted.

Several nanocomposites were prepared by extrusion from a commercial metallocene-type isotactic polypropylene (iPP) and different amounts of two types of graphene (G) nanofibers: ones with a high specific surface, named GHS, and the others with a low specific surface, labeled as GLS. The number of graphene layers was found to be around eight for GLS and about five in the GHS. Scanning electron microscopy (SEM) images of the resultant iPP nanocomposites showed a better homogeneity in the dispersion of the GLS nanofibers within the polymeric matrix compared with the distribution observed for the GHS ones. Crystallinity in the nanocomposites turned out to be dependent upon graphene content and upon thermal treatment applied during film preparation, the effect of the nature of the nanofiber being negligible. Graphene exerted a noticeable nucleating effect in the iPP crystallization. Furthermore, thermal stability was enlarged, shifting to higher temperatures, with increasing nanofiber amount. The mechanical response changed significantly with nanofiber type, along with its content, together with the thermal treatment applied to the nanocomposites. Features of nanofiber surface played a key role in the ultimate properties related to superficial and bulk stiffness.

The “comonomer effect” is an intriguing kinetic phenomenon in olefin copolymerization that still remains without a detailed explanation. It typically relates to the rate of enhancement undergone in ethylene and propene catalytic polymerization just by adding small fractions of an alpha-olefin. The difficulty lies in the fact that changes caused by the presence of the comonomer in reaction parameters are so conspicuous that it is really difficult to pin down which of them is the primary cause and which ones are side factors with marginal contribution to the phenomenon. Recent investigations point to the modification of the catalyst active sites as the main driving factor. In this work, the comonomer effect in the metallocene copolymerization of propene and 1-nonene is analysed and correlated to the comonomer role in the termination of the chain-growing process. The associated termination mechanisms involved furnish most of chain-free active sites, in which the selective interaction of the comonomer was proposed to trigger the insertion of monomers. A thorough characterisation of chain-end groups by means of the 1H NMR technique allows for detailing of specific transfer processes, ascribed to comonomer insertions, as well as evidencing the influence of the growing chain’s microstructure over the different termination processes available.

The preparation of nanocomposites, including styrene, tertbutylstyrene, and SiO 2 nanoparticles, in toluene solution was attempted by in situ polymerization using a cyclopentadienyltitaniumtrichloride–methylaluminoxane, CpTiCl 3 –MAO, initiator system. SiO 2 nanospheres (ca. 20 nm in diameter) were synthesized by the sol–gel method. The nanoparticles’ surface was modified with hexadecyltrimethoxysilane (Mod-SiO 2 Nps) in order to improve the interactions with the polymer. The polymerization activity increased as the proportion of p -methyl styrene was increased in the initial feed. With respect to the effect of the incorporation of nanoparticles in the reactions, the catalytic activity increased slightly in the presence of 5 wt% of nanospheres compared to neat copolymerization without any nanoparticles. Our studies achieved a convenient route through in situ polymerization, avoiding further treatment of the nanocomposite. The thermal stability of the PS increased with nanoparticle incorporation. The effect of SiO 2 -Npts on the catalyst’s activity and on the thermal properties of the resulting nanocomposites was determined.