Latest articles in this journal
Polymers, Volume 15; https://doi.org/10.3390/polym15112551
A detailed study of the different structural transitions of the triblock copolymer PEO27–PPO61–PEO27 (P104) in water, in the dilute and semi-dilute regions, is addressed here as a function of temperature and P104 concentration (CP104) by mean of complimentary methods: viscosimetry, densimetry, dynamic light scattering, turbidimetry, polarized microscopy, and rheometry. The hydration profile was calculated through density and sound velocity measurements. It was possible to identify the regions where monomers exist, spherical micelle formation, elongated cylindrical micelles formation, clouding points, and liquid crystalline behavior. We report a partial phase diagram including information for P104 concentrations from 1 × 10−4 to 90 wt.% and temperatures from 20 to 75 °C that will be helpful for further interaction studies with hydrophobic molecules or active principles for drug delivery.
Polymers, Volume 15; https://doi.org/10.3390/polym15112550
We studied the translocation of polyelectrolyte (PE) chains driven by an electric field through a pore by means of molecular dynamics simulations of a coarse-grained HP model mimicking high salt conditions. Charged monomers were considered as polar (P) and neutral monomers as hydrophobic (H). We considered PE sequences that had equally spaced charges along the hydrophobic backbone. Hydrophobic PEs were in the globular form in which H-type and P-type monomers were partially segregated and they unfolded in order to translocate through the narrow channel under the electric field. We provided a quantitative comprehensive study of the interplay between translocation through a realistic pore and globule unraveling. By means of molecular dynamics simulations, incorporating realistic force fields inside the channel, we investigated the translocation dynamics of PEs at various solvent conditions. Starting from the captured conformations, we obtained distributions of waiting times and drift times at various solvent conditions. The shortest translocation time was observed for the slightly poor solvent. The minimum was rather shallow, and the translocation time was almost constant for medium hydrophobicity. The dynamics were controlled not only by the friction of the channel, but also by the internal friction related to the uncoiling of the heterogeneous globule. The latter can be rationalized by slow monomer relaxation in the dense phase. The results were compared with those from a simplified Fokker–Planck equation for the position of the head monomer.
Polymers, Volume 15; https://doi.org/10.3390/polym15112549
Changes in the properties of resin-based polymers exposed to the oral environment can emerge when chlorhexidine (CHX) is incorporated to develop bioactive systems for treating denture stomatitis. Three reline resins loaded with CHX were prepared: 2.5 wt% in Kooliner (K), 5 wt% in Ufi Gel Hard (UFI), and Probase Cold (PC). A total of 60 specimens were submitted to physical aging (1000 cycles of thermal fluctuations, 5–55 °C) or chemical aging (28 days of pH fluctuations in artificial saliva, 6 h at pH = 3, 18 h at pH = 7). Knoop microhardness (30 s, 98 mN), 3-point flexural strength (5 mm/min), and surface energy were tested. Color changes (ΔE) were determined using the CIELab system. Data were submitted to non-parametric tests (α = 0.05). After aging, bioactive K and UFI specimens were not different from the controls (resins without CHX) in mechanical and surface properties. Thermally aged CHX-loaded PC specimens showed decreased microhardness and flexural strength but not under adequate levels for function. The color change was observed in all CHX-loaded specimens that underwent chemical aging. The long-term use of CHX bioactive systems based on reline resins generally does not impair removable dentures’ proper mechanical and aesthetic functions.
Polymers, Volume 15; https://doi.org/10.3390/polym15112547
The craving for controllable assembly of geometrical nanostructures from artificial building motifs, which is routinely achieved in naturally occurring systems, has been a perpetual and outstanding challenge in the field of chemistry and materials science. In particular, the assembly of nanostructures with different geometries and controllable dimensions is crucial for their functionalities and is usually achieved with distinct assembling subunits via convoluted assembly strategies. Herein, we report that with the same building subunits of α-cyclodextrin (α-CD)/block copolymer inclusion complex (IC), geometrical nanoplatelets with hexagonal, square, and circular shapes could be produced by simply controlling the solvent conditions via one-step assembly procedure, driven by the crystallization of IC. Interestingly, these nanoplatelets with different shapes shared the same crystalline lattice and could therefore be interconverted to each other by merely tuning the solvent compositions. Moreover, the dimensions of these platelets could be decently controlled by tuning the overall concentrations.
Polymers, Volume 15; https://doi.org/10.3390/polym15112548
The purpose of this work was to obtain an elastic composite material from polymer powders (polyurethane and polypropylene) with the addition of BaTiO3 until 35% with tailored dielectric and piezoelectric features. The filament extruded from the composite material was very elastic but had good features to be used for 3D printing applications. It was technically demonstrated that the 3D thermal deposition of composite filament with 35% BaTiO3 was a convenient process for achieving tailored architectures to be used as devices with functionality as piezoelectric sensors. Finally, the functionality of such 3D printable flexible piezoelectric devices with energy harvesting features was demonstrated, which can be used in various biomedical devices (as wearable electronics or intelligent prosthesis), generating enough energy to make such devices completely autonomous only by exploiting body movements at variable low frequencies.
Polymers, Volume 15; https://doi.org/10.3390/polym15112546
Patients with chronic kidney disease (CKD) suffer persistent decreased kidney function. Previous study of protein hydrolysate of green pea (Pisum sativum) bromelain (PHGPB) has shown promising results as an antifibrotic in glucose-induced renal mesangial culture cells, by decreasing their TGF-β levels. To be effective, protein derived from PHGPB must provide adequate protein intake and reach the target organs. This paper presents a drug delivery system for the formulation of PHGPB using chitosan as polymeric nanoparticles. A PHGPB nano delivery system was synthesized by precipitation with fixed chitosan 0.1 wt.%, followed by a spray drying process at different aerosol flow rates of 1, 3, and 5 L/min. FTIR results showed that the PHGPB was entrapped in the chitosan polymer particles. Homogeneous size and spherical morphology of NDs were obtained for the chitosan-PHGPB with a flow rate of 1 L/min. Our in vivo study showed that the highest entrapment efficiency, solubility, and sustained release were achieved by the delivery system method at 1 L/minute. It was concluded that the chitosan-PHGPB delivery system developed in this study improves pharmacokinetics compared to pure PHGPB.
Polymers, Volume 15; https://doi.org/10.3390/polym15112545
There is an ever-growing interest in recovering and recycling waste materials due to their hazardous nature to the environment and human health. Recently, especially since the beginning of the COVID-19 pandemic, disposable medical face masks have been a major source of pollution, hence the rise in studies being conducted on how to recover and recycle this waste. At the same time, fly ash, an aluminosilicate waste, is being repurposed in various studies. The general approach to recycling these materials is to process and transform them into novel composites with potential applications in various industries. This work aims to investigate the properties of composites based on silico-aluminous industrial waste (ashes) and recycled polypropylene from disposable medical face masks and to create usefulness for these materials. Polypropylene/ash composites were prepared through melt processing methods, and samples were analyzed to get a general overview of the properties of these composites. Results showed that the polypropylene recycled from face masks used together with silico-aluminous ash can be processed through industrial melt processing methods and that the addition of only 5 wt% ash with a particle size of less than 90 µm, increases the thermal stability and the stiffness of the polypropylene matrix while maintaining its mechanical strength. Further investigations are needed to find specific applications in some industrial fields.
Polymers, Volume 15; https://doi.org/10.3390/polym15112544
Polypropylene-fiber-reinforced foamed concrete (PPFRFC) is often used to reduce building structure weight and develop engineering material arresting systems (EMASs). This paper investigates the dynamic mechanical properties of PPFRFC with densities of 0.27 g/cm3, 0.38 g/cm3, and 0.46 g/cm3 at high temperatures and proposes a prediction model to characterize its behavior. To conduct the tests on the specimens over a wide range of strain rates (500 s−1~1300 s−1) and temperatures (25~600 °C), the conventional split-Hopkinson pressure bar (SHPB) apparatus was modified. The test results show that the temperature has a substantial effect on the strain rate sensitivity and density dependency of the PPFRFC. Additionally, the analysis of failure models demonstrates that with the melting of polypropylene fibers, the level of damage in PPFRFC under dynamic loading increases, resulting in the generation of a greater number of fragments.
Polymers, Volume 15; https://doi.org/10.3390/polym15112543
The influence of thermomechanical stress on the conductivity of indium tin oxide (ITO)-coated polycarbonate (PC) films was investigated. PC is the industry’s standard material for window panes. ITO coatings on polyethylene terephthalate (PET) films are the main commercially available option; as such, most investigations refer to this combination. The investigations in this study aim to investigate the critical crack initiation strain at different temperatures and crack initiation temperatures for two different coating thicknesses and for a commercially available PET/ITO film for validation purposes. Additionally, the cyclic load was investigated. The results show the comparatively sensitive behavior of the PC/ITO films, with a crack initiation strain at room temperature of 0.3–0.4% and critical temperatures of 58 °C and 83 °C, with high variation depending on the film’s thickness. Under thermomechanical loading, the crack initiation strain decreases with increasing temperatures.
Polymers, Volume 15; https://doi.org/10.3390/polym15112542
Despite natural fibers gaining significant attention in recent decades, their limited performance and poor durability under humid environments cannot allow them to fully replace their synthetic counterparts as reinforcement for structural composites. In such a context, this paper aims to investigate how exposure to a humid/dry cycle affects the mechanical response of epoxy laminates reinforced with flax and glass fibers. In particular, the main goal is to assess the performance evolution of a glass–flax hybridized stacking sequence in comparison with the full glass and flax fiber reinforced composites. To this end, the investigated composites were first exposed to salt-fog for 15 or 30 days and then to dry conditions (i.e., 50% R.H. and 23 °C) for up to 21 days. The presence of glass fibers in the stacking sequence significantly stabilizes the mechanical performance of composites during the humid/dry cycle. Indeed, hybridization of inner flax laminae with outer glass ones, acting as a protective shield, hinders the composite degradation due to the humid phase also promoting performance recovery during the dry phase. Hence, this work showed that a tailored hybridization of natural fibers with glass fibers represents a suitable approach to extend the service-life of natural fiber reinforced composites exposed to discontinuous humid conditions, thus allowing their employment in practical indoor and outdoor applications. Finally, a simplified theoretical pseudo-second-order model that aimed to forecast the performance recovery shown by composites was proposed and experimentally validated, highlighting good agreement with the experimental data.