Silicone elastomers filled with rare earth oxides

Silicones which possess, amongst others, remarkable mechanical properties, thermal stability over a wide range of temperatures and processability, and rare earth oxides(REO), known for their unique optic, magnetic and catalytic properties can be coupled into multifunctional composite materials(SREOs). In addition, the intrinsic hydrophobicity of REO and polysiloxanes makes them easily compatible without the need for surface treatments of the former. Thus, europium oxide (Eu2O3), gadolinium oxide (Gd2O3) and dysprosium oxide (Dy2O3)in amounts of 20 pph are incorporated as fillers into silicone matrices, followed by processing mixture as thin films and crosslinking at room temperature. The analysis of the obtained films reveals the changes induced by these fillers in the thermal, mechanical, dielectric and optical properties, as well as the hydrophobicity of the silicones. The luminescence properties of S-REO composites were investigated by fluorescence spectra and lifetime - resolved measurements with a multiemission peaks from blue to greenish register. The thermogravimetrical analysis indicates an increasing of thermal stability of the composites that contain REO, compared to pure silicone. As expected, the dielectric permittivity significantly increased due to nature of the fillers, while the dielectric loss values are relatively low for all samples, indicating a minimal conversion of electrical energy in the form of heat within bulk composites. The presence of rare earth oxides into the silicone matrix facilitates the motions of long-range charge carriers through the network resulting in higher values of conductivity of the composite films. The stress-strain measurements revealed the reinforcing effect of the rare earth metal oxides on a silicone matrix, leading to a significant increase of Young modulus. The known hydrophobicity of silicones is further enhanced by the presence of REO

Study on Poly(Vinyl Alcohol) CopolymersBiodegradation

In the study the biodegradability of some poly(vinyl alcohol)-g-aspartic acid copolymers was investigated, using Trichotecium roseum fungus. The biodegraded samples were examined after established days of inoculation (3–21 days). The modification of structure and surface morphology, caused by copolymers biodegradation was determined by atenuated total reflectance fourier transform infrared spectroscopy (ATR-FTIR) and scanning electron microscopy (SEM). By static light scattering analysis (SLS) was concluded that the weight average molecular weight (Mw) of poly(vinyl alcohol)- g-aspartic acid copolymers was major modified by biodegradation. The thermal characteristics of initial and biodegraded samples were studied by differential scanning calorimetry (DSC) and thermogravimetry (TG-DTG) analyses

New Hydrogel Network Based on Alginate and a Spiroacetal Copolymer

This study reports a strategy for developing a biohybrid complex based on a natural/synthetic polymer conjugate as a gel-type structure. Coupling synthetic polymers with natural compounds represents an important approach to generating gels with superior properties and with potential for biomedical applications. The study presents the preparation of hybrid gels with tunable characteristics by using a spiroacetal polymer and alginate as co-partners in different ratios. The new network formation was tested, and the structure was confirmed by FTIR and SEM techniques. The physical properties of the new gels, namely their thermal stability and swelling behavior, were investigated. The study showed that the increase in alginate content caused a smooth increase in thermal stability due to the additional crosslinking bridges that appeared. Moreover, increasing the content of the synthetic polymer in the structure of the gel network ensures a slower release of carvacrol, the encapsulated bioactive compound

Thermal Degradation of Carboxymethyl Starch–g-Poly(lactic acid) Copolymer by TG–FTIR–MS Analysis

In this study, carboxymethyl starch (CMS) was grafted with l­(+)-lactic acid (LA) in a CMS/LA molar ratio of 1/36, resulting in the CMS–g-PLA copolymer. The grafting reaction was carried out via a solution polycondensation procedure, in the presence of stannous 2-ethyl hexanoate [Sn­(Oct)₂] as a catalyst. Poly­(lactic acid) (PLA) was synthesized under the same conditions with the copolymer, for comparative analyses of the thermal properties. The CMS–g-PLA copolymer, CMS, and PLA were structurally characterized by Fourier transform infrared (FTIR) spectroscopy, while thermal degradation products were characterized by thermogravimetry analysis coupled with Fourier transform infrared spectroscopy and mass spectrometry (TG–FTIR–MS). The thermal degradation was achieved in a nitrogen atmosphere, in a temperature interval of 30–600 °C. The thermal degradation of CMS and PLA was studied under the same conditions to highlight the products resulted by the thermal decomposition of CMS–g-PLA copolymer. By processing the achieved data via thermal degradation at three different heating speeds (5, 7.5, and 10 °C min^–1) and using the multivariate nonlinear regression method (MNLR), the kinetic parameters were determined. The dependence of the activation energy of the degradation process versus the extent of conversion was evaluated using the Friedman and Ozawa–Flynn–Wall model-free analyses. This variation suggests that the degradation process is a complex one and can be divided in one or two steps, depending on the chemical structure of the compounds. The kinetic parameters and the most probable thermal degradation mechanisms were given

Epoxy Resins Cross-Linked with Bisphenol A/Methylenedianiline Novolac Resin Type: Curing and Thermal Behavior Study

A novolac type resin was synthesized from bisphenol A, 4,4′-methylenedianiline, and formaldehyde in the presence of HCl. The chemical structure was confirmed using elemental analysis, FT-IR spectroscopy, and ¹H NMR spectroscopy. The curing kinetics of these epoxy resins at an epoxy ring/amine proton molar ratio of 1/1, were studied by nonisothermal differential scanning calorimetry (DSC) at different heating rates. The kinetic analysis of the curing reactions was evaluated using the variable peak exotherm method of Flynn–Wall–Ozawa and Kissinger. The thermal degradation mechanisms for novolac resin (FR) and cured resins were identified taking place between two and four steps, depending on the chemical structure of the sample. The most probable kinetic model and kinetic parameters of the degradation process were estimated using Netzsch Thermokinetics software. The cured resins have good thermal stability, with activation energies of thermal degradation reactions having values situated in the range 127–184 kJ·mol^–1

Scaffolds Based on Collagen, Hyaluronan and Sericin with Potential Applications as Controlled Drug Delivery System

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Study on Thermal Behavior of Some Biocompatible and Biodegradable Materials Based on Plasticized PLA, Chitosan, and Rosemary Ethanolic Extract

Thermal characterization of some multifunctional environmentally friendly materials based on plasticized poly (lactic acid) (PLA)/chitosan (CS) and rosemary extract (R) previously obtained is presented. Differential scanning calorimetry (DSC) associated with other complex investigations such as chemiluminescence and coupled thermogravimetry (TG)/Fourier-transform infrared spectroscopy (FT-IR)/mass spectroscopy (MS) was performed in order to test both the thermal behavior and the biocomposition–property relationship. It was established that the rosemary ethanolic extract offers an efficient protection against thermoxidative degradation to the new developed plasticized PLA-based biocomposites which show good thermal properties, being suitable for both medical and food packaging applications

One-Step Preparation of Carboxymethyl Cellulose—Phytic Acid Hydrogels with Potential for Biomedical Applications

Hydrogels based on natural, biodegradable materials have gained considerable interest in the medical field due to their improved drug delivery profiles and tissue-mimicking architecture. In this regard, this study was devoted to the preparation and characterization of new physically crosslinked hydrogels based on carboxymethyl cellulose and an unconventional crosslinking agent, phytic acid. Phytic acid, in addition to its antioxidant and antibacterial effects, can improve the biological properties and stability of gels, without adding toxicity. Fourier transform infrared (FTIR) spectroscopy, rheological studies and thermal analysis confirmed the hydrogel formation. The influence of the ratio between the cellulose derivative and the crosslinker upon the morphological structure and water uptake was evidenced by scanning electron microscopy (SEM) and swelling measurements in simulated body fluids. Furthermore, procaine was entrapped within the hydrogels and used as a model drug for in vitro studies, which highlighted the dependence of the drug release on the phytic acid content of the matrix. The materials demonstrated antibacterial effects against Escherichia coli and Staphylococcus aureus bacteria. The biocompatibility was assessed on fibroblast cells, and according to our results, hydrogels can improve cell viability highlighting the potential of these systems as therapeutic scaffolds for skin tissue engineering