Differential Scanning Calorimetry Techniques Research Articles

Synthesis and solvatochromism of dipodal and tripodal dyes derived from Brooker’s merocyanine

Brooker’s merocyanine (BM) is a classic solvatochromic probe, which exhibits a band in the visible region sensitive to changes in the polarity of the medium. BM shows a reversion in its solvatochromism, which has inspired much research on studies involving different families of dyes. We synthesized four novel dipodal and tripodal solvatochromic dyes (1b–4b) inspired by BM molecular structure. Characterization of the compounds in their protonated form used spectrometric and differential scanning calorimetry techniques. Dyes 1b–4b have an electron–donating phenolate moiety connected through a CHCH conjugated bridge to two or three N–methylpyridinium electron–acceptor groups. The probes exhibit negative solvatochromism in the solvents studied, showing very different colors with the change in the polarity of the solvent. Multiparameter strategies of Kamlet–Abboud–Taft (KAT), Catalán, and a modified KAT fitted the experimental data. The HBD acidity of the solvent represented the main contribution to the solvation of the probes. Performing electronic–structure calculations of the compounds at LC–BLYP/ma–def2–SVP/D4 level and employing water and DMSO as implicit solvents (SMD model) using software ORCA5.0 revealed that the longest–wavelength absorption bands in the dyes are due to a π → π* transition, from the phenolate (electron–donating) group to the N–methylpyridinium (electron–acceptor) groups. The calculations did not reproduce the experimentally observed negative solvatochromism of the dyes in the solvents studied. However, comparing the theoretical and experimental data of the present study with data from the literature provided important information regarding the results obtained.

Synthesis, characterization, and applications of lanthanide ortho ferrites

In our current study, we demonstrate that lanthanum and yttrium ortho ferrites can be synthesized using a combustion process called self-propagating, high-temperature synthesis (SHS) using lanthanum(III) oxide and yttrium(III)oxide, chromium oxide, Iron metal, and potassium perchlorate as raw materials. Synthesized lanthanide and yttrium orthoferrites were characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and thermogravimetric differential scanning calorimetry techniques. The results show that the synthesized orthoferrites are of high quality with particle sizes less than 100 nm and showing less agglomeration. Synthesized lanthanum and yttrium orthoferrites exhibited electrical conductivities around 50 kHz for different temperatures ranging from 35 to 500°C. The rise in conductivity is found to be linear with an increase in temperature. Herein, our work paves way for low-cost, large-scale production of lanthanide orthoferrites without the need for reaction solvents, which greatly opens up the scope for combustion-based synthesis approaches.

Experimentally based testing of the enthalpy-porosity method for the numerical simulation of phase change of paraffin-type PCMs

The enthalpy-porosity method is generally applied as an economical resort for the numerical simulation of phase change materials (PCMs). However, having been developed strictly for metals, its suitability for the task is unclear, nor is the rationale for assigning its internal parameters, e.g., latent enthalpy and the constant of the momentum source term representing the “mushy” region. We first experimentally and exhaustively characterize a paraffin-type PCM, including differential scanning calorimetry (DSC) at several heating rates, T-history, and fusion visualization. Then, we develop a numerical model and systematically run simulations under different internal parameters and thermophysical properties of the PCM. Simulation results exhibit significant disagreement with experiments that cannot be reduced by any strategy for combining different material properties and model parameters. Among other effects, the constant of the momentum source term, which has to be assigned somewhat arbitrarily, has more relevance in the accuracy than any set of properties obtained by DSC and other experimental techniques. Thus, a rather negative, although interesting, conclusion is suggested: the enthalpy-porosity method may fail to model the phase change of paraffin-type PCMs. This is, of course, of paramount importance for the studies of their utilization in practical systems since it puts a fundamental point of uncertainty in any numerical study or lumped-type model derived thereof. The paper concludes with a tentative discussion of the possible causes of this failure and perspectives for developing more proper models.

Oxidation thermolysis kinetics of asphaltenes with various chemical prehistory

In this research, six various asphaltenes extracted from crude oil mixtures of three Russian refinery plants and some heavy residues of these plants were studied with applying thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) techniques. The kinetic experiments were performed at four various heating rates (5, 10, 15, 20 °C/min), all under air static atmosphere. The TGA data were transformed to conversions and first analyzed with the approved methods of Friedman, Ozawa-Flynn-Wall (OFW) and Kissinger-Akahira-Sunose (KAS). The results indicated of the complexity of decomposition-thermolysis process and a complicated and non-uniform dependency of the effective activation energy as a function of conversion, unique for each asphaltene studied. A kinetic model of two independent N-order reactions was proposed to make corresponding kinetic descriptions of complicated thermolysis reactions under non-isothermal conditions. The developed model was proved to be valid, and kinetic descriptions were obtained that fitted the experimental data. Activation energies for the first reaction and the second reaction were found to be in the interval 24–48 kJ/mol and 110–125 kJ/mol respectively (asphaltenes (1–3) extracted from the initial crude oil mixtures and pyrolysis resin). Activation energies for secondary asphaltenes (4–6) extracted from heavy refinery residues - 115–155 kJ/mol (1-st reaction) – 110–148 kJ/mol (2-nd reaction).

Chemical Characterization of Ultra High Molecular Weight Polyethylene Based Tibial Inserts After Ethylene Oxide Sterilization

Ultra-high molecular weight polyethylene (UHMWPE) has become the gold standard for total joint replacements such as tibial inserts because of its chemical inertness, superior mechanical properties, and biocompatibility. Ethylene oxide sterilization is one of the most common and effective methods used, especially for the sterilization of polyethylene-based polymeric implants. However, variable sterilization conditions can cause a change in the chemical structure of the polymeric material, which affects its mechanical properties and lifetime. The aim of this study is to investigate whether the chemical structure of UHMWPE tibial inserts sterilized with ethylene oxide undergoing certain conditions remains the same. Chemical characterization studies were performed with Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffractometer, differential scanning calorimetry, thermogravimetric analysis, mass spectrometry and elemental analysis techniques recommended for polymeric materials in ISO 10993-8:2020 standard. According to the FTIR results, the spectra of the non-sterile and sterile tibial inserts were compared, and it was determined that the similarity between them was 99.97%. XRD results revealed that after ethylene oxide sterilization, there was no significant shift in the Bragg (1 0 0) peak. The percentages of crystallinity calculated from the fusion enthalpies determined by DSC of sterile and non-sterile samples are 54.3% and 53.3%, respectively. Characterization results revealed that there was no significant change in molecular structure, crystallinity, elemental composition of UHMWPE materials after ethylene oxide sterilization. These results can provide assurance that tibial inserts keep their physical, chemical, and mechanical properties after sterilization.

Simultaneously cured diglycidyl ethers of bisphenol A and polyethylene glycol: DSC, TGA, and DMA measurements

AbstractIn this study, to improve the physico‐mechanical properties of epoxy thermosets, simultaneous curing of two resins with a stoichiometric amount of an aromatic amine hardener was investigated. The two resins used included the well‐known diglycidyl ether of bisphenol A (DGEBPA) with relatively rigid molecular structure and a diglycidyl ether derived from a popular polymer, polyethylene glycol (PEG), with loose molecular structure (DGEPEG). DGEPEG was used in amounts of 10 and 25 mol% in the resin mixture. A single‐resin curing process, including only DGEBA, was also examined. Before isothermal curing, differential scanning calorimetry (DSC) was used to determine the position of the curing exotherm. To ensure the completion of the curing processes, infra‐red (IR) and DSC techniques were performed on both simultaneously‐cured thermosets and the control thermoset. The thermogravimetric analysis (TGA) of the prepared thermosets showed that the addition of DGEPEG resin in the curing process of DGEBA resin has no significant effect on reducing the thermal resistance of the thermoset. In addition, the storage moduli (E′) and the damping coefficients (tan δ) were measured by dynamic mechanical analysis (DMA). As the mole percentage of DGEPEG resin increased, the rapid drop in the E′ value and the α‐relaxation, which is a measure of the glass transition (Tg), occurred at lower temperatures.

Synthesis, characterization and photophysical study of cholesterol functionalized azo-based room temperature liquid crystals

Four new liquid crystalline materials (HA1-HA4) with cholesteryl group and azo-ester linking group interconnected with two-side substituted flexible alkoxy side chains were deliberated and synthesized. The structure confirmation of the azo mesogens was investigated by using FT-IR, 1H NMR, and 13C NMR techniques. The phase behavior of the materials was investigated by crossed polarizing optical microscopy (POM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and X-ray diffraction (XRD) techniques. All four targeted materials shows smectic type mesogenic properties and further stabilized up to room temperature to lower temperature. The structure-property relationship of present azo-based materials was discussed to investigate the scope of mesogenic properties. All four materials (HA1-HA4) display wide temperature range mesophase as 52.5 °C, 54.7 °C, 52.7 °C, and 54.1 °C. The photoresponsive properties of the azo-based bi-substituted materials were well examined by UV study.

Solidification Kinetics of an Al-Ce Alloy with Additions of Ni and Mn

Heat-treated aluminum–silicon (Al-Si)-based alloys have dominated the cast lightweight alloy industry for several decades. However, in the last decade, Al-Ce-based alloys have shown promise in replacing Al-Si alloys as they remove the need for costly heat treatments. As the properties of Al-Ce alloys depend on the as-cast microstructure, it is important to characterize the solidification kinetics of these alloys. Therefore, this study focused on characterizing the solidification of an Al-Ce alloy with additions of Ni and Mn (nominal composition Al-12.37Ce-3.26Ni-0.94Mn-0.12Fe in weight percent). The alloy was cast in a wedge mold configuration, resulting in cooling rates between 0.18 and 14.27 °C/s. Scanning electron microscopy (SEM) coupled with the energy dispersive x-ray spectroscopy (EDS) and differential scanning calorimetry (DSC) techniques characterized the evolution rate of solid phases. The SEM/EDS data revealed that an Al10CeMn2 phase was present at higher cooling rates. At lower cooling rates, near the center of the casting, a primary Al23Ce4Ni6 phase was more present. It was observed that up to 2.6 atomic percent (at.%) of Mn was dissolved in this primary Al23Ce4Ni6 phase, thereby removing a large portion of the available Mn for forming the Al10CeMn2 phase. DSC analysis showed differences in the samples’ liquidus temperatures, which indicated compositional variations. Inductively coupled plasma–atomic emission spectroscopy (ICP-OES) and Scheil solidification simulations correlated the compositional differences with phase formation, which agreed with the SEM and DSC results. This experiment provides insight into novel Al-Ce-Ni-Mn alloys and where their potential lies in industrial applications.

Composition analysis of post‐consumer recycled blends of linear low‐ and low‐density polyethylene using a solution‐based technique

AbstractBlends of linear low‐density polyethylene (LLDPE) and low‐density polyethylene (LDPE) are commonly used in film applications, including those made with post‐consumer recycled (PCR) film resins. The ratio of LLDPE/LDPE in PCR resins can vary based on the complexity of the waste stream, making it essential to determine their composition before incorporating them into virgin resins through mechanical recycling. In this study, we propose a quantitative analysis using a solution‐based crystallization elution fractionation (CEF) technique to determine the composition of PCR LLDPE/LDPE blends. The results were compared with those obtained by a standard differential scanning calorimetry (DSC) technique. A series of Ziegler–Natta catalyzed LLDPE resins were blended with LDPE to establish the CEF calibration curves. The CEF calibration curves were found to be similar for 1‐butene LLDPE/LDPE and 1‐hexene LLDPE/LDPE blends. Fourier transform infrared spectroscopy and nuclear magnetic resonance were used as needed to determine the type of comonomer in the LLDPE component for the DSC methodology, which varies the calibration curve. We found that the CEF and DSC techniques provide comparable results in terms of LDPE content for neat polymer blends, depending on the density of each component. However, the proposed CEF technique provides more accurate and reliable results than previously published techniques in estimating LDPE content in PCR LLDPE/LDPE blends that may contain inorganic compounds.

Synthesis and electrical characterization of poly[(linoleic acid)‐g‐(styrene)‐g‐(ε‐caprolactone)] graft copolymers as gate insulator for OFET devices

AbstractThis study reports a one‐pot process used to synthesize poly[(linoleic acid)‐g‐(styrene)‐g‐(ε‐caprolactone)] (PLina‐g‐PSt‐g‐PCL) graft copolymers. The process was carried out by combining the atom transfer radical polymerization of styrene with the ring‐opening polymerization of ε‐caprolactone from polymeric linoleic acid having hydroxyl groups and bromine groups in the main chain. The characterization of the products was achieved using proton nuclear magnetic resonance, size‐exclusion chromatography, Fourier transform infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry techniques. Subsequently, an organic field effect transistor (OFET) was fabricated with PLina‐g‐PSt‐g‐PCL graft copolymers as the insulator layer. Poly(3‐hexylthiophene) (P3HT) was used as the active layer and prepatterned OFET substrates were used as the welding/discharge electrodes. To measure capacitance, an ITO/P3HT/PLina‐g‐PSt‐g‐PCL/Al structure was prepared using the same method. To obtain output and transfer current–voltage characteristics, electrical characterizations of OFET devices were conducted in darkness and an atmosphere of air. From a capacitance–frequency plot, the key characteristics of the devices, including the threshold voltage (VTh), field effect mobility, and current on/off ratio (Ion/off), were derived. The fundamental electrical parameters in the fabricated OFET devices based on styrene concentration were thoroughly examined. It was observed that the produced PLina‐g‐PSt‐g‐PCL OFETs display positive device characteristics such as low VTh, exceptional mobility, and Ion/off values. © 2023 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry.

Reactive Blending of Recycled Poly(ethylene terephthalate)/Recycled Polypropylene: Kinetics Modeling of Non-Isothermal Crystallization.

Plastics were developed to change our world for the better. However, plastic pollution has become a serious global environmental crisis. Thermoplastic polyesters and polyolefins are among the most abundant plastic waste. This work presents an in-depth non-isothermal crystallization kinetics analysis of recycled post-consumer poly(ethylene terephthalate) (rPET) and recycled polypropylene (rPP) blends prepared through reactive compounding. The effect of pyromellitic dianhydride (PMDA) on crystallization kinetics and phase morphology of rPET/rPP blends was investigated by differential scanning calorimetry (DSC) and microscopy techniques. DSC results showed that increasing rPP content accelerated rPET crystallization while reducing crystallinity, which indicates the nucleation effect of the rPP phase in blends. Further, it was found that the incorporation of PMDA increased the degree of crystallinity during non-isothermal crystallization, even though the rate of crystallinity decreased slightly due to its restriction effects. The non-isothermal crystallization kinetics was analyzed based on the theoretical models developed by Jeziorny, Ozawa, Mo, and Tobin. The activation energy of the crystallization process derived from Kissinger, Takhor, and Augis-Bennett models was found to increase in rPET/rPP blends with increasing PMDA due to hindered dynamics of the system. Rheological measurements revealed that rPET melt viscosity is remarkably increased in the presence of PMDA and reactive blending with rPP relevant for processing. Moreover, nanomechanical mapping of the rPP phase dispersed in the rPET matrix demonstrated the broadening of the interfacial domains after reactive blending due to the branching effect of PMDA. Findings from this study are essential for the recycling/upcycling thermoplastics through non-isothermal fabrication processes, such as extrusion and injection molding, to mitigate the lack of sorting options.

Cocrystallization of 5-fluorouracil with gallic acid: A novel 5-fluorouracil cocrystal displaying synergistic anti-tumor activity both in oral and intraperitoneal injection administration

Gallic acid (GA) is a naturally occurring polyphenolic compound exhibiting anti-tumor activity. To clarify the capability of GA in optimizing the in vitro/in vivo properties of the first line anti-tumor drug 5-fluorouracil (5-FU) and achieve synergistically enhanced anti-tumor activity, a novel cocrystal hydrate of 5-FU-GA-H2O was successfully screened and characterized based on various spectroscopic and experimental analysis including Fourier transform infrared spectroscopy (FT-IR), Raman spectra (Raman), powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), thermogravimetric (TG) and scanning electric microscope (SEM) techniques. The results suggested the existence of hydrogen bonding interactions between C=O group of 5-FU and O–H group of GA. Although the dissolution rate and solubility of 5-FU-GA-H2O cocrystal were slowed and lowered compared with that of 5-FU, respectively, the membrane permeability was enhanced for cocrystal compared with that of intact 5-FU and physical mixture (PM) of 5-FU and GA. For the cocrystal, the cumulative amount per unit area of permeated 5-FU in the first 10 h was 2.56 and 9.97 times of that of pure 5-FU and PM, respectively, in the case that transmembrane behavior of 5-FU depended on the type of solution from which the powder was dissolved. Meanwhile, improvement on oral bioavailability by co-crystallization was observed; AUC0-t of cocrystal was 2.78-fold higher than that of 5-FU. Furthermore, the cocrystal displayed a superior cytotoxic activity on 4T1 mouse breast cancer cells compared with pure 5-FU and even the PM. It was confirmed that the cocrystal solution induced higher autophagic flux than those of 5-FU and PM in 4T1 cell, suggesting that autophagy rather than apoptosis mainly mediated cell death. The obvious difference of tumor inhibition activity between PM and cocrystal in intraperitoneal injection administration indicated that some of the interactions formed in the solid cocrystal could retain in solution in some way. Benefiting from synergistic cytotoxicity, drug efficacy in vivo was enhanced through injection administration of solution from which cocrystal was dissolved.

Investigating the Effect of Curing Activators on the Cure Kinetics of Acrylonitrile–Butadiene Rubber Filled with Graphene Oxide and Reduced Graphene Oxides Nanocomposites

For the first time, acrylonitrile–butadiene rubber (NBR)–graphene oxide (GO) and reduced graphene oxide (rGO) composites were prepared without cure activators: zinc oxide/stearic acid (ZnO/SA) and studied. The vulcanization characteristics of the compounds were systematically studied at 160–190°C, with the aid of rheometer and differential scanning calorimetry (DSC) techniques. NBR revealed rapid curing time (t90) with greater cure rate index compared with NBR–GO/rGO composites for the rheometer measurement. This results were in correspondence with the activation energies Ea (kJ/mol) calculated by Ozawa and Kissinger models of vulcanization kinetics. NBR–rGO obtained reduced t90 and Ea (kJ/mol) than NBR–GO, perhaps due to lower oxygenated groups: epoxide (–C–O–C–), carboxyl (–O–C=O), and hydroxyl (–OH) present. Although, the composites delayed in curing, they significantly recorded high tensile properties with high reinforcing factors than NBR. The order of increasing mechanical properties: NBR < NBR–rGO < NBR–GO followed the same order of increasing crosslinking density. In terms of tensile strength, NBR–GO-1 obtained 62.5% and 18.2% increment than NBR and NBR–rGO-1, respectively. The findings from this study indicate that the absence of ZnO/SA in rubber compounds may slow down curing of rubber–GO/rGO composites and lower networks compared with those containing activators ZnO/SA. However, optimization of ZnO/SA and with desired functional groups on graphene and derivative graphene sheets (GDS) including other proposed factors may enhance the curing speed of rubber–GDS based systems, without compromising their mechanical integrity for advanced applications.

Thermoluminescence investigations and kinetic analysis of highly sensitive LiCaAlF6: Eu,Y phosphor for dosimetric applications

The paper presents detailed thermoluminescence characterization and kinetic analysis of highly sensitive and dosimetric grade lithium calcium aluminum fluoride doped with europium and co-doped with yttrium (LiCaAlF6:Eu,Y). It is synthesized by melt processing technique. The thermoluminescence (TL) and optically stimulated luminescence (OSL) correlation was systematically studied. The study reveals that the OSL signal is attributed to the observed TL peaks in this material. Thus, same defects are responsible for TL and OSL in LiCaAlF6:Eu,Y. Further characterization involved measurement of TL emission spectrum, OSL emission spectrum, steady state photoluminescence (PL) spectra, phosphorescence, sensitivity, fading, dose response etc. The TL sensitivity of this phosphor was observed to be ∼5 times and ∼3 times to that of CaSO4:Dy and commercially available Al2O3:C respectively. PL, TL and OSL emission spectra suggest that Eu2+ ion acts as a luminescence center in this material. Minimum measureable dose for the phosphor in TL mode was found to be 0.3 μGy with negligible fading post 10 days of irradiation. The fading of TL signal in this material is similar to the one observed for OSL signal. The thermal stability and hygroscopic nature of LiCaAlF6:Eu, Y were studied using thermogravimetric and differential scanning calorimetry techniques. Owing to the attributes like high sensitivity, wide dynamic dose range it stands as a viable and excellent phosphor material for various radiological and dosimetric applications.

Evading strength-ductility trade-off in directed energy deposited precipitation hardenable stainless steels: A pathway through precipitation kinetics modeling, design of heat treatment, and evolution of clusters

The kinetics of precipitation and austenite reversion phase transformations in an as-built arc-directed energy deposition (arc-DED) PH13–8Mo stainless steel are studied. The material in the as-built condition is analyzed using the differential scanning calorimetry (DSC) technique to determine the fraction of transformed precipitates and reverted austenite at any time/temperature during non-isothermal transformations. The Johnson-Mehl-Avrami-Kolmogorov (JMAK) kinetic equation is employed to model the transformed phase volume fraction during precipitation and austenite reversion processes. Using the non-isothermal phase transformation kinetics, an isothermal kinetics model is developed. The isothermal kinetics modeling results are then employed to design and develop direct aging heat treatments to enhance the hardness and strength of arc-DED-PH13–8Mo steel. The developed heat treatment results in the concurrent enhancement of strength and ductility in the material. Such an achievement is a result of the evolution of nano-scaled β-NiAl clusters. It appears that the formation of β-NiAl clusters increases the dislocation storage capability in the material, resulting in the evasion of the strength-ductility trade-off. The results of the current study provide great insight into the crucial role of clusters in the strength-ductility trade-off in PH stainless steels.

The role of counterion and concentration on the thermal behavior and structure of dioctadecyldimethylammonium bromide and chloride in water

Cationic dioctadecyldimethylammonium bromide and chloride (DODAB and DODAC) lipids assemble in water as unilamellar vesicles or more complex bilayer structures depending on the lipid concentration, counter-ion, solvent characteristics, etc. By using differential scanning calorimetry (DSC) and cryogenic transmission electron microscopy (cryo-TEM) techniques we investigated the structural and thermal properties of these two widely investigated molecules at 1–20 mM in water. Changes in the DSC thermogram profile indicate that DODAB bilayers undergo more structural changes than DODAC, while Cryo-TEM micrographs show that, in this range of concentration, DODAB assembles as more complex bilayer structures than DODAC, which assemble predominantly as unilamellar vesicles. These findings thus indicate that DODAC is preferable to DODAB at 1–20 mM for the preparation of unilamellar vesicles.

Melt Memory Effect in Polyethylene Random Terpolymer with Small Amount of 1-Octene and 1-Hexene Co-Units: Non-Isothermal and Isothermal Investigations.

Homo-polymers of reasonable molecular weight relax very fast in the molten state. Starting from a semi-crystalline structure, when the homo-polymer is heated up to a temperature higher than its nominal melting temperature, it relaxes quickly into a homogenous molten state. The following crystallization temperature during cooling remains constant irrespective of the melt temperature. However, the situation is evidently different in copolymers. A phenomenon named the crystallization melt memory effect denotes an increased crystallization rate during cooling after a polymer was melted at different temperatures, which is often observed. The melt temperature can be even higher than the equilibrium melting temperature of the corresponding polymer crystals. In this work, we investigated such memory effect in a polyethylene random terpolymer with a small fraction of 1-octene and 1-hexene co-units using differential scanning calorimetry techniques. Both non-isothermal and isothermal protocols were employed. In non-isothermal tests, a purposely prepared sample with well defined thermal history (the sample has been first conditioned at 200 °C for 5 min to eliminate the thermal history and then cooled down to -50 °C) was melted at different temperatures, followed by a continuous cooling at a constant rate of 20 °C/min. Peak crystallization temperature during cooling was taken to represent the crystallization rate. Whereas, in isothermal tests, the same prepared sample with well defined thermal history was cooled to a certain crystallization temperature after being melted at different temperatures. Here, time to complete the isothermal crystallization was recorded. It was found that the results of isothermal tests allowed us to divide the melt temperature into four zones where the features of the crystallization half time change.

Development of Halloysite Loaded Polypropylene Sutures with Enhanced Mechanical and Thermal Properties

Polypropylene is a crucial polymeric material in modern life, especially in the packaging and food industry, as well as the biomedical field. This study aimed to enhance the mechanical properties of polypropylene structures used as surgical suture material by preparing polypropylene-halloysite (PP-halloysite) composites. Halloysite was added in varying amounts (1%, 3%, 5%, and 10%) to polypropylene, and the resulting composites were passed through a double heated extruder. Structural characterization of the PP-halloysite composites was carried out using Fourier Transform Infrared Spectroscopy (FTIR), elemental analysis, Scanning Electron Microscopy-Energy Dispersive X-Ray Analysis (SEM-EDX), Differential Thermal Analysis (DTA), Thermogravimetric Analysis (TGA) ), and Differential Scanning Calorimetry (DSC) techniques to determine their thermal properties and softening temperatures. Mechanical tests were conducted to examine the composite suture structures obtained and determine the effect of halloysite doping on their mechanical properties. The results of the mechanical tests showed that the mechanical strength of the fiber structure increased with the amount of halloysite added. Therefore, the PP-halloysite suture structures could be used as non-melting suture material, especially in surgeries that require high strength compared to pure polypropylene structures.

Thermal and Electrical Characterization of Polyester Resins Suitable for Electric Motor Insulation

This paper undertakes the thermal and electrical characterization of three commercial unsaturated polyester imide resins (UPIR) to identify which among them could better perform the insulation function of electric motors (high-power induction motors fed by pulse-wide modulation (PWM) inverters). The process foreseen for the motor insulation using these resins is Vacuum Pressure Impregnation (VPI). The resin formulations were specially selected because they are one-component systems; hence, before the VPI process, they do not require mixing steps with external hardeners to activate the curing process. Furthermore, they are characterized by low viscosity and a thermal class higher than 180 °C and are Volatile Organic Compound (VOC)-free. Thermal investigations using Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) techniques prove their excellent thermal resistance up to 320 °C. Moreover, impedance spectroscopy in the frequency range of 100 Hz-1 MHz was analyzed to compare the electromagnetic performance of the considered formulations. They manifest an electrical conductivity starting from 10-10 S/m, a relative permittivity around 3, and a loss tangent value lower than 0.02, which appears almost stable in the analyzed frequency range. These values confirm their usefulness as impregnating resins in secondary insulation material applications.

Development of thin film coatings with polypyrrole (ppy) by physical plasma deposition technique (PAPVD) for electrochemical capacitor

In this study, new polypyrrole films (ppy) were synthesized using a physical plasma deposition (PAPVD) system; where the equipment design and methodology for plasma-assisted pyrrole polymerization were improvement. The morphology, functional groups, and thermal stability of the polymer network films were characterized by X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) techniques, respectively. The electrochemical properties of the films as capacitor were evaluated by cyclic voltammetry and electrochemical impedance spectroscopy. The results observed by SEM showed that the ppy 100W-1 and ppy 100W-2 films present uniformity in their structure. The analyses of TGA and DSC confirmed the improvement in stability; meanwhile for 100W-1 film, the presence of ppy bonds was corroborated by XPS. Plasma-activated ppy 100W-1 film exhibited higher capacitance and minor Rct resistance than that obtained for ppy 100W-2 film. The specific capacitances values of ppy 100W-1 and ppy 100w-2 films are 196 and 150 F/g in 1 M KCl. After charging and discharging tests of 1000 cycles at 5 mA cm−2 current density of ppy 100W-1 film retains 89% of its initial capacitance. Therefore, ppy 100W-1 film showed to be a promising material for use as an electrochemical capacitor.