Dynamic Scanning Calorimetry Research Articles

Isothermic and Kinetic Study on Removal of Methylene Blue Dye Using Anisomeles malabarica Silver Nanoparticles: An Efficient Adsorbent to Purify Dye-Contaminated Wastewater

Remediation of industrial discharged dyes to the water bodies is much needed in the current scenario. Here in this, we prepared silver nanoparticles using Anisomeles malabarica. The synthesized nanoparticles were characterized by Fourier transform infrared study, scanning electron microscopy, dynamic scanning calorimetry, and thermogravimetric analysis. All the characterization studies suggested that the formation of silver nanoparticles was successful. The synthesized silver nanoparticles were used as an adsorbent to adsorb the methylene blue. To achieve this, optimum pH of the adsorbent to adsorb the dye was studied, and it was found to be pH 7. The adsorbent dose to adsorb the dye was found to be 0.1 g/L. From the isotherm theoretical studies, it was found that the adsorption isotherm follows Langmuir adsorption, and the [Formula: see text] was found to be 97.08. From the kinetic study, the rate of the reaction follows the pseudosecond-order kinetics with [Formula: see text]. From the study, it was inferred the nanoparticles synthesized can act as a good adsorbent and can be used to purify the wastewater contaminated with methylene blue.

Cure mechanism and kinetic prediction of biobased glass/polyfurfuryl alcohol prepreg by model-free kinetics

This paper explains the cure reaction mechanisms of a novel bio-based glass/Polyfurfuryl prepreg using an experimental and numerical approach. It suggests optimized parameters of rapid curing for isothermal curing conditions. Dynamic scanning calorimetry (DSC) under non-isothermal conditions was used to determine parameters for the two model-free kinetic methods Friedman and Ozawa Flynn Wall. The average activation energy (88.9 ± 4.9 kJ/mol) was found to be higher than that reported for neat resin in literature. The validated models were used to gain insight into reaction mechanisms and were used to predict the evolution of reaction time under isothermal conditions for the PFA prepreg. This suggested that the curing time can be reduced to half by rapidly heating and maintaining isothermal conditions at 160°C, which provides faster curing using hot-press. In addition, dynamic mechanical analysis (DMA) was carried out to compare the manufacturer recommended cure cycle with the rapid cycle suggested.

Cationic UV Curing of Bioderived Epoxy Furan-Based Coatings: Tailoring the Final Properties by In Situ Formation of Hybrid Network and Addition of Monofunctional Monomer

Biobased monomers are becoming essential to develop green products to substitute for petroleum-based materials. In this study, biobased monomers, such as furfuryl alcohol and 2,5-furandimethanol, are successfully functionalized with epoxy functional groups producing glycidyl furfuryl alcohol (GFA) and diglycidyl furfuryl alcohol (DGFA), respectively. Herein, DGFA is investigated as an innovative cationic UV-curable monomer for coating applications. An easy tailoring of the properties of the final UV-cured coatings is demonstrated by varying the ratio of DGFA:GFA or creating a hybrid coating by using tetraethyl orthosilicate (TEOS) as a precursor of silica to form an inorganic network. Real-time Fourier transform infrared spectroscopy is used to monitor the cationic photopolymerization of DGFA formulations. Finally, glass transition, contact angle, thermal stability, and mechanical properties are investigated as a function of TEOS and GFA content in DGFA formulations. The thermal mechanical behavior is studied by dynamic mechanical thermal analysis. The thermal properties of the networks are analyzed by dynamic scanning calorimetry and thermogravimetric analysis.

Efficient One-Pot Preparation of Thermoresponsive Polyurethanes with Lower Critical Solution Temperatures.

This work reports a simple and scalable strategy to prepare a series of thermoresponsive polyurethanes synthesized via copolymerization of dicyclohexyl diisocyanate with glycerol ethoxylate in a single one-pot system. These polyurethanes exhibit lower critical solution temperatures (LCST) at 57 °C. The LCST of synthesized polyurethane was determined from Dynamic Scanning Calorimetry and UV-vis measurements. Both the LCST and Tg of synthesized polyurethane was tuned by varying the ratio between hard segment (dicyclohexyl diisocyanate) and soft segment (glycerol ethoxylate). Thus, Tg values could be tuned from -54.6 °C to -19.9 °C for samples with different flexibility. The swelling and deswelling studies were done at room temperature and above the LCST respectively. The results showed that the swelling ratio increases with the increase of soft segment (glycerol ethoxylate) in synthesized polyurethanes. Furthermore, the mechanical properties of the membrane were studied by universal tensile testing measurements. Specifically, stress at break values varied from 0.35±0.07 MPa to 0.91±0.15 MPa for the tested membranes, whereas elongation at break data ranged from 101.9±20.9 % to 192.4±24.4 %, and Young's modulus varied from 0.35±0.03 MPa to 1.85±0.19 MPa. Tensile strength of the films increased with the increase of the hard segment and elongation at break decreased.

Characterization of polymeric biomedical balloon: physical and mechanical properties

Abstract Tubes from nylon 12 and Pebax 6333 resins were produced using an extrusion process. The extruded tubes were used to produce balloons for angioplasty applications. The tubes were stretched using blow molding process to produce balloons. Melt rheology behavior for nylon 12 and Pebax were studied and nylon 12 showed a more pronounced shear thinning behavior compared to Pebax. Orientations of the tubes and the balloons were assessed using Fourier transform infrared spectroscopy (FTIR) and it was found that nylon material is more sensitive to molecular orientation when stretched compared to Pebax material. Melting behavior for the tubes and balloons were investigated using dynamic scanning calorimetry (DSC). The melting temperature shifted to higher temperatures when the tubes are stretched into balloons and the shift was more pronounced for Pebax balloon than nylon. Morphology of Pebax balloon surface revealed a hybrid structure consisting of hard segments dispersed in soft segments and amorphous phases. The hard segments are crystallized polyamides that are biaxially oriented in the balloon with higher molecular orientation in the radial direction compared to axial direction. This resulted in a higher tensile strength along the radial direction compared to axial for the balloons. Dynamic mechanical analyzer (DMA) tests showed that the glass transition temperature of the nylon tubes shifted to higher temperatures (from 51 to 82 °C) during the balloon forming process, which means the nylon becomes stiffer and less flexible when formed into a balloon.

The influence of propane and n-butane on the structure and separation performance of cellulose acetate membranes

This work presents the impact of propane and n-butane on the CO2/CH4 separation performance of both cellulose diacetate (CDA) and cellulose triacetate (CTA) membranes by exposing both pristine membranes to either propane (400 kPa) or n-butane (200 kPa) at room temperature (22 ± 2 °C) for 4 weeks. The propane and n-butane sorption isotherms in both membranes were anomalous at 35 °C. X-ray diffraction (XRD) results indicated that the crystalline nature of both polymers was altered by this exposure, although dynamic scanning calorimetry (DSC) did not detect a significant change in the overall crystallinity. Positron Annihilation Lifetime Spectroscopy (PALS) revealed that the average pore size of the CTA polymer and the number of free volume elements of both membranes also increased, even though the sorption uptake was less than 2 wt%. CO2 and CH4 permeabilities at 35 °C were essentially unaffected by the propane or n-butane exposure, indicating that while the crystalline regions of the polymer were affected, plasticization of the glassy amorphous region did not occur. There was a slight decrease in CH4 permeability for the CDA membrane after n-butane exposure, consistent with a slight decline in the CH4 solubility at this feed pressure. The propane and n-butane permeabilities were 0.029 Barrer at 300 kPa and 0.019 Barrer at 125 kPa for the fresh CTA membrane, but these fell significantly after long term exposure to these gases, possibly due to penetrant clustering.

Properties of aluminum metal matrix composites manufactured by selective laser melting

Abstract The most promising metal processing additive manufacturing technique in industry is selective laser melting, but only a few alloys are commercially available, limiting the potential of this technique. In particular high strength aluminum alloys, which are of great importance in the automotive industry, are missing. An aluminum 2024 alloy, reinforced by Ti-6Al-4V and B4C particles, could be used as a high strength alternative for aluminum alloys. Heat treating can be used to improve the mechanical properties of the metal matrix composite. Dynamic scanning calorimetry shows the formation of Al2Cu precipitates in the matrix instead of the expected Al2CuMg phases due to the loss of magnesium during printing, and precipitation processes are accelerated due to particle reinforcement and additive manufacturing. Strong reactions between aluminum and Ti-6Al-4V are observed in the microstructure, while B4C shows no reaction with the matrix or the titanium. The material shows high hardness, high stiffness, and low ductility through precipitation and particle reinforcement.

Effect of thermal exposure on carbon fiber reinforced composites used in civil infrastructure rehabilitation

In this work, characteristics related to the thermo-oxidative resistance of a wet layup ambient cured carbon-epoxy composite are investigated using dynamic scanning calorimetry, dynamic mechanical thermal analysis, and thermo-gravimetric analysis. Specimens of the unidirectional composite are exposed to temperatures between 121℃ and 232℃ for periods of time between 1 and 72 h. Initial exposure results in post-cure and enhancement of thermal characteristics whereas higher temperatures and longer periods of exposure at the higher temperatures result in deterioration. Degradation is determined through DMTA based on decreases in both peak loss modulus height and activation energy, Ea, and through TGA based on decreases in apparent decomposition activation energy, Ed, using the Coats-Redfern method. In both cases, there appears to be no deterioration within the 72 h period at the two lower temperatures of exposure, and minimal deterioration at the next two levels, whereas initiation of deterioration can be noted as early as between 8 and 16 h of exposure at the highest temperature of exposure, 232 ℃. The reaction order determined using the Kissinger method is seen to remain fairly constant except at the highest temperature level wherein drops are noted after 24 h of exposure. This provides thermal data at the materials level to guide field use within the time–temperature combinations suggesting that residual integrity can be reasonably assumed at all except the highest temperature level.

Effect of Uniaxial Stretching on Molecular Orientation, Crystallinity and Oxygen Permeability of Ethylene Vinyl Alcohol

Abstract This work studies the effects of uniaxial stretching on molecular orientation, crystallinity, crystallography and oxygen permeability of high barrier multilayer films based on EVOH barrier layer. Film samples were prepared using two different blow-up ratios (BUR) of 1 and 3. Uniaxial stretching was applied at 100°C using a tensile machine equipped with an environmental chamber. Fourier transform infrared (FTIR) spectroscopy was used to examine the molecular orientation in the EVOH layer before and after stretching and confirmed a considerable increase in the molecular orientation in the EVOH layer. Dynamic scanning calorimetry (DSC) and wide-angle X-ray diffraction (XRD) results point to the perfection of EVOH crystal structure by applying uniaxial stretching at high temperatures. Oxygen permeability results showed a considerable 25% decrease after stretching of the sample with lower BUR while a significant 80% reduction in oxygen permeability was observed for the sample prepared at higher BUR. The mechanism involved in increasing oxygen permeability due to the uniaxial stretching at high temperature is discussed in detail.

Influence of multiwalled carbon nanotubes on the structure and properties of poly(ethylene‐co‐vinyl acetate‐co‐carbon monoxide) nanocomposites

AbstractIn this work, composites of poly(ethylene‐co‐vinyl acetate‐co‐carbon monoxide) (EVACO)/surface‐modified multiwalled carbon nanotubes (m‐MWCNTs) were prepared using a solution casting technique. Acid treatment was employed for the surface modification of MWCNTs to improve the compatibility between polar EVACO and MWCNTs. The influences of m‐MWCNTs on the crystalline, mechanical, thermal, and electrical properties of EVACO at very low filler loading were systematically evaluated. The presence of m‐MWCNTs in the EVACO matrix influenced the crystallinity, and the respective changes were determined and quantified using dynamic scanning calorimetry and X‐ray diffraction. The mechanical properties of the composites were improved remarkably by the addition of a minute quantity (0.05, 0.1, 0.15, 0.2, and 0.25 wt%) of m‐MWCNTs. Additionally, m‐MWCNTs in the EVACO matrix improved the thermal stability and electrical properties of EVACO. However, the filler loading is below the threshold loading of the fillers, and there was no drastic improvement in the electrical conductivity of the composite.

Process Development for Flexible Films of Industrial Cellulose Pulp Using Superbase Ionic Liquids.

Due to environmental concerns, more attention has been given to the development of bio-based materials for substitution of fossil-based ones. Moreover, paper use is essential in daily routine and several applications of industrial pulp can be developed. In this study, transparent films were produced by industrial cellulose pulp solubilization in tetramethylguanidine based ionic liquids followed by its regeneration. Films were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), UV/Vis spectroscopy, proton nuclear magnetic resonance (1H-NMR), dynamic scanning calorimetry (DSC), thermal analysis (TG), and X-ray diffraction (XRD). Mechanical tests showed that films have a good elongation property, up to 50%, depending on ionic liquid incorporation. The influence of the conjugated acid and dissolution temperature on mechanical properties were evaluated. These results revealed the potential of this methodology for the preparation of new biobased films.

Impact of molecular structure of PP on thermo-rheological properties of polymer-modified bitumen

Polymers have been widely used to improve the performance of bitumen. Polypropylene (PP), one of the most common plastomer for bitumen modification, is utilized specially in roofing application adding up to 30 wt% to bitumen. This article presents an investigation of four different polypropylene (PP) polymers having differences in tacticity (atactic and isotactic), molecular weight (Mw ~ 12 000 g/mol and ~250 000 g/mol) and functional side groups (polar) producing modified bitumen with 5, 10 and 16 wt% polymer content, respectively. To investigate the polymers and the resulting polymer-modified bitumen (PMB) dynamical shear rheometer (DSR), dynamic scanning calorimetry (DSC) and fluorescence microscopy (FM) is performed. The aim of the study is to understand the dispersion of the polymer within the bitumen and its effect on the thermo-mechanical performance of PMB.Based on the obtained results molecular weight as well as functional side groups were identified as the key parameter affecting the dispersion behaviour of the polymer within the bitumen and, hence, the thermo-rheological properties of PMB.

High-temperature resistant polypropylene films enhanced by atomic layer deposition

Last two decades has witnessed various technical programs towards the development of new dielectric films for high temperature and high energy density capacitor technology. Yet, the organic polypropylene film still holds its top position for film capacitors required for electric and electronic power applications such as power grid, hybrid electric vehicles, oil and gas exploration, and aviation. However, its low temperature stability determined by its structural nature limits its further adoption for more rising markets. This work thus developed a creative method (ultrathin coating of inorganic compound using atomic layer deposition) to increase the high temperature stability and the dielectric strength of such a strategically important polymer film from below 105 °C to above 140 °C. Several techniques also confirmed the effective minimization of the dimensional change and crystallinity loss at higher temperatures, i.e., Thermomechanical analysis, Dynamic mechanical analysis, Dynamic Scanning calorimetry, x-ray diffraction and electron microscopy techniques. This breakthrough discovery adds a huge value to the commercial PP films and relevant capacitor industry and will extend the operation of high-performance PP film capacitors to various high standard applications.

Influence of the Presence of Disulphide Bonds in Aromatic or Aliphatic Dicarboxylic Acid Hardeners Used to Produce Reprocessable Epoxidized Thermosets.

The design of polymers from renewable resources with recycling potential comes from economic and environmental problems. This work focused on the impact of disulphide bonds in the dicarboxylic acids reactions with three epoxidized vegetable oils (EVOs). For the first time, the comparison between aromatic vs. aliphatic dicarboxylic acids, containing or not S–S bonds with EVOs was discussed and evaluated by dynamic scanning calorimetry. The obtained thermosets showed reprocessability, by the dual dynamic exchange mechanism. The virgin and reprocessed materials were characterized and the thermomechanical properties were compared. The thermosets derived from EVOs with high epoxy content combined with aromatic diacids containing disulphide bridges showed high glass transition values (~111 °C), high crosslink densities and good solvent stability.

Directing cation-cation interactions in thiamine compounds: Analysis of a series of organic salts based on vitamin B1

A series of ionic compounds based on the dicationic vitamin B1 structure have been synthesized and characterized. A set of perfluoroalkyl-based anions, each with a distinct structure, were paired with the cations and the solid-state structures of the salts were analyzed via single-crystal X-ray diffraction. Phase transitions and thermal stability of the compounds were examined via dynamic scanning calorimetry and thermogravimetric analysis. It was found that the salt of the cyclical anion, 1,3-disulfonylhexafluoropropyleneimide [NCyF]−, exhibited higher thermal stability while displaying comparable phase transition temperatures as compared to the linear anionic congeners. The cations within the [NCyF]− compound were found to interact as paired dimers, a form which is not observed in the other ionic species. Hirshfeld surface analyses supplemented with computational studies of the compounds is used to rationalize and evaluate the distinct properties of the compounds arising from changes in anion geometry.

Sustainable Additive Manufacturing: Mechanical Response of Polypropylene over Multiple Recycling Processes

The recycling of polymeric materials has received a steadily growing scientific and industrial interest due to the increase in demand and production of durable and lightweight plastic parts. Recycling of such materials is mostly based on thermomechanical processes that significantly affect the mechanical, as well as the overall physicochemical properties of polymers. The study at hand focuses on the recyclability of Fused Filament Fabrication (FFF) 3D printed Polypropylene (PP) for a certain number of recycling courses (six in total), and its effect on the mechanical properties of 3D printed parts. Namely, 3D printed specimens were fabricated from non-recycled and recycled PP material, and further experimentally tested regarding their mechanical properties in tension, flexion, impact, and microhardness. Comprehensive dynamic scanning calorimetry (DSC), thermogravimetric analysis (TGA), Raman spectroscopy, and morphological investigations by scanning electron microscopy (SEM) were performed for the different 3D printed PP samples. The overall results showed that there is an overall slight increase in the material’s mechanical properties, both in tension and in flexion mode, while the DSC characterization indicates an increase in the polymer crystallinity over the recycling course.

Effect of temperature on the heat treatment to recover green solvent from emulsion liquid membranes used in the extraction of Cr(VI)

One of the main difficulties to achieve a good performance with the emulsion liquid membranes technique for metal extraction is the solvent phase recovery. In the present work, heating is proposed as an efficient and easy method to destabilize extraction liquid membranes (ELM) used to recover Cr(VI) from wastewaters. The formulated ELM consists of sunflower oil as vegetable green solvent, PGPR and Tween 80 as surfactants, tri-n-octylphosphine oxide (TOPO) as an extractant and a sodium carbonate Na2CO3 (0.5 M) solution as the internal water phase.The effect of the temperature during demulsification process was investigated. The membrane phase was successfully demulsified by heating at 80 °C during 2 h, with a water content less than 4%. Emulsion were reformulated with recovered oil up to four times to extract Cr(VI) with an extraction efficiency (EE) up to 99 %. Physical properties of water-in-oil (W1/O) and ELMs formulated, using fresh and recovered oil, were characterized by dynamic light scattering (DLS) and multiple light scattering (MLS). Emulsions reformulated with recovered sunflower demonstrated to have not oil degradation, evaluated by dynamic scanning calorimetry (DSC) and Fourier transform infrared (FTIR), and were appropriate to form stable W1/O with high Cr(VI) removal capacity.

A facile approach to prepare cage‐ladder‐structure phosphorus‐containing amino‐functionalized POSS for enhancing flame retardancy of epoxy resins

AbstractThe cage‐ladder‐structure phosphorus‐containing amino‐functionalized polyhedral oligomeric silsesquinoxanes (CLNH2‐POSS) have been synthesized through a facile catalyst‐free hydrolytic condensation of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide‐vinyltrimethoxysilane (DOPO‐VTMS) with 3‐aminopropyl trimethoxysilane (KH540). The successful preparation of CLNH2‐POSS has been proven by the characterization of Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy (1H‐NMR, 29Si‐NMR), matrix‐assisted laser desorption ionization time of flight (MALDI‐TOF), and X‐ray diffraction (XRD). Then flame retardant (FR) epoxy resins (EPs) were prepared by the addition of different content of CLNH2‐POSS into EPs with thermal curing technology. The CLNH2‐POSS showed good solubility in EP matrix. The well‐dispersed CLNH2‐POSS contributed to thermal, mechanical, and FR properties of EP. Dynamic scanning calorimetry nonisothermal curing scans showed that CLNH2‐POSS had accelerating effect on the curing of EP. With the addition of only 3 wt% CLNH2‐POSS (0.30% phosphorus loading), the limiting oxygen index value of the EP composite increased from 25.5 of pure EP to 31.8, and vertical burning (UL‐94) V‐0 ratings was achieved. In addition, the EP composites showed improved thermal and mechanical properties. The investigations on char residue and pyrolysis volatiles of cured EP further revealed that CLNH2‐POSS exerted FR effects in condensed and gas phase simultaneously.

Increased fracture toughness of additively manufactured semi-crystalline thermoplastics via thermal annealing

Polymeric components manufactured via freeform fabrication (FFF) typically have poor inter-laminar toughness resulting from incomplete bonding across layers during production. Here we study the effect of printing and post-processing on the inter-laminar toughness of additively manufactured semi-crystalline (poly-lactide (PLA)) structures. Specimens were subject to post-print thermal annealing to promote inter-laminar bonding, while post-annealing quenching rates were chosen to vary the induced degree of crystallinity in the final structure, as characterized via dynamic scanning calorimetry (DSC). Critical elastic-plastic strain energy release rates (JIc) of annealed samples were evaluated using the single edge notched bend (SENB) geometry and post-testing fractography. The results show that as-printed PLA adopts an amorphous character with good inter-laminar toughness and ductility. Post-print annealing can double the toughness via increased interfacial wetting, but only if the material is quenched rapidly to preserve the amorphous character. In contrast, post-print annealing followed by slow cooling results in a semi-crystalline state (≈25% crystallinity) with low fracture toughness and brittle fracture behavior.

Elucidating the Role of Interfacial Hydrogen Bonds on Glass Transition Temperature Change in a Poly(Vinyl Alcohol)/SiO2 Polymer-Nanocomposite by Noncovalent Interaction Characterization and Atomistic Molecular Dynamics Simulations.

A thorough experimental investigation of polymer-glass transition temperature (Tg ) is performed on poly(vinyl alcohol) (PVA) and fumed silica nanoparticle (SiNP) composite. This is done together with atomistic molecular dynamics simulations of PVA systems in contact with bare and fully hydroxylated silica. Experimentally, PVA-SiNP composites are prepared by simple solution casting from aqueous solutions followed by its characterization using Fourier-transform infrared spectroscopy (FTIR), dynamic mechanical analysis (DMA), and dynamic scanning calorimetry (DSC). Both theoretical and experimentally deduced Tg are correlated with the presence of hydrogen bonding interactions involving OH functionality present on the surface of SiNP and along PVA polymer backbone. Further deconvolution of FTIR data show that inter-molecular hydrogen bonding present between PVA and SiNP surface is directly responsible for the increase in Tg . SiNP filler and PVA matrix ratio is also optimized for a desired Tg increase. An optimal loading of SiNP exists, in order to yield the maximum Tg increase arising from the competition between hydrogen bonding and crowding effect of SiNP.