Dynamic Mechanical Analysis Measurements Research Articles

Strong influence of magnetic field and non-uniform stress on elastic modulus and transition temperatures of twinned Ni–Fe(Co)–Ga alloy

The magnetization value and electric resistivity of the single-crystalline sample of Ni50Fe19Co4Ga27 shape memory alloy were measured. The elastic modulus was determined by the Dynamic Mechanical Analysis (DMA). The characteristic temperatures of martensitic transformation (MT) of the alloy were estimated from the temperature dependences of magnetization, electric resistivity and elastic modulus. A significant disparity between MT temperatures resulting from DMA and those estimated from magnetic and resistivity measurements was discovered. It was argued that the discrepancy is caused by the non-uniform mechanical stressing of twinned single crystal by the DMA analyzer. Moreover, the DMA measurements revealed a significant decrease of the elastic modulus of twinned martensite under the applied magnetic field of 1.5 kOe. To explain this effect, the temperature-dependent Young’s modulus of twinned crystal lattice was computed. The computations showed that the experimentally observed field-induced change of the elastic modulus is caused by the stress-assisted detwinning of the crystal lattice by the applied magnetic field.

Influence of reactive diluent composition on properties and bio-based content of itaconic acid-based additive manufacturing materials

Among the additive manufacturing techniques, UV-curing processes are of special interest, as they allow for the fabrication of thermosetting materials with high resolutions and optical clarity. Traditionally, these processes require the use of formulations, consisting of polyester or polyurethane oligomers, combined with photoinitiators and reactive diluents. The latter are usually vinyl monomers such as acrylates or acrylamides, used to reduce the viscosity of the formulation and render it processable by additive manufacturing machines. In this work, we investigate whether a combination of diluents can be used to tune the thermomechanical properties of the printed materials, and if it can be exploited to increase their overall bio-based content without compromising their performance. To do so, a series of itaconic acid-based polyesters with different chemical structures (aliphatic–aromatic) were synthesized and formulated with reactive diluents acryloyl morpholine (ACMO) and isobornyl acrylate (IBOA). The physicochemical properties of the prepared formulations, together with their reactivity towards UV-light were assessed via photo differential scanning calorimetry (photo-DSC) and photo-rheology measurements. The same formulations were then used to fabricate test specimen via digital light processing (DLP) 3D printing, which were characterized on their thermomechanical properties by means of dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) measurements. The glass transition temperature of the printed samples reached a maximum of 98 °C, while the diluent ratio could be used to manipulate the Tg in a linear trend. All materials of this study exhibited Td,5% above 250 °C, suggesting good thermal stability. These results show that materials with a very high bio-based content (up to 85%) and very promising thermomechanical properties could be obtained by employing a diluent mixture during the formulation phase.

Influence of Crystallization Kinetics and Flow Behavior on Structural Inhomogeneities in 3D-Printed Parts Made from Semi-Crystalline Polymers.

We report the results of a study focusing on the influence of crystallization kinetics and flow behavior on structural inhomogeneities in 3D-printed parts made from polyamide 12 (PA12) and poly(lactic acid) (PLA) by dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), fast scanning calorimetry (FSC), and wide-angle X-ray diffraction (WAXD). Temperature-dependent WAXD measurements on the neat PLA filament reveal that PLA forms a single orthorhombic α phase during slow cooling and subsequent 2nd heating. The PA12 filament shows a well pronounced polymorphism with a reversible solid-solid phase transition between the (pseudo)hexagonal γ phase near room temperature and the monoclinic α' phase above the Brill transition temperature TB = 140 °C. The influence of the print bed temperature Tb on structure formation, polymorphic state, and degree of crystallinity χc of the 3D-printed parts is investigated by height and depth-dependent WAXD scans and compared with that of 3D-printed single layers, used as a reference. It is found that the heat transferred from successive layers has a strong influence on the polymorphic state of PA12 since a superimposed mixture of γ and α phases is present in the 3D-printed parts. In the case of PLA, a single α phase is formed. The print bed temperature has, in comparison to PA12, a major influence on the degree of crystallinity χc and thus the homogeneity of the 3D-printed parts, especially close to the print bed. By comparing the obtained results from WAXD, DMA, DSC, and FSC measurements with relevant printing times, guidelines for 3D-printed parts with a homogeneous structure are derived.

Vinyl methyl oxazolidinone as reactive diluent to overcome the solubility limitations of highly polar unsaturated polyesters

AbstractVinyl methyl oxazolidinone (VMOX®) is studied as a new reactive diluent (RD) for highly polar unsaturated polyesters (UPs). Molecules with special structure properties are extensively investigated as components for unsaturated polyester resins (UPRs) and thermosets, particularly for high‐temperature applications. Special diols with a cyclic structure like isosorbide and tricyclodecanedimethanol or special diols with side groups like 2‐methyl‐2‐propyl‐1,3‐propanediol and 2‐ethyl‐2‐butyl‐1,3‐propanediol can provide interesting properties. Bio‐based diols such as isosorbide and 1,3‐butanediol improve the sustainability profile. However, UPs based on such special diols have a higher polarity, limiting their solubility in styrene. This demands a RD, which provides adequate solubility and is suitable for high‐temperature applications. Therefore, our study compares the solubility of highly polar UPs based on special diols in styrene and VMOX®. UPs with different formulations, polarities, and Hansen parameters were synthesized and characterized. The solubility sphere of styrene was determined experimentally with the synthesized UPs. The influence of the special diols on the thermoset properties was investigated in dynamic mechanical analysis measurements. In conclusion, VMOX® as a RD enables full utilization of special diols properties due to the wide solubility window. Moreover, a new class of high‐temperature styrene‐free UP resin was developed.

Copolymerization of pyrrole and carbazole onto polyester textile.

The purpose of this study was the polymerization of carbazole (Cz), pyrrole (Py) and copolymerization of them onto polyester (PES) textile with chemical oxidative method by using FeCl3. First, in order to determine the optimum conditions, the effect of polymerization steps, the immersion order of the PES to the oxidant and monomer solutions, time, monomer, oxidant, and surfactant concentrations and types on the conductivities of PES/PCz composite were investigated and at this conditions, conductive composite, PES/P[Py-co-Cz] was obtained. The highest conductivities were obtained as 12.4 mS/cm and 9.0 mS/cm for PES/PCz and PES/P[Py-co-Cz], respectively. Further characterization of PES/P[Py-co-Cz] was performed by conductivity, FTIR, scanning electron microscopy (SEM), and dynamic mechanical analysis (DMA) measurements, and results were compared with PES/PCz and also PES/PPy. The presence of Py and Cz in the same polymer chain created synergy and improved the conductivity and mechanical properties of the composite.

Mechanical, Rheological, and Heat Seal Properties of 1‐Octene Grafted Low Density Polyethylene Films

AbstractHeat seal and mechanical properties of 1‐octene grafted low density polyethylene films containing various concentrations of Dicumyl peroxide as the initiator and 1‐octene grafting agent is investigated through using experimental measurements. The results of differential scanning calorimeter (DSC) measurements revealed that the melting temperature shifts to higher values and the peak of the DSC curve becomes wider with the increase of 1‐octene concentrations. Thermogravimetric analysis (TGA) revealed a higher thermal stability up to 20 °C for 1‐octene grafted PE compared with neat LDPE alloy. The results of stress–strain measurements revealed that the 1‐octene grafted PE alloys has higher tensile strength in comparison with neat PE alloy and samples containing only DCP initiator. The results of heat seal analysis indicated that both DCP initiator and 1‐octene tended to offer a moderate increase peel strength of PE alloy. DMTA measurements for various grafted PE alloys show a higher damping factor in comparison with neat LDPE alloy. Rheological measurements indicated a higher storage modulus up to 25% and higher complex viscosity for grafted PE samples containing 1‐octene comonomer.

Dynamic mechanical properties of graphene and carbon fabric‐reinforced epoxy nanocomposites

AbstractThe present work attempts to estimate the impact of graphene and carbon fabric on the dynamic‐mechanical properties of epoxy nanocomposites with different weight percentages. By applying an oscillatory force to a composite, its response is measured, and by calculating the viscosity and the stiffness in relation to the temperature, time, or frequency, valuable information can be realized. It helps to identify “thermal transitions” occurring in polymers. The complex modulus shows the resistance of the composites to deformation caused by viscous and elastic effects. Though dynamic mechanical analysis (DMA) is used for the depiction of temperature‐dependent viscoelastic properties, in this investigation, the objectives were multi‐fold. It is aimed at understanding the role of carbon fabric and the incorporation of 1 wt% of graphene nanoplatelet (GNP) in the epoxy matrix, and the effect of 0.5 to 5 wt% of GNP. The dynamic mechanical properties, including storage modulus, loss modulus, and damping factor, are examined across a temperature range of 25–250°C. Based on the findings, the storage modulus of the composites exhibits a range between 2000 and 9000 MPa. Notably, the epoxy composite containing 1 wt% GNP filler demonstrates the highest storage modulus. The details of mechanisms involved in DMA measurement are schematically summarized.Highlights Epoxy‐GNP and Epoxy‐GNP‐carbon fabric composites were fabricated. Storage modulus of composites does not show much dependence on the GNP. An increase in storage modulus by 05 times is observed in the ECG1 composite. The loss modulus of EC and EG1 composite is much higher.

Viscoelastic materials are most energy efficient when loaded and unloaded at equal rates.

Biological springs can be used in nature for energy conservation and ultra-fast motion. The loading and unloading rates of elastic materials can play an important role in determining how the properties of these springs affect movements. We investigate the mechanical energy efficiency of biological springs (American bullfrog plantaris tendons and guinea fowl lateral gastrocnemius tendons) and synthetic elastomers. We measure these materials under symmetric rates (equal loading and unloading durations) and asymmetric rates (unequal loading and unloading durations) using novel dynamic mechanical analysis measurements. We find that mechanical efficiency is highest at symmetric rates and significantly decreases with a larger degree of asymmetry. A generalized one-dimensional Maxwell model with no fitting parameters captures the experimental results based on the independently characterized linear viscoelastic properties of the materials. The model further shows that a broader viscoelastic relaxation spectrum enhances the effect of rate-asymmetry on efficiency. Overall, our study provides valuable insights into the interplay between material properties and unloading dynamics in both biological and synthetic elastic systems.

High Durability of Pemion® Proton Exchange Membranes in Cross-Pressure Accelerated Mechanical Stress Tests

Polymer electrolyte membrane fuel cells (PEMFC) are the dominant technology for hydrogen-powered fuel cell electric vehicles in clean transportation systems. To be suitable for commercialization and applicability in real-world use-cases, light and heavy-duty fuel cell vehicles require lifetimes of over 8,000 and 30,000 hours, respectively [1]. Hence, enhancing the durability of all fuel cell components, particularly the proton exchange membrane (PEM), is of great importance.Recently, fuel cell membranes based on hydrocarbon (HC) chemistries have become increasingly common in the literature [2]. Materials with polyaromatic backbones, tunable electrochemical properties, and low reactant permeability are increasingly seen as potential alternatives to incumbent perfluorosulfonic acid (PFSA) materials [2]. Additionally, as restrictions on the use of fluorinated materials in various industries continue to grow, the importance of HC chemistries will as well. Sulfo-phenylated polyphenylenes (sPPPs) are a particular class of HC materials that show promise [3]. However, the phase separation between hydrophilic and hydrophobic domains within sPPPs may not be as discrete as in PFSAs [3], requiring higher ion exchange capacity (IEC) values than PFSAs to achieve similar protonic conductivity. High IEC typically results in greater material hydrophilicity, which can render membranes dimensionally unstable in a fuel cell [4].State-of-the-art commercial PEMs are now manufactured as thin films (≤ 18 µm), offering small ohmic loss and therefore high fuel cell performance. To improve dimensional stability and eliminate the risks of electrical shorting, PEMs are commonly mechanically reinforced using a porous, inert, and non-ionic substrate, such as expanded polytetrafluoroethylene (ePTFE). In a work by Miyake et al. [5], sulfonated polyphenylene-based ionomer membranes with flexible polyethylene mechanical reinforcement were prepared and the results indicated promising mechanical properties and improved longevity in RH cycling tests. However, there is still a lack of data about the fatigue durability of HC membranes in the literature, and evaluating and comparing the mechanical durability of numerous PEMs with a mechanical reinforcement layer in a traditional wet-dry cycling accelerated stress test would be a time-consuming and thus costly process [6].In our previous work, [7] we combined constant pressure differential across an ePTFE-reinforced perfluorosulfonic acid (PFSA) ionomer membrane with in-situ RH cycles (ΔP-AMST) to simulate the actual mechanical stresses in the fuel cell environment, while accelerating the durability testing for reinforced PEMs. In this study, ΔP-AMST is used to benchmark the fatigue lifetime curves for Pemion® membranes and compare it with a commercial reinforced PFSA-based PEM. The test temperature was set to 90 °C, and dry and wet (90% RH) phases were 60s and 30s, respectively. The hardware and semi-MEA specifications used for the test are shown in Figure 1a-c. A semitransparent polycarbonate spacer plate with 20 mm thickness and a circular aperture (25.4 mm) in the middle was used to allow free expansion of the membrane (Figure 1d). The cathode side was pressurized to create a cross pressure between the two sides and intensify the stress on the membrane during the RH cycling process. The ultimate failure of the membrane is shown in Figure 1e. The radial stress at the center of the deformed membrane is estimated by Hencky’s solution, as reported in our previous work [7]. Figure 1f demonstrates the estimated nominal stress on the membranes as a function of their lifetimes in terms of RH cycles. According to the fatigue S-N curves, reinforced Pemion® membranes afford longer lifetime than incumbent PFSA materials if the membrane edges are well protected. In addition, the impact of IEC on the fatigue durability of Pemion® membranes is investigated and the results are evaluated against stress of dehydration and dynamic mechanical analysis measurements. Acknowledgements This project was financially supported by Natural Sciences and Engineering Research Council of Canada (NSERC), Ionomr Innovations Inc, Canada Foundation for Innovation (CFI), British Columbia Knowledge Development Fund (BCKDF), Western Economic Diversification Canada (WD), and Canada Research Chairs (CRC).

Luminescent Hybrid BPA.DA-NVP@Eu2L3 Materials: In Situ Synthesis, Spectroscopic, Thermal, and Mechanical Characterization.

A series of homogeneous hybrid BPA.DA-NVP@Eu2L3 materials were obtained through an in situ approach where the luminescent dopant was formed at the molecular level with different contents (0.1; 0.2; 0.5; 1; and 2% by weight). A Europium(III) complex (Eu2L3) with quinoline-2,4-dicarboxylic acid was applied as a luminescence additive while a polymer matrix consisted of a combination of bisphenol A diacrylate (BPA.DA) and N-vinylpyrrolidone (NVP) monomers. Synthesis steps and the final materials were monitored by NMR and Fourier transform infrared spectroscopy (FTIR). The emission, excitation spectra, lifetime, and quantum yield measurements were applied for the determination of the photophysical characteristics. The thermal and mechanical properties of the obtained materials were tested via thermal analysis methods (TG/DTG/DSC and TG-FTIR) in air and nitrogen atmospheres, dynamic mechanical analysis (DMA), and hardness and bending measurements. Generally, even a small addition of the metal complex component causes changes in the thermal, mechanical, and luminescent properties. Hybrid materials with a greater europium complex content are characterized by a lower stiffness and hardness while the heterogeneity and the flexibility of the samples increase. A very small amount of an Eu2L3 admixture (0.1% wt.) in a hybrid material causes an emission in the red spectral range and the luminescence intensity was reached for the BPA-DA-NVP@1%Eu2L3 material. These materials may be potentially used in chemical sensing, security systems, and protective coatings against UV.

Preparation and properties of polyetherimide fibers based on the synergistic effect of carbon nanotubes and ionic liquids

AbstractPolyetherimide (PEI) has been widely applied in the form of plastics, films, and foam materials. But PEI fiber is confronted with some challenges, such as high melt viscosity and high spinning temperature during the spinning process, poor mechanical properties because of its amorphous structure. In this study, ionic liquids (ILs) and carbon nanotubes (CNTs) were used to prepare PEI composite fibers (PEI/CNT‐IL) successfully, which were further characterized by scanning electron microscope (SEM), Raman spectra, differential scanning calorimetry, dynamic mechanical analysis, thermalgravimetric analysis, mechanical property, and conductivity measurements. IL showed a plasticizing effect to reduce the processing temperature of PEI and SEM images showed that CNTs were uniformly dispersed in the PEI matrix by the assistance of IL. The synergistic effect of CNT and IL thus improved the tensile strength and antistatic properties of PEI fibers. When the contents of CNT and IL were 0.5 and 1.0 wt%, respectively, the optimal properties were obtained. PEI/CNT‐IL fibers exhibited a maximum tensile strength of 2.0 cN/dtex with the elongation at break being 90%, and the enhanced electrical conductivity of 10−5 S·cm−1, which was increased by 13 orders of magnitude compared to that of pristine PEI fiber.Highlights PEI composite fibers were prepared via melt spinning with the assistance of IL and CNT. IL can effectively disperse CNT and plasticize PEI to reduce the processing temperature. The synergistic effect of CNT and IL has improved the tensile strength and antistatic properties of PEI fibers.

Thermal softening properties of various wood species within an annual ring

Dynamic mechanical analysis (DMA) measurements of water-saturated earlywood (EW) and latewood (LW) of various wood species in the temperature range from 0 to 100 °C were focused to clarify the differences in thermal softening properties within an annual ring. The following results were obtained. The peak of tanδ caused by micro-Brownian motion of lignin was observed in both EW and LW all species. For softwoods, the peak temperatures of tanδ of EW appeared at higher temperatures than those of LW. For hardwoods, in the other hand, the peak temperatures of tanδ were slightly different between EW and LW in the diffuse-porous wood, whereas the temperatures were almost the same in the ring-porous wood. It was found that the difference in peak temperature of tanδ between EW and LW varied greatly among species. The difference in peak temperature between EW and LW was relatively large for softwoods. In addition, the thermal softening properties both in the radial and tangential directions differed depending on the species, so this suggested that there was anisotropy in the thermal softening properties depending on the species.

UV-Curing Additive Manufacturing of Bio-Based Thermosets: Effect of Diluent Concentration on Printing and Material Properties of Itaconic Acid-Based Materials.

In the quest toward sustainable thermosets, research has been conducted on various polymer classes like epoxy, benzoxazines, acryl-/methacrylates, etc. One particular group that can also be utilized as sustainable inks for additive manufacturing is itaconic acid-based unsaturated polyester resins. However, due to increased viscosity of the resins, the use of reactive diluents is required to increase their processability. While research has focused on creating different polymeric structures to expand the possible applications, the required amount of diluent has not received equal attention. In this work, a group of itaconic acid-based polyesters was synthesized to create a series of formulations with different reactive diluent contents. The physicochemical properties of the prepared formulations, along with their reactivity toward UV light, were assessed via photo-differential scanning calorimetry (photo-DSC), real-time attenuated total reflectance (RT-ATR), and photorheology measurements. The same formulations were then used to fabricate test specimens via digital light processing (DLP) three-dimensional (3D) printing, which were examined as to their thermomechanical properties by means of dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) measurements.

Phase-Separated Structure of NBR/PVC Blends with Different Acrylonitrile Contents Investigated Using STEM-EDS Mapping Analysis.

We investigated the phase-separated structure of nitrile butadiene rubber (NBR)/polyvinyl chloride (PVC) blends with different acrylonitrile (AN) contents in the NBR, using dynamic mechanical analysis measurements and scanning-transmission-electron-microscopy (STEM)-energy-dispersive-X-ray-spectroscopy (EDS) elemental analysis. Two separate sharp tan δ peaks were observed in the blend at the lower AN content of 18.0%, whereas a broad peak was observed in the blends with the higher AN contents of 29.0 and 33.5%, due to the increase in miscibility, as expected from the decrease in the solubility parameter difference with the increasing AN content. The STEM-EDS elemental analysis for the concentration distribution showed that the NBR was mixed in the large PVC domains with a diameter of several micrometers, and the excluded PVC existed around the interface of the domain-matrix phases in the blend with the lower AN content, whereas small domains with a diameter of several tens of nanometers were dispersed in the blend with the higher AN content. The concentration difference in PVC between the PVC domain and the NBR matrix became smaller with increasing miscibility as the AN content increased although the blends contained the same PVC content of 40 wt%.

Self‐healable, weldable, and reprocessable castor oil‐based poly(thiourethane‐urethane) networks

AbstractVegetable oil‐based polyurethane (PU) vitrimer is of significance for sustainable industrial development; however, development of vegetable oil‐based PU vitrimers with high mechanical properties and excellent malleability by a facile synthetic process remains a challenge. Herein, a series of versatile, self‐healable, weldable, and recyclable castor oil‐based poly(thiourethane‐urethane) networks are constructed by one‐pot reactions. Double bonds and hydroxy groups in castor oil can react with thiol in 2,2′‐(1,4‐phenylene)‐bis[4‐mercaptan‐1,3,2‐dioxaborolane] (BDB) and isocyanate in 4,4′‐diphenylmethane diisocyanate (MDI), respectively, as well as a reaction between the thiol of BDB and the isocyanate of MDI, which gives the castor oil‐based poly(thiourethane‐urethane) vitrimers. The obtained bio‐based networks are characterized by Fourier transform infrared (FTIR) and dynamic mechanical analysis (DMA) measurements. The castor oil‐based vitrimers show high thermostability (T5d > 312°C) due to the incorporation of rigid BDB and MDI with benzene group in the networks. Meanwhile, the castor oil‐based networks have been proved to possess more excellent functions in self‐healing, welding, shape memory, and reprocessing capabilities at moderate temperatures due to the dynamic boronic ester bonds. This work would be beneficial to developing of versatile vegetable oil‐based poly(thiourethane‐urethane) materials through a facile approach.

Phenoxy resin-based vinylogous urethane covalent adaptable networks

This work presents a post-polymerization approach to the preparation of vitrimers, exploiting the transamination of vinylogous urethane in linear phenoxy resins. Phenoxy vitrimers are obtained by a two-steps synthesis from a commercial phenoxy resin via partial conversion of hydroxyl groups to acetoacetates (AcAc), followed by network formation by reaction with m-xylylendiamine as crosslinker. Three different vitrimers with variable crosslinking density are obtained by tuning the density of AcAc moieties along the phenoxy resin scaffold (5%, 10% and 15% conversion of hydroxyl groups). The conversion of linear polymers to dynamic crosslinked networks is confirmed by dynamic mechanical thermal analyzer and rheology measurements, followed by stress relaxation tests to investigate the kinetics of bond exchanges. Tensile tests as a function of reprocessing cycles reveal an increase of the maximum elongation and stress at break and prove the good recyclability of the vitrimers. Enhanced adhesive properties compared to pristine phenoxy resins are demonstrated, including the possibility to thermally re-join the assembly after its mechanical failure. Finally, the solvent-free preparation of vitrimers is explored at 5% crosslinking density via melt reactive blending, providing a valuable alternative to the less environmentally sustainable synthesis in solution.

Effect of Molecular Organization on the Properties of Fractionated Lignin-Based Thiol-Ene Thermoset Materials.

In this study, the combination of sequential solvent fractionation of technical Kraft lignin was followed by allylation of most OH functionalities to give highly functional thermoset resins. All lignin fractions were highly functionalized on the phenolic (≥95%) and carboxylic acid OH (≥85%) and to a significant extent on the aliphatic OH moieties (between 43 and 75%). The resins were subsequently cross-linked using thiol-ene chemistry. The high amount of allyl functionalities resulted in a high cross-link density. Dynamic mechanical analysis measurements showed that the thioether content, directly related to the allyl content, strongly affects the performance of these thermosets with a glass transition temperature (Tg) between 81 and 95 °C and with a storage modulus between 1.9 and 3.8 GPa for all thermosets. The lignin fractions and lignin-based thermosets' morphology, at the nanoscale, was studied by wide-angle X-ray scattering measurements. Two π-π stacking interactions were observed: sandwich (≈4.1-4.7 Å) and T-shaped (≈5.5-7.2 Å). The introduction of allyl functionalities weakens the T-shaped π-π stacking interactions. A new signal corresponding to a distance of ≈3.5 Å was observed in lignin-based thermosets, which was attributed to a thioether organized structure. At the same time, a lignin superstructure was observed with a distance/size corresponding to 7.9-17.5 Å in all samples.

Development, physicochemical characterization and in vitro evaluation of chitosan-fish gelatin-glycerol hydrogel membranes for wound treatment applications.

Chitosan and fish gelatin, two natural polymers, coupled with glycerol, were used to develop hydrogel membranes. The membrane properties of the prepared membranes, have been improved after heat treatment, leading to materials with ameliorated mechanical performance and lower degradation rate. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and x-ray diffraction (XRD) tests were conducted to study the interactions between the biopolymers and the plasticizer. Biopolymers and plasticizer interact via secondary interactions with all plasticized materials being amorphous. Scanning electron microscopy (SEM) was used to evaluate the morphology of the materials and showed that increase in fish gelatin concentration leads to rougher surface morphologies. Dynamic mechanical analysis (DMA) measurements and tensile testing, indicated that increase in fish gelatin concentration leads to improved mechanical performance and in particular in terms of maximum strain at break as well as stress at break. Water absorption and degradation rates were found to be fully dependent on fish gelatin concentration as expected. Antimicrobial testing via the measurement of an inhibition zone, as well as ,endothelial cell attachment and proliferation results (in vitro endothelial cell colonization tests) indicate that the hydrogel membranes show promising potential for use in wound healing/care applications (protection against bacteria, providing a moist environment, etc.).

Effect of airborne particle abrasion treatment of two types of 3D-printing resin materials for permanent restoration materials on flexural strength.

This study aimed to assess the effects of airborne-particle abrasion (APA) on the flexural strength of two types of 3D-printing resins for permanent restoration. Two types of 3D printing resins (urethane dimethacrylate oligomer; UDMA, ethoxylated bisphenol-A dimethacrylate; BEMA) constituting different components were printed. The specimen surfaces were subjected to APA using 50 and 110µm alumina particles under different pressures. The three-point flexural strength was measured for each surface treatment group, and a Weibull analysis was performed. Surface characteristics were analyzed via surface roughness measurements and scanning electron microscopy. Dynamic mechanical analysis and nano-indentation measurements were limited to the control group. The three-point flexural strength according to the surface treatment was significantly lower in the UDMA group for large particle sizes and at high pressures; the BEMA group demonstrated low flexural strength for large particle sizes regardless of the pressure. After thermocycling, the flexural strengths of UDMA and BEMA significantly decreased in the group subjected to surface treatment. The Weibull modulus and characteristic strength of UDMA were higher than those of BEMA under different APA and thermocycling conditions. As the abrasion pressure and particle size increased, a porous surface formed, and the surface roughness increased. Compared with BEMA, UDMA featured a lower strain, greater strain recovery, and a negligible increase in modulus according to strain. Thus, surface roughness increased with the sandblasting particle size and pressure of the 3D-printing resin. Hence, a suitable surface treatment method to improve adhesion can be determined by considering physical property changes.

Molecular mobility of liquid crystalline polyurethanes modified by polyhedral oligomeric silsesquioxanes

Molecular mobility and liquid crystalline order formation of liquid crystalline polyurethanes (LCPU) modified by trisilanolphenyl-POSS was investigated by using dielectric spectroscopy (DRS), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Hybrid materials with 2, 4 and 6 wt% of POSS load were studied. Small-angle X-ray scattering (SAXS) results suggested that the nanoscale morphology was not significantly altered by the introduction of POSS into the LCPU matrix. The presence of liquid crystal phase transitions was confirmed by both DRS and DSC measurements. Dielectric study showed changes in relaxation steps and conductivity in the LC transitions region due to a shift in phase order. Using partially cross-linked POSS particles, an enhancement of the material's rubber modulus was observed in the DMA measurement. Deterioration in charge transfer was observed for the composites, which was attributed to the crosslinking nature of the silsesquioxane used. Further, dynamic calorimetric studies in different cooling rates were performed for detailed study of liquid crystalline transitions. In summary, it was found that the addition of POSS causes a nucleation effect and does not impair LC phase formation.