Heating Scan Research Articles

Melting Behavior of Compression Molded Poly(ester amide) from 2,5-Furandicarboxylic Acid.

PEA 46 is a biobased polymer with promising properties for sustainable packaging applications, which can be obtained via polymerization of a furan 2,5-dicarboxylic acid (2,5-FDCA) derivative and a diol monomer containing internal amide bonds (46 amido diol). In the literature, PEA 46 showed a complex series of thermal transitions during DSC scans. For this reason, in this initial exploratory study PEA 46 was subjected to compression molding and the melting behavior of film samples was investigated with parallel DSC and WAXS analyses. At room temperature, a mesomorph phase was the only one observed. Subjecting the samples to heating scans led to the formation of phase α, caused by a sequence of partially overlapping melting and recrystallization phenomena. An additional melting and recrystallization phenomenon resulted in the development of a phase β, which melted at approximately 173 °C, the temperature after which the material was completely amorphous and isotropic. Phase α could be enhanced via thermal annealing, whereas phase β could be enhanced via a melt crystallization treatment.

Preparation of Solid Electrolytes Containing Highly Concentrated Electrolytes and Effects of Solidifying on Physicochemical Properties

Currently, safety improvements for the electrolyte of conventional lithium-ion batteries is desired owing to their apprehending accidents of firing by contained flammable organic solvents. Safety ensuring is a very important issue for the expansion of larger sizes and applications. Recently, highly concentrated electrolytes containing an extremely high concentration of electrolyte salts are drawing attention as a new electrolyte design. The highly concentrated electrolytes reported unique characteristics such as greatly improved thermal stability and expanded electrochemical window(1). However, the solvation structure of highly concentrated electrolytes remains unclear. In this study, we proposed gel polymer electrolytes (GPEs) composed of highly concentrated liquid electrolytes using chemically cross-linked polyether-based polymers. We investigated the physicochemical properties and battery characteristics of GPEs. The aim of this study is to develop an electrolyte design that improved the safety and performance of rechargeable batteries.In this study, all GPEs were prepared in an Ar-filled glovebox. LiFSA+xEC (0.8≦x≦4) liquid electrolytes (LE) were prepared by mixing EC and LiFSA, and GPEs were also prepared by LiFSA+xEC (0.8≦x≦4), polyether-based polymers (P(EO/PO = 0.8/0.2)) and DMPA as a photoinitiator, and irradiated UV for 5 min. Prepared GPEs samples were evaluated for thermal properties, ionic conductivity, and solvation structure by thermogravimetry (TG), The self-diffusion coefficients (D) and Raman spectrometric method, respectively.To analyze the solvation structure of Li+ in the highly concentrated electrolytes, Raman spectra were measured in the wavenumber range of 680-860 cm−1. Figure 1 shows the obtained Raman spectra of prepared GPEs. The observed peak was attributed to the symmetric stretching mode of FSA- anion and confirmed shift to high wavenumber with LiFSA concentration. The peak shift of FSA- was suggested for the formation of aggregate structures by change of dissociation properties to contact ion pair (bound FSA-) from separated solvent ion pair (free FSA-).Figure 2 shows the TG curves of each GPEs. TG data was obtained the heating scan rate of 10 K min-1 from 303 K to 753 K. The thermal stability of GPEs improved with LiFSA concentrations. GPEs of high Li salt concentration were suggested the formation of aggregate structure, and the strong interaction between Li+- ethylene carbonate, formed a quite strong solvation structure. In general, the aggregate structure is caused by strong interaction between lithium cation and ethylene carbonate. Also, LiFSA+xEC electrolyte solution exhibited decreasing tendency of free EC and improvement of thermal stability(2). From the above results, a change of solvation structure in GPEs was suggested to improve thermal stability. Although LiFSA+xEC electrolytes showed multiple steps of thermal weight loss processes, prepared GPEs exhibited that in one step. Therefore, proposed component materials of GPEs achieved sufficient homogeneously without phase separation and lower thermodynamic activity of the solvent.The ionic conductivity(σ) of prepared GPEs was evaluated by alternating current(AC) impedance measurements using hermetically sealed cells. AC impedance measurements were conducted by cooling from 333 K to 263 K at 10 K intervals. The temperature dependence of the σ for the electrolyte using Arrhenius-type plots is shown in Figure 3. σ decreased with LiFSA concentration. σ also increased with temperature following with VFT equation. Also, LiFSA+xEC electrolyte solution exhibited tendency of the viscosity increased with LiFSA concentration(2). From the above results, decreased of σ with increasing concentration was due to increase viscosity.The self-diffusion coefficients (D) were measured by PFG-NMR with a superconducting magnet and equipped with a pulsed-field gradient multiprobe. Figure 4 shows the self-diffusion coefficients (D GPE and D LE) of ions and EC were measured between 333 K and 303 K to evaluate the diffusion behaviors in the electrolytes of x = 4.0.The order of D is D EC > D FSA > D Li for the diluted electrolyte of x = 4.0 and increasing D GPE with temperature. D GPE decreased with solidification compared to D LE. Figure 5 also shows the D GPE of ions and EC were measured between 333 K and 303 K to evaluate the diffusion behaviors in the electrolytes of x = 0.8. D Li increased compared to the electrolytes of x=4 relatively. Also, the order of D is D Li > D EC > D FSA in highly concentrated electrolytes at 333 K.The calculated t Li of the electrolyte at 333 K is shown in Figure 6. The t Li increases with the increased LiFSA concentration. The highest t Li was obtained when x = 0.80. The significant increase in the t Li at high LiFSA concentrations reflects faster diffusion of Li+ compared with anions.[1] Y. Yamada, A. Yamada, J. Electrochem. Soc., 162(14), A2406-A2423 (2015).[2] R. Furui, et.al, J. Phys. Chem. C, 127, 10748-10756 (2023). Figure 1

LOW TEMPERATURE CRYSTALLIZATION BEHAVIOR OF NATURAL RUBBER BY DYNAMIC MECHANICAL ANALYSIS

ABSTRACT A fundamental study of low temperature crystallization of natural rubber (NR) gum polymer (raw elastomer) was conducted using dynamic mechanical analysis (DMA) in oscillatory shear rheology mode. Isothermal crystallization was followed using DMA for crystallization temperatures ranging from −15 to −35 °C, with the maximum rate of crystallization noted at −25 °C. After the isothermal crystallization (annealing) for times from 6 to 9 h, DMA heating scans revealed two melting transitions (α and β) with locations that depended on the prior annealing temperature. The locations of these melting transitions were comparable with literature results for melting peaks by differential scanning calorimetry. At temperatures above these melting transitions, we identified two additional relaxations in the DMA heating trace that did not depend on the prior crystallization history. We also found evidence of the melt memory effect in polymer crystallization, which is discussed. During annealing at −25 °C, high cis-1,4 isoprene rubber (IR) showed considerably slower and lower extent of crystallization than NR, and crosslinked NR did not show noticeable crystallization within the 12-h experiment.

Effect of nucleating agent incorporation on the crystallization and mechanical properties of polylactide/polyamide elastomer blends

ABSTRACT The widespread application of polylactide (PLA) has been limited by its slow crystallization rate and poor toughness. In the present work, a low molecular weight nucleator, TMC 301, and polyamide elastomer (PAE) were incorporated into PLA through melt blending to mediate both the crystallization capability and impact toughness. It was found that the introduction of TMC 301 decreased the crystallization temperature of PLA during the cooling process, while enhancing its cold crystallization capacity of PLA in the heating scan. Accordingly, the presence of TMC 301 shortened the half-crystallization time of PLA at 95°C in the ternary blends with minimal influence on the Avrami index. Moreover, the dispersion size of PAE decreased when the concentration of TMC 301 increased to 0.3 wt%, leading to a substantial increase in the tensile toughness and the impact strength of the PLA/PAE/TMC 301 blend. It is suggested that the size of the elastomer particles is a critical factor influencing the toughening efficiency of TMC301 in PLA/PAE blends.

Implementation of inverse method for identification of process parameters in a laser heating process

Changes in process parameters can alter the temperature data of a solid body during the laser heating process. This paper proposes an inverse method to determine the laser heating parameters, namely, sheet width, sheet thickness, laser power, and scan speed of the work specimen for the given temperature response which is assigned by the user. The method uses an analytical tool on moving heat source as a forward model capable of real-time temperature prediction of the sheet under the laser heating process. The effectiveness of the present forward model that incorporated the temperature-dependent material properties is tested by experimental findings performed on Al 6061-T6 sheets. Next, an iterative search process based on heuristic method is carried out for satisfying a prescribed temperature response by the optimization of unknown parameters. To illustrate the implementation and assess the practicality of the inverse method, two examples based on laser heating applications are used. The method proposed herein recover the unknowns for the prescribed temperature response after a few iterations, provides an efficient way to optimize the laser heating process. Additionally, the effect of measurement error on the findings of the inverse problem is addressed.

Effects of the Charge Density of Nanopapers Based on Carboxymethylated Cellulose Nanofibrils Investigated by Complementary Techniques.

Cellulose nanofibrils (CNFs) with different charge densities were prepared and investigated by a combination of different complementary techniques sensitive to the structure and molecular dynamics of the system. The morphology of the materials was investigated by scanning electron microscopy (SEM) and X-ray scattering (SAXS/WAXS). The latter measurements were quantitatively analyzed yielding to molecular parameters in dependence of the charge density like the diameter of the fibrils, the distance between the fibrils, and the dimension of bundles of nanofibrils, including pores. The influence of water on the properties and the charge density is studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and broadband dielectric spectroscopy. The TGA measurements reveal two mass loss processes. The one at lower temperatures was related to the loss of water, and the second process at higher temperatures was related to the chemical decomposition. The resulting char yield could be correlated to the distance between the microfibrils. The DSC investigation for hydrated CNFs revealed three glass transitions due to the cellulose segments surrounded by water molecules in different states. In the second heating scan, only one broad glass transition is observed. The dielectric spectra reveal two relaxation processes. At low temperatures or higher frequencies, the β-relaxation is observed, which is assigned to localized fluctuation of the glycosidic linkage. At higher temperatures and lower frequencies, the α-relaxation takes places. This relaxation is due to cooperative fluctuations in the cellulose segments. Both processes were quantitatively analyzed. The obtained parameters such as the relaxation rates were related to both the morphological data, the charge density, and the content of water for the first time.

Fungal enzyme degradation of lignin-PLA composites: Insights from experiments and molecular docking simulations

Fungal enzymes are effective in degrading various polymeric materials. In this study, we assessed the initial degradation of composites consisting of lignin-poly(lactic acid) (PLA) with both unmodified lignin (LIG) and oxypropylated lignin (oLIG) incorporated at 10 % and 40 % weight within the PLA matrix in a fungal environment. Trametes versicolor fungi were used, and the samples were treated only for eight weeks. Although there was no significant difference in weight loss, the degradation process impacted the chemical and thermal properties of the composites, as shown by Fourier transform infrared spectroscopy (FTIR) and Differential scanning calorimetry (DSC) analyses. After the degradation process, the carbonyl index values decreased for all composites and the hydroxyl index values increased for LIG/PLA and a reverse trend was observed for oLIG/PLA composites. The first heating scan from DSC results showed that the melting peak and the cold crystallization peak disappeared after the degradation process. Microscopic analysis revealed that LIG/PLA exhibited higher roughness than oLIG/PLA. Molecular docking simulations were carried out using guaiacylglycerol-β-guaiacyl ether (GGE) and lactic acid (LA) as model compounds for lignin and PLA, respectively, with laccase (Lac) enzyme for Trametes versicolor. The docking results showed that GGE had the strongest binding interaction and affinity with Lac than lactic acid and oxypropylated GGE. The oxypropylated GGE formed a shorter hydrogen bonding with the Lac enzyme than GGE and LA. The trend associated with the degradation of composites from experimental and molecular docking findings was consistent. This combined approach provided insights into the degradation process using fungi and had the potential to be applied to different polymeric composites.

Synergism between yellow mustard gum and κ-carrageenan studied by structural and rheological methods

Yellow mustard gum (YMG), a clean-label hydrocolloid with commercial potential, has been found to synergistically interact with κ-carrageenan to form a stronger gel. The primary gelation mechanism has been proposed but needs a thorough investigation and understanding from multiple techniques. In addition to the rheological methods of dynamic oscillation, this study used transient mechanical tests (stress relaxation), differential scanning calorimetry (DSC) and cryogenic scanning electron microscopy (cryo-SEM) to evaluate gel characteristics, thermal properties and microstructure of YMG-κ-carrageenan binary gels. The stress relaxation spectrum showed that the interactions between the two types of gums were mainly polymer associations. The DSC cooling and heating scans revealed that YMG did not disturb the coil-to-helix transition of κ-carrageenan but affected its helix aggregation during gel setting. The microstructure of the binary gel network captured by cryo-SEM showed a denser and more compact gel structure with smaller pores in comparison with the κ-carrageenan gel structure. All these results supported a refined gelation mechanism proposed in this study. This thorough investigation of the synergistic gelation between YMG and κ-carrageenan not only supports applications of the binary mixtures as texturizers, gelling aids and thickeners but also expands the application of YMG to promote its eventual commercialization.

Pressure Scanning Volumetry of Physically Aged Polymer Glasses, Fictive Pressure, and Memory Effect.

Physical aging of a glass decreases its volume, V, entropy, and enthalpy, H, toward the equilibrium state values. For glasses usually formed by cooling a melt, the effect is modeled in terms of non-exponential, nonlinear structural relaxation by using a plot of the heat capacity, Cp = (dH/dT)p, against T obtained from differential scanning calorimetry (DSC) cooling and heating scans. A melt becomes glass also on isothermal pressurizing and the glass formed becomes liquid on depressurizing, showing a hysteresis of the sigmoid-shape plot of -(dV/dp)T against p, which resembles the thermal hysteresis observed in the Cp against T plots. By analogy with DSC, it was named pressure scanning volumetry (PSV). Here, we use the known values of non-exponential and nonlinearity parameters β and x and volume of activation for structural relaxation time, ΔV*, of atactic poly(propylene) to investigate the effect of aging pressure, page, of aging time, tage, and of the pressurizing rate on aging features in PSV scans. The scans show a post- feature on depressurizing before the -(dV/dp)T overshoot peak appears. We provide quantitative plots (i) of the monotonic decrease of V and increase of fictive pressure, pf, with tage and (ii) of the memory (Kovacs) effect in V and pf of the polymer and (iii) provide generic plots of -(dV/dp)T against p for different combinations of β, x, and ΔV*. The study is of academic significance because PSV scans show a change in the density fluctuation response. It is of technological significance in polymer-extrusion processing and it may stimulate the commercial development of computer-controlled, high-pressure equipment.

Decrease of heat capacity on aging, long and linear extrapolations for fictive temperature, and the case of 20-million-year-old fossil-amber

A glass and its melt have the same value of a physical property at fictive temperature, Tf, which is estimated by matching the area between two linearly extrapolated plots of the heat capacity, Cp, against temperature T, one from Cp of glass and the other from that of the melt. According to the DSC heating scans, the Cp values of 20-million-year-old fossil-amber and its melt-cooled fresh-amber are the same at T < 273 K, and Tf of fossil amber is 0.89 Tg→l, where Tg→l is the glass-liquid transition temperature of melt-cooled amber [Nat. Commun. 4 (2013) 1783]. A comparison of Tf with the variation of stress relaxation time with T led to the conclusion that relaxation dynamics of amber deviates from super-Arrhenius variation. Here we show that use of the same Cps of the two ambers at T > 0 K violates basic thermodynamics, and argue that Cp of (denser) fossil-amber would be less than that of fresh-amber at T < 273 K. The Cp,confof the melt, taken as the difference between the extrapolated Cps of fossil-amber and of its melt, increases by ∼13% on cooling from T= Tg→l to T= 0.72 Tg→l, and this increase and the corresponding increase of (Cp,conf/T)= (∂Sconf/∂T)p are too small to indicate an approach towards a second-order transition of the entropy theory. Hence we conclude that deviation from super-Arrhenius variation of relaxation time of amber is an artefact of a long and linear extrapolation of its melt's Cp used for determining Tf.

Crystallization kinetics and equilibrium melting temperature of poly(ether ketone ketone) with high terephthalate content utilizing fast scanning calorimetry

Fast scanning calorimetry (FSC) was used to analyze the crystallization kinetics and determine the equilibrium melting temperature (Tmo) of KEPSTAN PEKK 8001 (PEKK 80/20) with a terephthalate to isophthalate (T/I) ratio of 80/20. Quantitative 1H, qualitative 13C and 2D HSQC NMR spectroscopy for KEPSTAN 8001 and KEPSTAN 7002 were collected to confirm linear topology and comonomer composition. Utilizing FSC, the isothermal crystallization kinetics for PEKK 80/20 are reported for the first time over a large temperature range from 200 °C to 310 °C utilizing an interrupted isothermal crystallization method. The crystallization kinetics of PEKK 80/20 exhibits parabolic behavior with the most rapid crystallization occurring at 260 °C. Compared to earlier studies of PEKK copolymers with lower T/I ratios (i.e., PEKK 70/30 and 60/40) using conventional DSC, PEKK 80/20 is observed to crystallize up to 1 to 2 orders of magnitude faster (i.e., at rates inaccessible with conventional DSC). The Tmo of PEKK 80/20 was determined utilizing the zero-entropy-production temperature (TZEP) allowing for the first time an accurate determination of the equilibrium melting temperature of 382 °C. This value was compared to a traditional Hoffman-Weeks linear extrapolation over a range of heating rates (500 K/s – 20,000 K/s) to arrest melt-reorganization upon heating. Due to unavoidable crystalline reorganization during slow heating scans with conventional DSC, this new value for Tmo using FSC is significantly higher than the commonly referenced literature value of 368 °C. The double melting peak behavior observed after isothermal crystallization of PEKK 80/20 is discussed and understood to be due to reorganization during heating at relatively slow heating rates, as commonly observed with conventional DSC.

Highly stable petroleum pitches provide access to the deep glassy state.

Differential scanning calorimetry (DSC) was used to study the fast aging behavior of two petroleum pitch materials despite being only three to five years old. We observe that these highly aromatic pitches with broad distributions of both molecular weight and aromaticity exhibit large enthalpic relaxation endotherms in initial DSC heating scans, and 20-32 °C reductions in the fictive temperature and 0.35-0.87 of θK, which are indicative of aged glasses similar to ultrastable glasses and 20 MA aged amber. Quantifying the degree of thermodynamic stability relative to the Kauzmann temperature vs. the aging time demonstrates that these materials age just as quickly as low fragility metallic glasses. Additionally, we observe that pitches age faster than polymers reported in the literature when compared using down-jump experiments. We hypothesize that the fraction of higher aromaticity of pitch molecules plays a crucial role in faster dynamics. The unique aging behavior and the ability to produce pitches in bulk quantities using pilot-scale equipment, while being possible to tailor their molecular composition, make them a useful material for studying complex aging dynamics in the deep glassy state.

Preparation of stereocomplex-polylactide powder by precipitation method for potential use as nucleating agents in fully-biodegradable poly(L-lactide) composites

In this work, low-molecular-weight poly(L-lactide)/poly(D-lactide) (LMW-PLLA/LMW-PDLA) blend solutions were precipitated as stereocomplex polylactide (scPLA) powders. The obtained scPLA powders with nearly spherical shape and particle sizes in the range of 104–610 nm showed complete stereocomplex formation and had a single melting-temperature at approximately 220 ˚C. The influence of the scPLA powder on the crystallization behavior of high-molecular-weight PLLA (HMW-PLLA) was elucidated. For this purpose, HMW-PLLA was melt blended with the scPLA powder. As investigated by non-isothermal-crystallization differential scanning calorimetry (DSC) analyses, the cold-crystallization temperature (T cc ) of HMW-PLLA upon DSC heating scans shifted to lower temperatures and the crystallization temperature (T c ) upon DSC cooling scans shifted to higher temperatures by the addition of the scPLA powder. The HMW-PLLA/scPLA powder composites exhibited a shorter half crystallization-time than pure HMW-PLLA for the isothermal-crystallization DSC analysis. The crystallinity content of HMW-PLLA/scPLA powder composites increased as the scPLA powder content increased, as revealed by X-ray diffractometry (XRD). The scPLA powders were well dispersed and had good phase-compatibility in the HMW-PLLA matrices, as determined by scanning electron microscopy (SEM). In conclusion, these fully biodegradable, non-toxic, and bio-based scPLA powders showed good potential for use as heterogeneous nucleating agents to improve the crystallization properties of PLLA bioplastic. • scPLA powders were prepared by a simple precipitation technique. • scPLA powders had nearly spherical in particle shape and showed complete stereocomplexation. • PLLA/scPLA powder bio-composites were prepared by melt blending. • scPLA powder acted as heterogeneous nucleating agents to improve PLLA crystallization.

Erosion Resistant Hydrophobic Coatings for Passive Ice Protection of Aircraft

Novel polymeric coatings, namely slippery polyurethane (SPU) coatings, with high surface hydrophobicity and superior erosion resistance against high speed solid particles and water droplets were successfully developed to protect the leading edge of fast moving aerodynamic structures, such as aircraft wings and rotor blades, against ice accretion. The coatings comprise newly synthesized surface-modifying polymers (SMPs) bearing fluorinated and polydimethylsiloxane branches at a loading level of 1–5 wt.%, based on the total resin solid, which showed good compatibility with the erosion-resistant polyurethane matrix (PU-R) and rendered effective surface hydrophobicity and slipperiness to the coatings, as evidenced by the high water contact angles of 100–115°. The coatings can be easily be sprayed or solution cast and cured at ambient temperature to provide highly durable thin coating films. X-ray photoelectron spectroscopy (XPS) investigation showed concentration of fluorine on the surface. The presence of 1–5 wt.% of SMPs in the polyurethane matrix slightly reduced the tensile modulus but had no significant impact on the tensile strength. All coating films exhibited good thermal stability with no material softening or degradation after heating at 121 °C for 24 h. DSC heating scans revealed no thermal transitions in the temperature range of −80 °C to 200 °C. Ice adhesion strength (IAS) tests using a static push rig in a cold room of −14 °C showed IAS as low as 220 kPa for the SPU coatings, which is much lower than that of PU-R (i.e., about 620 kPa). Sand erosion tests using 50 μm angular alumina particles at an impinging speed of 150 m/s and an impinging angle of 30° revealed very low erosion rates of ca. 100 μg/g sand for the coatings. Water droplet erosion tests at 175 m/s using 463 μm droplets with 42,000 impingements every minute showed no significant coating removal after 20 min of testing. The combination of the high surface hydrophobicity, low ice adhesion strength and superior erosion resistance makes the SPU coatings attractive for ice protection of aircraft structures, where the coatings’ erosion durability is of paramount importance.

Effect of Phase Separation and Crystallization on Enthalpy Relaxation in Thermoplastic Polyurethane

Being composed of alternating soft segments and hard segments, thermoplastic polyurethane (TPU) always displays complicated thermal behaviors on the heating scans, such as enthalpy relaxation, crystallization, recrystallization, and so on. The dynamics of enthalpy relaxation and the effect of phase separation and crystallization on enthalpy relaxation in TPU have been investigated by utilizing fast scanning chip calorimetry (FSC). Enthalpy relaxation takes place below Tg, whereas crystallization occurs above Tg. It turns out that the enthalpy relaxation exhibits either α-relaxation or β-relaxation behaviors at different temperature regimes as described by the Vogel–Fulcher–Tammann function or Arrhenius function, respectively. Isothermal annealing time dependency of Tg illustrates that hard segments are embedded in soft segments in the molten state and represents the degree of phase separation as well. Moreover, FSC results combined with microbeam-small-angle X-ray scattering results elucidate that phase separation and crystallization can restrain chain motion and thus affect structural relaxation. With the same crystallinity, the system crystallized at low temperature has a more pronounced effect on decelerating enthalpy relaxation due to the larger specific surface area.

Lipase-Catalyzed Poly(glycerol-1,8-octanediol-sebacate): Biomaterial Engineering by Combining Compositional and Crosslinking Variables.

This study examined poly(glycerol-1,8-octanediol-sebacate) (PGOS) copolymers with low-level substitution of O (1,8-octanediol) for G (glycerol) units (G/O ratios 0.5:0.5, 0.66:0.33, 0.75:0.25, 0.8:0.2, and 0.91:0.09) prepared in bulk by immobilized Candida antarctica Lipase B (N435) catalysis. The central question explored was the extent that exchanging less than half of poly(glycerol sebacate) (PGS) glycerol units with 1,8-octanediol can be used as a strategy to fine-tune biomaterial properties. Synthesized copolymers having G/O ratios of 0.66:0.33, 0.75:0.25, 0.8:0.2, and 0.91:0.09 have similar molecular weights, where Mw varied from 52,800 to 63,800 g/mol, Mn varied from 5100 to 6450 g/mol, and ĐM (molecular mass dispersity, Mw/Mn) values were also similar (8.4-11.4). All of the copolymers were branched, and dendritic glycerol units reached 11% for PGOS-0.91:0.09:1.0. Analysis of DSC second heating scans revealed that copolymers with higher 1,8-octanediol contents have relatively higher Tm and ΔHf values. Over the copolymer compositional range studied herein, Tm and ΔHf values varied from 5.3 to 21.1 °C and 8.0 to 23.1 J/g, respectively. Stress-strain curves of PGOS copolymers cured at 140 °C for 48 h exhibited either a unimodal, bimodal, or trimodal response to tensile loading. Varying G/O from 10:1 to 2:1 resulted in significant increases in the peak stress (0.26-4.01 MPa), preyield modulus (0.65-62.59 MPa), failure to strain (64-110%), and failure toughness (0.1-0.56 MPa). This demonstrates that altering the G/O ratio over a narrow compositional range provides biomaterials with widely different yet tunable mechanical properties. Further investigation of PGOS-0.75:0.25:1.0 films revealed that varying the cure conditions from 120 to 160 °C for periods of 24-72 h provides access to biomaterials with a failure strain range from 15 to 224% and Young's modulus from 1.17 to 10.85 MPa. Hence, using the dual variables of compositional variation and changes in cure conditions provides an exciting platform for PGS analogues to optimize material-tissue interactions. Increased contents of 1,8-octanediol slowed in vitro degradation. Slowed degradation of PGOS relative to PGS will be valuable for use in slower healing wounds.

The Importance of Nonequilibrium to Equilibrium Transition Pathways for the Efficiency and Stability of Organic Solar Cells.

Controlled morphology of solution-processed thin films have realized impressive achievements for non-fullerene acceptor (NFA)-based organic solar cells (OSCs). Given the large set of donor-acceptor pairs, employing various processing conditions to realize optimal morphology for high efficiency and stable OSCs is a strenuous task. Therefore, comprehensive correlations between processing conditions and morphology evolution pathways have to be developed for efficient performance and stability of devices. Within the framework of the blend system, crystallization transitions of NFA molecules are tracked utilizing the first heating scan of differential scanning calorimeter (DSC) measurement correlating with respective morphology evolution of blend films. Real-time dynamics measurements and morphology characterizations are combined to provide optimal morphology transition pathways as NFA molecules are shown to be released from the mixed-phase to form balanced ordered packing with variant processing conditions. Polymer:NFA films are fabricated using blade coating incorporating solvent additive or thermal annealing as processing conditions as a correlation is formulated between performance and stability of solar cells with morphology transition pathways. This work demonstrates the significance of processing condition-controlled transition pathways for the realization of optimal morphology leading to superior OSC devices.

Effect of Cooling Rate on the Oleogel Properties of Wax–Wax-Hydrolyzate Mixtures

In this contribution, the effect of cooling rates on a wide compositional range of waxes as oleogel structurants was systematically investigated. The different waxes exhibited varying levels of wax esters (WE), fatty acids (FA), fatty alcohols (FaOH) and hydrocarbons (HC) and were systematically altered by combinations of sunflower wax (SFW), bees wax (BW) and their hydrolyzed variants (SFWh, BWh). By applying slow, medium and high cooling rates, the resulting gel properties were investigated in terms of firmness, calorimetry and microstructure. It was found that the calorimetrical signal is mainly affected by the waxes’ composition. However, due to enlarged dynamic induction times upon crystallization, a shift in dissolution temperature could be observed in heating scans. In our latest work we were able to formulate the degree of homogeneity (DoH), with which it was possible to predict the undercooling in SFW mixtures. The introduction of a novel method emerged for firmness measurements of oleogels treated with the different rates. Thus, it was possible to detect with high sensitivity for all waxes for applied cooling rates, caused by modification of microstructure. Combination of different methods further elucidated that higher rates need to be applied to further scale firmness of oleogels in industrial processes.

Using Successive Self-Nucleation and Annealing to Detect the Solid–Solid Transitions in Poly(hexamethylene carbonate) and Poly(octamethylene carbonate)

Solid–solid transitions in poly(hexamethylene carbonate) (PC6) and poly(octamethylene carbonate) (PC8), denoted the δ to α transition, have been investigated, using self-nucleation and the successive self-nucleation and annealing (SSA) technique. The SSA protocol was performed in situ for thermal (differential scanning calorimetry (DSC)), structural (wide-angle X-ray scattering (WAXS)), and conformational (Fourier transform infrared spectroscopy (FT-IR)) characterization. The final heating after SSA fractionation displayed an enhanced (compared to a standard second DSC heating scan) endothermic and unfractionated peak signal at low temperatures corresponding to the δ to α transition. The improved (i.e., higher enthalpy and temperature than in other crystallization conditions) δ to α transition signal is produced by annealing the thickest lamellae made up by α and β phase crystals after SSA treatment. As thicker lamellae are annealed, more significant changes are produced in the δ to α transition, demonstrating the transition dependence on crystal stability and, thus, on the crystallization conditions. The ability of SSA to significantly enhance the observed solid–solid transitions makes it an ideal tool to detect and study these types of transitions. In situ WAXS reveals that the δ to α transition corresponds to a change in the unit cell dimensions, evidenced by an increase in the d-spacing. This implies a more efficient chain packing in the crystal, for both samples, in the δ phase (lower d-spacing at low temperatures) than in the α phase (higher d-spacing at high temperatures). The chain packing differences are explained through in situ FT-IR measurements that show the transition from ordered (δ phase) to disordered (α phase) methylene chain conformations.

Melt-Blended Multifunctional PEEK/Expanded Graphite Composites

In this work, antistatic, high-performance composites of poly (ether ether ketone) (PEEK) and concentrations of 0.5–7 vol% expanded graphite (EG) were fabricated via twin-screw extrusion and injection moulding at mould temperatures of 200°C. The morphological, electrical, rheological, thermal, mechanical, and wear properties of the composites were investigated. Scanning electron microscope (SEM) images indicate that distribution and dispersion of EG platelets in the PEEK matrix are enhanced at higher EG loadings. The electrical conductivity of the composites with 5 vol% of EG exhibits a sharp rise in the electrical conductivity range of antistatic materials because of the formation of conductive paths. The formation of a three-dimensional EG network led to a rapid increase in the storage modulus of the melt of the 2 vol% of EG-loaded composite at a frequency of 0.1 rad/s and temperature of 370°C. The neat PEEK and composites containing 0.5–5 vol% EG indicated a cold-crystallisation peak in the first heating scan of a non-isothermal differential scan calorimetry (DSC) test and their crystallinity degrees changed slightly. However, after removing their thermal and stress histories, the EG platelets promoted nucleation and increased the PEEK crystallinity remarkably, indicating that annealing of the PEEK composites can improve their mechanical performance. The neat PEEK exhibits the standard tensile and flexural stress-strain behaviour of thermoplastics, and the composites exhibit elastic behaviour initially followed by a weak plastic deformation before fracture. The addition of 5 vol% of EG to PEEK increased the tensile and flexural modulus from 3.84 and 3.55 GPa to 4.15 and 4.40 GPa, decreased the strength from 96.73 and 156.41 MPa to 62 and 118.19 MPa, and the elongation at break from 27.09 and 12.9% to 4 and 4.6%, respectively. The wear resistance of the composite containing 3 vol% EG was enhanced by 37% compared with the neat PEEK.