DSC Heating Research Articles

A crude, cold-pressed oil from elderberry (Sambucus nigra L.) seeds: Comprehensive approach to properties and characterization using HPLC, DSC, and multispectroscopic methods

The physicochemical characterization of fresh, undiluted, cold-pressed oil from elderberry seeds (EO) is presented. The results showed EO's uniqueness for the 93 % presence of essential fatty acids, including linoleic n-6 (41 %), α-linolenic n-3 (38 %), and oleic n-9 (13 %) acids with favorable ratios for human nutrition, n-3/n-6 = 0.93. A γ-tocopherol is the dominant tocopherol (96 %), with a concentration of 20.62 mg/100 g, indicating low oil oxidative stability. DSC heating and cooling traces determined the thermal properties. These results also revealed the presence of metastable triacylglycerol (TAG) structures composed of polyunsaturated fatty acids. The presence of characteristic groups for fatty acids and TAGs in EO was confirmed by FTIR-ATR spectra. For the first time, Langmuir monolayer studies on EO revealed its low compressibility, indicating its low emulsifiability, and the presence of minor components of EO, including tocopherols, phenolic acids, polyphenols, flavonoids, and carotenoids, was determined using UV–Vis absorption and fluorescence excitation-emission matrix (EEM) along with the chemometric method.

Lead-free semiconductor materials with high phase transition temperature: [1-Methylimidazole][SbBr4]

Semiconductor with structure phase change is a special multi-functional material, which plays an important role in the field of Solar Energy, information computing, sensor technology, artificial intelligence, etc. In this paper, the organic–inorganic lead-free semiconductor phase change material [1-Methylimidazole][SbBr4] (1) was successfully constructed. The IR, TGA, DSC, VT-PXRD, solid-state UV–vis spectroscopy and temperature dependence of dielectric constant were characterized and analysed. Single crystal X-ray diffraction shows that at 298 K, the space group is P21/c, the point group 2/m; an endothermic and exothermic peak appeared near 386 K and 367 K in the DSC heating–cooling cycles. Near the corresponding phase transition temperature point, compound 1 exhibits a significant reversible change in the dielectric platform. Interestingly, the band gap of compound 1 is about 2.53 eV. The existence of such interesting physical properties is closely related to the interaction between cations and anions in the molecule and the connection of internal hydrogen bonds. By constructing organic–inorganic hybrid semiconductor materials, we hope to obtain semiconductor materials with phase transition properties and actively explore and provide some ideas and support for the application of new high-tech materials.

Ageing Characteristics of Stir Cast AZ 61 Alloy with Minor Additions

Background: Knowing that magnesium (Mg) alloys and its composites bear the potential of being used simultaneously for light structural as well as biomedical applications, it appears prudent to look for developing a novel Mg alloy; the concurrent demand is to monitor recent trend in development of functional Mg-alloy and its composite materials through extensive patent search. Review of recent patents in the related field makes it relevant to investigate this aspect. Objective: The authors aim to study the evolution of structure and properties in stir cast of AZ- 61 alloy with minor additions of scandium, calcium and manganese. This paper reports the results of this investigation. Methods: The castings are prepared by stirring the molten alloy at 600 rpm for 10 minutes, followed by pouring into a preheated metal mould. The solidified alloys are homogenized at 550°C for 12 hours. The homogenized alloys are then subjected to solutionising treatment at 500°C for 5 hours; subsequently, the alloys are quenched in iced water. The quenched alloys are subjected to ageing treatment at different temperatures between 100°C to 400°C at an interval of 100°C. Similar experiments are conducted with its statically cast counterparts. The structure and properties of all the samples have been characterized by optical and scanning electron microscopy, and XRD analysis; DSC heating run is conducted to study the kinetics of phase transformation. Mechanical behaviour of castings is studied with the aid of tensile testing and fractography. Moreover, tribological behaviour of alloys is assessed by wear testing with the help of pin on disc method. Results: The results show that the stir cast alloy produces a homogeneous structure with significant improvement in properties. The precipitates of Mg17Al12, Al Mn, Mg Zn2, Al2 Ca and Mg2 Ca are formed due to the ageing of both stir cast and statically cast alloy. It is found that the diffusion of Al in magnesium controls the precipitation process. The tribological properties are found to be satisfactory for the stir cast alloy. Conclusion: The modified AZ61 alloy with minor additives, achieves excellent structural homogeneity and mechanical properties after stir casting followed by quench ageing.

Extending the Physical Functionality of Bioactive Blends of Astrocaryum Pulp and Kernel Oils from Guyana

Natural lipids with nutritional or therapeutic benefits that also provide desired texture, melting and organoleptic appeal (mouthfeel, skin feel) are difficult to procure for the food and cosmetics industries. Natural Astrocaryum pulp oil (AVP) and kernel fat (AVK) from Guyana were blended without further modification to study the potential of extending the physical functionality of the blends beyond that of crude AVK and AVP. An evaluation of non-lipid components by ESI-MS indicated twenty-four (24) bioactive molecules, mainly carotenoids (90%), polyphenols (9%) and sterols (1%) in AVP, indicating important health and therapeutic benefits. Only trace-to-negligible amounts of these compounds were detected in AVK. The thermal transition phase behavior, solid fat content (SFC), microstructure and textural properties of five AVP/AVL blends were used to construct phase diagrams of the AVK/AVP binary system. Binary phase diagrams constructed from the cooling and heating DSC thermograms of the mixtures and description of the liquidus line indicated a mixing behavior close to ideal with a tendency for order, with no phase separation. Melting onsets, solid fat content and measurements of solid-like texture all predictively increased with increasing AVK content. The descriptive decay parameters obtained for SFC, crystal size, hardness, firmness and spreadability were similar and predictive and indicate the way the binary system structure approaches that of a liquid or a functional solid. The bioactive content of the blends was accurately calculated; the work provides a blueprint for the blending of AVP and AVK to deliver targeted bioactive content, stability, spreadability, texture, melting profile, organoleptic appeal and solid content. SFCs at 20 °C ranged from 9.1% to 39.1%, melting onset from −17.5 °C to 27.8 °C, hardness from 0.1 N to 3.5 N and spreadability from 3.3 N·s to 147.1 N·s; indicating a useful dynamic range of physical properties suitable for bioactive oils to bioactive butters.

The effect of water sorption on the calorimetric signature of aging in DGEBA epoxies

Epoxies hygrothermally aged in the relatively benign environment of a climate controlled experimental laboratory display a broad endothermic signature which extends from as much as 40 °C below the glass transition temperature, Tg, to over 100 °C above Tg upon an initial DSC heating ramp of an open pan. This is in addition to a shift in Tg to lower temperature associated with plasticization and the relatively sharp endothermic peak just above Tg that is characteristic of physical aging. All of these features are erased by the first heating to well above Tg and are not seen in subsequent heating ramps. The association of the broad endothermic peak with desorption of water from the polymer is demonstrated through systematic investigations of hydrothermally aged samples. The area of the desorption peak is proportional to the absorbed mass of water with a cumulative specific heat equal to the heat of vaporization of water (40 ± 4 kJ/mol). For typical equilibrium water saturation in epoxy (∼ 0.04 g water/g epoxy at room temperature and 100% relative humidity), this amounts to ∼80 J/g epoxy and is many times the enthalpy of the physical aging peak in the laboratory aged samples (∼2 J/g). Consequently, moisture desorption is a major contributor to calorimetric thermograms of aged epoxies, and disentangling desorption endotherms from other aging signatures is key to quantifying the role of each mechanism at play. Similarly, plasticization associated with moisture sorption must be considered when aging environments are not dry in order to avoid mis-associating observed Tg depressions with other mechanisms such as chain scission.

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.

Energy-releasing and phase transitions of Ti-based bulk metallic glass composites during heating

The energy-releasing and phase transitions of Ti-based bulk metallic glass composites (BMGCs) during heating largely remain elusive. Here, the effects of cooling rates and compositional changes on energy-releasing and phase transitions of two BMGCs containing relatively stable β-Ti crystals or metastable β-Ti crystals are investigated. With decreasing the cooling rates, both BMGCs transform from non-equilibrium BMGCs to quasi-equilibrium BMGCs. Moreover, decreasing the Co content reduces the phase stability of β-Ti. DSC heating, isothermal ω-Ti precipitates in β-Ti crystals before Tg, and as the temperature above Tx, the glass matrix undergoes crystallization. With decreasing the cooling rates, both the relaxation and crystallization enthalpies decrease, but which can be significantly enhanced by decreasing the Co content, suggesting that BMGCs with unstable β-Ti dendrites are of better energy-releasing properties. These findings not only reveal the energy changes and phase transitions of BMGCs during heating, but also promote their practical applications as energy-releasing materials.

The influence of poly(maleic anhydride - co - vinyl acetate) on polylactide/wood flour/calcium carbonate composites

In this paper, polylactide (PLA)/wood flour (WF)/calcium carbonate (CC) composites with different content of poly(maleic anhydride -co- vinyl acetate) (PMAVA) were prepared. PMAVA was obtained by radical solution polymerization and identified by FTIR. The torque - time curves showed that the balance torques of PLA/WF/CC composites with PMAVA were improved by the adding of PMAVA. SEM photographs showed that after the addition of PMAVA, the compatibility and interfacial adhesion between the filler (CC or WF) and PLA in each composite were increased. DSC heating curves showed that two cold crystallization temperature (Tcc) peaks appeared in each PLA/WF/CC composite, and the Tcc peak at high temperature and Tm peak in the composite containing PMAVA were split into two peaks, showing that the effects of WF and CC on the crystal of PLA were uncorrelated, and the presence of PMAVA decreased the crystal integrity of PLA. The tensile test results showed that the tensile strength and modulus of the composite were increased with the addition of PMAVA, and the composite with 0.5 wt% of PMAVA owned the best tensile performance. The hydrolysis results showed that the use of low content of PMAVA in the composite was beneficial to improve its hydrolysis rate.

Crystallization and melting of unentangled poly(ε-caprolactone) cycles containing pendants.

The Rouse model provides a basic framework to understand the chain dynamics of polymers, which is confirmed to be more suitable for exploring the linear dynamics of unentangled polymers. The crystalline morphology governed by chain dynamics and crystallization kinetics is expected to differ in linear and cyclic polymers. Cyclic poly(ε-caprolactone)s (c-PCLs) containing two bi-anthracenyl group pendants with molecular weights close to the critical molecular weight (Mc) were synthesized to investigate the chain dynamics based crystallization and melting behavior by DSC, POM, and in situ simultaneous small-angle X-ray scattering/wide-angle X-ray scattering (SAXS/WAXS) investigations during heating of the isothermally crystallized samples. Double endothermic peaks were observed in the DSC curves with a low heating rate of c-PCLs without entanglement after isothermal crystallization, especially for c-PCLs with Mc. The structure evolution of the crystalline structures observed from the in situ investigations during the heating and double endothermic peaks in DSC heating curves of the c-PCLs indicate the role of pendants in the chain dynamics, which leads to the reorganization of the metastable structures. Banded spherulites of c-PCL without entanglement were observed for the first time, and the uneven growth of spherulites along the radial direction may be caused by the mismatch between chain dynamics and crystallization kinetics.

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.

Crystallization and thermal stability of Ni-based metallic glass with high tungsten and boron

Non-isothermal crystallization behavior of the amorphous (Ni51W31.6B17.4)75Co25 alloy with high tungsten and boron content was investigated. Continuous heating DSC analyses of the amorphous samples revealed that the alloy undergoes crystallization with three-step. The thermal stability and crystallization kinetics of the samples were evaluated by Lasocka, Kissinger and Ozawa approaches. Activation energy calculated for the first crystallization step showed that the thermal stability of the NiCoWB alloy is higher than other Ni-based alloys. Avrami exponent value calculated for the early stage of the Niss-phase crystallization indicated a three-dimensional diffusion-controlled mechanism with increasing nucleation. The continuous heating transformation diagram plotted according to non-isothermal analyzes is consistent with the phases detected in isothermal heat treatments. The usability of the continuous heating transformation diagram of the alloy in isothermal heat treatment applications has been demonstrated.

The Thixoforming Process Window for Al-Si-Zn Alloys Using the Differentiation Method: The Role of Si, Heating Rate and Sample Mass

The effects of Si content (X = 4 to 7 wt.%), heating rate (5 to 25 °C/min) and sample mass (20 to 200 mg) on determination of the thixoforming working window by differential scanning calorimetry DSC were analyzed for the Al-Xwt.%Si-4wt.%Zn, or simply AlXSi4Zn, system. The critical lower and upper temperatures for thixoforming processing were determined by applying the differentiation method to DSC heating cycle data. Lower Si content, heating rate and DSC sample mass made identification of the working window temperatures more accurate because of the sharpening of the DSC curve when lower values of these variables were used. Data obtained when lower sample masses and heating rates were used agreed better with those obtained by Calculation of Phase Diagrams, (CALPHAD) simulation (near-equilibrium Scheil condition) for all the Si contents analyzed. Larger DSC sample masses were associated with significant heterogeneity in heat transfer through the sample, leading to results similar to those for a diffuse transition, an effect enhanced by an increase in the heating rate. Since Si content represented a limitation when identifying the working window by the differentiation method, alloys with high Si content should be analyzed with lower DSC masses and lower heating rates to allow more accurate determination of the interval at conditions near those used in thixoforming operations.

Influence of Cooling Rate on Ice Crystallization and Melting in Sucrose-Water System

The ice crystallization and melting in systems where the equilibrium state is difficult to reach is one of the growing areas in pharmaceutical freeze-drying research. The quality of the final freeze-dried product depends on the parameters of the cooling step, which affect the ice nucleation and growth. In this paper, we present a DSC study of ice crystallization and melting in a sucrose-water system. Using two different types of thermal cycles, we examine the influence of cooling and heating rates on the thermal behavior of sucrose-water solutions with water contents between 50 and 100 wt%.The DSC results show that low cooling rates provide crystallization at higher temperatures and lead to lower amount of non-freezing water. Consequently, the glass transition and ice melting properties observed upon heating depend on the cooling conditions in the preceding step. Based on the experimental results, we investigate the reasons for the existence of the two steps on DSC heating curves in sucrose-water systems: the glass transition step and the onset of ice melting. We show that diffusion of water can be the limiting factor for ice growth and melting in the sucrose-water system when the amorphous phase is in a liquid state. In particular, when the diffusion coefficient drops below 10−14 m2/sec, the ice crystals growth or melting becomes strongly suppressed even above the glass transition temperature. Understanding the diffusion limitations in the sucrose-water system can be used for the optimization of the freeze-drying protocols for proteins and probiotics.

Study on mechanism of starch phase transtion in wheat with different moisture content

Using Bainong 365 wheat starch as raw material, starch samples were preheated in a RVA to simulate DSC heating profiles. The thermodynamic properties, long-range orderliness, short-range orderliness, and structure of wheat starch were determined by DSC, XRD, FTIR, LF-NMR and SEM to explore the phase transformation mechanism of Bainong 365 wheat starch at different water contents. The results show that at different moisture contents, when the endothermic transition temperature of starch samples determined by DSC was reached or exceeded, the enthalpy of starch was 0, all free water was converted into uneasy flowing water and bound water, and the surface structure of starch was severely damaged. At this time, starch was completely gelatinized, but the short-range and long-range ordered structures of starch determined by FTIR and XRD still existed and gradually decreased with increasing temperature. Therefore, it was concluded that the temperature range of the starch endothermic transition does not represent the temperature range of complete gelation of starch, and the structure destroyed by complete gelation of starch may not be simple short-range and long-range ordered molecular structures.

Novel Co-crystals and Eutectics of Febuxostat: Characterization, Mechanism of Formation, and Improved Dissolution.

Co-crystallization studies were undertaken to improve the solubility of a highly water-insoluble drug febuxostat (FXT), used in the treatment of gout and hyperuricemia. The selection of co-crystal former (CCF) molecules such as 1-hydroxy 2-naphthoic acid (1H-2NPH), 4-hydroxy benzoic acid (4-HBA), salicylic acid (SAC), 5-nitro isophthalic acid (5-NPH), isonicotinamide (ISNCT), and picolinamide (PICO) was based on the presence of complementary functional groups capable of forming hydrogen bond and the ΔpKa difference between FXT and CCF. A liquid-assisted grinding (LAG) method was successfully employed for the rapid screening of various pharmaceutical adducts. These adducts were characterized based on their unique thermal (differential scanning calorimetry) and spectroscopic (Fourier transform infrared and Raman spectroscopy) profiles. Binary phase diagrams (BPD) were plotted to establish a relationship between the thermal events and adduct formed. Powder X-ray diffraction (PXRD) studies were carried out to confirm the formation of eutectic/co-crystal. Thermogravimetric analysis (TGA) was also performed for the novel co-crystals obtained. The propensity for strong homo-synthons over weak hetero-synthons and strong hetero-synthons over weak homo-synthons during supramolecular growth resulted in the formation of eutectics and co-crystals respectively. FXT:1H-2NPH (1), FXT:4-HBA (1), FXT:SAC (1, 2), and FXT:5-NPH (2-1) gave rise to pure eutectic systems, while FXT:ISNCT (2-1) and FXT:PICO (1) gave rise to novel co-crystals with characteristic DSC heating curves and PXRD pattern. Additionally, the impact of microenvironmental pH and microspeciation profile on the improved dissolution profile of the co-crystals was discussed. Graphical Abstract.

Study of thermoplastic elastomer synthesis, characterization, crystallization based on crystallizable amide segment contains conducting moiety

Thermoplastic elastomers (TPE'S) with a conducting moiety are made from Poly (tetramethylene oxide), hard segments TΦT, and sodium salt of Dimethyl-5-isothalate (DM5SIS). In the synthesis procedure, different mole percentages of the conducting moiety DM5SIS are used to see if the presence of salt affects the polymerization process and, as a result, the crystallinity of the hard segment. The synthesis of the polymer is confirmed using the 1H NMR method. The produced polymer had an inherent viscosity of 2.4–3.6 dl/g, indicating that the polymer had a high molecular weight. FT-IR techniques were used to determine the crystallinity of the hard segment in the copolymers, which revealed that the hard segment is entirely crystallised (>90%). The crystallinity is extremely reversible, according to a temperature-dependent IR investigation. The synthesised segmented copolymers DSC heating curve revealed two transitions: Tm of soft segment (SS) and melting of hard segment (HS). These materials have a very low undercooling value (about 20 °C), implying that the hard segment will crystallise quickly. The segmented copolymer that was created was clear, had a high molecular weight, and contained crystalline HS. Because the addition of a conducting moiety to the polymer chain has no effect on the polymerization process or the crystallinity of the hard segment, the polymer could be a good option for proton exchange membranes in fuel cells.

Cold crystallization event on DSC heating curves of bitumen

Cold crystallization event on DSC heating curves of bitumen

Temperature Dependent Stress–Strain Behavior and Martensite Stabilization in Magnetic Shape Memory Ni51.1Fe16.4Ga26.3Co6.2 Single Crystal

The superelastic properties and stress-induced martensite (SIM) stabilization have been studied in a shape memory Ni51.1Fe16.4Ga26.3Co6.2 single crystal. The single crystal, characterized by a thermally induced forward martensitic transformation temperature around 56 °C in the initial state, has been submitted to compression mechanical testing at different temperatures well above, near and below the martensitic transformation (MT). After each mechanical test, the characteristic MT temperatures and the transformation enthalpy have been monitored by means of differential scanning calorimetry. At temperatures below MT, the stress–strain (σ–ε) curves show a large strain, around 6.0%, resulting from the detwinning process in the martensitic microstructure, which remains accumulated after unloading in the detwinned state of the sample as a typical behavior of the shape memory alloys (SMAs). After just two “σ–ε + heating” cycles the accumulation of strain was not observed any more indicating the formation of a two-way shape memory effect which consists in a spontaneous recovery of the aforementioned detwinned state of the sample during its cooling across the forward MT. Whereas the thermally induced shape recovery in conventional SMAs occurs at the fixed value of the reverse MT temperature, the heating DSC curves of the mechanically deformed martensite in the present work show a burst-like calorimetric peak at the reverse MT arising at temperatures essentially higher than the thermally activated one. This behavior is the result of the SIM stabilization effect. After a short thermal aging in the stress-free state, this effect almost disappears, showing a slight impact on the MT characteristic temperatures and the enthalpy. At temperatures higher than the transformation one, the SIM is not stabilized, as the mechanically induced martensite fully retransforms into austenite after the unloading. From the σ–ε curves, the critical stress, σc, as well as the values of Young’s moduli of martensite and austenite are determined showing linear dependences on the temperature with a slope of 3.6 MPa/°C.

Preparation and Characterization of Fluorine-Containing Polybenzoxazole Composite Films including Graphene Oxide as a Reinforcing Material

The fluorine-containing polyhydroxyamide (F-75-PHA) was synthesized by using low-temperature solution polycondensation of 2,2-bis(3-amino-4-hydroxyphenyl) hexafluoropropane (BAHHFP, 75 mol%) and 3,3′-dihydroxybenzidine (DHB, 25 mol%) with terephthaloyl chloride (TPC) in N-methyl-2-pyrrolidinone (NMP) without metal salts. The F-75-PBO (polybenzoxazole)/GO (graphene oxide) composite films with different GO contents (0.01, 0.1, and 1.0 wt%, respectively) were prepared by heat-treatment of their precursors (F-75-PHA/GO composite films), and the effects of reinforcing material (GO) on the structural, thermal, and mechanical properties of them were studied systemically. FE-SEM images that the F-75-PBO matrix and GO sheets had a superior hydrogen bonding interaction and formed a three-dimensional (3D) network structure in composite films having a great bendability. FT-IR spectra indicated that the incorporation of GO in composite films could be reacting hydroxyl (−OH) groups on F-75-PHA matrix to carboxyl (−COOH) and/or −OH groups in GO sheets, and thus the O-H stretching peak (23.8 %) for F-75-PHA/GO-0.1 composite film mostly disappeared in comparison with that (100 %) of F-75-PHA film. DSC heating curves revealed that the thermal cyclization temperature (Tc) of the F-75-PHA/GO composite films decreased with an increment of GO content. Interestingly, for F-75-PHA/GO-0.1 composite film, the Tc decreased by up to 254 °C. However, despite the outstanding reinforcing effect of GO sheets, an interesting phenomenon was confirmed that 3D network structure including an excellent hydrogen bonding interaction did not largely influence the mechanical properties of F-75-PBO/GO composite films.

Effect of thermal annealing on crystal evolution and multiple melting behaviors of molded poly(L-lactic acid) and poly(butylene succinate) blends upon heating investigated by TMDSC

The influence of post-process annealing treatment on the structural and thermal behaviors of poly(L-lactic acid)/poly(butylene succinate) (PLLA/PBS) blend was investigated by temperature modulated differential scanning calorimetry (TMDSC) and wide-angle X-ray diffractometry. It is shown that the low-order α′-structure of PLLA was formed in the as-molded samples and the molded products annealed at the temperatures below the melting of PBS, whereas the high-order α-crystal was developed when the high temperature of annealing (152 °C) was applied. With the addition of poly(ethylene glycol) plasticizer to the blends, the formation of high-order α-structure was prohibited. During the DSC heating scan, the α′- to α-crystalline phase transformation did not occur. The evidence of multiple melting behaviors observed by TMDSC was ascribed to the simultaneous melting, recrystallization, and remelting of the PLLA and PBS crystals in the blends.