Fast Scanning Chip Calorimetry Research Articles

Combining fast scanning chip calorimetry and nanoindentation: Young's modulus and hardness of poly (l-lactic acid) containing α′- and α-crystals

Fast scanning chip calorimetry (FSC) allows subjecting polymer melts to well-defined vitrification, crystal nucleation, and crystal growth pathways and, therefore, precise control of morphologies, from fully amorphous glassy states to semicrystalline structures containing perfect crystals. Due to the required use of nanogram-sized samples, needed to achieve high cooling rates, their mechanical properties, in order to establish structure-property relations, are difficult to assess. In this work, indentation modulus and indentation hardness of FSC samples are successfully determined on example of semicrystalline poly (ʟ-lactic acid) (PLLA) containing spherulitically grown disorder α′- or rather perfect α-crystals, with the correctness of the applied preparation and analyses routes confirmed by nanoindentation measurements on milligram-sized samples prepared through hotstage microscopy, and by applying both static single-step and quasi-continuous stiffness measurements. Modulus and hardness data are consistent with prior analyses of bulk samples, confirming that semicrystalline PLLA containing α-crystals exhibits around 10–20 % higher values of these properties compared to PLLA containing α′-crystals, related to the different molecular-chain packing in the crystal lattice. This work demonstrates that combination of FSC and nanoindentation techniques is an effective tool for determining mechanical properties of samples solidified at specific thermal pathways which otherwise cannot be realized.

Isothermal crystallization of polyethylene droplets within the self-nucleated isotactic polypropylene matrix of a 70/30 iPP/PE immiscible blend via fast scanning chip calorimetry (FSC)

The escalating volume of waste related to polyolefins poses recycling challenges. Given the mixed composition of the post-consumer feedstock, studying blends of virgin polyolefins is a fruitful strategy to simulate such compositions. For the first time, this study investigates crystallization, self-nucleation (SN), and kinetics of a 70/30 iPP/PE blend, characterised by a "sea-island" morphology, using fast scanning calorimetry (FSC). Preliminary experiments on different chip sensors proved the technique's sensitivity and representativeness for polymer blends, even with minimal sample quantities. Application of the self-nucleation thermal protocol (employing fast scanning rates, from 500 to 1000 °C/s) to the iPP matrix phase revealed insights into the characteristic SN domains. The crystallization kinetics of PE-dispersed droplets within a SN iPP matrix was also investigated. Results indicate a 30 °C crystallization window for PE droplets within the self-nucleated iPP matrix, expanding the understanding of crystallization rates (up to four decades) compared to standard DSC measurements.

Detecting reorganization in semicrystalline polymers during heating: Insights from Fast Scanning Chip Calorimetry coupled with real-time optical microscopy

Thermal behavior of semicrystalline polymers is notoriously complex due to the metastable nature of polymer crystals. This complexity is evidenced in the multiple melting endotherms frequently observed in the heating traces of various plastics, a phenomenon known as ‘multiple melting behavior’. Extensive research indicates that calorimetric analysis alone may not suffice to fully elucidate the processes occurring during thermal experiments. In this study, we introduce an experimental setup that integrates Fast Scanning Chip Calorimetry, or nanocalorimetry, with real-time polarized optical microscopy. This combination enables in-situ morphological observations during rapid heating/cooling experiments. The setup not only complements thermal analysis but also rivals the capabilities of fast in situ X-ray scattering experiments conducted at synchrotron sources. Our findings show that the obtained data help in identifying melting/recrystallization processes and, therefore, enable the determination of the critical heating rate above which reorganization processes during heating are kinetically bypassed. This ensures that the thermal events detected in calorimetric curves are exclusively due to the initial sample structure, without being influenced by any reorganization that may occur during the heating process.

Controlling conjugated polymer morphology by precise oxygen position in single-ether side chains.

Recently, polar side chains have emerged as a functional tool to enhance conjugated polymer doping properties by improving the polymer miscibility with polar chemical dopants and facilitate solvated ion uptake. In this work, we design and investigate a novel family of side chains containing a single ether function, enabling the modulation of the oxygen atom position along the side chain. A meticulous investigation of this new polymer series by differential scanning calorimetry, fast scanning chip calorimetry and X-ray scattering shows that polymers bearing single-ether side chains can show high degree of crystallinity under proper conditions. Importantly, due to a gauche effect allowing the side chain to bend at the oxygen atom, the degree of crystallinity of polymers can be controlled by the position of the oxygen atom along the side chain. The further the oxygen atom is from the conjugated backbone, the more crystalline the polymer becomes. In addition, for all new polymers, high thermomechanical properties are demonstrated, leading to remarkable electrical conductivities and thermoelectric power factors in rub-aligned and sequentially doped thin films. This work confirms the potential of single-ether side chains to be used as polar solubilizing side chains for the design of a next generation of p- and n-type semiconducting polymers with increased affinity to polar dopants while maintaining high molecular order.

Crystallization Kinetics of Ethylene Vinyl Alcohol Copolymer Revealed by Fast Scanning Chip Calorimetry Analysis

Crystallization Kinetics of Ethylene Vinyl Alcohol Copolymer Revealed by Fast Scanning Chip Calorimetry Analysis

Poly (butylene succinate): Low-temperature nucleation and crystallization, complex morphology and absence of lamellar thickening

Melt-crystallization of poly (butylene succinate) (PBS) at largely different melt-supercooling was analyzed by X-ray scattering techniques, direct imaging using microscopy, and by fast scanning chip calorimetry, with the latter employed to achieve high melt-supercooling. Crystallization at 100 and 20 °C, representing structure formation at low and high melt-supercooling, respectively, yields lamellae with thicknesses of around 8 and 4 nm. In both cases, lamellar thickening is excluded as main mechanism of isothermal secondary crystallization, suggesting that absence of intracrystalline chain-sliding diffusion is not dependent on the absolute value of the thickness of lamellae. The wide-angle X-ray pattern of PBS crystallized at low temperature shows less and broader peaks than in case of PBS crystallized at high temperature, pointing to presence of crystal defects, and causing an enlargement of the unit cell. Secondary crystallization leads to an increase of the melting temperature, being distinctly larger (per unit annealing time) for low-temperature crystallized PBS. Since lamellar thickening is absent, and imperfection of the bulk crystal structure persists even on long-term annealing, merging of crystalline blocks and lateral crystal growth at the crystallization temperature, for explaining the observed increases of the crystallinity and melting temperature, are suggested. Though there is detected a large rigid amorphous fraction in PBS crystallized at high supercooling, vitrification only occurs continuously on cooling, after the isothermal crystallization process.

Equilibrium Melting Temperature of the Hexagonal Crystals of Polybutene-1 and Its Copolymer

TheLamellar structures of form I in polymorphic isotactic polybutene-1 (iPB-1) and forms I and I′ in butene-1/ethylene random copolymer (iPB-1/C2) were investigated by studying their melting behavior using the combination of small-angle X-ray scattering (SAXS) and fast scanning chip calorimetry (FSC) techniques. Hexagonal form I was transformed from tetragonal form II obtained by crystallization of a homogeneous melt of iPB-1 and iPB-1/C2. Hexagonal form I′ was crystallized directly from a heterogeneous melt of iPB-1/C2. Despite the same hexagonal crystallographic structure, forms I and I′ have obviously distinct melting behaviors due to different ways of crystal formation. Well-defined linear dependences of the melting temperature against the reciprocal lamellar thickness were observed for forms I and I′ with frozen chain mobility in crystals. The slopes of the thus obtained melting lines for forms I and I′ are different. Their extrapolations to imaginary infinitely large lamellar thickness provide the equilibrium melting temperature Tm∞ for forms I and I′, which is associated with the stability of the lamellar crystals. In spite of crystal defects in form I′, a higher Tm∞ is observed for this form in iPB-1/C2 than Tm∞ for form I in both iPB-1 and iPB-1/C2. The difference in Tm∞ indicates a less perfect structure of form I crystal lamellae that is caused by the fragmentation of form II crystal lamellae during the polymorphic phase transition from form II to I. The lamellae broke into crystal blocks along the lamellar direction. The smaller lateral sizes of the fragmented lamellae clearly induce a decrease in the stability of crystals, as expressed in a lower Tm∞ for form I.

Influence of Molecular Weight on the Nucleation and Growth of Different Crystal Forms in Isotactic Polypropylene: In Situ Synchrotron Microfocus X-Ray Scattering Combined with Fast-Scanning Chip Calorimetry Investigations

The molecular weight (Mw)-dependent formation of mesophase and the α phase of isotactic polypropylene (iPP) was explored by utilizing in situ synchrotron microfocus X-ray scattering measurements combined with a portable fast-scanning chip calorimetry (FSC) technique. A phase diagram illustrating the relationship between the lamellar long spacing (dac) and crystallization as well as melting temperatures of three iPP samples with different molecular weights suggests that a common crystallization line was shared by the mesophase of all three samples, whereas three different crystallization lines were observed for these iPP samples. Furthermore, unlike in the case of the α phase where the melting lines were significantly different from their crystallization lines, the melting line of the mesophase was found to overlap with its crystallization line. The results indicate that the crystallization of the α phase satisfied the multistage crystallization model in which an intermediate layer is suggested to be generated prior to the formation of native crystallites. The Mw-independent formation of the mesophase demonstrated that the nucleus size did not rely on the Mw of iPP because the final sizes of the mesophase were close to the initial nuclei sizes. The larger difference of the lamellar long spacing presented in the α phase of iPP with different Mw indicated that the growth from nuclei to crystallites was significantly influenced by the Mw.

The effect of POSS-NH2 and POSS-PEG on the crystallization kinetics of poly (l-lactic acid) by traditional DSC and fast scanning chip calorimetry

The effect of POSS-NH2 and POSS-PEG on the crystallization kinetics of poly (l-lactic acid) by traditional DSC and fast scanning chip calorimetry

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.

The bulk enthalpy of melting of α’-crystals of poly (l-lactic acid) determined by fast scanning chip calorimetry

Related to the wide scatter of information in the literature, recently the bulk enthalpy of melting of α-crystals of poly (l-lactic acid) (PLLA) has been re-determined by correlating the crystallinity-dependent heat capacity at a temperature slightly higher than the glass transition temperature and the corresponding enthalpy of melting [Macromol. Rap. Comm. 2022, 43, 2200148], using fast scanning chip calorimetry (FSC). For α-crystals, a value of 104 J/g is suggested, valid at 190 °C. Here, the initial study is expanded such to obtain the bulk enthalpy of melting of PLLA α’-crystals, containing conformational defects and forming at lower crystallization temperatures than the α-phase. Samples containing different amount of α’-crystals were generated by varying the time of isothermal crystallization at 90 °C. Extrapolation of the obtained relationship between the heat capacity at the crystallization temperature, that is, the crystallinity, and the enthalpy of melting on subsequent fast heating, suppressing the transition into α-crystals and simplifying therefore the analysis of the melting process of the formed α’-crystals, toward fully crystallized PLLA yields a bulk enthalpy of melting of 72 J/g at the thermal stability limit of α’-crystals of 150 °C. The used experimental approach to obtain the bulk enthalpy of melting of polymer crystals relies on the presence of a two-phase structure/absence of a glassy rigid amorphous fraction at the temperature of analysis of the crystallinity via the heat capacity (90 °C). Annealing experiments slightly below the analysis temperature support this assumption by absence of enthalpy-recovery peaks on subsequent heating.

Bulk Enthalpy of Melting of Poly(l-lactic acid) (PLLA) Determined by Fast Scanning Chip Calorimetry.

The bulk enthalpy of melting of α-crystals of poly (L-lactic acid) (PLLA) is evaluated by fast scanning calorimetry (FSC), by correlating the melting enthalpy of samples of different crystallinity with the corresponding heat capacity at 90 °C, that is at a temperature higher than the glass transition temperature of the bulk amorphous phase and lower than the melting temperature. Extrapolation of this relationship for crystals formed at 140 °C towards the heat capacity of fully solid PLLA yields a value of 104.5±6 J g-1 when melting occurs at 180-200 °C. The analysis relies on a two-phase structure, that is, absence of a vitrified rigid amorphous fraction (RAF) at the temperature of analysis the solid fraction (90 °C). Formation and vitrification of an RAF are suppressed by avoiding continuation of primary crystallization and secondary crystallization during cooling the system from the crystallization temperature of 140 °C to 90 °C, making use of the high cooling capacity of FSC. Small-angle X-ray scattering (SAXS) confirmed thickening of initially grown lamellae which only is possible if these lamellae are not surrounded by a glassy RAF. Linear crystallinity values obtained by SAXS and calorimetrically determined enthalpy-based crystallinities agree close to each other.

Crystallization behavior of impact copolymer polypropylene revealed by fast scanning chip calorimetry analysis

The crystallization behaviors of two impact copolymer polypropylenes (ICP) were investigated by using fast scanning chip calorimetry (FSC) and micro-focus wide-angle X-ray diffraction (WAXD) techniques. Different crystallization peaks of these two samples during cooling were observed at cooling rates from 50 to 4000 K/s. For ICP-A, the crystallization of polypropylene (PP) matrix into α crystallites, polyethylene (PE) sequences in ethylene-propylene segmented copolymer (EsP), PP segments in ethylene-propylene block copolymer (EbP), and PP matrix into mesophase successively occurred from high to low temperatures. As the cooling rate increased, the crystallization of PP matrix into α crystallites, PP segments, and mesophase were suppressed one by one. Nevertheless, the crystallization of PE segments was hardly suppressed. For ICP-B, it showed almost the same crystallization behavior as ICP-A, except for the absence of independent crystallization peak of PP segments. The different crystallization performance in these two samples could be ascribed to their different chain microstructures.

Pressure- and Temperature-Dependent Crystallization Kinetics of Isotactic Polypropylene under Process Relevant Conditions

In this study, a non-nucleated homopolymer (HP) and random copolymer (RACO), as well as a nucleated HP and heterophasic copolymer (HECO) were investigated regarding their crystallization kinetics. Using pvT-measurements and fast scanning chip calorimetry (FSC), the crystallization behavior was analyzed as a function of pressure, cooling rate and temperature. It is shown that pressure and cooling rate have an opposite influence on the crystallization temperature of the materials. Furthermore, the addition of nucleating agents to the material has a significant effect on the maximum cooling rate at which the formation of α-crystals is still possible. The non-nucleated HP and RACO materials show significant differences that can be related to the sterically hindering effect of the comonomer units of RACO on crystallization, while the nucleated materials HP and HECO show similar crystallization kinetics despite their different structures. The pressure-dependent shift factor of the crystallization temperature is independent of the material. The results contribute to the description of the relationship between the crystallization kinetics of the material and the process parameters influencing the injection-molding induced morphology. This is required to realize process control in injection molding in order to produce pre-defined morphologies and to design material properties.

The Extent of Interlayer Bond Strength during Fused Filament Fabrication of Nylon Copolymers: An Interplay between Thermal History and Crystalline Morphology.

One of the main drawbacks of Fused Filament Fabrication is the often-inadequate mechanical performance of printed parts due to a lack of sufficient interlayer bonding between successively deposited layers. The phenomenon of interlayer bonding becomes especially complex for semi-crystalline polymers, as, besides the extremely non-isothermal temperature history experienced by the extruded layers, the ongoing crystallization process will greatly complicate its analysis. This work attempts to elucidate a possible relation between the degree of crystallinity attained during printing by mimicking the experienced thermal history with Fast Scanning Chip Calorimetry, the extent of interlayer bonding by performing trouser tear fracture tests on printed specimens, and the resulting crystalline morphology at the weld interface through visualization with polarized light microscopy. Different printing conditions are defined, which all vary in terms of processing parameters or feedstock molecular weight. The concept of an equivalent isothermal weld time is utilized to validate whether an amorphous healing theory is capable of explaining the observed trends in weld strength. Interlayer bond strength was found to be positively impacted by an increased liquefier temperature and reduced feedstock molecular weight as predicted by the weld time. An increase in liquefier temperature of 40 °C brings about a tear energy value that is three to four times higher. The print speed was found to have a negligible effect. An elevated build plate temperature will lead to an increased degree of crystallinity, generally resulting in about a 1.5 times larger crystalline fraction compared to when printing occurs at a lower build plate temperature, as well as larger spherulites attained during printing, as it allows crystallization to occur at higher temperatures. Due to slower crystal growth, a lower tie chain density in the amorphous interlamellar regions is believed to be created, which will negatively impact interlayer bond strength.

Crystallization of Random Metallocene-Catalyzed Propylene-Based Copolymers with Ethylene and 1-Hexene on Rapid Cooling.

Propylene-based random copolymers with either ethylene or 1-hexene as comonomer, produced using a metallocene catalyst, were studied regarding their crystallization behaviors, with a focus on rapid cooling. To get an impression of processing effects, fast scanning chip calorimetry (FSC) was used in addition to the characterization of the mechanical performance. When comparing the comonomer type and the relation to commercial grades based on Ziegler–Natta-type catalysts, both an interaction with the catalyst-related regio-defects and a significant difference between ethylene and 1-hexene was observed. A soluble-type nucleating agent was found to modify the behavior, but to an increasingly lesser degree at high cooling rates.

Surface Crystal Nucleation and Growth in Poly (ε-caprolactone): Atomic Force Microscopy Combined with Fast Scanning Chip Calorimetry.

By using an atomic force microscope (AFM) coupled to a fast scanning chip calorimeter (FSC), AFM-tip induced crystal nucleation/crystallization in poly (ε-caprolactone) (PCL) has been studied at low melt-supercooling, that is, at a temperature typically not assessable for melt-crystallization studies. Nanogram-sized PCL was placed on the active/heatable area of the FSC chip, melted, and then rapidly cooled to 330 K, which is 13 K below the equilibrium melting temperature. Subsequent isothermal crystallization at this temperature was initiated by a soft-tapping AFM-tip nucleation event. Crystallization starting at such surface nucleus led to formation of a single spherulite within the FSC sample, as concluded from the radial symmetry of the observed morphology. The observed growth rate in the sub-micron thin FSC sample, nucleated at its surface, was found being much higher than in the case of bulk crystallization, emphasizing a different growth mechanism. Moreover, distinct banding/ring-like structures are observed, with the band period being less than 1 µm. After crystallization, the sample was melted for gaining information about the achieved crystallinity and the temperature range of melting, both being similar compared to much slower bulk crystallization at the same temperature but for a much longer time.

Extending Cooling Rate Performance of Fast Scanning Chip Calorimetry by Liquid Droplet Cooling

The liquid droplet cooling technique for fast scanning chip calorimetry (FSC) is introduced, increasing the cooling rate for large samples on a given sensor. Reaching higher cooling rates and using a gas as the cooling medium, the common standard for ultra-fast temperature control in cooling requires reducing the lateral dimensions of the sample and sensor. The maximum cooling rate is limited by the heat capacity of the sample and the heat exchange between the gas and the sample. The enhanced cooling performance of the new liquid droplet cooling technique is demonstrated for both metals and polymers, on examples of solidification of large samples of indium, high-density polyethylene (HDPE) and poly (butylene 2,6-naphthalate) (PBN). It was found that the maximum cooling rate can be increased up to 5 MK/s in room temperature environment, that is, by two orders of magnitude, compared to standard gas cooling. Furthermore, modifying the droplet size and using coolants at different temperatures provide options to adjust the cooling rate in the temperature ranges of interest.

Full-composition-range glass transition behavior of the polymer/solvent system poly (lactic acid) / ethyl butylacetylaminopropionate (PLA/IR3535®)

The polymer/solvent system poly (lactic acid)/ethyl butylacetylaminopropionate (PLA/IR3535®) is considered as a drug-delivery system, in which a polymer hosts a liquid with a functionality as insect repellent. Such devices require solubility of the components at high temperature and observation of crystallization-induced solid-liquid phase separation on cooling. Precise knowledge of the thermodynamic solubility of the components is then difficult to obtain due to possible superposition of liquid-liquid phase separation with polymer crystallization. Therefore, in the present study the miscibility of the polymer/solvent system PLA/IR3535® was explored by employing non-crystallizable PLA, by analysis of the glass transition behavior in the full composition range. The data revealed that the two components are miscible regardless the system composition, with the glass transition temperature of solutions showing a negative deviation from the linear mixing rule, suggesting rather weak enthalpic interactions of the system components. The study included application of conventional and fast scanning chip calorimetry, which allowed for controlled and stepwise evaporation of solvent by repeated exposing the system to elevated temperature and evaluation of the glass transition temperature during in-between cooling and reheating. This novel approach permits an efficient analysis of the glass transition temperature as function of the system composition in a single experiment in a wide range of solvent concentrations.

Influence of side-chain isomerization on the isothermal crystallization kinetics of poly(3-alkylthiophenes)

Abstract