Conventional Differential Scanning Calorimetry Measurements Research Articles

Novel approach to characterize the cross‐linking effect of liquid silicone rubber via cavity pressure analysis during injection molding

AbstractThe processing of liquid silicone rubber (LSR) in the injection molding process to molded parts offers high economic potential due to its great scalability. Unlike the well‐researched and understood injection molding process of thermoplastics, LSR still lacks basic process knowledge. The cavity pressure curve shows a completely different pattern, as the cold LSR expands strongly once placed in the hot mold due to volume dilation. During processing of LSR exothermic and irreversible cross‐linking, occurs. In this work, a method is introduced to display the cross‐linking reaction in the cavity pressure curve. Using a self‐developed testing device and conventional differential scanning calorimetry measurements, a correlation between cross‐linking and the pressure signal can be demonstrated. A typical deflection is evaluated in the pressure curve by differentiating, which is attributed to the cross‐linking. The relationships established are confirmed by pressure measurements in the mold during the processing of LSR in the injection molding process. The knowledge gained contributes to a better understanding of the process, helps to optimize existing processes and save resources. Existing cavity‐pressure‐measuring‐systems are to be supplemented by an evaluation logic and thus, in addition to cycle time optimization, process variations are to be detected, energy consumption optimized and quality ensured and verified.

Non‐isothermal crystallization of polypropylene with sorbitol‐type nucleating agents at cooling rates used in processing

AbstractSorbitol‐type nucleating agents used as clarifiers for polypropylene (PP) show a complex interplay of phase and crystallization behavior. To study the crystallization behavior, cooling measurements were performed by fast scanning calorimetry using rates between 10 and 4000 K s−1. These rates correspond to cooling rates used in processing. These measurements were combined with conventional differential scanning calorimetry (DSC) measurements at 10 K min−1. The optical properties were characterized by haze measurements. For this investigation the commercially available clarifiers 1,3:2,4‐bis(3,4‐dimethylbenzylidene)sorbitol and 1,2,3‐tridesoxy‐4,6:5,7‐bis‐O‐[(4‐propylphenyl)methylene]nonitol were added to PP in various amounts up to 0.6 wt%. At relatively slow cooling rates only a single crystallization process was observed. In contrast, fast cooling leads to a complex crystallization behavior with up to four different crystallization processes. It was found that the temperature of the main crystallization process during fast cooling correlates with the optical properties from haze measurements. Finally, the cooling rate dependence of the different crystallization processes is discussed in terms of nucleating efficiency of the clarifiers. We conclude that the results of conventional DSC measurements cannot be extrapolated in a simple way to describe the nucleation activity of nucleating agents at cooling conditions relevant during processing. © 2018 Society of Chemical Industry

A novel approach to study the isothermal and non-isothermal crystallization kinetics of Poly(Ethylene Terephthalate) by Raman spectroscopy

This paper focuses on the study of the crystallization kinetics of an initially quasi-amorphous Poly(Ethylene Terephthalate) (PET) during controlled heating treatments using Raman Spectroscopy. Characteristic vibrational bands of both crystalline and amorphous phases are then investigated in terms of wavenumber values, full widths at half maximum and integrated intensities variations which led to the establishment of a more accurate crystallinity ratio criterion than the one obtained by standard differential scanning calorimetry (DSC) analysis too much dependent on the low polymer thermal conductivity. Applying this last criterion, isothermal and non-isothermal crystallization kinetics were investigated following the Avrami’s and Ozawa’s theories in order to identify the germination and growth modes of the triclinic crystals of PET as a function of thermal treatment. Moreover, all the specific microstructural transitions such as cold crystallization, crystallization from the melt, melting and glass transition are detected and characterized. Similar thermal behaviors were obtained from Raman results and conventional differential scanning calorimetry measurements.

Study of dynamic features of highly energetic reactions by DSC and High-Speed Temperature Scanner (HSTS)

ABSTRACTThe dynamic features of Al2O3 - polytetrafluoroethylene (PTFE) and Al - PTFE reactions in non-isothermal conditions are presented. The Differential Scanning Calorimetry (DSC) and High-Speed Temperature Scanner (HSTS) were used to characterize the Al2O3/Al – PTFE reactions at different heating rates. The study shows that the HSTS instrument can give more information about the reaction mechanism and kinetics than the conventional DSC measurements. In this work we show that high heating rates may reveal exothermic reaction between Al2O3 and PTFE that were previously unidentified. The PTFE can potentially remove the oxide layer from aluminum in the initial period of the reaction and increase the direct contact area between oxygen and aluminum, which increases the reaction velocity and improves the energy release abilities of the system.

Microwave calorimetry using X-rays

An alternative approach for microwave calorimetry is proposed which relies on the synchrotron radiation powder diffraction technique as well as on the Grüneisen formalism for the analysis of thermal expansion. Cobalt was selected as suitable magnetic material for the present evaluation of the method. First results are reported concerning the calorimetric assessment of the HCP (hexagonal close-packed) to FCC (face centered cubic) transition of cobalt from in situ time-resolved X-ray diffraction experiments performed during magnetic (H-field) microwave heating. The X-ray calorimetry method yields specific heat capacity estimations that compare well with results from conventional differential scanning calorimetry measurements. In the presence of the 2.45 GHz microwave H-field, an ‘anomalous’ behaviour of the heat capacity across the structural phase transition is detected, which can be correlated with the magnetic spin reorientation transition of cobalt in the same temperature range.

In situ TEM observation of the glass-to-liquid transition of metallic glass in Fe–Zr–B–Cu alloy

The glass-to-liquid transition was evaluated by in situ transmission electron microscope observation of crystalline Cu globule aggregation in Fe–Zr–B amorphous or supercooled liquid matrices in Fe 50 Zr 10 B 20 Cu 20 melt-spun ribbon. Globule aggregation was not observed near the critical glass transition temperature, but was observed near the glass transition temperature evaluated by conventional differential scanning calorimetry measurements. The viscosity of Fe–Zr–B-based metallic glass may decrease during the glass-to-liquid transition, and a polygonal crystalline phase may form by Cu globule aggregation.

Two-dimensional Calorimetry: Imaging Thermodynamics and Kinetics of Phase Transitions of Biological Membranes

Differential scanning calorimetry (DSC) is a relatively rapid and informative biophysical method for studying thermotropic phase behavior of biological membranes. More recently a pressure perturbation calorimetry has been introduced. The latter method is capable of characterizing membrane thermal volume expansion coefficient and kinetics associated with the phase transition. Notably, pressure perturbation calorimetry requires both pressure jump accessory and, most importantly, fast and sophisticated temperature control system to ensure constant sample temperature upon the pressure jump. Here we describe a calorimetry procedure and associated method of data analysis to characterize sample thermal properties as a two-dimensional (2D) object (temperature-time thermal image) whereas data obtained by conventional calorimetry are essentially one-dimensional. In brief, the method utilizes mathematical formalism of the Radon transform (back-projecting algorithm) to separate temperature and time dimensions from a series of thermal flux measurements obtained by a conventional DSC calorimeter at different scanning rates. By this manner static and time-dependent (i.e., relaxation) thermodynamic parameters of an object become resolved and displayed as a single 2D temperature-time thermal image. There are two main advantages of our 2D-calorimetry method: 1) 2D temperature-time thermal image separates and characterizes equilibrium and non-equilibrium thermal properties of a sample; 2) the method improves signal-to-noise ratio for conventional DSC measurements of equilibrium heat capacity as a function of temperature. We demonstrate these advantages of the 2D calorimetry method on examples of imaging thermodynamics and heat relaxation properties of lipid bilayers composed from single and mixed phospholipids with and without cholesterol. We also show that confining lipid bilayers inside nanopores of ca. 175 nm in diameter results in heterogeneous heat transfer kinetics while conventional equilibrium calorimetry curves remain unperturbed. Supported by the DOE Contract DE-FG02-02ER15354.

Differential scanning calorimetry study on thermal behaviors of freeze‐dried poly(L‐lactide) from dilute solutions

AbstractGlass transition, cold crystallization, and melting of freeze‐dried poly(L‐lactide) (PLLA) prepared from dilute 1,4‐dioxane solutions were investigated by differential scanning calorimetry (DSC). Conventional DSC measurements of heating scans revealed that freeze‐dried PLLA prepared from a 0.07 wt % solution undergoes a two‐step cold crystallization (or reorganization) with a lower exotherm appearing at about 78 °C and with a higher broad exotherm between 110–155 °C. The peak temperature of the former exotherm is about 50 K lower than that observed for a reference bulk sample. Step‐scan mode DSC, which provides information essentially equivalent to that obtained from the temperature‐modulated DSC, revealed that the glass‐transition temperature is about 6 K lower than that of the reference bulk. These findings suggest enhanced chain mobility for freeze‐dried PLLA. Freeze‐dried PLLA that crystallized at 80 °C for 40 min was revealed to contain a rather large amount of rigid amorphous material (42%). © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 115–124, 2005

Development of a microwave calorimeter for simultaneous thermal analysis, infrared spectroscopy and dielectric measurements

An instrument has been developed for monitoring cure processes under microwave heating conditions. The main function of the instrument was a calorimeter for performing microwave thermal analysis. A single mode resonant cavity was used as the heating cell in the microwave calorimeter. Thermal analysis measurements were obtained by monitoring the variation in the microwave power that was required to maintain controlled heating of the sample. The microwave thermal analysis data were analogous to conventional differential scanning calorimetry measurements. The dielectric properties of the sample, as a function of the extent of cure, have been obtained using perturbation theory from the changes in resonant frequency and quality factor of the microwave cavity during heating. Additionally, remote sensing fibre-optic probes have been employed to measure real time in situ infrared spectra of the sample during the cure reaction. In this paper, we describe the design and operation of the microwave calorimeter. Examples of experimental results are also presented.

Differential thermal lens temperature scanning approach to glasstransition analysis in polymers: application to polycarbonate

In this paper, mode mismatched thermal lens spectrometry isapplied to determine the thermal and optical properties of polycarbonate as afunction of temperature. The focus of the experiments was in thetemperature range between 120 °C and 170 °C, where thesample glass transitions occurs. In order to validate and evaluate thesensitivity of the proposed method we have also carried out conventionaldifferential scanning calorimetry measurements. The results showed that thetemperature dependence of the signal amplitude of the thermal lens provided abetter definition in locating the glass transition compared to thedifferential scanning calorimetry data. In addition, a sharp decrease in thethermal diffusivity values at the beginning of the sample glass transition wasobserved. According to the Debye model, this change was attributed to thevariation of the sample elastic constant throughout the glass transition.Finally, we propose this procedure, called the differential thermal lenstemperature scanning approach, as a new method for the investigation of phasetransitions in transparent polymers.}\\fnm{3}{Author to whom correspondence should be addressed.

Temperature modulated differential scanning calorimetry during isothermal curing of phase separating polymer networks

Temperature modulated differential scanning calorimetry (TMDSC) and conventional differential scanning calorimetry (DSC) have been applied for investigation of isothermal curing of two component polymer networks separating into two phases during network formation. The network component consists of diglycidylether of bisphenol A (DGEBA) cross-linked with diaminodiphenyl methane (DDM) and the linear polymer component is polyethersulfone (PES). Isothermal curing experiments at 373 K and heating experiments after defined isothermal curing times are combined to investigate the evolution of the glass transition temperatures during reaction. While in the initial stages of the reaction the systems are homogeneous mixtures, phase separation takes place in the course of curing into a DGEBA/DDM-rich and a PES-rich phase. Since in the conventional isothermal DSC measurements the changes in the heat capacity, when the system undergoes a transition from a liquid to a glassy solid during network formation, are masked by the heat of reaction, TMDSC was applied to resolve both effects. In the heating experiments after defined isothermal curing periods the changes in the heat capacity due to the glass transition were resolved for both phases by TMDSC whereas in the conventional DSC measurements the glass transition temperature could only be detected for the DGEBA/DDM-rich phase. The phase separation process is indicated by TMDSC for curing times above 50 min for a curing temperature of 373 K.