High-pressure Differential Scanning Calorimetry Research Articles

High-pressure cure kinetics and unexpected cure separation of peroxide-cured silicone rubber under compressed CO2

In this study, high-pressure differential scanning calorimetry (HP-DSC) was used to examine the curing process of a peroxide-cured silicone rubber (SR) system under compressed CO2 to investigate the influence of pressure and CO2 on the curing process. We found that the curing reaction occurred in two parts, described as cure separation, because of the dual effect of CO2 pressure and solvation at 6 MPa CO2. Consequently, peak fitting was used to calculate the kinetic parameters of the two-part reaction at 6 MPa CO2. Results indicate that pressure and CO2 exerted a combined effect on the curing reaction. In particular, pressure and CO2 solvation effects changed with varying conversion rates and CO2 pressures. This study provides an effective analysis methodology and an accurate kinetic model for characterizing and predicting high-pressure cure kinetics and unexpected cure separation in a peroxide-cured SR system under compressed CO2.

Development of strategies for continuous desalination of weak black liquor based on phase-behaviour analysis

This paper investigated different strategies to prevent salt deposition during weak black liquor (WBL) desalination under hydrothermal liquefaction conditions based on phase behaviour analysis. Phase equilibria of model salt solutions replicating the WBL composition were studied by high-pressure differential scanning calorimetry (HP-DSC) and different strategies to induce the Type 1 salt behaviour were applied. Two strategies led to an optimised salt separation: adjusting the concentrations of Type 1 salts, NaOH and NaHS, present in the WBL, and selectively exchanging carbonate from the model salt solution by replacing it with hydroxide. These strategies were tested in PSI’s continuous salt separation test rig, considering the recovering of salts. Although increasing the concentration of the Type 1 salts (NaOH and NaSH) impacted the precipitation temperature and extent of the salts, the strategy was not able to prevent it entirely. The HP-DSC results confirmed the efficiency of carbonate replacement by hydroxide since the Type 1 behaviour was observed after exchanging 75% of the carbonate. In the presence of organics, some salt accumulation and overflow into the desalinated stream occurred, which was addressed by optimising the brine flow rate.

Age‐related hair denaturation related to protein carbonyls

AbstractObjectiveHair ageing is accompanied by hair fibres becoming irregularly shaped causing them to stick out in irregular directions or have more curliness and being spread out. This is believed to be due to changes within the hair fibre structure which occur with ageing, and one of the causes of these changes could be an increase in the number of protein carbonyl groups present in the hair. The aim of this study is to investigate the internal denaturation of hair related to protein carbonyls in attempt to gain new insight into age‐related changes that occur in hair.MethodsThe degree of carbonylation of the hair structural protein as determined by fluorescent labelling and Western blotting analysis was used to investigate the primary structure of hair protein. The amount of helix, a common conformation in the secondary structure of proteins, in hair in groups of women with different ages was also analysed using infrared microscopy coupled with multivariate curve resolution (MCR). From the results of this, an image of the two‐dimensional distribution of the α‐helices was generated for the hair taken from each age group. Also, high‐pressure differential scanning calorimetry (HPDSC) of the hair in water was performed on the hair taken from each age group to determine the peak temperature of endothermic effect and the enthalpy of denaturation.ResultsWe found that the amino group content in hair proteins decreased and Type II keratin, one of the subunits of intermediate filament, was more carbonylated with age. The results of the MCR indicated eight separate components, including components of the secondary structure of proteins, such as α helices and β sheets. Two‐dimensional images of the hair cross‐sections revealed that the presence of α helices decreased with age. In addition, data from the HPDSC showed that the enthalpy associated with the denaturing temperature also significantly decreased with age.ConclusionThese results suggest that there is a negative correlation between age and structural integrity of the helix segment in intermediate filament. The results of this study also show that there is a positive correlation between age‐related hair denaturation and protein carbonyls.

Thermal decomposition characteristics and thermal safety performance evaluation of HAN-based propellant under different external environmental stimulations

This research aims to investigate thermal characteristics and assess thermal hazards of hydroxylamine nitrate (HAN)-based liquid propellant using a combination of accelerating rate calorimeter and high-pressure differential scanning calorimetry. Adiabatic experiments revealed that the exothermic reaction initiated at 115.7 °C and a rise sharply was at 128.4 °C with a maximum self-heating rate of 164.3 °C/min and the exothermic event was accompanied by a pressure rise of 3.7 bar in 0.03s. The corrected values of adiabatic temperature rise and time to maximum rate were 605.6 °C and 1.46 min, which confirms the vulnerability of the propellant to undergo a catastrophic explosion. To prevent thermal loss prevention accidents, time to maximum rate was obtained as 24 h under 111.3 °C. The apparent activation energy calculated decreased greatly with the increase of storage temperature from 25 °C to 45 °C, and so did the thermal explosion temperature (Tb) and self-accelerating decomposition temperature (TSADT). Additionally, the linear relationship between Ea and T was E = 991.7–2.7904T. The reliability of TSADT prediction was validated through slow cook-off test. Furthermore, the propellant exhibited more violent thermal decomposition under high pressure, resulting in a higher peak power. The thermokinetic parameters related to this phenomenon were identified, specifically at pressure of 4.0 MPa.

Investigation into the key factors influencing the establishment and propagation of combustion front in ultra-deep high-temperature heavy oil reservoirs

The in-situ combustion technique is currently on the exploratory stage for ultra-deep high-temperature heavy oil reservoirs. In this work, the oxidation experiments of heavy oil were conducted using thermogravimetry, high-pressure differential scanning calorimetry, and combustion tube. Based on these experimental results, a reaction kinetics model was developed, which was then integrated into the Computer Modeling Group (CMG) STARS reservoir simulation software by adjusting stoichiometric numbers, kinetic parameters, and reaction enthalpy to match the experimental data obtained. Furthermore, a corrected reservoir simulation approach was employed, combining the variance analysis and a Pareto chart, to identify the key factors influencing the establishment and propagation of combustion front in the absence of electrical ignition. The results indicate that a reservoir temperature of 148 °C leads to the establishment of combustion front approximately 7 m away from the injection well, with a delay time of around 25.21 days. The Pareto chart reveals that reservoir temperature and water saturation are the primary controlling factors for combustion occurrence. Specifically, a reservoir temperature above 148 °C and water saturation below 60% increase the likelihood of combustion front formation. Among the examined factors, the reservoir temperature has the most significant effect on combustion front propagation. Once the reservoir temperature reaches 208 °C, a stable combustion front is formed, and the average temperature of combustion front remains around 400 °C throughout 8 years of model operation. When the water saturation was 50%, a consistently stable combustion front can be established within the first 6 years of model operation. However, beyond the 6th year, the average front temperature decreases below 400 °C. Therefore, it is recommended to introduce a certain amount of oxidation catalysts into the oil reservoirs after 6 years of air injection to enhance the combustion reactions. Increasing the air injection rate or pre-exponential factor does not have a significant effect on the average front temperature after 8 years of model operation, which remains below 350 °C. This study can provide significant references for future assessments and decision-making processes related to the application of ISC in ultra-deep high-temperature heavy oil reservoirs.

Investigation of how pressure influences the thermal decomposition behavior of azodicarbonamide

Azodicarbonamide (ADC) is a type of azo compound with outstanding application performance, it is always used as a blowing agent in the production of foamed plastics. Based on previous studies, it has been considered harmless in its practical application process. Nevertheless, our research has overturned this standpoint and denoted the special exothermic behavior of ADC under specific use processes, especially when it was placed in a high-pressure system. In this study, a simultaneous thermogravimetric analyzer (STA) was employed to preliminarily evaluate the thermal stability of ADC under atmospheric pressure. Followed with calorimetric experiments by high-pressure differential scanning calorimetry (HP DSC), the exothermic behaviors of ADC under different initial furnace pressures were investigated. The obtained results revealed that the thermal decomposition rate of ADC linearly increases along with increasing testing pressure, which shows a highly autocatalytic characteristic. The peak power of DSC curve breathtakingly reached 73 W/g when the initial testing pressure was set at 4 MPa, and the overall decomposition heat reached 1261 J/g with the scanning rate at 4 °C/min. Furthermore, the decomposition mechanism, thermal hazards, and explosion potential were comprehensively evaluated in this study for the first time.

Effect of Ethylene Comonomer Content on the Foam Processing Window of Long-Chain Branched Polypropylene

The non-optimized foam processing window (FPW) can create processing challenges and limit the possible materials with which a polymer of interest can be processed in emerging foaming technologies. To address this drawback, we aim to investigate the effect of ethylene comonomer content on the foaming behavior of polypropylene (PP), particularly the FPW. Two PP resins containing 0.75 and 1.5 wt % of ethylene comonomers were studied, while using a PP homopolymer as a control. High-pressure differential scanning calorimetry confirmed the decrease in the onset crystallization (Tc-onset) and end melting (Tm-end) temperatures with increasing ethylene comonomer content as a result of the defects the ethylene units induce in the crystalline structure of PP. Rheological measurements suggest that the addition of ethylene comonomer content resulted in negligible changes in the extensional and shear rheological responses of the PP-based resins. In addition, the foam expansion results and the observed morphologies reveal no significant change in the resins’ foamability, characterized by the shape of their expansion profiles with respect to the foaming temperature. Interestingly, the FPW was found to be the sole affected parameter, as 1.5 wt % of ethylene comonomers resulted in a 10 °C shift in the FPW toward lower temperatures, compared to the PP homopolymer. The resins with 0 and 1.5 wt % of ethylene comonomer content showed similar mechanical responses under compression tests for their optimally expanded samples. These findings reveal a potentially effective approach for tuning the FPW of processed PP resins without compromising their foaming and mechanical performances. Consequently, foam processing techniques are further enhanced, resulting in a wider span of potential applications.

Synthesis, thermal stability, and hydrogen storage properties of poorly crystalline TiVFeCuNb multi-principal element alloy: Dedicated to the memory of Michel Latroche and his great contribution to the field of metal hydrides

Multi-principal element alloys and high-entropy alloys are currently extensively studied for their hydrogen storage abilities. In this context, they offer a wide variety of properties that can be precisely tuned by the proper design of, among others, the chemical composition, crystal structure, valence-electron number, or lattice distortion parameter. However, so far, the community's primary attention has focused on highly crystalline materials with body-centered-cubic solid solutions structure or intermetallic Laves phases (type C14 and C15), and very little attention has been paid to poorly crystalline or amorphous alloys. Here we present the results obtained for poorly crystalline TiVFeCuNb alloy synthesized by mechanical alloying. The alloy showed an even distribution of all constituent elements and thermal stability up to 450 °C. The high-pressure DSC experiments under optimized conditions (without activation, at 30 bar H2) demonstrated that the alloy absorbs hydrogen between 150 and 250 °C within a two-step reaction. The X-ray powder diffraction patterns proved that the poorly crystalline structure is kept after the hydrogenation process. The combined DSC/TG/MS studies revealed that the hydrogenated alloy releases up to 0.59 wt% of H2 in a multi-step desorption process (between 170 and 450 °C). The kinetic hydrogen absorption measurements showed that the studied alloy reached half its capacity within 20 s of the process.

Pressure-thermal hysteresis phenomena in BaTiO3 upon phase transition

The phase transition into the ferroelectric phase in barium titanate occurs in many stages with the appearance of nonlinear phenomena. The mixed nature of the transition: displacive and order-disorder type, causes the occurrence of a thermal hysteresis, which span depends significantly on the pressure imposed on the sample. Theoretical calculations performed within the framework of Landau phenomenological theory showed a nonlinear dynamics of the thermal hysteresis with pressure. The existence of unusual relaxation phenomena was predicted in the pressure range of 130–145 MPa. Experimental and theoretical studies have shown the periods of slowing down of the domain structure upon the evolution process, the duration of which depends on the pressure and quenching temperature. It was assumed that relaxation processes near the tricritical point are similar to those observed near the Curie temperature. Theoretically, the parameters recommended for further experiments using high-pressure differential scanning calorimetry were calculated.

Synergistic effect of sulfonated castor oil and porous medium on kinetics of gas hydrates formation

In recent years, interest in gas hydrates has increased as they represent a potential energy source and an alternative to the current environmentally friendly method of storing and transporting natural gas. In this study, the synergistic effect of a new promoting reagent – sulfonated castor oil (SCO) – and a porous medium on the formation and decomposition of methane and methane-propane hydrates was compared to that of sodium dodecyl sulfate (SDS) using the high-pressure differential scanning calorimetry (HP-μDSC) method. DSC tests demonstrated that water conversion in the presence of SCO in a porous substrate for methane hydrates reached 95% at high water saturation, which can be attributed to improved mass transfer in the presence of surfactants. However, this value did not exceed 60% for the hydrate of methane–propane mixture, indicating that the mechanism of promotion of the sI and sII hydrates differs. According to kinetic calculations based on the Avrami equation, both SDS and SCO accelerate the formation of hydrates, but for SCO, this is possible with less supercooling. The calorimetric measurements and kinetic parameter calculations demonstrated that SCO is comparable to the well-known reagent SDS in promoting activity in porous media with varying water saturation.

Hydrothermal carbonization enthalpy using differential scanning calorimetry: Assessing the accuracy of the exhaust sample method

High pressure differential scanning calorimetry (DSC) is suitable to study the thermodynamics and kinetics of hydrothermal carbonization (HTC). To isolate the thermal effect of the process from the heat required to increase the DSC system temperature, a recently proposed method uses an additional run on the already reacted sample as the blank. The method assumes that the blank system is in equilibrium during the whole run; it neglects the potential for secondary reactions in the blank run, which may affect the results. This work assesses the effect of such an assumption on the final enthalpy results by performing additional re-runs on the same specimen and adopting longer isothermal segments to push the system composition closer to equilibrium. The study of HTC of cellulose at 250°C demonstrates that the thermal contribution of reactions in the second run is negligible compared to the primary HTC effects in the first run and within the experimental error. A deeper investigation of the thermal effect during re-runs shows that the biggest effect of reactions in such runs is to change the system composition rather than a direct exothermicity. Further, the exothermic activity disappears after 12 hours, suggesting that the sample has reached thermal equilibrium.

Experimental study on the in-situ combustion retorting of domanik oil shale

Oil shale is a critical strategic resource with enormous reserves. In-situ combustion technology offers great potential for the development of oil shale reserves. In this study, the combustion behavior and kinetics of Domanik oil shale were investigated using High Pressure Differential Scanning Calorimetry. Additionally, the thermal behavior of the oil shale during combustion was studied by using a self-designed Porous Medium Thermo-Effect Cell. Furthermore, the stability of the combustion front and the upgrading effect of the combustion process were investigated with Visual Combustion Tube, and the produced oil was analyzed to evaluate its quality. The results showed that the combustion process of oil shale is characterized by two reaction stages. The oil shale was found to form enough coke residue during the oxidation reactions to allow for stable propagation of a combustion front. The produced oil was of better quality compared to the naturally produced bitumen in oil shale, which indicates that the combustion process had a good upgrading effect. The findings of this study provide a better understanding of the in-situ upgrading process of kerogen and provide significant knowledge about the combustion mechanism of oil shale for its potential development using the in-situ combustion technology.

Glass transition of PLA-CO2 mixtures after solid-state saturation

Polymer foams offer high sustainable performance in terms of their lightweight potential, insulation and high specific mechanical properties. The foaming of polymers depends on the properties of gas-laden solids or liquids. For foaming in the solid state, the foaming temperature must be higher than the glass transition temperature of the saturated polymer system. Moreover, the knowledge of sorption conditions and thermal properties is crucial for foam formation. In this study, the correlation between the glass transition temperature and the sorption conditions was investigated. This comparison was made by determining the sorption behavior for different pressure levels and the corresponding glass transition temperature using a high-pressure differential scanning calorimetry. The time, pressure and CO2 content were varied. For the first time, the Chow model could be verified for PLA with a coordination number of 3.

Uncovering the transition between hydrothermal carbonization and liquefaction using differential scanning calorimetry

The in situ analysis of hydrothermal carbonization (HTC) and liquefaction (HTL) processes can be accomplished using high-pressure differential scanning calorimetry (DSC), a continuous, relatively inexpensive, and rapid technique for pressurized processes. A recently published DSC method is newly applied across conditions spanning both HTC and HTL to continuously assess the heat release profile of cellulose across the hydrothermal spectrum. The resulting DSC curves are deconvoluted and the peaks are assigned to reaction sets. HTC and HTL are both exothermic, with enthalpy changes of ~0.3–0.9 and ~0.9–1.2 kJ g−1 for HTC and HTL, respectively. A thermodynamic transition in overall process enthalpy occurs at the transition from HTC to HTL, which can be explained by the relative importance of hydrolysis, polymerization, and bulk carbonization reactions within the two processing regimes. This novel DSC technique could reduce cost and time in the initial evaluation of potential HTC and HTL feedstocks, which may hasten the commercialization of these thermochemical processes.

Enhancing hydrogen storage performance via optimizing Y and Ni element in magnesium alloy

Magnesium-based hydrogen storage materials are considered as one of the most promising candidates for solid state hydrogen storage due to their advantages of high hydrogen capacity, excellent reversibility and low cost. In this paper, Mg91.4Ni7Y1.6 and Mg92.8Ni2.4Y4.8 alloys were prepared by melting and ball milling. Their microstructures and phases were characterized by X-ray diffraction, scanning electron microscope and transmission electron microscope, and hydrogen absorbing and desorbing properties were tested by the high pressure gas adsorption apparatus and differential scanning calorimetry (DSC). In order to estimate the activation energy and growth mechanism of alloy hydride, the JMAK, Arrhenius and Kissinger methods were applied for calculation. The hydrogen absorption content of Mg92.8Ni2.4Y4.8 alloy reaches 3.84 wt.% within 5 min under 350 ℃, 3 MPa, and the maximum hydrogen capacity of the alloy is 4.89 wt.% in same condition. However, the hydrogen absorption of Mg91.4Ni7Y1.6 alloy reaches 5.78 wt.% within 5 min, and the maximum hydrogen absorption of the alloy is 6.44 wt.% at 350 ℃ and 3 MPa. The hydrogenation activation energy of Mg91.4Ni7Y1.6 alloy is 25.4 kJ/mol H2, and the enthalpy and entropy of hydrogen absorption are -60.6 kJ/mol H2 and 105.5 J/K/mol H2, separately. The alloy begins to dehydrogenate at 210 ℃, with the dehydrogenation activation energy of 87.7 kJ/mol H2. By altering the addition amount of Ni and Y elements, the 14H-LPSO phase with smaller size and ternary eutectic areas with high volume fraction are obtained, which provides more phase boundaries and catalysts with better dispersion, and there are a lot of fine particles in the alloy, these structures are beneficial to enhance the hydrogen storage performance of the alloys.

Influence of water on thermo-oxidative behavior and kinetic triplets of shale oil during combustion

The oxidation reactions between oxygen and shale oil directly affect the feasibility and performance of air injection. In this work, the influence of water on thermo-oxidative behavior of shale oil was studied using high-pressure differential scanning calorimetry (HP-DSC). Subsequently, the kinetic triplets for shale oil oxidation in the absence and presence of water were determined using Friedman and Ozawa-Flynn-Wall (OFW) models as well as one advanced integral master plots method. The HP-DSC results showed that at 5 MPa, the shale oil was vulnerable to obviously higher heat release at the low-temperature oxidation (LTO) region compared to the high-temperature oxidation (HTO) region, resulting in shortening the oxidative induction time and achieving in-situ upgrading of shale oil. Water delayed the initial heat release due to the fact that heat release yielded by LTO compensated the heat adsorption yielded by evaporation of water and light hydrocarbons. Additionally, the heat release was reduced with the elevated water saturation as a result of the reduction in exothermic rates and intensified evaporation of water and light hydrocarbons. The higher energy was needed to trigger off the LTO reactions while increasing water saturation from 10% to 20%. Therefore, it was believed that the presence of water extended the oxidative induction time, thereby hindering the smooth and rapid transition from the LTO to HTO stages. Water changed the reactivity of each oxidation stage for shale oil, resulting in higher energy required for the initial LTO reactions and lower energy required for the subsequent oxidation reactions. The water saturation range of 10% to 15% could accelerate the occurrence of high-temperature combustion most effectively, demonstrated by values of activation energy for the conversion greater than 0.6. The appropriate oxidation reaction models for shale oil alone and water saturations of 10%, 15%, and 20% were determined to be D2, F1, F3, and R3, respectively. The determination of kinetic triplets assisted in building the reaction schemes for modelling the air injection process of shale oil reservoirs.

Thermal characteristics of dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate in contact with nitrocellulose/nitroglycerine under continuous heat flow

Dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50) and nitrocellulose/nitroglycerine (NC/NG) possess good energy properties, which were widely used in propellants, explosives and pyrotechnics. They are easy to contact with each other during their application and storage. However, their thermal characteristics under continuous heat flow have not been reported yet. Therefore, it is of great practical significance to study the thermal properties of TKX-50/NC/NG (mixture of TKX-50 and NC/NG). In this paper, the thermal characteristics and pressure behaviors of TKX-50/NC/NG, TKX-50 and NC/NG were characterized by high pressure differential scanning calorimetry (HPDSC) and adiabatic scanning calorimetry (ASC). The results showed that TKX-50 and NC/NG can promote each other to decompose under continuous heat flow, especially the thermal decomposition which affected by gases generation and heat feedback was more violent in the confined space. The decomposition peak temperature of TKX-50/NC/NG shifted to low temperature when the heat loss was ignored and the removal of decomposition gas was suppressed. The possible decomposition mechanism of TKX-50/NC/NG was speculated. It was considered that the intermediate products of TKX-50 and NC/NG decomposition under thermal stimulation would react with each other, which promoted TKX-50/NC/NG decomposition in one step at lower temperature. Thus, TKX-50 has high reactivity and high potential risk after contact with NC/NG under continuous heat flow. TKX-50 is not suitable for application with NC/NG. This study provides a reference for the structural design of nitrogen rich explosives and further broadens the researchers’ understanding of the application of TKX-50.

Oxidation Characteristics and Kinetics of Shale Oil Using High-Pressure Differential Scanning Calorimetry

In situ combustion (ISC) has received much attention in the area of the development of shale oil reservoirs in recent years. The primary mechanism of interest for ISC is the oxidation kinetics of t...

Exothermicity of hydrothermal carbonization: Determination of heat profile and enthalpy of reaction via high-pressure differential scanning calorimetry

Hydrothermal carbonization (HTC) is known for being exothermic, an aspect that can lower the external energy demand necessary to face thermal losses and therefore be conducive to the overall HTC process thermal efficiency. Also, heat profiles can help explore kinetics and generally provide an insight into the HTC process. Despite the potential of the HTC exothermicity, only a few studies examined it and with different methodologies. This work aims to deepen this aspect by exploring heat profiles, enthalpy of reaction, and comparing two experimental methods by performing an experimental campaign using a power-compensated high-pressure differential scanning calorimeter (DSC). Three substrates (glucose, cellulose, and grape seeds) were hydrothermally carbonized at 180, 200, 220, and 250 °C at a biomass to water mass ratio of 0.25. To determine net heat profiles and enthalpies, water thermal effects were removed using two approaches, consisting of running a thermal program on the water alone or the exhaust, i.e. the products after the reaction. An instrument baseline considering both a zero-line and a time-drift was considered. Results show that both methods allow inferring similar enthalpy values at low operating temperature, while at high temperature a difference in the heat capacity of the liquid phase (due to the production of compounds dissolved in the liquid phase and absorbed on the solid) can affect the results related to the exhaust approach. In both cases, higher temperatures favor the exothermic peak intensity, the curve sharpening, and the increase (in absolute value) of reaction enthalpies. These are in the ranges −0.20 ÷ −0.86 MJ/kg, −0.61 ÷ −1.33 MJ/kg, and −0.42 ÷ −1.53 MJ/kg for glucose, cellulose, and grape seeds, respectively.

High pressure differential scanning calorimetry of poly(lactic acid) in presence of CO2 up to 100 MPa

For the processing of sustainable polymers with compressed CO2 to produce innovative products, knowledge of the thermodynamic properties of the polymer-CO2 system is essential. In this work, the thermal behaviour of three different poly(lactic acid) (PLA) grades, 2003D, 3251D and 8052D, from NatureWorks was determined experimentally using high pressure differential scanning calorimetry (HP-DSC) at CO2 pressures up to 100 MPa. After the HP-DSC had been extensively calibrated using potassium, sodium and indium, the thermal transition temperatures of the biopolymers were determined as a function of CO2 pressure. The melting and crystallization temperatures of the PLA grades were found to be up to 84 K lower in the presence of CO2. In addition, the crystallinity of the three biopolymers was investigated. It was shown that the degree of crystallinity was dependent on both the melting temperature and the CO2 pressure. In fact, a striking parabolic dependency which is also correlated with D-lactide content and molar mass was observed.