Depressurization Time Research Articles

Assessing the Impact and Suitability of Dense Carbon Dioxide as a Green Solvent for the Treatment of PMMA of Historical Value.

Surface cleaning of plastic materials of historical value can be challenging due to the high risk of inducing detrimental effects and visual alterations. As a result, recent studies have focused on researching new approaches that might reduce the associated hazards and, at the same time, minimize the environmental impact by employing biodegradable and green materials. In this context, the present work investigates the effects and potential suitability of dense carbon dioxide (CO2) as an alternative and green solvent for cleaning plastic materials of historical value. The results of extensive trials with CO2 in different phases (supercritical, liquid, and vapor) and under various conditions (pressure, temperature, exposure, and depressurization time) are reported for new, transparent, thick poly(methyl methacrylate) (PMMA) samples. The impact of CO2 on the weight, the appearance of the samples (dimensions, color, gloss, and surface texture), and modifications to their physicochemical and mechanical properties were monitored via a multi-analytical approach that included optical microscopy, Raman and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopies, and micro-indentation (Vickers hardness). Results showed that CO2 induced undesirable and irreversible changes in PMMA samples (i.e., formation of fractures and stress-induced cracking, drastic decrease in the surface hardness of the samples), independent of the conditions used (i.e., temperature, pressure, CO2 phase, and exposure time).

PS-BPC03-1: DEVELOPMENT OF CUFFLESS AND CALIBRATION-LESS BLOOD PRESSURE MEASUREMENTS

Objective: The characteristics of dynamic short-term blood pressure variability caused by numerous triggers vary greatly among individuals. Wearable devices that continuously and noninvasively capture beat-by-beat blood pressure values are a necessity to further study blood pressure. The development of cuffless blood pressure measurements, which, unlike sphygmomanometers, do not require pressurization and depressurization time, has attracted much attention in recent years for its potential to capture beat-by-beat blood pressure values. However, cuffless blood pressure measurements approved in Europe and the United States require calibration before use. This indicates that the function is limited to estimation of blood pressure variation from the time of calibration. In this study, we conducted a measurement test aiming at the practical application of the cuffless and calibration-less blood pressure measurements. Design and Method: In this study, we recruited adults aged 20 years and older to evaluate whether a wearable device without pre-calibration could meet the standards of BHS, ESH, ISO81060–2:2018 and IEEE1708a-2019 and ensure the same accuracy as existing sphygmomanometers. For each measurement test, the cuff was wrapped around the subject's upper left arm and a wearable device was attached to the ipsilateral wrist, and the subject was asked to maintain a sitting posture. Measurements were taken with the reference sphygmomanometer every 3 minutes for 7 times. To minimize the effect of the venous congestion on the measurements, the measurement period with the wearable device was from 30 seconds after the completion of the cuff depressurization until the start of the next pressurization. The blood pressure value measured by the wearable device was evaluated against the average of the values measured by the reference sphygmomanometer before and after. Results: 219 participants were included in the analysis. Participants with systolic blood pressure values ranging from 80 to 204 and diastolic blood pressure values ranging from 46 to 140 were included. The mean and SD of the differences between the estimates and the reference were -1.27 ± 4.97 mmHg for SBP and 0.74 ± 2.55 mmHg for DBP. Conclusion: The overall accuracy of the cuffless and calibration-less blood pressure measurements device satisfied the criteria shown in ISO81060–2 against various adults in the sitting posture. This study showed the strong potential of the cuffless and calibration-less blood pressure measurements.

Supercritical CO2 versus water as an antisolvent in the crystallization process to enhance dissolution rate of curcumin

Antisolvent crystallization approach using either water (in conventional crystallization process (WAS)), or supercritical CO2 (in supercritical anti-solvent crystallization (SCAS)), was employed in presence of hydroxypropyl methylcellulose (HPMC) to enhance the dissolution of curcumin. The impact of pressure, temperature and depressurization time on the SCAS process was studied using the Box-Behnken design to achieve the highest saturation solubility. A physical mixture of curcumin-HPMC was prepared for comparison purposes. Saturation solubility, scanning electron microscopy, differential scanning calorimetry, X-ray diffraction analysis and Fourier transform infrared spectroscopy were conducted to characterize the solid-state characteristics of the crystallized samples. Dissolution studies helped in ascertaining the effects of the crystallization techniques on the performance of the formulation. Curcumin crystalized by different antisolvent displayed varied shapes, sizes, saturation solubility’s and dissolution properties. In SCAS process, the maximum saturation solubility (2.83 µg/mL) was obtained when the pressure, temperature and depressurization time were 275 bars, 55 °C, and 22 min respectively. The SCAS samples showed the highest dissolution (70%) in 30 min compared to WAS (27%), physical mixture (18%) and unprocessed curcumin (16%). The improved dissolution rate of SCAS sample originates from the development of sponge-like particles with augmented porosity, decreased crystallinity as well as increased solubility of curcumin.

Mitigation of long-term station blackout accident of advanced boiling water reactors

Taiwan Power Company proposed ultimate response guidelines (URGs) to mitigate the so-called ‘Fukushima type accident’ of nuclear power plants. As stipulated in URGs, operators will depressurize the reactor coolant system if necessary to bring in low-pressure water. Containment venting is then used to dissipate the heat generated from the decay. These collective actions are called DIVing (depressurizing, injecting and venting) in URGs. The actions are designed to avoid large-scale evacuation of the public around the damaged plant during an accident. In this study, the effectiveness of DIVing in preventing radioactive emission to the environment is evaluated using RELAP5 codes. The plant analyzed is Lungmen Nuclear Power Station, which has two 1350-MWe advanced boiling water reactors (ABWR) designed by General Electric. In the Standard Operating Procedure of DIVing in URGs, controlled depressurization is executed to bring the pressure to the lowest operating pressure of Reactor Core Isolation Cooling (RCIC) system. The core water level is kept high while RCIC is in operation.. Emergency depressurization is carried out when RCIC fails. The executing time of DIVing as specified in URGs is too conservative. The study identifies the acceptable initial states for operators to carry out DIVing actions. The success criterion is to keep the peak cladding temperature below 1088 K (1500°F) during the transient, which is the temperature of cladding breach and the initiation of gap release of radionuclide from fuel rod.In this study, depressurization transients in the station blackout accident of ABWR are simulated using RELAP5/3D. The results show that the peak cladding temperature obtained during a depressurization transient depends on the time of depressurization, initial pressure, initial water level and injection rate of low-pressure water. When the water level and injection rate are fixed, a region of successful depressurization on the depressurization time vs pressure plot is delineated based on the results of RELAP5 simulations. Regions of successfully depressurization for typical combinations of injection rate and water level are identified, and acceptable region’s boundary is linear.A computation aid, Guidance for Emergency Depressurization (GfED), was developed based on the simulation results of the RELAP5/3D code to assist operators in determining whether the emergency depressurization under given conditions can be performed successfully. GfED uses low-pressure injection flow rate, water level and initial pressure upon emergency depressurization as input parameters to calculate the latest time that is acceptable for emergency depressurization. The technique of linear interpolation is adopted. By comparing the result and value input by the operators, GfED can predict whether it is safe to depressurize.GfED also guides operators to determine the initial condition of a successful depressurization. Three of the four input parameters are fixed in the guidance, and the limiting value of the fourth parameter of a successful depressurization is calculated. These values are informative for operators to manoeuvre the system while the reactor core isolation cooling system is still running.

Exfoliation and distribution behavior of graphene nanoplatelets in polystyrene-based foams fabricated by supercritical CO2 assisted microcellular foaming

The effects of supercritical CO2 (scCO2) on polymer chains’ mobility and graphene nanoplatelets (GNPs) exfoliation and distribution in a microcellular foaming process are investigated by the molecular dynamics (MD) simulations and experiments. The results of MD simulations and visualization analysis confirm that the synergistic effect of scCO2 molecules and polystyrene (PS) chains is beneficial for them to penetrate into the interlayer of GNPs during the scCO2 treatment at high saturation pressure. The scanning electron microscope images show that some cells exist in the interlayer of GNPs in the foam fabricated in the highest saturation pressure and shortest depressurization time. With foaming in different depressurization time, the growing cells facilitate the movement of GNPs after their exfoliation, leading to alignment around the cells. As compared to large diameter GNPs, the GNPs with small diameter rearrange easily and distribute more homogeneously due to lower resistance of GNPs’ movement.

Analysis of steam generator tube rupture accident for OPR 1000 nuclear power plant

Evaluation of radionuclide releases to the environment from operating nuclear power plants has increased in importance in the Republic of Korea following the 2015 amendment to its Nuclear Safety Act that includes not only design basis accidents but also severe accident management. Containment bypass accidents are among the crucial scenarios that should be considered under the new circumstances due to their high consequences, even though the probability of such accidents is low. In this study, analysis of a thermally induced steam generator tube rupture (TI-SGTR) accident caused by a severe accident has been conducted with MELCOR. To increase the reliability of the analysis results, qualification processes were performed in the process of producing the input. In addition, computational fluid dynamics analysis was performed to simulate the natural circulation phenomena in the reactor coolant system (RCS) during the accident and major flow parameters were obtained for the target plant. Thermal-hydraulic and fission product behavior was found during the accident for the base case scenario, and uncertainty band for CsOH release fraction to the environment were presented through the uncertainty analysis on the natural circulation flow parameters. Sensitivity calculations were also performed on uncertain parameters such as the number of ruptured tubes and the depressurization time of the secondary system, and the CsOH release fraction to the environment without passing through the containment were evaluated.

Pressure oscillation controlled CH4/CO2 replacement in methane hydrates: CH4 recovery, CO2 storage, and their characteristics

The recovery of CH4 from natural gas hydrates via CH4/CO2 replacement is a highly attractive method for achieving the recovery of CH4 and storing CO2. However, although extensive simulation and experimental studies have been conducted, applying CH4/CO2 replacement is currently hampered by a lack of in-depth understanding about the replacement mechanism and the insufficient replacement efficiency and rate achieved. Therefore, to enhance CH4 recovery and CO2 storage, we propose a method that uses pressure oscillation during CH4/CO2 replacement. The effects of depressurization pressure, depressurization time, and depressurization frequencies were analyzed in this study. The characteristics of pressure and temperature were analyzed during the depressurization process, and the decomposition and regeneration of hydrates relating to the oscillation pressure were observed on a macro level. The results show that this newly proposed combined method effectively improves CH4/CO2 replacement, and the maximum amounts of CH4 recovered and the CO2 storage efficiency are nearly double than those achieved without pressure oscillation. CH4/CO2 replacement is promoted by the pressure oscillation mechanism by breaking the balance of the hydrate layer, which results in the dissociation of CH4 hydrates and finally forms a CO2/CH4 mixed hydrate layer with free water. The results of this study provide a valuable method that can be used to enhance CH4 recovery and CO2 sequestration.

Effects of Mg/PTFE pyrotechnic compositions on reignition characteristics of base bleed propellants and heating mechanism

The effects of magnesium/polytetrafluoroethylene (Mg/PTFE) pyrotechnic compositions on the coupled flow field and reignition mechanism are important aspects governing the performance and range of base bleed projectiles (BBPs). Owing to a decrease in pressure and temperature when the BBP leaves the muzzle, rapid depressurization occurs, which extinguishes the base bleed propellant. The Mg/PTFE pyrotechnic composition pressed in the igniter of the base bleed unit (BBU) provides additional energy to the BBU via a chemical reaction. Thus, the extinguished base bleed propellant is reignited under the effect of high-temperature combustion gas jets from the igniter. In this study, a numerical analysis is conducted to evaluate the effects of PTFE and Mg granularity as well as Mg/PTFE pyrotechnic compositions. Owing to the rapid depressurization, the temperature and pressure was found to decrease for different Mg/PTFE pyrotechnic compositions. However, the depressurization time increased as the PTFE granularity increased, the Mg granularity decreased, and the Mg content increased. When the pressure in the combustion chamber of the BBU decreased to the atmospheric pressure, the combustion gas jets from the igniter expand upstream (rather than downstream). However, these combustion gas jets exhibit different axial and radial expansion characteristics depending on the pyrotechnic compositions used. The results show that the reignition delay time, td, of the base bleed propellant was 377.608, 94.27, 387.243, 523.966, and 221.094 ms for cases A–E, respectively. Therefore, it was concluded that the Mg/PTFE pyrotechnic composition of case B was the most beneficial for the reignition of the base bleed propellant, with the earliest addition of energy and mass to the BBP.

Breath figures makes porous the “so-called” skin layer obtained in polymer foams prepared by supercritical CO2 treatments

In this article, the preparation of porous polymeric scaffolds of the synthetic poly (isopropylideneglycerol methacrylate) (PIPGMA) is described combining two complementary techniques. Supercritical CO2 (SCCO2), has been used as foaming agent to obtain internal porosity by varying parameters such as pressure and depressurization time. However, the disadvantage of SCCO2 technology is the formation of a non-porous skin layer described in the majority of the samples. This skin layer was modified by the breath figures technique (BF), providing superficial porosity to the polymeric sample. The result of using both techniques subsequently showed the formation of a porous network throughout the samples with inner and outer pores interconnected, characterized by scanning electron microscopy (SEM), micro X-ray computerized tomography scanning (micro CT), and processing those images with Image J. Finally, preliminary biological evaluation of the porous samples has been carried out in order to evaluate the biocompatibility and cellular viability of these scaffolds.

Production of drug-releasing biodegradable microporous scaffold impregnated with gemcitabine using a CO2 foaming process

The use of supercritical fluids technology, in particular the use of CO2, is an important advantage over other production techniques of controlled release systems. The impregnation and foaming process can be carried out in a single step. By adjusting the conditions of pressure, temperature, depressurization time or type of polymer used, microcellular scaffolds can be obtained with desired characteristics and adapted to the patient's requirements. Moreover, it has been demonstrated that the use of polymeric solutions allows carrying out impregnation process at mild conditions. In this work, Gemcitabine impregnation in PLGA foams from polymeric solutions of ethyl lactate has been studied. The effect of polymer lactide to glycolide ratio (50:50 or 75:25), pressure (120 or 200 bar) and temperature (25 or 40 °C) were studied for three initial drug ratios (175, 105 or 35 mg GEM/g PLGA). Cell size of the foams varied between 35 μm and 158 μm, achieving an impregnation efficiency higher than 90 %. Finally, a study of the release profile of Gemcitabine in Phosphate Buffered Saline (PBS) was investigated and a mathematical modelling was carried out. In this model it was considered that the release process was divided into three different steps controlled by the external diffusion in the first place, by the internal transfer of mass in the second and then by the degradation of the polymer.

Production of biodegradable PLGA foams processed with high pressure CO2

Microcellular scaffolds were prepared using high pressure fluids. Solutions of biodegradable material Poly (lactic-co-glycolic) acid (PLGA) in a green solvent such as ethyl lactate was used as the scaffold matrix. To carry out polymer foaming from polymer solutions allows the possibility of reducing the working temperature. The effect of the ratio lactide to glycolide of the polymer, the working pressure, the initial concentration of the polymer in the solvent and the depressurization time were the variables studied at a temperature of 25 °C. The morphology of the foams obtained was characterized based on the cell diameter and its standard deviation, indicator of the homogeneity of the scaffolds obtained, as well as the density of cells. In addition, a study was performed on how the glass transition temperature (Tg) of a polymer is modified by the plasticizing effect of CO2 pressure.

Supercritical CO2 for the drying and microbial inactivation of apple’s slices

Supercritical CO2 (Sc-CO2) drying has been recognized as a promising low temperature drying technique for food products. In this regard, this work focuses on the feasibility of Sc-CO2 drying of apple’s slices: both the microbiological stability and mechanical behavior of the test product after the process have been investigated in dependence from different process parameters, namely drying time, pressurization time, and depressurization time. The microbiological stability was determined for both inoculated pathogenic bacteria (Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes) and naturally present microorganisms (yeasts and molds, mesophilic bacteria and spores and Enterobacteriaceae). Results demonstrated a complete inactivation of pathogenic bacteria under the detection limit (<1 CFU/g) just after the pressurization (10 min) and depressurization (20 min) phases. After the same steps, a strong reduction of vegetative bacteria and yeasts and molds was also observed in comparison with air drying and freeze drying samples. As regards the mechanical behavior, the Young Modulus, measured before and after the CO2 processes to provide a measurement of samples’ stiffness, resulted dependent from the final water activity, but independent from the length of pressurization and depressurization phases at longer drying time. Overall, these results are promising to foster the development of the technology at industrial level.

Allowing for the Stochastic Nature of Corrosion Damage in Marine-Based Objects Including Submerged Radiation-Hazardous Objects

A mathematical model of corrosion damage to the protective barriers of radiation hazardous marine-based objects, taking account of the stochastic nature of this process, is constructed. The rate of pitting corrosion is determined by many mutually independent factors containing random components. This makes it possible to model pitting corrosion as a random walk process in which the corrosion rate changes discreetly and remains constant for one computational time step. The Monte Carlo method is used to calculate the depressurization time of an object with one protective barrier. The obtained estimates agree with expeditionary observations.

Efficiency analysis of depressurization process and pressure control strategies for liquid hydrogen storage system in microgravity

In order to investigate dynamic characteristics of pressure fluctuation and thermal efficiency of a liquid hydrogen (LH2) storage system during depressurization process under microgravity condition, a transient CFD model of LH2 tank is established. Based on the assumption of lumped vapor, a UDF code is developed to solve phase change and heat transfer between liquid phase and vapor one. The thermal efficiency is provided for assessing the performance of different pressure control methods. Results show that raising the injection velocity and decreasing the temperature of the injection liquid can enhance the effect of fluid mixing and shorten the depressurization time. Increasing the pressure lower limit can also improve the efficiency of depressurization process. The model can predict the tendency of pressure changes in the tank, and provide theoretical guide to design LH2 tank and optimize its parameters for space application.

Combining Breath Figures and Supercritical Fluids To Obtain Porous Polymer Scaffolds.

Supercritical fluids technology is a clean methodology to foam polymeric materials. However, this technique provides only the formation of inner porosity, whereas the so-called skin layer is commonly observed at the polymer surface. This article describes a new method for the preparation of outer and inner porous poly(ε-caprolactone) (PCL) scaffolds by combination of supercritical CO2 (SCCO2) foaming and the breath figures technique. In the first step, experiments with a SCCO2 reactor were performed at 35–45 °C, 100–250 bar, and 1–20 min depressurization time. The effect of these parameters in the formation of inner porosity was investigated for an adequate optimization. In a late stage, to provide also surface porosity to the polymeric samples and remove the skin layer, the breath figures technique was employed. The evaluation of porosity was determined by scanning electronic microscopy, mercury porosimetry, and micro X-ray computerized tomography scanning processing the images obtained with the ImageJ software. The results of this study using these two complementary techniques showed the existence of interconnectivity between inner and outer porosity of the samples. Furthermore, thermal transitions and crystallinity of the PCL samples have been analyzed by differential scanning calorimetry. Finally, a preliminary biological evaluation of the resulting scaffolds with mouse endothelial cells (C166-GFP) was performed to assess their biocompatibility and cellular viability.

Research on simulation and test of braking performance of ultra-deep mine hoist

With the utilization of the deep resources of the earth, it has become a new trend to develop a ultra-deep mine hoist which can meet the conditions of long distance, high speed and heavy load. The research on its braking performance is directly related to the safe operation. This paper is based on a ultra-deep mine hoist simulation test platform. The simulation model of the braking system is established in AMESim software by analyzing the hydraulic working principle. Finally, the field running data of the ultra-deep mine hoist simulation test platform are used to test and verify. The results of simulation and test show that some parameters’ changing rules and impacts such as the greater the spring preloading, the shorter the depressurization time and the response time in the case of no more than a certain value (8.5MPa in this paper). It provides guidance for the research and application of ultra-deep mine hoist brake system in the future.

Preparation of a Menthol/beta-Cyclodextrin Inclusion Complex Using Supercritical CO2

A menthol/β-cyclodextrin inclusion complex was produced using supercritical CO2 while varying the temperature, pressure, co-solvent, inclusion time and depressurization time. The complex resulted was characterized with X-ray diffraction, scanning electron microscopy and differential scanning calorimetry. The characterization data confirmed the production of the inclusion complex at a maximum yield of 93.75 %. The dissolution rate of the complex was signii¬?cantly higher than those of either untreated menthol or a physical mixture of menthol and β-cyclodextrin. This work thus demonstrated that supercritical CO2 could be successfully used to achieve inclusion complexes of menthol with β-CD.

Effect of a wearable patient sensor on care delivery for preventing pressure injuries in acutely ill adults: A pragmatic randomized clinical trial (LS-HAPI study)

ImportanceThough theoretically sound, studies have failed to demonstrate the benefit of routine repositioning of at-risk patients for the prevention of hospital acquired pressure injuries. ObjectiveTo assess the clinical effectiveness of a wearable patient sensor to improve care delivery and patient outcomes by increasing the total time with turning compliance and preventing pressure injuries in acutely ill patients. DesignPragmatic, investigator initiated, open label, single site, randomized clinical trial. SettingTwo Intensive Care Units in a large Academic Medical Center in California. ParticipantsConsecutive adult patients admitted to one of two Intensive Care Units between September 2015 to January 2016 were included (n = 1564). Of the eligible patients, 1312 underwent randomization. InterventionPatients received either turning care relying on traditional turn reminders and standard practices (control group, n = 653), or optimal turning practices, influenced by real-time data derived from a wearable patient sensor (treatment group, n = 659). Main outcome(s) and Measure(s)The primary and secondary outcomes of interest were occurrence of hospital acquired pressure injury and turning compliance. Sensitivity analysis was performed to compare intention-to-treat and per-protocol effects. ResultsThe mean age was 60 years (SD, 17 years); 55% were male. We analyzed 103,000 h of monitoring data. Overall the intervention group had significantly fewer Hospital Acquired Pressure Injuries during Intensive Care Unit admission than the control group (5 patients [0.7%] vs. 15 patients [2.3%] (OR = 0.33, 95%CI [0.12, 0.90], p = 0.031). The total time with turning compliance was significantly different in the intervention group vs. control group (67% vs 54%; difference 0.11, 95%CI [0.08, 0.13], p < 0.001). Turning magnitude (21°, p = 0.923) and adequate depressurization time (39%, p = 0.145) were not statistically different between groups. Conclusions and RelevanceAmong acutely ill adult patients requiring Intensive Care Unit admission, the provision of optimal turning was greater with a wearable patient sensor, increasing the total time with turning compliance and demonstrated a statistically significant protective effect against the development of hospital acquired pressure injuries. These are the first quantitative data on turn quality in the Intensive Care Unit and highlight the need to reinforce optimal turning practices. Additional clinical trials leveraging technologies like wearable sensors are needed to establish the appropriate frequency and dosing of individualized turning protocols to prevent pressure injuries in at-risk hospitalized patients.

Mathematical simulation of heat and mass transfer during controlled depressurization of supercritical CO2 in extraction vessels

Even after almost forty years of industrial application, companies are still reluctant to use supercritical (sc) CO2 as a solvent for extractions due to the perceived high production costs. Literature on the matter suggests that, because extraction at high pressure needs to be done in batches, using multiple extraction vessels with simulated-countercurrent flow could reduce operational costs. However, the more extraction vessels used, the less time there is to recondition them in order to have a semi-continuous operation; and if the reconditioning, and particularly the depressurization, is done too fast, the vessel could become brittle and permanently damaged. With the goal of optimizing the depressurization process in mind, numerical simulation of temperature and mass was carried considering a 1-dm3 vessel filled with a packed bed made with model materials using a mass flow function that depends on the chocked mass flux and a valve opening area. The correlation Nu=0.0777Da−0.0373Ra0.397 was obtained for convective heat transfer at the vessel wall, and temperature, pressure, and vented mass flow were simulated with about 20% improvement in predictions in comparison to our previous correlation. To explore the use of the model for practical purposes, it was used to simulate depressurization processes with volumes up to 1m3 and with different initial conditions and vessel geometries so as to have a first approach on the effect of these parameters on the depressurization time. Simulated depressurization times reached a maximum value of 54.5min for depressurizations of a 1-m3 extraction vessel starting at 60°C and 70MPa, which are very plausible extraction conditions. This model can be used to determine optimal reconditioning time in industrial plants for cost minimization.

Foaming of poly(vinylidene fluoride-co-hexafluoropropylene) using supercritical carbon dioxide

Abstract This work studied the foaming behavior of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) in supercritical carbon dioxide (scCO 2 ). The effects of foaming temperature, foaming pressure, saturation time, depressurization time on the foam structure and crystallinity of samples were investigated. The foaming ability varies with different combinations of the foaming temperature and foaming pressure. However, a lower foaming temperature and a higher foaming pressure are more favorable for obtaining uniform foam than a higher foaming temperature and a lower foaming pressure. At a given foaming temperature and saturation time, increasing the foaming pressure leads to the decreased crystallinity and an increase in the melting temperature.