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1.
Microcellular foaming of amorphous rigid polymers, polymethylmethacrylate (PMMA) and polystyrene (PS) was studied in supercritical CO2 (ScCO2) in the presence of several types of additives, such as triblock (styrene-co-butadiene-co-methylmethacrylate, SBM and methylmethacrylate-co-butylacrylate-co-methylmethacrylate, MAM) terpolymers. This work is focused in the two-step foaming process, in which the sample is previously saturated under ScCO2 being expanded in a second step out of the CO2 vessel (e.g. in a hot oil bath) where foaming is initiated by the change of temperature near or above the glass transition temperature of the glass/polymer glassy system. Samples were saturated under high pressures of CO2 (300 bar), at room temperature, for 16 h, followed by a quenching at a high depressurization rate (150 bar/min). In the last step, foaming was carried out at different temperatures (from 80 °C to 140 °C) and different foaming times (from 10 s to 120 s). It was found that cellular structures were controlled selecting either the additive type or the foaming conditions. Cell sizes are ranging from 0.3 μm to 300 μm, and densities from 0.50 g/cm3 to 1 g/cm3 depending on the polymers considered.  相似文献   

2.
This study has been dedicated to the foaming of modified poly (lactic acid) with supercritical CO2. The first part of this work consisted in a rheological modification of neat PLA through chain extension. Improvement of the melt viscosity and elasticity has been achieved by the use of an epoxy additive during a reactive extrusion process. Rheological characterizations confirmed an increase of the melt strength due to this chain extension process. Foaming was then performed on the neat and modified PLAs using a batch process with supercritical CO2 as blowing agent. The investigation of the foaming temperature revealed an enlarged processing window for modified PLAs compared to neat PLA. Depending on the foaming parameters, foams with a cellular structure ranging from macro scale to micro scale have been obtained. A concomitant effect of the CO2-plasticization and the crystallisation on the melt rheology could explain this wide range of cellular morphologies.  相似文献   

3.
Limei Xu  Hui Yang  Chunsheng Li 《Polymer》2010,51(16):3808-4000
A novel route for a preparation of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) block copolymer vesicles induced by supercritical carbon dioxide (scCO2) is demonstrated. When PS-b-PEO block copolymer solutions in tetrahydrofuran (THF) are treated with scCO2 at 70 °C for different times, PS-b-PEO copolymers first assemble into aggregated spheres; then aggregated spheres change into large compound micelles and finally evolve into vesicles. The possible formation mechanism of the vesicles is discussed.  相似文献   

4.
Copolymerization of acrylic acid and 3-[tris(trimethylsilyloxy)silyl]propyl methacrylate (TMSPMA) in supercritical carbon dioxide was successfully carried out. The products were obtained in the form of dry white powder with diameter about 0.2 μm. Viscosities of 2% aqueous solution of the copolymers dramatically increased as the content of TMSPMA in the copolymer increased and it was much higher than that of poly(acrylic acid). In addition, the viscosity of the copolymers showed a strong dependence on pH with a maximum at pH 5.0, which is due to the cooperation of intermolecular association and electrostatic repulsion.  相似文献   

5.
Zhi Ma 《Polymer》2004,45(20):6789-6797
Dispersion polymerization of 2-hydroxyethyl methacrylate (HEMA) has been successfully performed in supercritical carbon dioxide at P=370 bar and T=65 °C with azobis(isobutyronitrile) as initiator and a hydrophilic/CO2-philic poly(ethylene oxide)-b-poly(1,1,2,2-tetrahydroperfluorodecyl acrylate) (PEO-b-PFDA) block copolymer as steric stabilizer. The PEO-b-PFDA (2K/21K) block copolymer was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. Spherical particles of poly(HEMA) were obtained in the range of 200-400 nm diameter size with a narrow particle size distribution (Dw/Dn<1.1). The effect of the stabilizer concentration on the dispersion polymerization was investigated from 20 w/w% down to 3.5 w/w% versus HEMA. Precipitation polymerization in the absence of stabilizer lead to the formation of large aggregates of partially coalesced particles whereas discrete spherical particles of poly(HEMA) were obtained by dispersion polymerization even at low concentration of PEO-b-PFDA (3.5 w/w% versus HEMA).  相似文献   

6.
Rosmarinus officinalis (rosemary) extracts were obtained in a supercritical pilot-scale plant. Based on experimental information available in the literature for analytical or low-scale processes, extraction temperature and pressure were selected to be 313 K and 30 MPa. At these extraction conditions, the kinetic behavior of the pilot-scale overall extraction curve were determined with respect to yield, antioxidant activity and carnosic acid content. The overall extraction curve was represented using Sovova's model; the average deviation between measured and calculated yields was lower than 2%. Mass transfer coefficients in the fluid and solid phases were determined and were compared with previous data reported in the literature for low-scale rosemary supercritical extraction.A two-stage depressurization procedure was accomplished and the effect of both on-line fractionation and extraction time on the antioxidant activity of the samples collected was studied. The antioxidant activity of the different fractions could be straight correlated with the carnosic acid content with a regression coefficient of 0.92.  相似文献   

7.
New perfluorinated BINAP ligands and their cationic rhodium complexes have been synthesized and characterized. The catalysts have been tested in homogeneous hydrogenation of the styrene in both methanol and supercritical carbon dioxide (scCO2). The selective hydrogenations of the styrene in scCO2 were carried out under the same reaction conditions of 343.15 K temperature and 120 bar CO2 pressure after 3 h (molar ratio of substrate to catalyst = 500). While all catalysts showed 100% conversion in methanol, same activity was not carried out in scCO2. (R)-6,6-diperflorooktil-2,2-bis(diphenylphosphino)-1,1-binaphtyl-[Rh(COD)]BArF was showed the highest conversion (96.4%) in scCO2. Furthermore, methanol was used as co-solvent in the supercritical media in hydrogenation of styrene for the perfluorinated catalysts, which were inactive in scCO2. Addition of methanol in scCO2 has rather increased the conversion.  相似文献   

8.
In this work we investigated the solid-state supercritical CO2 (scCO2) foaming of poly(?-caprolactone) (PCL), a semi-crystalline, biodegradable polyester, and PCL loaded with 5 wt% of hydroxyapatite (HA) nano-particles.In order to investigate the effect of the thermal history and eventual residue of the crystalline phase on the pore structure of the foams, samples were subjected to three different cooling protocols from the melt, and subsequently foamed by using scCO2 as blowing agent. The foaming process was performed in the 37-40 °C temperature range, melting point of PCL being 60 °C. The saturation pressure, in the range from 10 to 20 MPa, and the foaming time, from 2 to 900 s, were modulated in order to control the final morphology, porosity and pore structure of the foams and, possibly, to amplify the original differences among the different samples.The results of this study demonstrated that by the scCO2 foaming it was possible to produce PCL and PCL-HA foams with homogeneous morphologies at relatively low temperatures. Furthermore, by the appropriate combination of materials properties and foaming parameters, we prepared foams with porosities in the 55-85% range, mean pore size from 40 to 250 μm and pore density from 105 to 108 pore/cm3. Finally, we also proposed a two-step depressurization foaming process for the design of bi-modal and highly interconnected foams suitable as scaffolds for tissue engineering.  相似文献   

9.
Foamable high melt strength polypropylene (HMSPP) was prepared by grafting styrene (St) onto polypropylene (PP) and simultaneously introducing polydimethylsiloxane (PDMS) through?a?one-step?melt extrusion process. The effect of PDMS viscosity on the foaming behavior of HMSPP was systematically investigated using supercritical CO2 as the foaming agent. The results show that the addition of PDMS has little effect on the grafting reaction of St and HMSPP exhibits enhanced elastic response and obvious strain hardening effect. Though the CO2 solubility of HMSPP with PDMS (PDMS-HMSPP) is lower than that of HMSPP without PDMS, especially for PDMS with low viscosity, the PDMS-HMSPP foams exhibit narrow cell size distribution and high cell density. The fracture morphology of PDMS-HMSPP shows that PDMS with low viscosity disperses more easily and uniformly in HMSPP matrix, leading to form small domains during the extrusion process. These small domains act as bubble nucleation sites and thus may be responsible for the improved foaming performance of HMSPP.  相似文献   

10.
Response surface methodology (RSM) was applied to optimize the variables affecting the supercritical carbon dioxide (SC-CO2) extraction of non-polar compounds from Anastatica hierochuntica using the Central Composite Design technique (CCD). Independent variables were temperature (32–46 °C) and pressure (22–46 MPa). Dependent variables were the percentage of the content of hexadecanoic acid, 9,12-octadecadienoic acid, heneicosane and heptacosane. Pressure was the most significant parameter that affected the content of the compounds. The hexadecanoic and 9,12-octadecadienoic content decreased while heneicosane and heptacosane increased with pressure. A number of choices can be run either at low pressure and low temperature or at low pressure and high temperature in order to optimize extraction of the selected compounds. Extraction either at low temperature (33 °C) and low pressure (25.6 MPa), or at high temperature (42 °C) and low pressure (22.0 MPa) maximized the yield of hexadecanoic, 9,12-octedecanoic, heneicosane and heptacosane.  相似文献   

11.
The structure and properties of highly stereoregular isotactic poly(methyl methacrylate) (it-PMMA) and syndiotactic poly(methyl methacrylate) (st-PMMA) blends with crystalline stereocomplex formed by supercritical CO2 treatment at temperatures ranging from 35 to 130 °C were investigated by means of differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and dynamic mechanical analysis (DMA) measurements. The melting temperature, Tm, and the heat of fusion, ΔHm, had maximum values at about 200 °C and 25 J/g, respectively. The degree of crystallinity evaluated by WAXD ranged in value from 32 to 38%. The fringed-micellar stereocomplex crystallites were formed in case of treatment temperatures below 90 °C, and the orderliness perpendicular to the helix axis of the fringed-micellar crystallites was considered to be increased with increasing treatment temperature. In case of treatment temperature of 130 °C, the fringed-micellar crystallites and the lamellar crystallites with high orderliness parallel to the helix axis coupled with the perpendicular orderliness were formed, and the respective double endothermic peaks, Tm1 and Tm3, were observed in DSC due to the melting of the two kinds of stereocomplex crystallites. The it-PMMA/st-PMMA blends containing the fringed-micellar crystallites maintained high values of storage modulus, E′, up to higher temperature compared with the amorphous blends. The E′ of the blend treated with CO2 at 130 °C decreased twice at temperatures corresponding to Tm1 and Tm3.  相似文献   

12.
Bimetallic Pd–Ru nanoparticles of different elemental ratios are prepared via in situ reduction of their simple salts in reverse micelles in supercritical carbon dioxide (scCO2). The optimised Pd:Ru (1:1) nanoparticle shows the highest activity for hydrogenation of functionalised alkene under mild conditions, which can be easily recycled under the reaction conditions without use of organic solvent.  相似文献   

13.
Mesoporous silica molecular sieve SBA-15 has been grafted with monolayer and doublelayer of titanium dioxide via surface sol–gel process in supercritical carbon dioxide (SC CO2). The materials were characterized by nitrogen adsorption, X-ray photoelectron, X-ray diffraction (XRD), and Raman spectroscopy. The results suggest that the incorporated titanium dioxide is present mainly as anatase phase. The pore diameter decreases with the modification cycle number, and the titanium dioxide exists as a 5 Å thick film chemically anchored on the mesopores of SBA-15.  相似文献   

14.
Jingya Shi  Peiyi Wu  Lei Li  Tao Liu  Ling Zhao 《Polymer》2009,50(23):5598-5604
The solid-solid crystalline transformation of isotactic polybutene-1 (iPB-1) from tetragonal form II to hexagonal form I could be accelerated by supercritical carbon dioxide (scCO2). In this study, in-situ Fourier transform infrared spectroscopy (FTIR) and two dimensional correlation spectroscopy (2DIR) is used to observe and investigate the crystallization behaviour of iPB in scCO2 and compressed CO2. Based on the transform sequence given by 2DIR analysis, this transformation of helical chain structures is found to be initiated with the motion of side chains and followed by the movement of main chains. It is speculated that the motion of polymer chains was enhanced with the diffusion of CO2. Also this crystalline transition is observed even in compressed CO2, suggesting that CO2 could also diffused into polymer under high pressure near the critical pressure. This diffusion of CO2 is indicated by the growth of IR bands being assigned to the stretching vibration of C–O. A further investigation on the mechanically heating and freely cooling of iPB provides more evidences on the process of structure transition. The result implies that the nucleus of tetragonal form II formed in the melt is not affected by the existence of scCO2, but the crystallization temperature become obviously lower.  相似文献   

15.
Quartz crystal microbalance (QCM) was used as an in situ detector to investigate the potential application in the phase equilibrium determination of supercritical CO2-drug-polymer systems. CO2 solubility in two biodegradable polymers, poly(d,l-lactic acid) (d,l-PLA) and poly(l-lactic acid) (l-PLA) was primarily measured at 313.15 K and pressures up to 10.0 MPa. d,l-PLA showed a better CO2 absorption ability due to its amorphous structure. Four drug model compounds of poor solubility in water, ibuprofen, aspirin, salicylic acid and naphthalene were selected as representatives for the examination of drug uptake in PLA matrices, as well as partition coefficient during supercritical impregnation. It was found that partition coefficients of drugs can reach as high as 103-104 orders of magnitude and greatly affected by the intermolecular interactions between drugs and PLA. Aspirin exhibited the best partitioning during the supercritical impregnation at pressures of 8.0-10.0 MPa due to the existence of carboxylic acid and acetyl groups. Drug partitioning is additionally related to the drug concentration in ScCO2, i.e. salicylic acid showed little absorption in PLA according to its poor solubility in ScCO2 at 7.5-8.0 MPa, whereas the well CO2-soluble compound, naphthalene, exhibited a moderate partition coefficient although its polarity was different from l-PLA.  相似文献   

16.
The solubilities of mixed clozapine and menthol also lamotrigine and menthol in supercritical carbon dioxide were determined at 313 and 323 K and over pressure ranging from 123 to 337 bar. The solubility of both solutes with solid cosolvent system is observed to increase relative to the value of the corresponding without solid cosolvent system. As compared with their respective binary system (without solid cosolvent), the mixed clozapine (with solid cosolvent) solubility enhancement greatly by around 56 times and the lamotrigine one does by approximately eight times. In presence of menthol these chemicals have solubilities with values ranging from 1.88 × 10−4 to 4.48 × 10−4 (clozapine) and 0.09 × 10−4 to 0.36 × 10−4 (lamotrigine) mole fraction. The solubility data were correlated using five semi-empirical density-based models (Chrastil, Bartle, K-J, M-T and Thakur models). Correlated results for clozapine with the Chrastil, M-T, K-J, and Bartle models and for lamotrigine with the Chrastil, M-T and Bartel models are in excellent agreement with the experimental data.  相似文献   

17.
Partially biodegradable porous scaffolds incorporating bioactive molecules prepared by clean techniques posses an enormous interest in tissue engineering applications. Poly(methyl methacrylate)-poly(l-lactic acid) (PMMA-PLA) blends were submitted to CO2 supercritical conditions (P = 160-260 bar, T = 60 °C) after certain time and then rapidly depressurized to obtain porous structures that have been related with the supercritical parameters and to the polymer blend composition. In some cases ibuprofen was also incorporated to the formulations previously to the CO2 treatment and studied the appropriate conditions for avoiding its extraction in SCCO2. Scaffolds purity, thermal transitions, swelling and degradation behaviour, and the ibuprofen release were also studied to determine the appropriate scaffolds with a desired porosity for cell seeding. Cell culture was performed on the selected porous scaffolds using human fibroblast examined by scanning electron microscopy (SEM).  相似文献   

18.
单体坤  马文良  杨涛 《橡胶工业》2018,65(5):514-517
用超临界二氧化碳制备热塑性聚氨酯弹性体发泡材料(E-TPU),分析发泡机理并研究发泡性能。结果表明:泄压速率和发泡温度是影响E-TPU发泡性能的两个重要因素;增大泄压速率有利于提高气泡成核速率和成核数量;升高发泡温度使气泡易膨胀长大,E-TPU密度减小;但发泡温度过高会导致气泡破裂和塌陷,E-TPU密度增大;当发泡温度为130℃左右时,E-TPU密度最小,发泡性能最好。  相似文献   

19.
Novel inorganic/organic epoxy based materials were fabricated using both poly(styrene-b-ethylene oxide) (SEO) block copolymer and synthesized TiO2 nanoparticles as modifier. The influence of the ratio between modifiers on the final morphology generated in the investigated epoxy systems was studied by atomic force microscopy (AFM) and transmission electron microscopy (TEM). Results indicated that even for high nanoparticle content, TiO2 nanoparticles synthesized via sol-gel were homogenously dispersed in the epoxy-rich phase. The morphology of the inorganic/organic epoxy based composites consisted of both well-dispersed TiO2 nanoparticles and microphase separated PS block in the continuous PEO block/epoxy-rich phase since block copolymer acted as templating agent for selective location of TiO2 nanoparticles. Differential scanning calorimetry (DSC) was used to study the curing behavior and the influence of the type and quantity of modifier on the glass transition temperature of epoxy matrix. Additionally, optical properties, transparency and UV-shielding efficiency of these new multiphase advanced thermosetting materials were also investigated.  相似文献   

20.
仲华  孙少俊  奚桢浩  刘涛  赵玲 《化工学报》2013,(5):1513-1519
通过高温高压磁悬浮天平(MSB)测定表观溶解度、高温高压视窗釜进行溶胀度校正的方法研究了CO2在PET熔体中的溶解度,考察了温度、压力对改性前后PET在CO2环境中的溶胀度和CO2溶解度的影响。结果表明,PET在CO2环境中的溶胀度和CO2溶解度均随温度的增加而减小,随压力增加而增加,但高压下溶胀度的增加趋势减缓并趋于某定值;与常规线性PET相比,改性PET具有较小的溶胀度和溶解度。在250~280℃,4~6 MPa下,CO2在PET熔体中的溶解度具有10-2 g CO2·(g PET melt)-1的量级。1~6 MPa下CO2在PET熔体中的溶解行为符合亨利定律,利用最小二乘法拟合得到了CO2在PET熔体中的溶解热。  相似文献   

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