PP/超临界CO2连续挤出发泡成型

以超临界CO2为发泡剂,在连续挤出发泡过程中研究了超临界CO2用量对高熔体强度均聚聚丙烯(PP)发泡成型过程的影响.随着超临界CO2用量的增加,发泡挤出机口模压力降低,试样发泡倍率降低,泡孔尺寸变小,泡孔密度提高.在w(CO2)为3%,5%时,得到发泡倍率最高为13左右的PP发泡材料.w(CO2)为7%,发泡温度为12...     

Precipitation of PMMA/PCL blends using supercritical carbon dioxide

Solutions of a poly(methyl methacrylate)–poly(ε‐Caprolactone) (PMMA/PCL) polymer blend in dichloromethane (DCM) and mixtures of the same polymer blend and cholesterol in DCM were sprayed into supercritical carbon dioxide. Carbon dioxide was contacted with 0.23–1 wt % polymer solutions and with 0.3–1 wt % polymer plus 0.1–0.6 wt % cholesterol solutions in a continuous mode of operation. Pressure and temperature were constant for almost all of the experiments, 11 MPa and 314 K, respectively. Fibrous networks composed of many smaller microfibrils were obtained by spraying the different solutions through a conical nozzle into concurrently flowing supercritical carbon dioxide. This morphology suggests such an important degree of agglomeration that primary particles are no longer discernible. Processing the polymers with CO₂ leads to the removal of contaminants as the precipitate was free of monomer and initiator. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2422–2426, 2004     

用ES共聚物对PE—PS共混物增容的研究

准无规乙烯－苯乙烯共聚物是由一种限定几何结构的催化剂制备,对聚乙烯－聚苯乙烯共混物的增容是非常有效的。     

Mechanical and thermal properties of epoxypolymethyl methacrylate blends synthesizedin supercritical carbon dioxide

A series of epoxy/polymethyl methacrylate (E/PMMA) blends was synthesized through impregnation polymerization of methyl methacrylate at concentrations ranging (0–1.5 phr) into diglycidyl ether of bisphenol‐A (0.1 mol) in presence of 2,2‐azobisisobutyronitrile (2 × 10^?2 mol) at 3000 psi, (60–90 ± 1)°C for 3 h in supercritical carbon dioxide, followed by curing of treated epoxy with triethylene tetramine (10 phr) at (40 ± 1)°C. The progress of all such impregnation polymerization reactions was monitored rheoviscometrically. Formation of E/PMMA blends was ascertained through of PMMA mass uptake (%) into epoxy, UV–vis and FTIR spectra, and TEM. With PMMA mass uptake (%), compression strength and resistance against wear of E/PMMA blends were increased with simultaneous decrease in their Rockwell hardness (R scale), charpy impact, and tensile strength, respectively. All E/PMMA blends have shown nonuniform photoelastic behavior at applied load ranging 4–20 kgf and significant stability against thermooxidation with T_g/T_m and char yield (%) ranging 0.53–0.59, 29.31–31.66, respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1303–1310, 2007     

Preparation of titanium dioxide/activated carbon composites using supercritical carbon dioxide

The penetration of titanium tetraisopropoxide (TTIP) dissolved in supercritical CO₂ into the nano-spaces of an activated carbon was studied for the preparation of a TiO₂-coated activated carbon. The conversion of TTIP to TiO₂ through thermal decomposition was confirmed by evolved gas analysis during heat treatment under a N₂ flow. Acetone was detected in the evolved gas, which suggested that some isopropoxide groups in TTIP reacted with the carbonyl groups on the activated carbon surface. This chemical reaction with carbon is expected to be advantageous for favorable attachment to the carbon surface. The crystallite size of anatase in the TiO₂/carbon composites was 4.1 nm, as estimated from the X-ray diffraction pattern, which almost corresponded to the graphene crystallite size; L_a (3.3-3.4 nm), as estimated from both the Raman spectrum and X-ray diffraction pattern. As the size of the crystallite prepared by bulk condensation of TTIP was more than 15 nm, these results confirmed that the anatase crystals were present in the carbon pores. Also, it was suggested that the crystal growth of TiO₂ was influenced by the carbon nano-spaces.     

超临界CO2清洗技术

介绍了超临界CO2清洗的工艺及其应用,分析了超临界CO2清洗在技术、经济及环保方面的特点。     

Extraction of woolgrease with supercritical carbon dioxide

Supercritical carbon dioxide was used to extract unrefined woolgrease. The resulting product had no color and little odor, resembling high-grade commercial lanolin. The amounts of woolgrease extracted for fixed volumes of supercritical fluid solvent were measured at 60, 70 and 80°C and at pressures from 200–520 bar. In this study, the highest recoveries were obtained at 80°C and pressures in excess of 380 bar. Analysis of the extracts by capillary supercritical-fluid chromatography and thin-layer chromatography indicated that the composition of the extract changed with extraction time. The earliest fractions were enriched in cholesterol and contained relatively small amounts of species with higher molecular weight. The results suggest that supercritical fluid extraction may be used to obtain an enriched cholesterol fraction from wool-grease.     

Effects of supercritical carbon dioxide on crystallisation behaviour of polycarbonate/poly(methyl methacrylate) blends

SnCl₂·2H₂O-modified polycarbonate (PC)/poly(methyl methacrylate) (PMMA) (80/20?w/w) blends were prepared by melt blending using a torque rheometer. Supercritical carbon dioxide (scCO₂) has been used to induce the crystallisation of PC/PMMA blends while the crystallisation behaviour and morphology of these blend systems under different saturation temperatures, saturation pressures, saturation times and co-solvent contents were characterised by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The gravimetric experiment shows that the solubility of scCO₂ in PC/PMMA blends increases with the increase of saturation temperature, pressure and time. The DSC curves demonstrate that in these blend systems, the induced crystallisation of PC has been found and two kinds of crystals with different thicknesses exist in it. From the SEM images, it can be found that the structure of PC crystal becomes more perfect and its crystallinity also increases with the increase of saturation temperature, pressure, time and co-solvent content.     

Compatibilization of PE/PS and PE/PP blends. I. Effect of processing conditions and formulation

The objective of this work was to study the effectiveness of low‐cost commercial compatibilizers and several processes (internal mixer, single‐ and twin‐screw extruders) for two types of plastic blends: high‐density polyethylene/polypropylene and high‐density polyethylene/polystyrene blends, to gain insight into the recycling of wastes from those frequently encountered mixed plastics. Blends going from a pure A to a pure B component, with and without a compatibilizer, were prepared using an internal mixer, a corotating twin‐screw extruder, as well as a single‐screw extruder to follow an industrial‐convenient process. In both cases, the analyses of blend morphologies highlighted the poor adherence between the two phases in the uncompatibilized blends. Compatibilized blends display better adherence between phases and the ability to process blends made from both single‐ and twin‐screw extruders. When adding a compatibilizer, the viscosity of each blend (PE/PP or PE/PS) increased due to a better adhesion of the phases. Charpy impact tests showed that the presence of the compatibilizer in PE/PS blends increased their impact properties. Indeed, the improvement of the adhesion between the two phases enabled stress transfer at the interface. A single‐screw extruder seems to be efficient as a processing method on an industrial scale when a compatibilizer is used. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2475–2484, 2003     

Dye distribution in supercritical dyeing with carbon dioxide

The measurement of equilibrium dye uptake in PET fiber is carried out using a flow-type cylindrical vessel. Using the expanded liquid model in which both phases are supposed to be liquid mixtures, the equilibrium uptake of C.I. disperse red 60 may be calculated from each binary interaction parameter of carbon dioxide–dye, carbon dioxide–PET and dye–PET binary systems. The calculated uptake is compared with the observed one with the same order of magnitude, even though the former is overestimated. The binary interaction parameter of dye–PET system that is obtained from the equilibrium dye uptake in PET is smaller by about 1.5 than that obtained by the binary system. Nevertheless, it is found that the predicted uptake of dye with using the interaction parameter regressed from the ternary data is in excellent agreement with the experimental one. The distribution of C. I. disperse red 60 into supercritical fluid and PET phase at equilibrium can be predicted and compared with the experimental one. The estimated distribution coefficient increases with the pressure increase, because the sorption of dye in PET fiber increases slowly with the pressure than the dye solubility in carbon dioxide does. This tendency is weakened with increase of temperature.     

Polar attributes of supercritical carbon dioxide

Supercritical carbon dioxide (scCO(2)) is increasingly promoted as an environmentally benign alternative to conventional organic solvents. The supercritical state bridges the gap between liquid and gaseous states by offering gaslike diffusion rates and liquidlike solvent densities, thereby enabling potential opportunities as a reaction and separation medium in chemical industry. Understanding the solvent behavior of liquid and scCO(2) is of critical importance to enable the design of CO(2)-philic molecular systems and to expand the use of these solvent systems to a wider range of chemical processes. Historically CO(2) was treated as a nonpolar solvent, primarily because of its low dielectric constant and zero molecular dipole moment. CO(2) has also been described as a quadrupolar solvent because of its significant quadrupole moment. Recent studies suggest that, as far as the microscopic solvent behavior of CO(2) is concerned, CO(2) has the potential to act as both a weak Lewis acid and Lewis base. Also, strong theoretical and experimental evidence indicates that CO(2) can participate in conventional or nonconventional hydrogen-bonding interactions. All of these site-specific solute-solvent interactions are important to understand the fundamental nature of CO(2) as a solvent. In this Account, we discuss these polar attributes of CO(2) and their relation to solvation.     

超临界二氧化碳/聚合物体系扩散度的测量方法

基于国外先进技术的发展,介绍了超临界二氧化碳/聚合物体系扩散度的各种测量方法.测量二元体系扩散度的方法包括测压法、测重法、光学观测法和光谱技术.测压法和测重法简单易用,是最重要的2种测量方法,但测压法难以测量高温高压体系,测重法需要防止因气体泄漏引起的误差,并需对结果进行浮力校正.光学观测法和光谱方法用于瞬态测量,不对溶解度量化测量.三元体系的测量方法只需对二元体系方法进行适当修正,目前使用的有经过修正的测重技术、利用紫外-可见吸收光谱法和傅里叶变换红外光谱技术等.另外,三元体系方法还包括测量超临界空气条件下的添加剂的传递性质的卷薄膜方法和强制Rayleigh散射法.     

Lampante olive oil refining with supercritical carbon dioxide

Lampante olive oil has been treated in a supercritical CO₂ extraction plant operating in a continuous countercurrent mode. We report the results of a systematic investigation to define the optimal operative parameters. We also have examined the compositional variation of lampante olive oil samples with different characteristics and of different geographic origins before and after refining at optimal conditions. Although practical feasibility of the proposed procedure can be questioned, the results demonstrate the possibility of fractionating components contained in the starting oil even if present at trace levels.     

Synthesis of PCL/clay masterbatches in supercritical carbon dioxide

Pre-exfoliated nanoclays were prepared through a masterbatch process using supercritical carbon dioxide as solvent and poly(?-caprolactone) as organic matrix. In situ polymerization of ?-caprolactone in the presence of large amount of clay was conducted to obtain these easily dispersible nanoclays, collected as a dry and fine powder after reaction. Dispersion of these pre-exfoliated nanoclays in chlorinated polyethylene was also investigated. All the results confirm the specific advantages of supercritical CO₂ towards conventional solvents for filler modification.     

Synthesis of polypyrrole/polythiophene copolymers in supercritical carbon dioxide

Synthesis and processing of polymer-based materials through green friendly methods involving supercritical fluids particularly supercritical carbon dioxide (SCC) has recently received substantial technological importance because of the commercial and industrial benefits involved. In the present work, a SCC assisted green and sustainable process has been developed to synthesize polypyrrole/polythiophene copolymers (PPCs). The process of synthesis has been conducted through ferric chloride-initiated chemical oxidative polymerization in the presence of various molar proportions of pyrrole to thiophene 0:1.0, 1.0:0, 1.0:1.0 and 1.0:2.0 at temperature ranging from 50 to 90 °C, 1,200 psi over 12 h in SCC. Polymerization below 90 °C afforded PPCs in semi-solid products, whereas polymerizations conducted at 90 °C under identical conditions have afforded the end products in complete solid state. The structure and properties of PPCs have been evaluated through ultraviolet–visible absorption and Fourier transform infrared spectra, elemental analysis, atomic force microscopy, simultaneous thermogravimetric–differential thermal analysis–differential thermogravimetry and four-point probe electrical conductivity methods. With molar proportion of thiophene, time and temperature, all the polymerization reactions have been conducted to completion resulting in PPCs with enhanced polymerization yield, rheoviscosity, dispersion of polypyrrole into polythiophene matrix and thermal stability. This has contributed a simultaneous loss in the electrical conductivity of PPCs.     

Preparation of polystyrene/montmorillonite nanocomposites in supercritical carbon dioxide

The preparation of polystyrene (PS)/montmorillonite (MMT) composites in supercritical carbon dioxide (SC? CO₂) was studied. Lipophilic organically modified MMT can be produced through an ion‐exchange reaction between native hydrophilic MMT and an intercalating agent (alkyl ammonium). PS/clay composites were prepared by free‐radical precipitation polymerization of styrene containing dispersed clay. X‐ray diffraction and transmission electron microscopy indicated that intercalation of MMT was achieved. PS/clay composites have a higher thermal decomposition temperature and lower glass‐transition temperature than pure PS. The IR spectrum analysis showed that the solvent of SC? CO₂ did not change the structures of the PS molecules, but there were some chemical interactions between the PS and the clay in the composites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 22–28, 2005     

Synthesis of montmorillonite/polystyrene nanocomposites in supercritical carbon dioxide

Monomer styrene and initiator N,N′‐azobis(isobutyronitrile) were impregnated into montmorillonite (MMT) galleries using supercritical CO₂ at 35°C and 12.0 MPa, after thermal polymerization of monomer at 65°C, resulting in MMT/polystyrene nanocomposites. The morphology and structure of the products were characterized by FTIR, powder X‐ray diffraction, transmission electron microscopy, differential scanning calorimetry, and thermogravimetric analysis. The results indicate that MMT is dispersed in the composite with intercalated and exfoliated structures, enhancing the thermal stability of nanocomposites. Changing the soaking time and the content of MMT in the supercritical solution during the impregnating process can control the exfoliated extent of MMT. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1194–1197, 2004     

Microcellular foaming of silicone rubber with supercritical carbon dioxide

In spite of great concern on the industrial application of microcellular silicone rubber foams, such as in electric and medical devices, only a few works can be found about the foaming of silicone rubber. In this study, microcellular silicone rubber foams with a cell size of 12 μm were successfully prepared with curing by heat and foaming by supercritical CO₂ as a green blowing agent. The microcellular silicone rubber foams exhibited a well-defined cell structure and a uniform cell size distribution. The crosslinking and foaming of silicone rubber was carried out separately. After foaming, the silicone rubber foam was cross-linked again to stabilize the foam structure and further improve its mechanical properties. Foaming process of cross-linked silicone rubber should be designed carefully based on the viscoelastic properties because of its elastic volume recovery in the atmosphere. The basic crosslinking condition for small cell size and high cell density was obtained after investigating the rheological behavior during crosslinking.     

Fluoropolymer synthesis in supercritical carbon dioxide

Herein we review the environmentally friendly synthesis of fluorinated polymers in supercritical carbon dioxide (scCO₂). Historically, many high-performance fluorinated materials are commercially synthesized in aqueous media using fluorinated surfactants or in non-aqueous conditions using fluorinated solvents. Our group has pioneered both the homogeneous and heterogeneous polymerization of fluorinated monomers in scCO₂. This review includes discussions on the synthesis of main-chain and side-chain fluoropolymers conducted via a chain-growth or continuous process. Specific materials consist of acrylate- and styrene-based systems, poly(vinyl ether)s, tetrafluoroethylene- and vinylidenefluoride-based, as well as novel fluorinated elastomers and thermoplastics.