Quantitative analysis of polymer additives in low density polyethylene using supercritical fluid extraction/supercritical fluid chromatography

Analysis of low concentration polymer additives has been a challenging problem. The commonly used methods of analysis involve the initial extraction of polymer additives with solvents, often in a Soxhlet apparatus, followed by liquid, size exclusion, or gas chromatography. This paper describes the on-line super-critical fluid extraction (SFE)-supercritical fluid chromatographic (SFC) determination of different additives from low density polyethylene. Cryogenic collection was used as an interface between SFE and SFC to focus the extraction eluate before transfer to an analytical SFC column for quantitative analysis.     

A Unified Sample Preparation System for Extraction of Various Analyte/Matrix Combinations

A supercritical fluid extraction/enhanced solvent extraction system (SFE/ESE) was used to remove polar and non-polar analytes from various matrices. Extraction of environmental pollutants from soil, additives from low density polyethylene, sulfa drugs from animal tissue, and drug from tablet was performed using both SFE and ESE. Results showed that a single instrumental system can be used to perform both ESE with organic solvents and SFE with carbon dioxide-based fluids. Each method has its own unique advantages and applications. The ability to carry out both solvent extraction and supercritical fluid extraction with one system has obvious economical advantages.     

The use of nitrous oxide for supercritical fluid extraction of pharmaceutical compounds from animal feed

Supercritical fluid extraction (SFE) coupled “off-line” with HPLC analysis has been applied to pharmaceutical analysis: two different matrixes (rodent and dog feed) were spiked with compounds under investigation in pharmacological studies in order to study the supercritical extraction of such matrixes prior to further analysis and quantification of the compounds of interest. The fluid flow-rate in the SFE system was governed by the geometric characteristics (internal diameter and length) of the linear fused silica capillaries. The changes in fluid flow-rate, between experiments, for each new restrictor, required the introduction of the term Total Gaseous Fluid Volume (TGFV), which enabled a series of extraction results to be compared. The comparative behavior of nitrous oxide and carbon dioxide as supercritical extraction fluids was investigated. Results obtained using pure supercritical fluids with high solvating power (density 0.79 g ml^?1) and fluids modified with a polar liquid solvent (methanol and acetonitrile) are discussed.     

Supercritical fluid extraction in herbal and natural product studies - a practical review

Due to increasingly stringent environmental regulations, supercritical fluid extraction (SFE) has gained wide acceptance in recent years as an alternative to conventional solvent extraction for separation of organic compounds in many analytical and industrial processes. In the past decade, SFE has been applied successfully to the extraction of a variety of organic compounds from herbs and other plants. This review article presents the practical aspects of SFE applications in sample preparation, selection of modifiers, collection methods, on-line coupling techniques, means for avoiding mechanical problems, and approaches to optimization of SFE conditions. SFE can also be used to clean up pesticides from herb medicines. SFE processes can be modeled to acquire useful information for better understanding of the extraction, mechanisms and optimization of the extraction procedures. With increasing public interest in natural products, SFE may become a standard extraction technique for studying herbal, food and agricultural samples.     

Determination of partition coefficients and residual solvent for polymer drying applications

Summary Gas-solid partition coefficients (K) for n-hexane in high density polyethylene (HDPE) have been measured at conditions applicable to large-scale drying utilizing a novel headspace method. The method features considerable versability and simplicity due to the control of experimental conditions designed to favor full extraction of the analyte into the headspace. By combining this full extraction technique with a traditional static headspace experimental scheme, a method which measuresK and residual concentration is achieved. The results show that partition coefficients differ significantly between HDPE in its virgin powder and pellet forms, as well as among various HDPE grades. The differences are shown to be attributable to differences in % crystallinity of the specific polymer. Data collected over a wide range of hexane concentrations reveals saturation levels (solubilities) which correspond to crossover from evaporative to diffusion-controlled drying.     

The quantitative effect of microextractor cell geometry on the analytical supercritical fluid extraction efficiencies of environmentally important compounds

Summary The quantitative effect of microextractor cell geometries on supercritical fluid extraction (SFE) efficiencies of polycyclic aromatic hydrocarbons (PAHs) and methoxychlor from octadecyl-bonded sorbents has been evaluated and compared to similar effects seen upon increasing the supercritical fluid density. For the PAHs studied, correlations between the fused ring number and the relative increase in recoveries have been established. SFE recoveries can be increased by greater than a factor of two by decreasing the diameter to length ratio from 120 to 11. The relative recovery increase upon decreasing the diameter to length ratio of the extraction vessel is dependent on the analyte extractability, increasing in proportion to the fused ring number for the PAHs. Recoveries increased linearly as a function of supercritical fluid density for the PAHs studied. The change in the relative recovery upon increasing the supercritical carbon dioxide density again was dependent on the analyte type, decreasing linearly with fused ring number. Although fluid density generally had the greatest effect on achievable SFE recoveries, the cell geometry had effects of a similar order of magnitude, highly dependent on the initial extractability of the analyte.     

Theoretical optimization of analyte collection in analytical supercritical fluid extraction

Summary Optimizing the extracted analyte collection step in analytical supercritical fluid extraction (SFE) is of key importance in achieving high analyte recoveries and extraction efficiencies. Whereas the extraction step in SFE has been well characterized both theoretically and experimentally; the analyte collection step after SFE has few theoretical guidelines, aside from a few empirical studies which have appeared in the literature. In this study, we have applied several theoretical approaches using experimental data to optimize analyte trapping efficiency in SFE. A vapour-liquid equilibrium model has been formulated to predict the trapping efficiency for extracted solute collection in a open collection vessel. Secondly, a simple solution thermodynamic model for predicting solute (analyte) activity coefficients in various trapping solvents has been shown to have utility in predicting collection efficiencies. Finally, effective trapping efficiency after SFE using sorbent media is related to the extent of analyte breakthrough on the sorbent-filled trap after depressurization of supercritical fluid. Using experimental data determined via physico-chemical gas chromatographic measurements (i. e., specific retention volumes), we have shown the relationship between analyte breakthrough volume off of the trapping sorbent and volume of depressurized fluid through the collection trap. The above theoretical guidlines should prove of value to analysts in designing and optimizing the best conditions for trapping analytes after extraction via analytical SFE. Names are necessary to report factually on available data; however the USDA neither guarantees nor warrants the standard of the product, and the use of the name by USDA implies no approval of the products to the exclusion of others that may also be suitable.     

Extraction of Peppermint Essential Oils and Lipophilic Compounds: Assessment of Process Kinetics and Environmental Impacts with Multiple Techniques

Consumers are becoming more mindful of their well-being. Increasing awareness of the many beneficial properties of peppermint essential oil (EO) has significantly increased product sales in recent years. Hydrodistillation (HD), a proven conventional method, and a possible alternative in the form of microwave-assisted hydrodistillation (MWHD) have been used to isolate peppermint EO. Standard Soxhlet and alternatively supercritical fluid (SFE), microwave-assisted, and ultrasound-assisted extraction separated the lipid extracts. The distillations employed various power settings, and the EO yield varied from 0.15 to 0.80%. The estimated environmental impact in terms of electricity consumption and CO₂ emissions suggested that MWHD is an energy efficient way to reduce CO₂ emissions. Different extraction methods and solvent properties affected the lipid extract yield, which ranged from 2.55 to 5.36%. According to the corresponding values of statistical parameters, empiric mathematical models were successfully applied to model the kinetics of MWHD and SFE processes.     

Study and characterization of virgin and recycled LDPE/PP blends

Recycling of mixed plastic wastes composed of low-density polyethylene (LDPE) matrix and polypropylene (PP) was carried out by compounding using single-screw or twin-screw extruders. Blends of virgin polymers have been prepared to compare mechanical properties of both virgin and regenerated materials. First, a model composition of virgin LDPE/PP blend was prepared to study the effect of process parameters and that of different types of compatibilizers. Second, the results were applied to plastic wastes coming from industrial post-consumer plastic wastes. By adding compatibilizing agents such as ethylene-propylene-diene monomer, ethylene-propylene monomer, or PE-g-(2-methyl-1,3-butadiene) graft copolymer, elongation at break and impact strength were improved for all blends. The effect of these various copolymers is quite different and is in relation with their chemical structure. The recycled blends exhibit suitable properties leading to applications that require good mechanical properties.     

Extraction of essential oil from Pimpinella anisum using supercritical carbon dioxide and comparison with hydrodistillation

Supercritical fluid extraction (SFE) of essential oil from Pimpinella anisum, using carbon dioxide as a solvent is presented in this work. An orthogonal array design OA9 (3(4)) was applied to select the optimum extraction condition. The effects of pressure, temperature, dynamic extraction time and methanol volume on the extraction efficiency were investigated by the three-level orthogonal array design. Results show that pressure has a significant effect on the extraction efficiency. The extract obtained from P. anisum by using supercritical fluid extraction was compared with the essential oil obtained by hydrodistillation, considering both quantity and quality of the product. SFE products were found to be of markedly different composition, compared with the corresponding hydrodistilated oil. The total amount of extractable substances obtained in SFE (7.5%) is higher than that obtained by hydrodistillation (3.1%) and SFE is faster than hydrodistillation method.     

Supercritical fluid extraction in plant essential and volatile oil analysis

The use of supercritical fluids, especially carbon dioxide, in the extraction of plant volatile components has increased during two last decades due to the expected advantages of the supercritical extraction process. Supercritical fluid extraction (SFE) is a rapid, selective and convenient method for sample preparation prior to the analysis of compounds in the volatile product of plant matrices. Also, SFE is a simple, inexpensive, fast, effective and virtually solvent-free sample pretreatment technique. This review provides a detailed and updated discussion of the developments, modes and applications of SFE in the isolation of essential oils from plant matrices. SFE is usually performed with pure or modified carbon dioxide, which facilitates off-line collection of extracts and on-line coupling with other analytical methods such as gas, liquid and supercritical fluid chromatography. In this review, we showed that a number of factors influence extraction yields, these being solubility of the solute in the fluid, diffusion through the matrix and collection process. Finally, SFE has been compared with conventional extraction methods in terms of selectivity, rapidity, cleanliness and possibility of manipulating the composition of the extract.     

超临界流体萃取与其它分析技术的联用

用超临界流体萑取进行分析样品处理，有快速，高效，低消耗，污染少等优点。本文对ＳＦＥ的原理，特点，与其它技术的联用及其在分析化学诸领域的应用作了综述，其中重点介绍了ＳＦＥ与色谱技术的在线联用，内容包括接口等。     

Analysis of Organic Pollutants in Aqueous Samples by Supercritical Fluid Extraction Combined with Solid Phase Adsorption

The application of supercritical fluid extraction (SFE) to prepare samples in analytical laboratories is a rapidly expanding area. In comparison with traditional extraction methods, SFE have many advantages, such as short time, low consumption, low pollution, high precision and high selectivity. SFE of analytes from aqueous samples has received little attention as compared with the SFE of solid samples. Since it is difficult to prevent the coextraction of water with the contaminants, which would result in the plugging of the restrictor, generally, SFE is combined with solid phase adsorption (SPA) in treating aqueous samples.     

Comparative study of the properties of post-consumption high density polyethylene used in the injection process

The high-density polyethylene, thermoplastic widely-used in the production of industrial domestic utilities, was collected in two situations: virgin high-density polyethylene (JV 060) and post-consumption high-density polyethylene (with features of low-density polyethylene). After collecting the samples, they were submitted to natural aging with the quantification of the incident solar radiation for 180 days. The samples were characterized by melt flow index, differential scanning calorimetry, tensile strength, rupture load, elongation at break and infrared. The results showed that after 180 days of exposure the virgin high-density polyethylene presented physical properties similar to the post-consumption polyethylene. This revised version was published online in August 2006 with corrections to the Cover Date.     

稀土聚乙烯的形态结构及性能

本文研究了用稀土催化剂聚合得到的聚乙烯(稀土聚乙烯)的结构及性能。发现初生聚乙烯粉末具有条状形态结构,其支化度、结晶度及晶粒尺寸均与低压聚乙烯相似,但其熔点和特性粘数较高。用各种物理方法初步证明,稀土聚乙烯熔点较高的原因可能与其具有伸展链结晶结构有关。     

Liquid–solid disk extraction followed by supercritical fluid elution and gas chromatography of phenols from water

A method combining the techniques of liquid – solid disk extraction (LSDE) and supercritical fluid elution (SFE) has been developed for the phenols regulated by the Clean Water Act. LSDE uses a disk or membrane made of polytetrafluoroethylene (PTFE) fibrils impregnated with small particles, e.g. styrene divinylbenzene (SDB) resin, to extract phenols from water. After disk extraction the retained analytes are eluted from the disk using SFE. SFE is used as an alternative to liquid solvent elution with an organic solvent. Analytes are separated, identified, and quantified using gas chromatography – ion trap detector mass spectrometry (GC-ITDMS). The method is capable of sub parts per billion detection limits, and precision of 5–28% RSD. Evaluation of various disks or membranes, such as C₁₈-silica disks, SDB disks, and ion exchange membranes, has also been performed for the extraction of phenols from water. The results obtained from the in-situ aqueous acetylation of phenols and extraction of their acetates are quantitative. The utilization of LSDE and SFE techniques has proven to be a more effective approach than liquid – liquid extraction in minimizing air pollution and solvent waste.     

超临界流体萃取在天然药物分析中的应用

按物质的不同性质综述了１９９５年以来超临界流体萃取技术在天然药物分析中的一些进展情况,常见的分析主要包括萜类、生物碱、黄酮类、挥发油及苯丙素类。超临界流体萃取作为一门新型的样品前处理技术,在天然药物的分离分析中展示了其特有的优点。该技术操作温度低,不会引起热敏性的分解变质;使用的有毒溶剂少,从而减少化学药品对药物的污染。     

Direct solventless supercritical fluid extraction of chlorbiphenyls from aqueous solutions at 0.1 × 10–12 g/g level and whole extract analysis by GC/ECD

A method of PCB determination in water based on direct supercritical fluid extraction (SFE) and off-line solventless SFE/GC coupling has been developed. High SFE recovery of the targeted compounds from water and high efficiency of their solventless transfer into GC were achieved. The method can be used for fast screening of water samples for PCBs at ultratrace levels.     

The effect of chemical composition on microfibrillar cellulose films from wood pulps: water interactions and physical properties for packaging applications

The interactions with water and the physical properties of microfibrillated celluloses (MFCs) and associated films generated from wood pulps of different yields (containing extractives, lignin, and hemicelluloses) have been investigated. MFCs were produced by combining mechanical refining and a high pressure treatment using a homogenizer. The produced MFCs were characterized by morphology analysis, water retention, hard-to-remove water content, and specific surface area. Regardless of chemical composition, processing to convert macrofibrils to microfibrils resulted in a decrease in water adsorption and water vapor transmission rate, both important properties for food packaging applications. After homogenization, MFCs with high lignin content had a higher water vapor transmission rate, even with a higher initial contact angle, hypothesized to be due to large hydrophobic pores in the film. A small amount of paraffin wax, less than 10%, reduced the WVTR to a similar value as low density polyethylene. Hard-to-remove water content correlated with specific surface area up to approximately 50 m²/g, but not with water retention value. The drying rate of the MFCs increased with the specific surface area. Hornified fibers from recycled paper also have the potential to be used as starting materials for MFC production as the physical and optical properties of the films were similar to the films from virgin fibers. In summary, the utilization of lignin containing MFCs resulted in unique properties and should reduce MFC production costs by reducing wood, chemical, and energy requirements.