M.L Marı́n

Thermal degradation of ethylene (vinyl acetate)

Ethylene (vinyl acetate), EVA, is a copolymer which is thermally degraded at high temperatures, with acetic acid release at approximately 620 K. This release can be studied by using thermal methods, and in particular thermogravimetric analysis.The present work was focused on establishing the polymer weight loss with temperature in order to calculate the activation energy of the overall deacetylation process. To obtain the final results, a Mettler TC50 instrument coupled with a Mettler TC11 microprocessor was used.The activation energies of four different industrial EVA formulations were calculated. The results obtained by applying different kinetic methods reported in the literature agreed reasonably well; they were compared in order to select the best method of reporting EVA deacetylation results.

Determination of aromatic amines formed from azo colorants in toy products.

A study for the determination of the aromatic amines formed after reduction of the azo colorants mostly used in toys was conducted. Sodium dithionite was used in the reductive cleavage of the azo group for the dyes, and the released amines were subsequently analysed by high-performance liquid chromatography with UV detection. The influence of different variables related to the reduction process was investigated by the use of a full-level factorial design, where most significant parameters as well as order interactions were studied. Reduction profiles for each colorant were obtained by studying the changes in the amount of amine obtained with different dithionite/colorant ratios. The expected aromatic amines forming azo colorants were detected, and in the presence of a nitro group a further reduction was observed. The yield of the total reduction process was determined by using standard addition of different quantities of amines to the colorants.

Analysis of poly(vinyl chloride) additives by supercritical fluid extraction and gas chromatography

The use of supercritical fluid extraction (SFE) is growing, with an expanding range of applications in many different fields as a consequence of its advantages compared with traditional extraction methods. In order to develop an analytical method to determine dibutyl phthalate (DBP) and dioctyl phthalate (DOP) traces (<20 ppm) in flexible poly(vinyl chloride) (PVC) formulations, a maximum efficiency in the extractive process and an adequate separative system are needed to avoid interferences between these two plasticizers and other additives that could be present at high concentrations in flexible PVC formulations. In order to determine the optimum SFE conditions, the extraction time, temperature and pressure were controlled. The separation and quantitation of individual components in the PVC extracts were carried out off-line by using a semicapillary column in gas chromatography (GC). Samples with different DOP content (41.18%, 33.33% and 23.08%) and DBP content (41.18%), as well as samples with both plasticizers (20.59% DOP and 20.59% DBP) were prepared. Some other samples were also prepared to study detection limits for these two PVC additives. Recoveries and reproducibilities were studied in every sample. Finally, this method was compared with Soxhlet liquid extraction. Determination by gravimetric analysis of the total extracted material was found to be particularly suitable for PVC. This study demonstrates the potential of SFE to shorten extraction times with similar or even better extraction efficiencies compared with traditional liquid methods.

OPTIMIZATION OF VARIABLES ON THE SUPERCRITICAL FLUID EXTRACTION OF PHTHALATE PLASTICIZERS

Abstract Supercritical fluid extraction (SFE) has become an important and useful technique to prepare samples before analysis. The use of supercritical CO2 yields a rapid and quantitative extraction of phthalate plasticizers added to poly(vinyl chloride) (PVC) products. One of them is the plasticized PVC which is a material commonly used in toy manufacturing and other industries. SFE conditions affecting the extraction efficiency have been studied and optimized when pure CO2 is used. Firstly, the influence of the sample particle size in the extraction process has been studied. A fast and quantitative extraction is obtained when the surface/volume ratio of the sample is increased. In addition, the influence of temperature, pressure and time for different phthalates has been studied.

Optimization of parameters for the supercritical fluid extraction in the determination of N-nitrosamines in rubbers

The study of the possibilities of supercritical fluid extraction (SFE) with N-nitrosamines in rubbers has been carried out. Home-made materials fortified with several N-nitrosamines were prepared in order to optimize the SFE parameters. A Plackett-Burman design was employed to evaluate the influence of those parameters to be controlled in SFE, such as pressure, temperature, static and dynamic time, restrictor temperature and volume of modifier while CO2 was used as the extraction fluid. An extra central composite design for the main factors (according to the previously obtained results) was also developed in order to refine the best supercritical conditions for the extraction of N-nitrosamines from rubbers. Gas chromatography with a nitrogen and phosphorus sensitive detector was used to achieve sensitivity and limits of detection for the concentrations expected in plastic materials. The proposed analytical method has shown to be useful in the determination of N-nitrosamines even for complex matrices.

Optimization of the extraction of azo colorants used in toy products

Azo dyes are widely used in formulations intended for children use. But their potential toxicity raised the need of an efficient and fast method of analysis. A study for the optimization of the extraction of some azo colorants used in toys was conducted. Several extraction methods for the selected analytes were evaluated and compared, i.e., supercritical fluid extraction (SFE), microwave-assisted extraction (MAE) and Soxhlet extraction. Poly(vinyl chloride) samples spiked with known quantities of the studied dyes were prepared. The influence of critical variables on analyte recoveries in SFE and MAE was investigated by using a full-level factorial design, where most significant parameters as well as order interactions were studied in each case. The analytes were subsequently detected by high-performance liquid chromatography with UV detection. The three extraction techniques were compared in terms of reproducibility, selectivity and analyte recoveries. MAE showed higher recoveries (above 98%), except for the diazo dye (nearly 60%). Reproducibilities were generally good for the three methods (relative standard deviation lower than 2.0%).

Analysis of citrates and benzoates used in poly(vinyl chloride) by supercritical fluid extraction and gas chromatography.

Supercritical fluid extraction (SFE) has been demonstrated to be a useful tool in the determination of additives in polymeric materials. This paper describes the determination of some citrates and benzoates in poly(vinyl chloride) blended with 33-34% of plasticizer using off-line SFE followed by gas chromatography. Experimental factors affecting SFE have been studied by gravimetric analysis, followed by analysis of the extracts using a gas chromatograph equipped with a flame ionization detector. The extraction process is governed by the solubility of the plasticizers in the supercritical fluid or by their diffusion through the polymer matrix, which depend on the pressure and temperature used. Maximum extraction (>99%) is obtained at pressures and temperatures higher than 40 MPa and 80 degrees C, respectively. Due to purge losses, the collection efficiency of plasticizers into a liquid solvent ranges from 85 to 90%. The applicability of the SFE method is demonstrated using real samples and comparing the results with those obtained by conventional Soxhlet extraction.

Determination of phenol in polymeric materials by supercritical fluid extraction combined with gas chromatography-mass spectrometry

A two-level factor design has been used to optimise the supercritical fluid extraction (SFE) of phenol in polymeric materials with four main factors (temperature, pressure, static time and amount of modifier). The minimum conditions required were 40°C, 13.9 MPa, 5 min as static time and no methanol, while optimal conditions were 110°C, 48.3 MPa, 15 min as static time and 80 μl of methanol. After the static time, all experiments took 15 min to be run in dynamic mode. Extractions were performed using an off-line mode with a single vial filled with a few millilitres of methanol. Determination was carried out by capillary gas chromatography with mass spectrometric detection. Samples were prepared using a known amount of phenol mixed with a poly(vinyl chloride) resin that was plasticized with dioctyl phthalate. Maximum recoveries were obtained at 110°C, 48.3 MPa and a static time of 5 min in the absence of methanol. Therefore, the use of modifier does not seem to be important for the analysis of phenol in polymers. Under the optimum conditions found, the SFE method was compared favourably with Soxhlet liquid extraction for different real samples.

Effect of pressure, temperature and time on supercritical fluid extraction of citrate and benzoate plasticisers from poly (vinyl chloride)

Supercritical Fluid Extraction (SFE) has been demonstrated as a useful tool in the analysis of polymeric materials. This paper describes the off-line SFE followed by Gas Chromatography determination of some citrate and benzoate plasticisers used in poly (vinyl chloride) (PVC). Experimental factors affecting SFE with carbon dioxide have been studied by gravimetric analysis. Recoveries of analytes were calculated with the use of a Gas Chromatograph with a flame ionisation detector. The extraction process can be kinetically controlled by the solubility of plasticisers in the supercritical fluid or by their diffusion through the polymer depending on pressure and temperature conditions. Quantitative extractions (>99%) are obtained at 39.5 MPa, 100 °C and 20 min, while some losses in the collection of plasticisers in a liquid solvent (ranges from 85 to 95%) are observed.

Determination of N-nitrosamines in latex by sequential supercritical fluid extraction and derivatization

A new method to determine N-nitrosamines in latex products has been developed by combination of supercritical fluids and chemical derivatization. A new design for a liquid trap has been introduced. A factorial fractional design was used in order to evaluate the influence of the different factors affecting the process. Factors such as pressure, temperature, static and dynamic time, restrictor temperature and volume of an hydrobromic acid-acetic anhydride mixture (1:10, v/v) were included in the design. CO2 was used as the extraction fluid. Gas chromatography with nitrogen and phosphorus sensitive detection was employed to achieve good sensitivity attending to the molecular structure of these compounds (N-nitrosamines and their corresponding secondary amines). The obtained results have shown to be useful to increase selectivity and reduce sample handling.