Accelerated Solvent Extraction for Additives in Polymer Materials

In the book, M. Fundamentals of Polymer Science: An Introductory Text, ‘synthetic polymers are defined as large organic molecules with a range of applications that far exceeds any other class of material.’ Current applications extend from adhesives, coatings, foams, and packaging materials to textile and industrial fibers, composites, electronic devices, biomedical devices, optical devices, and precursors for newly developed high-tech ceramics. Due to the diversity of these applications, polymers are manufactured to meet the intended application through the addition of compounds that reduce oxidation, stabilize the polymer for environmental exposure (e.g. heat or light), and soften the polymer.

Compounds, such as heat stabilizers, light stabilizers, slip agents, plasticizers, and antioxidants represent some of the most common classes of additives used to tailor polymers for use*. (*Principles of Polymer Engineering)

Extraction and chromatographic analysis of these additives are required to monitor their formulation levels and are critical steps in evaluating a polymer for its intended use. While chromatographic analysis can be automated, the extraction process is accomplished using the Soxhlet technique, which is time consuming, and requires large amounts of solvents. Laboratories testing additives in polymers are required to process multiple samples, which are difficult to extract, on a daily basis. Consequently, the process of sample preparation is often a severe bottleneck in the analytical workflow. The accelerated solvent extraction technique provides fast extraction times and low solvent usage to benefit laboratories extracting additives from polymer materials.  Keep reading to see the results of an analysis comparing the accelerated solvent extraction technique to Soxhlet extraction using Polyvinyl chloride (PVC) samples.

The accelerated solvent extraction technique improves the extraction efficiency of plasticizers from polymers by using elevated temperature and pressure. Many of the organic solvents used in these extractions boil at relatively low temperatures at atmospheric pressure (e.g., acetone boils at 56 °C). By exerting a pressure of 1500 psi (10 MPa) on the solvent, the boiling point is elevated and the extraction solvent remains in a liquid state. When extractions occur at temperatures ranging from 50–200 °C, several factors, including those below, contribute to improved speed and efficiency.

• Temperature:  Elevated temperature increases analyte diffusion from the matrix and improves analyte solubility in the extraction solvent (e.g. petroleum ether) for plasticizer extraction.
• Solvent Viscosity: Decreases as temperature increases, improving solvent migration through the matrix to increase extraction efficiency.
• Solvent Surface Tension: Decreases as temperature increases. Allows solvent to better coat the matrix and helps improve analyte diffusion.

In order to compare the accelerated solvent extraction technique to Soxhlet extraction, Polyvinyl chloride (PVC) samples were extracted using a six-hour Soxhlet extraction method (ASTM D-2124) and the accelerated solvent extraction technique. The extracts were analyzed using gas chromatography with flame ionization detection and the extraction efficiencies of four plasticizers were compared. The accelerated solvent extraction technique produced equivalent performance to Soxhlet but required approximately 40 mL of solvent and 12 min of extraction time per sample. The Soxhlet extractions required six hours and 120 mL of solvent per sample.  Here are the results:

The extraction efficiencies of the accelerated solvent extraction technique are equivalent to Soxhlet for polymer samples but require only 12 min of extraction time and approximately 40 mL of solvent per sample.  Since Soxhlet extraction requires up to six hours and more than 500 mL of solvent per sample, use of the accelerated solvent extraction technique for additive extraction from polymers can significantly reduce the amount of time and solvent required for sample preparation.

For additional information, including advantages, summaries of application notes, and references, see the Accelerated Solvent Extraction for Additives in Polymer Materials white paper.