Printer Friendly

Determining the n-hexane extractables content of polyolefin resins.

This improved method offers simplicity, speed, greater reproducibility, cost-effectiveness, and safety, and promises to benefit the entire polyolefin industry.

An improved procedure has been developed for determining the n-hexane extractables content of polyolefin resins used in food contact applications. The new method offers significant advantages over the FDA procedure currently in use:

* Test results are more reproducible;

* Evaluations can be completed faster;

* The procedure is simpler;

* Smaller amounts of solvent are used, reducing solvent cost and disposal problems; and

* There is less exposure to the solvent.

This new n-hexane extractables test has been accepted by the ASTM under code D-5227 and has also been submitted for approval by the U.S. Food and Drug Administration (FDA) as an alternate TABULAR DATA OMITTED procedure under regulation 21 CFR 177.1520 (d) (3) (ii).


The FDA has set strict limitations on n-hexane extractables when polyolefins are used in specified food-contact applications. The procedure for this determination, detailed in CFR Title 21, Part 177.1520, consists in extracting 2.5 g of one-inch-square film sections (|is less than~4 mils thick) with 1000 mL of n-hexane at 50|degrees~C for 2 hrs in resin kettle. After removal of the film sections by filtration, the solvent is evaporated on a steam bath under a nitrogen cover. The residue is then desiccated overnight and weighed to determine the extractables.

A modification of the FDA method, developed at Quantum Chemical Corp., was recently evaluated by ASTM. In this improvement, the extracted film sections are collected by gravity filtration and vacuum-dried for 2 hrs at 80|degrees~C. The extractables content is determined from the weight loss of the original film sample. Other modifications include the use of a constant temperature water bath and an air-driven submersible magnetic stirrer. While equivalent results are obtained and the need for solvent evaporation eliminated, assembly, disassembly, and retrieval of the film sections from the resin kettle remains a cumbersome process. In addition, the film sections (about 40) must be counted before and after extraction to ensure that none are lost.

Improved Basket Technique

To eliminate these problems, a flow-through basket was designed for use with a conventional flask and condenser. The remaining equipment, including water bath and submersible magnetic stirrer, is unchanged.

The circular basket is fabricated from perforated stainless steel sheet; it is 1-1/2 inches in diameter and 1-5/8 inches high. There are about thirty-three 1/8-inch-diameter holes per square inch, thus yielding about 40% open area. A solid lid is secured to the basket by means of a stainless steel machine screw welded to the base.

In use, the basket with lid is tared and the 2.5 g sample of one-inch-square film sections vertically positioned in a circular manner around the center post. The lid is replaced and the basket again weighed to determine the exact sample weight. The basket is then suspended in the solvent, previously heated to 50|degrees~C, by means of a hanger rod that passes through the condenser. After extracting takes place for 2 hrs, the basket is removed, drained, rinsed briefly with fresh n-hexane, and vacuum dried for 2 hrs at 80|degrees~C. The basket is then cooled in a desiccator and again weighed to determine the weight of material extracted from the film sample. There is no need for "film counting," and the basket is ready for reuse after removal of the extracted sample.

Studies conducted in several Quantum laboratories using a variety of polyethylenes and ethylene/propylene copolymers showed that the same solvent charge can be used for at least twelve successive determinations, provided the total of accumulated extractables does not exceed 1.5 g and the warm (50|degrees~C) n-hexane solution remains clear. While some turbidity may result on cooling and standing if a series of determinations is interrupted, the solvent must clear on rewarming to 50|degrees~C before further analyses are made.

The ability to reuse the solvent is an obvious advantage, as a relatively large volume (1000 mL) is required for each determination. Solvent cost and disposal and exposure problems are significantly reduced. The basket technique is ideally suited for solvent reuse as samples can be introduced and removed with a minimum of effort and exposure.


Five resin samples (2-LDPE, 1-LLDPE, 1-HDPE, 1-PP) previously used in an ASTM evaluation of the n-hexane extractables procedure were analyzed in replicate using the basket technique. These samples covered the range 0.3 to 3.6% extractables. As shown in the Table, excellent reproducibility was obtained, as evidenced by the small standard deviations. In addition, the results obtained by the improved basket technique are in very good agreement with the ASTM values obtained by the D20-70 subcommittee round robin in 1990. Finally, the extractables data obtained using the same solvent charge for multiple determinations were in good agreement with determinations using a single solvent charge, as well as the ASTM values. In fact, these samples were successfully analyzed up to twenty times using the original solvent charges. However, since the data are limited, we are recommending a conservative twelve successive determinations, provided the conditions mentioned earlier are satisfied. Even this represents a considerable advantage in terms of cost and safety.
COPYRIGHT 1992 Society of Plastics Engineers, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1992 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Title Annotation:Quantum Chemical Corp. introduces more efficient and economical n-hexane extractables measurement process
Author:Budke, Clifford C.; Peat, Ian R.
Publication:Plastics Engineering
Date:Aug 1, 1992
Previous Article:Plastics testing.
Next Article:Twentieth century blow molding.

Terms of use | Copyright © 2016 Farlex, Inc. | Feedback | For webmasters