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Finding challenges Fraunhofer assessment that virgin cap layer may become contaminated during extrusion, rendering the functional barrier inadequate.

Clare Goldsberry

March 9, 2017

2 Min Read
Study reaffirms FDA guidelines on use of virgin PET cap layers as functional barriers

An independent study reaffirms FDA guidelines for the use of virgin PET cap layers as functional barriers over post-consumer recycled (PCR) PET flake materials for use in direct food packaging at room temperature. The study, which was completed in conjunction with Processing Technologies International (PTi; Holland, OH), a global manufacturer of high-performance sheet extrusion machinery, and Container Science Inc. (Atlanta, GA), a materials science company, found that a 1-mil-thick virgin PET cap layer meets the necessary functional barrier requirements, eliminating surface contaminants within multilayer food packages made of PCT PET materials for room temperature (70° F/21° C) applications.

The study was prompted by a recent 2016 European industry report, “Assessment of Recyclates behind Functional Barriers,” by Dr. Frank Welle of the Fraunhofer Institute that questioned the efficacy of an ABA structure with PET recyclates behind a functional barrier. The report suggested that the virgin cap layer may become contaminated during extrusion, rendering the functional barrier inadequate. The findings were based on testing of recycled PET packaging at elevated use temperatures as high as 212° F/100° C, which is not in keeping with guidance stipulated by the FDA recommendation (i.e., room temperature and below).

“Our study set out to examine the elevated application temperature relevance used as part of the Fraunhofer assessment and reaffirm virgin PET for suitability as a functional barrier,” said PTi’s Sushant Jain, Senior Scientist—Applications and Technology. “Our simulation results demonstrate that a 1-mil virgin cap layer is adequate protection for a PET food package when used at room temperatures.”

In co-extruded multilayer PET structures, the FDA recommends a 1-mil-thick virgin cap layer for room-temperature applications and 2 mil for higher temperature use (up to 150° C) to prevent permeation of contaminants migrating from the PCR PET regrind core layer of the packaging material into the contained food, said PTI’s information on the study. The virgin cap layer provides protection from unhealthy contact or transfer of inks, adhesives, chemicals or other materials not meant for consumption.

The study was effective in demonstrating the importance of various factors with regard to contaminant migration, the most significant of which is the correlation of higher migration rates at increased application temperatures. In the Fraunhofer assessment, the relative permeation rate at 212° F (100° C) used as a point of origin is several orders of magnitude higher than the rate at room temperature, according to Jain.

Other conclusions from this study indicate that exposure time during extrusion processing has some impact: The simulation models show primary contaminant migration occurring in the feed block and die area. However, at this point migration is found primarily at the interface and not through the virgin cap layer, according to Jain. Furthermore, this study demonstrates that virgin cap layers can remain uncontaminated at a layer thickness greater than 1 mil, proving the functional barrier remains intact during the extrusion process. “Our study eliminates any doubt regarding virgin PET’s effectiveness as a functional barrier,” Jain concludes. 

About the Author(s)

Clare Goldsberry

Until she retired in September 2021, Clare Goldsberry reported on the plastics industry for more than 30 years. In addition to the 10,000+ articles she has written, by her own estimation, she is the author of several books, including The Business of Injection Molding: How to succeed as a custom molder and Purchasing Injection Molds: A buyers guide. Goldsberry is a member of the Plastics Pioneers Association. She reflected on her long career in "Time to Say Good-Bye."

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