Plastics Technology

APR 2017

Plastics Technology - Dedicated to improving Plastics Processing.

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basic performance, quality, and economics of PET and other plastic container materials. The company (containerscience.com) provides a fundamental knowledge of the chemistry and science associated with plastic containers, and translates that understanding into practical solutions that address the needs, issues, and opportuni- ties for this industry. This study was prompted by a recent 2016 European industry report by Dr. Frank Welle of the Fraunhofer Institute. Titled Assessment of Recyclates Behind Functional Barriers and presented last March at the PET Recycling for Food Contact Conference, the report questioned the efficacy of an A-B-A structure with PET recyclates behind a func- tional barrier and suggested that the virgin cap layer may become contaminated during extrusion, rendering the functional barrier inadequate. The European report 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 stipu- lated by a 2006 FDA recommen- dation (i.e.; room temperature and below) using a minimum of 1-mil-thick virgin PET cap layer to encapsulate the PCR PET materials for direct food-contact packaging applications. The PTi study set out to examine the elevated applica- tion temperature relevance used as part of the Fraunhofer Assessment and reaffirm virgin PET for suitability as a func- tional barrier and its corre- sponding FDA guidelines. The simulation results demonstrate that a 1-mil virgin cap layer is adequate protection for a PET food package when used at room temperatures. In coextruded multi-layer PET structures, the FDA recommended in 2006 a 1-mil-thick virgin cap layer for room-temperature applications, and a 2-mil-thick cap layer for higher-temperature use (up to 302 F/150 C) to prevent permeation of contaminants migrating from the PCR PET regrind core layer of the packaging material into the contained food. The virgin cap layer provides protection from unhealthy contact or transfer of inks, adhesives, chemicals, or other materials not meant for consumption. The simulation was focused on migration in the die and feedblock. It was done at the typical melt temperature of PET: 525-550 F. The Fraunhofer report mentioned migration measure- ments that were done at 212 F and came to conclusions about migration during the extrusion process. In reality amorphous PET packages are used at room temperature and it would be relevant to measure migration or perform challenge tests at room temperature. At the elevated temperature of 212 F, the amorphous PET package would lose structural integrity. THE METHODOLOGY PTi performed four simulations of the FDA recommended chal- lenge test (coextrusion of virgin/PCR/virgin with 780 ppm of toluene in PCR) as part of this study. The accompanying illustra- tion depicts a model of the feedblock and die that was used to simulate expected permeation of toluene out of the core PCR layer. The graphs on pg. 54-55 show the predicted concentration of toluene in the core and cap layers at the end of the extrusion process for the four simulations. The accompanying table sum- marizes data from four different simulations that modeled the production of a 40-mil-thick PET sheet with a 10/80/10% virgin/ regrind/virgin layer structure at a combined rate of 2000 lb/hr. The first simulation assumed a conventional single-screw extruder (i.e.; no devolatilization capability) processing the 80% core layer using only PCR PET flake. The second simulation Simulations show the virgin cap layers maintain their suitability as a functional barrier since the resultant uncontaminated virgin cap-layer thicknesses exceed the 1-mil FDA recommendation. QUESTIONS ABOUT PACKAGING? Visit the Packaging Zone. Process PIR, % PCR, % Net Toluene Concentration, ppm Cap Layer, mils Core Layer, mils Contaminated Cap Layer Depth (each), mils Resultant Cap Layer Barrier Thickness (each), mils Single Screw w/o PIR 0 80 780 4 32 2.0 2.0 Single Screw w/PIR 50 30 585 4 32 1.8 2.2 HVTSE w/o PIR 0 80 195 4 32 1.6 2.4 HVTSE w/PIR 50 30 84 4 32 1.2 2.8 Functional Barrier Layer Simulation for 40-Mil Sheet Each of these simulations demonstrate that the virgin cap layers maintain their suitability as a functional barrier since the resultant uncontaminated virgin cap layer thicknesses exceed the 1-mil FDA recommendation. The third and fourth simulations further demonstrate the devolatilization benefits using the HVTSE dryerless process. Simulation model assumes a sheet structure of 10/80/10% virgin/regrind/virgin at 2000 lb/hr and HVTSE operating at 75% devolatilization of PCR. @plastechmag 53 Plastics Technology PE T Sheet

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