Experimental Procedure
Installation of Test Laminate
The test film was glued to the open side of one chamber using epoxy glue mixed with its hardener and spread as a thin layer onto the 6mm rim of the open side. After drying, a small amount of epoxy glue was evenly spread onto the rim of the other chamber that is directly placed onto the test film aligning and joining the two chambers together with the test film in the middle. The contact line between the two chambers was later tapped with a 2cm-wide strip of high-pressure aluminium tape to guarantee tight sealing.
Conditioning of Test Laminate
After installation, the film laminates were conditioned for a minimum of 40 h at standard laboratory conditions (23±2°C and 50±5 % relative humidity) immediately prior to testing according to ASTM D618 Practice for Conditioning Plastics for Testing (6). The conditions were controlled and monitored using the HVAC system of the laboratory.
Source Chamber Gas-Purge
The source chamber was totally purged with the pure, dry N2 gas, following the dynamic purge process described by Elkhial (2), but using dry rather than humidified N2 gas. Gas was purged through the inlet port fitted with the on/off valve. At this stage, the sampling port of the source chamber remains open. After a complete purge, reaching 100% N2, the septa and plug are installed at the sampling port, followed by a quick shutdown of the ball valve then the gas regulator to avoid pressure build-up and guarantee an O2-free gas path.
Gas Sampling and Analysis
The concentration of fumigant (N2) is measured by monitoring the concentration of O2 inside the bag using Dansensor® Checkmate® 3 Headspace O2 analyser, measuring range 0-100%, accuracy ±0.01%, and measuring three numbers after the decimal point. The utilised O2 sensor is headspace Dansensor® CheckMate 3, MOCON, Inc., USA, the most accurate modified atmosphere packaging gas analyser. It uses the latest zirconia O2 sensor, which has the inherent benefits of low cost, fast response, high sensitivity, and feedback control (7). The analyser was calibrated using fresh air at 20,9460% O2.
Test Duration
Each experiment was repeated three times and the mean values are considered. The duration of each iteration was one month at constant laboratory conditions (23±2°C and 50±5 % relative humidity).
Calculations and Data processing
For easily calculating the oxygen permeability and the OTR of the test membrane, the Film Permeability Evaluation System, FilmPC software, v. 3.0.4, 2011, United States Department of Agriculture, CA, the US, was utilized to obtain graphical and statistical data, especially as a report comprising all analytical data about the test film.
The software was provided with the sampling time and concentration data for each chamber sampled at the same time of the day. As high oxygen gas barriers were used in this experiment, the time is measured in days and the duration of each experiment was 30 days. The initial concentration of oxygen in the source chamber was 0.000% and the fumigant (N2) concentration was 100% and the fumigant subsequent measurements (the source room concentrations) were the actual measurements of oxygen concentration (%) subtracted from 100%. As for the collecting chamber, the initial value of oxygen (20.9%) was normalised to 0.000%, and the difference between the actual initial value and measured values due to oxygen transmission was recorded (the collecting room concentrations). After data entry, the run button was pressed to start the calculations automatically, recording the measurements in the form of a graph, and preparing a Rich Text report of the film permeability analysis, which can be saved, printed, or copied and pasted elsewhere. Afterwards, the OTR was calculated by multiplying the oxygen permeability by 100 to relate the permeability to one squared metre of a laminate.
Experiment Termination
After completing each test duration, the valve in the source chamber was opened and the chamber vented. The system was then disassembled by removing the aluminium tape, softening the silicon glue, disengaging the collecting chamber, removing the tested film, and cleaning the chamber rims.
≠Swagelok® Company, OH, U.S.
§Septa are not installed until the gas concentration is reached and a tight sealing is to start (after completion of step 2.1.4.32.1.4.3. Source Chamber Gas-Purge).
" This software is developed by Scott Yates of ARS, USDA at Riverside, CA, and is available at: https://data.nal.usda.gov/dataset/filmpc.