Stress Cracking
Purpose
This procedure evaluates the performance of bottle bases when they are exposed to a 0.2% solution of NaOH (Sodium Hydroxide) to simulate the failure associated with Stress Cracking.
Description
International Society of Beverage Technologists and Special Protocols
PTI employees are members of the International Society of Beverage Technologists. As members it is our objective to enhance the promotion, development, and dissemination of knowledge relating to the Art and Science of Beverage Technology.
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PTI employees have an active role in committees and meetings to promote continuous improvement of quality. PTI can administer a significant number of the Voluntary Standard Test Methods for PET Bottles. See the list below:
Physical Performance Tests
This procedure evaluates the performance of bottle bases when they are exposed to a 0.2% solution of NaOH (Sodium Hydroxide) to simulate the failure associated with Stress Cracking.
Top Load
Purpose
To ensure that the vertical strength of PET bottles is sufficient to meet minimum performance standards for vertical loading as might be encountered during bottle filling, capping and stacking of filled product.
Description
Twelve test samples are individually placed under the test platen on an Instron test device. The downward movement of the load platen is initiated at a constant rate, and continues downward until the bottle’s resistance to loading peaks and the bottle loses column strength and deforms. The maximum load and deflection at max load are recorded and reported by the machine, and the failure location is added by the operator. Loads at other preset points may also be included in the recorded data.
Hot Fill Distortion
Purpose
This procedure evaluates the performance of a heat set bottle when filled with heated water. The methodology used simulates filling and capping as found in production.
Cystallinity: Gradient Column
Purpose
This procedure determines a sample density and correlates that density to crystallinity using theoretical PET amorphous and crystalline densities according to ASTM D1505.
Description
Five samples are prepared by cutting approximately 1/4″ samples from a preform or bottle without touching the samples to prevent oils from disturbing the testing. The entrapped air is removed from the surface of the sample and the samples are then dropped into a density gradient column and allowed to settle for approximately 15 minutes. The height of the samples is then carefully measured. Standard density balls are used to calibrate the density of the column. The sample density is then correlated to the theoretical amorphous (1.3331) and crystalline (1.45234) PET densities to determine the % crystallinity.
Burst
Purpose
This procedure evaluates the performance of a bottle when the container is pressurized to very high levels. Failure location reveals weak areas of the bottle.
Description
Bottles are pressurized with air and water in the AGR PPT burst testing device. Pressure is added until the bottle fails or the testing limits are met. The PPT burst tester can be programmed to run many different pressure profiles from quick jumps to elevated pressures with hold times. Profiles can also be created for cycle testing and step pressure increases.
Thermal Stability
Purpose
The Thermal Stability Test is designed to insure that dimensional changes in carbonated PET bottles will not be excessive during their expected lifetime. This is also known as a “creep” test.
Description
Representative bottles are measured under “as-received” non-carbonated conditions. Bottles are then carbonated and placed in an environmental room at 37.8°C ± 2.5° (100°F ± 5°) and 85% ± 10% humidity for 24 hours. After this time, bottles are removed from the room and re-measured (final measurements). These final measurements must be completed within 4 hours of removal from the environmental chamber and must be made at the same locations as the initial measurements. A comparison is then made between the “as-received” and the final measurements.
Reference Test
Reference Stress Cracking
Purpose
This procedure evaluates the performance of bottle bases when they are exposed to a 0.2% solution of NaOH (Sodium Hydroxide) to simulate the failure associated with Stress Cracking.
Description
Each bottle is filled to net target content with water equilibrated to 22°C +/- 1°C (72 +/- 2°F). Bottles are pressurized with compressed air to the equivalent internal pressure of 531 +/- 4 kilopasclals (77 +/-0.5 psi). After 5 minutes, the fill line on each of the bottles is marked and they are placed in individual pockets of 0.2% Sodium Hydroxide solution. The containers remain in the caustic solution until they fail by either catastrophic burst or leaking through cracks that develop in the base. The time to failure is recorded for each container. Failed containers are removed and the location of the failure is determined and recorded.
Carbonation Retention Tests
FTIR
Purpose
This procedure utilizes Fourier transform infrared spectroscopy to measure the CO2 concentration within carbonated beverage containers.
Description
CO2 absorbs IR radiation in a very specific range of wavelengths. As the concentration of carbon dioxide decreases the measured CO2 absorption correspondingly decreases. The IR absorption value is divided by the length of the path through the container to account for the change in the container shape (there is usually a slightly shorter path length by end of test) over the time of the test. This calculation yields a concentration value for a particular sample. The concentration is then plotted against time to determine the rate of CO2 loss. During the first 10 days after carbonation, the bottle is equilibrating. During this time, the CO2 is dissolving into both the bottle walls and the closure. In addition the bottle is “creeping” by growing from the pressure of carbonation. After 10 days, these processes have theoretically all reached equilibrium so that there is no additional significant creep. The rate of CO2 loss through the bottle and closure is now constant as is the leak rate between the bottle finish and the closure liner.
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