Material Testing
Acetaldehyde
AA Generation, Resin
Purpose
Determine the AA generated by a resin as a function of time at a given temperature.
Description
Resin is dried to <50 ppm moisture in a vacuum oven at 165°C and loaded into a capillary rheometer that has been equilibrated to a specified temperature. The capillary rheometer temperature is typically 285°C for this test but can be set anywhere between 260°C-290°C in order to match the temperatures that the resin would encounter during injection molding. The resin samples are extruded from the rheometer into cold water after holding for timed intervals of 4 minutes, 6 minutes, 8 minutes, 10 minutes and 12 minutes, (typically a sample of the resin at 0 dwell time is run also in order to determine a dried resin content value). The extrudate is quickly towel and air dried and is then cryogenically ground to a small particle size and analyzed for AA content as described in the AA Content description. The AA generation rate is shown graphically as a function of dwell time.
Carboxyl End Group Analysis for PET
Purpose
Confirm the carboxyl end group content in a PET sample.
Description
The procedure involves the titration of the carboxyl end groups with potassium hydroxide in an o-cresol/chloroform medium to a bromophenol blue endpoint. A known weight of PET sample is dissolved in o-cresol then chloroform and bromophenol blue are added to the solution. The solution is then titrated with potassium hydroxide until the color changes to blue as a result of the end group reaction. Based on the amount of KOH required for the titration, the quantity of carboxyl end groups is calculated.
Coefficient of Friction Testing
Purpose
Find out the coefficient of friction between two PET film samples using an adapted version of ASTM D1894-90.
Description
Bottle samples are prepared and handled with gloves during both injection and blow molding to prevent contamination that might affect the COF results. The bottle sidewalls are cut from the bottle and one sidewall is mounted to a metal sled while the other sidewall is mounted to a flat plane. The COF assembly is then attached to the Instron machine and the force required to move the sled across the plane is measured using the 10lb load cell. The data is plotted as force (lbs) vs. the sled travel (in.) and is typically reported graphically. Our typical test usually results in a series of static COF values rather than an initial static value followed by a kinetic value; this is because our samples usually “jump” across the sidewalls rather than pull uniformly. The COF value is calculated by dividing the measured force by the weight of the sled.
Color/Haze
Preform/Bottle
Purpose
Determine the amount of haze and the degree of color exhibited by a preform or container sidewall. This is an indication of how effectively the material was processed and/or the material’s ability to be processed.
Description
The samples are measured in terms of L*, a*, b*, DE* and Haze: L* (100=white; 0=black), a* (positive=red; negative=green; 0=gray), b* (positive=yellow; negative=blue; 0=gray), DE is a mathematical equation which takes into account the values of L*, a* and b*. Haze measures the scattering of light through the sample; the higher the number the more haze. The haze can be used as an indicator of the presence of crystallinity in the sample.
Density
Purpose
Identify a sample density and correlate that density to crystallinity using theoretical PET amorphous and crystalline densities according to ASTM D1505.
Impact
Dart Impact – Bruceton Staircase Method
Purpose
Discover the weight, height and energy where a sample fails when it is impacted with a free-falling weight using the Bruceton Staircase Method.
Description
Samples are prepared as for ASTM D3029-F and impact tested using the drop weight impact tester. If the sample did not fail at a given height/ weight, either the height or weight is increased incrementally until failure occurs. Once failure has occurred, the height/weight is decreased by the same increment and the process is repeated until all samples are utilized. Typically, an odd number of samples are used for the Bruceton Staircase technique to obtain several data points around the breakage point.
Melt Flow Curves
Purpose
Measure the melt flow curve of a PET sample at 3 temperatures and 8 shear rates.
Description
A resin sample is dried overnight to remove residual moisture. The test is run by quickly packing the rheometer melt chamber at a predetermined temperature with the dried PET sample under a stream of nitrogen. After a preset heat soak time, the capillary rheometer is started at a defined speed, causing the resin to be pushed through a small orifice. The force required to make this happen is recorded. Once all the sample has been pushed through the orifice, the melt chamber is cleaned and reloaded from the same sample lot. Eight different shear rates are evaluated for each temperature with at least two replicates completed to verify accuracy at a given temperature. The correlation between the shear rate and viscosity may be used to determine the zero-shear viscosity using the “Modified Cross” relationship.
Additional temperatures may be evaluated by choosing the MFCadd test. For standard testing, only 3 temperatures are evaluated.
Melt Index
Purpose
Determine the rate of extrusion of molten resin or ground samples through a die of specified length and diameter under prescribed temperature, load, and piston position as a function of time according to ASTM D1238.
Description
A resin sample can be analyzed directly, but preforms or other samples must first be ground to a particle size that can be loaded into the melt indexer. All samples are dried overnight to remove water. The test is run by quickly packing the melt indexer chamber with the dried sample. After a preset heat soak time, a piston with a defined dead weight load is applied to the melted material, forcing it through the capillary orifice. The amount of material pushed through the orifice within a defined time interval is collected and the length of time interval is recorded. This process is repeated a total of three times and an average weight is determined. The ASTM D1238 procedure defines the barrel temperature, piston load and standard designations for standard materials that should be used.
This test is routinely used for polyethylene and polypropylene; it is not recommended for PET.
Moisture Analysis
PET
Purpose
Measure the amount of moisture within a sample using the coulometeric Karl Fischer technique.
Description
A sample is deposited into the analyzer and heated to release all of the moisture within the sample. The moisture then reacts with the iodine and generates a current which allows for an accurate measurement to be made. Once the analyzer moisture reading falls to within the background reading, the analyzer calculates the ppm moisture by the calculated weight of water (reacted with the iodine) divided by the input sample weight.
Sieve Analysis Particle Size
Sieve Analysis Particle Size Distribution
Purpose
Identify the particle size distribution of plastic material as received from the source. Designed for samples of incoming resin or flake used in recycling operations.
Description
A dry plastic sample is placed into a series of sieves that are arranged into a column in order of increasing fineness. The sieves are then shaken to allow the material to separate into it’s weight distribution according to the sieve sizes. The weight of sample on each sieve is determined after shaking and the particle size distribution is reported.
Percent Ash
Purpose
Determine the percentage of ash in a submitted sample.
Description
A sample of known weight is heated at 900°F for 4-6 hours in a furnace. After 4 hours, the sample is removed and quickly placed into a desiccator and cooled for 30 minutes. The sample boat is then weighed, placed back into the furnace for 30 minutes, cooled, and reweighed. This procedure is iterated until the sample weight remains constant. The percent of ash is calculated as (ash weight / sample weight) x 100%. The ash results from any inorganic species within the submitted sample that does not decompose during high temperature exposure.
Stress Crack
ISBT
Purpose
Evaluate 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.
Tilt Test
Purpose
Learn the angle at which a bottle will tip and fall once the center of gravity has been overcome on tilting.
Description
A tilt test device is fitted with the appropriate surface. The test device is then tipped until a test bottle breaks the plane of contact because the center of gravity of the bottle has been overcome. The angle at which this tipping occurs is considered the tilt angle. Typically, twelve bottles are tested and the average tilt angle is determined for the set of bottles.
UV/Visible/Near Absorption Spectra
Purpose
Identify absorbance values in a material at varying wavelengths.
Description
A sample is placed in the UV/VIS Spectrometer where it is scanned A Spectrometer detects when UV-visible radiation is absorbed by a sample and plots this on a graph. This test can be used for both PET film, preforms and other flat surfaces.