PETpla.net Insider 03 / 2014

BOTTLE MAKING 35 PET planet insider Vol. 15 No. 03/14 www.petpla.net stress cracking resistance is the time period until the bottle starts to leak or burst. The fill level is marked, and the time is noted when it falls. Specifica- tions usually include a time before which no bottle may fail, and then a time at which a percentage of failures is acceptable (e.g., no bottle fails for 20min, then a maximum 50% failure rate after a further 20min). Fillability In laboratories equipped with the appropriate filling valves, tests are carried out to find out whether the bot- tles are suitable for trouble-free filling with the proposed filler. Although this is not so critical for long-tube fillers, the filling behaviour is more impor- tant in the case of fillers where the contents flow down the inside of the container wall, especially if a strongly foaming product is being bottled. Crystallinity For hot-fill bottles, the degree of crystallinity, which is a measure of the temperature resistance, is determined. The crystallinity is usually determined by measuring the density of the PET in the container wall. For this purpose hydrostatic balances based on the Archimedes principle can be used. The cheapest solution is a density gradient column in which fluids of vari- ous densities are layered on top of each other. Depending on how deep the PET sample sinks, its density can be read from a scale on the vessel. A relatively quick method, which unfortu- nately requires significant investment, is the Fourier transform infrared crys- tallinity index measurement in which the crystallinity can be directly derived from an infrared spectrum. Droptest In this test filled and closed bottles are dropped onto the floor in free fall from a height of 2m. The bottle must not burst. A variant is the drop test on an inclined plane in which the bottle hits the plane with one of its feet. Drop tests are usually performed at ambient temperature but may also be carried out at 4 or 6°C, depending on the specification. Please order your copy at the PETplanet insider book shop: https://www.petpla.net/books Bottles, Preforms and Closures A Design Guide for PET Packaging Second Edition by Ottmar Brandau € 115,00 180 pages © Copyright Elsevier 2012 Barrier Various methods are used to determine the barrier properties depending on whether a barrier against the ingress of oxygen or against CO 2 loss is specified. Barrier against oxygen As a rule, the tested bottles are filled with the intended contents and are stored at higher temperatures to accelerate the diffusion processes. This yields faster results than real- time shelf life. One of the possible O 2 barrier test methods (available from PreSens, Germany) comprises a low-cost sensor spot that is placed on the inner wall of the PET bottle. This sensor spot is then excited with blue light from the outside and sends an optical signal back through the PET wall. The captured signal is propor- tional to the oxygen content. Barrier against loss of CO 2 There are also several possi- ble test methods for measuring CO 2 retention. In one of these tests a sample bottle is pressurized with pure CO 2 an internal pressure that is main- tained constant. The bottle is placed within a measuring chamber. This may be a gas-phase chromatograph, and in this case, the CO 2 increase in the measuring chamber outside the bottle will be measured directly. Another possibility would be to use a pressure measurement chamber in which the pressure increase outside the bottle is measured. Both measurements allow statements on the amount of CO 2 dif- fusing through the container wall. There are also measuring methods involving bottles filled with carbon- ated water or product. The bottles are filled, closed, and stored. Special instruments permit the determination of the residual CO 2 in the bottle. Segment weight distribution As a preparation of a subsequent online quality assurance or a subse- quent determination of the machine capability, sample bottles conforming to all specifications are cut with a hot wire into three segments at exactly defined positions (bottom, label or lateral area, and shoulder); hot-fill bot- tles may even be cut into as many as five segments. These segments are weighed and the results are recorded. This approach permits a good approx- imation to the material weight distribu- tion in production bottles by compar- ing these benchmark values with the easily determined segment weights of sample bottles from production runs. If the segment weight distribution is identical, then it is assumed that all other specifications are met as well. This method also allows an easy iden- tification of excessive variations or fluctuations in the production process. * This article was published in Bottles, Preforms and Closures, Ottmar Brandau, Chapter 1.8.3.1. to 1.8.3.4., Copyright Elsevier 2012