Measure Aseptic Tightness During Dynamic Load

Sammanfattning: One of Tetra Pak’s product segments is food filled packages distributed outside the refrigeration chain. These packages are required to keep the content fresh for a long time, up to a year. To achieve this, the inside of the package must stay aseptic until the consumer opens it. In the distribution chain packages will be exposed to different mechanical loads, such as vibrations, shear forces and various pressure loads. These loads can be either transient or continuous. Ageing and variations in pressure and temperature add additional stresses to the packages. To ensure the aseptic tightness of the packages, tests are continuously performed. The goal of this master thesis was to find and suggest new or different ways of detecting and measuring leaks. The focus was packages using a mechanical tightening. The use of this type of tightening involves the risk of a temporary leak to appear, if the package is submitted to a load. The process of gathering information included several brainstorms followed by personal meetings with specialists from different areas. Literature studies and information from the internet helped sort out and put together a list of ideas. The ideas were evaluated and the most promising were presented as potentially useful to detect temporary leaks. Additionally the practical use of the oxygen measuring equipment, Dansensor 9000, was evaluated. A test was performed where the practical detection limit was found. The equipment was then used to measure the oxygen level in the head space of a new type of package. The aim was to distinguish between diffusion and a present leak but the diffusion rate itself was also of interest. The use of equipment, based on physical measurements, for detection of small temporary leaks has limitations. Calculations show the existence of a lower detection level that exceeds what is needed to contaminate the content. The report concludes that a gas-sensor mounted inside the package is the method best fitted to fulfil the demands. Statistics and methods involving bacterial growth must be used to fill the gap under the detection limit of physical measurements.