A test apparatus for evaluating edge wicking in sized paperboard suitable for retortable packaging

摘要

The development of packaging board for liquids has been followed by the development of packaging laminate based on paperboard for canned food. This packaging will be filled with a food product and then exposed to high-temperature steam. A test apparatus is needed to simulate the preservation process and facilitate study of critical factors affecting such boards that must be highly water repellent. This paper presents an example of one such apparatus that can be used to study edge wicking in boards. The test apparatus consists of a large mixing chamber, where saturated steam and pressurised air can be mixed, and a smaller test chamber in which the test sample is placed on a cooling plate to simulate the temperature gradient occurring when a package of cold food is preserved by heat sterilisation. Test samples can also hang freely in the test chamber. In this study, one commercial board and one laboratory-made board were exposed to saturated steam at temperatures between 112℃ and 130℃, corresponding to a pressure of between 1.53 and 2.70 bar. The temperature of the cooling plate was regulated by varying the temperature of the inlet water between 24℃ and 72℃. The results show that the temperature of the saturated steam has a large effect on edge wicking - the higher the temperature, the greater the edge wicking. -The study also examined the effect of the magnitude of the temperature gradient that occurs when the board is placed on the cooling plate and exposed to saturated steam. It was found that differences in the temperature of the cooling plate do not affect edge wicking at a constant steam temperature. When samples on the cooling plate are exposed to high-temperature steam, water condensation takes place at the board edge, resulting in water migration into the structure and a clear liquid front in the board. In freely hanging samples, which were not exposed to condensation, the water uptake was uniform throughout the structure. Vapour phase transport took place rapidly throughout the structure and was followed by much slower water uptake into the fibres.