Product-package system: thermal aging and its influence on the mechanical performances of blown bottles. Relationship with design and process conditions

An optimisation procedure for a correlation between the material, the design and the forming process of two blown cosmetic bottles is presented. Two thermoplastic materials in the form of bottles are used: polyethylene low density PELD and clear polypropylene PP. The bottles are filled with cosmetic formulations and put into a steam room at 42°C for 15, 30, 60 and 90 days. This experimental technique allows us to accelerate the aging of the system ‘product-package’. Mechanical properties (wall thickness distribution, Young modulus, top-load compression and under-pressure resistance) are studied on emptied bottles, before and after aging. We propose a solution which consists of correlating the design shape, for both given materials, in terms of mechanical results which are significant. This work could lead to a new optimisation methodology, allowing us to anticipate the initial packaging design so that the corresponding in-time dimensional stability after the conditioning step is conserved.