Modifying the structure and properties of polyethylene foams using thermal treatments

BACKGROUND: The physical properties of polymer foams depend on many factors: density, cellular structure, matrix polymer morphology, etc. Therefore, these properties can be adapted by appropriate control of the structure. However, this simple and attractive concept has some limitations because the cellular structure of foams cannot be fully controlled during manufacturing. Therefore, in order to make possible the control of properties, it is highly desirable to develop simple procedures, such as thermal treatments, to modify the cellular structure. In the work reported, low‐density polyethylene foams were thermally treated at temperatures below the melting temperature of the base polymer. The cellular structure, polymer base morphology and several thermal and mechanical properties were studied before and after the thermal treatments. RESULTS: It is shown that the anisotropy of the cellular structure is reduced by using adequate treatments. This modification of the structure influences physical properties that are sensitive to the cell shape, such as thermal expansion, elastic modulus and collapse stress. CONCLUSION: A simple procedure to allow further control of the structure and properties of polyethylene‐based foams has been presented. The use of adequate thermal treatments is able to modify the cellular structure and hence the physical properties of these materials. Copyright © 2009 Society of Chemical Industry