Characterisation of Plastic Foams used as Backer Rod in the Construction Industry

Abstract

Six polyethylene (PE) and two polyurethane (PU) commercially available foams typically used in the construction industry were investigated in terms of their mechanical, morphological and surface chemistry properties. Both PU foams were open cell foams, while all PE foams had closed cells; this led to a significantly lower hardness and compressive strength, but to a higher water absorption in the open cell foams. It was found that a higher density leads to a smaller cell size, which resulted in lower water absorption. Optical microscopic pictures were taken and they revealed a broad distribution of cell size and cell shape; skin cells were generally smaller than bulk cells. A new concept, the “theoretical solid foam surface”, is introduced with which an estimation of the contact area between foam and sealant (or any other solid/highly viscous material) is possible. XPS and IR experiments showed that all PE foams had an oxidised surface, and several PE foams also contained oxygen in their bulk phase. The PU foams contained silicon at a high concentration; some of the PE foams also had silicon incorporated though to a lesser extent. Nitrogen was found in some PE foams. The silicon and nitrogen contamination was assumed to arise from additives such as release agents. These impurities probably led to the high surface free energies found on PE foam. In particular, the skins with larger amounts of contamination had higher surface free energies. The measurement of the surface free energy of foams with the VCA method proved to be difficult because a large distribution of distorted contact angles was measured, caused by the roughnesses of the foam surfaces. Recommendations are made for the practical application of the research in the context of construction.