Foam

Abstract

Phenolic foam is a unique cellular material that can be utilized in either a fully open cell structure or a completely closed cell structure in a diversity of applications such as open cellular material for floral foam, soil propagation media and/or orthopedic use, and closed cell phenolic foam primarily for thermal insulation. Thus, phenolic foam is much more versatile than other competitive organic foams such as polystyrene and polyurethane with the latter materials being more heavily involved in thermal insulation. Foam processing can consider batch, semi-continuous, or continuous conditions, and the features and weaknesses of the appropriate processes are discussed along with continuous mix heads involving high and low pressure conditions.

The use of phenolic foam for thermal insulation is quite active in Europe, particularly in the UK, and is being revisited in North America because of the efforts of a program sponsored by the US Department of Energy leading to proposed neutral pH foam and improved mechanical strength/performance. The latter is accomplished by the introduction of small amounts of chopped cellulose fibers into the resole resin prior to foaming.

New foam areas are described and include the use of foam for air filtration for dust control, carbon foam prepared by carbonization of phenolic foam and then used for high temperature structural composite sandwich panels or for composite tooling, and pultruded phenolic foam. The latter offers an interesting opportunity as a means of preparing sandwich structures continuously by foaming/pultruding between phenolic glass and carbon fiber prepreg face sheets. In a related matter, fiber reinforced pultruded phenolic foam is being developed to possibly replace balsa core currently used by the US Navy in naval ship sandwich panel structures.

Different test methods are described such as fire testing, insulation efficiency, strength testing, and open/closed cell content. Saturation properties determination for floral foam is detailed.