MECHANICAL PROPERTIES OF STRUCTURAL LDPE FOAMS COMPARED WITH THOSE OF CONVENTIONAL NON-STRUCTURAL LDPE FOAMS

摘要

The application of sandwich structural foams has rapidly increasing in the last decade. Structural foams are composed of two solid layers enclosing a foamed core. This sandwich combination results in better mechanical properties compared with classical foams at an equivalent density, A high surface quality is also achieved which makes them perfect for several industrial applications (structural panels, parts, etc). Normally, injection moulding is used to produce these foams. One of the disadvantages of this technology is the use of expensive moulds that increase the price of the parts especially for series with a low amount of parts to be produced. In this paper a much simpler procedure to produce structural foams that uses very cheap moulds is used, getting a perfect surface quality and different density profiles across the foam. Mechanical properties of these structural foams strongly depend on the local density and its distribution. From this point of view, skin thickness is a very important parameter. This skin thickness strongly depends on the processing parameters and formulation. Using an universal testing equipment, mechanical properties in tension, compression and bending have been characterized. All these properties have been compared with the ones corresponding to foams produce under classical methods (non structural materials) of the same density. The characteristic sandwich structure of these foams greatly improves the mechanical behaviour of these materials. Consequently, we have a material with high specific mechanical properties (strength to weight ratio) compared with non structural foams that present also a very high surface quality and that is produced using a very simple technique in comparison with injection moulding.