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Mechanical properties of low density polyethylene filled with various organic fillers were investigated. Different effect of different fillers on the properties was observed and the effect of crosslinking of these materials is also different. Fine anisotropic fillers behave similarly as inorganic fillers. The effect of crosslinking is the highest for composites containing large particulate fillers like beech wood flour. The effects are discussed in terms of mechanical behaviour and crosslinking degree determined from extraction or equilibrium swelling data. A formation of covalent bonds between the filler surface and polymeric matrix is proposed as a result of crosslinking.

Thermal capacity of a particulate composite LDPE filled with graphite was measured by a non-steady state method at 25°C. A non-additive dependence of thermal capacity on the concentration of the filler was observed. A three-phase model was proposed, where the capacity of the interphase was included besides the parameters for matrix and the filler. The model reasonably describes the experimentally observed behavior.

The method of chemically initiated oxidative modification of polypropylene particles in suspension by pyrrole was used for preparation of conductive polypropylene/polypyrrole composites. Their properties were compared with another type of polypropylene/polypyrrole composites prepared by melt mixing of pure polypropylene with chemically synthesized polypyrrole and with polypropylene/carbon black composites also prepared by melt mixing.The composites were characterized by elemental analysis and by rheological testing. The antistatic properties of prepared composites were demonstrated. The electrical and flow properties depend on the concentration of filler and on the processing conditions of composites.