The studies on the production of polyethylene film with reduced flammability

            Natural and synthetic polymers and plastics made of them, are an integral part of the urban environment  in many different areas . Polyethylene is one of the most widely used polymers. Production of films of different kinds and purposes is determined by the specific properties of polyethylene. Among the polymers and polymeric materials only a small portion can be considered non-flammable. The vast majority (including the above-mentioned polyethylene) undergoes a process of thermal destruction under the influence of a sufficient amount of energy, emitting a considerable amount of heat and smoke. Studies on the flammability of polymers and methods of its reduction are driven by factors of ecological, economic and safety aspects.

            The experimental section describes a procedure for preparing a film material and a comparison of properties, with respect to the used filler: colloidal silica, calcium phosphate or hydroxyapatite. With Differential Scanning Calorimetry (DSC) we tested properties such as melting and crystallisation temperature, heat of fusion and the content of crystalline phase. Studies were carried out using the flammability test LOI UL-94 and microcalorimetry of pyrolysis-combustion to determine the burning rate, the limiting oxygen index as well as the rate and the amount of released heat. Optical microscopy was also used to examine the morphology of the polymer matrix.

            On the basis of the results, the modification of polyethylene matrix was found effective. The addition of fillers had a significant impact on the mechanism of combustion of the investigated films. It revealed a reduction in burn rate, a reduction in rate and amount of released heat and an increase of the value of LOI. At the same time, there were no significant effects on the other properties of the composites. The most prominent flame retardant effect as compared to a pure polyethylene film was provided by hydroxyapatite. There was no occurrence of synergistic effect between the phosphorus compounds and the silica, so there is no reason to apply them in such combination as a mixture of fillers, giving the effect of fire retardant in the composite material.