As it is known, polyethylene (PE) is one of the common materials in the modern world, and PE products take the major share on industrial and trade markets. For example, various types of technical PE like PE-63, PE-80, and PE-100 have wide industrial applications, i.e., in construction, for pipeline systems etc. A rapid development of plastics industry outstrips detailed investigation of welding processes and welds’ formation mechanism, so they remain unexplored. There is still no final answer to the question how weld’s microstructure forms. Such conditions limit our way to the understanding of the problem and, respectively, prevent scientific approaches to the welding of more complicated (from chemical point of view) types of polymers than PE. Taking into account state-of-the-art, the article presents results of complex studies of PE weld, its structure, thermophysical and operational characteristics, analysis of these results, and basing on that some hypotheses of welded joint and weld structure formation. It is shown that welding of dissimilar types of polyethylene, like PE-80 and PE-100, leads to the formation of better-ordered crystallites, restructuring the crystalline phase, and amorphous areas with internal stresses in the welding zone.

The paper presents results of the investigation of structure relaxation and thermal properties of PE-80 and PE-100 polyethylene hot-tool butt welds. It was found that a weld with the re-crystallized crystalline structure is formed during the welding of dissimilar types of polyethylene. It is shown that within a long period (1 year) the relaxation occurs not only in amorphous but also in the crystalline phase (crystalline α-form transforms into mixed αβ-form), with respective changes in polyethylene properties.

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