Studium teplotní odolnosti termoplastů

The use of thermoplastic materials is constantly increasing in technical branches. Their indisputable advantage is low weight, good mechanical properties, excellent chemical resistance and low processing temperatures. Relatively low temperature stability belongs to its huge disadvantages. Any improvement of this property can considerably expand the application area of thermoplastic polymers. Among the ways allowing an increase in temperature stability there are various modification methods, above all cross-linking of thermoplastic polymers. The doctoral thesis deals with the influence of radiation cross-linking of thermoplastic materials on their temperature stability. The influence of irradiation dose on temperature stability of radiation cross-linked polymers is examined in this study. Moreover, there is a study of irradiation dose influence on other properties, mainly the influence of repeating temperature load on the products made of radiation cross-linked polymers. This study searches the dependencies between irradiation dose and the properties of radiation cross-linked polymers, especially from the group of polyolefins, with the aim of a more thorough understanding of their mechanical behaviour, temperature stability of selected thermoplastic polymer types and expanding their application in practice. Testing specimens of non-modified and modified PE-LD, PE-HD by Beta (electron) ray in dosage from 0 to 198 kGy with step of 33 kGy were heated for one hour below and above the melting temperature of original material. Mechanical, thermomechanical, thermal and structural tests were performed at ambient temperature (23 °C) after the first and the fifth heating cycle. According to measuring there was confirmed considerable influence of radiation cross-linking on improvement of PE-LD and PE-HD mechanical properties (especially at elevated temperature), as well as increasing temperature stability of PE-LD and PE-HD. Temperature stability depends mostly on cross-linking density, which is rising with increasing dose of radiation. Radiation cross-linking is an important method of thermoplastic modification, therewith we can achieve required properties during very short time. The main advantage is that this process takes place on a final product. This requires another, mainly logistics expenses, which increase price of the final product. Determination of an optimal radiation dose and subsequent changes in behaviour of modified thermoplastics is crucial part of thermoplastic modification by radiation cross-linking.