Crosslinked polyethylene offer better mechanical and thermal properties

- Feb 21, 2019-

Material modification is needed in order to obtain better material properties as required in the plastics industry. One of many ways of how to modify polymers is beta radiation crosslinking. In most cases, crosslinked polymers offer better mechanical and thermal properties. The beta radiation sources for the industrial crosslinking of polymers are electron beam accelerators, which allow one to obtain high-radiation doses in a short time. Ionizing radiation (electron beam radiation) can change the macroscopic properties and the molecular structure of polymeric materials. Thermoplastic materials demonstrate better resistance to temperature-induced deformation or flow, and do not melt after the creation of crosslinking bonds. After crosslinking, the impact resistance, chemical resistance, toughness, and thermal stability are all improved. This study focuses on the electron beam crosslinking of various types of polymers. Herein, the individual polymers are described, as are the studies already carried out on their crosslinking by electron beam radiation.

The first polymer used in our study is polyethylene. Polyethylenes are commodity polymers, which account for more than 70% of total plastics consumption, and are low-cost, easily processable, and available. Typical applications of these polymers include packaging, household items, net ropes, medical applications, fishing rods, water pipes, etc. There are many types of polyethylenes, including linear low-density polyethylene, low-density polyethylene, ethyl vinyl acetate copolymer, polyolefin elastomer, high-density polyethylene, and many others. After the addition of crosslinks in low-density polyethylene (LDPE), the material displays ductile plastic behavior below its melting range. After the melting of all crystallites, the behavior of LDPE becomes elastomeric. Crosslinked LDPEs (XLDPEs) have found to have a wide range of applications in the production field—Films, sheets, and foams. Nowadays, LDPE has, in most cases, been replaced by XLDPE. The heat deformation behavior of XLDPE is superior in comparison to LDPE. The crosslinking of LDPE can be initiated by using peroxide, introducing silane groups into polyethylene, or by radiation; e.g., electron beam or gamma ray radiation .

High-density polyethylene (HDPE), was used as a second commodity polymer, it is a semi-crystalline thermoplastic material belonging to the polyolefin family. Mehrjerdi et al. studied HDPE, containing 2.5 wt % of carbon black (CB), and talc—Fully blended by the supplier. They realized that CB proved to be an effective additive for the improvement of thermal stability, while it had a poor influence on mechanical properties, especially on impact resistance. In the case of the influence of talc on material properties, the thermal diffusivity and conductivity, and the specific density and the toughness perpendicular to the direction of flow, were improved, while the specific heat capacity of the composites decreased. Another investigation concentrated on HDPE, which focused on critical considerations for the accelerated ageing of high-density polyethylene potable water materials; this was the first investigation to demonstrate water sorption and desorption by HDPE resin and HDPE potable water pipes. The scientists they determined the recommended water quality conditions for the accelerated ageing of polyethylene materials, which they then inserted into tables.