As the fourth polymer for our study, we selected polybuthylene terephthalate (PBT), a semi-crystalline thermoplastic polymer that belongs to the polyester family, is characterized by its high rigidity, low tendency to creep, high strength, dimensional stability, good impact strength, very low thermal expansion coefficient, good wear and frictional resistance, good chemical resistance to acids, and very low moisture absorption, etc. PBT is mainly used in the automotive, consumer applications, electric, and textile industries and is very often modified with particulate fillers, like other polymers. It was found that beta radiation crosslinking can significantly improve the mechanical properties, such as micro-hardness, indentation modulus, and indentation creep. The most important aspect is to choose the appropriate dose of beta radiation which, in the case of indentation modulus improvement, is 132 and 66 kGy in the case of micro-hardness improvement. This depends on which property is required, how to improve it, and for which applications.
Polyamides (PA) very often find their use in industrial practice. Two types of polyamides were used, namely, Nylon 6 (PA6) and polyamide 9T (PA9T). Nylon 6 is a semi-crystalline aliphatic polyamide, whose advantages are low friction coefficient, high fatigue strength, and high resistance to a wide range of chemicals, oils, and fuels. It is an important engineering polymer—Used in a widespread spectrum of applications—For example, the automotive, construction, transportation, and other industries,. The scientists Dadbin, Frounchi, and Goudarzi dealt with electron beam-crosslinked nylon 6, and changes in the absorbed dosage dependency on its properties.
As a crosslinking agent, researchers used TAC (triallyl cyanurate) and, for crosslinking purposes, they used an electron accelerator with an energy level of 5 MeV, under irradiation doses from 40 to 150 kGy. These confirmed that various amounts of crosslinking agent had various influences on polymer properties. The higher the absorbed dose of beta radiation and the amount of TAC, the lower the water absorption of polyamide 6. Crystallinity, in a very similar way, decreased to 1.2% and 3% of TAC, in line with the increasing absorbed dose, in comparison with virgin nylon 6 without TAC.
The melting temperature was the lowest at a dose of 80 kGy, amounting to 3% TAC, which can be positively used in working practice to lower cost production. In order to obtain even better mechanical properties, it is possible to reinforce a polyamide by using glass fiber. Glass fiber-reinforced polymer (GFRP) represents a conformable design solution due to its special production adaptability, structural efficiency, and high durability. Its usage is also advantageous due to increasingly low production and erection costs. Porubska et al. examined the effect of electron beam irradiation on the properties of virgin and glass fiber-reinforced polyamide 6. They determined that crosslinking is more beneficial for virgin polyamide because of the increase in tensile strength at break and Young’s modulus. Properties at yield were not influenced by crosslinking, thermal resistance was only marginally influenced by irradiation for both GFRD (a marginal decrease), and for virgin polyamide, a small increase. Their finding is that electron beam irradiation leads to more changes in the properties of virgin polyamide in comparison with GFRD.
Polyamide 9T (PA9T) is a new, semi-aromatic, high-performance, engineering polyamide. This polymer has a long, flexible aliphatic linkage that consists of nine methylene groups in a sequence included in the main aromatic polymer chain. This polymer has a good balance of manufacturing cost and properties, and has good heat stability, low water absorption, considerable resistance to hot water, acid, alkali and organic solvents, and high heat moisture resistance. Due to these properties, PA9T is used in electrical, electronic, and automobile parts. Due to production factors, its fiber is also now used for the production of fishing nets and other industrial and textile materials.