The Effect of Ageinig the Structure and Mechanical Properties of Modified Polyoxymethylene Composite

Polyacetal or polyoxymethylene (POM) is one of the most important engineering polymers and it has wide usability (automotive, aerospace, sport, medicine, household etc.), because of good balance between mechanical and chemical properties. It is considered as an excellent alternative material for replacement of metals due to its high strength and stiffness. However, range of POM application is limited due to some properties, for example, poor impact strength and sensitivity under ultraviolet light (UV). To tailor exploitation properties for customer, POM is modified with other thermoplastic polymers, as well as inorganic or organic fillers. Apart from ease of manufacturing and desirable intrinsic exploitation characteristics, an important aspect in materials design is its durability, i.e., resistance to the effects of the factors of external environment: UV-irradiation, moisture, aggressive chemical agents etc. There are many publication about POM modification, but in these researches practically no information is devoted to the durability aspects of POM/elastomer blends and their nanocomposites. Consequently this research is devoted to investigation of POM blends with ethylene octene copolymer (EOC) and nanosized ZnO, exposed to ageing (in water or oil ambience or UV light ). POM composites with various EOC (0, 10, 30, 50 wt. %) and ZnO (0 and 2 wt. %) contents were prepared by roll milling at 180 0 C. Compounding time was 7 min after introduction of ZnO in the polymer blend melt. Test specimens for ageing tests were manufactured by injection molding. Test specimens were immersed in water or hydraulic oil for 4 weeks at room temperature (25 o C). Dimensions, mass changes and tensile properties were measured at various exposure times (Day 7th and Day 28th). UV weathering test was carried out by using Q-Lab QUV accelerated weathering tester. Test specimens were exposed to the sequence of the following cycles: UV light for 8h at 60 0 C (irradiance 0.76 W*m -2 *nm -1 measured at 340nm), condensation without UV irradiation for 4h at 50 0 C). Tensile, structure properties were determined at various exposure times (366, 672 and 1344 hours). Results show that stress-strain characteristics (modulus of elasticity, tensile strength ultimate deformation) of the investigated POM/EOC blends after ageing in water or oil ambience are somewhat lower than those before ageing, however, keep similar trend along with changing the elastomer content. Addition of ZnO, in its turn, assisted in increasing of modulus of elasticity and strength of the investigated nanocomposites. In general it has been shown that selected POM/EOC compositions have certain applicability in the submerged state (immersed in oil or water). It has been shown that addition of small amount of ZnO considerably improves UV resistance and tensile properties after ageing in water (tensile strength, deformation at break) of POM/EOC composites, as confirmed by corresponding structural and stress-strain investigations