Study On POM Modified By Ultrafine Composite Powder

Polyoxymethelene (POM) is widely used as an important engineering plastic due to its good mechanical properties. POM is easy to form big spherical crystals due to its regular chain structure, resulting in low notched impact strength, sensitive to notch. On the other hand, POM is incompatible with most modifiers and difficult to be modified.In this article, ultrafine composite powder was employed to modify POM. Based on results of modifying POM by thermalplastic polyurethane(TPU) and ultrafine inorganic powder, ultrafme composite powder with the structure of TPU coating ultrafine calcium carbonate was prepared by means of pan-milling, which combines the merits of TPU and ultrafine inorganic powder and greatly decreases the amount of TPU needed, endows POM with good comprehensive properties. This offers a theoretical and experimental basis for preparing POM with high performances but low cost.1. The mechanism of TPU toughening POM was studied. A kind of TPU with proper ratio of soft to hard segments was selected from 9 kinds of TPU as the modifier of POM. Effect of TPU content and processing temperature on properties of POM was studied. Results showed that TPU can reduce thecrystallization degree of POM, increase notched impact strength and thermal stability of POM. When the content of TPU is 40%, brittle-tough transition happens. When the content is 45%. notched impact strength of material reaches 57 kJ/m2, which is 12-folds that of POM matrix. Toughening of POM results from the high elasticity of TPU and decrease of crystallization degree of POM.2. Toughening POM by ultrafme calcium carbonate and talcum was studied. Effects of sort, content, particle size and different coupling agents treating of ultrafme inorganic powder on the mechanical properties of POM were also investigated. Results showed that heavy calcium carbonate and talcum can only strengthen POM, and light calcium carbonate can toughen and strengthen POM. Ultrafme inorganic powder with smaller size can improve the properties of POM. Calcium carbonate modified by KH550+ON330 can increase notched impact strength of POM. When the content of calcium carbonate is 2%, both the notched impact strength and the tensile strength of POM are improved, because ultrafme calcium carbonate can increase crystallization degree and decrease the spherical crystal size of POM.3. Pan-milling was used to prepare untrafine composite powder, in which TPU was shell and ultrafme calcium carbonate was core. The formation mechanism of ultrafme composite powder and effect of ultrafme composite powder on properties of POM were studied. The result showed that in ultrafme composite powder, TPU is thin sheets with thickness of about 200nm, width of about 5m and calcium carbonate particles scatter in them. After thermal treating, a structure of TPU coating calcium carbonate was formed. The mechanical properties of POM modified by ultrafine composite powder is better than that of the conventional way. When the content of ultrafine composite powder is 10% (the content of TPU is 6.5%), the notched impact strength of the modified POM reaches 15.3kJ/m2, twice that of pure POM, one time higher than that of POM modified by conventional way. In addition, thetensile strength of POM modified by ultrafine composite powder reaches 52 MPa, 12MPa higher than that of POM/TPU blend with the same notched impact strength, due to the much lower loading of TPU.