Research On Enhancement Of Toughness And Strength Of Polyoxymethylene(POM)

As one of the five major engineering plastics,polyformaldehyde(POM) shows excellent mechanical properties and good processing performance.Recently,how to modify POM has drawn lots of attention in industrial and academic area.In this paper,POM/EVA and POM/TPU blends were prepared by means of melt blending. Furthermore, the morphology,structure and performance of these two blending were studied systematically.By adjusting the content of VA in EVA,the component of blending,thicknesses,some achievements were made.The main contents are summarized as follows:(1)Effect of VA content on properties of POM/EVA binary blends: POM and EVA with various contents of VA were mixed together through melt blending, characterizations of POM/EVA blending were carried out on scanning electron microscope(SEM), transmission electron microscopy(TEM) and universal material machine.It turned out that VA content can influence the structure and properties significantly.Results of TEM and SEM showed that the morphology of POM/EVA was phase separated,the morphology and distribution were affected by VA content.The study had revealed that in POM/EVA50(VA content is 50%) blend,the microdistribution was mimimum which indicate that the compatible of EVA50 with POM was the best. Thermodynamic analysis showed that there were changes in glass transition temperature of POM and EVA50 in POM/EVA50 blend.However,in POM/EVA28,POM/EVA50 blending,no changes of glass transition temperature were found for any component.Mechanical properties proved once again that best compatibility happened between POM and EVA50.Compared with neat POM,POM/EVA50 got a much longer elongation.While this improvement was confined in POM/EVA28 and POM/EVA70 Blending.(2)Properties of the different proportions of the POM/EVA50 blending: In all the ethylene vinyl acetates, EVA50 had the best consistency with the POM. In this article, we discussed the property of different proportions of POM and EVA50 blending. When the proportions of POM/EVA50 blending varied from 95/5 to 70/30, the change of dispersed phase regions and sizes of the EVA50 in the POM matrix were studied mainly. What’s more,we also put attention on thermal analysis and mechanical properties of blending materials. When the component of the POM/EVA50 changed, it was well worth paying attention to the change values of the tensile and impact property. Results showed that with the addition of EVA50,the ductility increased and the strength decreased. When the proportion of the POM/EVA50 was 80/20,the blending material has the best mechanical properties,besides,thermal property, crystallizing performance were all good. Thus this proportion was the best one for toughening the POM.(3)The preparation and the characterization of POM/TPU/Tale alloy:Nowadays thermoplastic polyurethane is an elastomer which has the effect of toughening POM. In this article, we prepared a series compositions of the POM/TPU binary blend, POM/TPU(T1020/Talc) alloy,its morphology, structure and properties were studied systematically. Research suggested that TPU,as the dispersed phase, was packed by the spherulites in the POM matrix mainly, and it made the rigid POM spherulites becomes softer to some extent than before,and then increased the toughness of blending material. What’s more, when the composition of the TPU was 5%, it had the best effect to toughening POM. When a certain amount of(T1020/Talc) were added in the POM/TPU binary blend,the T1020/Talc were mainly distributed in the amorphous region of POM, making the POM/TPU/(T1020/Talc) quaternary blending maintain a certain toughness, compared to the POM/TPU binary blending, its yield intension increased in the same time.(4)Effect of sample thickness on properties of POM/EVA,POM/TPU binary blends:POM is a polymer with high degree of crystallinity,it’s easy to form large size of spherulites during processing.With different film thicknesses,the growth of POM spherulites will subject to different constraints. Research suggested that in POM/EVA50=80/20 blending, the elongation and strength at break reached the maximum when thickness was 500um;when sample thickness varied from 500 um to 2000 um,the elongation at break became shorter gradually,while the strength at break didn’t change much.In POM/TPU=95/5 blending,as the thickness of blend film increased from 300 um to 2000 um,the elongation at break of the blending decreased gradually,while the strength at break didn’t change much. For samples with thickness of 100 um, they lost their heat quickly, the growth of spherulites were limited in space and time,thus it was impossible to get perfect spherulites and possible to have large amount of broken crystal.The interaction between EVA50 and POM enabled POM to refine its spherulites,while the nucleation effect on POM of TPU reduced the size of spherulites, refined grain and increased the number of unit cell.