| Polyoxymethylene,which has excellent mechanical properties,fatigue resistance,wear resistance,self-lubrication and electrical properties,is widely used in automotive,mechanical and electronic fields as transmission components,connectors,instruments and zippers instead of steel.The Crystallization characteristics make it can only form thin-walled and small-sized products only directly.Defects such as surface depression,warping and even internal cavity may occur when forming thick-wall and large-size products,which restricts its size and application.All of this is due to its high crystallization rate,high crystallinity and large spherulites,which can be solved by regulating the crystallization behavior during molding process to meet the requirements of rapid moulding,while maintaining high crystallinity and forming small spherulites.Our team used crystal growth inhibitors to control or interfere with the orderly arrangement of POM molecular chains,which forced the crystallization rate to decrease in order to meet the rapid prototyping of large products.At the same time,nucleating agents were used to reduce the nuclear energy formation in the growth-restricted environment and increase the density of crystal nucleus to ensure high crystallinity and fine small size spherulites.Based on the previous work,the effects of MWCNT,nano-MMT and Diatomite nucleating agents on the crystallization of POM were studied in this paper.The experimental results show that the three nucleating agents selected in this paper have the effect of heterogeneous nucleation on the POM,which increases the number and the density of spherulite.At the microcosmic level,the corresponding nucleation density are 83/mm2(1.0wt%)?62/mm2(2.0wt%)and 76/mm2(1.5wt%)at 158 oC when nucleating agent is the best dosage of each other,but the nucleationdensity of neat POM at this temperature is only 21.6/mm2;Their diameters are 10~15?m,15~20 ?m,20~30 ?m and 35~50 ?m(neat POM)when POM 156 o C isothermally crystallize at 156 oC for 30 min.At the macro level,when nucleating agent is the best dosage of each other,the corresponding ?Hc are 195.9J/g,192.7J/g and 187.5J/g,which is higher than neat POM,and the ?Hc of POM/1.0wt% MWCNT is the highest one.Theoretically,the effects of the three nucleating agents on the Avrami index n and the modified crystallization rate constant Kc of POM were relatively small,indicating that this three nucleating agents didn't change the nucleation mode and growth mechanism of POM,and were still non-thermal nucleation and three-dimensional spherulite growth mechanism.The ?e was decreased by the equation H-L,indicating that the three nucleating agents could promote the growth of POM spherulites when the optimal dosage of the three nucleating agents was used.WAXD showed that POM with these three nucleating agents showed diffraction peaks at 23.3°,35.0° and 48.5°,and there was no deviation and no new peaks compared with pure POM.The results showed that the crystal form of POM did not change. |
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