The Study Of Crystallization Control In POM Processing

POM products appear shrinkage, warpage and surface depression in processing which caused by the high crystallization rate and have a low impact strength because of large spherulites. In the view of above problems of POM, this paper has done the following researches:1.Modifing the crystallization rate of POM by adding crystallization inhibitors like ABS, NBR, TPU. The study found that when the ABS amount during 20wt% to 60wt%, the nucleation ability of POM at high temperature unchanged and has double effects on crystallization. Not only can promote the nucleation, obviously inhibit the spherulite growth of POM, and the crystallinity decreased severely. When the content over 60wt%, the fractional crystallization phenomenon occured, Tc and ?Hc have severely decreased with the increase of ABS content. NBR and acrylate have a similar effect on POM crystallization behavior. The nucleation ability at high temperature unchanged, the crystallization degree decreased with increase of inhibitor content, and the crystallinity decreased more severely when adding NBR. The crystallization rate of POM/NBR decreased slightly but is unconcerned with NBR content.2. Effect on the POM crystallization behavior of inhibitor TPU is that the nucleation ability keeps stable at high temperature after adding TPU-1, TPU-2, TPU-3, but Ti will decreased after TPU-4 and TPU-5 adding. Five kinds of TPU will inhibit the crystallization of POM, making the Tc and the crystallization rate decreased. With the increase of TPU, the perfection degree of spherulite is destroyed and the crystallinity is reduced. But the crystallization enthalpy of TPU-3 and TPU-4 is higher than that of pure POM at 5wt%. TPU could not play a role in grain refinement and will be excluded from the outside of the lattice which can be observed in photo.3. In order to solve the problem of large spherulite size and the crystallinity decreasing, we study the effect of crystallization properties and crystallization morphology by adding the compound nucleating agent N and ZC-3 etc. It shows that nucleating agent N can effectively increase the crystallinity and the crystallization enthalpy improved about 3.0J/g, Tc and crystallization rate are higher than pure POM. Other nucleators will make the crystallization enthalpy decreased, maximum value up to 12.2J/g. From the photo, we can see that the POM spherulite is refined and has a high nucleation density after adding compound nucleating agent N.4. Studying on the influence of inhibitor/nucleator on the crystallization behavior of POM found that the Tc of POM/inhibitor/nucleator agent decreased about 1.5-2.2?, the crystallization rate of POM was significantly decreased comparing with the pure. It shows that inhibitor/nucleator agent can modify crystallization rate of POM. The crystallization enthalpy of the agent decreased about 3.6-15.4J/g, compared with the agent of single inhibitor, POM/inhibitor/nucleator agent has a higher crystallinity.