The Study Of The Synergistic Control Between Crystallinity And Crystallization Rate Of Pom In POM Processing

Due to the crystallization characteristics of POM,such as high crystallization rate,high crystallinity and large grain size,it's easy for the POM products to appear surface depression,warpage and even internal voids when forming large POM parts.The root of the problem that POM is difficult to be molded into big parts rapidly is its crystallization properties,which mainly includes high crystallization,high crystallinity and coarse grain,etc.The report of the comprehensive control of POM crystallization in the literature,especially in the study of reducing crystallization rate of POM is less.Therefore,the POM crystallization inhibitors which can interact with POM in some degree and common nucleators were prepared firstly in this paper in order to make clear the effect of them on POM crystallization behavior.Then,by selecting the efficient POM crystallization inhibitors and nucleating agents,their combined effects on POM crystallization properties were studied in detail,which provides an important theoretical guidance for the implementation of prototyping big products of POM rapidly.The results are as follows:Thermoplastic Polyurethane(TPU),phenolic resin(PF),NBR,polyoxyethylene(PEO),polyacrylate polymer(ACR)and ABS were used as inhibitors to study the effects of their dosage and dispersion morphology on crystallization behavior of POM.The results showed that several kinds of polyester and polyether TPU with different chain structure have little effect on the Ti and Tc of POM,but the grain was obviously refined and crystallization enthalpy significantly decreased.The stronger the rigidity of TPU molecular chains,the more significant the inhibitory effect.A small amount of(3wt%~5wt%)PF could reduce Tc by 2oC and crystallization enthalpy by 10~15J/g,as well as refined grain.Ti was not affected when PF was less than 10 wt%.NBR made POM show step crystallization phenomenon.Ti and Tc were slightly moved to low temperature and(35)Hc obviously reduced,grain refinement.When the amount of NBR was increased to 10 wt%,(35)Hc was significantly reduced.PEO could not be used as inhibitor: A small amount of PEO50(3wt% ~5wt%)made Ti of POM move to high temperature,Tc increase by 0.3~2.4?and(35)Hc increase by 7.8~13.2J/g.When the amount was more than 10wt%,(35)Hc was significantly lower than that of pure POM.In the experimental dosage range PEO100(3~15wt%)had no effect on the Ti but made Tc slightly improved.The stronger the rigidity and the length of ACR molecular chains,the stronger the inhibition of growth rate and crystallinity.When 5 wt% polymer were used the inhibition of ACR was inferior to PF and NBR but better than TPU.0 ~ 40wt% ABS had no effect on Ti of POM,but Tc increased by 0~2.5?.The crystalline morphology showed that these polymers were excluded from the lattice during the growth of the POM spherulites and were wrapped in the spheroidal microfibers as foreign matter.The effects of nucleating agents(nano-diatomaceous earth,montmorillonite,carbonaceous materials and complex phosphoric acid ester nucleating agents)on nucleation(nucleation rate,nucleation density),POM crystallization kinetics,growth Rate,crystallinity and crystal morphology of the mechanism and the law.It was found that the three kinds of inorganic nucleating agents had no effect or slight influence on the Ti and Tc of the POM,and they were allowed to migrate from 0 to 0.8 ° C to the low temperature.The free surface energy of the folded chain was slightly increased and the spherulite growth rate decreased slightly.(35)Hc significantly increased,half-width significantly increased: 2wt% of diatomite to POM(35)Hc increased ~ 9J / g,half-width increase of 32%;1.5 wt% of montmorillonite POM(35)Hc increased ~ 13 J / g,half-width increase of 15%;1wt% of the carbon material to POM(35)Hc increased ~ 21 J / g,half-width increase of 18%.Under the condition of inhibiting growth,the distribution and dispersion of the nucleating agent in the two phases affect its nucleation.When PF was an inhibitor,the 1wt% carbon material exhibited a prominent nucleation effect.3wt% PF under the growth conditions,1wt% carbon material increased(35)Hc 7.3%,compared to pure POM increased 3.5 J/g,half width and width than the pure POM widening 19.4%,but no effect on Ti and Tc,While achieved a lower crystallization rate,maintaining high crystallinity and refining grain.When NBR was an inhibitor,the nucleation of diatomaceous earth,montmorillonite and carbon material did not appear,and Tc was shifted to low temperature,and(35)Hc was significantly reduced.The reason may be that almost all of the three inorganic particles are enriched in the inhibitor phase,and the detailed reason is still under analysis and experiment.