Study On The Crystallization And Rheological Properties Of PA6 Composite Modified By Complexation

In the paper, we employed a rheological method to study the crystallization behavior of PA6/Ca Cl₂（PA6/Li Cl） complex and the mechanism of confined crystallization of PA6, because the real crystallization behavior of PA6 could not be detected by DSC when small crystallization heat flux caused by confined crystallization of PA6. What’s more, the crystallization and rheological properties of PA6/elastomer/Ca Cl₂ and PA6/epikote/Ca Cl₂ were also studied. The main contents are follows:Firstly, the study concentrated on the influence of the contents of Ca Cl₂（Li CI） on the crystallization and rheological properties of PA6/Ca Cl₂（PA6/Li CI） composites. From the results of X-ray diffraction（XRD）, DSC, infrared spectroscopy（FTIR）, and rheology, as the contents of Ca Cl₂（Li CI） increased, the onset temperature of nucleation and the growth temperature of crystal reduced, nucleation density and the rate of nucleation reduced significantly, the total crystallinity of γ-phase and α-phase and crystallinity of γ-phase values of specimens reduced dramatically, γ-α crystal transformation occured, and the crystallinity of α-phase initially increased and then decreased. These were due to the complex reaction of Ca Cl₂（Li CI） with the carbonyl oxygen atom in the amide group disrupted hydrogen bonding of PA6. Besides, the complexation interactions between Ca2+ and carbonyl were expected to confine the mobility of PA6 molecules in the process of crystallization, so crystallization of PA6 was confined. Compared PA6/Ca Cl₂ complex with PA6/Li Cl complex, Li Cl was more capable of confining crystallization of PA6 and improving mechanical properties of composite materials.Secondly, we employed the elastomer as a modifier to improve mechanical properties. The results showed that POE-g-MAH on the effect of the crystallization and melting behavior of PA6 was small, but can significantly improve the notched impact strength of the composites. When contents of POE-g-MAH were 10-15 phr, PA6/Ca Cl₂/POE-g-MAH composites had the better mechanical properties. Besides, complex reaction between Ca Cl₂ with PA6 made the N–H bond of PA6 released and polarity of PA6 reduced, which made the interfacial tension of composite materials abated, and compatibility of composite materials improved. Compared with compatibility of PA6/POE-g-MAH and PA6/POE with different contents of Ca Cl₂, to a certain extent, we can use POE instead of POE- g-MAH for toughening system.Lastly, we employed the epoxy resin（E51） as a modifier to improve mechanical properties. The results showed that extender chain reaction between E51 and PA6 made crystallization of PA6 confined, and imperfect degree of the crystal increased. When PA6 crystallization restricted seriously, DSC can’t represent the crystallization and melting behavior of PA6/Ca Cl₂/E51 composite. In the linear viscoelastic region, G’’ initially increased and then decreased. When the contents of E51 was equal to 3 phr, G’’ reached optimum values. What’s more, the addition of Ca Cl₂ could limit E51 and PA6 extender chain reaction, and made G’and G’’ reduced. But complexation reaction of Ca Cl₂ and PA6 made friction force of segmental motion increases with the increase of Ca Cl₂ contents, then G’ and G’’. In conclusion, using the right amount of E51 and Ca Cl₂ to modification of PA6 could effectively reduce the melting point of PA6, and improve its mechanical properties and rheological properties. When contents of E51 and Ca Cl₂ were 3 phr and 6 phr respectively, PA6/E51/Ca Cl₂ had the better mechanical properties and low melting point PA6.In conclusion, compared with DSC, the rheological method was more capable of detecting crystalline information of PA6. Besides, it is an effective and objective method on the study of change of polymer microstructure and the mechanism of crystallization of PA6 limited...