Study Of Solid State Polymerization Of Rare-Earth PA6

Rare-earth polyamide 6 can absorb and store lights in the bright and emit lights in the dark in a recycle way. It can be used as lightening, safety mark and decoration.In this thesis, Rare-earth polyamide 6 was synthesized through in-situ polymerization. Infrared spectrum analysis （FTIR）, microscope, SEM and end-group titration were employed to measure the structure and properties of sample. It was indicated that there is chemical coalescence between luminous pigments and polyamide 6 by FTIR and end-group titration. Rare-earth polyamide 6 prepolymer prepared via in-situ melt polymerization had low molecular weight and it was difficult to meet the demand of some field. It was needed to increase molecular weight by further solid-state polymerization（SSP）. The effect of different polymerization temperatures, polymerization time, prepolymer grain size and the addition of luminous pigments on solid-state polymerization were studied. The higher polymerization temperature was, the quicker molecular weight increase of samples during solid-state polymerization was. It should be pointed out that too high reaction temperature will lead to thermodegradation of Rare-earth polyamide 6 and grains adhesion, so the appropriate reaction temperature should be choosed. Rare-earth luminous pigments in the amorphous regions of PA6 impeded the mobility of the end group and furthermore there is chemical coalescence between luminous pigments and PA6, it made reaction rate of Rare-earth polyamide 6 become slower than that of neat PA6. Comparison with the unextracted grains, the molecular weight of extracted grains was increased at the same solid-state polymerization conditions. Prepolymer with high molecular weight had fast reaction rate for the reason of end group distance distribution. The smaller prepolymer grains had the quicker diffusion rate of by-product and the higher molecular weight after solid-state polymerization.The effect of the luminous pigments and molecular weight of neat PA6 and Rare-earth polyamide 6 on the isothermal crystallization was investigated by differential scanning calorimetry（DSC）. The Avrami equation was used to study the isothermal crystallization kinetics. The crystallization rates of PA6 composites increased with increase of luminous pigment content, which indicated the luminous pigments act as effective nucleating agents. In the other hand, the crystallization activation energy also increased, which showed that the transport of PA6 segments is retarded by the luminous pigments. The increase of molecular weight of PA6 and rare earth luminous PA6 after SSP led to increase of intermolecular forces and lowered the activation energies of crystallization, while the crystallization rate of PA6 and rare earth luminous PA6 decreased after SSP due to the decrease of the reptation rate of which long chains passed through the reptation tube to arrive the melt-crystal interface.The non-isothermal crystallization and melting behavior of PA6 and its composites before and after SSP were also investigated by DSC and three methods were adopted to analyse the non-isothermal crystallization process. The results showed that the Ozawa analysis seemed not to suit, while Mo’s analysis was successfully used. Although Jeziorny analysis had some problem for whole crystallization process, it could be applied to analyse the main crystallization process well. The addition of luminous pigments resulted in the decrease of crystallization rate, which indicated the luminous pigments had dominated effect on hindering the motion of PA6 chains instead of nucleating agents during the non-isothermal crystallization, the result was different from the isothermal process. From the non-isothermal crystallization DSC curves of neat PA6 and rare-earth luminous PA6, dual melting endotherms peaks were found for rare-earth luminous PA6, while there is only one single peak for neat PA6. The addition of the luminous pigments favored the formation ofγcrystalline form which is related to the lower temperature peak. In addition, high cooling rates also favored the formation ofγcrystalline form for both neat PA6 and rare-earth luminous PA6. Furthermore, the crystallization degree of rare-earth luminous PA6 is higher than that of neat PA6, which further proved that the luminous pigments acted as a heterogeneous nucleation agents .The extraction kinetics of PA6 and rare earth luminous PA6 grains in hot water was studied. The effects of hot water temperature, bath ratio, stirring or not etc on the extraction efficiencies of PA6 grains were analyzed. The concentration of the extractable in water was tracked by refractive index at different extraction time. It was obtained that the hot water temperature had the key effect on the extraction efficiencies. Based on mass transfer theory between solid and liquid, a kinetic extraction model of PA6 grains was proposed. Two model parameters C₁, C₂ and the slope of equilibrium line m as a function of extraction temperature, can be obtained by fitting the experimental data. The higher temperature was, the larger the value of C₁ and C₂ was and the higher the concentration of the extractable in water was, and the slope of equilibrium line m increased exponentially as the hot water temperature increased, which indicated that the hot water temperature had very large effect on the extraction efficiencies of PA6 grains.