Study On Preparation And Performance Of Melt Stretched Aliphatic Polyketone Film

Extrusion casting has become an important method for preparing polymer film materials because of its simple process and suitable for high-speed production.In the melt stretching flow field,the polymer melt is subjected to the combined action of the high-speed tensile stress field and the variable temperature field within the adjustable distance between the die and the warm casting roll,and the molecular chain is along the direction of the stress field,which induces the formation of lamellae perpendicular to the stretching direction.As an excellent engineering plastic,there are currently few reports on its extrusion casting.The processing flow field directly affects the crystal morphology and properties.The aliphatic polyketone terpolymers has a large number of electronegative carbon groups on the molecular chain which induces tightly packing and a fast crystallization rate.The influence of melt stretching on its crystalline morphology and amorphous entanglement network is worthy of in-depth discussion.In the first part of this paper,three different aliphatic polyketone raw materials were evaluated and discussed the rheological and crystalline properties.In the second part,the POK1 films with different melt-drawing ratios(MDR)were prepared.The effect of melt-drawing ratio on crystal structure was followd by the synchrotron radiation small-angle/wide-angle X-ray diffraction(SAXS/WAXS).In the third part,the step cycle test is used to clarify the critical strain,and the in-situ small-angle X-ray scattering(SAXS)is used to study the deformation behavior and structure evolution of aliphatic polyketone films.The main work and conclusions of this thesis are as follows:1.The molecular weight has a great influence on the rheology and crystallization ability of the aliphatic polyketone terpolymers.The POK2 shows higher melt strength then POK1 due to the more high molecular weight parts,and it is easier to establish entanglement network and unentanglement during the stretching.Experimental data shows that POK2 has a larger extensional viscosity than POK1,and POK2 has a disentanglement behavior at a smaller melt extension rate.In the cooling process,the POK1 shows lower crystalline active energy(253.2 KJ/mol)and short half crystallization time than its of POK2.Compared to the above two raw materials,the melt index of POK3 up to66g/10 min,which is not suitable for extrusion casting.Therefore,we do not make further analysis on the rheological properties and crystallization ability of POK3.2.On the basis of the first part,POK1 was used as a raw material to prepare a cast film with a melt-drawing ratio(MDR)of 20?70(one interval per 10 times),using AFM,FTIR,DSC,XRD,2D-SAXS/WAXS and universal drawing Tensile testing machine and so on made a systematic characterization of it.The experimental data shows that the cast films with different melt-drawing ratios have formed a parallel sheet structure perpendicular to the extrusion direction.The crystallinity measured by DSC is about 31%.This is because of the rapidity crystallization of the aliphatic polyketone terpolymers.We found that the thickness and long period of the crystal regions of all samples are basically the same,maintained at about 5.4nm and 12.5nm,which induced its melting point and melting range to be almost the same.This shows that MDR has little effect on its crystalline morphology,but the entanglement modulus of its amorphous region has a strong dependence on the MDR.With the increase of the melt-drawing ratio,the entanglement modulus of the amorphous zone increased from 8.1 MPa to 14.1 MPa,so POK film with different melt-drawing ratio can be used to study the influence of the entanglement density of the amorphous zone on the critical strain.3.We used a step cycle test to test all samples at 25,100,and 150 ?.The experimental data showd that with the increase of the entanglement density in the amorphous region,the critical strain decreases from ln?=0.5 to ln?=0.36.This is because the increase in the entanglement density in the amorphous region leads to an increase in the entanglement modulus of the amorphous region.The strain required to reach the critical stress becomes smaller.At the same time,we found that samples with the same melt-drawing ratio have the same critical strain at different temperatures.In addition,we used in-situ 2D-SAXS to explore the crystalline structure derivation of POK1 films with MDR 20 at different stretching temperatures,indicating that stretching at lower temperatures tends to break and collapse of the lamellae piles.Orientation along the stretching direction,stretching at a higher temperature,tends to be parallel to the lamella piles,and the crystals are still perpendicular to the stretching direction.