| The preparation of high molecular weight poly(ethylene terephthalate)(PET)via melt poly-condensation technology,which is a world-class problem for polymer industry in the past decades,has been solved recently,so that the production mode of melt direct spinning began to be truly industrialized in industrial yarn.As a new technology,the melt direct spinning PET industrial yarn still needs systematic research,and its key technology mainly involves the preparation of high intrinsic viscosity(?)melt,high ? melt conveying and the process of multistage drawing and heat setting.It is a difficult problem to produced high ? melt by the formation flow and process matching of PET melt on the support of the falling film in reactor.After the preparation of high ? melt,the key technology of melt conveying is how to control the ? drop and keep ? uniform stability.The numerical simulation of the two production processes involving melt flow can provide equipment structure and process parameter optimization scheme for melt quality control.In view of the change of aggregation structure and improvement of properties during PET industrial yarn process,it is closely related to multistage drawing and heat setting.The direct relationships between process-structure-property can provide theoretical support for regulating the performance of melt direct spinning PET industrial yarn.In this paper,a high-viscosity polymer fluid with similar rheological properties to PET melt was selected as the simulation medium to carry out numerical simulation of falling film flow under different viscosity and flow conditions,the thickness and free surface curve velocity distribution characteristics of falling film flow were obtained.Experimental results show that the biggest influence on the film thickness is the fluid viscosity,velocity distribution curve can better conform to the classic Nusselt parabolic velocity distribution,with the increase of fluid viscosity or falling film flow,the velocity distribution curve will gradually deviate from the theoretical curve.The melt surface update frequency,with the increase of flow rate increased until reach a stable value,but decreases with increase of viscosity.The average residence time of high-viscosity polymer falling film is long with a wide distribution and a trailing sign.On the self-built thermal model test platform,the falling film experiments of different support structure and reaction conditions were carried out.The study shows that the effect of falling film poly-condensation is closely related to the internal support structure and process conditions.The high efficiency production of PET melt of industrial yarn grade can be achieved by optimizing and selecting the liquid state polymerization reactor and matching the suitable process conditions.The three-dimensional models of melt booster pump,melt pipe and static mixer are established for numerically simulated to find the key factors of the melt conveying quality.The results show that the conveying characteristics of the melt booster pump are greatly influenced by the gear structure,the output variation of melt conveying is high for spur gear,the helix gear and double helical gear have a good melt conveying stability.The temperature rises and shear rate of gear pumps with helix gear and double helical gear are lower than that of spur gear.The static mixer with inner component rotation angle of 120 degree has better separation scale area extension and narrower residence time distribution.The pressure drops in static increases with the flow rate,and the residence time distribution moves towards the short time as the flow rate increases.The pressure drop per unit length of the melt pipe remains constant at a constant flow rate and the pressure drop of melt pipe increases with the increase of flow rate,while the residence time shifts towards the short time direction.The fitting combination of the numerical simulation results of the booster pump,melt pipe and static mixer can obtain the flow information of the whole melt pipe from point to point,and obtain the variation of each field quantity along the flow direction,which is conducive to the optimization design of conveying process and geometric structure.In this paper,the fiber samples were obtained from the different forming stages at multistage drawing and heat setting process in the actual melt direct spinning industrial yarn of super low shrinkage(SLS)through a special online sampling method,which structure characterized through a variety of methods combination with DSC,DMA,sound velocity,infrared spectrometer and WAXD/SAXS.The process-structure-property relationship of industrial yarn in the multistage drawing and heat setting procedure was described clearly.At the same time,a kind of four-phase structure model including crystalline lamellae,interlamellar rigid amorphous fraction(RAF),mobile amorphous fraction(MAF)and interfibrillar extended non-crystalline molecules is revealed with a series of concise three-dimensional structure models.Research results show that the crystallinity of the fiber samples at different forming stages increase gradually during the drawing and heat setting process and the significant structural changes of crystallization take place in the first and second drawing stage,while the crystal structure keeps similar same in addition to perfection during the following two-stage relax heat setting process.In the multistage drawing and heat setting process,the crystalline orientation factor(fc)increases all the time,while the amorphous orientation factor(fa)increases in the first drawing stage at low temperature,decreases slightly in the second drawing stage at high temperature,and decreases significantly in the two-stage relax heat setting at high temperature.The mechanical physical properties of the fiber at different forming stage in the drawing and heat setting process have a good linear correlation with the structure of amorphous phase and the tilting angle(?)of lamellar surface. |
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