Study On Self-reinforcement Technology And Mechanism In Blow Film Process Of Polyethylene

Polyethylene film is currently the most widely used and most productive film material.Extrusion blow molding is the most common method for processing it.However,due to the blow up ratio(BUR)being much larger than the draw down ratio(DDR),the film generally suffers from poor mechanical properties along transverse direction and difficulty in improving it.With the increasing demand for low-carbon,environmentally-friendly,low-cost and highperformance films,it is very important to improve the molding method to change the aggregation structure of polymer molecular chains in the film to achieve self-reinforcement effect without using additives.The interface homogenization co-extrusion film blow molding equipment developed by Professor Qu Jinping of South China University of Technology has the characteristics of achieving uniform distribution of the melt circumference,reducing energy consumption and improving mechanical properties.However,the mechanism by which the device achieves self-reinforcement of polymer films is not thorough,the application and structure optimization of this method and equipment are limited,so further study on the mechanism of the device on polymer materials has great practical and theoretical significance.In this paper,three different systems of polyethylene films were prepared using laboratorymade interface homogenization co-extrusion film blow molding equipment.The effects of process parameters draw down ratio,blow up ratio,and mandrel speed on the mechanical properties and heat shrinkage properties of three-layer LDPE films were studied.The results show that the draw down ratio mainly affects the machine performance of the film,the blow up ratio and the rotating mandrel mainly affect the transvers performance of the film,moreover,increasing the rotating speed of mandrel is more significant than increasing the blow up ratio.Therefore,in this paper,bilayer LDPE / HDPE film and bilayer LDPE / m LLDPE film were further prepared by controlling the rotation speed of the mandrel The influence of the strength of the mold circulation on the structure and properties of the film was studied.The results show that the two material systems have a lamellae structure in the composite flow field,and the lamellae are mainly arranged in the machine direction,and a small number are randomly arranged in other directions.During the growth process,the lamellae are twisted and inclined with the increase of the mandrel speed,showing a kind of interlocking structure.Increasing the rotating speed of the mandrel will improve the overall crystal structure and increase the crystallinity of the samples,especially the transverse performance.The transverse tensile strength of LDPE / HDPE film increased from 23.03 MPa at 0 rpm to 28.96 MPa at 4 rpm,and the transverse heat shrinkage rate increased by 50.05%.The transverse tensile strength of LDPE / m LLDPE film was 35.49 MPa at 0 rpm,and reached a maximum of 43.02 MPa at 4 rpm,an increase of 21.22%,and exceeded the machine tensile strength.The transverse thermal shrinkage rate was increased from 10% at 0 rpm to 41% at 5rpm.The machine heat shrinkage rate decreased slightly.This shows that by adjusting the parameters such as the speed of the mandrel and the material formula,it is possible to prepare film products with uniform transverse and machine properties.The interface homogenization co-extrusion film blow molding equipment can ensure the stable and high-quality production of films when preparing polyethylene with different structures,indicating that it has universal adaptability to polyethylene with different structures.By adjusting the microscopic morphology of the film,the equipment improves the crystallinity,orientation degree,and lamellar boundary force,thereby improving the film performance,especially the transverse performance has been greatly improved,and finally achieving selfreinforcement of the film.This provides technical innovation for the production of highperformance films,and promotes the development and application of co-extruded film blow molding equipment.