Study On Properties And Quality Improvement Of Linear Low Density Polyethylene

Linear low-density polyethylene（LLDPE）is a high-performance polymer material with excellent mechanical properties,heat resistance,chemical resistance,and processability.It has a wide range of applications and a high market demand.However,there exists a complex relationship between the structure and properties of LLDPE,which is influenced by factors such as co-monomer type,content,and distribution.Therefore,exploring the effects of different co-monomers,catalyst structures,and process conditions on the structure and properties of LLDPE,optimizing catalyst selection and process conditions,and improving the quality and stability of LLDPE resin have significant theoretical and practical value.In this study,LLDPE was selected as the research object to investigate the effects of 1-butene/1-hexene ratio,Ziegler-Natta catalyst（Ti Cl₄/Mg Cl₂）structure,and processing parameters on the properties of LLDPE.The main contents are as follows:1.Ethylene/α-olefin polymerization was conducted in the slurry phase.By varying the amount of 1-butene/1-hexene,the catalyst activity and LLDPE rheological properties were studied.Through polymer characterization and catalyst characterization,it was found that increasing the amount of 1-butene/1-hexene enhanced catalyst activity,and higher catalyst specific surface area and titanium content exhibited higher activity.With the addition of 1-butene/1-hexene,the molecular weight decreased,resulting in a decrease in storage modulus and loss modulus.2.Blown film experiments were conducted using a statistically designed approach to study the effects of molecular weight distribution and processing conditions on the rheological characteristics and physical properties of LLDPE films.By relating the polymer’s maximum molecular relaxation time(τ_max)to the process time（t_p）as the Deborah Number（De）,the complex interactions between molecular weight distribution and processing conditions on film properties were understood rheologically.Lower frost line height and narrower molecular weight distribution exhibited optimal optical properties.3.Improvements were made to the LLDPE device and additive formulations,and the control method for hydrogen feed was improved by changing from concentration ratio control to flow ratio control.This enabled stable hydrogen flow control,accurately controlling the resin’s melt index（MI）within the range of 1.82-2.12 g/10min.Multiple tests were conducted on the finished products,including appearance,physical properties,and chemical composition.The improved product showed a decrease in the number of large fish eyes from 8 to 3,a reduction of 62.5%,haze was reduced to 14%,and light transmittance increased to 95.2%.This effectively enhanced the product quality.