Study On Branches Structure,Crystallization Behavior And Mechanical Properties Of High Density Polyethylene

High density polyethylene(HDPE)has been widely used in the fields of pipe,container manufacturing,film and wire and cable because of its excellent properties such as rigidity,toughness,impact resistance,abrasion resistance and chemical resistance.However,the molecular structure of the high density polyethylene,the type of catalyst and the monomer differences directly affect the properties of the material.It is necessary to understand the relationship between the properties of the polyethylene and the molecular structure in order to provide theoretical support for the production process.In this paper,four high-density polyethylene(DQDN3711,XRT70,LH4100,QHM22F)with different grades at home and abroad were selected.Four kinds of polyethylene molecules were represented by nuclear magnetic resonance(13C NMR).The results show that the main chain containing high density polyethylene is methyl and ethyl,and the content of long chain is very small.The molecular weight of polyethylene was characterized by gel permeation chromatography(GPC).Differential scanning calorimetry(DSC)was used to test the temperature under normal pressure.We found that the greater the degree of branching,the arrangement of polyethylene and the worse the degree is,the worse the crystallinity.The results of mechanical tests such as universal tensile testing machine and cantilever impact testing machine show that the degree of crystallinity is an important factor that directly affects the merits of mechanical properties.The higher the orderly degree of molecular branching are,the higher the crystallinity and the impact strength,tensile strength and yield strength increase.However,the methyl chain content has a positive correlation with the mechanical properties of the material such as impact strength,tensile strength and yield strength.The larger the relative molecular weight,the greater the impact strength,the tensile strength but the effect on the elongation at break.The viscoelastic properties of polyethylene materials were studied at the temperature of 190 ? and 210 ?.The viscoelastic properties of polyethylene materials were studied under the conditions of dynamic viscosity,storage modulus,loss modulus and loss angle.It was found that the short chain branch had little effect on the viscoelasticity of polyethylene.Compared to a small amount of long chain on the viscoelasticity of the material has a significant change.