Study On The Kinetic Behavior And Crystallization Properties Of Ultra-high Molecular Weight Polyethylene Chain By Unentanglement

Polyethylene(PE)is the polymer material with the simplest molecular structure.It has excellent properties such as non-toxic and odorless,good chemical stability,etc.It is widely used in films and packaging materials.Due to the many advantages made in the synthesis of polyethylene in the last few decades,the microstructure,morphology and functionalization of the polymers can be well controlled to produce different types of polyethylene.Among them,ultra-high molecular weight polyethylene has excellent performance,but it is difficult to process.In this paper,polyethylene samples with different molecular weight and entanglements were prepared.Differential scanning calorimeter(DSC),X-ray diffraction measurements(XRD)and fast scanning calorimetry(FSC)were used to study the crystallization behavior of polyethylene,and low field solid state NMR was used to study the chain kinetics of polyethylene.The effects of entanglement on the crystallization behavior and chain kinetics were explored intensively,in order to provide inspiration for solving the processing difficulties of ultra-high molecular weight polyethylene.Polyethylene samples with different molecular weights and entanglements were prepared by dilute solution crystallization.DSC was used to study the melting point and crystallinity of polyethylene samples,XRD was used to study the crystal phase and crystallinity of polyethylene samples,and FSC was used to study the inhibition of crystallization of polyethylene.The experimental results show that the sample with lower concentration has less entanglement and higher crystallinity.Ultra-high molecular weight polyethylene has longer molecular chain,thicker crystal lamellar and higher melting point.The low-field solid-state nuclear magnetic resonance method was used to study the effects of temperature,entanglement,molecular weight and annealing on the crystallization behavior and chain kinetics,and the free induction decay(FID)curve was fitted with a fitting formula.The results show that the higher the temperature,the fewer the crystals,the stronger the mobility of the molecular chain,and the slower the FID signal attenuation.For polyethylene with a molecular weight of 700,000 and sample concentrations of 0.1wt% and 10wt%,between 30? and 120?,10wt% sample has lower crystallinity,and its FID signal attenuation is slower;at 130?,the molecular chain of 10wt% sample is easier to rearrange,making the crystal lamella thicker,and the crystal melting is slower than that of the 0.1wt% sample,so there are more crystals in the 10wt% sample,and the FID signal decays faster;at 140? above the melting point,since the two samples have been completely melted and there is no crystal phase,there is almost no difference in the FID signal attenuation curve.After annealing,there are more entanglements and less crystals,so the FID signal of the annealed sample decays slowly.In recent years,few studies have been done on polyethylene entanglement from the perspective of chain kinetics.The molecular weight of polyethylene used herein ranges from low-medium molecular weight to ultra-high molecular weight.Ultra-high molecular weight polyethylene has many excellent properties,but its processing is very difficult.Therefore,in this paper,DSC,XRD and low-field solid-state NMR were used to study the effects of entanglement on the crystallization behavior and chain kinetics of polyethylene,so as to provide ideas for improving the processing properties of ultra-high molecular weight polyethylene.