HDPE Toughened By Crosslinking And Elastomers

High-density polyethylene(HDPE)has insufficient toughness at low temperatures and complex conditions,requiring further toughening modification.In this paper,the effects of molecular structure,gel content,and crystallization on the brittle-ductile transition behavior of the HDPE by chemical cross-linking,elastomer blending,and synergistic toughening of HDPE were analyzed.The brittle-ductile transition curves were quantitatively analyzed,and the mechanism of brittle-ductile transition was explored.The main work and conclusions are as follows:(1)The effects of cross-linking on the brittle-ductile transition of HDPE were explored by preparing cross-linked HDPE with different cross-linking degrees.The structural changes of the cross-linked HDPE were analyzed by gel permeation chromatography(GPC),rotational rheometer,differential scanning calorimeter(DSC)and X-ray diffraction(XRD).The cross-linking process was analyzed through non-isothermal cross-linking kinetics.The tensile,bending and notched impact properties were tested.The crystal morphology and impact cross-sectional morphology were observed by polarizing microscope and scanning electron microscope(SEM)respectively.The results show that crosslinking increases the complex viscosity of HDPE and inhibits its crystallization.With the increase of BIPB content,the complex viscosity gradually increases,the crystal size decreases,the crystal is sparse,and the crystallinity Xc decreases.The pre-crosslinking reaction of HDPE is well described by the Avrami model modified by Jeziorny.The Avrami index is maintained between 1.06-1.31,and the crystals of cross-linked HDPE grow in a nearly one-dimensional direction.The fitting results of Mo Zhishen method show that HDPE with different cross-linking degrees follows the same cross-linking reaction path.Cross-linking improves the toughness of HDPE,so that its elongation at break rises first and then decreases with the increase of BIPB content.The elongation at break of cross-linked HDPE2911 can reach 700%when the BIPB is at 0.3wt%.The impact strength of cross-linked HDPE increases with the increase of BIPB content and temperature.When the content of BIPB is at 1.5wt%,cross-linked HDPE2911 can reach more than 80 kJ/m2 at-50?.The brittle-ductile transition curves were well fitted by Boltzmann function model.With the increase of the BIPB content,the brittle-ductile transition temperature(TBD)shifts to the lower temperature,and the transition temperature range narrows.According to the SEM images of the impact section,the fracture mechanism of the brittle-ductile transition is from the silver-crack mode to the shear-yield mode.(2)The effects of POE on its brittle-ductile transition were investigated by preparing HDPE/POE blends with different ratios.The properties of HDPE/POE blends were analyzed by GPC,infrared spectroscopy(FTIR),rotational rheometer and DSC.The tensile,bending and notched impact properties of the blends were tested,and the crystal morphology and impact fracture of the blends were observed by the polarizing microscope and SEM.The results show that the addition of POE to HDPE increases the complex viscosity of the blends and inhibits the crystallization of HDPE.The increase in POE content causes the complex viscosity to rise continuously,the grain refinement,and Xc to gradually decrease.The Han curves and the cole-cole curves all indicate that HDPE and POE have good compatibility.The use of high molecular weight POE can improve the toughness of HDPE well,and the elongation at break of HDPE:POE 1=60:40 is up to 700%.The impact strength of the blends varies with the POE content and temperature.The notched impact strength of HDPE:POE 1=60:40 is 84.7 kJ/m2 at-30?,which is 21 times that of HDPE.Boltzmann function model fitting results show that TBD of the blends decreases with the increasing of POE content,which is consistent with the change of the interface bonding strength value,and the transition temperature range is narrowed.The SEM pictures of the impact section show that the fracture mechanism changes from the silver-crack mode to the shear-yield mode during the brittle-ductile transition of the blends.At low molecular weight POE,silver-yield-plastic deformation failure modes will also appear.(3)The effects of cross-linking on the brittle-ductile transition of HDPE/POE were investigated by preparing crosslinked HDPE/POE with different crosslinking degrees.The performance of cross-linked HDPE/POE was analyzed by rotary rheometer and DSC.Its tensile,bending and notched impact properties were tested,and the photos of crystal morphology and impact fracture were observed under polarizing microscope and SEM.The results show that cross-linking increases the complex viscosity of HDPE/POE blends,and the complex viscosity rises with the increase of BIPB content.Under the joint suppression of cross-linking and POE,Grain size and Xc decreases.Cross-linked HDPE/POE is obviously toughened,and the elongation at break of HDPE:POE1:BIPB=90:10:0.1 reaches more than 900%.The notched impact strength of cross-linked HDPE/POE increases with the increase of BIPB content and temperature.The notched impact strength of HDPE:POE1:BIPB=90:10:0.3 reaches 77.7 kJ/m2 at-20?,which of the other cross-linked HDPE/POE at this temperature can also reach about 25 kJ/m2.The fitting results of the Boltzmann function model show that its TBD shifts to the lower temperature as the content of BIPB increases,and the transition temperature range of cross-linked HDPE/POE1 gradually narrows,while the others increase first and then decreases.It can be seen from the SEM pictures of the impact section that the brittle-ductile transition fracture mechanism is consistent with the first two formulations.