An Investigation On Structure Evolution, Rheology And Dynamics Of Low-density Polyethylene In The Process Of Peroxide Crosslinking

Polyethylene (PE) is one of the most widely used thermoplastic plastics in the world. While the thermostability, corrosion resistance, physical and mechanical properties of polyethylene can not meet actual requirements, which limit its application in some areas. To solve the above problems, cross-linking is widely used to improve properties of polyethylene. After being cross-linked, the structure and properties of polyethylene will change largely.In this experiment, the lowdensity polyethylene (LDPE) was used as matrix resin. The dynamic rheological method was used to investigate the relationship between structure evoluation and rheological behaviors, and the difference in rheological properties between crosslinked low-density polyethylene (XLDPE) and LDPE was also researched. The effects of temperature, time, rotating speed and DCP content on the torque were investigated in a Haake torque rheometer. Besides the dynamics of cross-linking, the effects of cross-linking temperature, time and DCP content on the gel content were also studied. In addition, the differences in structure and properties of LDPE and XLDPE were investigated.The results showed that the DCP cross-linking LDPE was first order reaction, and the activation energy (EA) and lnKo of cross-linking reaction did not change with DCP concentration. The gel content, cross-linking density and tensile strength of XLDPE showed an increase with the increase in DCP content, while the elongation at break, degree of crystallization, melting temperature and crystallization temperature showed a decrease with the increase in DCP content. The gel content of XLDPE reached its maximum value with a DCP content of2.0%. The torque of XLDPE increased with the increase in cross-linking time, while it showed a decrease with the increase in temperature. The loss modulus (G’) and loss tangent values (tanδ) were more sensitive to the changes in cross-linked structures than that of storage modulus (G’). The effects of scanning frequency on complex viscosity and tan8of LDPE was different from that of cross-linked LDPE. With increase in gel content, G,G and complex viscosity were not affected by temperature. The tanδ of LDPE increased with the increase of temperature, while the temperature showed no effect on tanδ of cross-linked LDPE.