DR LI YUN YAN
Dr Li Yun yan, graduated from Tianjin University, China, with a doctor's degree in polymer materials, a senior engineer with the honor of "Nantong 510 Talents ". Mainly engaged in the research and development of new materials, with better experience in plastic formula and process optimization. Once presided over and participated in the National Science and Nature Fund project (50390094), China Nanjing Science and Technology Plan project "High temperature resistant nylon synthesis", China Sinopec Yangzi Petrochemical Co., Ltd. "Rotational plastic grade polyethylene resin development", and Hebei Province major achievements transformation project "High performance PEX pipeline development and application". Also developed a number of products, published 20 professional papers, authorized more than 10 invention patents. Served as a senior scientist in GE, Wanhua Chemical and currently engaged in product development in Hongyue Plastic Group Co., Ltd. Mainly focused on the development of high chlorine and weather resistant pipes, the high value utilization of waste pipe materials, and the development of UV resistant master batch for plastic pipes.
ABSTRACt
Investigation on cross-linking reaction of pipe grade of HDPE
In this paper, the coupling effect of peroxide and antioxidant, and influence of the concentration of peroxide and processing temperature on the cross-linking reaction of pipe grade of polyethylene were studied. The results show that, at the reaction temperature employed in this work, the torque and viscosity of polyethylene with different concentration of peroxide are different for the whole reaction period. At the initial stage of the reaction, polyethylene mainly shows a transition state from solid to melt, and the viscosity of the polymer, as a whole, shows a decreasing trend, and at this stage, the viscosity decreasing speed is not affected by the concentration of peroxide. With the increasing in melting time, the viscosity of polyethylene with different concentration of peroxide changes differently. For polyethylene with low concentrations of peroxide, the initial time for viscosity to increase is about 19 seconds, while the increasing speed is relatively slow. With the increase in the concentration of peroxide, the initial time for viscosity and torque to increase is advanced to 15 seconds, and the increasing speed is also faster.
In addition, increasing the concentration of peroxide could improve the cross-linking degree at the initial stage of the reaction, but it could not shorten the complete cross-linking period of the system. Under the test temperature set in this work, the time for polyethylene to complete the cross-linking reaction was about 80S regardless of the concentration of peroxide, and then the cross-linking reaction basically ended when the torque was balanced. It was also shown that, without antioxidant, the greater the concentration of peroxide is, the greater the balance torque and the higher the cross-linking degree of the system is, while the oxidation induction time remained unchanged.
The addition of antioxidant can significantly improve the oxidation induction time of the system, and with the increase in antioxidant, the oxidation induction time of the polymer system shows an increasing trend. However, the selection of antioxidants is significant, that is to say, inappropriate antioxidants may have a certain inhibitory effect on the cross-linking reaction. A reasonable combination of antioxidants can effectively avoid the conflict between antioxidants and peroxide peroxides, improve the thermal oxygen aging performance of the material, and maintain sufficient cross-linking degree and physical strength of the material.
In the temperature range of 210-230℃, with the increase in temperature, the cross-linking degree of the system fluctuates within a small range, and even decreases slightly. The higher temperature also increases the fluidity of the un-crosslinked polyethylene, resulting in a decrease in the viscosity of the entire system. In actual production, choosing the right production process is very important for energy reduction, production efficiency and product quality.