The Modification On Environmental Stress Cracking Resistance Of High Density Polyethylene And Its Properties Study

The long chain branching(LCB) introduced into linear high density polyethylene can make molecular chain and chips not easy to move or slip with the entanglement, and help to steady the Intergranular displacement of the material under stress, so improve the environmental stress cracking resistance(ESCR). How to relate long chain branched structure with the macroscopic properties is important to the development of polymer industry and relevant theories. Here, one kind of LCB-PE was prepared via molten radical branching reaction, using a torque rheometer as reactor. The modified HDPE possesses low gel degree, high mechanical strength, and excellent ESCR.(1) In examining the impact of temperature and different kinds of free radical regulator on molten branching reaction found, ZDMC at higher temperature could not fully regulate the free radicals and the reaction was out of control, while too low temperature would make a deficient melting of HDPE, the appropriate temperature was about 170?. Different central atoms and substituent groups made various regulating effects on the activity of the radical. ZDMC had the best free radical regulation effect among the free radical regulators used owing to its smaller substituent group and higher activity.(2) The research on preparing LCB-PE via the coupling of macromolecular radicals was conducted, the structure of samples gradually varied from a linear structure to branching structure with the reaction times going by. When the reaction reached to the reactive torque peak, the molecular weight reached maximum. The reactive time corresponding to the torque peak was optimal for HDPE branched reaction, because the performances of all were the best. The ESCR and mechanical strength of the modified HDPE increased significantly, for instance, the maximum ESCR test time was 202 hours, 11.2 times longer than that of pure HDPE, and the tensile strength, bending strength and notched impact strength extremely increased by 46.3%, 24.2% and 251%, respectively. With the reaction continuing, the degradation of backbone would occur, especially when the torque reduced to the balance, the ESCR and mechanical strength of material became weaken.(3) The research on fabricating LCB-PE via molten radical branching reaction in presence of monomer(NPGDA) was conducted. NPGDA has played an important role in promoting the branching, and increase the branching degree in the HDPE melten branching reaction. The ESCR and mechanical strength of modified HDPE increased significantly. The ESCR test time was more than 1000 hours, which was significantly better than LCB-PE fabricated via the coupling of macromolecular radicals. At the same time, the mechanical properties of modified HDPE were improved significantly, compared with the samples of same DCP content without adding monomers, the impact strength, bending strength and tensile strength were increased by 11.2%, 32.5% and, 42.5% respectively.(4) The research on molten radical branching reaction of HDPE mixtures with different molecular weights was conducted. The MFR gradually increased with the increased of the content of the low molecular weight components HDPE8920, which improving the processing performance of the materials. Because the molecular weight was decreased when adding HDPE8920, leading the material mechanical strength of the modified HDPE was decreased. A small amount of HDPE8920 did not change the ESCR of materials, and the ESCR time obtained was more than 1000 hours.(5) Compared with linear structure, the complex viscosity(?*), storage modulus(G') and loss modulus(G'') increased, the loss angle ? at the low frequency decreased, the ?-? curve showed a similar rubber platform area and the Cole-Cole figure deviated from the semicircle. Those indicated that the introduction of long branches chain changed the linear relaxation mechanism of HDPE. AS well, the introduction of long branches chain changed the material crystallization behavior, such as, the initial crystallization temperature and melting temperature of the material increased, and the crystal structure became stabilize.