Study On The Self-crosslinking Polyethylene And Fiber Reinforced Crosslinked-PE In Room Temperature

Polyethylene (PE) is a volume leader in the global plastic industry with numerous applications because of its excellent properties like electronic property, toughness, and chemical resistance. However, its low thermal-stability and mechanical intensities make ordinary polyethylene unsuitable for the applications requiring continuous use under stress or high temperature in some area. Some researchers studyed various methods, in order to improve the properties of polyethylene, included the method of crosslinking. The three different crosslinking methods: radiation crosslinking, peroxide crosslinking and Silane crosslinking were widely used in modified polyethylene industry.Silane crosslinking PE usually conducted in hot water or in steam. In order to reduce the process, a self-crosslinked polyethylene method was presented in this study. With added a kind of homemade coagents into polyethylene, a self-crosslinking method which have simpler process, lower cost and energy consumption was used at room temperature. The PE, initiator, coupling agent, coagents, catalyst and anti-oxidant were all well premixed by the high speed mixer. Then the mixture was added into the twin-screw extruder to get the grafted-PE. Crosslinking can actually take place at room temperature.The thesis discussed the preparing method, the effect of the process, the influence of coagents on gel content, the processing properties, thermal properties and mechanical properties of self-crosslinking PE compared with pure PE. The crystallization behavior and crystal constructor of the self-crosslinked PE were also studied by DSC measurements and wide-angle X-ray diffraction. In the mean time, various properties of fiber reinforced silane crosslinked PE were studied in the paper. And finally we got the following conclusion:1. The self-crosslinking PE could be successfully made in the process which added the water bringing coagents in the extrusion, and then the crosslink took place at room temperature.2. Compared with the one step and two step methods, the self-crosslinking polyethylene omitted the boiling or vapor treating process, and reduced the cost and saved the energy.3. As the coagents content were 0.5phr, 1.0phr and 1.5phr, the gel content of the self-crosslinking PE increased with evolving time until stable at 40 days later. And the gel content of LDPE and HDPE could reach to 50.0% and 57.8%, respectively.4. The mechanical properties improved with evolving time in the self-crosslinking process. When the coagents content were 0.5phr, 1.0phr and 1.5phr, the tensile yield strength of LDPE and HDPE samples were 16.41MPa, 17.18MPa, 12.73MPa and 21.22MPa, 23.77MPa, 25.74MPa 40 days later, respectively, and improved about 20.0%. and theirs elongation at break decreased 39.69%, 8.21%, 5.99% and 42.5%, 50.7%, 36.1%, respectively, compared to the pure samples. The Rockwell hardness increased 27.1% and 46.8%, respectively.5. Thermal properties of self-crosslinking PE have all been improved dramatically compared with pure PE. The thermal decomposition of LDPE and HDPE were 471.96℃and 485.00℃, and improved 60.48℃and 32.00℃, respectively. The thermal deformation temperature improved 2.5℃and 6.1℃.6. There was huge influence of self-crosslinking process on crystallization behaviors. The crystallinity of self-crosslinking LDPE and HDPE decreased 5.3%,10.3% (measured by DSC) and 7.59%,21.41% (measured by XRD ), respectively. The crystal size decreased and the regularity destroyed with the evolving time.7. The self-crosslinking process of HDPE could carry out all the time while the glass fiber added into the mixture. The compatibility between polyethylene and glass fiber could hardly be influenced by the self-crosslinking process, but the mechanical properties and thermal properties have been promoted a lot. The tensile yield property of self-crosslinking HDPE contains 20 percents glass fiber improved from 18.49MPa to 37.56MPa and increased 103.14%, the elongating at break decreased 558.43%, the elastic modulus improved 332.45MPa and increased 184.28%, the thermal deformation temperature improved from 42℃to 109.2℃and increased 160%. The crystallinity of glass fiber reinforced self-crosslinking HDPE dropped about 30% and the crystal size become smaller compared with the unreinforced HDPE.