Synthesis Of Trimodal HDPE And Research On The Preparation And Process Of Tube Materials

With the rapid development of the global plastics industry,plastic pipes have gradually replaced traditional metal pipes in fields such as construction,petrochemicals,energy,agriculture,and municipal services.PE pipes are highly favored for their excellent chemical corrosion resistance,long service life,and ease of installation and manufacturing.However,the development and application of specialized materials for PE pipes in China have been relatively late,and high-performance products,as well as catalytic technology and production processes,have long relied on imports,resulting in a lack of diversity and unstable performance of domestic PE production lines.Therefore,this thesis aims to optimize the performance of trimodal high-density polyethylene(HDPE)pipes and improve their long-term usage and processing properties.Different molecular weight distributions of trimodal and bimodal HDPE were prepared in a laboratory-scale reactor,and they were characterized and analyzed alongside commonly used models in foreign markets.The study found that compared to bimodal HDPE and 3490-LS,trimodal HDPE exhibited better sag resistance,processing performance,crystallization rate,and slow crack growth(SCG)resistance.These characteristics were attributed to the broad molecular weight distribution and the introduction of ultra-high molecular weight polyethylene chains in the multi-modal HDPE.Then,using monomer pre-polymerization technology,the effects of hydrogen content and co-monomer type at various stages of the ethylene polymerization process on the SCG resistance and melt flow properties of the products were investigated by controlling the polymerization conditions.Experimental conclusions were drawn that a small amount of hydrogen added in the second stage significantly improved the resin’s SCG resistance and flowability,while changes in hydrogen content in the first stage(within the studied range)had an extremely minimal effect on the material.Additionally,the type of co-monomer played a decisive role in the SCG resistance of the HDPE resin.Finally,using the Taguchi method and employing the produced HDPE particles,extrusion machine,traction machine,and other equipment,the influence of process parameters during the material forming stage on the static hydraulic strength of the final pipes was analyzed and studied.Three key factors were identified,and through further combination experiments,it was determined that pipes produced with the optimal combination of a pushing zone temperature of 166℃,a screw speed of 8 r/min,and a die temperature of 192℃ significantly increased the static hydraulic strength of HDPE pipes from 8.71 MPa to 14.58 MPa compared to the original material.The results demonstrate that trimodal HDPE exhibits superior material processing performance while also demonstrating improved mechanical properties,wear resistance,and corrosion resistance in pipe materials.Performance enhancement of HDPE can be achieved at the molecular level by adjusting the hydrogen content in the second stage and incorporating higher levels of α-olefins.Furthermore,adjusting the operating parameters of the extrusion machine during HDPE pipe production can significantly enhance the material’s static hydraulic strength.The aforementioned research provides strong technical guidance for the independent research and development and production of high-performance PE pipes in China.