Current status of UHMWPE and application of its fiber products in the marine industry

Ultra-high molecular weight polyethylene (UHMWPE) is a linear structure engineering plastic with excellent comprehensive performance. UHMWPE ranks first among plastics in terms of wear resistance, which is several times more wear-resistant than carbon steel and brass, and its wear resistance is more than dozens of times that of ordinary polyethylene; the friction coefficient is also smaller than other engineering plastics. UHMWPE also has excellent water resistance, impact resistance, chemical resistance, low temperature resistance, good non-stickiness, non-toxicity, excellent electrical insulation performance, etc., and its application scenarios are very wide.

Companies in the world that produce UHMWPE basically use the low-pressure polymerization process of Ziegler catalysts to produce ultra-high molecular weight polyethylene, which is very similar to the low-pressure slurry process of high-density polyethylene (HDPE). At present, companies that can provide UHMWPE process packages include Shanghai Research Institute of Chemical Industry, Asahi Kasei Industries, AlliedSignal, Hoechst, Samsung Chemical, Basell, DSM, etc. At present, among the UHMWPE industrial enterprises in the world, most of the industrial units that have been put into production use their own processes, such as Germany's Ticona, Japan's Mitsui Chemicals, and the United States Honeywell. Chinese UHMWPE production enterprises mainly use the Chinese Academy of Sciences, Shanghai Institute of Chemical Technology and their own processes. China National Petroleum Corporation and Sinopec both have their own UHMWPE production processes. Kettle polymerization process. Kettle polymerization includes Hostalen process and Mitsui CX process. At present, most UHMWPE polymerization uses Hostalen stirred tank process. The Hostalen process includes two reactors. Ethylene, hydrogen and catalyst are added to the first reactor to produce resin with a higher melt index. The obtained polymer slurry enters the second reactor, and the polymerization reaction of the remaining ethylene is completed in the second reactor. The operating pressure and operating temperature of this process unit are low, the operating flexibility is high, the production is flexible and the stability is good. In addition, using this process, the catalyst has strong resistance to impurities and low requirements for the purity of ethylene gas raw materials. At present, more than two-thirds of the world's UHMWPE polymerization uses the Hostalen kettle process. Loop polymerization process. The loop process mainly includes Phillips' Phillips single loop process and Ineos' InnoveneS double loop process. Both processes use isobutane as the reaction medium. The loop process is different from the kettle stirring of the Hostalen process and the CX process. Its materials rely on the axial flow pump to flow at high speed in the loop to remove the heat of polymerization reaction. Phillips uses modified silica or alumina fixed catalysts to produce UHMWPE. No hydrogen is required during polymerization, and the investment is low, but the requirements for catalysts are high. The InnoveneS process is also relatively mature, with a compact layout and stable product quality control. It is characterized by short material residence time and fast brand switching.

The polymerization of ethylene is mainly affected by polymerization temperature, pressure, catalyst composition and dosage, external electron donor and hydrogen. The catalyst is the core of polymerization technology and has an important influence on the average molecular weight, molecular weight distribution, bulk density, crystallinity, and particle size and morphology of the polymerization product. The main UHMWPE catalysts at present are Ziegler-Natta (Z-N) catalysts, metallocene catalysts and non-locene transition metal catalysts.

Z-N catalysts dominate the current industry. International companies such as Celanese, Mitsui Petrochemical, Braskem, DSM, and Petrochemical, as well as domestic resin manufacturers including Shanghai Research Institute of Chemical Industry Co., Ltd., all use Z-N catalysts to produce UHMWPE resins.

Market supply and demand In recent years, domestic companies have gradually achieved technological breakthroughs, mastered UHMWPE production technology, and expanded production capacity rapidly. As of 2022, the total domestic ultra-high molecular weight polyethylene production capacity is about 250,000 t/a, and it is expected that 300,000-400,000 t/a will be added before 2025. In addition to the new capacity, some HDPE units will also switch to UHMWPE. Driven by the demand for ultra-high molecular weight polyethylene in the new energy field, Celanese has built a new ultra-high molecular weight polyethylene production line at its Nanjing base, with a cumulative capacity expansion of 15,000 t/a, mainly producing special polyethylene materials for lithium battery separators. In the past two years, the new ultra-high molecular weight polyethylene units of Sailboat Petrochemical and Henan Watson New Materials Co., Ltd. have been put into production one after another, adding 50,000 t/a of new production capacity; Daqing Petrochemical and Lanzhou Petrochemical have successfully converted to ultra-high molecular weight polyethylene using the original HDPE units, and the domestic ultra-high molecular weight polyethylene production capacity has expanded rapidly.

Broad prospects

As the manufacturing industry has higher and higher requirements for the properties of materials, UHMWPE sheet  has a broad market prospect with its excellent properties. The main product forms include industrial pipes, plates, profiles, fibers, lithium battery separators, etc. In 2022, my country's total consumption of ultra-high molecular weight polyethylene will be 230,000 tons, a year-on-year increase of 19%, and the main source of growth will be fiber and battery separator products. Ultra-high molecular weight polyethylene fiber is the largest downstream application field in 2021, accounting for 31%; battery separators, plates and industrial pipes account for 28%, 22% and 15% respectively.

In the next five years, energy storage batteries and power batteries will continue to maintain rapid growth, which will further promote battery separators to become the most important growth area for ultra-high molecular weight polyethylene. It is estimated that by 2026, the total domestic consumption of ultra-high molecular weight polyethylene resin will reach 412,000 tons, with a CAGR of 17%, of which the total consumption of fibers and battery separators will account for three quarters. At present, the largest downstream of ultra-high molecular weight polyethylene fiber is the marine industry, accounting for 26%. It is mainly used in materials such as cables, and is commonly used for negative force ropes, heavy-load ropes, salvage ropes, towing ropes, sailboat ropes, etc. Ultra-high molecular weight polyethylene fiber ropes are used for fixed anchor ropes of supertankers, offshore operating platforms, lighthouses, etc., which solves the problems of rust encountered in the past when using steel cables and corrosion, hydrolysis, ultraviolet degradation, etc. encountered by nylon and polyester cables, which cause the strength of the cables to decrease and break, and need to be replaced frequently. More subdivided, the cable products used in the marine field are divided into shipping mooring cables, marine engineering mooring cables, marine buoy mooring cables, offshore energy facility mooring cables, marine scientific research cables, leisure marine cables, offshore hoisting cables, and marine fishery cables. For shipping mooring cables, the safety and stability issues are research hotspots.

Advantages of UHMWPE fiber in the marine industryUHMWPE fiber has significant advantages in the marine industry. First, its strength is extremely high, and its breaking length under deadweight is 8 times that of steel rope and 2 times that of aramid, which enables it to withstand huge tension and pressure in the marine environment and ensure the reliability of products such as ropes. Secondly, it has excellent corrosion resistance and can effectively resist the erosion of seawater, avoiding the reduction of strength and service life due to corrosion like traditional ropes. In addition, UHMWPE fiber is light in weight and low in density, which is convenient for transportation and installation, reducing operating costs. At the same time, it also has good weather resistance and UV resistance, and can maintain stable performance under harsh marine climate conditions. For example, in the application of fixed anchor ropes for supertankers, offshore operating platforms, lighthouses, etc., the rust encountered in the use of steel cables and the corrosion, hydrolysis, and UV degradation encountered by nylon and polyester cables in the past have solved the problems of reduced strength and breakage of cables, which require frequent replacement.

Safety research on marine applications of UHMWPE fiberIn the marine application of UHMWPE fiber, safety is a crucial research direction. On the one hand, its high strength and corrosion resistance ensure the reliability of products such as ropes in the marine environment and reduce safety risks caused by problems such as rope breakage. For example, in the application of shipping mooring cables, its stability and safety are directly related to the docking and navigation safety of ships. On the other hand, for applications such as marine aquaculture cages, the safety of fibers is also reflected in their protective effect on aquaculture organisms; however, attention should also be paid to some potential safety issues, such as changes in fiber performance after long-term use, and performance in extreme marine environments. Researchers are conducting in-depth research and solving these problems through continuous experiments and monitoring to ensure the safety of ultra-high molecular weight polyethylene fibers in marine applications. Future replacement trends for cables in the marine industry In the future, in the marine industry, the replacement of traditional steel anchor chains with new cables such as synthetic fiber mooring cables, mooring combined connecting cables, UHMWPE fiber mooring cables, and carbon fiber composite mooring cables and their combined cables will be the main development trend. For example, in the field of mooring cables for offshore energy facilities, new synthetic fibers and composite mooring cables such as high-performance fiber mooring cables and carbon fiber composite mooring cables will be more widely used, complementing the advantages of traditional steel mooring cables. This trend is due to the advantages of new fiber materials such as higher strength, better corrosion resistance and lighter weight, which can better meet the needs of the growing marine industry. Deputy Secretary-General of the Rope (Cable) Net Branch of the China Industry Association, Director of the Shandong New Materials Rope Net Research Engineering Laboratory. Jiang Runxi, who has served as Vice President of the Research Institute of Sinopec Yizheng Chemical Fiber Company, Chief Engineer of the Technology Center, and Sinopec Academic Leader, will attend the "2024 Ultra-High Molecular Weight Polyethylene Innovation and Development Forum" and will personally present an authoritative in-depth report on "Performance Characteristics and Applications of Ultra-High Molecular Weight Polyethylene Fiber Ropes and Cables".