the intro duction of Polypropylene fibre

1 Introduction of polypropylene fiber

1.1 Development history

Foreign polypropylene fiber industry started earlier, technical system and application fields are perfect. In 1954, Italian scientist Natta synthesized isotactic polypropylene for the first time. In 1957, the Italian company Montecatini took the lead in the industrial production of isotactic polypropylene under the trade name Meraklon, and after that, the United States and Canada began to develop polypropylene fibers.

Since the 1960s, polypropylene short fiber and film-split fiber have been developed one after another, and Japan has continuously invested in the research and development of high-performance and functional polypropylene fiber, which has broadened the application of polypropylene fiber in decoration and industrial fields.

In the 1970s, the development of short-range spinning technology and equipment increased the output of polypropylene fiber. The development of fine polypropylene fiber arose in European and American countries, and expanded its application in sportswear, underwear and high-grade clothing. At the same time BCF carpet yarn came into use.

In the 1980s, metallocene catalyst was successfully developed. The United States and Western Europe have made progress in using concrete reinforced polypropylene fibers for the construction industry. BCF one-step equipment, air deformers, complex spinning equipment and nonwoven equipment began to emerge. Since the 1990s, polypropylene fiber varieties are more diversified. The United States and Western European countries have developed new differentiated functional polypropylene fibers, such as flame retardant, antistatic, conductive, electrothermal, bioabsorption and degradation, which greatly expanded the application field of polypropylene fibers.

Polypropylene fiber industry in China started late, varieties and application fields imperfect, began in the 1970 s of the polypropylene fiber research and development, in 1982 built the first demonstration of polypropylene fiber, the end of the 20th century have developed a fine denier, flame retardant, antibacterial, ultraviolet resistant, anti-aging, such as far-infrared differentiation of polypropylene fiber (figure 1).

1.2 Performance characteristics

Polypropylene fiber (marked as polypropylene fiber in the table) has remarkable performance. Compared with other fibers, polypropylene fiber has the lightest, the most thermal, the most hydrophobic fiber properties (Table 1). The density of polypropylene fiber is only 0.91g /cm3, which is the smallest among the five synthetic fibers, and it is about 34% lighter than polyester fiber. The insulation rate of polypropylene fiber is 36.49%, which is the highest among the five synthetic fibers and 1.7 times that of polyester fiber. The standard moisture regain of polypropylene fiber is almost zero, and the hydrophobic and moisture conductivity performance is the best. The fine denile polypropylene fiber prepared has good feel, soft texture and soft luster, and the core absorption effect makes it has the characteristics of moisture conductivity and sweat.

At the same time, polypropylene fiber has good acid and alkali resistance and heat aging performance. After proper modification treatment, polypropylene fiber with excellent weather resistance, heat resistance and acid and alkali resistance can be made (Table 2). It has a wide range of applications in the fields of concrete, geotextile, medical material, sports warm clothing and carpet.

Table 1 Basic physical properties of several fibers

Table 2 Weather resistance, heat resistance, acid and alkali resistance of several synthetic fibers

2. Current situation of polypropylene fiber industry

2.1 Current situation of polypropylene fiber production and demand

(1) The polypropylene monopoly pattern was broken, and private and joint venture enterprises developed rapidly. For a long time, the upstream of China's polypropylene fiber industry belongs to oligopoly industry, and the supply is relatively concentrated. The enterprises are dominated by Sinopec and PetroChina, supplemented by private and joint venture enterprises, which results in the backward development of polypropylene raw materials.

For example: in 1999, the unit price of fiber-grade polypropylene was 5800 ~ 6300 yuan /t, and polyester was 8200 ~ 8500 yuan /t; In 2018, the annual average price of polypropylene was about 9,480 yuan /t, and the annual average price of polyester was about 7,600 yuan /t. Instead of decreasing, the price of polypropylene rose, which highlighted the embarrassing situation of the development of the polypropylene industry. After the monopoly pattern was broken, a large number of private capital entered. In 2015, China's polypropylene production capacity reached 23.111 million tons, 2.4 times that of 2010, with an average annual growth rate of more than 10%.

In 2018, the new two production lines are both owned by private enterprises and joint ventures. By the end of the year, the production capacity reached 11.28 million tons, accounting for 48.79% of the total production capacity, nearly half. On the other hand, the production capacity of Sinopec and PetroChina, represented by the traditional olefin from oil, continued to remain the same as last year, with their proportions and output both declining to 34.70% and 16.62% of the original ones respectively (Table 3).

Table 3 The production capacity of polypropylene in China according to enterprise ownership in 2018

(2) China's polypropylene fiber international division of labor is insufficient, and there is an obvious gap with other major synthetic fiber varieties. In 2016, the global output of synthetic fiber was about 596.99 million tons, and China was about 41.27 million tons, accounting for 69.00% of the global output of synthetic fiber. The global polyester fiber production is 52.02 million tons, China is about 3800million tons, accounting for about 73.00% of the global polyester fiber production; The global output of polyolefin fiber is about 5.49 million tons, while that of China is about 1.02 million tons, accounting for only 19.00% (Fig. 2), which is far behind that of polyester fiber.

In 2018, China's chemical fiber output was 50.110 million tons, up 7.68% year on year; The yield of polyester fiber was the highest, accounting for more than 80.00%; It was followed by polyamide fiber, which accounted for 6.59% of the total output, while other synthetic fibers accounted for less (Figure 3). The output of polypropylene fiber enterprises was 347,800 tons, accounting for about 0.70%, with a year-on-year increase of 2.31%; Among them, polypropylene filament production capacity accounted for about 50.00% of the polypropylene fiber production capacity, the actual production accounted for even less.

In 2012, the global production of fiber-grade polyester was about 43.33 million tons, accounting for about 75.00% of the total production of fiber-grade polymer, and that of fiber-grade polypropylene was about 2.43 million tons, accounting for about 4.00%, much higher than that of domestic polypropylene fiber, which was about 0.700%. The development of domestic polypropylene fiber industry was obviously lagging behind (Figure 4).

(3) The demand structure of polypropylene fiber gradually improved, and the demand for used fiber increased significantly. In 2018, the global industrial polypropylene fiber accounted for about 30.00% of the total polypropylene fiber, and the demand in various fields expanded fully. In 2012, the proportion of polypropylene fiber for consumption, household use and industrial use in China was 5.00%, 34.00% and 61.00% respectively. By 2014, the proportion of drug use, household use and industrial use was 12.00%, 39.00% and 49.00%, respectively. The demand for polypropylene fiber for drug use was less but the increase was larger, and the demand for industrial polypropylene fiber continued to occupy the dominant position.

2.2 Application status of polypropylene fiber

(1) The demand of industrial polypropylene fiber is large, and the rapid growth of polypropylene fiber for filtration and separation and construction. In 2018, the global industrial accounted for about 30.00% total polypropylene fiber and polypropylene fiber silk production capacity of 155000 t polypropylene industry in China in 2015, is mainly used in the safety net belt, industrial condole belt, flexible bag, geotextile, industrial filter cloth, cable, fiber optic cable, high-pressure fire hose, conveyor belt, industrial sewing thread, sail, plastic woven bag, etc; Geotextiles play an important role in modern infrastructure design and maintenance technologies, such as fixed, drainage, protection, isolation and other diversified functions, and the annual yield increase is expected to reach 9.00%.

In 2017, China's textile output for filtration and separation was 1.3090 million tons, up 8.20% from the previous year, making it the fastest growing category in the industrial textile industry. In 2018, the global polypropylene fiber used in construction accounted for about 14.00% of the total polypropylene fiber. Due to the excellent mechanical properties and chemical resistance of polypropylene fiber, it can significantly improve the crack resistance and strength of concrete when used as concrete reinforcing fiber.

In 2017, China produced 996,000 tons of geotextiles, up 6.80 percent from the previous year. Construction textile output is 75.00 million tons, an increase of 7.00% over the previous year. It is expected that the geotextile synthetic materials industry will continue to grow at an average rate of 11.50% in the future, which will bring a large market demand for the polypropylene fiber industry. In 2015, the domestic production capacity of polypropylene staple fiber is about 240 million tons, mainly used in the industrial field, for the production of non-woven fabrics, sanitary materials, filtration materials, filling materials, automotive interior, etc.

(2) The development of civil home textile is stable. In 2015, the production capacity of ordinary polypropylene filament is about 52,000,000 tons, and the production and sales are basically balanced. It is mainly used in traditional industries such as luggage belt, luggage surface and decoration. The production capacity of PP-BCF in China is about 120 million t/a, accounting for 70.00% of the total production capacity of BCF, and the consumer market is mainly concentrated in hotels, restaurants, office buildings and automobile fields.

2.3 Technical status of polypropylene fiber

2.3.1 Polypropylene raw material

With the development of metallocene catalyst and hydrogen-regulating technology, the relative molecular weight and processing property of polypropylene resin are controllable, and the polypropylene resin products with narrow distribution and adjustable melting point can be produced. The development of new transition metal catalysts has also realized the copolymerization of propylene with ethylene alcohol and other polar monomers to prepare hydrophilic polypropylene with hydroxyl groups.

2.3.2 Superfine polypropylene fiber

The development of fine and ultrafine polypropylene fibers has been promoted by the breakthrough in the preparation technology of high fusion finger, narrow distribution and low fluctuation polypropylene resins. However, the preparation of ultrafine polypropylene fibers and fine functional polypropylene fibers with linear density lower than 0.55 dtex by melt spinning is still a technical problem.

At present, solution electrospinning is generally used to prepare nano-polypropylene fibers, but harmful solvents and spinning efficiency are always the limitations of their industrialization development. Recent development of Zetta method and electrostatic spinning melt spinning method to overcome the electrostatic spinning solution require the use of harmful organic solvent, low efficiency, can be in the melt spinning/melt-blown existing device for technological transformation, and realize the electrospinning multicomponent polymer blending system, low cost, high efficiency, is a feasible scheme of polypropylene superfine fiber industrialized production.

2.3.3 Functional polypropylene fibers

Functional modification of polypropylene fiber is an important means to expand the application field and increase the added value of polypropylene fiber products.

The existing methods, first, give full play to the intrinsic properties of polypropylene as light and warm, endowing polypropylene fiber with antibacterial and intelligent temperature regulating functions through blending modification or post-finishing technology, so as to meet its application needs in the fields of underwear, thermal clothing, cold-proof clothing and medical materials. Or by electrostatic spinning, blending pore agent and surface grafting modification technology, preparation of ultrafine, porous and surface functionalized polypropylene fiber, enhance the oil absorption performance of polypropylene fiber.

The second is to make up for the performance defects of polypropylene fiber, using polar additives, flame retardant and ultraviolet absorbent polypropylene dyeing, antistatic, flame retardant and anti-ultraviolet properties of modification.

2.3.4 Polypropylene fiber for engineering purposes

The performance of polypropylene fiber reinforced concrete is limited by the fact that polypropylene fiber is not hydrophilic, dispersing in concrete and combining with concrete is not strong. The dispersion and bonding of polypropylene fiber in concrete can be significantly improved by hydrophilic modification of the surface of polypropylene fiber or by adjusting the morphology and structure of the fiber, and the anti-freezing and anti-cracking properties of concrete can be improved.

The research on polypropylene fiber reinforced concrete was carried out relatively late in China, and started with the large-scale application of polypropylene fiber in domestic construction projects. At present, the research mainly focuses on the physical and mechanical properties of polypropylene fiber reinforced concrete.

2.3.5 Polypropylene fiber regeneration technology

The waste materials in the process of polypropylene filament production (such as transition filament, etc.) can be recycled to produce darker filament, but there are many impurities in the renewable polypropylene material on the market, so it is not recommended to be used for spinning filament. Polypropylene regeneration technology mainly focuses on physical recovery and gradually develops towards high value recovery.

China's annual waste woven bags close to 300 million tons. The waste polypropylene has large stock, low recovery rate and serious waste of resources. The physical regeneration technology is simple in process and low in cost, but the performance of the regenerated products decreases greatly, so it is not suitable to make high-grade polypropylene products.

Recently, Nextek has developed a technology for recycling and purification of food-grade recycled polypropylene, which can be used to prepare food-grade and medical-grade polypropylene materials, broadening the application field. Tianjin Petrochemical Jinghua Co., Ltd. has transformed the recycled polypropylene to produce the far infrared recycled polypropylene staple fiber, which has improved the quality and added value of the recycled polypropylene fiber. Chemical regeneration technology is a method to produce polypropylene by catalytic cracking of waste polypropylene to recover monomers and then polymerization. Due to the high price of catalyst, short life and large investment of equipment, the recovery profit is very low and it is difficult to popularize.

2.3.6 Polypropylene fiber equipment technology

With the technological progress and equipment development of chemical fiber industry, polypropylene fiber spinning technology has gradually developed from the traditional low spinning speed and two-step process technology to the high-speed spinning and one-step process technology. Fully-oriented filament (FDY) one-step spinning technology has the characteristics of short process, small occupation, high strength and high efficiency. Most enterprises have used automatic control FDY one-step spinning process equipment.

Domestic polypropylene FDY one-step spinning technology has become increasingly mature after decades of development, and the corresponding spinning equipment has been originally imported from the United States and Germany, developed into domestic equipment. However, there is a certain gap between China's spinning equipment and foreign advanced spinning equipment. The configuration, technical level and cost efficiency of domestic equipment are still lower than those of foreign equipment.

3. Thinking about the development of polypropylene fiber

The long-term monopoly of polypropylene fiber raw materials will be broken, showing the momentum of the development of polyester fiber. For a long time, the raw material of polypropylene fiber in China is monopolized by oligopoly, and the supply is relatively concentrated. At the same time, China's polypropylene fiber production technology, equipment level and foreign there are many gaps. This kind of domestic oligopoly production raw materials, foreign enterprises monopoly technology pattern, resulting in the development of China's polypropylene fiber industry is limited, the international division of labor is not increased but decreased.

With polypropylene industry policy to relax, diversified development of polypropylene production enterprises, especially private into refining rate faster, is bound to digest olefin, accelerate the growth of polypropylene production, between polypropylene production enterprises will become more and more fierce competition, which will lead to new development of polypropylene raw materials, to further expand production, reduce production cost, provides the foundation for the development of new type of polypropylene fiber. From the application status of polypropylene fiber, polypropylene fiber in the industrial field of the greatest demand.

With the advancement of national "One Belt And One Road" initiative and the implementation of infrastructure construction projects, the demand for industrial fiber for basic engineering will increase greatly. There are many extreme geographical and climatic environments such as permafrost, saline-alkali land, sandy land and poor temperature along the "One Belt And One Road" route, while the polypropylene fiber has excellent heat, cold and resistance

source: HUa Xian Tou Tiao