Market demand for high melting point PP
The melt flow performance of polypropylene is closely related to its molecular weight. The average molecular weight of commercial polypropylene resin prepared by conventional Ziegler Natta catalytic system is generally between 3×105 and 7×105. The melt index of these conventional polypropylene resins is generally low, which limits their application range.
With the rapid development of chemical fiber industry and textile machinery industry, the non-woven fabric industry has risen rapidly. The series of advantages of polypropylene make it the preferred raw material for non-woven fabrics. With the development of society, the application fields of non-woven fabrics are becoming broader. In the field of medical and health, non-woven fabrics can be used to manufacture isolation suits, masks, surgical gowns, women’s sanitary napkins, baby diapers, and so on; As a building and geotechnical material, non-woven fabrics can be used for roof waterproofing, road construction, water conservancy engineering, or advanced roof felt can be produced using spunbond and needle punched composite technology. Its service life is 5-10 times longer than traditional asphalt felt; Filter materials are also one of the fastest developing products for non-woven fabrics, which can be used for gas and liquid filtration in industries such as dry chemical, pharmaceutical, and food, and have great market potential; In addition, non-woven fabrics can be used in the manufacturing of synthetic leather, luggage, clothing linings, decorative fabrics, and wiping cloths for household use.
It is precisely because of the continuous development of non-woven fabrics that the requirements for their production and application are constantly increasing, such as melt blown, high-speed production, thin products, etc. Therefore, the requirements for the processing performance of polypropylene resin, the main raw material of non-woven fabrics, have also been correspondingly increased; In addition, the production of high-speed spinning or fine denier polypropylene fibers also requires polypropylene resin to have good melt flow performance; Some pigments that cannot withstand high temperatures require polypropylene as a carrier with relatively low processing temperatures. All of these require the use of ultra-high melt index polypropylene resin as raw material that can be processed at lower temperatures.
The special material for melt blown fabric is polypropylene with high melt index. Melt index refers to the mass of molten material passing through a standard capillary tube every 10 minutes. The higher the value, the better the processing fluidity of the material. The higher the melt index of polypropylene, the finer the fibers sprayed out, and the better the filtration performance of the melt blown fabric produced.
The method for preparing high melt index polypropylene resin
One is to control the molecular weight and molecular weight distribution of polypropylene by controlling the polymerization reaction process, such as reducing the molecular weight of the polymer by increasing the concentration of cationic agents such as hydrogen gas, thereby improving the melt index. This method is limited by factors such as catalytic system and reaction conditions, making it difficult to control the stability of melt index and implement it.
Yanshan Petrochemical has been directly polymerizing melt blown materials with a melt index of over 1000 using metallocene catalysts in the past few years. Due to the difficulty in controlling stability, large-scale polymerization has not been carried out. Since the outbreak of the epidemic this year, Yanshan Petrochemical has adopted the controllable degradation polypropylene melt blown material production technology developed in 2010 to produce polypropylene melt blown non-woven fabric special material on February 12. At the same time, industrial tests have been conducted on the device using metallocene catalysts. The product has been produced and is currently being sent to downstream users for trial.
Another method is to control the degradation of polypropylene obtained through conventional polymerization, reduce its molecular weight, and increase its melt index.
In the past, high-temperature degradation methods were commonly used to reduce the molecular weight of polypropylene, but this high-temperature mechanical degradation method has many drawbacks, such as additive loss and thermal decomposition, and unstable processes. In addition, there are methods such as ultrasonic degradation, but these methods often require the presence of solvents, which increases the difficulty and cost of the process. In recent years, the methods of chemical degradation of polypropylene have gradually been widely applied.
Production of High Melt Finger PP by Chemical Degradation Method
Chemical degradation method involves reacting polypropylene with chemical degradation agents such as organic peroxides in a screw extruder, causing the molecular chain of polypropylene to break and reduce its molecular weight. Compared with other degradation methods, it has the advantages of complete degradation, good melt fluidity, simple and feasible preparation process, and is easy to carry out large-scale industrial production. This is also the most commonly used method by modified plastic manufacturers.
Equipment requirements
High melting point is completely different from ordinary PP modification equipment. Equipment for spraying molten materials requires a longer aspect ratio, and the machine head needs to be vertical or use underwater granulation (Wuxi Huachen has a similar underwater cutting); The material is very thin and needs to come into contact with water immediately after coming out of the machine head for easy cooling;
For the production of conventional polypropylene, the cutting speed of the extruder is 70 meters per minute, while for high melt polypropylene, the cutting speed is required to be above 120 meters per minute. In addition, due to the fast flow rate of high melt polypropylene, its cooling distance needs to be increased from 4 meters to 12 meters.
The machine for making melt blown materials requires continuous mesh changing, usually using a dual station mesh changer. The motor power requirements are much higher, and more shear blocks will be used inside the screw components; According to Koyapan, the twin screw line made of melt blown special materials has considerable uniqueness.
1. Ensure stable feeding (PP, DCP, etc.);
2. Determine the appropriate aspect ratio and axial position of the opening based on the half-life of the composite formula (evolved to the third generation to ensure smooth extrusion of the CR-PP reaction);
3. To ensure that the melt finger has a high yield within the tolerance range (more than 30 finished strips have a higher cost-effectiveness and blending basis compared to only a dozen);
4. Special drainage mold heads must be equipped. Melt and heating should be uniform, and the amount of waste should be small;
5. It is preferable to be equipped with a mature cold cutting granulator for melt blown materials (which has a good reputation in the industry) to ensure the quality of finished particles and a higher grade rate;
6. It would be even better if there is online testing feedback. In addition, the addition of liquid degradation initiators to the side feed requires higher accuracy due to the small proportion of additives. For side feeding equipment, such as imported Brabenda, Kubota, domestically produced Matsunai, etc.
The currently used degradation catalysts
1: Dit-butyl peroxide, also known as di-tert-butyl peroxide, initiator a, vulcanizing agent dTBP, is a colorless to slightly yellow transparent liquid that is insoluble in water and miscible with organic solvents such as benzene, toluene, and acetone. Strong oxidizing, flammable, relatively stable at room temperature, insensitive to impact.
2: Double five sulfurizer, abbreviated as DBPH, chemical name 2,5-dimethyl-2,5-bis (tert butylperoxy) hexane, molecular weight 290.44. Pale yellow liquid with a relative density of 0.8650 in the form of sound and milky white powder. The freezing point is 8 ℃. Boiling point 50~52 ℃ (13Pa). The refractive index ranges from 1.418 to 1.419. The viscosity of the liquid is 6.5mPa. s. Flash point (open cup) 58 ℃. Soluble in most organic solvents such as alcohols, ethers, ketones, esters, aromatic hydrocarbons, etc., insoluble in water.
3: Testing of fused fingers
The melt finger test needs to be conducted in accordance with GBIT 30923-2014 Polypropylene Melt Spray Special Materials; Ordinary melt finger instruments cannot be tested. High melting refers to using the volumetric method rather than the mass method for testing.
Domestic equipment includes Chengde Youte, Guangxin Electronic Technology, Hangzhou Jinmai, Jilin Science and Education Instrument Factory, and imported equipment includes Zwick;Chengde Jinjian Testing Instrument Co., Ltd. produces an MFL-2322H melt flow rate meter specifically designed for NVR measurement of ultra-high flow polypropylene materials, which meets the factory testing requirements of GB/T 309232014 Polypropylene Melt Spray Special Materials. The testing range is (500-2500) cm/10min.
Currently, there are:
1. Shandong Daoen Polymer Materials Co., Ltd
2. Hunan Shengjin New Materials Co., Ltd
3. Jinfa Technology Co., Ltd
4. Beijing Yishitong New Materials Development Co., Ltd
5. Shanghai Huahe Composite Materials Co., Ltd
6. Hangzhou Chenda New Materials Co., Ltd
7. Basel, Dalin, South Korea
Post time: Apr-01-2024