According to the actual production and part of the test, the quality problems of small bulk polypropylene powder products were analyzed and discussed. The phenomenon of product quality was analyzed and discussed, and the methods to solve these problems were proposed.
Since the 1960s, the development of polypropylene technology in China has achieved certain results in more than 30 years. In particular, the batch-based bulk polymerization process developed by ourselves has become a unique and mature polypropylene production process. However, while the bulk polypropylene has been rapidly developed, its application range has not been greatly developed due to its production characteristics, namely raw materials, equipment, processes, operating conditions, storage and transportation environment and many other factors. Fluctuation leads to insufficient quality of products, and many quality problems occur. On the one hand, it limits the scope of use of products. Most products are only used to produce low-grade products such as woven bags, tying ropes, daily necessities, etc.; on the other hand, it has caused certain processing for users. Difficulty, the user has raised many shortcomings.
Influencing factors of melt index MFR: The control index for controlling product quality is the melt index MFR. Other indicators can not be analyzed at present. In the future, with the development of the company and the transfer to formal, the analytical indicators such as ash, isotacticity, volatile matter, apparent density, and tensile yield strength should be improved. MFR is regulated by hydrogenation. Only by studying the variation of MFR can the MFR distribution of the product be effectively controlled. Under the same isotactic index, the MFR increases, the molecular weight of the polypropylene chain decreases, the yield tensile strength increases, and the impact strength decreases. When the MFR decreases, the elongation at break of the polypropylene increases. Therefore, the distribution of MFR should be controlled in production to improve the quality and processing properties of polypropylene. The factors affecting MFR, catalyst performance, process parameters, raw material ratio, and hydrogen hand-operated operation are all major factors affecting MFR. The use of high-efficiency catalysts has achieved a high level of polymerization stability, catalyst yield and anti-impurity interference, which provides a convenient condition for further understanding of the main factors affecting MFR changes. The actual production proves that the key to the MFR control depends on the hydrogen regulation method of operation. Hydrogen adjustment is achieved by the dissolution, diffusion and adsorption of hydrogen in the gas phase. As the mass ratio of hydrogen to propylene (ie, hydrogen to olefin ratio) increases, the relative molecular weight of the polypropylene decreases accordingly, and the MFR increases accordingly.
The main factors affecting ash: harmful impurities in raw material propylene, trace water, oxygen, sulfur, arsenic, carbon monoxide, alkyne, diolefin, nitrogen and the addition of constant oxygen in the recovery of propylene are all harmful impurities, which seriously damage the catalyst. The activity and orientation ability, for which an activator is added to eliminate the activity of the impurities to protect the catalyst, which leads to an increase in the ash content of the product. The amount of activator added is small, the activity of the catalyst is difficult to exert, the reaction is weak, the yield per well is low, and the product is high in ash content. As the amount of catalyst added increases, the yield per unit increases and the ash content of the product decreases. When the catalyst is increased to a certain extent, the single-pot yield will decrease and the ash will rise. This is because when the amount of the catalyst added is too low, the polymerization is not normal due to the limitation of the catalyst itself and the destruction of impurities. In the later period, there was no reaction, resulting in a decrease in the output of the single kettle. Excessive amount of catalyst will cause a violent reaction. At this time, it can only be forced to adopt an emergency recovery method to reduce the reaction temperature and pressure, which will eventually lead to a decrease in the yield of the single kettle and an increase in the ash content of the product. Therefore, the proper amount of catalyst to be added must be strictly controlled.
The stability of the product is poor, and the isotacticity of the product is poor. The influencing factors are:
(1) The influence of propylene raw materials, such as other unsaturated hydrocarbons.
(2) The influence of hydrogen regulation, the high melt index and other regulations have decreased.
(3) The influence of the aluminum alkyl component, such as the impure aluminum component, may affect the isotacticity.
The high and low isotacticity mainly affects the strength of processed products, and the low isotactic polypropylene has low strength, but the isotacticity is not as high as possible, and it is more than 96%. In addition, the isotacticity also affects the fluidity of the processing. The irregularities of the products with low isotacticity are more likely to clog the filter screen, the feeding of the extruder is easily interrupted, the feeding is uneven, and the quality of the processed products is affected. Therefore, in the production process, it is more important to strictly control the various indicators of the product, and it is also a prerequisite for ensuring product quality.
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