M-xylylenediamine type semi-aromatic polyamide and preparation method thereof

Abstract

The invention provides a method for preparing a m-xylylenediamine type semi-aromatic polyamide salt solution (a salt forming method for short) and a method for preparing m-xylylenediamine type semi-aromatic polyamide from the m-xylylenediamine type semi-aromatic polyamide salt solution (a polymerization method for short). According to the salt forming method, the stable m-xylylenediamine type semi-aromatic polyamide salt solution is prepared by directly mixing m-xylylenediamine with an aqueous solution of one or more binary acids. According to the polymerization method disclosed by the invention, the m-xylylenediamine type semi-aromatic polyamide is prepared from the m-xylylenediamine type semi-aromatic polyamide salt solution by adopting a normal-pressure or micro-positive-pressure pre-polymerization process.

Description

technical field [0001] The invention belongs to the field of polyamide preparation, and in particular relates to m-xylylenediamine type semi-aromatic polyamide and a preparation method thereof. Background technique [0002] m-xylylenediamine-type semi-aromatic nylon (MX-type nylon), as an important species of semi-aromatic nylon, has been developed since the 1980s due to its excellent rigidity, excellent processability, and good barrier properties , is favored by people. Among such materials, the most famous variety is PA MXD6 (poly-m-xylylene adipamide), which has many advantages and is widely used. [0003] PA MXD6 is a semi-crystalline special nylon, which has the characteristics of low water absorption, high heat distortion temperature, high tensile strength and bending strength, small molding shrinkage, and good barrier properties to oxygen, carbon dioxide and other gases. These excellent Its performance makes it especially suitable for the application of packaging ma...

AI Technical Summary

Problems solved by technology

Although this method eliminates the salt-forming step, the raw material is heated to a higher temperature during the preparation process, which easily leads to the decomposition of the raw material, resulting in many defects in the product, such as fish eyes, yellowing, etc.

The modified formula for the above shortcomings is also troublesome

Simultaneously, this method requires excessively high raw material purity.

In the mixing process, it is necessary to maintain a stable molar ratio, so the requirements for equipment are extremely complex, so it is difficult to scale up production

And it is difficult to achieve complete continuous production at this stage

[0006] The production of MX-type nylon by direct melt polymerization mainly has the following technical disadvantages: (1) the requirement for the purity of raw materials is too high, the cost of raw materials with higher purity is relatively high, and the preparation process is relatively complicated; (2) in the monomer mixing process, because there is no The additional molar ratio adjustment system needs to maintain a stable molar ratio, which requires extremely complex equipment, resulting in high production costs, difficult device commissioning, high equipment debugging, maintenance time and cost; (3) The method is Semi-continuous production cannot achieve complete continuous production, and the final polymerization reaction device is a screw, so it is difficult to accurately control the polymerization parameters

However, the salt prepared by this method needs to be centrifuged, redissolved during use, and heated repeatedly, which directly increases energy consumption and waste of resources, and is not easy to store, and it is difficult to scale up production. There is no cost advantage in industrial continuous production

[0010] At present, the preparation of MX-type nylon by salt-forming melt polymerization mainly has the following technical disadvantages: (1) MXDA and dibasic acid are prepared in a fixed ratio to form an aqueous salt solution, which is separated and dried to prepare a solid salt, and then secondary dissolution is required before polymerization , so there are two times of heating and water removal in the above process (one is when preparing solid salt, and the other is when polymerizing), causing problems such as large energy consumption, low efficiency, and long time consumption; (2) Salt-forming melt polymerization is currently Batch-type small reactors are mostly used for production and preparation, and it is difficult to scale up the device. At the same time, this method has inherent defects such as uneven distribution of properties of the prepared materials, low production capacity, and low production efficiency; (3) In the current nylon condensation polymerization, All adopt high pressure polymerization process

The high positive pressure in this type of reaction means that the nylon polymerization equipment is required to ensure the stability of mass and heat transfer in the reaction process, and the reactor must be kept absolutely sealed against pressure. This situation greatly increases the pressure of nylon polymerization equipment. manufacturing difficulty

In addition, the high pressure in the reaction process is also accompanied by high risk of explosion, which to some extent greatly affects the personal safety of operators and causes unnecessary safety hazards

At the same time, the high-pressure polymerization process is subject to environmental impact assessment and land use restrictions when the device is approved and put into production, which also indirectly hinders the development of the nylon industry; (4) In terms of process, the main cause of high pressure is high-temperature water vapor, etc.

This kind of gas is directly discharged during the polymerization process. While causing environmental hazards, it also takes away the heat in the polymerization reactor, resulting in unnecessary temperature drop during the reaction process, thereby increasing energy consumption during the nylon polymerization process.

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