What Is Polyamide?

Polyamide is also nylon.

Polyamides are linear polymers containing repeating amide groups in the backbone of the molecule. It can be formed by the condensation polymerization of diamine and dibasic acid. The polycondensation product of hexamethylenediamine and sebacic acid is called polyamide 610. 6 and 10 respectively refer to the number of carbon atoms contained in hexamethylenediamine and sebacic acid in the repeating unit. It can also be made from amino acids or lactams, such as caprolactam. The polymer is called polyamide 6, with the number 6 indicating the number of carbon atoms in the repeating unit.

There are basically two types of chemical structures of nylon: one is made by the polymerization of omega-amino acids or its lactams, and the other is made by the polycondensation of dibasic acid and diamine.

Type

Nylon-6 is named after the number of carbon atoms in caprolactam. Nylon-66 is a copolymer of hexamethylenediamine and adipic acid. Nylon-6/12 is a binary compound of hexamethylenediamine and dodecanoic acid or dodecanoic acid. Acid copolymers, etc. There are many types of nylon, including nylon-6, nylon-66, nylon-69, nylon-610, nylon-612, nylon-11, nylon-12, nylon-46 and nylon-1212, etc.

Single monomer homopolymer

Polyamide 6: [NH - (CH 2 ) 5 - CO] N made from ε-caprolactam;

Polyamide 11, (polyω-aminoundecanoic acid): [NH - (CH 2 ) 10 - CO] N Made from 11-aminoundecanoic acid;

Polyamide 12, (Polylaurolactam): [NH - (CH 2 ) 11 - CO] N Made from 12-aminolauric acid;

double monomer homopolymer

Polyamide 66: [NH - (CH 2 ) 6 - NH - CO - (CH 2 ) 4 - CO] N Made from hexamethylenediamine and adipic acid;

Polyamide 610: [NH - (CH 2 ) 6 - NH - CO - (CH 2 ) 8 - CO] N Made of hexamethylenediamine and sebacic acid;

Polyamide 6T: [NH - (CH 2 ) 6 - NH - CO - (C 6 H 4 ) - CO] N Made of hexamethylenediamine and terephthalic acid;

Polyamide 6I: [NH - (CH 2 ) 6 - NH - CO - (C 6 H 4 ) - CO] N Made from hexamethylenediamine and isophthalic acid;

Polyamide 9T: [NH - (CH 2 ) 9 - NH - CO - (C 6 H 4 ) - CO] N Made from 1,9 nonanediamine and terephthalic acid;

Polyamide M5T: [NH - (C2 H 3 ) - (CH 3 ) - (CH 2 ) 3 ) - NH - CO - (C 6 H 4 ) - CO] N from 2-methyl-1,5-pentan Made from diamine and terephthalic acid;

Copolymer:

Polyamide 6/66: [NH-(CH2)6−NH−CO−(CH2)4−CO]n−[NH−(CH2)5−CO]m composed of caprolactam, hexamethylenediamine and adipic acid production;

Polyamide 66/610 [NH−(CH2)6−NH−CO−(CH2)4−CO]n−[NH−(CH2)6−NH−CO−(CH2)8−CO]m composed of hexamethylene Made from diamine, adipic acid and sebacic acid.

Characteristic

Polyamide is the earliest engineering thermoplastic. It has high tensile strength, impact toughness, good oil resistance, fatigue resistance, wear resistance and self-lubrication. It can be used as bearings, gears and other engineering machinery components. The disadvantages are low thermal deformation temperature, high hygroscopicity, and high creep property. The long-term use temperature must be lower than 80°C.

[Modification of polyamide compound]

Due to the strong polarity of polyamide, it has strong hygroscopicity and poor dimensional stability, but this can be improved through modification.

1) Glass fiber reinforced PA

By adding 10-50% glass fiber to polyamide, the mechanical properties, dimensional stability, heat resistance, and aging resistance of polyamide are significantly improved, and the fatigue resistance strength is 2.5 times that before it is not reinforced. The molding process of glass fiber reinforced PA is roughly the same as that without reinforcement, but because the flow is worse than before reinforcement, the injection pressure and injection speed should be appropriately increased, and the barrel temperature should be increased by 10-40°C. Since glass fiber will be oriented along the flow direction during the injection molding process, the mechanical properties and shrinkage will be enhanced in the direction of orientation, causing the product to deform and warp. Therefore, when designing the mold, the location and shape of the gate should be reasonable, and the process can be improved. After taking out the product, place it in hot water and let it cool slowly. In addition, the greater the proportion of glass fiber added, the greater the wear on the plasticizing components of the injection molding machine. It is best to use bimetallic screws and barrels.

2) Flame retardant PA

Since flame retardants are added to PA, most flame retardants are easy to decompose at high temperatures and release acidic substances, which have a corrosive effect on metals. Therefore, plasticizing components (screws, glue heads, rubber rings, glue rings, etc.) Gaskets, flanges, etc.) need to be hard chromium plated. In terms of technology, try to control the temperature of the barrel not to be too high and the injection speed not to be too fast to avoid discoloration of the product and a decrease in mechanical properties caused by decomposition of the rubber material due to excessive temperature.

3) Transparent PA

It has good tensile strength, impact strength, rigidity, wear resistance, chemical resistance, surface hardness and other properties. It has high light transmittance, similar to optical glass. The processing temperature is 300--315 ℃. During molding and processing, it needs Strictly control the barrel temperature. If the melt temperature is too high, it will cause discoloration of the product due to degradation. If the temperature is too low, the transparency of the product will be affected due to poor plasticization. The mold temperature should be as low as possible. High mold temperature will reduce the transparency of the product due to crystallization.

4) Weather-resistant PA

Adding UV-absorbing additives such as carbon black to PA greatly enhances PA's self-lubricity and wear on metal, which will affect cutting and wear of parts during molding. Therefore, it is necessary to use a screw, barrel, rubber head, rubber ring, and rubber washer combination with strong feeding capacity and high wear resistance.

The raw materials for the production of polyamide are mainly processed and refined from petroleum products. Due to different monomers, the production methods are divided into 3 categories: made from a monomer of lactam or amino acid, and subjected to a series of reactions such as hydrolysis, ring-opening, addition, and polycondensation under certain catalysts and temperature conditions. Such as nylon 6; it is synthesized from two monomers: dibasic acid and diamine, often using condensation polymerization and reduced pressure water removal methods, such as nylon 66; it is made from aromatic diamine and aromatic diformyl chloride through solution polymerization at low temperature. into, for example, poly(m-phenylene isophthalamide).

Due to its low melt viscosity, polyamide has good fluidity. Mainly used for injection and extrusion molding. According to needs, sintering and casting can also be used.