Polyamide 66 (PA 66)
Polyamide PA 66 was synthesized for the first time in 1935, its production began in 1938. Polyamide PA 66 is a product of polycondensation of adypic acid and hexamethylenediamine (hexamethylene diamine adipate). It corresponds to the chemical formula ([-NH-(CH2)6-NH-CO-(CH2)4-CO-]n).
Polyamide PA 66 is distinguished in higher strength properties, high hardness and deformation stability, increased heat resistance. It belongs to the group of linear polyamides as well as Polyamide 6. High impact resistance, rigidity and hardness of Polyamide PA 66 can be increased by filling it with glass wool. Polyamide PA 66 has also good dynamic strength and cracking resistance. It is resistant to cyclic loadings and exhibits properties of sound and vibration isolation.
Polyamide PA 66 is distinguished in chemical and climate resilience. It is resistant to lubricants, oil products and organic solvents. Comparing to PA 6 Polyamide PA 66 has smaller degree of water absorption, exhibits higher heat resistance and better insulating characteristics. Melting temperature of Polyamide PA 66 is about 260 °C. Polyamide PA 66 is capable to hold its shape constantly at temperature up to 180 °C and temporary at 200 °C.
Polyamide PA 66 is widely applied in textile industry, in production of plastic of engineering and technical assignment in vehicle manufacturing, machine building industries, in electrical products, household appliances, sports equipment.
At the present time Polyamide 66 takes the second place on production volume. The general use of this polyamide is production of artificial fibers.
Modifications of Polyamide PA 66Modifications of Polyamide PA 66 are produced by adding various additives: glass fiber, mineral fillers, fire retardants and various modifying additives. They allow improving such properties as heat resistance, durability, rigidity, impact strength, to reduce water absorption and combustibility of materials.
Depending on modification the constructional Polyamide PA 66 can be classified as follows:
Basic unreinforced materials
Primary and modified Molding Polyamide PA 66 can be used both as constructional material and for the subsequent reinforcing. The material does not collapse at tests on Charpy impact strength without cut at -40 °C. The category of burning resistance for basic materials is PV-2, the resistance temperature at glow-wire tests is 750 °C.
Increase of impact resistance is reached by adding special additives – modifiers of impact strength. Density of impact-resistant materials is 1.06 - 1.10 g/cm³. These materials are characterized by freeze-thaw resistance (up to -60 °C) and are applied in vehicle manufacturing industry and at production of sports equipment. Impact-resistant materials with the lowered water absorption are intended for production of the parts of technical and household purpose which are used in the conditions of increased dynamic loads and impact shocks and also in friction units (without lubricant or if the quality of it is limited).
General technical assignment materials are applied at production of parts of the increased rigidity in vehicle manufacturing, aviation and furniture industries and also in the electrical engineering. Filling ratio is 10-50 %. The most distribution was gained by the materials which were filled with fiber glass by 30 %.
With increasing the content of fiber glass the shrinkage decreases and the following characteristics improve:
– density from 1.2 to 1.6 g/cm³;
– tensile strength from 110 to 230 MPa;
– load bending temperature (190 - 210 °C);
– dielectric strength (40 - 45 kV/mm).
These materials are resistant to kerosene, gasoline, benzene, mineral oils, alkalis, acids.
Glass-filled materials with the lowered water absorption retain operational qualities at lowered temperatures and increased humidity. They are applied in machine building and instrument making industries.
Polyamide 66 filled with minerals is characterized by isotropy of mechanical properties, heat resistance, size stability, low buckling and shrinkage, decorative appearance. Usually they are filled with talc, chalk, kaolin or mica. Filling ratio is 20 - 30 %. Mineral-filled Polyamide PA-66 is applied for production case and other industrial parts which require the increased accuracy of the sizes of molding products without additional machining and which are operated at various temperatures and ambient humidity. When processing they provide low wear of casting machines and equipment.
Materials filled with glass and minerals (totally 30 - 45%) retain all benefits of mineral-filled compositions exhibiting the increased rigidity. These materials are intended for production of the parts applied in machine building, vehicle manufacturing, electrical engineering and furniture industries, and also for production of consumer goods and other products.
Materials with the low coefficient of friction against steel 0.15 - 0.30 are produced by addition of molybdenum dioxide. Antifriction Polyamide PA 66 is produced in various modifications: reinforced by fiber glass and not reinforced. The most widespread products from antifriction materials are bearing cages, plugs, rollers, lock plates, slides, etc.
Materials containing fire-retardants (self-extinguishing, fire-resistant) are produced in various modifications: glass-filled, mineral-filled, with lowered water absorption. These materials are characterized by resistance temperature at glow-wire tests 960 °C and combustion resistance category PV-0. They are applied in instrument-making, electrical engineering industries and in the radio electronics.
High-viscosity Polyamide 66 is characterized by lowered density (up to 1.04 g/cm³), melt uniformity, high impact strength, elasticity, frost resistance, oil and benzine resistance, lowered water absorption, chemical resistance. The material is recommended to be processed by methods of direct extrusion, blown extrusion, coextrusion and injection molding.