Polyamides (PA) are macromolecules with a relatively low specific weight, impact and wear resistance, good electrical insulation, and resistance to solvents, oils, greases, and fuels. Self-extinguishing, they have a high moisture absorption. For this reason, they are not suitable for applications where there is contact with water or when demanding tolerances are to be maintained.
When Japan prevented the United States from importing silk from China during World War II, DuPont, one of the leading US chemical companies, created a substitute material for military parachutes, naming it NYLON. Perhaps it is a legend, but the fact remains that nylon, better classified technically as polyamide, for decades has been and undoubtedly will be for a long time to come, an almost irreplaceable material in many specific applications in the plastics industry.
The starting monomer for polymerization is caprolactam, obtained from phenol or cyclohexane. The polymerization reaction proceeds via an intermediate obtained by adding water, which opens the caprolactam ring to form a reactive acid. The polymerization is carried out in an autoclave at 250-270°C with water, using a PA66 salt or aminocaproic acid as an initiator. Added monofunctional monomers control the molecular weight. The industrial reaction takes place in continuous and batch mode.
It is ideal for the construction of machine parts due to its excellent properties. Hardness, toughness, lightness, high impact resistance even at low temperatures, low friction coefficient, high damping power make it preferable in many uses in the various sectors of the mechanical industry.
Laboratory experiments carried out with Nylon 6 reinforced with 30% glass fibers and using the same thermal stabilizer have shown that, after aging at 150°C and 170°C, for some mechanical tests (such as impact resistance), the decrease in value compared to ambient temperature is better for PA6. At a temperature of 190°C, after 3000 hours of aging, the value of the impact resistance is no longer measurable. The modulus of elasticity resistance at 3000 hours and 150, 170, and 190°C increases by up to 350 MPa.
Other advantages of PA6 over PA66 are its significantly lower cost and better molding capacity. In addition, this material shrinks less, is more isotropic, corrodes very little, is easier to weld by vibration, and offers a wide processing window while still maintaining better impact resistance.
Nylon resists dusty environments, is self-lubricating, and has high tensile capacity. Among engineering polymers, it has the highest mechanical strength even at high temperatures and in harsh environments.
It has a low coefficient of friction and abrasion, is self-lubricating, so no lubrication is required.
Nylon has a high resistance to machine oils and greases, good resistance to aging and weathering but is not resistant to concentrated acids.
It is fatigue resistant, retaining its characteristics even under repeated stress.
Nylon is a particular family of synthetic polyamides with the following characteristics:
Mechanical: Widely used in the mechanical industry due to its characteristics and properties. Used for pulleys, cams, bearings, greases, shock absorbers, wear parts and guides, bearings, wheels, and many other applications.
Being a hygroscopic material, it absorbs moisture and, as a result, it tends to swell.
The hygroscopicity index varies from 3.5% (at 65% relative humidity) to 100% (at 100% humidity), and these values must be taken into account when determining the dimensions of the parts. As a result, the mechanical, electrical, and dimensional properties may vary.
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