Properties of Nylon: A Complete Guide to Polyamide Fibers

What Is Nylon? Key Properties at a Glance

Nylon is a synthetic polyamide polymer known for its exceptional strength-to-weight ratio, high tensile strength (75–90 MPa), abrasion resistance, and chemical resistance. Developed by Wallace Carothers at DuPont in 1935, nylon was the first commercially successful synthetic polymer and remains one of the most widely used synthetic fibers worldwide. Its key properties include a melting point of 265°C (509°F) for Nylon 6,6, moisture regain of approximately 4.5%, and an excellent balance of mechanical performance and processing flexibility that makes it suitable for applications ranging from textile manufacturing to engineering plastics.

Nylon belongs to the polyamide family of polymers, characterized by repeating amide groups (-CONH-) in the polymer backbone. The two most common types—Nylon 6,6 and Nylon 6—dominate the synthetic fiber market and are distinguished by their chemical structure, melting points, and manufacturing processes.

Property	Nylon 6,6	Nylon 6
Melting Point	265°C (509°F)	220°C (428°F)
Density	1.15 g/cm³	1.13 g/cm³
Tensile Strength	75–90 MPa	70–85 MPa
Moisture Regain (20°C, 65% RH)	4.5%	4.0%
Degree of Polymerization	100–180	100–180
Molecular Weight	15,000–30,000 Da	15,000–30,000 Da
Monomers	Adipic acid + Hexamethylene diamine	Caprolactam
Polymerization Type	Condensation	Ring-opening

Quick-Reference: Key Nylon Specifications

First commercial synthetic polymer — invented 1935 by Wallace Carothers at DuPont
Tensile strength — 75–90 MPa (fibers); comparable to many metals at a fraction of the weight
Melting range — 220°C to 265°C depending on type (Nylon 6 vs. Nylon 6,6)
Moisture absorption — 4–4.5% regain at standard conditions (20°C, 65% RH)
Chemical resistance — resistant to hydrocarbons, ketones, and esters; attacked by strong acids and phenols
Tenacity — 5.0–8.0 grams per denier (excellent for synthetic fibers)

Polyamides

Polyamides are a class of polymers characterized by an amide group (-CONH-) repeating in the polymer backbone chain. The molecular structure consists of repeating units linked by peptide bonds, creating strong intermolecular forces. They are widely known by the trademarked term “Nylon,” which refers specifically to aliphatic polyamides with thermoplastic properties and a silky texture. Polyamides are used extensively in textile manufacturing, engineering plastics, and industrial applications due to their exceptional strength-to-weight ratio and chemical resistance.

Nylon in Textile Manufacturing

When less than 85% of amide linkages attach directly to two aliphatic groups, the resulting polyamides are classified as Nylon. This includes Nylon 6 and Nylon 6,6, which dominate the synthetic fiber market. Aromatic polyamides, where at least 85% of amide linkages connect directly to two aromatic rings, are classified as Aramid fibers and possess distinct thermal properties. Aramid fibers such as Kevlar and Nomex degrade without melting and cannot be melt-spun, making them unsuitable for conventional textile processing methods used for aliphatic nylons.

Invention

Wallace Carothers, inventor of nylon synthetic polymer at DuPont — Wallace Carothers, DuPont Research Director

Nylon holds the distinction of being the first commercially successful synthetic polymer in industrial history
Wallace Carothers, research director at DuPont, invented both synthetic rubber and nylon through condensation polymerization in 1933
DuPont’s polymer research program began in 1927, spanning an eleven-year development period
The first Nylon 6,6 was produced on February 28, 1935 at the DuPont Experimental Station in Wilmington, Delaware
The patent was obtained in 1938, with the first commercial application in toothbrushes
Nylon stockings debuted commercially in 1940, selling 4 million pairs within hours of launch
DuPont recouped the entire Nylon 6,6 plant investment within 30 days of startup—unprecedented in the chemical industry

Nomenclature and Classification

Nylon polymers form primarily through condensation polymerization, where monomers with carboxylic acid and amine groups react, releasing water molecules as a byproduct. Ring-opening polymerization represents an alternative synthesis route, particularly for Nylon 6 production from caprolactam monomer. The polymerization reaction conditions, including temperature, pressure, and catalyst selection, determine the resulting polymer’s molecular weight and mechanical properties.

Nylons are classified using a numerical system based on their monomer composition:

Chemical formation and polymerization of nylon through condensation reaction

Nylon 6,6

Nylon 6,6 (polyamide 6,6) forms from the condensation of adipic acid and hexamethylene diamine. Both monomers contain exactly 6 carbon atoms in their molecular chains, giving Nylon 6,6 its numerical designation. The balanced equimolar ratio of the two monomers produces a highly regular polymer structure with a melting point of 265°C (509°F). Prior to its formal nomenclature, Nylon 6,6 was known by the internal DuPont code name “Fiber 66.” The polymer’s density is 1.15 g/cm³, and its tensile strength ranges from 75 to 90 MPa in fiber form.

Nylon 6

In 1938, Paul Schlack of IG Farben in Germany polymerized caprolactam to create Nylon 6 (polyamide 6). Unlike Nylon 6,6, which uses two different monomers, Nylon 6 is a homopolymer formed by ring-opening polymerization of a single monomer. The resulting polymer structure contains 6 carbon atoms per repeating unit. Nylon 6 exhibits a lower melting point of 220°C (428°F) compared to Nylon 6,6 due to differences in hydrogen bonding capability between the polymer chains.

The degree of polymerization for Nylon 6 and Nylon 6,6 ranges between 100 to 180, with an average molecular weight between 15,000 and 30,000 daltons. Higher molecular weights produce superior mechanical properties but increase melt viscosity, requiring careful processing control.

Spinning Process for Nylon Fiber Production

Nylon fibers are produced through melt spinning, where the polymer is heated above its melting point to form a viscous melt that extrudes through spinneret holes. The extruded filaments are then cooled, drawn, and oriented to align polymer chains along the fiber axis, achieving the strength characteristics required for textile applications.

Melt spinning process diagram showing polymer extrusion cooling and drawing stages for nylon fiber manufacturing

Chemical Properties of Nylon

The chemical behavior of nylon stems from the polar amide (-CONH-) groups in the polymer backbone. The carbonyl oxygen carries a partial negative charge while the imino hydrogen carries a partial positive charge, creating dipolar interactions that significantly influence the polymer’s swelling behavior, dye affinity, and moisture absorption characteristics.

Swelling and Solvent Interactions

Amide group structure showing dipolar character and polar nature of polyamide polymers

The polar amide group in nylon attracts water molecules and polar solvents, causing the polymer to swell. This property directly influences dye uptake during textile processing, as nylon fibers dye readily with disperse dyes and metallized dyes due to the availability of hydrogen bonding sites. The moisture regain of nylon 6,6 at standard conditions (20°C, 65% RH) is approximately 4.5%, significantly higher than polyester.

Melting Behavior and Thermal Properties

The melting temperature of nylon polymers varies based on three primary structural factors: the ratio of amide groups to methylene groups, hydrogen bonding capability between chains, and the presence of aromatic rings or side chains in the polymer backbone.

Effect of Amide-to-Methylene Ratio

Peptide bond showing partial double bond character and planar structure affecting polymer chain flexibility

Hydrogen Bonding Effects

Interchain hydrogen bonds between amide groups provide the primary cohesive force in nylon polymers. The number of methylene groups between amide linkages, and whether that number is odd or even, significantly affects crystallinity and melting point. When the number of methylene groups is even and chain orientation is anti-parallel, complete hydrogen bonding occurs. Nylon 6,6 achieves complete hydrogen bonding due to its even-numbered methylene sequence, while the odd-numbered sequence in Nylon 6 results in slightly lower crystallinity and a melting point approximately 45°C lower than Nylon 6,6.

Hydrogen bonding arrangement in polyamide 6 showing antiparallel and parallel chain orientations — Fig: Hydrogen bonded sheet of PA 6 with antiparallel (A) and parallel (B) orientation of amide groups

Converting from parallel to anti-parallel chain alignment in odd-methylene nylons requires full chain inversion, whereas even-methylene nylons achieve this reorientation through lateral segmental movement only. This structural difference explains why Nylon 6 has a lower melting point than Nylon 6,6 despite similar chemical composition.

Side Chain Introduction

Branching or side chain introduction into the carbon skeleton disrupts regular chain packing and interferes with intermolecular amide hydrogen bonding. This structural irregularity reduces crystallinity, lowers melting temperature, and increases solubility in organic solvents. Copolyamides with controlled side chain content are engineered for specific processing requirements where lower melt viscosity is beneficial.

Aromatic Ring Incorporation

Connecting amide groups directly to aromatic rings (as in aramid polymers) creates chain stiffening through resonance stabilization and steric constraints. Aromatic polyamides (aramids) exhibit melting points exceeding 500°C and decompose without softening, necessitating solution spinning rather than melt processing. Kevlar, a para-aramid, degrades at approximately 450°C without melting.