Polyamide PA, PA66 (Nylon)
Polyamide is the most widely used fibre for making high-quality ropes from synthetic materials. It has been used for a long time and its properties are well understood. It is widely available and generally considered robust and an excellent material for manufacturing rope. Polyamide is abrasion-resistant, pretty strong and very elastic. This makes nylon ideal in applications where energy absorption is a requirement, for example dynamic ropes are made entirely from polyamide. Polyamide can be heated and permanently formed – a property that is used during thermofixing. Polyamide fibres are also widely used to make static ropes, although material types with less stretch are chosen. The disadvantage with polyamide is that it absorbs a comparatively high amount of water, which can cause it to shrink if it gets wet. It also becomes substantially heavier and loses strength when wet.
Main Types: Nylon (PA 6.6) from DuPont and Perlon (PA 6)
Polyamide – PA
Polyester – PES
Polypropylene – PP
| PA 6.6 | PES | PP | |
| Specific strength (N/tex) | 0.8 | 0.9 | 0.7 |
| Specific weight (g/cm3 ) | 1.14 | 1.38 | 0.91 |
| Melting temperature (°C) | 255 | 250 | 160 |
| Water absorption (%) | 3.5 – 4 | 0.4 | 0 |
| Material stretch | high | medium | medium |
| UV resistance | average | very good | very good |
| Abrasion resistance (dry) | very good | good | satisfactory |
| Abrasion resistance (wet) | satisfactory | good | satisfactory |
| Resistance to acids | low | very good | very good |
| Resistance to alkalis | good | good | very good |
Technical comparisons of PA6 and PA66
- The number of units within the polymer chains of nylon 6 and 66 is 130 and 65 respectively.
- Both iterations comprise weak basic amino acids and acidic carboxylic acid end groups.
- They are both strong fibres of moderate elasticity, even after being drawn.
- Both nylons have high tenacity variants that are applied to industrial applications, and both have multiple strands of property definitions based on changes in polymerisation and drawing conditions.
- Nylon 6 has a lower elastic modulus and better elastic recovery and therefore provides softer, more flexible fabrics.
- At higher temperatures, like 180°c, nylon 6/6 shows markedly better heat age strength at 11.5kg, compared to nylon 6 of only 2.5kg.
- The fibres of nylon 66 are 33% more resistant to abrasion than nylon 6, withstanding up to 60,000 cycles compared to 40,000 in the case of nylon 6.
- With low creep, and more crystallinity, nylon 66 is slightly more rigid, allowing good stretch recovery and higher abrasion resistance.
Why we talk about PA6 and PA66 is because there are still a lot of fabric and webbing made of PA when PA66 is slightly better for climbing and rigging applications.
Marlowropes.com – material-types/
Honor-safety.nl – Static Ropes Handbook
Ropelab.com.au – Physics