Nylon PA

Nylon is polyamide, or PA, extruded and drawn into monofilament. It is used in more of our brushes than any other fill, in hand brushes, tube brushes, rollers, strips, discs and floor brushes, because it does three things well at once. It bends and springs back many thousands of times without breaking, which is what makes a brush keep scrubbing. It wears slowly against most soils. And it can be drawn in a very wide range of diameters, from about 0.08 mm to 2.5 mm, so one material covers soft dusting and hard scrubbing.

The trade-off is water. Most nylons absorb some water, and absorbed water makes them softer. How much depends on the grade, which is why the grade matters more than the word “nylon”.

The heat figures are the continuous and short-term limits published for nylon brush filaments by grade. The finished brush has its own limits, set by the block, handle and anchoring as well as the fill.

It softens it. Nylon 6 takes up about 1.5–3.0% water in 24 hours (ISO 62), and PA6 and PA66 can hold 7–10% at saturation. The water acts like a plasticizer: the filament gets softer and recovers more slowly, so a brush that feels firm on the shelf can feel limp after an hour in a wash tank. It dries out and stiffens again afterwards.

For jobs that are always wet, there are two ways round it. Use a long-chain nylon, PA610 or PA612, which takes up far less water. Or move to PBT or PP, which take up almost none. For dry or occasionally wet work, PA6 and PA66 are the better value.

Nylon resists water, oils, greases, fuels, most solvents, mild detergents and dilute alkalis. That covers most cleaning. It is attacked by strong mineral acids, such as concentrated hydrochloric and sulfuric acid, by phenols and by strong oxidizers. So nylon belongs ahead of the acid on a pickling line, in the alkaline degreasing section or the neutral rinse, not in the acid bath; PP or PBT go there. With any cleaner, the concentration, temperature and contact time decide the result, so give us all three.

With filament diameter and trim length, more than with the grade. Stiffness rises steeply with diameter and falls steeply with trim length, so a 0.6 mm filament on a 15 mm trim is far harder than a 0.3 mm filament on a 30 mm trim, in the same nylon. Density, the number of tufts and filaments per area, adds to it. Choose the surface first: fine, long fill for polished or soft surfaces, coarse, short fill for textured surfaces and set-on soil. Nylon can also be crimped, which gives a wavy filament that holds water and soil in the fill and feels softer, or loaded with abrasive grit for cutting.

• Nylon: the best wear life and bend recovery for dry and mixed work, and the widest range of sizes.
• PBT: nearly as springy, takes up almost no water, so it keeps its stiffness in wet and washdown work.
• PP: the lowest cost, takes up no water and resists acids, but wears faster and softens sooner in heat.

Where heat goes beyond what nylon takes, the next step is a high-temperature polymer such as PPS or PEEK, or wire.

• The job and the surface, and whether the brush works dry, wet or in hot water.
• Cleaners or chemicals, with concentration and temperature.
• Filament diameter and trim, if you know them, or a sample to match.
• Any food-contact or other material requirement, so the grade and evidence are agreed before sampling.