White nylon has no dye in it, but it is one of the longest processes in the dye house: a scour, a reducing bath with the optical brightener at 98°C, a peroxide step and a final bath. Here is the full process from our floor, step by step.
At a glance
pH 4.5Brightening bath
98°C × 45Brightener hold
2°C/minHeating rate
4 bathsScour, brighten, peroxide, soften
Nylon greige is never truly white. It carries spinning oil and a slight yellow or grey cast, and nylon picks up yellowing easily. A white order is made white in two ways at once: the fabric is cleaned and cleared, and an optical brightener is put into the fibre. The brightener absorbs invisible ultraviolet light and gives it back as blue light, which cancels the yellow and makes the fabric look whiter than white.
The route for nylon white
Process flow: nylon white
- Scour: soda at 80°C for 20 minutes, then wash and neutralise with acid at 40°C.
- Reduction and brightening bath: auxiliaries at 50°C, pH 4.5 at 60°C, a reducing agent, then the optical brightener at 80°C and a 45-minute hold at 98°C.
- Peroxide step: hydrogen peroxide at 60–70°C for 15 minutes, then a hot wash.
- Softener at 50–70°C for 10 minutes, then wash and unload.
Step 1: scour
- Fill the machine and heat to 40°C. Inject the scouring and sequestering auxiliaries.
- Load the fabric. Dose the soda over 10 minutes.
- Heat to 80°C and run 20 minutes.
- Drain and wash 10 minutes.
- Neutralise with acid at 40°C for 10 minutes, then wash 10 minutes.
The scour is mild: 80°C, not the 95°C soda scour used before dyed nylon shades.
Step 2: reduction and optical brightening
- Fill and heat to 50°C. Dose the levelling agent and the auxiliaries.
- Heat to 60°C and check the pH: 4.5.
- Inject the reducing agent (sodium hydrosulphite, hydrose). Run 5 minutes and check the pH again: 4.5.
- Heat to 80°C at 2°C per minute.
- Dose the optical brightener over 30 minutes and run 5 minutes.
- Heat to 98°C at 2°C per minute and run 45 minutes.
- Cool to 78°C, drain and wash 10 minutes.
The reducing agent goes in first, in the same bath, so the yellow cast is cleared before the brightener goes on. The brightener is dosed slowly at 80°C and fixed into the nylon at 98°C.
Tip: check the pH twice: once before the reducing agent and once after it. The brightener is applied at pH 4.5, and the reducing agent can move the pH.
Step 3: peroxide
- Fill and heat to 60°C. Dose the hydrogen peroxide and run 5 minutes.
- Heat to 70°C and run 15 minutes.
- Drain. Normal hot wash at 70°C for 10 minutes, then wash 10 minutes.
The brightener goes on first, under controlled conditions. The peroxide step after it is kept mild, at 60–70°C for only 15 minutes, because harsh peroxide conditions can degrade the optical brightener and lower the whiteness.
Step 4: softener
- Fill and heat to 50°C. Inject the softener.
- Heat to 70°C and run 10 minutes.
- Wash and unload.
The final auxiliary is usually a softener, often a cationic or silicone type, depending on the recipe.
What to watch on white nylon
- pH. The brightening bath runs at pH 4.5; check it before and after the reducing agent.
- Heating rate. 2°C per minute up to 80°C and 98°C, so the brightener goes on evenly.
- Heat in finishing. Nylon yellows at high temperature, which undoes the brightening. Keep finishing at 110°C on the stenter, as for dyed nylon.
See the 100% nylon dyeing process for dyed shades.
The common complaint on white nylon is yellowing, or not enough whiteness. The first fix is to check the brightener dosage, the bath pH, the temperature and the peroxide conditions before adding more chemicals.
Textile engineer with 14+ years in dyeing and fabric development. He writes every guide on Dyeing Solution from real production work. Full profile