Uneven Absorbency in a Cotton Poplin Lot
A unit receives 300 m of cotton poplin from a new supplier. The fabric is described as scoured and bleached, but no mercerisation record is supplied. Before printing, the printer runs a water-drop test: some areas wet out in 2 seconds, while others take 20 seconds. After printing a 5 m trial with a red pigment paste, pale patches appear in bands across the width, and the colour rubs off more in those areas after drying. The fabric also shows faint drying marks along both selvedges. Production is under pressure, and the supervisor suggests increasing binder in the paste to stop the crocking.
1. What is the most likely cause of the pale bands and crocking, and what tests would confirm it?
Read the worked answer
The 2-second versus 20-second wet-out times show uneven absorbency, which usually comes from uneven scouring, residual size, or drying water marks rather than from the pigment paste alone. The bands across the width and the selvedge drying marks support a preparation fault. Increasing binder would mask crocking on the surface but would not correct uneven penetration, and it could stiffen the fabric. I would confirm with a capillary rise test at several points, a pH check on the fabric, and a re-wetting test after a small laboratory scour. If the slow areas improve after re-scouring, the problem is preparation, not the paste.
2. Should the lot be printed as received? Give your decision and the conditions for proceeding.
Read the worked answer
I would not print the full 300 m as received. The trial already shows a visible defect and a fastness risk. I would either return the lot to the supplier with the test records or re-scour and dry it under controlled tension, then repeat the drop test and a 5 m print trial. The lot should proceed only if wet-out is uniform within a narrow band, the fabric pH is within the dye system's tolerance, and the washed trial meets the rub-fastness requirement. If only part of the lot is affected, I would cut out the banded sections rather than upgrade them by adding binder.
3. What incoming-goods controls would you set for future lots?
Read the worked answer
For each lot, record supplier, batch, claimed preparation route and mercerisation status. Run a wet-out or drop test at five points across the width and at the beginning and end of the piece, check pH, and retain a 0.5 m sample. Print a small trial with the actual paste before bulk release. Reject lots with wet-out times outside the agreed range or with visible drying marks. These records make it possible to price in re-treatment or to claim against the supplier instead of discovering the fault after printing.