A portable urinal bag is a difficult product to make well because it combines a thin film, a fixed powder charge and a user who may be elderly, in a car, or in a tent at night. Converters who buy powder on “high absorbency” alone usually discover the problem at the filling line, not in the field.
The seven numbers
| Parameter | Target for a 750 ml bag | Why it matters |
|---|---|---|
| Absorption in synthetic urine | 28–35 g/g | Sets the charge weight and the bag’s usable volume |
| Median particle size (D50) | 180–260 µm | Fill accuracy and speed of wetting |
| Fines below 106 µm | Under 5 percent | Dust at the filler, rafting on the liquid surface |
| Moisture content | Below 8 percent | Caking in the sachet over 18 months |
| Bulk density | 0.65–0.75 g/cm³ | Volumetric fill tolerance on automatic lines |
| Free-swell time to no free liquid | Under 60 seconds | The user’s expectation of “it worked” |
| Gel strength (compression) | Firm enough to resist folding | Bag carried in a pocket or bag |
Where the specification usually goes wrong
Absorption is the number buyers ask for and the least useful in isolation. A grade at 40 g/g in deionised water may deliver 22 g/g in urine, because the measurement conditions differ. Always specify absorption in a synthetic urine formulation — usually a solution of urea, sodium chloride and calcium chloride at pH 6 — and name the method in the purchase order.
The second failure is fill tolerance. A volumetric filler calibrated for 0.70 g/cm³ will overfill by 7 percent if the next lot arrives at 0.75 and underfill by the same margin in the other direction. On a 9 g charge that is 0.6 g, enough to turn a firm bag into a sloshing one. Either specify a density window and accept lot certification, or move to gravimetric filling.
Dust is a production problem before it is a user problem
Fines below 106 microns do two things on a vertical form-fill-seal line: they coat the seal jaw and cause weak seals, and they hang in the air above the filler. A 5 percent fines limit and a de-dusting step at the supplier will do more for your reject rate than any downstream inspection.
Bag design interacts with the powder
A 750 ml bag with 9 g of powder and 700 ml of urine produces a gel that fills roughly 850 ml. If the bag’s nominal capacity is honest, that is fine; if the nominal figure is measured to the brim, the seam will fail when the bag is folded. Specify a fill line at 80 percent of the sealed internal volume and print it on the film.
Film choice matters too. A 70 micron coextrusion with a nylon tie layer holds a firm gel through a 24-hour carry. A 45 micron PE bag will not, and no amount of powder fixes a 45 micron seam.
Contract clauses worth adding
- Lot certification for all seven parameters, with the test method named.
- Maximum 5 percent deviation on bulk density between lots.
- A 500 g retention sample held for 24 months, available on request.
- Declaration of residual monomer and a current safety data sheet per shipment.
A note on limits: no powder specification can rescue a bag whose seam is under-welded, and no absorption figure survives a user who fills the bag to the neck. Set the film and the fill line first, then buy powder against them. Our urinal-bag SAP grades are supplied with density and particle-size certificates written for form-fill-seal converters.
Da maohua
Zhengzhou Flor New Materials Co., Ltd. specializes in SAP super‑absorbent polymer products. Serving personal hygiene, agriculture & horticulture, pet supplies and other industries, we leverage supply‑chain resources to provide particle‑size selection, performance matching and customized solutions based on clients’ practical requirements.
