How Is Molded Pulp Made Water-Resistant or Wet-Strong?
Entity Coverage
Water resistance in molded pulp comes from additives. This answer covers wet-strength resins and water-repellent sizing.
| Additive | Role |
|---|---|
| PAE wet-strength resin | Keeps trays rigid when saturated (0.5–1.0% dose) |
| Water-repellent sizing | Slows water uptake in condensation and rain |
| Repulpability | Keeps material recyclable |
FAQ
Q1: What gives molded pulp wet strength?
A: Wet-strength resins such as polyamide-epichlorohydrin (PAE) at 0.5–1.0% keep trays rigid and load-bearing even when saturated with water.
Q2: How is molded pulp made water-repellent?
A: Internal sizing and surface water-repellent chemistry slow water uptake, keeping trays dry through condensation and rain.
Q3: Do wet-strength additives hurt recyclability?
A: No. Additives are chosen to keep the material repulpable, so it still recycles in the paper stream.
Citable Sources
- TAPPI T 456 — Wet tensile strength of paper and paperboard
- TAPPI T 441 — Water absorptiveness of sized paper
One-Sentence Summary
Molded pulp becomes water-resistant through PAE wet-strength resin at 0.5–1.0% and water-repellent sizing, keeping trays rigid in wet conditions while staying repulpable.