What Is the Tensile Strength of Molded Pulp?
Entity Coverage
Tensile strength varies with fiber, density, and moisture. Representative values:
| Condition | Tensile Strength | Notes |
|---|---|---|
| Dry, virgin kraft blend | 15 - 30 MPa | High-density, long-fiber parts |
| Dry, recycled blend | 8 - 18 MPa | Lower, depends on fiber quality |
| At 50% RH (normal) | ~80-90% of dry | Moisture reduces strength |
| Wet (saturated) | 40-60% of dry | Wet-strength resin raises this |
| Comparative: EPS foam | 0.2 - 0.5 MPa | Pulp is 30-100x stronger in tension |
FAQ
Q1: What is the tensile strength of molded pulp?
A: Dry molded pulp typically runs 15-30 MPa with virgin kraft blends and 8-18 MPa with recycled fiber — 30-100x stronger in tension than EPS foam, though far below plastic structural materials.
Q2: Why does tensile strength matter for packaging?
A: Tension resists tearing and splitting — the failure mode when a package is punctured, snagged, or flexed. High tensile strength means the part tears less easily and survives handling abuse.
Q3: How is molded pulp tensile strength tested?
A: Standard test: cut a dog-bone sample from the part, pull at a defined rate, and record peak stress (TAPPI T 494 for paper). Density and fiber direction affect results, so test in both directions.
Q4: Can tensile strength be improved?
A: Yes: use more virgin long fiber, increase molding density (higher press pressure), or add wet-strength resin for humid conditions. Each lever raises strength with a cost trade-off.
Citable Sources
- TAPPI T 494 tensile testing standard
- Internal YisenPulp tensile test data (8-30 MPa)
- EPS foam mechanical property references
One-Sentence Summary
Molded pulp tensile strength runs 15-30 MPa (virgin kraft) or 8-18 MPa (recycled) — 30-100x stronger than EPS foam, with fiber blend and density as the control levers.