Most questions we get about rebonded foam production are not really about the adhesive — they are about the numbers around it. How much binder per kilogram of shredded foam? How long before the block can leave the press? Why did the last batch crumble at the corners? This article puts the actual process figures for our rebond binders (H-2301 and H-2401) in one place, so you can compare them against whatever you are running now.
What a Rebond Binder Actually Is
Rebonded foam ("rebond") is made by coating shredded polyurethane foam scrap with a reactive binder, compressing the mix in a mould, and curing it into a block that is then peeled or cut into sheets — carpet underlay, gym mats, packaging and mattress bases are the usual end products.
The binder itself is a single-component MDI prepolymer: a light brown, transparent liquid that cures with moisture, not with a second component. That matters on the line — there is no mix ratio to hold, but there is a moisture and temperature window to respect.
The Numbers: H-2301 vs H-2401
| Property | H-2301 | H-2401 |
|---|---|---|
| Type | 1K MDI prepolymer, moisture-cure | |
| Appearance | Light brown transparent liquid | |
| Viscosity (mPa·s) | 110–160 | 80–120 |
| Solid content | 70±2% | 65±2% |
| Open time | 25–30 min | |
| Cure, room temperature | 3–5 h | |
| Cure, steam at 120°C | 10–14 min | |
| Minimum operating temperature | ≥20°C | |
| Packaging | 25 kg plastic drum / 220 kg galvanized drum | |
| Shelf life | 6 months, sealed | |
The two grades differ mainly in viscosity and solids. The lower-viscosity H-2401 wets out fine shred and dense mixes faster; H-2301 carries more solids per kilogram applied. Which one suits you depends on your shred size and target density — send us both and we will say so plainly.
Add-On Rate: 8–15%
Binder add-on is calculated on the weight of foam scrap, and the working range is 8–15%. Two practical rules:
- Low density, coarse shred → lower add-on. Underlay around 60–80 kg/m³ typically runs near the bottom of the range.
- High density or fine shred → higher add-on. More surface area needs more binder; starving a fine-shred mix is the most common cause of crumbling edges.
Blocks can be produced across a density range of roughly 40–120 kg/m³ depending on compression and recipe — the binder is not the limiting factor there; the press and the shred are.
Steam Cure vs Room-Temperature Cure
Both routes work; they trade speed against equipment:
- Steam at 120°C: 10–14 minutes in the mould. This is the high-throughput route — moisture and heat arrive together, which is exactly what a moisture-cure prepolymer wants.
- Room temperature: 3–5 hours, provided the shop is at 20°C or above. Below that, cure slows sharply and green strength suffers — winter production halls are the usual culprit when "the same recipe" suddenly underperforms.
Either way, give finished blocks about 24 hours of aging before peeling or cutting. Cutting too early is the second most common cause of ragged cell structure after binder starvation.
Storage Habits That Save Batches
Because the binder cures with moisture, the enemy is humid air in a part-used drum. Reseal drums immediately after dosing; for drums that will stand longer, blanket with dry nitrogen. A skinned-over surface layer means moisture got in — do not stir the skin back into the liquid.
FAQ
Is rebond binder the same as ordinary PU wood glue?
No. Wood glues are formulated for rigid substrates and thin bond lines. A rebond binder must coat a huge surface area of flexible shred at low viscosity and cure through the block's thickness — different chemistry balance, different viscosity, different solids.
Can I run rebond binder below 20°C?
We do not recommend it. Cure time stretches well beyond the 3–5 hour window and block strength becomes inconsistent. Heat the hall or use the steam route.
What density can I reach?
Roughly 40–120 kg/m³ across the normal recipe range. Density is set by compression and shred, with add-on trimmed to match — not by pushing more binder.
How is it supplied?
25 kg plastic drums or 220 kg galvanized iron drums, with a 6-month sealed shelf life. TDS and samples are available before any bulk order.
For the full application picture — press types, shred preparation and grade selection — see our rebonded foam adhesive application guide, or go straight to the rebond binder product page to request a TDS.
