# Heat-Sensitized Gelation

Human page: https://retifist.com/literature-reviews/liquid-heat-sensitized-gelation

> **Safety.** Ammonium nitrate sensitizer added just before use; avoid entraining air.[^2] Heat plus closed mould: burn/scald risk. No Cu/brass in latex contact.

## Executive summary

Heat-sensitized compounds gel in **heated closed moulds**. Slush: fill, dwell, pour out.[^1] Rotational: meter + rotate for uniform walls.[^1] Kaysam example: ~4 min @ 82 °C gel, leach, supported dry, cure.[^2] Dry completely before vulcanizing; moisture causes blisters.[^3]

Use after [Former dip, mould cast, and flat spread](/literature-reviews/liquid-former-dip-vs-mould-cast-vs-flat-spread). Coagulant on a former is a different trigger: [Coagulant dipping](/literature-reviews/liquid-coagulant-dipping-wearable-thickness).

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## Heat-gel vs coagulant-gel

| Mechanism | Trigger | Hardware |
| --- | --- | --- |
| Coagulant | Coacervant on former | Dip tank, leach |
| Heat-sensitized | Mould temperature + sensitizer | Closed metal mould, rotation |

Plaster moulds gel by water absorption + Ca²⁺ diffusion, not heat sensitizer.[^1]

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## Kaysam industrial cycle

Fill closed mould; biaxial rotation; heat to gel (~4 min @ 82 °C); cool; demold wet gel; leach running water; dry supported; warm-air cure. Sensitizer (20% ammonium nitrate solution) added just before use.[^2]

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## Slush on metal

Heat-sensitized NR in metal moulds preheated 90–100 °C; gel 2–5 min depending on deposit. Zn-ammine (ammonium acetate) or PVME sensitizer packages.[^1]

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## Rotational casting

Metered compound; rotation while heating. Magnesium moulds preferred over aluminum for alkaline corrosion resistance in balloon-class processes.[^1]

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## Decision cues

```text
Closed hollow cavity + metal mould? → heat-sensitized slush or rotational
Need wall uniformity? → prefer rotational (if equipment exists)
Plaster one-off? → absorption gel branch (forming article), not metal slush
Have supported dry + leach? → if no, do not scale gel time alone
```

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<details>
<summary>Deep dive: Kaysam timings</summary>

Biaxial rotation; ~4 min @ 82 °C gel; cool 2–5 min @ 15 °C; leach 15–27 °C; dry 82 °C ≥3 h supported; cure 104 °C 20–60 min (thickness-dependent).[^2]

</details>

<details>
<summary>Deep dive: Slush formulation classes</summary>

Industrial NR slush: zinc-ammine or PVME in metal moulds preheated 90–100 °C. Nonionic ethoxylates stabilize ZnO/ammonia systems at ambient.[^1]

</details>

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## Endnotes

[^1]: *Polymer Latices Vol 3 — Application of Latices* — §23.3 slush vs rotational; plaster vs metal gel; slush formulation classes; rotational balloon mould materials.
[^2]: Vanderbilt Latex Handbook — Kaysam cycle (Ch 19).
[^3]: Vanderbilt Latex Handbook — dry before cure (Ch 19).