Wacker Catalyst T 21® – Catalyst for ELASTOSIL® M Condensation Silicones & PU and Epoxy Casting
Wacker Catalyst T 21® – Catalyst for ELASTOSIL® M Condensation Silicones & PU and Epoxy Casting
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Variant: 50 gram bottle of WACKER® Catalyst T-21
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Standard condensation-cure catalyst for PU- and epoxy-resistant silicone moulds
Wacker Catalyst T 21 is the standard catalyst (Part B) for the condensation-cure ELASTOSIL® M silicone rubbers for mould making: Elastosil M 4511, M 4512, M 4514 and M 4541. This colourless, low-viscosity catalyst based on an organotin compound has a density of 0.96 g/cm³ and a dynamic viscosity of 15 mPa·s at 23 °C. According to Wacker, T 21 gives excellent chemical resistance to polyurethane resins, which considerably extends the service life of the mould. For Elastosil M 4514, Wacker also specifies T 21 for casting epoxy. The standard dosage is 5% by weight of Part A (ratio 100:5). At a 5% dosage in Elastosil M 4514, the pot life is approximately 60 to 90 minutes and the demoulding time 8 to 12 hours at 23 °C and 50% relative humidity.
Key Benefits
- Dosage 5% (100:5) – a fixed weight ratio to Part A that is easy to measure, for reliable curing.
- Excellent PU resistance – Wacker positions T 21 for a high number of casts in polyurethane casting resin.
- Also for epoxy – with Elastosil M 4514, the specified catalyst for casting epoxy resins.
- Density 0.96 g/cm³ and viscosity 15 mPa·s – very thin and mixes quickly into the base component.
- Can be blended with Catalyst T 47 – at 95:5 (T 21 : T 47) the pot life drops to 20 to 40 minutes and the mould can be demoulded after 4 to 6 hours; at 90:10 the pot life is approximately 20 minutes and the demoulding time 2 to 4 hours.
- Colourless – the catalyst does not discolour the mould.
Typical Applications
- Curing Elastosil M 4511, M 4512, M 4514 and M 4541 condensation-cure silicones.
- Mould making for casting polyurethane casting resin.
- Mould making for casting epoxy resins.
- Catalyst for our Silicone Condensation 20 Resin, which is supplied with T 21 as standard.
- Blending with Catalyst T 47 for faster curing in time-critical production.
Processing Instructions
- Stir the condensation-cure silicone (Part A) thoroughly before use to redistribute any settled material.
- Weigh out the catalyst at 5% of the weight of Part A, i.e. 5 grams of T 21 per 100 grams of silicone. You can use 0.5% less or more: less extends the cure (more time for de-airing), more speeds it up but increases shrinkage. Never use too little catalyst, otherwise the silicone will not cure (properly).
- For faster curing you can blend T 21 with Catalyst T 47, for example in a 95:5 ratio (per 100 grams of Part A: 4.75 grams of T 21 with 0.25 grams of T 47).
- Mix the catalyst carefully and evenly into the silicone, scraping the sides and bottom of the mixing container. T 21 is colourless, so you cannot tell from the colour when the catalyst is evenly distributed; mix generously for that reason.
- Use the mixture within the pot life and never mix more than you can process within the pot life.
- Do not demould until the silicone has fully cured.
Please note: pot life (working time) and demoulding time depend strongly on the mix ratio and the humidity. With more catalyst or higher humidity, both pot life and demoulding time become shorter. Below 40% relative humidity the silicone surface may remain tacky; in that case, increase the humidity in the room.
Casting epoxy: Wacker recommends post-curing condensation-cure moulds for epoxy for a few hours at approximately 150 °C before first use. Casting polyester? Then use Catalyst T 51, which Wacker developed specifically for polyester resins. You will find more information on the right combination under silicones for aggressive resins.
Wacker Chemie AG is the global market leader in the development and production of silicones for industrial and technical applications.
Shelf life: when stored dry and cool in sealed packaging, the shelf life is at least the period stated on the label. Exceeding this period does not automatically make the product unusable; in that case, check its properties before use.
This product is intended for the business market. For larger quantities or custom products, please contact us at info@siliconesandmore.com.
Professional Support
Undecided between T 21 and T 51, or unsure about blending with T 47 for faster curing? Our specialists will gladly advise you on the best catalyst combination for your resin and application. Please do not hesitate to contact us.
Application
- Use caseCatalyst for ELASTOSIL M condensation silicones, optimized for polyurethane and epoxy castingIntended use
- Silicone type["Auxiliary material"]Type of silicone or polymer
- Cure conditionRoom temperatureCondition under which the material cures
Safety Information
Wacker Catalyst T 21 contains an organotin compound and may cause damage to organs through prolonged or repeated exposure (H373). Signal word: Warning. When processing, wear protective gloves made of butyl rubber (thickness greater than 0.3 mm), safety glasses and protective clothing, and work in a well-ventilated area. If mist or spray is formed, use a combination filter ABEK-P2. Dispose of contents and packaging via an approved waste disposal company. Always consult the safety data sheet for the complete safety information.| Safety Pictograms | Safety Data Sheets (SDS) |
|---|---|
GHS hazard pictograms
Required protection (ISO 7010)
    |
| Signal Word | H‑code | Hazard Statement | P‑codes | P‑statements |
|---|---|---|---|---|
| Warning | H373 | May cause damage to organs through prolonged or repeated exposure | P260 P501 |
|
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