Name: HMDI Aliphatic PU Sealant Prepolymer
Brand: Coatingsink
SKU: hmdi-prepolymer-aliphatic-sealant
Availability: PreOrder

Question 1

Why is H12MDI preferred over TDI for facade and curtain-wall sealant applications?

Accepted Answer

H12MDI (4,4'-methylenebis(cyclohexyl isocyanate)) is a fully saturated aliphatic diisocyanate. Unlike aromatic TDI, its urethane linkages lack UV-reactive conjugated systems, so the cured sealant resists photooxidative yellowing and chalk formation over years of weathering. This makes it suitable for exposed glazing joints and light-colored facade panels where color stability is a specification requirement.

Question 2

What crosslinker systems are compatible with this HMDI prepolymer for a two-component sealant formulation?

Accepted Answer

For a 2-component system, polyether polyols (e.g., PPG-triol, OH value 28–56 mg KOH/g) or polyester polyols with Mn 1,000–3,000 g/mol are suitable curatives. Target an NCO:OH index of 1.05–1.15 to ensure full cure with minimal residual isocyanate. Avoid amine curatives unless extended open time is required, as they significantly accelerate gel time and may reduce elongation.

Question 3

How does the higher viscosity of this aliphatic prepolymer affect sealant processing versus aromatic grades?

Accepted Answer

The elevated viscosity (35,000–55,000 mPa·s at 25°C) reflects the higher molecular weight of the H12MDI backbone. For gun-grade application, warming the prepolymer to 40–50°C reduces viscosity to a workable 8,000–12,000 mPa·s range. Heated drum follower plates or drum heaters are recommended for production scale. Do not exceed 60°C during heating to avoid accelerated moisture ingress and premature NCO consumption.

NCO Content	2.8–3.2%
Color (Gardner)	≤1
Density (25°C)	1.12 g/ml
Moisture Content	<0.05%
Viscosity (25°C)	35,000–55,000 mPa·s

HMDI Aliphatic PU Sealant Prepolymer

Specifications

FAQ

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