Differences in Core Physical Properties Between High-Quality and Low-Quality Polyurethane Sealant (Determining Sealing and Bonding Effectiveness)

Differences in Core Physical Properties Between High-Quality and Low-Quality Polyurethane Sealant (Determining Sealing and Bonding Effectiveness)
Physical properties are the “core strength” of a sealant, directly affecting its ability to withstand external forces, expand and contract, and maintain a tight seal.
1. Bond Strength (Key Parameter)
Good quality: Strong adhesion to substrates (such as glass, metal, stone, and concrete). After curing, peeling requires considerable force, and peeling is often “substrate damage” (e.g., the concrete surface is removed) rather than “separation” (separation of the adhesive from the substrate) (separation of the adhesive layer).
Poor quality: Loose adhesion, easy to peel by hand after curing, with the adhesive layer peeling directly from the substrate surface (“interfacial failure”), or even cracking after curing (poor cohesive strength). 2. Elasticity and Flexibility (Adaptability to Substrate Deformation)
The core advantage of polyurethane sealant is its “elastic seal.” It must adapt to substrate expansion and contraction caused by temperature and vibration (e.g., building curtain walls, door and window gaps).

Good quality: Excellent elasticity after curing. Even after stretching to 200%-300% of its original length (in compliance with GB/T 14683), it can still return to its original shape without cracking or permanent deformation. It also rebounds quickly after compression.
Poor quality: After curing, it can be too hard (e.g., plastic blocks) or too soft (e.g., plasticine). It can easily break when stretched (elongation <100%) or fail to rebound after stretching (permanent deformation). It can also crack due to insufficient expansion and contraction after temperature fluctuations.
3. Hardness (Moderate is Best)
Good quality: The Shore A hardness (A scale) is typically between 30 and 60 (adjusted depending on the application, e.g., door and window sealants may be softer, structural sealants may be harder). The hardness is uniform, with no areas of excessive hardness or softness. Poor quality: abnormal hardness (such as <20 or >80), either too soft and easy to collapse and stick to dust, or too hard and brittle and unable to adapt to the deformation of the substrate.