6.4.3 Polyurethanes (PUs): 1C PU and 2C PU

PU adhesives are supplied as 1C and 2C systems that range in viscosity from self-levelling liquids to non-slumping pastes. They cure to form thermoset polymers with good solvent and chemical resistance. They are highly versatile and can vary in cured form from extremely soft elastomers to rigid, tough plastics. PUs offer a good blend of cohesive strength and flexibility, which makes them very tough, durable adhesives. They bond well to most unconditioned substrates, but may require solvent-based primers to achieve high bond strengths. They offer good toughness at low temperatures but typically degrade in strength after long-term exposure over 150°C (302°F). Since the cure of 1C moisture-curing PUs is dependent on moisture diffusing through the polymer, the maximum depth of cure that can be achieved in a reasonable time is limited to approximately 9.5 mm (0.38 in); 2C systems, on the other hand, offer an unlimited depth of cure.

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