High-performance eco-friendly waterproof coatings: New applications of waterborne polyurethane dispersions.

The industry-standard waterproof coatings primarily utilize polyurethane systems, which are prepolymers containing isocyanate groups synthesized through addition polymerization of isocyanates and polyethers. These are processed through mixing with catalysts, anhydrous fillers, solvents, and other additives. Unlike acrylic resins that exhibit thermal adhesion but low-temperature brittleness, polyurethane resins demonstrate hardness without brittleness and flexibility without stickiness. Waterproof coatings formulated with such resins exhibit exceptional performance in low-temperature fracture elongation and fracture strength, meeting the waterproofing requirements of most applications.

With the upgrading of consumption and increasingly stringent environmental requirements, eco-friendly coatings have gained significant attention. The industry is currently focusing on upgrading conventional solvent-containing waterproof coatings to high-solid or solvent-free systems, as well as transitioning to water-based waterproofing solutions. Conventional water-based coatings typically use resin emulsions such as acrylic, EVA, and polyurethane types. The water-based conversion of polyurethane resin not only retains its superior performance but also enhances environmental sustainability, demonstrating great application potential.

When comparing waterproof coatings with identical formulations, what are the distinctive features in terms of mechanical properties, water absorption rate, and bonding strength? The following analysis provides detailed explanations: 1. Mechanical Properties Mechanical performance remains a key indicator of coating quality, with resin composition having the most significant impact. The aqueous polyurethane dispersion retains both flexible and rigid segments from polyurethane resin molecules, exhibiting excellent elasticity and strength. This results in outstanding low-temperature and high-temperature elongation at break as well as fracture strength in waterproof coatings. 2. Alkali Resistance When directly applied to concrete substrates, waterproof coatings may be affected by alkali efflorescence in base materials. Indoor applications also face challenges from alkaline cleaning agents. Superior alkali resistance extends coating durability and ensures long-lasting waterproofing. Notably, aqueous polyurethane waterproof coatings demonstrate exceptional alkali resistance performance.

3. Excessive water absorption: When the coating absorbs too much water, it may swell and bubble after prolonged exposure, reducing its adhesion to the substrate and consequently compromising waterproofing performance.

Waterproof coatings formulated with polyurethane and acrylic emulsion demonstrate the following water absorption rate comparisons: Experimental results indicate that the PA coating exhibits distinct deformation characteristics. 4. Adhesion Strength: This parameter characterizes the coating's adhesion to the substrate. Higher strength indicates superior adhesion and reduced detachment tendency. The waterborne polyurethane waterproof coating demonstrates high adhesion strength with consistent performance across various substrates, thereby expanding the application scope of waterproof coatings.

5. VOCs (Volatile Organic Compounds) pose significant health risks. When VOC concentrations in indoor environments reach critical levels, individuals may experience symptoms such as headaches, nausea, vomiting, and fatigue within hours. Severe cases can lead to convulsions, coma, and damage to the liver, kidneys, brain, and nervous system, potentially causing memory impairment. Paints used in home decoration and renovation are a major source of indoor VOCs, prompting global regulations to limit VOC content in decorative materials. Water-based waterproof coatings demonstrate exceptional VOC performance: Under identical formulation conditions (as shown in the figure), water-based polyurethane dispersion coatings exhibit superior mechanical properties, lower water absorption, higher bonding strength, and reduced VOC emissions. For instance, water-based PU waterproof coatings achieve a 620% elongation at room temperature, 4MPa breaking strength, 8% water absorption, 1.5MPa substrate bonding strength, and VOC levels of approximately 10g/L. These coatings effectively seal minor wall cracks, minimize water leakage, extend building lifespan, reduce waterproofing repair rates, and enhance living quality.