Polyurethane adhesive - A versatile material

Polyurethane adhesives are a type of high-performance adhesives whose main film-forming material is Polyurethane Resin. The core chemical basis of these adhesives stems from the gradual polymerization reaction between isocyanate groups (-NCO) and compounds containing active hydrogen. Their chemical properties are distinctly manifested in both synthesis and application. 

 

From a chemical composition perspective, the main raw materials are mainly polyisocyanates and polyols (or polyamines). The highly reactive isocyanate groups in the polyisocyanate molecules can undergo stepwise addition polymerization reactions with the hydroxyl groups (-OH) of the polyols, generating high-molecular chains containing repeating amide groups (-NHCOO-). This is the origin of the name "polyurethane". By adjusting the types of polyols (such as polyester type or polyether type), the structure of polyisocyanates, and the addition amounts of crosslinking agents and chain extenders, the flexibility, polarity, and crosslinking density of the molecular chains can be precisely controlled, thus adapting to different bonding requirements. 

 

Based on the classification of curing mechanisms, polyurethane adhesives are mainly divided into solvent-based, water-based, and reactive curing types. Reactive curing products are often in a two-component system. Component A is the end-terminated hydroxyl prepolymer, and Component B is the polyisocyanate curing agent. After mixing, the isocyanate groups and hydroxyl groups rapidly react to form a three-dimensional cross-linked network, achieving curing and bonding; single-component wet-curing type relies on the reaction with water molecules in the air. The isocyanate groups hydrolyze to form amines, which then react with the remaining isocyanate groups to form a film. 

 

The strong polarity of the carbamate bond enables it to form hydrogen bonds and van der Waals forces with various substrate surfaces such as metals, plastics, woods, and fabrics, resulting in excellent bonding strength. Additionally, the designability of the molecular chain endows it with good flexibility, low-temperature resistance, and impact resistance. It can also be chemically modified to enhance weather resistance and chemical corrosion resistance, and is widely used in fields such as packaging, construction, automobiles, and light industry. It is an important category of high-molecular adhesives that combines both versatility and high performance.