I. Coupling Agents
Definition and Core Logic: Compounds with a bifunctional structure. Their core function is to act as "molecular bridges," firmly connecting incompatible inorganic materials (such as glass fiber) and organic materials (such as plastics) through chemical bonds.
Main Characteristics:
Asymmetric Molecular Structure: One end is an inorganic-loving group, and the other end is an organic-loving group.
Chemical Bridging: The inorganic-loving end reacts with the filler, and the organic-loving end reacts with the resin, eliminating interfacial defects.
Performance Gains: Improves the mechanical strength, weather resistance, and electrical insulation of composite materials, and reduces hygroscopicity.
Typical Types:
Silane Coupling Agents: The most widely used, such as KH-550 (amino type, suitable for epoxy resins) and KH-570 (methacryloyloxy type, suitable for unsaturated polyesters).
Titanium Ester Coupling Agents: Effective for filler systems such as calcium carbonate, reducing viscosity and achieving high filler content.
II. Crosslinking Agents
Definition and Core Logic: Substances containing multiple active functional groups or capable of initiating free radicals. Its core function is to establish chemical bonds between polymer chains, connecting linear structures into a three-dimensional network structure.
Main characteristics:
Multifunctional groups/High activity: Able to simultaneously bind two or more molecular chains.
Dimensional change: Through irreversible reactions, it transforms thermoplastic materials into thermosetting materials (or elastomers).
Qualitative performance change: Imparts high elasticity, heat resistance, solvent resistance, and dimensional stability to materials.
Typical types:
Vulcanization systems: Such as sulfur, used in rubber (natural rubber, styrene-butadiene rubber), forming polysulfide bonds.
Peroxides: Such as DCP (dicumyl peroxide), used in polyethylene, ethylene propylene rubber, forming carbon-carbon bonds.
Isocyanates: Such as MDI, TDI, used in polyurethane materials.
III. Dispersants
Definition and core logic: A surfactant or polymer. Its core function is to prevent solid particles from re-aggregating in a liquid, ensuring a uniform and stable system.
Key Features:
Anchoring and Dissolution: The molecule contains anchoring groups (adsorbed onto particles) and solvation chains (compatible with the medium).
Stabilization Mechanism: Prevents particle aggregation through electrostatic repulsion (ionic) or steric hindrance (polymer chain barrier).
Rheological Control: Reduces system viscosity, improves grinding efficiency, and prevents precipitation.
Typical Types:
Ionic: Such as sodium polyacrylate, relying on electrostatic repulsion.
Nonionic: Such as fatty alcohol polyoxyethylene ether, insensitive to pH, relying on steric hindrance.
Polymer: Such as polyurethane dispersants, with strong anchoring force and high stability, used in high-grade coatings.
