What materials are used to make PU foam?

The preparation of polyurethane (PU) flexible foam is based on the step-growth addition polymerization reaction between isocyanates and compounds containing active hydrogen. Its cellular structure and physical-mechanical properties depend on the precise proportioning of the raw material system and the regulation of reaction kinetics. The raw materials required for production can be divided into the following four categories of functional components:

Main Raw Materials

Polyether Polyol (hydroxyl value 28–56 mg KOH/g): Provides the soft segment structure, determining the flexibility and resilience of the foam.

Isocyanate: Primarily toluene diisocyanate (TDI-80/20), with some high-load-bearing formulations using MDI or TDI/MDI blends to control crosslink density.

Blowing System

Deionized Water: Chemical blowing agent, reacts with -NCO to generate CO₂, while producing urea bonds that contribute to the foam's skeletal strength.

Physical Blowing Agent (optional): e.g., methylene chloride or low-boiling alkanes, auxiliarily adjust cell open/closed ratio and density.

Additive System

Tertiary Amine Catalyst (e.g., A-33): Mainly catalyzes the blowing reaction between water and isocyanate.

Organotin Catalyst (e.g., T-9): Mainly catalyzes the gelation reaction between hydroxyl groups and isocyanate.

Silicone Surfactant (e.g., L-580): Reduces surface tension, stabilizes the gas-liquid interface, controls cell size and the ratio of open to closed cells.

Functional Additives

Crosslinkers (diethanolamine, glycerol), flame retardants (TCPP, TCEP), antioxidants, color pastes, etc., added in amounts according to the end-use application.

By adjusting the molecular weight and functionality of the polyol, the isocyanate index, catalyst ratio, and blowing agent dosage, PU foam products with different load-bearing capacities, air permeability, and compression set characteristics can be obtained over a wide density range (8–80 kg/m³). The choice of raw material system directly determines the stability of the production process and the foam microstructure.

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