Henry polyurethane is used to analyze the influence of various polyurethane raw materials on soft foam.

1. Polyether

Polyether is used as the main raw material to react with isocyanate to form carbamate, which is the skeleton reaction of foam products. When the molecular weight is increased, the tensile strength, elongation and resilience of the foam increase, and the reactivity of the same kind of polyether decreases. When the equivalent value (molecular weight / functionality) is the same, the functionality increases, the reaction is accelerated, the crosslinking degree of the polyurethane is increased, the hardness of the foam increases, and the elongation decreases. The average energy of polyols should be above 2.5. If the average energy consumption is too low, the recovery of foam will be poor after compression.

If the amount of polyether is much, it is equivalent to other raw materials (TDI, water, catalyst, etc.) to reduce, resulting in foam products cracking or collapse.

If the amount of polyether is small, foam products are hard and flexible, and the handle is not good.

2. Foaming agent

Generally, when making polyurethane block foam with density greater than 21, only water (chemical foaming agent) is used as foaming agent, and low boiling point compounds (physical foaming agent) such as methylene dichloride (MC) are used as auxiliary foaming agent in low density or ultra-soft formulation.

The auxiliary foaming agent will reduce the density and hardness of the foam, because its gasification will absorb some of the reaction heat, which will slow down the curing and increase the amount of catalyst. Because of absorbing heat, the danger of core burning is avoided.

The foaming ability can be expressed by foaming index (the equivalent amount of water or water used in 100 phr of polyether):m--the amount of foaming agent used

Foaming index IF=m(water)+m(F-11)/10+m(MC)/9(100-polyether)

As a foaming agent, water reacts with isocyanate to form urea bond and release a lot of CO2 and heat, which is a chain growth reaction.

The amount of water is more, the density of foam decreases, the hardness increases, and the bubble pillar becomes smaller and weaker, which reduces the bearing capacity, collapses and bubbles. The consumption of TDI increased, heat release increased and heartburn prone. If the water content exceeds 5.0 phr, physical foaming agent must be added to absorb part of the heat and avoid the occurrence of core burning.

When the amount of water is less, the amount of catalyst decreases correspondingly, but the density increases.

3. Toluene diisocyanate

TDI80/20, 2, 4 and 2, 6 isomers are commonly used in soft foams. T100, pure 2,4 TDI, can be prepared by cooling method.

TDI dosage=(8.68+m water *9.67)*TDI index. TDI index is generally 110-120.

When the isocyanate index increases in a certain range, the hardness of the foam increases, but after reaching a certain point, the hardness is no longer significantly increased, and the tear strength, tensile strength and elongation decrease, the foams form macropores, the closed pores rise, the resilience rate decreases, the surface is sticky for a long time, and the curing time is long, which leads to core burning.

Low isocyanate index will cause foam crack, poor resilience, poor strength, compression permanent deformation and wet feeling on the surface.

Henry shares with you the impact of various raw materials of polyurethane on soft foam. For more information, please continue to pay attention to Henry's official website. We are dedicated to serving you!

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