Summary:The chemical principles of core foam plastics can be divided...
The chemical principles of core foam plastics can be divided into two categories:
① Using chemical foaming agents, they decompose to release gas when heated. Commonly used chemical foaming agents, such as azodicarbonamide, azobisisobutyronitrile, N,N'-dinitrosopentamethylenetetramine, sodium bicarbonate, etc. Many thermoplastics can be made into foam by this method.
For example, polyvinyl chloride foam shoes are made of resins, plasticizers, foaming agents and other additives, and put them into an injection molding machine. The foaming agent is decomposed in the barrel, and the material is foamed in the mold. .
Foam artificial leather is to mix the foaming agent into the polyvinyl chloride paste, smear or calender on the fabric, and continuously pass through the tunnel heating furnace. Get foam artificial leather. The rigid PVC low-foaming sheet, pipe or profile is formed by extrusion. The foaming agent is decomposed in the barrel. When the material leaves the machine head, the pressure drops to normal pressure, and the gas is dissolved to expand and foam. When the foaming process and the cooling and setting process are properly coordinated, structural foam products can be obtained.
②Using the by-product gas in the polymerization process, a typical example is polyurethane foam. When isocyanate and polyester or polyether undergo a polycondensation reaction, some isocyanates will react with water, hydroxyl or carboxyl groups to generate carbon dioxide. As long as the gas evolution rate and the polycondensation reaction rate are properly adjusted, a highly foamed product with very uniform cells can be produced.
There are two types of polyurethane foams. The soft open-cell type is like a sponge and is widely used as seat cushions for various seats and sofas, as well as sound-absorbing and filtering materials. The hard closed-cell type is ideal for heat preservation, insulation and shock absorption. and floating material.