Foaming is the process of making plastics have microporous structure. Almost all thermosets and thermoplastics can be made into foam plastics. The commonly used resins are polystyrene resin, polyurethane resin, PVC resin, polyethylene resin, urea formaldehyde resin, phenolic resin and so on.
According to the bubble structure, foam plastics can be divided into two categories: if most stomata are interconnected, they are called open cell foam plastics; if most pores are separated from each other, they are called closed cell foam plastics. The foam structure with open or closed holes is determined by the manufacturing method.
(1) Chemical foaming is a gas produced by the heat decomposition of specially added chemical foaming agent or chemical reaction between raw materials, which makes the plastic melt full of bubbles.
The gases released by chemical foaming agent during heating include carbon dioxide, nitrogen, ammonia, etc.
Chemical foaming is often used in the production of polyurethane foam.
(2) Physical foaming physical foaming is a method that dissolves gas or liquid in plastic and then makes it expand or vaporize. There are many kinds of plastics suitable for physical foaming.
(3) Mechanical foaming is a foaming method in which the gas is mixed into the liquid mixture by means of mechanical stirring, and then the bubbles are formed through the shaping process. This method is commonly used in urea formaldehyde resin, other such as polyvinyl formal, polyvinyl acetate, polyvinyl chloride sol, etc.
