Classification of polyurethane foam

Polyurethane refers to a polymer that contains amino acid ester chain ends (- NH-COO -) in its molecular structure, but the amino acid ester segment is not the dominant segment in the polymer. They are the gradual polymerization reaction products of hydroxyl terminated polymers such as polyether polyols or polyester polyols with isocyanates. Due to the diversity of raw material sources, it is usually not possible to represent all polyurethane in a universal empirical way.
Most of the polyurethane produced at present are foam plastics. There are soft, semi hard and hard foam products. In addition, there are various polyurethane products such as elastomers, coatings, adhesives, fibers, films, etc.
Polyurethane foam can be classified according to raw materials, production process and product performance.
According to the type of polyol used, it can be divided into polyether type, polyester type, etc. Due to factors such as raw material source, price and performance, polyether foam currently accounts for more than 90% of the total amount of soft foam, and is the dominant type. Polyester foam still retains a market share of 5% -10% in some special application fields due to its excellent solvent resistance and other properties.
From the perspective of product bearing performance, polyurethane soft foam can be mainly divided into three categories: ordinary type, high bearing type and high resilience type. In addition, there are special foam such as slow resilience, self skinning, super soft, hydrophilic foam, network foam, etc.
If divided by the isocyanates used, there are mainly three types: TDI, MDI, and TDI/MDI mixed type. At present, TDI is still mainly used as raw material in the production of block foam, but in recent years, the full MDI type high resilience soft foam block shows a strong growth momentum; In molded foam, TDI/MDI mixed isocyanate and full MDI have been widely used, and the trend is rising.
From the perspective of synthesis process, the vast majority of them use one-step method, and only in a few special occasions do they use pre polymerization (two-step method) or semi pre polymerization method.
From the perspective of production methods, there are two types: continuous method and intermittent method. Continuous method is the main production process of block foam. At present, more than 80% of soft foam is produced by this method. The block foam produced is then cut and processed into the required foam parts. Intermittent molding process is mainly used to directly foam foam parts in the mold to obtain the required shape. It is particularly necessary to produce foam body with complex geometry. Box foam is a form of molding process that is widely used in China due to its flexible and versatile products.