Polymethylene Polyphenyl Polyisocyanate

Polyphenyl polymethylene polyisocyanate—also known as PAPI or crude MDI—is an important chemical raw material. It is a viscous liquid ranging in color from pale yellow to dark brown and possesses a pungent odor. It consists of a mixture of 50% MDI and 50% polyisocyanates with a functionality greater than 2.

Safety Risks and Storage Requirements

Hazardous Chemical Properties: This substance is classified as a hazardous chemical. GHS classifications include hazards such as acute toxicity, skin corrosion/irritation, and respiratory sensitization; inhalation or contact may cause harm to health.

Storage Conditions:

Must be stored in a cool, well-ventilated, and dry warehouse; the recommended temperature range is 5–30°C.

Strictly protect against water and moisture; contact with water triggers a violent reaction releasing carbon dioxide, which may cause packaging to bulge or even burst.

Keep away from ignition sources and heat, avoid direct sunlight, and do not store together with amines, alcohols, or strongly alkaline substances.

Regulation and Case Studies: Recently (August 2026), the Emergency Management Bureau of Qushui County, Tibet, penalized an enterprise for failing to maintain safety records for this hazardous chemical, emphasizing the necessity of providing protective equipment and ensuring standardized storage practices.

Product Usage

Rigid foam plastics: A primary raw material for building insulation, automotive interiors, and thermal insulation in electrical appliances.

Adhesives: Used to manufacture polyurethane adhesives, significantly improving the bonding performance between rubber and nylon or polyester cords.

Other applications: Also used in the production of coatings, elastomers, synthetic wood, and casting molds.