There are many types and grades of primers for extrusion compounding, which can be roughly divided into two categories: water-based and solvent-based. Water-based primers include polyethyleneimine primers, and solvent-based primers include titanium-based primers and isocyanate-based primers. Water-based primers are generally used for materials that do not contain water and do not require high composite strength. Solvent-based primers are generally used for materials with high water content and high composite strength requirements.