Calculation of the bonding strength of semi-crystalline polymers during overmolding

Injection molding is widely used in the plastics manufacturing industry. However, there is a need to better understand and calculate the bonding strength between the injection-molded part and the insert, especially for semi-crystalline polymers. The weldability of semi-crystalline polymers differs from that of amorphous polymers. Semi-crystalline polymers cannot heal until they reach their glass transition temperature, unlike amorphous polymers, as the crystalline particles prevent molecule motion below this temperature. To account for this difference, we have developed a method that takes into effect the crystalline parts of semi-crystalline polymers in the calculation of healing. We used polypropylene (PP) in our experiments, and calculated healing with a new method based on the method we previously described for the healing of amorphous polymers. • Innovative method: Developed new calculation for semi-crystalline polymer bonding. • Incorporated crystalline effects: Integrated crystals to understand bonding in polymers. • Defined limit temperatures: Introduced method for precise healing range determination. • Validated with polypropylenes: Confirmed accuracy, <10 % error, in practical testing.