Short Chain Branching

Melt Behavior

Flow behavior during injection molding is influenced by the length and frequency of these branches, which alter the chain entanglement and viscosity of the melt. More branched polymers exhibit different shear-thinning behavior compared to linear polymers, which affects the mold filling and pressure requirements during the molding cycle. Molders must select resin grades with the correct branching structure to ensure consistent mold filling.

Mechanical Impact

Stress cracking resistance is significantly improved by the presence of these short branches, which increase the number of tie molecules that connect different crystalline domains. These tie molecules prevent the propagation of cracks under continuous mechanical load or environmental stress, making the material more durable in demanding applications. This is a critical factor for pipes and other load-bearing components.

Moulding Variable

Processing conditions must be adjusted to account for the slower crystallization rates of resins with high branching levels. Parts molded from these resins require longer cooling times in the mold to prevent excessive shrinkage and warpage after ejection. Molders must balance the benefits of higher flexibility and stress crack resistance against the longer cycle times and higher processing costs.