Brittleness in PVC Granule Injection Molding Causes and Effective Solutions

For manufacturers using PVC granules for injection molding, product brittleness is a common issue that leads to easy cracking, affecting quality and increasing costs. Beyond external aging factors (temperature, pH, sunlight), internal formation causes mainly involve three aspects: materials, mold design and process parameters, which are detailed below.

1. Material Factors

Material issues are the primary cause of PVC product brittleness. Firstly, high quality PVC pellets are essential—impurities mixed in PVC granules, improper or excessive additives, will damage material uniformity and toughness. Secondly, insufficient drying of PVC before processing triggers catalytic cracking with water vapor during heating, generating internal strains. Additionally, excessive use of recycled PVC or multiple recycling cycles reduce molecular weight, while low-quality granules with wide molecular weight distribution also weaken toughness.

2. Mold Design Factors

Unreasonable mold design easily induces brittleness. Products with thin walls, sharp corners, uneven thickness or excessive hollowing tend to have stress concentration. Small runners or gates lead to insufficient PVC melt filling and poor fusion. Moreover, adding metal inserts to brittle PVC (with large thermal expansion and contraction coefficients) and abnormal injection cycles caused by poor mold structure also aggravate brittleness.

3. Process Parameter Factors

Inappropriate process parameters are key triggers for PVC granule brittleness solution. Improper temperature control: low barrel/nozzle temperatures cause insufficient melting; overly high or low mold temperatures lead to residual stress or poor weld line fusion. Besides, low injection speed/pressure results in incomplete filling, while excessive pre-plastic back pressure or screw speed causes material degradation, both reducing product toughness.

Against the above causes, targeted solutions include: prioritizing pure PVC granules for injection molding and fully drying materials; optimizing mold design to eliminate stress concentration points; fine-tuning process parameters; reducing weld lines, which is effective for brittleness in injection molded PVC.

In short, PVC injection molding brittleness is closely related to materials, molds and processes. Grasping these formation causes and taking corresponding measures can effectively improve product quality. For more questions, leave a message for consultation.