Rotary Footwear Injection Molding & Soles · Critical

Winter Sub-Zero Sole Cracking & Flex-Groove Fracture

सर्दियों में सोल कटना व ग्रूव से टूटना

What the defect looks like

Finished footwear soles, slippers, or safety shoe outsoles develop clean, brittle transverse fractures across the flex grooves within 2,000 to 8,000 walking cycles during winter temperatures (2°C to 10°C in North India).

Root-cause mechanism

Glass transition temperature (Tg) freeze. While pure DOP has a low Tg (-80°C to -86°C), a flexible PVC compound plasticized with ~40-50 PHR DOP exhibits an effective compound Tg around -16°C. When compounded with high mineral filler (CaCO3 > 40 PHR) and secondary extenders, this effective glass transition shifts upward into the positive Celsius range (+4°C to +8°C). Under cold-weather flexural strain, the polymer chains cannot uncoil, leading to catastrophic brittle fracture.

This diagnosis is a technical starting point. Confirm the cause with controlled checks before changing production.