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Interfacial crystalline structures in injection over-molded polypropylene and bond strength
Bowen Yan1, Hong Wu, Genjie Jiang
1The State Key Laboratory of Polymer Materials Engineering, Polymer Research Institute of Sichuan University, Chengdu 610065, China.
ACS Applied Materials & Interfaces
|October 15, 2010
Summary
This study reveals how crystalline structures like "shish-kebab" layers (SKL) and transcrystalline layers (TCL) affect polypropylene overmolding bond strength. Optimizing TCL formation enhances bond strength, while SKL dominance weakens it.
Area of Science:
- Materials Science
- Polymer Science
- Manufacturing Engineering
Background:
- Injection overmolding of polypropylene (PP) components creates complex interfacial crystalline structures.
- Understanding these structures is crucial for predicting and controlling the bond strength between overmolded parts.
Purpose of the Study:
- To investigate the interfacial crystalline structures in injection overmolded PP components.
- To determine the relationship between these structures and the interfacial bond strength.
- To elucidate the influence of thermomechanical conditions on interfacial structure development.
Main Methods:
- Polarized Light Microscopy (PLM), Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC), Wide-Angle X-ray Diffraction (WAXD), and infrared dichroism spectroscopy were employed.
- Lap shear measurements were used to quantify interfacial bond strength.
Main Results:
- Competitive formation of "shish-kebab" layer (SKL) and transcrystalline layers (TCL) was observed at the interface.
- Shear stress significantly influences SKL formation, while thermal conditions (melt and mold temperature) impact TCL formation.
- Higher interfacial temperatures and thermal gradients promote beta-iPP (β-iPP) growth, favoring TCL.
Conclusions:
- Interfacial bond strength is enhanced by promoting the formation of transcrystalline layers (TCL).
- A predominance of "shish-kebab" layers (SKL) leads to reduced interfacial bond strength.
- Control over molding parameters (shear stress and thermal conditions) is key to optimizing interfacial morphology and bond strength in overmolded PP.
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