Practical work of crack growth and environmental stress cracking resistance of semicrystalline polymers

The area fraction of tie molecules at the crystal-amorphous interface, amorphous phase dynamics, average crystal strength against stem sliding, and crack growth tortuosity concepts have been used simultaneously, for the first time, to develop a model for predicting the environmental stress cracking resistance of semicrystalline polymers. The model is based on the analogy of crack growth through the amorphous phase of semicrystalline polymers in a harsh environment at adhesive polymer-substrate interfaces. The model variable consists of the practical work of crack growth (Gc) times the crack growth path tortuosity (Γ) and correlates very well with the time to failure in the full notch creep test (FNCT) through a sigmoidal-type equation: FNCT = a{1 + exp[(b - GcΓ)/c]}⁻¹, where a (3386), b (0.16), and c (0.006) are constants (r² = 0.999). Gc is calculated by multiplication of the area fraction of tie molecules at the crystal-amorphous interface, the amorphous phase loss factor value at -25°C, and the sample storage shear modulus at the test temperature, whereas Γ is estimated as the product of the sample molecular weight and its distribution. The application of the Kendall rank correlation coefficient test as a primitive gross criterion of comparison among the proposed correlations also shows reasonable values of the rank correlation coefficient (0.891) and probability (0.000) for the new model. In other words, a point-to-point increasing or descending trend among the experimentally found data is ignored in comparison with the sound physical basis of the correlation toward the development of a comprehensive model.