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

Abstract

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 polymersubstrate interfaces. The model variable consists of the practical work of crack growth (G c ) times the crack growth path tortuosity (C) and correlates very well with the time to failure in the full notch creep test (FNCT) through a sigmoidal-type equation:, where a (3386), b (0.16), and c (0.006) are constants (r 2 ¼ 0.999). G c is calculated by multiplication of the area fraction of tie molecules at the crystal-amorphous interface, the amorphous phase loss factor value at À25C, and the sample storage shear modulus at the test temperature, whereas C 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.

Toughening of Poly(L-Lactic Acid) by Annealing: The Effect of Crystal Morphologies and Modifications

“…Accordingly, their resistance can be estimated on the basis of their population and the lamellar stem sliding strength against pullout. [28,29] It is well known that tie-molecules concentration is greatly dependent on the degree of super-cooling and molecular weight. The number of tie-molecules is greater in the quenched materials because the number of nuclei for crystallization increases and crystal thickness decreases with the degree of supercooling.…”

Effect of the particle size of expandable graphite on the thermal stability, flammability, and mechanical properties of high-density polyethylene/ethylene vinyl-acetate/expandable graphite composites

“…Polyethylene (PE) is one of the most widely used polymeric materials owing to its low cost, balanced mechanical properties, good processability, and so on . However, there are some disadvantages for PE, such as low environmental stress‐cracking resistance, poor compatibility with various additives, and so on, which have restricted its applications in some important fields . Therefore, many attempts have been made to ameliorate such limitations and improve the compatibility of PE by blending it with different fillers.…”

Model prediction of the ESCR of semicrystalline polyethylene: Effects of melt cooling rate

“…In an attempt to predict the SCG rate of PE, Huang and Brown22 introduced a model by scaling approach‐based characterization of tie molecules disentanglement rates as follows: where δ 0 , A , β, B , ℓ c , t , σ, n , Q , R , and T are the rate of crack opening displacement, a constant, fraction of mobile tie molecules, a constant related to the anchoring strength of tie molecules in the crystals, crystal thickness, number of taut tie molecules per unit cross‐section area of the fibril, applied stress, material parameter, activation energy for the micromolecular motion, gas constant, and test temperature, respectively. Quite recently, Sharif et al23 proposed a model based on the analogy of crack growth through amorphous phase of semicrystalline polymers in harsh environments with crack growth at adhesive polymer–substrate interfaces. They showed that time to failure, t f , of various PEs with different weight‐average molecular weights, M w , and molecular weight distributions, PDI, correlated quite well through a sigmoidal‐type equation with sample molecular characteristics.…”