Research on slow crack growth resistance of polyethylene pipe based on strain hardening modulus

Slow crack growth (SCG) is the principal factor for determining the operating lifetime of polyethylene (PE) pipes. Exploring the relationship between the molecular structure and the strain hardening (SH) modulus is helpful to evaluate the SCG resistance of PE pipe materials accurately. This paper uses an efficient SH test method to study the SH modulus for four kinds of PE pipes. Meanwhile, the correlation between SH modulus and sample thickness, material crystallinity (X-c), comonomer type and content, weight-average molecular weight, and molecular weight distribution has been established and investigated respectively. The results represent that the comonomer type and the X-c of PE materials played significant roles in the SH modulus. The SH modulus of ethylene-hexene copolymer is 5-7 MPa higher than that of ethylene-butene copolymer. The amount in the range of 1 x 10(3) to 1 x 10(5) of the molecular weight distribution of PE materials has a significant contribution to the establishment of the tie molecular network. In addition, the higher X-c and the thinner thickness were beneficial to obtain the higher measured SH modulus.