The influence of molecular design variables of bimodal HDPE on the slow crack growth resistance measured by accelerated methods

Papers # 2018 Las-Vegas

New generations of PE100 and PE4710 pressure pipe materials exhibit a superior balance of mechanical properties. The slow crack growth performance of these materials measured by traditional tests such as PENT and FNCT can exceed one year. Accelerated test methods, including strain hardening modulus, accelerated FNCT, accelerated point loading, and cracked round bar have been used to quantify the performance of the improved PE100/PE4710 materials. The results of the accelerated test methods generally correlate with the traditional SCGR test methods. The strain hardening modulus was correlated to PENT and NPT. Additionally, the SHM showed good correlation with accelerated FNCT. 

New generations of PE100 and PE4710 pressure pipe materials exhibit a superior balance of mechanical properties. The slow crack growth performance of these materials measured by traditional tests such as PENT and FNCT can exceed one year. These high performance materials deliver significant advantages to the end uses, especially to challenging installation techniques such as horizontal directional drilling which may cause damage to the pipes during installation. However, these exceptional material properties present some challenges for the raw material suppliers during product development. First, the product development cycle for new polymer structures becomes very long since the evaluation of SCGR performance may take one year or longer. Additionally, quality control of the materials cannot be conducted with traditional methods. 

The pipe industry is developing and implementing new accelerated test methods for the characterization of SCGR performance. These new techniques include the strain hardening modulus (SHM), accelerated FNCT (ACT), cracked round bar (CRB), and the accelerated point loading test (PLT). Although these tests significantly reduce the time-to-failure of the improved HDPE resins, the mechanisms of polymer deformation may be different. These differences must be considered when establishing correlations (or lack thereof) between results from different tests and their ability to rank resins consistently. This paper presents preliminary results from PENT, ACT, SHM, PLT, and CRB of various resins and discusses relationships between time-to-failures, molecular design and deformation mechanisms. 

Related keywords : Slow Crack Growth, Accelerated Tests, PE100, PE4710.
Please note that the whole article content is available on PPCA website onlySource : 2018 Las-Vegas


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