Suleyman Deveci, Senthil K. Kaliappan, Joel Fawaz, Umesh Gadgoli
Papers # 2018 Las-Vegas
A series of non-commercial bimodal high density ethylene-α-olefin copolymers with systematically controlled molecular parameters over a wide range that would result in extremely low and high strain hardening modulus were prepared and tested
Strain hardening modulus has been published as a standard test method (ISO 18488) to differentiate slow crack growth (SCG) resistance of PE100 and PE100RC materials. SCG is a time-dependent brittle-type failure that polyethylene pipes show when under low stress levels. The polyethylene's molecular weight (and its distribution), crystallinity, co monomer type, concentration (and its distribution), tie molecules and entanglement density are parameters that are known to affect the SCG of polyethylene. The concept of the strain hardening modulus (Gp) proposed by Haward is based on the entanglement density of a polymer structure. Several research groups have investigated how strain hardening modulus was affected by polymer structure. Most of these studies were based on polyethylene samples with a limited range of molecular parameters. In this study, we prepared a range of polyethylene samples of controlled molecular weights, viscosities and strain hardening moduli that are distributed between lowest and highest values with controlled increments. Findings of this study will help scientist and engineers to understand better the response of strain hardening modulus to molecular properties of pipe grade polyethylene materials.
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