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Molecular weight

Molecular weight is the critical parameter in determining abrasion resistance, impact resistance and chemical resistance.

It is what sets apart ultra-high molecular weight polyethylene from other polyethylenes. Stamylan® UH’s advantages here can be best tested using the viscosity in dilute solution (ISO 1628-3 or ASTM D4020) to quantify the molecular weight. The average molecular weight is calculated from the intrinsic viscosity [η], with the Margolies-equation: Mw = 5.37 x 104 x [η]1.49 where: Mw = average molecular weight (g/mol) and [η] = intrinsic viscosity in decalin at 135°C (dl/g)

Note: Several relations exists (see ASTM D4020), resulting in strongly different molecular weights at the same intrinsic viscosity. A suitable alternative method to characterize the molecular weight of Stamylan® UH is the determination of “elongational stress” (For details of this method, see ISO 11542-2A or ASTM D4020). Elongational stress F(150/10) is the stress (N/mm2) at which an elongation of 600% is reached in 10 minutes, immersed in silicone oil at 150°C.

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