Density and molecular weight have NOTHING to do with each other.
The higher the density of the unfilled polyethylene the higher the crystallinity. The higher the crystallinity of the PE, the higher the flexural modulus or stiffness.
Without knowing the density of the UHMWPE I cannot say for sure, but I very strongly suspect that the UHMWPE you are talking about is LDPE or MDPE and therefore is more flexible than the HDPE you mention.
Regards
Pat
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You can get elastic modulus (tensile or flexural) information on these materials from suppliers (like LyondellBasell) or from MatWeb. HDPE comes in so many flavors that it is likely to bracket UHMWPE properties.
Regards,
Cory
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