Crystallization of polyamides shows memory of shear even after undergoing a melting process at high temperatures for a long period to erase their thermal history

which was seldom noticed in the past．Considerable change of crystallization behavior of polyamides took place in the samples pre—sheared in various kinds of processing or measuring equipmerits

such as MFR instrument

rheometer

mixer and extruder．The peak crystallization tenaperatures increased bv 5 to 18 ℃ and the half crystallization time decreased to about a half compared to the sample without shear history．What’s more

the most obvious change generally occurred at a very low shear level

beyond which the changes levelled off．Polarized light microscopy revealed the decrease of spherulite size．On the contrary

crystallization of the pre—sheared polyolefins and popsters did not exhibit considerable difference from the unsheared samples．The hydrogen bonding was proposed to account for the memory of shear in polyamides．