Thermodynamic properties of liquid and semicrystalline linear aliphatic polyamides

Abstract

Abstract Heat capacities have been measured for liquid and semicrystalline nylon 6, 11, 12, 6.6, 6.9, 6.10 and 6.12 from above their respective glass transition temperatures (ca. 320 K) to 600 K. Combining those data with all prior literature, a new set of ATHAS recommended values is derived, including a general equation of heat capacities as a function of amide content: where N C and N N are the numbers of methylene and amide groups, respectively, in the average repeating unit. A full set of thermodynamic functions (H, G and S) is available through the ATHAS data bank. Large amounts of reorganization during heating and the possible existence of a rigid amorphous fraction in semicrystalline nylons make the analysis of the detailed thermal behavior of semicrystalline nylons between the glass and melting transition uncertain. It seems, however, that the heat capacity of the crystalline portion above 330–410 K is higher than predicted from the heat capacity of vibration. A similar observation was also made for polyethylene and has recently been linked to conformational disorder and mobility.