NEW DEVELOPMENTS IN THE MELT RHEOLOGY OF NYLONS .1. EFFECT OF MOISTURE AND MOLECULAR-WEIGHT

Peculiar observations on the melt rheology of ultra-dry nylon resins, nylon 6 in particular, are reported. One aspect of this study deals wi th a sharp increase in zero shear melt viscosity (e.g. 2 to 5 times) a s the nylon 6 resin moisture is taken from 0.10 down to 0.00%; the eff ect being reversible. Changes of such magnitude are unexpected conside ring that there are no detectable variations of the chemical/compositi onal/molecular weight type in the starting resin, when subjected to th e imposed drying conditions. Another aspect of this study deals with a deviation of nylons (6, 6,6, and 12) from the Bueche (1952) relations hip, well accepted for polymers to date. Under moderate drying conditi ons (e.g. 50 degrees C/17 h/110 millitorr), the molecular weight expon ent is found to be 3.8, which is within the range of 3.4 to 3.8 report ed for nylon 6. However, under more severe drying conditions (e.g. 110 degrees C/17 h/110 millitorr), the molecular weight exponents for nyl on 6, nylon 66, and nylon 12 are 4.8, 5.4, and 4.6, respectively. We a re proposing that a sharp increase in melt viscosity of ultra-dry nylo n 6 is partly due to an increase in the molecular weight of the melt ( extrudate) which then, has a more pronounced impact on melt viscosity in view of the 4.8 exponent. Such unique results, in contrast to polye thylene (free radical polymer) and poly(ethylene terephthalate) (conde nsation polymer), are tentatively attributed to H-bonding in nylon mel ts. Yet another aspect of this study deals with the rheology of superc ooled molten polymers that can offer advantages for analytical charact erization.