Consider nylon 6/6 pellets going from solid to melt in an extruder. My thoughts are that if you increase moisture content before they are melted, you can increase the monomer units that can self-catalyze under the right conditions (extrusion temperatures below degradation temp). That is, if you operate with the same moisture content but at temperatures 300°C and over, you will not reach the same degree of polymerization as you would with the same moisture content but at lower processing temperatures.
The assumption made collides with the fact that nylon 6/6 is made by the condensation polymerization of adipic acid HOOC-(CH2)4-COOH with hexamethylene diamine H2N-(CH2)6-NH2 which involves elimination of a large number of water molecules until a polymer of high average molecular weight is built. When nylon 6/6 is pelletized, further loss of water occurs.
Increasing water content before extrusion does not lead to an increase in average DP. It may do so if applied to nylon 6 which is made by polymerizing caprolactam “the cyclic amide which needs moisture in ring opening that gives 6-aminohexanoic acid which undergoes a condensation polymerization eliminating water in this last step ”.
Dear Tomáš, according to the thermodynamic laws, the water addition will decrease the equilibrium conversion to lower values and thus decrease the degree of polymerization.of your polymer. Therefore, you can expect the effect that is just opposit to your considerations. Nevertheless, due to water evaporation at 300 °C the effect will probably be quite negligible.
Best regards, J.V.
Thank you all for your answers! I was spending time looking at self-catalysis and this has definitely helped my understanding. Thanks!
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