Determination of the accessible carboxyl and amino end groups in structurally modified PA 6 using titration methods

Changes in fine structure of fiber-forming polymers influence the fiber morphology and consequently the surface properties which define their adsorption characteristics [ 10, 20, 22]. Another very important magnitude, which defines the adsorption behavior of the polymer, is the number of polymer accessible functional groups [10, 20]. In the present work, the adsorption characteristics of PA 6 fiber-forming polymers were structurally modified using temperature and phenol treatment. The influence of structural modifications on the content and accessibility of PA 6 end groups (-COOH, -NH2) was studied. The results of two titration techniques [19, 23] (potentiometric and complexometric titrations) and the standard iodine sorption method [12] are related to several characteristics of the fibers such as molecular mass, density, crystallinity and the amount of different structural modifications. It has to be noted that, to our knowledge, determining the correlation between the polymer fine structure and the accessibility of functional groups using titration methods is a new approach in the polymer research field. Results show an evidently good correlation between the PA 6 structural changes (degree of crystallinity, amount of crystallinity) and the quantity of accessible end groups. The quantity of accessible carboxyl and amino groups is decreased by an increase in the degree of crystallinity. Results of potentiometric titration were confirmed using a conventional "iodine-value" method. It can be concluded that the potentiometric titration is an appropriate tool for determining the influence of structural modifications on the content of accessible end groups of the PA 6 fibers. Unfortunately, the complexometric titration did not give good results due to the fact that PA 6 was not brought into the reactive - dissociable stage. The ion exchange reaction, on which this technique is based, was not possible.