Calculation of kinetic parameters of amino-formaldehyde polymers formation in the presence of calcium ions

Abstract

Calcium carbonate is on of widely used fillers of composite materials. The area of its application depend on disperse structure, particle shape and other. The modification of calcium carbonate by high-molecular polymers allows changing its characteristics and surface properties in a wide range. The modification of calcium carbonate often carried out with use of amino-formaldehyde polymers (AFP). Aim: The aim of this work is to determine the kinetic characteristics of amino-formaldehyde polymers polycondensation process in the presence of calcium ions. Materials and Methods: The mechanism of AFP polycondensation is complex and depends on various factors. Polycondensation of AFP took place under following conditions: the temperature is 20, 30, 60° C; the molar ratio of carbamide to formaldehyde is 1:1.25; the polycondensation duration is 2 hours; the mass ratio of CaCO₃:AFP = 1:1. The polycondensation process was carried out in calcium chloride solution with рН=2…5.5. The concentration of formaldehyde and metilol groups determined during the experiment using chemical titrimetric method. Results: It is shown that polycondensation process of AFP in the presence of Сa²⁺ ions at their concentration from 0 to 2.25 mol/l (0…90 g/l) leads to acceleration of process more than by 1.8 times at temperature of 20°C. Further increase of Сa²⁺ concentration leads to reduction of process speed. At temperature of 30°C the speed of process almost does not change in the range of Сa²⁺ concentration from 0 to 2.25 mol/l and further decreases slightly. For all range of Сa²⁺ concentration at temperature of 60°C the reduction of process speed is observed. Influence of Сa²⁺ on process of polycondensation confirms assumption made earlier of formation of weak bonds between AFP and calcium ions which at low temperatures interfere with hydrolysis of methyleneurea and collapse at increasing of process temperature.