Grafting of vinyl monomers by the xanthate method

Abstract

SynopsisThe removal of oxygen from swollen pulp is very difficult. At least 1-2 h of purging with oxygen-free nitrogen or argon is required as well as efficient mixing and a low concentration of pulp (not higher than 1%). During the grafting reaction, in which the xanthate cellulose is a part of the redox system, the concentration of oxygen falls to zero and stabilizes at this level even if air is purged through the system or a higher rate of stirring is applied. Primary sulfur radicals created in the reaction of the xanthated groups with H,O, are further oxidized by H,O, or by particles of oxygen dissolved in the reaction mixture. The observed increase in reaction caused by an increase in stirring speed is due to the higher rate of diffusion of hydrophobic monomers as well as the diffusion of oxygen to active centers at high stirring speed. The low rate of grafting at lower agitation speeds is caused by agglomeration of monomer molecules to bigger particles and, as a result, decreased diffusion of monomer to active centers. Above 300 rpm, the effect of monomer diffusion diminishes and further increase in conversion is caused only by a higher rate of oxygen diffusion to active centers from reaction mixture or passing gas. However, above a certain level of oxygen, the effect of termination by oxygen prevails and the rate of reaction decreases. Additives increase the conversion in the lower range of agitation speed only. The application of additives and agitation are two equivalent methods, both of which lead to an increase in conversion in the lower range of stirring speed.

Graft Copolymerization of Methyl Acrylate by Ceric Ion in the Presence of a Controlled Amount of Oxygen

“…The effect of traces of oxygen on conversion in the presence of 99% nitrogen (Method 3) was studied at 310 and 810 rpm, i.e., above 300 rpm, where the influence of monomer diffusion to active centers can be neglected [14]. The latter was arbitrarily chosen as being high enough for comparison while low enough to prevent significant shearing.…”

Preparation and Properties of Interpenetrating Polymer Network Films from Prevulcanized Natural Rubber Latex/Chitosan Blends

“…However, there still a few problems concerning the use of NR latex and its products, for example, the allergy of protein, the potential carcinogen of nitrosamines, the poorer of NR latex-made products in tear strength and aging-resistance, and bio-compatibility such as blood compatibility and cytotoxicity comparing with such bio-compatible silicone and polyurethane products as well. Therefore, many successful attempts have been made to modify NR latex for property improvement [1][2][3][4][5][6][7][8][9].…”