Лако-красочные материалы — производство

1. Methyl Methacrylate Homopolymer:

This example is the simplest formulation for an emulsion polymerisation consisting of one of each of the four essential components i. e. water, surfactant, monomer and initiator.

1. An aqueous phase is first prepared by dissolving 0.8 parts of sodium lauryl sulphate in 55 parts of de-ionised water in the reaction vessel.

2. An initiator solution consisting of 0.1 part ammonium persulphate dissolved in 4.5 parts of de-ionised water is prepared in a separate vessel.

3. 40% of this initiator solution is added to the reaction vessel, together with 4 parts of methyl methacrylate.

4. The temperature of the reaction vessel is raised to 75°C. An inert gas flow is sustained through the reaction mass throughout the reaction.

5. At the onset of polymerisation a sample taken from the reaction vessel has a blue hue.

Thi is due to the formation of small particles of polymer which scatter blue light

mo re than the longer wavelengths of the spectrum; red light which is scattered least, passes through the liquid giving the reactants a red appearance when viewed through the body of the liquid. The appearance of the blue tinge, which can be almost phosphorescent in intensity, is an indication that polymerisation has commenced.

6. Once polymerisation has commenced, the remaining initiator solution and monomer are fed to the reaction vessel over a predetermined period of time (3-4 hours), whilst keeping the reaction temperature at 75-80°C. It is usual to add the initiator to the reaction vessel over a slightly shorter period than the monomer.

7. On completion of the monomer addition, the reactants are maintained at 75-80°C for a further 45 minutes to ensure complete conversion of monomer to polymer.

The course of the polymerisation is monitored by measurement of the solids content of the reactants or by analytical methods to detect the presence of free monomer. Additional initiator may be added if required, to complete the reaction.

8. Once polymerisation is complete, the latex is cooled to below 40°C and filtered via a vibrating screen filter. The agitation must be maintained during the cooling period.

Properties

Particle size 0.09 — 0.10 pm

Molecular weight ca 600,000