Water Based Polymer Emulsion

Water based polymer emulsion -- Properties

Generally speaking, emulsion polymers have the following properties.

(1) Appearance

From milky white (often with blue phase) to translucent, uniform and viscous fluid.

(2) Viscosity

It has nothing to do with the molecular weight of the polymer and is generally low. Emulsion is a non Newtonian fluid, and its stress is not linear in one strain. Viscosity is measured by rotational viscometer. The measured values are expressed in PA · s and MPa · s.

(3) Condensate

In the process of emulsion polymerization, micro aggregates can be allowed, but can not exceed a limited value.

(4) Minimum film forming temperature (MFT)

This value is related to the glass transition temperature of the polymer. When the temperature drops below MFT, the emulsion can not be film-forming, and film forming auxiliaries must be used.

(5) Ionic properties

The use of emulsifiers in emulsion polymerization can be divided into the following categories: the use of anionic emulsifiers alone, the use of non ionic emulsifiers, the use of cationic emulsifiers alone, and the use of anionic and nonionic emulsifiers.

(6) Particle size and particle size distribution

The polymer emulsion is an uneven system, and the polymer is irregular dispersed in the emulsion. Because the emulsifier and polymerization process used in emulsion polymerization are different, the emulsion particles and their distribution are very different. The size and distribution of emulsion are directly related to the appearance of emulsion. Therefore, different emulsions have different appearance, mainly on hue.

(7) Residual monomer (VOC) content

Emulsion polymerization can generally achieve a relatively complete degree, but there are often a small number of incomplete reaction of monomer, resulting in high VOC content, which is not conducive to environmental protection. Therefore, the content of residual monomer in emulsion should be limited, usually below 0.1%, and different compositions of emulsion should have different requirements.

(8) Stability

Because emulsion is an uneven system, there must be stability. Testing molecular weight and molecular weight distribution including chemical stability, mechanical stability, storage stability, freeze-thaw stability, dilution stability and so on, no matter how to determine the molecular weight of emulsion polymer, we should first aggregate the emulsion, then wash the polymer, and then dissolve it in the proper solvent with less polarity. Brookfield Viscometer and format tube can be used to determine the viscosity average molecular weight. When determining the number average molecular weight, use an osmotic pressure gauge. When determining the weight average molecular weight, a light scattering photometer is used. The determination of polymer molecular weight and its distribution is often a matter of polymer scientific research. In modern polymer research, these classical methods are still applied, and large advanced analytical instruments such as gel chromatography have been applied more and more widely. The glass transition temperature (TG) of polymer is a very important data. Polymer development is inseparable from this data, and polymer users also need to know this data: as mentioned earlier, the TG value of polymer can be checked by the data provided by predecessors and calculated by formulas. Based on its importance, even if it is not engaged in basic research, it is sometimes necessary to measure it. The main method for determining TG is the expansion method. The instruments used are called differential thermal analyzer or thermal spectrometer, which are expensive instruments.

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