Emulsion polymerization

Plastics are materials that consist of synthetic or semi-synthetic organic compounds that can be formed into objects of various shapes. They are usually high molecular weight organic polymers containing a number of other substances called additives that are designed to change the processing and performance properties.

Polymerisation is a reaction consisting of low-molecular mass chemical compounds (monomers) or a mixture of these types of compound reacting with one another until their functional groups are depleted. This reaction results in the formation of particles with a significantly higher mass compared to substrates that are referred to as polymers.

Emulsion polymerisation is a technological method of polymerisation. This process is also used to produce polymer dispersions, also referred to as latex. These products are widely used, such as for adhesives, water-based paints, wood coatings, rubbers, sealants or non-woven fabrics.

There are several variants of the emulsion polymerisation process. One of them is the batch process, in which the reaction is initiated provided that all the reagent portions are in the reactor. Another is the semi-continuous process, in which at the beginning only some of the reagents are placed in the reactor, with the remainder dispensed in controlled portions during the process.

Emulsion polymerisation is a commonly known and applied method in the plastics industry. This is why the PCC Group provides a wide range of products dedicated to this technology. It includes, for example, dispersers, emulsifiers, co-emulsifiers and other additives.

Emulsion polymerisation — from monomers to polymers, or how plastics are made

You have certainly heard of this group of products many times. What is more, you use them every day in a number of different fields. Plastics have become one of the most diversified product groups. They have been widely applied in packaging production, transport, medicine, households and many other fields. Have you ever considered what is the meaning of their name? What chemical compounds can be included in this group? One of the first plastics was polyvinyl chloride, abbreviated to PVC. It is currently ranked second when classified as frequency of application as part of this group of materials.

Polyvinyl chloride – a versatile substance

Polyvinyl chloride gained its popularity owing to the properties that depend on its form. Two types of PVC are available: unplasticised (hard) and plasticised (soft). The former has good insulation properties, and is resistant to corrosion, chemicals, fire and weather conditions. It also resistant to mechanical factors, such as tension or crushing. It is used in the construction and medical industries, as well as for the manufacture of sewer and drain pipes or containers.

Soft PVC, on the other hand, is a highly flexible material. Despite its flexibility, it is characterised by high resistance to mechanical damage and weather conditions, and it can be shaped at lower temperatures than hard PVC. It is used as a cable insulator in the electrical industry. Some of its applications deal with the clothing and automotive industries, and for manufacturing of linings, plastic dpc sheets and packaging. These are only a few among numerous applications of both PVC types.

Then what on what do the final physical properties of PVC depend? The decisive stage is the selection of the type of polymerisation of polyvinyl chloride. It can be obtained by way of emulsion polymerisation, suspension polymerisation or bulk polymerisation. In this case we will focus on emulsion polymerisation.

A few words about emulsion polymerisation

Emulsion polymerisation is a method of polymerisation of a monomer in a dispersion medium, which in most cases is water. It consists in the emulsification of hydrophobic monomers using an emulsifier, such as oil in water. Then a reaction is initiated with a water-soluble initiator or an oil-soluble initiator with a stabiliser. Emulsifying agents are surfactants, ensuring the stability of the initial monomer emulsion and resulting polymer dispersion.

To create a dispersion, it is common to use various additives, called dispersing agents, to support the process.

Anionic surfactants are the substances most commonly used during emulsion polymerisation. This a relatively complex process as the growth and stabilisation of polymer molecules are controlled by mechanisms of free-radical polymerisation in combination with various colloidal phenomena.

Preparation of polyvinyl chloride by way of emulsion polymerisation

When the surfactant concentration exceeds the critical micellar concentration (CMC), surfactant molecules aggregate and form spherical micelles. As a consequence, hydrophobic monomers penetrate into the micelles. Water-soluble initiators also get into these spherical structures. Free radicals are propagated there. The micelles act as a point of contact between water-soluble initiators and hydrophobic vinyl monomers. The reaction of formation of a polymer chain takes place until the utilisation of all monomer droplets suspended or dissolved in water, which leads to the preparation of polyvinyl chloride (PVC-E). The compound obtained is formed of small-size grains. As a result it is used in the production of, but not limited to, pastes as they are not prone to fast swelling in softening agents.

Importance of emulsion polymerisation for the industry

Emulsion polymerisation is a process widely used at an industry and academic level, and its importance is still being increased. Polymers produced using the emulsion polymerisation method can be divided into elastomers (nitrile rubber, acrylic rubber, polybutadiene), engineering polymers (PVC, polystyrene, PMMA) and emulsions (polyvinyl acetate, polyacrylic latex, styrene-butadiene latex). These products are used in almost all branches of industry. For example, vinyl polymers (CH2=CH-) are commonly used as synthetic rubbers, thermoplastics, coatings, adhesives, binders, rheology modifiers and plastic pigments. Their advantages include fast reaction rate, process safety, high molecular weight of the polymer produced and process continuity. Their drawback, however, is difficult removal of all the residues of the emulsifier or other additives.

Suggested products supporting emulsion polymerisation

During the first half of 2020, PCC Group introduced subsequent products dedicated to emulsion polymerisation. The product range was extended by additional anionic surfactants, such as Sulforokanol L430/1, SULFOROKAnol® L725/1 and SULFOROKAnol® L1230/1, with excellent emulsifying and stabilising properties. They are used for the production of styrene-acrylic, acrylic and vinyl dispersions. What is more the portfolio of PCC Group consists of dispersing agents (R, RP, SBRP) intended for the production of styrene-butadiene rubbers as supporting agents. They are compatible with other chemical compounds used in emulsion polymerisation, such as emulsifiers or stabilisers. Owing to low moisture content and low bulk density, they allow transport and storage costs to be reduced.