Emulsion PVC (E-PVC)

E-PVC is a type of PVC produced through emulsion polymerization. To better understand its physical properties and chemical structure, let us first look at PVC.

Polyvinyl Chloride (PVC)

PVC is a polymer. Its monomer is vinyl chloride monomer (CH2=CHCl), obtained from ethylene and chlorine. The boiling point of vinyl chloride monomer is -13.4°C. At room temperature and atmospheric pressure, it exists as a gas. For this reason, it is used as a compressed volatile liquid in all polymerization processes.

Physical Properties

[caption id="attachment_104825" align="aligncenter"] Table 1. Physical properties under standard temperature and pressure (25°C and 100 kPa)[/caption]  

Production Method

PVC is obtained by combining vinyl chloride monomers, formed by passing ethylene through a chlorinated environment, under temperature and pressure using an appropriate catalyst. The basic component of PVC is chlorine obtained from rock salt, and crude oil material accounts for 43% of the composition. [caption id="attachment_104826" align="aligncenter"] Figure 1. PVC production flow chart[/caption]

Emulsion PVC (E-PVC)

As mentioned above, PVC produced through the emulsion polymerization method is called emulsion PVC. Through emulsion polymerization, conjugated dienes such as butadiene and isopropene, vinyl acetate, vinyl chloride, various acrylates, and methacrylates can be polymerized, and various copolymers of these monomers can be produced.

Emulsion Polymerization

Emulsion polymerization is the method of polymerizing monomers finely dispersed in water with the aid of emulsifiers. Emulsifiers are chemicals where one end is soluble in water and the other end is soluble in the monomer. The emulsifier dissolves in water and the hydrophilic portions arrange themselves in a ball-like structure with the interior facing inward. These balls are called "micelles." In emulsion polymerization, the environment contains water, monomer, micelle-forming agent, and initiators. • Sodium laurate and dodecyl trimethyl ammonium bromide are used as micelle-forming agents. • The chemicals used as initiators are listed in Table 2 according to reaction temperature. The type and concentration of the initiator is one of the factors affecting the degree of polymerization. As initiator concentration increases, the degree of polymerization generally increases and the molecular weight decreases proportionally. In polymerization processes, initiator is typically used at 0.1-1.0% of the monomer. In emulsion polymerization, water-soluble peroxides and persulfates are frequently preferred as initiators. [caption id="attachment_104827" align="aligncenter"] Table 2. Initiator chemicals[/caption]  

The stages of emulsion polymerization are as follows:

1. Initially, the micelle-forming agent and water are mixed. 2. Some of the micelles in the mixture dissolve in water, while others combine to form spherical micelles. 3. After the micelles dissolve in water, the mixture is stirred and monomer is added to the system. 4. Monomers move toward the micelles, and as the micelles grow, they adsorb emulsifier molecules from the environment. 5. Over time, as polymer particles grow, monomer molecules decrease, and when polymerization advances at 50-80%, the monomer molecules are depleted. 6. When chain reactions within the polymerization particles end, polymerization is complete. [caption id="attachment_104828" align="aligncenter"] Figure 2. Stages of emulsion polymerization[/caption]   (a) Before starting; (b) Start of polymerization; (c) Continuation of polymerization, all micelles depleted; (d) Monomer droplets depleted; (e) End of polymerization (o- : Micelle, M: Monomer, P: Polymer, R: Free Radical) Advantages of Emulsion Polymerization • Polymerization rate is high. • High molecular weight polymers can be obtained. • Reaction temperature is low and therefore temperature control is easy. • Viscosity is low. Consequently, mixing and heat transfer are easier. • It is safer compared to bulk and solution polymerization methods. • No organic solvents are used; water is the solvent. For this reason, it is a low-cost and healthier method.

Disadvantages of Emulsion Polymerization

• More additives are used compared to other processes. • It is difficult to remove the micelle from the polymer.

E-PVC Applications

• Labels • Tarpaulins • Synthetic leather • Floor tiles • Traffic cones • Wallpapers • Fabric coating • Printing inks • Plastisol ink production • Under-body coating in automobiles

E-PVC Demand in Turkey

There are E-PVC producers and recycling companies in our country. At the same time, the product is also imported. The HS code (Harmonized Tariff System) is defined as 3904.10.00.00.11. According to Turkish Statistical Institute data, total E-PVC imports in 2019 were approximately 45,000 tonnes. The countries with the highest imports are Germany, Sweden, and France, respectively.

References

1- Polymer Chemistry. PVC. Access Date: 26.08.2020 www.lisans.cozum.info.tr 2- "Polyvinyl chloride". Access Date: 26.08.2020 en.wikipedia.org 3- "Polyvinyl chloride". Access Date: 26.08.2020 www.pagev.org/polivinilklorur 4- Sümer İ. Effect of Initiator on Vinyl Acetate and Butyl Acrylate Copolymerization. (2003). Access Date: 26.08.2020. www.dspace.yildiz.edu.tr 5- "What is Emulsion Polymerization". (2015, October). Access Date: 26.08.2020. www.plastikciyiz.wordpress.com 6- Evcin A. Polymer Materials. (2017). Access Date: 26.08.2020. blog.aku.edu.tr 7- "What is Emulsion PVC?". Access Date: 26.08.2020 www.eymenpetrokimya.com.tr   Öznur Kurt Product and Service Development Specialist Aleph Trade