Polymer Initiators

PVC

Polyvinylchloride (PVC) is one of the most explored polymers in the world. The material is characterized by a very wide range of properties and its low cost. This explains its use in many applications.

Classical examples of PVC applications are: pipes, fittings, profiles, packaging, cable insulation, sheets, flooring, artificial leather, medical equipment, bottles, and molded articles.

Polymerization of vinyl chloride is exclusively done via a free radical mechanism. The reaction is generally performed between 40 and 80°C over 3 to 10 hours. The molecular weight and density can be regulated by temperature. Temperature is constant during polymerization for a given grade, for example, Kw67 (most produced grade of S-PVC) is manufactured at 57°C. There are 4 processes used: Suspension, emulsion, microsuspension and mass process.

Suspension processing represents 80% of PVC worldwide production. The main characteristics of this process are:

• Batch technology
• Reaction in water, liquid VCM in droplets of 5 to 10µm
• Oil soluble initiators.
  Autoclave reactor : 8-12 bars, 50 - 70°C
• Polymerization conducted up to 75% conversion, where pressure drop is observed
• Reaction finished or stopped at about 90% conversion

There are three other processes used:

Mass PVC

Batch process

Primary reactor:
prepolymerization up to 10% conversion to fix particle size (seed polymerization)

Secondary reactor(s):
reaction completed up to 85% conversion
polymer grains: 80-200 µm
process yields purest PVC (VCM+ initiator only)

Typical organic peroxide used: Luperox^® 223 (EHP)

Emulsion PVC

Continuous process
In emulsion: water + emulsifier, prepared in a special tank, water soluble initiator (K2SO4)

VCM droplet size: 10-30 µm, process conducted at 65°C, discharging of 40% dispersion. Yields porous PVC grains

Most appropriate for paste applications

Microsuspension PVC

Pseudo emulsion process
Emulsifier instead of protective colloid

VCM droplet size: 0,1-2 µm
two stages
prepolymerization: seed latex
completion by emulsion process

Most appropriate for paste applications

Typical organic peroxide used: Luperox^® 26 (TBPO), Luperox^® LP (LPO)

• Suspension PVC
• Benefits with Multiple Peroxides
• Safer Organic Peroxide Formulations (V-Series)