Chemistry | Chemical Analytics | Reaction Monitoring in the Production of Polysterene

Real-Time Monitoring of Particles Size Dimension and Conversion Ratio During the Production of Expandable Polystyrene

Polystyrene can be found in many areas of everyday life

Polystyrene is a widely used, low-cost plastic and highly versatile. Depending on the type of production, a distinction is made between fine-pored extruded polystyrene (XPS) and the more coarse-pored expanded polystyrene (EPS), which characteristically consists of small plastic beads that are fused together. Due to its technical properties such as low weight, stiffness and formability, expanded polystyrene can be used in a variety of applications, for example as a shock-absorbing packaging material or for thermal insulation for buildings.

During the production process of expandable polystyrene beads, continuous monitoring of the polymerization reaction is essential for the Italian chemical manufacturer »Versalis S.p.A« in order to obtain a high-quality product and high yield and to ensure optimal control of the production line. Important parameters that must be controlled during the suspension polymerization of EPS are the measurement of the polymer particles that form and grow during the reaction, as well as the degree of conversion of the styrene monomer into the polymer.


Precise endpoint determination during the polymerization reaction of expandable polystyrene



Area of Application

Continuous monitoring of critical parameters during the production of polystyrene beads



Scope of Application

  • Industrial Production of Polymers

  • Production of Plastics

  • Polymer Industry



  • Process Analytical Technology (PAT)

  • NIR Spectroscopy

  • Online Spectroscopy


  • NIR Spectroscopy

  • Inline Measurement

  • Reflection Measurement


  • Precise Process Control
  • High Process Security
  • Increase in Efficiency
  • Process Optimisation

The Challenge

It must be possible to determine the end point of the polymerization reaction precisely

Polystyrene is an amorphous, transparent thermoplastic and is produced in two process steps in chain polymerization from the monomer styrene. During these two process steps, the particle size and the progress of the conversion of the styrene monomer must be continuously monitored. The degree of conversion is crucial for determining the end point of the reaction. The conversion reaction of the monomers is very fast. The reaction must therefore be monitored very accurately and in real time.

If the end point of the polymerization is not detected in time, it can happen that the styrene monomers, which develop into pellet-like beads in the course of the reaction, clump together to form a large ball and cause a blockage at the reactor outlet. In the worst case, this large ball causes the blockage of the entire plant.

Critical process parameters must be continuously monitored

The current procedure involves manual sampling and estimation of the particle size of these beads in front of a light beam. This procedure requires a great deal of expertise and is difficult to reproduce.

For a more precise and efficient monitoring of these control parameters in the heterogeneous phase, a method is needed that is reproducible, can ensure the monitoring of the relevant parameters continuously and does not require frequent maintenance interventions at the plant. The measuring technology used must not interfere with the fluid dynamics of the reactor, not be susceptible to contamination and must be ATEX Zone 2 IIB T3 compatible.    

The Application

In two reaction steps, expandable polystyrol granules are produced that can be used in many different ways

During the polymerisation the monomer is in a first step mixed with additives. In the second reactor, the conversion process from styrene to polystyrene occurs. During the polymerization process, gas inclusions are formed. With the aid of pentane as a blowing agent and pure steam, the polystyrene granulate expands. The expansion of the gas can be used for further processing of the granulate. The beads expand up to 50 times their own volume. In this final step, the polystyrene granules can be formed into any geometric shape.

You want to know how this measurement task was solved the best possible way?

A more detailed description on how this application was realized using online measurement technology can be found in our detailed application report, which you can download from the info column at the top of the page.

Products of the brand:


Hellma USA Inc.
120 Terminal Drive
11803 Plainview, NY
United States

Phone: +1 5169 3908 88


Disabled, please use email.

Real-Time Monitoring of Particles Size Dimension and Conversion Ratio During the Production of Expandable Polystyrene


Thank you very much for your interest in our download of "Real-Time Monitoring of Particles Size Dimension and Conversion Ratio During the Production of Expandable Polystyrene". Please fill in the form below and we will send you the requested link to the given e-mail address.

Note: Your data will of course be treated confidentially and will not be shared with third parties. You can revoke your consent at any time by clicking on the end of each e-mail.
Required Field