Pressure measurement in the production of PBAT, a biodegradable plastic, faces a special challenge: Temperatures of up to 330 °C prevail in the process. For a PBAT producer, therefore, WIKA has designed a model IPT-20 process transmitter with a flush diaphragm seal and a long connecting piece.
Polybutylene adipate terephthalate, PBAT for short, is a copolymer from the polyester group. The plastic can replace polyethylene and is completely biodegradable. PBAT thus contributes to greater sustainability. Among other things, it can be used to make protective sheeting for agriculture and gardening, compost bags, shopping bags and medical disposables.
Pressure monitoring during esterification and melt polymerisation
The process steps in production include esterification and melt polymerisation. In these two processes, WIKA’s customer, a petrochemical company, uses the IPT-20 transmitter for pressure monitoring.
Corresponding to the task, WIKA supplied the instruments with three basic measuring ranges: 0 … 16 bar, 0 … 40 bar and 0 … 250 bar. The exact measuring ranges can be set for this type of transmitter using the turndown function. This means that the output signal is distributed only over the scaled range. Thus, the measured values can be more precisely determined.
Connecting element as a cooling element
Pressure measurement in plastics production in the case of PBAT is subject to process temperatures between 100 °C and 330 °C. For this reason, WIKA has designed a measuring unit consisting of an IPT-20, a flush diaphragm seal and a 200 mm long connecting piece. Due to its length, the connecting element acts as a cooling element. Thus, the measuring instrument remains protected against adverse effects caused by the high process temperatures. The entire design is also minimised in volume to reduce any temperature error effects during measurement to a minimum and thus achieve the best possible accuracy.
Plastic is highly viscous at the pressure measurement points
At the measuring points of the IPT-20, the plastic is in a highly viscous form. The diaphragm seal, combined with the transmitter, is therefore implemented with a flush diaphragm. As a result, it enables pressure measurement without the risk of media entrapment.
Technical details on the model IPT-20 process transmitter are available on the WIKA website. There you will also find an overview of other products and solutions for the chemical industry and petrochemical industry sectors, as well as a brochure to download. If you have any questions, your contact will gladly help you.
You can also find out more about the turndown function of WIKA process transmitters in the following video: