How Dynisco online rheometers can help PET recyclers?

Azadeh Farahanchi, Rheological Scientist, Ph.D

12.17.2019

Many polymers used in plastic industry are hygroscopic such as polyester, nylons, etc. For these kinds of materials, intrinsic viscosity (IV) is commonly used as the specification of various resin grades. As a result, it is necessary for the hygroscopic resin manufactures to consistently ensure the intrinsic viscosity of their materials are within the specification.

Dynisco online rheometers can be easily installed in variety of extrusion lines and continuously measure the intrinsic viscosity parameters of the extrudates during an extrusion process. This is performed by using a mathematical correlation between polymer`s shear viscosity and intrinsic viscosity. Figures below show the online measurements of shear and intrinsic viscosity of polyethylene terephthalate resins (both dried and under-dried PET resins) over time during an extrusion process.

PET resins need to be carefully dried before the process in order to reduce the amount of moisture contents and prevent degradation during the process. Under-dried PET had residual moistures, which caused the polymer to be degraded inside the extruder. This reaction mainly reduced polymer`s molecular weight and/or broadened polymer’s molecular weight distribution resulting in reduction of polymer`s shear and intrinsic viscosity parameters. By proper drying of PET however; the online rheometer monitored intrinsic viscosity in consistent with the resin`s IV specification.

This feature of Dynisco online rheometers have mainly generated interest among PET recyclers since it helps them to ensure the quality of the regrinds, reduce the waste amount, and increase the efficiency of their process.