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Online viscosity control aids polymer production

A Hydramotion product story
Edited by the Engineeringtalk editorial team Jan 26, 2007

An on-line viscometer from Hydramotion is an essential tool in the production of polyethylene terephthalate (PET) and polyetheylene naphthalate (PEN) at a large polymer plant in Scotland.

An online viscometer from Hydramotion is an essential tool in the production of polyethylene terephthalate (PET) and polyetheylene naphthalate (PEN) at a large polymer plant in Scotland.

These polyesters are made by reacting ethylene glycol with either terephthalic acid, dimethyl terephthalate or naphthalene 2,6-dicarboxylic acid to create long-chain molecules.

The longer the polymer chains, the stiffer is the material and the higher the viscosity.

Production engineers can therefore control the chain length by monitoring the viscosity of the mixture in real time.

Shorter chain-length polymers are used for making polyester fibres or films, while longer chain-length (stiffer) polymers are used for making plastic bottles or tyre cords.

The Scottish plant specialises in polyester films, so it is vital that polymerisation is stopped before the chains grow too long.

This is where the Hydramotion XL7 online viscosity control system comes in.

The XL7 provides continuous real-time dynamic viscosity measurement with unlimited range - an important consideration when the viscosity of the product can be as high as 500,000cP.

The instrument has very high sensitivity, giving engineers precise control over the degree of polymerisation.

Yet despite its sophistication it is an easy-to-use, "bolt-on-and-go" device that can be installed in minutes.

The single, solid sensor is specially shaped to present minimum disruption to flow, resulting in reliable, uninterrupted performance at high temperatures and pressures.

The instrument needs no special cooling, and with no moving parts maintenance is virtually eliminated.

Outputs include a 4-20mA analogue signal and a serial data link for continuous viscosity monitoring and control.

Correlation between measured on-line viscosity and calculated melt viscosity is excellent.

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