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Correlation between mixer tests and extrusion behaviour of PVC dry blends

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article image HAAKE laboratory mixer

On July 1st, 2006, the EU Directive 2002/95/EG (RoHS-Directive, Restriction of Hazardous Substances) was put into force. It restricts producing and trading of products containing i.e. lead, mercury and cadmium.

Because a lot of PVC compounds still contain lead as stabilising media, there is urgency for the PVC industry to replace these stabilisers by less dangerous materials like CaZn stabilisers.

Changing the formulation of a PVC compound by using a new stabiliser, always takes the risk that also the production behaviour will change. The reason behind this is the fact that stabilisers also work as a lubricant.

So the change of stabilisers will influence the fusion behaviour of the PVC compound.

To make sure that the PVC compound keeps its processing properties it is necessary to adapt the whole compound formulation.

The common tool to check the fusion behaviour of PVC compounds is the laboratory mixer test. It is an easy and reliable method to characterise the fusion and degradation behaviour of PVC compounds.

The samples used for this investigation were three PVC dry blends with new lead free formulations.

Materials and methods polymer:

  • Three samples of a PVC dry blend with different CaZn-stabilisers

Test arrangements mixer test:

  • Torque-rheometer: RheoDrive 4
  • Double range torque CAN sensor
  • Analysis software PolySoft OS
  • Mixer rheomix600 OS
  • Roller rotors
  • Pneumatic feeding ram

Extruder test:

  • Laboratory twin screw extruder: Rheomex CTW100 OS
  • Extruder screws: Standard screws
  • Sheet die 50 x 1.0mm
  • Hopper with vibrator
  • Melt-pressure sensors

More details are available with Rheology Solutions.

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