Enhanced uPVC processing using supercritical CO2


uPVC is inherently viscous and processing it requires high pressures and temperatures – which in turn demands significant energy consumption.  Also because it is thermally unstable, processing PVC at high pressures and temperatures may result in thermal degradation. Often, expensive additives are used to reduce the damage caused by processing.

Inclusion of carbon dioxide into the melt is known to reduce melt viscosity of some polymers, in some cases by orders of magnitude.  Recent research at Queen’s University Belfast (QUB) has explored the use of carbon dioxide, in a supercritical state, as an aid in the processing of uPVC to overcome these limitations, to increase efficiency and reduce costs.

QUB has developed a modified technology whereby the introduction of supercritical carbon dioxide (scCO2) into PVC compounds and dry blend formulations has a strong influence on levels of gelation.  The technology enables the extrusion of solid profiles at lower temperatures, with the associated benefits of reduced melt viscosity, allowing processing at faster output rates, and with significantly lower energy consumption – nearly 50% reduced with small profile grades.

Sample practical results from PVC compounding using a Haake internal mixer or a twin-screw extruder are shown in the table below.


CO2 Flow Rate (ml/min)

Pressure at end of barrel (bar)

Motor current (amps)

Reduction in motor current (%)

Power saving

Clear PVC blow-moulding grade


222 ± 1.5

2.89 ± 0.15




209 ± 2.9

2.77 ± 0.07

PVC tube grade


74.3 ± 0.73

1.79 ± 0.12






uPVC small profile grade










The inventors estimate that the additional equipment required – essentially an scCO2 pump with a satisfactory specification - could be produced with a selling price of around £4,000.  This projected pump cost compares well with cost reduction through the energy savings calculated above.  For a high throughput pipe grade compounder, for example, the additional capital cost is repaid in less than a year.  Such a short payback period is generally regarded as a sound justification for a capital investment.

QUB is working with industrial partners in various parts of the PVC supply chain to commercialise this technology.  Current and planned R&D includes work to:

  • develop a low cost industrial standard scCO2  pump;
  • develop a ‘retro-fit’ solution for compounding and extrusion machines;
  • further investigate and quantify energy savings;
  • investigate and quantify additive savings.

Enhanced uPVC processing using supercritical CO2

Lead Institution

Queen's University Belfast

Project Funding

We have access to a range of potential funding mechanisms to support your business collaborate with this project including

ktp Knowledge Transfer Partnerships are based on partnerships between academic groups and companies who need access to skills and knowledge in order to innovate. The academic and industrial partners jointly devise and manage a two or three year programme to achieve the advances the company needs. This programme of work is carried out in the company by a KTP Associate and the resulting relationship can be very challenging and rewarding to all parties
4k-vouchers Innovation Vouchers are designed to enable small Northern Ireland enterprises to access knowledge and expertise to develop innovative solutions to business issues. The programme provides a voucher of up to £4000 to enable small enterprises to engage with one of the 41 universities, colleges and other publicly funded research organisations throughout Northern Ireland and the Republic of Ireland
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