Gammadot Rheology Testing & Consultancy Services
Unit 5C, Leaton Industrial Estate, Bomere Heath. Shrewsbury. Shropshire. SY4 3AP. UK
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  Gammadot Rheology Bi-Annual Newsletter - March 2010
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*Only orders received with a valid purchase order before midnight on the closing date will be eligible for the 20% discount. Normal volume discounts given for sample batch sizes of 5+ will not apply during this promotion. Offer related to the services highlighted above and does not include thermal & physical testing such as specific heat capacity, thermal conductivity, tensile strength, etc.
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Gammadot Rheology is the only demonstration site in the UK for Reologica rheometers as supplied exclusively in Britain by Infra Scientific Ltd.

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FOCUS ON: MFR - One Pointless Measurement

The Melt Flow Index or latterly known as the Melt Flow Rate (or Melt Volume Rate), is one of the industries oldest, and widely used rheological quality control tools. It has been around for decades and comes in many shapes & configurations, although all are basically a crude form of capillary rheometer.
The MFI value quoted for a particular material is an average weight of material "cut offs" collected at set time intervals under isothermal constant load extrusion.

A minimum three lengths of cleanly cut, air bubble-free extrudate are required for calculations. These are weighed to the nearest milligram and the weights recorded. The average weight of extruded samples is then calculated.
Unfortunately, because the MFI is a low shear, single point test, it is woefully inadequate at providing the full picture in relation to process-range data. Due to the pseudoplastic (shear thinning) behaviour of most polymer melts it is important to determine the magnitude of viscosity across as wide a shear rate range as possible, as the material will experience changes in flow geometries (extrusion die lands, injection mould gates & runners, etc), and hence shear rate during the process, (Fig.1).

Figure 1

As an example, a typical Polypropylene having a MFI value of 2.4 g/10 mins (determined using a 2.16 kg applied mass @ 230°C), assuming the density is known, an approximate shear rate of 6.7 1/s can be calculated [Ref.1]. (It is an approximation because of the fact that MFI is driven by constant stress and not rate controlled; there is an increase in velocity as the MFI barrel empties under the constant applied stress (load)). As typical polymer processing techniques involve shear rates of ~100 1/s up to 100,000 1/s it can be seen that the MFI is a poor representation of the process, as it is unable to compare polymer flow behaviour at the shear rate levels experienced during conversion.

For accurate, reproducible quality control of pre-process feedstock, either capillary or rotational rheometers are an excellent choice. Which instrument is best for your application is dependent on what is important to your product. If material viscosity is sensitive to high shear / extensional rates or mapping of extrusion-orientated phenomena such as melt fracture is required, then use a capillary rheometer. If your process works within narrow tolerances sensitive to factors such as variance in Mw / MwD, melt stability, filler / masterbatch content, etc, a rotational rheometer in oscillation mode can be used to “fingerprint” material structural properties and predict the causes of variation in compared samples .

Ref.[1] Fleming, D.J, Melt Fracture and Elongational Viscosity via Convergent Flow Analysis , Proceedings of Polymer Testing '96 , RAPRA (1996).
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Gammadot Rheology exhibiting @ PDM'10

After enjoying a successful show last year, Gammadot will be exhibiting for a third time at the Plastics Design & Moulding event held in Telford, Shropshire between 18th - 20th May. In addition to ongoing contract work secured through the show, another direct outcome from PDM'09 was the visit to Gammadot's laboratory by Mr. Kenny Lui, Head of global sales for Moldex3D (Taiwan), and the resultant awarding of Moldex3D 'Materials Characterization Partner' status in late 2009. The show has been condensed into two halls this year, although our stand is in a similar position to previous events so don't forget to drop in to say 'hello' or come and discuss your materials testing requirements - you may be surprised how quickly & cheaply your materials characterisation issues can be addressed!

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Mark Edwards discussing a prospect's needs at last year's PDM event.
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Gammadot's stand is in a similar position to last year - see you there!
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Gammadot Rheology is a preferred supplier of materials characterisation data to Moldex3D. Taiwan
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For further information about Gammadot's testing & consultancy services, or if you have a specific problem / testing requirement which you would like Gammadot to provide a solution to, please contact us using the details at the top of the page or via the enquiry form HERE.

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Rotational Rheometry Services including:  shear viscometry, oscillatory Rheometry,  Cure Kinetics, Thermal Stability Studies, Yield Stress Analysis Capillary Rheometry Services including: Shear viscometry, Extensional Viscometry, Melt Density, No Flow Temperature Measurement Brookfield Viscometry Services including: shear viscometry  using  a combination of LV/RV/5xHBT instruments, Std. spindles/UL viscosity adaptor,SSA with water jacket or thermosel heating Oscillating Die Rheometry for rubber cure PvT Characterisation Services including: Specific Volume (or density) versus temperature & pressure, Bulk Modulus & Volume Coefficient of Thermal Expansion Compression moulding services for thermoplastic,  rubber & thermosetting materials