materials development | Optimising formulations
Polymaterials is headed by two polymer chemists, Gerhard Maier (left) and Jürgen Stebani (right)
injection moulding and to work on the mixing aspect that would enable us to generate a melt that would have the same morphologies and physical properties that you would normally obtain using a twin-screw extruder and conventional injection moulding.” Early work to establish the validity of the system
extruder, it is normally only possible to produce no more than three or four different compositions in a day.
Mixing and moulding What makes the system rather remarkable is that no traditional twin-screw extrusion compounding equip- ment is used at all. Instead, materials are added directly at the injection moulding machine, which makes test pieces for various mechanical and optical tests; mixing is done via a cascade of static mixers – de- tails of which the company is understandably reluctant to discuss. Up to eight components can be mixed together for any one test run. Maier says that, assuming that 10 test samples are required per test, Polymateri- als can process up to 40 different compositions in a day. “We can handle relatively complex systems in a very easy way,” he says.
The injection moulding machine is a two-component
Formulations are added
directly to an injection moulding
machine which makes the test pieces
type configured in a rather unusual way, since it does not actually make two-component parts. Instead, each injection unit processes different materials, which are then all fed together into the static mixing section and then to the mould. “One way to operate the machine so as to achieve fast changes is to feed all that is to remain constant into one of the injection units, and those components that will change into the other,” says Maier. The different concentrations are then achieved by changing the ratio of both melt flows. All in all, the system is very conservative with its
materials. “We need about 1 kg material in total per compound, depending mostly on the type and number of test bars desired,” Maier says. Fewer than five shots are lost when changing compound recipes “Thus, it is also ideal to study experimental materials, where there is only a small sample of 20 kg or so available.” Maier explains: “Combinatorial screening entered the
polymer world some 10 years ago, but most institutes have used it only for miniaturized samples. We wanted it to work with standard test pieces in standard tests, just as you do in conventional product development. It was clear to us that we needed to base our system on
12 COMPOUNDING WORLD | July 2014
www.compoundingworld.com
involved fairly conventional polymer blends, such as polycarbonate/ABS and rubber-modified polyamides and polyesters. More recently the company has also looked at blends based on biopolymers such as PLA. “We have always found that we can make materials with the same physical properties as obtained using a twin-screw extruder with an error of 5-10%,” Maier says. The only exception to date is with flame retardant
compounds, where the Polymaterials process produces compounds with slightly higher flame retardance than is normally achieved with twin-screw extruders. Maier says this is probably for two reasons. Firstly, when using inorganic flame retardants that do not dissolve in the polymer matrix, the very good distributive mixing obtained with the static mixers in the HTC system works in their favour. Secondly, the HTC system produces materials with only one heat history, whereas com- pounding followed by moulding has two, so the material suffers less degradation and hence less of the flame retardant is consumed. The equipment works best with pellets and free-
flowing powders and Polymaterials is now working on using liquid dosing, which should be available later in the year. Production of compounds with free-floating
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