Need to disperse challenging additives or get demanding fillers integrated into your polymer matrix? Want to set up a reactive extrusion? Looking to characterize your process by measuring flow behavior online?

These are only a few application needs you can satisfy with our flexible, proven twin-screw compounders.

The formulation of modern polymer compounds can be quite complex and include many ingredients. It can be challenging to disperse some of these additives and fillers homogeneously in the polymer matrix; this makes it very important to optimize set-up of the compounding line equipment solutions.

Metal injection molding (MIM) is a process where a feedstock consisting of a polymeric binder and a high percentage of fine metal powder is processed in injection molding equipment. Injection molding allows mass production of complex shaped parts in one step. Parts produced using MIM are often used in the medical, dental, aerospace, or automotive industries. For MIM, the feedstock is usually prepared in an extruder where the challenge is to obtain a high fill level of metal powder while simultaneously ensuring good flowability for injection molding.

Compounds containing nanomaterials are used for the production of light-weight but sturdy parts. Compounding materials like carbon nanotubes (CNTs), nanoclays or graphene is demanding due to the need for a homogeneous dispersion inside the compound and to exfoliate the nanomaterial so no lumps remain in the final goods. Different approaches using parallel twin-screw extruders can be used to achieve these goals, depending on the properties of the starting material.

Compounding resources

After compounding has occurred inside the extruder barrel, the actual process of extrusion takes place as the plasticized material is pushed through a die into its final shape. A simple strand die with one or multiple round holes is usually used when the material is processed further after extrusion (e.g., cut into pellets). More sophisticated shapes are used when the material is the final product after extrusion; for example, catheter dies or dies for co-extrusion.

Catheter dies are often used to create the small tubing used in many medical applications. The tubing is produced using a variety of polymers, some of which are biodegradable. Depending on the desired dimensions of the final tubing, the processing throughput and take-off speed of the hollow strand are importnat parameters to control for a high quality end-product. To prevent collapsing of the tube, air is often applied in the center of the catheter until the hot polymer is solidified.

A co-extrusion die is another complex die structure used to directly produce the end product. In this set-up, two or more extruders supply polymers into a single die where the polymers are distributed evenly and leave the die through one opening. A popular shape for pharmaceutical applications is a co-extrudate with a round inner core covered by a thin outer layer forming one concentric strand. In processing, the control of the two extruders determines the ratio of inner to outer mass fraction of the co-extrudate, and the optimal processing parameters have to be applied to produce an even layer with no defects.

Shaping resources

It’s essential during processing to know the rheological properties of polymers in shear as well as in extensional flow. Being able to measure the flow behavior of a polymer melt directly in the process helps avoid failures due to sample preparation and delivers value in real-life conditions. This measurement also helps to investigate structural changes during compounding.

The Thermo Scientific™ HAAKE™ MiniLab 3 Micro-compounder is a small conical twin-screw extruder with a patented slit-capillary backflow channel. The channel has two pressure transducers which are used to measure the pressure drop in the capillary. A shear stress can be calculated from the pressure drop and the geometry of the slit capillary. A shear rate is correlated from the selected screw speed and the measured back pressure. Together, the shear stress and shear rate values are used to calculate the relative sample viscosity at different screw speeds.

A capillary rheometer is best suited for measuring shear viscosity at process-relevant shear rates. The Thermo Scientific™ HAAKE™ PolyLab OS Torque Rheometer System is advantageous for polymer materials because screw plastification in an extruder is ideally suited for homogeneous preparation of the sample material for rheological measurement. The PolyLab Torque Rheometer System offers different die types for rheological measurements. 

Processing Resources

Make and analyze polymer nanocomposites

Compared to unfilled polymers, polymer nanocomposites show improved properties that make them interesting for various technical applications. Highly desired properties of these polymeric materials include their greater mechanical strength and low weight. The incorporation of nanocomponents can also lead to an improved heat and chemical resistance as well as electric conductivity. Nowadays, polymer nanocomposites are frequently used in the automotive and aviation industries as well as in construction materials for windmill blades.

Polymer nanocomposites are produced by mixing nanoparticles into a molten polymer matrix using extrusion. One way to achieve proper mixing during the extrusion process is to use nanoparticles that are predispersed in a carrier liquid and feed that dispersion into an extruder. The composite material will only exhibit the desired properties when the particles are distributed homogeneously inside the polymer matrix and no large clusters are formed. Using carrier liquids also ensures safe handling of the nanoparticle raw material. Avoiding particle dust in the workplace environment is of utmost importance for safety. 

Learn more about how nanoparticles can be incorporated into a polymer matrix and how rheology can help to investigate the final product properties of polymer nanocomposites.

Download the application note