Analyzing solid and molten polymers with rotational rheometers
Polymers are large molecules consisting of repetitive units of smaller molecules bound together in long chains. They are used in a broad variety of applications and are ubiquitous in our everyday life. In a solid state, they are used for casings, packaging and composite materials. For these types of applications, polymers are processed at elevated temperatures in a molten state.
Due to their chemical structure and high molecular weight, polymers exhibit a complex flow and deformation behavior. They are so-called viscoelastic materials, showing both viscous and elastic properties. Which behavior dominates depends on the molecular structure itself, as well as the testing or processing conditions.
Knowing the viscoelastic properties of a polymeric material is therefore essential to optimize formulations and blends or to adapt a process to the properties of a given material.
Rheology has proven to be an excellent tool to analyze the mechanical properties of polymers in their different states.
Rheological measurements provide valuable information about the flow and deformation resistance as well as the viscoelastic properties of polymer melts. The results can be used to optimize processing and forming steps such as extrusion and molding. In addition, rheological parameters obtained from oscillatory tests hold information about the molecular weight as well as the molecular weight distribution of thermoplastic polymers.
Rotational rheometers can be utilized to perform dynamic mechanical thermal analysis (DMTA) where a solid specimen is exposed to oscillatory excitation while the temperature is continuously changing. The data obtained during measurement are used to identify characteristic phase transitions such as the glass transition or melting and crystallization. In addition, DMTA is used to determine the final product performance and key application-related properties such as stiffness, brittleness, damping, or impact resistance.
After rotation and oscillation, extension is the third type of flow that can be investigated with rheological methods. Extensional flow occurs during many technical processes such as spraying, filling, or, more related to polymer melts, film blowing, foam extrusion or fiber spinning.
The Sentmanat Extensional Rheometer (SER) fixture enables you to perform extensional testing of polymer films with a rotational rheometer. The extensional behavior of polymeric materials can differ quite significantly from the behavior in shear flow. Phenomena like strain hardening can be observed. A solid understanding of the extensional properties of a polymer sample can help to optimize the final product properties of materials processed and formed by the above mentioned techniques.
Compound. Shape. Analyze.
You have only a few grams of material that you need to compound and shape into a specimen for rheological characterization. How best to do that?
The Thermo Scientific Process 11 small scale compounder provides a workflow enabling small scale compounding with 20g of material. Together with Thermo Scientific HAAKE MiniJet Pro injection molding machine, different specimens can easily be produced from the compounded material to run tests for rheological characterization of the material.
Do you have even less material available? Eliminate worries of limited material quantities and produce various sample geometries with the MiniJet Pro system. You can reduce costs by efficiently preparing specimens from as little as 2 to 5mL of material.
Polymer rheology deals with the investigation of the viscoelastic properties of polymeric materials in different states. This webinar will provide an overview of common rheological techniques for the investigation of solid and molten polymers. The manufacturing and application related information that can be gained from these tests will be discussed and rheometer configurations for the investigation of polymers are presented.