Rheology, which is the study of how a material flows, is a powerful and useful part of understanding fundamentals of polymeric materials. Rheological findings can help you make changes to significantly improve your product’s performance.
With proper experimental design, you can better understand your material’s thermal transitions (e.g. glass transition temperature, melt temperature), molecular weight, structure/morphology, shear-thinning behaviors, long term performance models and much more.
Dynamic Mechanical Analysis (DMA)
PDI offers Dynamic Mechanical Analysis (DMA) in both torsion (-80°C to +450°C) and tensile (-130°C to +450°C) modes. DMA can provide temperature- and frequency-dependent viscoelastic properties such as storage and loss modulus and loss tangent. DMA also reveals subtle thermal events that cannot be detected by Differential Scanning Calorimetry (DSC), like glass transition in high crystalline polymers and beta transition.
Viscoelastic Properties of Polymeric Materials
We measure viscoelastic properties of liquids, like polymer melt (above Tg and/or Tm), solids (below Tg/Tm) and polymer solution and suspension, measuring both steady state and transient properties. We have cone-and-plate, parallel plates, concentric cylinder and cup, as well as custom-made fixtures for customized experiments for liquid/melt type materials and rectangular tensile/torsion, cantilever and three point bending for solid-type materials. From viscoelastic properties, we can learn characteristics including:
- Molecular weight
- Molecular weight distribution
- Degree of branching
- Dispersion of interactive fillers (such as carbon nanotubes)
- Cure kinetics
- Gelation/fusion kinetics
- Stress relaxation
Capillary rheometry provides shear rate-dependent shear stress, shear viscosity and die swell, which are critical parameters for extrusion and injection molding process design. We have a selection of dies that allow Bagley correction for true viscosity calculations. Combined with frequency dependent properties, we can also find the degree of slip. For PVC (rigid, semi-rigid and flexible) and CPVC based materials, capillary rheometry can also reveal work-level and temperature history.
Our stress and strain control fatigue testing ranges from -40°C to 120°C. This technique sheds light on the endurance limit of your materials, which is important for design of products that will experience stress/strain cycles during service.
Tensile Properties and Poisson’s Ratio
Our environmental chamber allows us to perform the tensile test (e.g. ASTM D638 or ISO 527) at non-ambient temperatures from -40°C to 120°C. We can provide you an accurate Poisson’s ratio measurement.