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Dynamic Mechanical Analysis

Introduction

Dynamic Mechanical Analysis (DMA) is a proven technique for the characterisation of the viscoelastic properties of materials, in particular polymers and composites, as it not only gives a quantitative assessment of materials’ properties such as stiffness and damping, but also provides important structural information. The dynamic mechanical properties of materials are sensitive to all kinds of thermal transitions, relaxation processes, structural heterogeneity and morphology of multiphase systems such as crystalline polymers, polyblends and composites. DMA can also pinpoint thermal transitions e.g. typical output of tan d versus temperature will display a peak at glass transition temperature (Tg). Above Tg, peaks correspond to the crystalline regions and eventually melting temperature (Tm). As a technique, DMA is also sensitive for the characterisation of polymers of similar chemical compositions, as well as detecting the presence of moderate quantities of additives such as plasticizers or leachable materials.

Technical Specifications

  • The Perkin-Elmer DMA 7e is used for mechanical analysis of solid and near-solid samples. It measures mechanical properties such as modulus (elasticity) and viscosity (damping) as a function of time, temperature, frequency, stress, or combinations of these parameters. The DMA 7e provides the performance and flexibility necessary for the characterization of a broad range of materials, from soft samples such as elastomers, thin films, and single filament fibers to hard samples like composites, ceramics, and some metals. The DMA 7e can also apply a constant force to perform standard thermomechanical analysis (TMA). Comprehensive calibration, verification, and validation assure the highest confidence in results reported by the DMA 7e. It has been certified to perform standard test methods defined by international organizations including ASTM and ISO.
  • Force Control- Force motors are used to cause the sample to deflect. Precise force control is critical to obtaining accurate modulus results. The DMA 7e force motor can accurately control from very low forces for the analysis of samples in the molten or flowing state to high forces for the analysis of very high modulus solids. Forces can be calibrated and verified using traceable mass standards providing traceable modulus results.
  • Displacement Sensitivity- Displacement sensors are used to measure sample deflections. High displacement sensitivity is important for characterizing a wide variety of sample types from polymer pellets to single filament fibers and thin films. High dynamic displacement sensitivity allows measurement of subtle mechanical transitions. Long static displacement range allows the sample to expand or contract many times its original size, up to 300%.
  • Furnace Systems- Two furnace systems are available for use with the DMA 7e. These systems allow DMA measurements over the range of –170°C to 1000°C. Based on a resistance-heating design, these furnace systems allow continuous monitoring and temperature control, resulting in improved accuracy and reproducibility. Low-mass design permits rapid cool-down at the completion of an experiment, often requiring only a few minutes to cool back to the starting temperature. Fast-cooling experiments are best performed with the DMA 7e’s unique quartz measuring systems. The result is that you can run more samples and characterize more materials. The precise temperature control features of this furnace allow heating and cooling rates from 0.1°C/min to 100°C/min.
  • Sample Types and Geometries- The practical advantages of the DMA technique have expanded to almost every material and sample type. It is not uncommon for a single laboratory to test raw materials, intermediate products, and finished products to verify materials and end-use performance. To accommodate this broad range of sample types and test geometries, numerous measuring systems have been developed for the DMA 7e. These systems are designed to handle materials in a variety of geometries, from semisolids in the form of flat bars, pellets, cylinders, disks, films, and even fibers. Included are Extension Analysis systems for the analysis of thin films and fibers; 3-Point Bending, Dual Cantilever, and Single Cantilever systems for the analysis of a variety of thermoplastics and thermosets; and nine different Parallel Plate systems
  • Frequency Range- With a frequency range of 0.01 to 50 Hz, the DMA 7e provides a valuable tool for the characterization or “fingerprinting” of materials. Frequency scanning provides a convenient way to observe differences between materials as a result of long and short chain branching, chain entanglements, and molecular weight distribution differences. Frequency scanning also provides a means for calculating the “zero shear viscosity” or for identifying the Newtonian region in polymers, which may then be applied to molecular weight calculations. Lower frequency data, such as one cycle per day or one cycle per week, is generated through creep recovery tests.

Typical Applications For Which The DMA 7e Is Used

Polymers And Composites

Quality factor/tan delta
Impact performance
Effects of filler, modifiers, blending, grafting, and copolymerization
Heat set
Strength
Effect of drying
Effect of heating
Effect of chemicals, solvents, or humidity
Effect of stress or pressure
Stiffness/Modulus
Glass transition

Fiber/Film

Shrinkage
Orientation

Food/Pharmaceutical

Effect of additives

Biological/Environmental

Effect of aging, drying, or sunlight

Examples Of Work Undertaken At The Institute

DMA has been extensively used for the characterisation of the thermal and mechanical properties of polymers and composites for biomedical applications. In particular DMA of scaffolds developed for tissue engineering have been a focus of interest. Numerous forms of scaffolds have been developed through gas foaming, particle leaching, thermally induced phase separation (TIPS), and the electrospinning of nano-fibres into porous structures. Figures 1 and 2 show the DM properties of highly porous (>90% porosity) foams of Bioactive glass incorporated PDLLA that were produced through TIPS and subsequent solvent sublimation. Figure 3 shows typical stress-strain curves obtained for highly dense native collagen scaffolds (cellular and acellular) as a function of time in culture.

Figure 1
Figure 2
Figure 3

For more information, please contact
Professor Jonathan Knowles
Email. j.knowles@ucl.ac.uk
Tel. +44 (0)20 3456 1189
Eastman Dental Institute
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