Humidity-Controlled Dynamic Mechanical Analyzer

What is the Humidity-Controlled Dynamic Mechanical Analyzer?

A humidity-controlled dynamic mechanical analyzer mounts a humidity generator on the sample chamber, so viscoelastic properties can be measured at defined relative humidity and temperature. It is used for hygroscopic polymers, fibers, biomaterials and packaging films.

Overview

A controlled humidity generator supplies air or nitrogen at a set relative humidity, typically from 5 to 95 percent, through a heated chamber so that condensation does not occur at the specimen. Because moisture uptake is slow in thick specimens, films and fibres are preferred and equilibrium times must be established before measurements. Relative humidity acts like a plasticiser, lowering the glass transition temperature and the storage modulus, so humidity sweeps at fixed temperature and temperature sweeps at fixed humidity are both used to map behaviour. Typical instruments cover 5 to 95 percent relative humidity, 5 to 85 degrees Celsius chamber temperature and a frequency range from 0.01 to 100 hertz, with confirmation that the humidity at the specimen, not at the inlet, is controlled. Applications include cellulose and paper, nylon and other hygroscopic polymers, hydrogel and biological tissue mechanics and food packaging performance.

How does it work?

The instrument clamps the specimen in a chosen geometry and applies a sinusoidal stress or strain while measuring the response. Because a viscoelastic material does not respond instantaneously, the strain lags the stress by a phase angle, and the ratio of amplitudes together with that phase angle yields the complex modulus. Its real part is the storage modulus, describing elastic energy stored per cycle; the imaginary part is the loss modulus, describing energy dissipated as heat; and their ratio is the damping factor, tan delta, whose peak defines the glass transition temperature. Measurements are made in single or dual cantilever, three-point bending, tension, compression or shear mode, with the geometry chosen to suit the sample stiffness. Temperature ramps of 0.5 to 5 degrees Celsius per minute, frequency sweeps from 0.01 to 100 hertz, and single or multi-frequency operation allow activation energies, cure profiles and master curves to be derived.

What are the key features?

• Relative humidity control from 5 to 95 percent at the specimen
• Heated humidified gas path preventing condensation
• Humidity sweep and fixed-humidity temperature sweep programs
• Compatible with film, fibre and thin bar clamps
• Chamber temperature control from 5 to 85 °C
• Software for humidity-modulus and tan delta mapping

What are the technical specifications?

A typical humidity-controlled dynamic mechanical analyzer configuration offers relative humidity range of 5–95% RH, humidity accuracy of ±2% RH, chamber temperature of 5–85 °C, temperature accuracy of ±0.5 °C, frequency range of 0.01–100 Hz and force range of 0.001–20 N. Values are indicative of the product class; the exact figures for each configuration are confirmed on the quotation and the calibration documents supplied with the instrument.

Which applications is it used for?

The Humidity-Controlled Dynamic Mechanical Analyzer is used in cellulose, paper and textile behaviour, hygroscopic polymer and nylon testing, hydrogel and biological tissue mechanics, food packaging film performance and coating performance under humid conditions. Across the wider DMA class, laboratories also deploy it for composite and laminate viscoelastic characterisation, elastomer and rubber compound testing and thermoset cure monitoring.

Which standards and certifications apply?

Relevant standards and methods include ASTM D4065, ASTM D5023, ASTM D5024, ASTM D5026, ASTM E1640 and ISO 6721-1. Certification candidates for this model are CE, IEC 61010-1 safety and ISO 9001 manufacturing; each is to be confirmed for the specific configuration before shipment, and certificates are supplied only where they have been issued.

Specimen geometry must be measured accurately, because modulus depends on the cube of thickness in bending and on cross-sectional area in tension, so a dimensional error is amplified. Clamp the specimen without pre-stress or slippage, verify that the measured stiffness lies in the instrument's reliable range, and check linearity by repeating at a second amplitude. Calibrate the instrument with certified stiffness standards or reference materials and record the geometry, amplitude, frequency and atmosphere for each run. Beware of thermal lag at higher heating rates, which shifts transition temperatures upward, and of clamp expansion that can add apparent strain. For thermosets, run the cure in a multi-frequency mode so gelation and vitrification can be separated. Purge gas is required for measurements above room temperature to avoid oxidation, particularly in elastomers.

How do I select the right Humidity-Controlled Dynamic Mechanical Analyzer?

Choose the humidity-controlled configuration when moisture changes the property you are measuring and results must be reported at a defined relative humidity, as with cellulose, nylon or hydrogels. For dry or moisture-insensitive materials, a standard instrument is sufficient. In an RFQ, specify humidity range, chamber temperature, equilibration protocol and clamping mode.

How does it compare with other DMA variants?

Choose the clamping geometry before anything else, because it determines the specimen dimensions and the usable stiffness range: three-point bending suits stiff bars, single and dual cantilever suit medium-modulus plastics and composites, tension suits films and fibres, and compression or shear suit soft gels and foams. Then match the force range to the material: stiffer samples and composites need higher force and a rigid frame, while thin films and gels need very low force with high displacement resolution. Check the temperature range and the cooling system, since liquid nitrogen is needed for sub-ambient glass transitions. Frequency range, multi-frequency capability and the software for master curve generation matter for research, while a simple temperature sweep with specification limits is enough for quality control. For hydrogels, biological samples or humid environments, ensure the instrument can accept a submersion or humidity accessory.