TMA Measurements on Synthetic Fibers - METTLER TOLEDO

TMA Measurements on Synthetic Fibers

Sample

Fibers for use as textiles: PA66 (95 detx), PET (22 detx), and Kevlar (50 detx).
Note: The linear density of threads and fibers is expressed in detx (g/10 km)

 

Conditions

Measuring cell: TMA40 with fiber accessory made of fused silica

Sample preparation: Two U-shaped copper clamps about 13 mm apart are fixed to an approx. 20-mm length of fiber. The clamps allow the fiber to be mounted in the fiber accessory

TMA measurement: Heating from 25° at 10 K/min to the individual end temperatures

Load: For comparison purposes, a tensile stress of 0.1 mN/dtex is used for all fibers. This is less than 1% of tensile strength of about 50 mN/dtex or 500 N/mm2

 

Evaluation

As examples, the change in length relative to that at 25 °C is calculated in percent at different temperatures (a negative sign indicates shrinkage):

 

Interpretation

The macromolecules of the fibers are strongly oriented in the longitudinal direction. On heating, the fibers shrink due to drying and - sufficiently high temperature - random coil formation. The disorder of entropy of random coils is higher than that of parallel macromolecules. These effects usually overcompensate the expansion. Toward the crystallite melting range, rapid expansion occurs until the fiber finally breaks (e.g. PET at 245°C). The peak temperature of shrinkage can be used for identification. 

On a TMA curve, shrinking is displayed in the downward direction. 

 

Conclusions

The shrinkage or expansion of fibers on heating is easily measured in the TMA using the fiber accessory. Even very small deformations can be detected as is shown using the aramid fiber Kevlar. The TMA curve can be used to identify the fiber. 

 

TMA Measurements on Synthetic Fibers | Thermal Analysis Handbook No.HB257 | Application published in METTLER TOLEDO TA Application Handbook Thermoplastics