Automated Swell Index Measurement Using Thermo Mechanical Analyser

1449 Words Dec 26th, 2014 6 Pages
Automated Swell Index Measurements of Films Using
THERMO MECHANICAL ANALYZER (TMA)

SWAYAJITH SAHADEVAN swayajith@gmail.com Abstract
Dimensional instability on finished plastics products due to changes in humidity is one of the leading causes of product failure. The test lead times associated with measuring changes in dimensions due to humidity changes are prohibitively longer & lot of machine time is consumed in the process. This can become a limiting scenario wherein multiple materials are scaled up for measurements or multiple formulation variables are being analyzed. In this paper, we propose to use the “Swell Index” as the prime factor to be used for evaluating the changes in dimensions. Swell Index of a material is defined as
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Instrumentation
TMA measures the dimensional changes of a material as a function of temperature, time or force. These data provide us with information on the modulus, coefficient of thermal expansion, creep stress relaxation transition temperatures, softening points etc of polymeric materials. It is widely used in quality control as well as research environment.

Generally the TMA is used to measure CTE (Coefficient of Thermal Expansion) and other parameters like modulus, creep, stress relaxation, etc. These parameters are measured or calculated by employing different modes and clamps. For this study the TMA 2940 from TA Instruments as well as TMA 6 from Perkin Elmer were used.

Figure 2

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Figure 3

Schematic of the automated swell measurement set up

Sample Preparation
Polycarbonate was investigated for this study. The sample is made in the form of films from pellets using solvent casting. film sample was prepared by casting from solution of the copolymer in chloroform. This solution was poured in Petri dishes of identical sizes for having consistency in the thickness of films. After the evaporation of the solvent, the films were kept in vacuum oven at 60 deg C for a period of 12 hrs to remove the residual solvent. They were then kept in the desiccator in order to avoid moisture

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