| dc.description.abstract | The viscoelastic properties of soft lining materials are of enormous interest and
importance as they clearly govern the biomechanical function of these materials.
Forced vibration (Non-resonant) dynamic mechanical analysis was used to characterise
the viscoelastic properties of a wide range of commercial (8 brands) as well as
experimental soft liners (7 formulations). Forced vibration DMA is the ideal way of
studying these materials as it can closely and accurately mimic physiological
temperatures and frequencies under which they operate.
The materials were studied as processed, and subsequently after simulated ageing for
time periods up to twelve months. The water absorption and the subsequent changes in
the viscoelastic behaviour of these materials are important as they spend a large part of
their working lifetime immersed in solution.
The results, where possible, were compared with the work of other researchers, and any
sources of discrepancy examined. It was noted that the materials whose glass to rubber
transition (Tg) was near their operating temperature (i.e. the acrylics) were particularly
prone to any changes in the time and temperature domain of the experiment.
A large variation was observed in the properties of the commercial materials available.
At 37°C and 1 Hz a seven fold range was seen in the real part of the modulus (2.79-19.7
MPa), and a fifty fold range was observed in the loss tangent (0.029-1.52). Given this
wide disparity it is surprising that a universally recommended range of properties does
not exist, although there is some speculation in the literature.
The study of the ageing behaviour of these materials in water showed that the traditional
hardening of the acrylics has been overcome. A heat cured silicone material was seen to
be virtually unaffected by time, while for a cold cured competitor the opposite was true.
New and experimental materials showed a wide range of behaviour after immersion in
water. | en_US |
