Determination of the mechanical properties of pellets and film coated pellets using dynamic mechanical analysis (DMA).

The elastic and viscoelastic properties of pellets and film coatings applied to pellets were studied using Dynamic Mechanical Analysis (DMA). Four batches of spherical pellets produced with different methods were compared without film coating and after application of a plasticised ethylcellulose film of average thickness of 25 microm. The modulus of elasticity of the uncoated pellets was found to be related to the porosity of the pellets, as was the slope of the linear portion of the storage modulus-dynamic force curves. None of the other parameters obtained from DMA of the uncoated pellets appeared to be related to the macroscopic properties of these pellets. After application of the film coating the dynamic force at the onset of the linear portion of the storage modulus-dynamic force curve and the maximum storage modulus obtained at a dynamic force of 600 mN were found to be significantly different from the values of the uncoated pellets, but similar for all four coated pellet batches. Hence these parameters represented the viscoelastic behaviour of the film coatings.