Browsing by Author "Friedrich, K"

Now showing 1 - 2 of 2
  • Item
    Dynamic mechanical properties of hydroxyapatite-ethylene vinyl acetate copolymer composites
    (MATERIALS CHEMISTRY AND PHYSICS, 2005) Velayudhan, S; Ramesh, P; Varma, HK; Friedrich, K
    Dynamic mechanical thermal analysis (DMTA) was carried out to explore the dependence of temperature on the viscoelasticity of composites consisting of synthetic hydroxyapatite (HAP) particulate filled ethylene vinyl acetate copolymer (EVA). Two forms of HAP, differing in their surface characteristics and particle size, were used for the study. The freeze-dried HAP (FDHAP) had a mean particle size of 49.18 mum and an irregular surface morphology. In the contrary the spray dried form of HAP (SDHAP) had a mean particle size of 5.84 (m and a spherical morphology. The dynamic mechanical analysis of the composites showed that both, particle size and morphology, had a significant effect on viscoelastic properties. A tremendous increase of the storage modulus was noted with the addition of HAP. Above the T-g of the polymer matrix, the values were marginally higher for the composites containing FDHAP than for those with SDHAP. The damping (tan delta) was found to decrease with the inclusion of HAP. A marginal upper shift in the value of the glass transition temperature (T-g) was observed for the composites fabricated from SDHAP indicating a slightly strong interaction between this HAP and the EVA matrix. (C) 2004 Elsevier B.V. All rights reserved.
  • Item
    Stamp forming of hydroxyapatite filled ethylene vinyl acetate co-polymers: Process optimization using a right angle V-mould
    (COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING, 2007) Velayudhan, S; Ramesh, P; Varma, HK; Schmitt, S; Friedrich, K
    Hydroxyapatite (HAP) filled ethylene vinyl acetate co-polymer (EVA) composites are developed in an attempt to formulate a surgeon friendly material for renovating impaired skull contours. A cost effective technique for obtaining these composites in the clinically significant forms would indeed be a landmark accomplishment. Stamp forming is one of such processes where the cost as well as the performance of the product strikes the right balance. This study was carried out prior to the stamp forming process optimization of the composites into three-dimensional (3-D) contours, essential for applications like cranioplasty. This paper discusses the V-bending results for HAP filled EVA and an attempt to identify a processing window for real manufacturing situations (3-D forming) is made. The processing conditions, such as the stamping temperature, time, and stamping rate, required to give high-quality right angle bends, have been established. The quality of stamped forms is also examined in terms of shape conformance and variation in wall thickness. It has been found that the stamping temperature and velocity were the key factors, which determined the quality of the stamped part. Too high temperatures as well as too high stamping rates lead to severe thinning and degradation of the formed parts. On the other hand, when the temperatures and the stamping rates are too low, the composites do not conform to the mould contour. (c) 2007 Elsevier Ltd. All rights reserved.