Injection Molding of a Starch/EVOH Blend Aimed as an Alternative Biomaterial for Temporary Applications RUI A. SOUSA, 1,2 GU ¨ RHAN KALAY, 1 RUI L. REIS, 2 ANTO ´ NIO M. CUNHA, 2 MICHAEL J. BEVIS 1 1 Wolfson Centre for Materials Processing, Brunel University, Uxbridge, Middlesex, UB8 3PH, United Kingdom 2 Department of Polymer Engineering, University of Minho, Campus de Azure ´m, 4800 Guimara ˜es, Portugal Received 15 July 1999; accepted 26 December 1999 ABSTRACT: Biodegradable polymers show great potential to be used as materials for temporary implants and bone replacement applications in orthopedics. However, its use in high load-bearing applications will depend on the successful development of biode- gradable implants with a mechanical performance matching that of human bone. This article describes the optimization of the injection molding process of an alternative biodegradable starch-based polymer aimed at biomedical applications. A blend of starch with a copolymer of ethylene–vinyl alcohol (SEVA-C) was studied. Both conventional injection molding and shear controlled orientation (SCORIM) were optimized with the support of design of experiments and analysis of variance techniques. The mechanical characterization was performed by tensile testing. The structure developed within the moldings was assessed by wide-angle X-ray diffraction and differential scanning calo- rimetry. Increases up to 30% in the tangent modulus and 20% in the ultimate tensile strength compared with conventional molding were achieved with the application of SCORIM. The holding pressure and the frequency of the shear applied have the strongest influence on the morphology development and consequently on the mechan- ical performance. The solidification of SEVA-C at high cavity pressures enhances stiffness for long durations of the shearing stage in SCORIM. However, the effect of viscous heating of SEVA-C is important and ought to be considered. A decrease of the material phase miscibility in SEVA-C occurs as result of the shear fields imposed. The microstructure evaluation suggests that the mechanical properties enhancement in SCORIM molded SEVA-C is attributable to preferred orientation developed during processing. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1303–1315, 2000 Key words: starch; biodegradable; biomaterial; injection molding; SCORIM; design of experiments INTRODUCTION Polymer-based composites are found in clinical applications more extensively now than in the past. 1–3 Orthopedics is one of the main areas of potential use for these composites, 4–6 where it is essential to achieve a mechanical performance of the implant as close as possible to that of human bone, to avoid clinical problems related to the mechanical mismatch between the bone and the surgical implant. 7,8 In fact, the use of very stiff materials leads to stress protection of the healing bone, i.e., resulting in osteoporosis phenomena due to the absence of normal functional loading. 8 Biodegradable polymers are a promising alterna- Correspondence to: G. Kalay (Gurhan.Kalay@brunel.ac.uk). Contract grant sponsor: Subprograma Cie ˆ ncia e Tecnologia do 2° Quadro Comunita ´ rio de Apoio, Ministe ´rio da Cie ˆncia e Tecnologia, Portugal (to R.A.S.). Journal of Applied Polymer Science, Vol. 77, 1303–1315 (2000) © 2000 John Wiley & Sons, Inc. 1303