JOURNAL OF POLYMER ENGINEERING

 Vol. 19, No. 4, 1999, page 243

ABSTRACT

STUDY ON EPOXY NOVOLAC AND CARBON-FIBER REINFORCED EPOXY NOVOLAC COMPOSITES FOR USE AS IMPLANT MATERIALS. PART 1. MECHANICAL AND VISCOELASTIC PROPERTIES

H.-A. Federolf, P. Eyerer, C. Mebus, B. Moginger; R. Jin¹ and W. Scheer²

Institute of Polymer Testing and Polymer Science, University of Stuttgart, Pfaffenwaldring 32, D-7 05 69 Stuttgart, Germany; ¹Hefei University of' Technology, Hefei 230 009, Anhui, P.P. China; ²MAN-TechnologieAG, Liebigstr. 50, D-85757 Karlsfeld, Germany

We investigated the physical, mechanical, and dynamic mechanical properties of epoxy novolac resin cured with 4,4-diaminodiphenyl sulfone (EPR) and carbon-fiber reinforced epoxy novolac composites (EPC). The general characterization included flexural strength, modulus, glass transition temperature, density, thermal expansion of both EPR and EPC, concentration of network chains, and the mean molecular weight between two crosslink points of cured EPR. The dynamic mechanical behavior of EPR AND EPC was measured in the frequency range from 1 to 46 Hz and a temperature range of-150@C to 300@C. Although EPC exhibited the same three transition regions as EPR; their magnitudes differed. We postulated the mechanisms of a-, co-, and y-relaxation processes. Dynamic mechanical properties such as ' storage modulus G' and loss factor tangent tan(5) were determined. The material properties of both EPR and EPC were not significantly affected by vapor sterilization at 134@C. Annealing just below the glass temperature at 190@C in vacuum caused the intensities of a- and y-relaxation of tan(5) to decrease, the width of a- and y-relaxation oftan(5) to become narrower, and the storage modulus G' to increase. Such changes are a consequence of densification and homogenization. The master curves of reference and annealed EPC were constructed with Tg as reference temperature and a measuring frequency of 1 Hz. The master curve of annealed EPC showed a glass transition that was shifted 5 decades to lower frequencies, corresponding to an increase of the glass transition of nearly 25 K. The constants C, and C; in the WLF equation had the same magnitude as in other amorphous polymers. The EPC exhibited excellent mechanical, dynamic mechanical,@ and thermal properties, which are of fundamental need 'for implant materials used for hip and knee implants. Furthermore, one may expect that the resistance to degradation and chemical aging of epoxy novolac resin systems is considerably improved by annealing. Hence, EPC exhibits all the presumptions of an excellent material for implants.

KEYWORDS

mechanical behavior, annealing, density of crosslink points, glass transition shift, WLF constants of EPR and EPC

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