Study on epoxy novolac and carbon-fiber reinforced epoxy novolac composites for use as implant materials. Part 1. Mechanical and viscoelastic properties

We investigated the physical, mechanical, and dynamic mechanical properties of epoxy novolac resin cured with 4,4-diaminodiphenyl sulfone (EPR) and ca rbon-fiber reinforced epoxy novolac composites (EPC). The general character ization included flexural strength, modulus, glass transition temperature, density, thermal expansion of both EPR and EPC, concentration of network ch ains, and the mean molecular weight between two crosslink points of cured E PR. The dynamic mechanical behavior of EPR AND EPC was measured in the freq uency range from 1 to 46 Hz and a temperature range of -150 degrees C to 30 0degrees C. Although EPC exhibited the same three transition regions as EPR ; their magnitudes differed. We postulated the mechanisms of a-, w-, and g- relaxation processes. Dynamicmechanical properties such as storage modulus G' and loss factor tangent tan(d) were determined. The material properties of both EPR and EPC were not significantly affected by vapor sterilization at 134 degrees C. Annealing just below the glass temperature at 190 degrees C in vacuum caused the intensities of a- and g-relaxation of tan(d) to dec rease, the width of a- and g-relaxation of tan(d) to become narrower, and t he storage modulus G' to increase. Such changes are a consequence of densif ication and homogenization. The master curves of reference and annealed EPC were constructed with T-g as reference temperature and a measuring frequen cy of I Hz. The master curve of annealed EPC showed a glass transition that was shifted 5 decades to lower frequencies, corresponding to an increase o f the glass transition of nearly 25 K. The constantsC(1) and C-2 in the WLF equation had the same magnitude asin other amorphous polymers. The EPC exh ibited excellent mechanical, dynamic mechanical, and thermal properties, wh ich are of fundamental need for implant materials used for hip and knee imp lants. Furthermore, one may expect that theresistance to degradation and ch emical aging of epoxy novolac resin systems isconsiderably improved by anne aling. Hence, EPC exhibits all the presumptionsof an excellent material for implants.