POLYMERIZATION KINETICS, GLASS-TRANSITION TEMPERATURE AND CREEP OF ACRYLIC BONE CEMENTS

Sulfix-6 and Zimmer LVC 60/30 bone cements were selected and the polymerization kinetics and resulting glass transition temperature T-g; creep behaviour in the dry or water-saturated state; and sorption and diffusion of water were studied. The calculation of conversion was based on a comparison of the residual polymerization heat measured by differential scanning calorimetry and the corresponding theoretical value. The conversion reached 99% after 90 min of quasi-adiabatic polymerization starting at 23 degrees C or after 10 min of isothermal polymerization at 37 degrees C. The T(g)s of the cements prepared in the former way were about 82 and 100 degrees C, respectively. Creep rate of the bone cements at 37 degrees C decreased with the time of creeping. Sorbed water enhanced the compliance, but reduced the creep rate for long times so that water sorption during the service time may not have detrimental effects on the creep resistance of the cements. Both types of cements contained about 1% of low molar mass substances extractable by water. Measurements of the sorption kinetics of water showed that the diffusion coefficient is 0.14 x 10(-11) and 0.22 x 10(-11) m(2)/s and 1 yr sorption achieves 2.11% and 2.89% for Sulfix and Zimmer, respectively.