The development of theoretical relationships between some handling parameters (setting time and setting temperature), composition (relative amounts of initiator and activator) and ambient temperature for acrylic bone cement.

Commercially available acrylic bone cements are two-component systems based on the polymerization of methyl methacrylate around poly(methyl methacrylate) particles. When benzoyl peroxide (BPO), which is the initiator, in the powder component meets accelerator (N,N-dimethyl-p-toluidine (DMpT)) in the liquid component, radicals are produced, initiating the polymerization. This solidifies the cement. In this work, kinetic expressions have been developed that describe the relationship between bone cement setting time on the one hand, and BPO and DMpT concentrations on the other. Changes in setting time with ambient temperature follow a complex relationship, because both the polymerization process (initiation, propagation, and termination) and the swelling and dissolution of the polymer particles contribute to setting. The contribution of polymer swelling and dissolution to the setting process was determined by developing a relationship between the doughing time, which is substantially independent of DMpT or BPO concentrations, and ambient temperature. A value of 64 kJ mol(-1) was found for the activation energy for this process. An activation energy for the overall setting process of 68 kJ mol(-1) was determined from setting-time measurements over several ambient temperatures. This indicates that the sensitivity of setting time to temperature depends more on swelling and dissolution than on the polymerization process.