Analysis of acrylic cements polymerization process with different concentration of polymers and monomers

Arkadiusz Szarek Politechnika Częstochowska, Wydział Inżynierii Mechanicznej i Informatyki, Instytut Obróbki Plastycznej, Inżynierii Jakości i Bioinżynierii al. Armii Krajowej 21, 42-200 Częstochowa, Poland

Quarterly No. 2, 2008 pages 206-209

DOI:

keywords: composite, modified PMMA, polymerization

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abstract One of the examples of the composite material which is widely used in medicine, mainly in orthopaedics, is modified polymethyl methacrylate (PMMA). Surgical cement is composed of methyl ester polymer and acrylic acid and, after mixing with liquid monomer undergoes further polymerization, resulting in a hardened mass. In a macroscopic scale such a solid is composed of aggregates in the form of polymer spheres of 1018 micrometers connected with the polymerized monomer bridges. During polymerization this material is so plastic that it can be freely formed and penetrates inside a tiny trabecular structure of bone. Technological aspect of application of PMMA seems to be favourable. Polymer is solidified within less than 10 minutes from the initiation of mixing (powder + liquid), which is sufficient to fix the prosthesis. Its compressive strength amounts to 60100 MPa and it is sufficient for limb load after implanting prosthesis. It is very brittle, however. Its crack resistance is expressed as a KIc coefficient and it amounts to 1.2 0.1 MPa  m1/2. After polymerization, 4-6 minutes from the moment of its initiation, a considerable rise in temperature from 5580C, and even 125C, depending on the environment temperature and a type of cement. In order to reduce it a ‘freezing of polymerization’ is sometimes applied, regulation of grain and additions (crystalline polyethylene, TiO2, Al2O3). Many authors deal with PMMA, describing in their works a process of polymerization, however, it is difficult to find complex information concerning phenomena which occur during polymerization of modified PMMA with different concentration of polymers and monomers. This issue is very important both due to the course of polymerization and quality, strength and homogeneity of the structure of the obtained material. During the work an attempt was made to determine differences in the course of polymerization of PMMA with various percentage concentration of polymers and monomers. As an investigation material a commercial bone cements (PMMA) CEMEX RX - by TECRES SPA and SIMPLEX P - by HOWMEDICA LIMERICK was used modified Al2O3. As a pattern of polymerization a process was assumed where percentage concentration of both polymers and monomers was kept following the manufacturers recommendations (TECRES SPA; 40 g powder and 13.3 g liquid, Howmedica Limerick; 40 g powder and 20 ml liquid). In order to analyse changes in the process, a concentration of each component was decreased by 5% while the time and temperature of polymerization was determined. Final product was additionally analysed; this means polymerized cement mass on the basis of which homogeneity of the investigated structure was determined.