Poly(methyl methacrylate) (PMMA) filled with hydroxyapatite (HA) filler has been widely used in biomaterial

application. Acrylic denture base material was prepared from PMMA filled with HA

A Azlan, A Azlan

H, K Tay

Mohd Ishak, Z A

W, S Chow

English

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Proceedings of the Polymer Processing Society 24th Annual Meeting ~ PPS-24 ~ June 15-19, 2008 Salerno (Italy) MECHANICAL AND THERMAL PROPERTIES OF HYDROXYAPATITE FILLED POLY(METHYL METHACRYLATE) COMPOSITES  W.S. Chow*, H.K. Tay, A. Azlan and Z.A. Mohd Ishak  School of Materials and Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia, Nibong Tebal 14300 Penang, Malaysia – chowwenshyang@yahoo.com  Poly(methyl methacrylate) (PMMA) filled with hydroxyapatite (HA) filler has been widely used in biomaterial application. Acrylic denture base material was prepared from PMMA filled with HA. This research work attempted to investigate the effects of hydroxyapatite (HA) on the flexural properties, fracture toughness, and thermal properties of poly(methyl methacrylate). PMMA powder was mixed with monomer of methyl methacrylate (MMA) stabilized with hydroquinone. Benzoyl peroxide (BPO) and ethylene glycol dimethacrylate (EGDMA) were used as initiator and crosslinking agent, respectively. The HA loading was ranged from 5- 20%. The PMMA/HA composites were prepared by using heat-processing polymer powder and liquid method. The polymerization of PMMA/HA were carried using water bath. The thermal properties of the PMMA/HA composites were characterized using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The flexural modulus of PMMA was increased by the addition of HA. This is attributed to the reinforcement effects of HA. Experimental data of flexural modulus for PMMA/HA composites was compared with several theoretical models and equations. In addition, it was found that the storage modulus (E’), glass transition temperature (Tg), and fracture toughness properties of PMMA were influenced by the HA loading.  Introduction   A lot of polymeric materials have been used as dental base materials such as vulcanized rubber, plastic molding materials, and phenol formaldehyde resin.  Most of these materials have poor aesthetics, tasted bad and became foul smelly [1]. Recently, polymer-hydroxyapatite composites have attracted great attention due to their ability to substitute the bone tissue and dentistry implant.  The polymer system can be used are high density polyethylene (HDPE), polymethyl methacrylate (PMMA), polylactic acid (PLA) and ultra-high molecular weight polyethylene (UHMWPE).  PMMA is used almost universally for denture base construction [2-3]. Hydroxyapatite (HA) has been extensively used as a substitute material for damaged teeth or bone over the past three decades, and its compatibility with surrounding tissues has been experimentally proven. An ideal bone tissue engineering approach would incorporate osteoconductivity and osteoinductivity into the design of the supporting biomaterial, as well as biocompatibility, degradability, mechanical integrity, and the ability to support cell transplantation. Hydroxyapatite is an important bioceramic with tremendous potential for biomedical applications depending on stoichiometry, crystallinity and particle size. Its unique bioactivity promotes rapid bone growth on a strong interfacial fixation that has particular benefit to orthopaedic and dental applications.  In this research work, the objective is to study the effect of HA on the flexural properties, fracture toughness and thermal behaviors for PMMA. In addition, the experimental data will be compared with several theoretical models and equations in order to understand the flexural behavior of the PMMA/HA composites.  Materials and Experimental   Materials Solid components consist of PMMA (Sigma Aldrich, USA) and 0.5% benzoyl peroxide (BPO) (Merck Chemical, Germany).  The liquid components consist of methyl methacrylate (MMA) (Fluka, UK) stabilized with 0.025% hydroquinone and ethylene glycol dimethacrylate (EGDMA) (Sigma Aldrich, USA). Hydroxyapatite (HA) powders were supplied by Sigma Aldrich, USA.   Experimental- Preparation of PMMA/HA composites The powder component was prepared by mixing PMMA, HA and BPO using ball milling. The liquid component was prepared by mixing MMA and EGDMA. The mixing of powder to liquid was carried out according to dental laboratory practice. The ratio of powder to liquid was set at 2.5: 1. After reaching dough stage, the mixture was packed into a mold followed by pressing under a pressure of 14MPa at room temperature for 30 min. The final polymerization was carried out using a water bath at 78oC for 90 min.  Experimental – Sample characterization Three point bending tests were performed according to ASTM D790 using an Instron 3366 machine. The support span length was set at 50mm.  The testing speed was set at 5mm/min. The flexural modulus, strength and displacement were recorded.   The fracture toughness of specimens was determined by using single edge notch bending test (SEN-B) according to ISO 13586:2000. A natural crack was generated by tapping on a new razor blade placed in Proceedings of the Polymer Processing Society 24th Annual Meeting ~ PPS-24 ~ June 15-19, 2008 Salerno (Italy) the notch formed by band saw cutter. The SEN-B specimens were tested at a crosshead speed of 1.00 mm/min. The value for KIC was calculated by using the following equation:  ]8.251.2553.1407.393.1[644322 ⎟⎠⎞⎜⎝⎛+⎟⎠⎞⎜⎝⎛−⎟⎠⎞⎜⎝⎛+⎟⎠⎞⎜⎝⎛−=wawawawaWBSPKcIC    Pc    = load at break (N) B   = specimen thickness (mm) W  = specimen width (mm) a    = notch length (mm)  S   = span length (mm)  The determination of the glass transition temperature (Tg) of the PMMA and PMMA/HA composites were characterized by using a Perkin Elmer Differential Scanning Calorimeter (DSC 6). The DSC tests were carried out at a heating rate of 10oC/min in nitrogen atmosphere. The storage modulus (E’), loss modulus (E’’), and tan delta as a function of temperature (T), were assessed by dynamic mechanical analyzer (DMA) using a Mettler Toledo DMA machine. DMA spectra were taken in three point bending mode at 1 Hz frequency in a temperature range of 30-150oC. The heating rate was set at 10oC/min.    Results and Discussion   From Figure 1, it can be seen that the flexural modulus of PMMA was increased significantly by the addition of HA. The HA could act as a good reinforcing filler in PMMA. Figure 2 shows the flexural modulus of PMMA/HA composites obtained from experiment and calculated by several theoretical models. The theoretical model and equations include Guth Model, Kerner’s Equation, Ahmed & Jones Equation and Hirsch’s Model. Hirsch’s model gives the most accurate prediction value among all the theories.   Figure 1: Effects of HA loading on the flexural modulus of PMMA.   Figure 2: Comparison between experimental and several equations calculated flexural modulus values as a function of filler volume fraction.  Figure 3 shows the effects of HA loading on the flexural strength of PMMA.  It can be found that the flexural strength of PMMA was decreased by the incorporation of HA. This is maybe due to the agglomeration of HA particles in PMMA matrix. In addition, the reduction of strength could be related to the incompatibility between PMMA and HA, as well as the presence of matrix-particle interfacial defects.   Figure 3: Effects of HA loading on the flexural strength of PMMA.  Figure 4 shows the storage modulus as a function of temperature for PMMA and PMMA/HA composites. Note that the storage modulus of PMMA was increased significantly by the addition of HA.   From Table 1, it can be seen that the Tg of PMMA was slightly increased by the addition of HA.   Table 1: Glass transition temperature (Tg) of PMMA and PMMA/HA composites recorded from DSC.  Materials Tg (oC) PMMA 103.8 PMMA/5HA 107.4 PMMA/10HA 110.1 PMMA/15HA 108.4 PMMA/20HA 111.3 a1/2 Proceedings of the Polymer Processing Society 24th Annual Meeting ~ PPS-24 ~ June 15-19, 2008 Salerno (Italy)  Figure 4: Storage modulus vs temperature traces for PMMA and PMMA/HA composites.  Figure 5 shows the effects of HA loading on the fracture toughness of PMMA. It can be observed that the KIC of PMMA increased until an optimum loading of HA is attained at 5 wt%. Further incorporation of HA reduced the KIC gradually.     Figure 5: Effects of HA loading on the KIC of PMMA.  Conclusions   The flexural modulus and storage modulus of PMMA was increased significantly by the addition of HA. However, the flexural strength of PMMA was reduced by the incorporation of HA. The fracture toughness of PMMA was influenced by the addition of HA. Hirsch’s model gives the reasonable close prediction value to the experimental results of flexural modulus.  From the DSC analysis, it was found that the Tg of PMMA was slightly increased in the presence of HA. The optimum loading of HA was achieved at 5 wt% attributed to the balance of good flexural properties and fracture toughness.   Acknowledgements  WSChow would like to thank MOSTI (Malaysia) for the eScience Fund research grant support.  References   1. J.L. Ferrancane, Materials in dentistry principles and application, 2nd ed, Philadephia, USA, 2001. 2. W.J. O’Brien, Dental materials and their selection, 3rd ed, Quintessence, USA, 2002. 3. A. Balamurugan; S. Kannan; V. Selvaraj; S. Rajeswari Trends Biomater. Artif. Organs. 2002, 18, 41.    

Mechanical And Thermal Properties Of Hydroxyapatite

Filled Poly(Methyl Methacrylate) Composites.

http://eprints.usm.my/13529/1/mechanical_and_thermal.pdf

Mechanical And Thermal Properties Of Hydroxyapatite Filled Poly(Methyl Methacrylate) Composites.

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