Source: https://pubs.rsc.org/en/content/articlehtml/2019/na/c8na00006a
Timestamp: 2019-04-23 21:54:53+00:00

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Hydroxyapatite/poly(methyl methacrylate) (HA–PMMA) nanocomposites are extensively used in biomedical fields. Therefore, the design and development of low-cost and industrially viable novel methods are essential to synthesize HA–PMMA nanoparticles. In this letter, we report such an economical, simple and industrially applicable novel method to synthesize nanosized HA–PMMA composite particles using extensively distributed dolomite.
Herein, sucrose, potassium persulphate (K2S2O8), ammonium dihydrogen orthophosphate ((NH4)H2PO4) and methyl methacrylate (MMA) were purchased from Sigma-Aldrich to use as raw materials for the synthesis. First, a calcium sucrate solution was prepared by adding 5.00 g of calcined dolomite (CaO·MgO) into 0.5 M sucrose (100 mL) while stirring and by continuing the stirring for 6 h. The mixture was filtered under suction and the solution was collected.18 Then, 1.00 g of potassium persulfate was dissolved in 100 mL of 0.5 M prepared calcium sucrate solution in a three-neck rounded bottom flask and heated to 80 °C. 10 mL of freshly distilled MMA and 100 mL of 0.3 M ammonium dihydrogen orthophosphate were added (until Ca/P ratio of 1.67) to the reaction mixture using two dropping funnels while stirring. The mixture was further stirred for 12 h and filtered under suction to obtain a precipitate. The precipitate was washed with distilled water 3 times and allowed to dry under ambient conditions. The yield of the obtained HA was 84%.
X-ray diffraction (XRD) patterns of the synthesized products were obtained using a Siemens D5000 powder diffractometer. Fourier Transform Infrared (FT-IR) spectra of the products were recorded on a Shimadzu IR Prestige 21 instrument with the KBr pellet method. Raman spectra of both HA and HA–PMMA samples were recorded on a Bruker Senterra 2 instrument. The morphology of the products was examined using Transmission Electron Microscopy (TEM) with the help of a JEOL JEM-2000FX Electron Microscope. Differential scanning calorimetry (DSC) was performed using an STA S-1500 instrument.
Preparation of HA–PMMA nanocomposites through calcium sucrate without using CaO directly is a better solution to prevent the inclusion of impurities such as MgO, and unreacted CaO and CaCO3 in the final product.18 Hence, dolomite is employed as a raw material for the proposed method.18,19 A white precipitate is formed towards the end of stirring (Section 2.2). The synthesized HA–PMMA composite is a white colored crystalline powder with fine particles. The XRD pattern of HA/PMMA given in Fig. 1A(b) has peaks at 2-theta values of 25.78°, 31.74°, 32.88°, 39.68°, 46.62°, 49.43°, and 53.02° which represent hydroxyapatite (JCPDS card no. 72-1243). The XRD pattern of the synthesized HA–PMMA is similar to the XRD pattern of bare HA (Fig. 1A(a)). Also, the synthesized product only contains pure HA as the crystalline material and hence, it does not contain any other crystalline impurities such as unreacted reactants. The estimated average particle size of HA in the composite from the Debye–Scherrer formula is 11 nm. XRD peaks of PMMA are not found in the XRD spectrum of the composite because it is amorphous (Fig. 1A(c)).
Fig. 1 (A) XRD pattern of (a) HA, (b) the HA–PMMA composite and (c) PMMA. (B) FTIR spectrum of (a) HA, (b) the HA–PMMA composite and (c) PMMA.
Fig. 2 shows the Raman spectra of both HA and HA–PMMA samples. The Raman spectrum in Fig. 2a shows the characteristic bands of HA at 440 cm−1, 600 cm−1, 960 cm−1 and 1050 cm−1 which reveal the presence of HA in the HA–PMMA composite.22 Raman spectra of PMMA and HA are recorded to compare with the spectrum of the composite. It is clearly identified that absorption bands at 440 cm−1, 600 cm−1 and 960 cm−1 are common for both HA and the composite.22,23 Raman shifts of the major bands of PMMA those appeared in our HA–PMMA spectrum (Fig. 2b) are comparable with those reported by Thomas et al. (2008).24 The bands around 1400 cm−1 are attributed to the C–H, O–CH3 and –CH3 groups of PMMA in the HA–PMMA composite. The intense band at around 1260 cm−1 is attributed to the C–O and C–COO functional groups which are present in the PMMA component of the composite.24 The bands around 1100 cm−1 are related to the symmetric stretching mode (ν3) of the PO4 groups of HA. The bands 999 cm−1 (O–CH3) and 1081 cm−1 (C–C skeletal mode) are masking each other in the prepared HA–PMMA composite due to the hydrogen bonding and coordination bonding. These bands are not found in HA synthesized in the absence of PMMA. These results are also comparable with FTIR spectra and further confirm the presence of PMMA in the composites.
Fig. 2 Raman spectrum of (a) HA and (b) the HA–PMMA composite.
Fig. 3 TEM images of the HA–PMMA composite at two different magnifications.
Fig. 4 [A] TGA curves of (a) HA and (b) the PMMA–HA nanocomposite [B] DSC curves of (a) HA and (b) the PMMA–HA nanocomposite.
A nanosized HA–PMMA composite was prepared by a novel, simple and industrially applicable method using dolomite. The synthesized HA–PMMA nanocomposite was 30 nm in size and had a spherical morphology with 84% yield.
The research was funded by the National Research Council, Sri Lanka (Grant no. NRC/11-46).
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