Nondestructive testing of defects in adhesive joints

polymer-matrices to produce composites that can initiate osteogenesis when implanted in
bony sites [11]. In biomedical applications, cellulose, a polysaccharide, is used either as
regenerated films, fibers or as derivatives (esters, ethers) [14-16]. Considering, the
biodegradability, biocompatibility, non-toxicity, muco-adhesive nature and the carboxyl
groups on structure of carboxymethyl cellulose, we expect that CMC can interact with
precursors and direct the nucleation and growth of hydroxyapatite to produce bioactive
ceramics. Thus, the present study is to prepare nanohybrids of carboxymethyl cellulose
(CMC) and hydroxyapatite (HA) nanoparticles and to study the effect of CMC on size,
structure and morphology of HA.
2. Experimental
Keeping the molar ratio of calcium / phosphate as constant ~1.67, the CMC content was
varied from 0 to 2 wt. % of total weight formulations were calculated as represented in
Table 1. The weighed amounts of polymer and calcium reagent (CaCl2) were dissolved in
aqueous ammonia at room temperature (~27 °C). After 15 min, the phosphate reagent,
diammonium hydrogenphosphate ((NH4)2HPO4) was added to this solution and stirred for
2 weeks at room temperature (~27 °C). During the reaction, the pH was monitored and
adjusted at 10 by addition of ammonia solution. After reaction, precipitate was washed
with deionized water and dried in a vacuum oven at 40 °C for 12 h. Portions of the
prepared samples were calcined at 1000 °C for 1.5-2 h. The physico-chemical
characterizations were done before and after calcination using Fourier transform infrared
spectroscopy, solid state 31 P nuclear magnetic resonance (NMR) spectroscopy and
thermogravimetric analysis (TGA). The formation of nanohybrid was observed by wide
angle X-ray diffraction (WAXD), scanning electron microscopy (SEM) with energy
dispersive X-ray analysis (EDX) and transmission electron microscopy (TEM).
3. Results and Discussion
3.1. FTIR spectroscopy
In Figure 1, the characteristic peaks at 2800-3000 cm -1 , 3100-3500 cm -1 , 1650-1700 cm -1 ,
and 1100 cm -1 , which are assignable for C-H, hydroxyl, carboxylate and C-O- group
regions, respectively, indicate the presence of CMC. The absorption bands at 3571 cm -1 and
631 cm -1 , arise from stretching and bending modes of OH - ions, respectively. The
absorbance at 1040 and 1090cm -1 is attributed to (v3) phosphate PO4 3- . The other bands at
962 cm -1 (for v1), 601 and 574 cm -1 (for v4), and 472 cm -1 (for v2) are also attributed to
unique characteristic vibrations of PO4. The weak intensity of bands in 2200 -1950 cm -1
region derives from overtones of bands and combinations of v3 and v1 phosphate modes.
The sharpness of bands, especially at 631, 601 and 574 cm -1 indicate a well crystallized
HA [22]. The 1037 cm −1 and 1096 cm −1 bands in Figure 1a and b are PO4 3− ν3 mode and
asymmetric HA, respectively.
31
3.2. P-NMR Spectroscopy
Figure 2 Shows the solid state 31 P NMR Spectra of as-synthesized and calcined calcium
hydroxyapatite. The peak at 2.3 - 2.5 ppm, which is typical for hydroxyapatite, can be
observed for all the samples. They, however, differ in the line width, and the broadening of
peak at foot is also observed for the as-synthesized nanohybrids. The broadening of peak is
attributed to nanoscale crystalline particles [25].
2