Nondestructive testing of defects in adhesive joints

loading. Na+MMT system shows a decrease in the tensile strength and stress at break indicating
brittleness characteristics predominantly due to presence of clay agglomerates which leads to
microcrack formation at the interface. The nanocomposites prepared using C30B &B109 shows an
increase of 21.85 %and 20.91 % respectively as compared with the matrix polymer. PMMA/C20A
nanocomposites exhibit less tensile strength of 67.94 MPa confirming comparatively less
compatibility with the matrix polymer. Further grafted samples in all the systems exhibits lower
tensile strength as compared with ungrafted nanocomposites system revealing brittleness
characteristics of PMMA with interface modification in the nanocomposites system. Strain at break
decreases with the incorporation of nanoclays, PMMA/C30B nanocomposites exhibited a decrease of
62.71% with PMMA/B109 to 54.1% and PMMA/C20A to 91.6 % respectively as compared with the
matrix polymer. Grafting of PMMA with MA and influence of organic modifier /intercalant type had
virtually no effect on the stress as well as strain at break of the nanocomposite hybrids.
Dynamic Mechanical Analysis:
The temperature dependence plots of storage modulus E’ of PMMA and its nanocomposites as
measured from –150 0 C to 150 0 C are depicted in fig.5. As observed in the figure, the glassy state
storage modulus at 25 0 C increases to the tune of 9.2% in PMMA/C30B, 15.5 % PMMA/B109 and
29.3% PMMA/C20A respectively as compared with the virgin matrix. The grafted nanocomposites
also demonstrated moderate increase in E’ of PMMA. PMMA-g-MA/C30B exhibits maximum
increase in storage modulus Above 80 0 C, the E’ drops with considerable fall in matrix modulus
observed in the vicinity of Tg indicating that the material undergoes a glass/ rubber transition. DMTA
tests indicated remarkable increase in E’ in the nanocomposites system as compared with virgin
matrix. The E’ values display improvement in glassy regions (except deviations in PMMA/B 109
system) confirming that incorporation of nanoclay induces reinforcing effect. At high temperature
regions the nanocomposites system as well as PMMA displayed similar modulus and approaches
constant level of temperature beyond 130 0 C
Conclusion:
PMMA nanocomposities were prepared using melt blending technique. The effect of organic
modifier on the mechanical, thermal and flammability properties of nanocomposites has been
investigated. Mechanical properties indicated optimum tensile modulus is PMMA/C30B 5% as
compared to virgin PMMA matrix and other nanocomposites. WAXD & TEM micrographs showed
evidence of exfoliation and intercalation in PMMA/C30B nancomposites. Thermal study indicates an
increase in onset of decomposition temperature and marginal increase in Tg of nanocomposites. DMA
studies revealed substantial increase in the E’ of the nanocomposites with the incorporation of C30B
nanocomposites.
References
1. Blumstein, A.J Polym sci. part A: Gen pap 1965, 3, 2653
2. Wang, D.; Zhu, J.; Yao, Q.; Wilkie, C.A. Chem mater 2002,14,3837
3. Bandyopadhyay, S.; Giannelis, E. P.; Hsieh, A. J. Polym2000, 82, 208.
4. Hsieh, A. J.; Giannelis, E. P. Presented at the American Physical Society Symposia
Presentation, Atlanta, GA, March 1999.
5. Salahuddin, N.; Shehata, M. Polymer 2001, 42, 8379.
6. S.u, S.; wilkie, C.A. J.Polym Sci. Part A: polym Chem 2003, 41, 1124
7. Lee, D.C.; Jang, L.W. J Appl Polym Sci., 1996,61,1117
8. Huang, X.; Brittain, W.J. Macromolecules, 2001,34,3255
9. S.Kumar, J.P. Jog, U.P, J. Appl. Polym. Sci. 2003, 89, 1186