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Nondestructive testing of defects in adhesive joints

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the observed high values <strong>of</strong> its T-peel strength (15.5 N/25mm as aga<strong>in</strong>st 9.8 N/25mm for Fevicol SR<br />

998).<br />

Fig.4.T-peel failure surface <strong>of</strong> rex<strong>in</strong> / rex<strong>in</strong> bonded with (a) Fevicol and (b) PCNSL based PSA<br />

CONCLUSION<br />

Adhesion strength higher than that <strong>of</strong> Fevicol SR 998 was obta<strong>in</strong>ed for PCNSL based PSAs<br />

with <strong>in</strong>creases <strong>in</strong> solids content from 15% to 25% and storage time <strong>of</strong> test specimens prior to <strong>test<strong>in</strong>g</strong><br />

from 1 to 7 days which <strong>in</strong>dicates time dependent diffusion characteristics <strong>of</strong> the latter caus<strong>in</strong>g a<br />

change <strong>in</strong> failure pattern from ‘<strong>adhesive</strong>’ to ‘cohesive’ type. Increase <strong>in</strong> the extent <strong>of</strong> phosphorylation<br />

/ oligomerisation <strong>of</strong> CNSL dur<strong>in</strong>g synthesis <strong>of</strong> PCNSL resulted <strong>in</strong> a res<strong>in</strong> hav<strong>in</strong>g higher viscosity<br />

which enhanced the cohesive strength <strong>of</strong> the PSA and consequently the T-peel adhesion strength with<br />

flexible substrates. Rex<strong>in</strong> specimens bonded with the PCNSL based PSAs showed an optimum high<br />

value <strong>of</strong> T-peel adhesion strength at a CR dosage <strong>of</strong> 90 phr, irrespective <strong>of</strong> the type <strong>of</strong> PCNSL and<br />

solids content.<br />

Acknowledgement: Thanks are due to the Kerala State Council for Science Technology &<br />

Environment<br />

(KSCSTE), Thiruvanthapuram for sponsor<strong>in</strong>g this work and to Pr<strong>of</strong>. T.K. Chandrasekhar, Director,<br />

NIIST, Thiruvananthapuram for provid<strong>in</strong>g the necessary facilities.<br />

REFERENCES<br />

1. Wake, W.C. Adhesion and the formulation <strong>of</strong> <strong>adhesive</strong>s; 2 nd Edn., Appl Sci Pub., New York, 1982,<br />

Ch.10, pp. 220-223.<br />

2. John, N.; Joseph, R. J Appl Polym Sci, 1998, 68, 1185.<br />

3. Poh, B.T.; Kwo, H.K. J Appl Polym Sci, 2007,105 (2), 680.<br />

4. Kozakiewicz, J.; Kujawa-Penczek, B.; Penczek, P.; Puton, K. J Appl Polym Sci, 1981, 26,<br />

3699.<br />

5. Menon, A.R.R.; Pillai, C.K.S. ; Nando, G.B. J Adhesion Sci Technol, 1995, 9(4), 443.<br />

6. Menon, A.R.R.; Pillai, C.K.S.; Nando, G.B.; Bhattacharya, A.K.; Gupta, B.R. Kauts Gummi<br />

6

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