Nondestructive testing of defects in adhesive joints

depend largely on concentration, molecular weight, additives and conditions of mixing ie,
stirring or sonication. An average particle size of 310 to 490 nm was obtained with isopropanol
and 347-438 nm with acetone, when chitosan of molecular mass of 8KDa was used Fig-1. The
PKa of chitosan is 6.5 and below this pH, chitosan behaves as a poly cationic material, the
phosphoric ions of TPP forms ionic cross linking with NH3 + groups of the chitosan and has a net
positive charge on the surface (IEP-9.0 ) and the surface is comparatively hydrophobic [17].
3.2 Effect of cross linking agent on the size of nano particles of galactomannans: The
cross linker used was either borate or sodium tripolyphosphate (TPP). Table 1. Two Guar
gum chains cross links with borate ions -B (OH) 4 preferentially due to the cis diols
present in the mannose ring. The reaction is favored at neutral pH conditions. TPP cross
links with the hydroxyl groups of the polysaccharide forming phosphate bonds between
the two polysaccharide chains
3.3 Effect of non solvent on the formation of nano particles: The production of nano
particles dispersed in aqueous media by precipitation with non solvents involve the use of
acetone, methanol, ethanol, isopropanol, amyl alcohol etc. The final mean particle size of
NPs was clearly dependent on the nature of the non solvent used. The results showed that
the use of isopropanol and acetone led to smaller particles, as measured by (DLS), where
as other solvents gave larger particles (above 500 nm). Even though low log P values
tend to give nano particles, there is not much correlation with the Log P values and nano
particle formation. However the dielectric constants which are a measure of solvent
polarity played a significant role. A slow reduction in the dielectric constant of the
solution brings about nanoprecipitation. Acetone and isopropanol has similar medium
dielectric constant value of 18-20, which favors the nano precipitation of chitosan
molecules in water medium which is having a dielectric constant of 80