as i cross linked the blend film in ionic salt solution.but when this ionically cross linked film is dipped in distilled water it is dissolving in it completely not swelling..According to literature it should swell in distilled water as it behaves physical hydrogel..Then why it is melting in water?i also have ried hcl acid of ph 2 for swelling of film then also it is failed. Why?
You probably do not have sufficient crosslinking so the swelling capacity/turgor pressure is >> than the mechanical integrity of your sample
See:
J. Berger 2004 Structure and interactions in covalently and ionically crosslinked chitosan hydrogels for biomedical applications,. European Journal of Pharmaceutics and Biopharmaceutics 57: 19–34
Hi
What is the cross-linking gent you have added? What concentration of the cross-linker you have added? Did u add any sweeling agent like gums, starch etc? What is the time you have given for the cross-linked networks to form?
Networks formed due to the presence of cross-linker should be strong with good mechanical strength. Actually this is the problem associated with hydrogels.
That is the reason we should optimize the concentrations.The other reason is did u find swelling studies in any ph solutions?
please find out
If your material is completely dissolved in water may it was not cross-linked or the number of ionic interactions between the molecules is very low.
Be sure that you do not have any electrolytes in distilled water that could be exchanged with those used for cross-linking.
Did you use tripolyphosphate for crosslinking the chitosan? If so, that should work, but make sure that you have sufficient chitosan relative to PVA. PVA can form hydrogen bonding with acids (like polyacrylic acid) to make pH sensitive hydrogels, but in this ionic system, I doubt it brings much to the hydrogel other than pure water solubility and unless you have a large amount of crosslinked chitosan to hold it the PVA will just dissolve. If it is dissolving I would suggest increasing ratio of chitosan to PVA and then making sure you are using sufficient sodium tripolyphosphate to crosslink the chitosan.
I agree all the mentioned reasons that possibly may lead to such phenomena. Let me add that an additional literature survey about crosslinking chitosan with PVA to decide the most suitable ratios of monomers and crosslinker as well as the optimum experimental conditions for such reaction (temp., salt conc., pH....etc. This will help to save time and effort in the lab.
is swelling depend upon blending ratio or ionic crosslinker ratio with blend?
If your polymer is dissolved this mean that there is no cross links or few cross links that cant resist the solving power and so now swelling as a result. you need to be sure of the cross linking agent is work properly under the specific conditions of pH temperature media etc
I'm not sure about calcium chloride for crosslinking chitosan. Typically that agent only works with sodium alginate/alginic acid. If you want to crosslink chitosan you will need to use sodium tripolyphosphate. Check out: Shen, E‐C., et al. "Tetracycline release from tripolyphosphate–chitosan cross‐linked sponge: a preliminary in vitro study." Journal of periodontal research 43.6 (2008): 642-648. (http://onlinelibrary.wiley.com/doi/10.1111/j.1600-0765.2007.01045.x/full)
I'm not sure about calcium chloride for crosslinking chitosan. Typically that agent only works with sodium alginate/alginic acid. If you want to crosslink chitosan you will need to use sodium tripolyphosphate. Check out: Shen, E‐C., et al. "Tetracycline release from tripolyphosphate–chitosan cross‐linked sponge: a preliminary in vitro study." Journal of periodontal research 43.6 (2008): 642-648. (http://onlinelibrary.wiley.com/doi/10.1111/j.1600-0765.2007.01045.x/full)
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