I think this is not strange. Chitosan is not an individual compound but a polymer of variable length (and MW), i.e. a mixture of compounds, and thus different samples have different composition. So chitosan just cannot have a unique melting point. 

I think this is not strange. Chitosan is not an individual compound but a polymer of variable length (and MW), i.e. a mixture of compounds, and thus different samples have different composition. So chitosan just cannot have a unique melting point. 

Igor's comment is spot on - heterogenity of chitosan by length and possible N-acetylation up to 25% make it unlikely that it would melt in a well-behaved fashion.  Decomposition might also be partly due to air oxidation of free amino groups, so you might see what it does under inert atmosphere or in a melting point capillary sealed under vacuum.  You also might want to try mixing in small amounts of another polymer - I'd suggest polyethylene glycol (Himedia sells several lengths and grades).  Very uniform mixing could be accomplished by using a mill.  (I've long used small handheld electric coffee grinders for powdering ammonium sulfate for protein work.  These are available for $15-25 in the US, and presumably you can find them in India.)  You might start by trying, say, 1-5 weight percent PEG20000 and possibly one shorter length (4000, 6000 and 8000 are commonly available).  Also doping with long-chain fatty acids might give interesting results, including better stability toward oxidation.

I see that Igor Dubey opinion  was true becouse the chitosan is not one pure compound but  it is known the deacetylation process does not yield  all CH3CONH to convert NH2  or you know only by micro analytical data How many amino group becomes free  to determine % 

It depends on which type of chitosan are you using i.e. Degree of deacetylation and molecular weight. DD>85 generally shows Tg in range of 80-120 degree centigrade.

The intra- and inter-molecular hydrogen bonds which generate a stable and rigid semi -

crystalline structure makes chitosan also degradable before melting because of the melt high viscosity, which is typical for polysaccharides with extensive hydrogen bonding.

Find enclosed attachment.

Regards

Shakeel

see this link

https://repositorium.sdum.uminho.pt/bitstream/1822/14291/1/file.pdf

https://www.google.iq/url?sa=t&rct=j&q=&esrc=s&source=web&cd=10&cad=rja&uact=8&ved=0ahUKEwjsoZ635uvQAhWL8RQKHRH6DxIQFghqMAk&url=http%3A%2F%2Fwww.cjps.org%2FEN%2Farticle%2FdownloadArticleFile.do%3FattachType%3DPDF%26id%3D11157&usg=AFQjCNG7tJIYqcQiOW_lWTfmqJAiPP2zJA&sig2=4Jug2LEqIFJfuO_OmWPGug&bvm=bv.141320020,d.bGg

The melting point of chitosan is depended on Mwt of chiosan  and source extraction 

the melting point for chitosan (medium molecular weight) -Aldrich- was about 290^C.