Hi Firdos

As you are ncreasing the crosslinker conc. the degree of crosslnking is increasing.This is making the resulting system more rigid leading to higher Tm.Due to higher rigidity the system looses on tensile strength.Actually you have to optimize the degree of crosslinking as ncreasing the crosslinker may not be advantageous sometimes.

Hi Firdos,

The melting point determines on number of factors such as lon-ion Forces, Dipole-Dipole Forces, Hydrogen-Bonding, Van der Waals Forces, Molecular Shape etc. and Tensile strength depends on Yield strength which is the stress which will cause a permanent deformation of the original dimension.

Ultimate strength - The maximum stress a material can withstand.

Breaking strength - The stress coordinate on the stress-strain curve at the point of rupture. So increasing melting point not necessarily increase the tensile strength. 

when crosslinking is inceasing, the bond number is increasing. when you make macrmolecules move or fluctuate, it will need more energy.so the Tm is inceasing.but when the crosslinking is inceasing, the orientation force is decreasing, and total material is one macromolecule which becomes stiff and brittle like the rubber aging.

Firdos,

"What happens exactly if a biopolymer has increasing melting temperatue and decrease in tensile strength? "

To answer exactly to your question you'll have to provide us with more details about your system and its exact experimental conditions both for the preparation of the mixture and the measurements of the thermo-mechanical properties.

Then we would need to have a look at the curves you obtained before and after "crosslinking".

Without these informations everything would be pure blind speculation.