A peak in a differential scanning calorimeter (DSC) indicates a phase transition which is first-order. The sign of the phase transition can be exothermic or endothermic.

Don't be surprised - both epoxy and lignin are polymers and, like many other polymers, can exist in amorphous and crystalline forms, particularly epoxy.

Crystallization generally occurs after glass transition.

lignin contains multiple -OH groups. they can react with epoxy groups to form an ether. this is an exo- reaction.