[kahynickel]

I am working for a 3d printing company and we are looking for an exothermic reaction that will heat two sides of the flexible plastic to 240 C. What chemical should we apply on both sides to have this temperature?? I thought of LDPE in molten form... Can someone suggest the chemical.

[Enthalpy]

The query is a bit obscure to me.

Do you want a chemical reaction to provide the heat? I suppose you need an accurate and adjustable temperature to tinker and stabilize your process, and no side products. A reaction uses to have side products and a badly defined temperature.

Or do you want to heat to 240°C the polymer you deposit? Then a heated nozzle looks more adequate, espeically if you regulate locally its temperature against the variations in polymer throughput.