There is nothing magical about thermoplastics.
Synthetic plastics can be broadly divided into two types, thermoset and thermoplastic. Thermoset resins, such as epoxy, have permanent crosslinks between their long chain polymers. Once these plastics are fully cured, they cannot be melted down again (unless dissolved using an appropriate solvent). In contrast, thermoplastics, such as nylon, lack these crosslinks; therefore they can be re-liquified through heat alone.
The only racquets made out of thermoplastics were those produced using the injection molding process, most famously the Dunlop Max 200G, because molten thermoplastics flow much better than thermoset resins. The trade-off is that these thermoplastic frames are by nature heat-labile; they will melt if given enough thermal encouragement!
As I understand it, these Yamaha TP racquets are conventional thermoset (epoxy) frames coated in a layer of thermoplastic, which acts as a vibration dampener. This is easy enough to do during manufacturing - you only need to wrap the epoxy fiber-reinforced prepreg in a sheet of nylon before laying the whole thing in the mold.
No idea how well the vibration-dampening works, as I've never handled one of these. I rather doubt it's anything earth-shattering.
