If it's plastic then it should burn off in a flame. Care the fumes will be toxic so make sure you do this outside and stand up wind. Too much heat will alter the temper on the file so don't overheat - most plastics will carbonize (burn) well before you do any damage.
If you have cyano clogging the tines then heat is not a good idea as the fumes are dangerous. There are Cyano removers that may soften the glue and it may then be possible to remove with a wire brush etc.
Traditionally engineers used to use Sulphuric Acid from a car battery (the wet type not SLA) to clean and sharpen the tines but this is both toxic and corrosive so you need to wear the correct protective clothing, gloves and facewear to protect you from any splashes or spillage. Should you manage to use this method please make sure you dispose of the acid correctly. it will melt your bin and pollute the drains so put it back in the battery or contact the local council for disposal instructions.