Hi, All,
Brant's suggestion is sensible, because, unlike hot air guns, hot water is a controllable method of adding heat (you know the temperature will always be below 100°C), and only one commonly used plastic will melt around this temperatiure, Cellulose Acetate at 110°C (depending on grade and fillers).
The green grips on G519 bicycles are made from a Cellulose Acetate, commercial name Tenite, so keeping the temperature down is important.
Note that not all grips (especially more modern ones) are made from the same polymer, so may behave differently.
Because plastic does not transfer heat well, hot air guns also tend to overheat the surface of the grip before there is a sufficient temperature difference at the steel/polymer interface.
Plastic (except for grades filled with Carbon Fibre), generally expands at a greater rate per °C than metal, so the interference fit at 100°C will be less than at 20°C, making grips easier to remove. The polymer may also be slightly more 'rubbery', since 100°C is the Transition Glass temperature of Cellulose Acetate, a point where it does not melt, but the molecular chains have sufficient energy and space to move more freely.
Try to rotate the grip slightly, even a few degrees on the bar before pulling, this will help break the corrosion between the bars and grip, with less chance of pulling the end of the grip.
Finally, the Cellulose Acetate grips when made will have contained a plasticiser, or high boiling point lubricant, such as Di-Octyl Phthalate, which made them slightly more flexible when made. Today, the chances are that this has evaporated out, and so the grips will be more brittle and easy to damage.
Good Luck! (Honestly, I'd leave them on if possible).
Best Regards,
Adrian
