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In the mid-20th century film switched to modern plastics like cellulose acetate, and later PET (which are still quite flammable). But before that, it was the f
by retrac 3y ago
In the mid-20th century film switched to modern plastics like cellulose acetate, and later PET (which are still quite flammable). But before that, it was the first kind of plastic invented -- nitrocellulose plasticized with camphor. Nitrocellulose is also known as gun cotton; it's literally explosive.
It degrades over time, with the plasticizer separating and the film becoming brittle, eventually turning into a powder that can ignite from friction or even auto-ignite. More than anything else, that's why so many early major films are lost. They turned to dust. And then exploded.
> The use of volatile nitrocellulose film for motion pictures led many cinemas to fireproof their projection rooms with wall coverings made of asbestos. Those additions intended to prevent or at least delay the migration of flames beyond the projection areas. A training film for projectionists included footage of a controlled ignition of a reel of nitrate film, which continued to burn even when fully submerged in water. [...] Owing to public safety precautions, London Underground forbade transport of movies on its system until well past the introduction of safety film.
https://en.wikipedia.org/wiki/Nitrocellulose#Nitrate_film_fires https://en.wikipedia.org/wiki/Nitrocellulose#Nitrate_film_fi...
- naikrovek 3y agogun cotton and nitrocellulose are not "explosive." they both burn very easily and quickly, but they do not explode. explosions are another class of reaction.
- retrac 3y agoYou might mean that it does not detonate -- it does not. It is not a high explosive. But gunpowder (of both smoking and non-smoking varieties) is still generally considered an explosive. An explosive is something that can produce an explosion - a blast. And they can certainly do that.
- naikrovek 3y agoshow me a video of a reel of old nitrocellulose film producing a pulse wave and I'll change my mind. I was conventional munitions (non-nuclear) maintenance in the USAF. I am trained on these things.
- hexane360 3y agohttps://en.wikipedia.org/wiki/Explosion https://en.wikipedia.org/wiki/Explosion >An explosion is a rapid expansion in volume associated with an extreme outward release of energy, usually with the generation of high temperatures and release of high-pressure gases. Supersonic explosions created by high explosives are known as detonations and travel through shock waves. Subsonic explosions are created by low explosives through a slower combustion process known as deflagration. Doesn't have to be supersonic to be an explosion. This is a disagreement about definitions, not about the properties of nitrocellulose.
- naikrovek 3y agoI'm not talking about a shock wave, but a pulse wave. would you feel the event from a reasonable distance? true shock waves will generally kill you because they move faster than sound.
- gabrielhidasy 3y agoSo you are talking about a detonation, a specific type of explosion that involves a supersonic wave, almost everything you would see as a munitions expert would be one of those. A dictionary definition of explosion is "a rapid expansion in volume associated with extreme outward release of energy", that includes things like, gunpowder deflagration, aerolized gasoline burning, or even a pressurized container (like a pressure cooker) rupturing. Film burning on a metal tin as they were stored could fit this definition pretty well.
- hexane360 3y agoI can't quickly find any resources that distinguishes between a 'shock wave' and a 'pulse wave' in the context of explosions. Do you have some resources? If you're defining pulse wave as a sub-sonic pressure wave, deflagarations can definitely produce those, even with relatively poor fuels (e.g. wood dust). Why do you expect nitrocellulose couldn't? Not enough gas volume?
- 3y ago