If you refer back earlier in this same thread, you will find that I did some work on hydrolyzing PET with NaOH (sodium hydroxide). It works and coats beautifully. There are two problems, though. One, it is difficult to process a large sheet because the material must soak for about two hours for the necessary hydrolysis to occur. So if you want to process something larger that you can do in a print tray, for example, you need a machine or some kind of spool setup, think like a large developing tank, which means lots of caustic 3.0M NaOH around. Two, the PET surface MUST be thoroughly washed or it will spoil the emulsion, processed or unprocessed, after a few weeks.
Flame treating PET is a much more convenient process but unfortunately gives inconsistent results. Beautiful when it works and useless when it doesn't.
Gotta tell you, subbing is vexing. If you start you will want to find a solution to the problem and it can make you nuts. The trouble is you are trying to get a water based concoction to tick to a hydrophobic surface. Essentially the same problem as putting latex water-based paint over oil-based paint. The paint peels off and so does emulsion.
And, when you read old recipes like Mr. Glafkides, you will find that our materials are not exactly the same as they were 50 to 75 years ago. Today's gelatin is different. Subtle denaturants have been added to liquids so people can't make drugs out of them and so forth that ruin the basic idea. If I had a nickel for every time I thought I had this one licked ....
Someday, we will lick this one. We need to because I am concerned that the pre-subbed material can be hard to get and IDK what the market for it is.
Yeah, PE, don't say it.