Take 50mg sample, add a few drops of 2mol/L sodium hydroxide, using phenolphthalein as an indicator, if it is alkaline (red), then add a few drops of hydroxylamine hydrochloride. 0.5 to 1 min after the addition of hydrochloric acid to make it acidic, then add 2% of 1 drop of ferrous chloride, showing a purple polyester polyurethane, showing a yellow polyether polyurethane.
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