I think this is good, but not implemented well. It’s likely to stop people from buying up materials on the market and selling them for more, using the market to try and have a monopoly on items.
However, there’s no real reason you shouldn’t be able to trade materials from person to person. I agree with having them become untradeable after buying them off the market, but not when trading person to person.
The only issue with that, is that you can’t buy a material for your friend and give it to them later. It’s hard to juggle. Maybe materials should just all have potential of 3/3? That would give enough leeway to trade around, I think.