Polypropylene seems to be ok, at least as an outer sleeve for 45s first stored in paper and cardboard sleeves. I've been using them for over 20 years with no haze developed on any clean 45s. PVC is another matter completely. That stuff is total poison.
I have noticed haze develop on 45s that have NEVER been cleaned. There is a kind of greasy film on some of those, which is normally not a problem because it cleans off 100% easily, usually leaving shiny mint vinyl. But very occasionally the greasy film has been known to leave a permanent hazy stain after cleaning. A large number of 45s purchased on eBay arrive with traces of mould on them, when inspected with a strong magnifier. I clean every 45 as soon as I get it, both sides. Mould feasts upon fingerprints if given half a chance. I have a dehumidifier in my record bunker. The amount of water that it pulls out of the air in any location is a real eye-opener. Half a bucket per day from an average sized room, all year round. Mould can not survive in dehumidified air.