I was the person who answered the other “Virgin Vinyl” question so I will bring a flavour of that answer to this question.
There is quite a good page on Wikipedia about “Gramophone Records” in which the claim that virgin vinyl produces better sound quality is restated – but not substantiated.
I am far from being an audiophile but my experience is that recycled vinyl does produce a lower quality sound. I have a theory as to why this is but I must stress that I have no evidence to back it up.
First, I want to dispute the idea that “better” is subjective, the audiophile community like to pretend that’s the case but really, you CAN measure these things objectively if you want to. That’s how hi-fi manufacturers work every day. But that’s an aside…
“Vinyl” is actually shorthand for Polyvinyl Chloride – PVC – the same material that has a thousand and one uses in everyday objects. You’ll notice that the proper name for most “plastics” has a “poly” in it somewhere, e.g.: PVA-Polyvinyl Acetate, Polyethylene. That’s because these materials are Polymers, long chains of small molecules that are bonded together with strong atomic bonds (chemists are probably laughing at my terminology now, but I think I’m along the right lines).
However, you may have noticed that plastics can actually lose their strength over time – often as a result of sunlight. The light can break some of these bonds apart, deteriorating the polymer into its component parts and removing the strength with it.
So, PVC (vinyl) is used in records because the material needs to be strong. The point pressure of a stylus on a groove is incredibly high, it may only be tracking with a matter of grams, but the force is pressing onto an area of about 1/10th (probably somewhat smaller) of a square millimetre. This is why records can wear out; the friction literally scrapes the vinyl away from the walls of the groove. With every little bit removed, the musical information stored on the vinyl decreases. We hear this as noise and distortion.
This is where I start speculating. As I stated in my answer to the other question, I believe the vinyl is degraded in some way when it is recycled. My theory is that when it is heated to melting point, that heat will cause some proportion of the bonds in the vinyl to break. This leads to shorter polymer chains and a weaker material. As the stylus passes over the groove it will scrape away more of the groove wall with each pass, rendering the sound quality lower and lower with each play.
If I’m right, this happens to some extent even with “virgin” vinyl – but if the vinyl is recycled then another batch of the molecules will be affected – and, even worse, the previously affected molecules may be shortened even further.