As I said previously, I have not done any research on SDR35. I should because it's my business to know what is and is not in it.
I have on the other hand done a lot of research on PVC and have been assured by our manufacturer (Cresline) that all of their PVC pipe is made from the same basic material.
I can't speak for other manufacturers but according to our rep the potable water pipe and the DWV pipe (as well as the D&S) is made from the same material.
Each person will have to decide for his or her self if they feel this is a safe material to use in cheese making. Personally I don' t have a problem with it, but if it's like everything else...in 10 years or so we'll find out that it can cause about every health problem imaginable.
On the other board I frequent, there are a few people who are adamantly opposed to using even the potable water PVC as a cheese mold. They are convinced that it will leach out into the cheese causing all sorts of health related problems.
Of course neither I, nor anyone else can say with total assurance that this is a safe product to use in the long term. All I'm doing is giving my opinion that I feel it is safe and I'm not worried about using it personally.
Just my two cents.