TT belts...clean before ??

The powder is a preservative for the rubber to keep it from drying in storage. DO NOT use alchohol that will shorten its life. Simple Green works real good on rubber parts

The powder is there to improve traction; I would leave it on. VPI belts are powdered, and it makes sense to repowder them every few years as the powder wears off. Just put them in a baggy with powder and shake.

Many flexible plastic and rubber products have chemical softeners in them to keep them flexible for years. Many commonly available cleansers have agents that remove such softeners, causing the item to become brittle before their time. This is why we shouldn't clean a vinyl car seat or dashboard with common "household cleansers," or else the vinyl will crack in less than a year. Same with rubber belts.