Polysorbate 20 is not a preservative: It's a solubilizer that will help you incorporate small amounts of fragrance or essential oil into your product.
Propylene glycol isn't a preservative: It's a humectant that draws water from the atmosphere to our skin. It acts as an anti-freeze, reducing the freezing point of water and water soluble things in our products, making it easier to ship things in cold weather.
Stearic acid isn't a preservative. It's a fatty acid that we find in our oils and butters that makes them thicker, as well as a thickener we can add to our lotions.
Preservatives are ingredients like liquid Germall Plus - INCI: Propylene glycol, diazolidinyl urea, and iodopropynyl butylcarbamate - or Germaben II - INCI: Propylene Glycol, Diazolidinyl Urea, Methylparaben, and Propylparaben - or Phenonip - INCI: Phenoxyethanol (and) Methylparaben (and) Ethylparaben (and) Butylparaben (and) Propylparaben (and) Isobutylparaben - or Optiphen ND - INCI: Phenoxyethanol (and) Benzoic Acid (and) Dehydroacetic Acid - and so on.
Why do we need preservatives in products containing water?
Preservatives: How the heck do they work?
What you need to know about making products (part one)
What you need to know about making products (part two)
Vitamin E is an anti-oxidant, not a preservative
Packaging and preservation