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PVC was Useless!
PVC is one of the oldest polymers in existence. However, in its pure form it is useless, absolutely useless, incapable of being turned into any useful item. But over the years by the judicious addition of various substances to enable it to survive the various extrusion and moulding processes it has become the most versatile and widely used of all polymers. And yet its production only consumes half of the volume of petrochemicals that other polymeric materials such as polyethylene or polypropylene do. And at the end of its useful life it is fully recyclable.
“Various Substances” eh? Go on..
To turn it into any of those everyday products it must be mixed with one type of lubricant to assist its mixing, a different lubricant to allow it slide over the metal in extruders and tooling, fillers to enhance its physical properties, impact modifiers and/or plasticisers to change its rigidity, a few other titbits and finally stabilisers.
Stabilisers huh, what are they good for?
Stabilisers are of two types, internal and external. The internal stabilisers are designed to protect the PVC from the thermal stresses of extrusion or moulding. Get it wrong and the material degrades and carbonises, producing hydrochloric gases. Get it right and any degradation ions get absorbed and/or recycled back into the matrix. External stabilisers do the same job in protecting against the damage caused by high energy UV radiation. They mop up the disrupted ions and in the best cases replace the ion thus keeping the product intact.
So it’s all good then?
The range of stabilisers approved for use has shrunk as focus has turned to their impact on human health. Available stabiliser types proven to be safe in use have largely shrunk to two family types, Tin based and Calcium Zinc based. There are two tin variations approved as being REACH friendly: Octyltin and Methyltin, each one being excellent for use as both Internal and external in various formulations. CalciumZinc, now more generally referred to as Calcium Organic, is based on a mix of up to 20 chemical components (varied according to the producer). There is agreement that Calcium Organic is perfectly satisfactory for white products. However, its performance for darker colours and for cellular PVC which retains it higher core heat for longer, is not so certain and is a matter of debate.
What is clear is that any claims for the moral or ‘green’ credentials of Calcium Organic rest mainly on its well chosen name and not on any superior ‘greenness’ of any or all of the chemical components, which as already said, vary from supplier to supplier.
