Technical Data - Chemical Resistance - PVC, Nylon, LDPE & EVA


 
Plasticisers are incorporated in PVC compounds so as to confer flexibility and softness. Plasticised compounds can cover a very wide range of flexibility and softness and will also differ in other respects e.g. tensile strength and resilience , according to the type and/or amount of plasticiser(s) used. For example, the type of plasticiser used will affect chemical resistance, but in this note it has been assumed that a commonly used, fairly resistant plasticiser such as Dioctyl Phthalate (DOP) would be present.

The amount of plasticiser incorporated will also effect the chemical resistance, an increase in plasticiser content leading to a deterioration in chemical resistance because the plasticiser is less resistant to attack than PVC.

The chemical resistance to be expected from plasticised PVC when DOP is used as the plasticiser is summarised in the following paragraphs.

a) Acids and Alkalis:

Dilute acids and alkalis have little effect at room temperature, but at elevated temperatures some hydrolysis and extraction of plasticiser may occur. Concentrated acids and alkalis hydrolyse plasticisers slowly in the cold and more rapidly when heated.

b) Organic Liquids:

The main effect of organic liquids on plasticised PVC is to extract the plasticiser and this results in some hardening, particularly when the PVC is removed from contact with the liquid. The compound may become rigid and less tough.

Most organic solvents will extract plasticiser and give rise to these effects, but with aromatic and chlorinated hydrocarbons, aliphatic and cyclic ethers, this plasticiser extraction is accompanied by a softening of the PVC and the overall effect is difficult to predict. With certain solvents too, plasticiser extracted is replaced by the solvent so that the compound remains flexible provided it remains in contact with that liquid. On allowing the solvent to evaporate the material will stiffen and will not soften on re-immersion.

The undesirable effects previously mentioned which can occur with PVC compounds containing a monomeric ester-type plasticiser, such as DOP, can be prevented or reduced by the use instead of a polyermic type of plasticiser which affords a higher resistance to extraction. Such plasticisers include polypropylene adipate (PPA) and polypropylene sebacate (PPS), the former being of value in contact with oils and fuels and the latter showing a high degree of resistance to soap and detergent solutions.

The symbols used to denote performance are as follows:

G = Good resistance

L = Limited resistance, attack will occur giving shortened life

P = Poor resistance, attack will occur

For materials which have been rated as L or P, the material should only be considered for use when alternative materials are unsatisfactory and where limited life is accepted. When PVC is to be used with such chemicals, full scale trials under realistic conditions are particulary necessary.

It may be safely assumed that chemical resistance decreases with both increasing temperature and with increasing concentration of reagent, and that the reverse is also true. No valid assumptions can be made, if the temperature and concentration move in compensating directions. The rating “Some Attack or Absorption” (Symbol “L”) cannot be assumed to apply for conditions different to those described.

The following Chemical Resistance Chart is not intended to be complete. Chemicals missing from this chart does indicate unsuitability. If in doubt, contact BAT for further advice.


 
The following Chemical Resistance Chart is not to be complete. Chemicals missing from this chart does indicate unsuitability. If in doubt, contact BAT for futher advice.