chemist wanted ? Polyethylene and toxins

[Bad Inferno]

I was buying some poly tubing from an industrial supply shop and they questioned my purpose. I said it was for fish so they stated I needed to use a special tubing which I think was "Low Density Polyethylene" as the other tube the manufacturer put chemicals in to make it flexible. I have also been told that your garden hose has many additives for durability and antialge which is why you should not use it for drinking water.

Can anybody shed some light on both "low" & high" denisty polyethylene...what is better as I notice my water drums are HDPE

rob

[fishgeek]

High density polyethylene is a linear polymer that has crystalline regions and is used to make rigid containers . Low density polyethylene is a branched polymer whose molecules pack more loosely than those of high density polyethylene. Low density polyethylene is more transparent and waxy than the high density polymer and it is used to make flexible bottles and plastic wrap.

cut and pasted from chemistry web site

the other things have nothing to do with the definitions
basically both types can have additives that may be toxic added
food grade plastics are always safe for aquatic usage

i believe that both high and low density is used in food grade products

[Bad Inferno]

I had, until a few years ago, assumed platics not to leach out toxins in our foods/drink, this is obvisouly not the case if we use non-food grade containers...If we reheat takeaway that comes in plastic I always change to a glass container to heat it these days....

So I wonder about these cheap drums we use for water storage...if they indeed have toxins. I know the larger ~120 litre black drums that are around Melb are from a chemical supply company that transports dry chemicals from Asia to Australia. Once the chemicals are here they sell the shipping drums cheap.

[fishgeek]

i think it more to do with products used to inhibit growth of algae on the plastics

food grade plastics can not have these additives so not a problem to reheat your takeaway, except when you melt it!

i have standard old pvc plumbing (rumour has it that it is full of nasty toxins) for the plumbing on my mii system
did so on the advice of some other forum members who had run similar wih no problems over long periods

[oscar]

Getting away from the chemical treatment side...Low Density poly is lighter, cheaper, and easier to work with than the high density stuff. This is because it is designed to deal with lower pressure e.g some garden bed sprinklers as opposed to lawn pop-ups which require high density.

It may just be possible that the person made the recommendation based on the fact that you really didn't need to spend the extra cash and have the extra difficulty in working with the product based on your low pressure application?

Not sure but it may be a contributing factor.

[Bad Inferno]

yeh HDPE has a higher pressure rating than LDPE and they said they put a chemical in the HDPE to make it flexible. The LDPE is already flexible. This does make sense...

thanks fishgeek & oscar...bottom line is don't use HDPE poly tube from a supply shop....cheers rob

[xmasfish]

I use poly tubing from our local pump and irrigation supply. It creases rather than bends but this can be overcome using angle fittings. It is very cheap by the 25m roll and I havn't had any problems with it yet. I cannot imagine anything leaching from it into aqueos solution at the temperatures involved as the basic matrix involves fairly massive molecules. The use of right angles and tee-pieces will promote turbulent rather than laminar flow but I would consider this an advantage. The major drawback with these angles is an increase in back-pressure on your pump. The tubing is marked "NETAFIM TYPE 30 CLASS IRRIGATION 13 MM I.D. 0503/202 A52 MADE IN AUSTRALIA".