Joining PET Plastic

In the past, I've had luck using plastic cements for such applications (just make sure you use some sandpaper to get a rough surface on the plastic first).

How it would fair with exposure to mineral oil and weight? I'm not 100% certain.

Over time, the mineral oil will likely destroy any type of glue used.

Why not just use PVC pipe, and reduce it where needed? It is compatable with mineral oil, and since the plastic is fused, it won't leak.

it needs to be as lightweight as possible and clear.

Oh.

I find myself envisioning the IV drip bags, but longer. If constriction in the center was needed, it would be pretty easy to do.

Fiber Glass Epoxy?

Plain old Silicon Caulk?

I know what Plain old Silicon Caulk is. Actually it's silicone.

But, I've never heard of Fiber Glass Epoxy.

Can you enlighten us?

I was referring to the liquid stuff that comes in a fiber glass repair kit. I repaired a hole in a little sail boat a number of years ago. If I remember correctly, I mixed two things together to form a goo that I soaked the fiberglass mat in. Thats what I meant. Perhaps a poor use of terms.

The stuff is pretty tough; but brittle.

Thanks for pointing out my spelling error. As a crystal grower in silicon valley back in the early 70's I should have picked up on that.

I would cut a hole in a piece of wood just large enough to fit my outer piece into; put some silicone caulk around the fitting edge; and stuff the other piece into it. Let it dry and give it a shot. Cheap and available.

Sorry to be so anal.

The majority of resins used today with glass cloth, mat and in chopper guns is polyester.

Epoxy will work just fine, as well, but it's usually more expensive and the added strength is not necessary.

Bondo

Are you familiar with spin welding?

Spin Welding Joins Plastic Parts Fast & With Ease - HeatStaking.com

I think kramarat has a valid point about mineral oil migration into the bond line, depending on the service life required.

I was thinking JB weld but it would have to be flexible so I would try this :

Loctite E-40FL Hysol Epoxy Adhesive

http://www.amazon.com/Loctite-E-40FL-Adhesive-Flexible-CARTRIDGE/dp/B000WSIXW2

Not to be pendantic, but with a cured hardness of 75 Shore D, I'd say this isn't soft/flexible enough for thin PET bottles.

But, it's worth a try.

Does it have to be configured like that?

A single, clear, one gallon bottle would give roughly the same capacity. No joining required.

Given the relative price of mineral oil and the mess it can make I have no clue as to why you would be trusting a pair of glued together soda bottles to contain it when there are countless numbers of gallon jugs and containers in countless shapes and materials designs that can be bought for next to nothing.

So what do you need this highly specific type of containment vessel for anyway? Given the relative weight of a gallon of mineral oil at 8.5 - 12 LBS an extra few more ounces for a proper container that's guaranteed to not leak or come apart can't possibly be an issue.

MEK is a solvent that will dissolve PET. You may find a light coating to the contact areas will bond it. If not chop up the discarded parts and dissolve in MEK to make a glue.

Not to be condescending, but I work in the coatings industry and never heard MEK will dissolve PET, so instead of just saying it won't, I just took a Mountain Dew bottle and filled it up with MEK. Nothing is happening, I will leave it over the weekend, but I think PET has good solvent resistance. I know MEK will dissolve other plastics like ABS, but polypropylene, polyethylene, and PET, I don't think so.

<edit> I am correct : please read link

http://www.proplasticsinc.com/chemical_resistance_guide.pdf

align MEK and PET, MEK will not touch it.

I agree with you. PET has outstanding chemical resistance. That's why it can withstand the acidic fluids it is used to store.

I spent over 20 years as a materials engineer in the aerospace industry. But am out of date with the latest technology now.

http://www.plasticseurope.org/Documents/Document/20100301162055-050303GeneralChemicalResistanceofPET-20050303-003-EN-v1.pdf

Here is a list of solvents and effects on PET.

Ok, one link says MEK will attack PET and one says it wont, the proof is in the pudding, I have a 20oz Mountian Dew bottle, 3/4 full with straight MEK sitting on my desk right now, it has been there for a couple of hours, no discoloration, no nothing. I am leaving for the weekend and I will leave it there. Monday when I come in, I will take a picture of whatever happened and post it.

As I suspected, MEK did not dissolve Mountian Dew bottle, there is a little discoloration, probably would not use such thin PET as a storage medium.

With that being said, your glue would have to attack the plastic to seal it. The only 2 chemicals that will dissolve PET according to my link are chloroform, and methyl chloride, I wouldn't play with either..

I am willing to learn. but PET is one of the most difficult plastics to glue. I wouldn't even think of trying. The oldtimers inter nos may remember the first edition plastic PET bottles with a cup attached at the bottom to hold it standing. This was glued onto the PET bottle with a sticky elastic glue. These glues are categorized hotmelt glues of the soft to medium soft type. It is also used to glue the labels on. I have done a lot of experiments on it when I did research in a PET bottle production unit and later in the packing industry. Suppliers are 3M and Henkel, to name a few. The application viscosity is temperature controlled. So you can use it very thin or like a bead. The glue has a sticky appearance like a non fully cured thixotropic glue and the blocks or bricks are packed in a gelattine or siliconized paper. These PET bottles are very strong too. A bottle can withstand pressures up to 10 bar.

Make sure you know the bottles are PET since, if I am not mistaken, Coke product bottles are not.

Good manufacturing policy is using the identification code on plastics.

This is the old "7" code

I just checked a Coke bottle and it's a "1". But, according to an article on the web, some of them are up to 30% mono-ethylene glycol derived from sugar cane.

You are probably right. They may have dumbed down the FAQ's so normal Coke drinkers could understand it.

They are used to dealing with consumers, not engineers.

Is where they get it from important? As long as they don't steal it from me. They all pretend to be greener than green. Part of (1. education),2. brainwash, Chose your preference.

You may be thinking of the "new" plastic they are developing made partially from plants.

From: The Coca-Cola Company: Plantbottle Frequently Asked Questions

What's the difference between PlantBottle® packaging and a traditional PET plastic bottle?

A: The difference is in the materials used to make the bottle. Traditional PET plastic is made using fossil fuels, like petroleum. PlantBottle™ is made with a combination of traditional materials and up to 30% made from plants.

Because the end product is still PET plastic, the PlantBottle™ package delivers the same performance (e.g. shelf life, recyclability, weight, chemical composition, appearance), but it reduces potential carbon dioxide emissions from our PET plastic bottles and dependence on fossil fuels, like petroleum, when compared to traditional PET plastic.

Correct. The question is does the added "chemical" change it's properties to where "normal" adhesive qualities for PET no longer apply?

After insertion of the one bottle into the other, invert it and press into a hot plate.

That will form a seem and weld the two bottles together permanently.

If you do this with an old non-stick teflon coated pan it should work well. But if it sticks, remove the heat and fill the pan with cold water and the bottles should solidify and pop right off.

I like this!

And then could still run a bead of silocone or similar to help the joint also.

I have a very easy fix, but the "glued" section will not be transparent. Go to a heating and air conditioning supply store and buy some tape which is aluminum on the outside and has a thick mastic on the sticky side. Use the tape to wrap around the area where the two bottles meet. This stuff is extremely difficult to get off duct work and sticks in cold (A/C A coils) and hot (furnaces). If the mineral oil will be creep up to the adhesive, you may have some contamination. I don't see the oil eating all the way through the mastic.

Hope this helps.