Let me start with a couple off-topic comments.
1) I've been making hoops, mostly fire hoops, for more than 10 years. I started with irrigation tubing, and switched to HDPE as soon as it was made available to me. I now sell two types of HDPE hoops: thick wall for fire hoops and thin wall for featherweights.
2) I have watched with dismay as people tried to describe their tubing using PSI, color, place of purchase and a myriad of other unrelated attributes. None of these things actually define the material. The type of plastic, the Outside Diameter (OD) of the tube, the wall thickness and Inside Diameter (ID) are usually all that truly matters. Fortunately other pertinent issues like fiber reinforcement and chirality have not yet come into play.
Recently I was asked if i was planning to switch to polypro hoops; like so many others since an oft repeated article on how to make your own hoops. As with everything that hits my desk, I took this seriously and put some research into this. I decided to put these two materials through a fair, side-by-side test.
First, I purchased 10' of High Density Polyethylene (HDPE) and 10' of Polypropylene (PP, or Polypro) from the same online location. Both are listed as pure materials, both are 1" OD tubing with 1/8" thick walls (3/4" pipe size). Upon arrival, i found the actual products to have wildly different lengths, so I cut them both down to 9.5 feet circumference and split them into 3 parts (as if for shipping).
The first thing I noticed was a distinctive chemical smell when heating the PP tubing. Generally, this is an indication that toxins are being released. The HDPE only released a smell when actually convinced to burn. In mass production, this toxin could start building up.
The Polypro feels a bit stiffer, but ultimately has less resistance to bending. The clearer walls mean that internal hardware (like wires and such) will be more visible, but so should any light sources.
Weight (with 3 nylon connectors): [US postal scale, legal for trade to 0.1 oz]
HDPE: 1lb 6.1 oz
Polypro: 1lb 5.6 oz
The site does not list the temperature limits for the PP tubing, so I will use descriptions from neutral sources instead.
According to wikipedia, HDPE can resist 248(f) for short periods and 230(f) for duration. PP melts at a wider range of temps ranging from 266(f) to 340(f) depending on the form of crystallinity.
PP is used in a few things and can be recycled into a limited number of goods. However, it has a major drawback of being a UV degrader. Photo degrading plastics contribute to serious environmental issues. This may also have an impact on overall lifespan. Hazardous chemicals are a byproduct of PP production, and some Canadian research indicates that it may leak toxins under certain conditions. And the nail in the coffin for use as a fire hoop material: it's vulnerable to aromatics (a type of chemical found in cheaper grades of petrol fuels)
HDPE is used in many many things and is commonly recycled into a variety products. It does not photo degrade, nor are any biotoxins released or used in it's creation. It's completely resistant to aromatics and other petrol byproducts.
I don't see Bearclaw ever switching to polypro. The miniscule weight savings and extra heat resistance do not warrant the 3-4x cost of the tube. The environmental impact of this tubing is poor enough to veto it alone. But since the bulk of my hoops are fire hoops, the chemical vulnerability is a complete deal breaker.
However, for LED hoops, I can see the clear walls being a juicy pick over the translucent white of the HDPE. Time will tell if the UV vulnerability reduces the lifespan of PP hoops not completely covered in tape. I have no idea how long the average hoop stays in use, nor do I know the rate of degradation. [FWIW, Kevlar also has a UV vulnerability, discoloration is evident in as little as a week in sunlight.]
I will say that if you have a polypro hoop, it's probably in your best interest to keep it away from UV lights, and out of direct sunlight (unless completely taped). Also, if you have a PP fire hoop, you should make very sure to use very pure fuels (like Coleman's camp fuel, crystal K, or UPLO) and wipe it down religiously after fueling and spinout.
Actually, I just added my name.
Yes, the black tubing is typically used for irrigation. Any time you see a pop-up sprinkler system, you can bet it's being carried by this stuff.
The white tubing is rated as acceptable for food transport by the FDA, so it's used mostly as a modern replacement for copper tubing in homes and restaurants. Typically, it's used for conveniently going around corners and such when retrofitting new hardware.
Some of the smaller sizes are used to transport caustic materials and bio hazards in medical or scientific labs. This is where polypro is popular, as it has enough heat resistance to be autoclaved and reused, rather than destroyed.
As a chemist, and hooper, I really appreciate this discussion and you've clarified some technical details I've been wondering about.
Thank you so much for this post! Not only is it interesting to see the weight different first hand, but its fire aspects too. I may be purchasing some HDPE for fire and keep my poly for regular hooping.
So you mentioned using pure materials--does this mean you used homogenous polypro? Homo PP has higher crystallinity, whereas copopolymer PP, made with ethylene, tends to have less tolerance for heat, etc--though it is more flexible. Also, much polypro has HALS as an additive, which is super-effective at preventing UV degradation--but if flame retardants are added that are acidic they wear away at the HALS, which are more alkaline. The nice thing about HALS is that when the polypro's polymers cleave apart(which is what happens during its degeneration caused by UV light or heat sources--this happens during combustion too but combustion reactions require more to stabilize them) they consume the free radicals that would otherwise form and continue the break down. So they stabilize the reaction. But once again, they can't do much to prevent a combustion reaction and most flame-retardants destabilize the HALS themselves. It seems that it's pretty tough to find any polypropylene material that has a harmonious balance of flame-retardants and UV protection.
Sorry, I didn't get that deep into the chemistry. I had to go with the extrusions that were available. No, by "pure materials" I meant that mixed materials (poly blend of propylene and ethylene) were available. And that they were not used. Also, Many tubes are available with fiberglass or metal inserts in the plastic. Those were also not used.
Also, polypro is one of the top recycled products. It's resin number 5, on margarine containers and lots of catering products that require highly heat-resistant plastics. I think this goes for tubing too--I know a couple irrigation companies that pick up used polypro irrigation pipes from farmers for other companies to recycle.
I have to say though it is pretty hard to get all the details from companies. There's a lot that goes into a polypropylene product that will either or make or break the deal for me, but it's damn near impossible to get a clear picture of the material they're selling. Also, I can't seem to find any totally comprehensive resources on HDPE that aren't wikipedia. The nice thing about polypro is that it's such a new product, and looking through my university library I managed to find the Handbook of Polypro--awesome! However, I've found useful enough articles on HDPE, though nothing that so clearly detailed its composition and various uses as the handbook--but I do feel pretty positive about it. It's generally considered a 'safe' plastic all around and has been used for a while, meaning it also has reliable market value and is super recyclable as well. The most helpful info I've found has been through this thread(which has actually been super useful!). I definitely appreciate your investigation because it certainly gave me something to think about. While I still feel pretty positive about my choice of polypro, I haven't actually tested out HDPE before so now I'm getting all antsy to try it out soon too.
Also, because polypro manufacturing methods are constantly evolving, it's not that surprising to find that some products have been found to leach--then again, if you got that data from wikipedia, it's pretty unreliable. Not that I wouldn't take it into consideration, but the sources they cite for the claim that polypro leaches are from a news article that doesn't once mention polypro but 'plastics' in general, and a cosmetics website that uses polypropylene for skin care products(which I think WOULD be pretty harmful, and gross, and very very wrong--ick). But if it's polypro in particular that's under the radar i wouuuld like to know--I put a halt on making hoops out of PEX because there's enough controversy about it leaching and because it's unrecyclable.
I don't put total faith in any single source. Most of the leeching articles I found were from the BBC. And yes, I'm always open to new information. As for the recycling info, much of that comes from plastics industry and ecology websites.
Wow, that was alot of information. I also make hoops and I am always looking for new knowledge on the actual tubing. So this is AWSOME stuff to know. Thanks so much. -Nadine
Glad I didn't buy that spool of PP today blind! Thank you :)