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.
what size quick wicks do you order for poly pro?
that's gonna depend on the size of the hoop.
Ted, this is great. Thank you. When you say photodegrading plastics may have an impact on overall lifespan -- do you mean the hoops or the hoopers?
Also, have you had any experience with polypro splitting?
Thanks for all your great feedback. This is helpful.
Actually, yes, a little, as I was cutting one of the joints, it snapped in a most unusual way. I wrote it off at the time, but there's a distinctive break pattern to it that might indicate a "grain".
Just thoughts on the toxicity... I A few years ago I checked with a UC Berkeley Chemical Science expert on burning PE, HDPE, and PPE. I was very happy to find out that all three plastics are Carbon based, which means, on fire the smoke is akin to campfire smoke. No worries about smoldering hoop smoke on a firehoop.
That's awesome as some burning materials such as fiberglass, are HIGHLY toxic cancer causing agents when burning.
Excuse me, if we're gonna get technical I Shoulda have said "hydro-carbon" based.
A lot of plastics are nasty to burn but PE and PP are pretty clean-burning as they are pure, simple hydro-carbons. There are others, like polycarbonate, from which cds and nalgene bottles are made, that if they aren't burned very hot will let off benzene, which is bad. There is a question of fillers, because plastics are almost never purely polymer but I wouldn't think they would use anything that nasty in plastic lines intended to carry liquids for human consumption. None of these are super-clean to produce, but these two tend to be better than a lot of them because ethylene gas and propylene gas won't kill you instantly like phosgene or isocyanates (polycarbonate and polyurethane precursors) will.
One thing to add is that ethylene and propylene are petroleum by-products, so take from that what you will. If I were doing PR for Chevron I would tell you that these by-products used to be burned since there was no use for them. Now they are made into plastic, essentially sequestering the carbon that would have gone into the atmosphere. Nevermind that that carbon was sequestered underground as oil before you piped it to the surface...
:) But as long as we're getting technical, they all are. Here's some pics:
Polyethylene may start out as h2C=Ch2 simple ethylene, but yes, ends up as an aliphatic hydrocarbon (much like white gas, lamp oil, and propane). Like any other hydrocarbon, partial burn by-products are a possibility, so Carbon Monoxide and soot are distinctly possible. Accidental recombination into exotics are also possible.
Each repetition of Lexan has Two benzene rings in it (leading to the increased possibility of benzene release while heating). Suffice to say that burning any of these isn't the greatest idea. But, yes, polycarb seems to be the worst.