OK you guys out there in the know. What is this stuff? I heard some guys talking today about this"new foam for surfboards" called compressed EPS. “It does not outgass”. Can anyone tell me whats going on here? I just got my EPS foam and I’m being told that I’m going to have an outgassing problem when I glass it. Help.
There are many ways to manufacture EPS…some better than others depending on the application. For surfboards that are hand layup you want tight well fused beads. This will prevent outgassing and water intrusion and is easier to shape
EPS is now being manufactured specifically for surfboards like Markofoam which uses steam blown into molds or Segway/American foam that gets foam made specifically for surfboard application.
Ok Bagman here goes:
15 years in the EPS business and a minor in Chemistry.
Hobby shaper since 1969.
EPS stands for Expanded Poly-styrene. This is styrene plastic that is made in a long thread (styrene monimer to poly) and formed into a ball, sort of like a loosely woven ball of yarn. This is done in a reactor vessel with the gaps in the ball formed by water. The ball (called a bead) is then dryed out by hot air. In the middle of the bead, the space is then filled with a liquid that becomes a gas when heated above room temperature. This is pentane. The amount allowed by the federal government is now highly regulated and is around 5%. This is the blowing agent and when the bead is heated by steam to soften and melt the plastic, this liquid turns to a gas and expands the bead. The plastic outside of the bead then melts (fuses) with the bead next to it.
Jason: there is only one way that EPS is made, and that is by steam fusion. There are two different ways of forming EPS products; that is by block molding, and custom molding. Marko blanks are custom molded, Segway blanks are cut from block.
The finished bead, now called “raw bead” is sorted according to size. The manufacturer (usually ARCO or BASF) controls the reactor so the beads fall into a range, but still must be sorted. Thus we have the largest bead called “A” thru “B” & “C” down to the smallest which for some stupid reason is called “T”. (We used to joke that it was T for tiny because you could never get the damn things out of your hair even after showering!) The last time I talked to Greg he said there were some new varieties on the market but for surfing needs, A, B & C should do just fine.
These raw beads are very dense, I don’t remember the weight, but a 1000 lb gaylord (a type of reusable box) fit on a pallet and the box was about four x four ft. From here the bead must be “pre-expanded” to its finished density weight in a reactor called a “pre-expander” (duh!). This is when the molder specifies 1 lb., 2 lb., 2.5 lb. per cubic foot foam. This process is similar to the molding process but is precisely controlled in both the temperature of the steam used and the time the bead is in the expander. This finished bead is then dried again and blown into giant storage bags. The amount of pentane is again reduced to around 1 to 2% at this stage. The bead must be used quickly as the pentane will out-gas at room temp. but this does not happen in less than 24 hrs. in most cases. Bead in the bag with no pentane (remember I said that) is called “dead” and is unmoldable and must be recycled by mixing it with fresh bead. (I used to fire guys for doing this without telling me)
Anyway, the molding process is next. The bead it conveyed by hose to large molding machines. Some of these are truely giant since they make large blocks of finished foam and some are so small (cup machines) you could have a couple in your garage. The bead is then blown into a mold which is held shut by hydralics until it is full. Steam is then blown into the machine causing the pentane to soften, beads to fuse, etc. The block or molded part is then cooled by water, vacuum or both and then removed from the mold.
This is where it gets interesting, and a lot of the informational errors occur.THE DIFFERENCE IS THIS: 1. Block machines must push steam into the middle of the beads to get them to expand and melt together forming a solid whole and are bad at this because of the physics of the material. The beads closest to the mold expand first, blocking off steam from the inside beads. Large beads fuse quicker on the inside of the block than smaller beads which is why their have traditionally been used. However they leave gaps between themselves and this air (not pentane) is what gets hot in the sun and causes delams. Properly molded block does not do this. Segway blanks do not “gas”. (I do not work for the EPS industry today so nobody has paid me to say this!) 2. Custom molding traditionally uses smaller beads, B or C sizes. Correct molding causes total bead fusion all the way through the foam. You can see this by breaking a piece of properly molded foam; the beads all tear through the middle, not at the points of attachment to each other. A poorly molded foam tears at the joints between beads and the beads themselves are easy to seperate. (PUKAS!)
So, to finally answer your question, your friend is talking about custom molded foam, not blank cut foam. XPS is extruded styrene foam with no beads and does trap pentane (or whatever the blowing agent is used) in the structure of the foam. This when heated does cause blow-outs in the lam.
THERE IS NO PENTANE LEFT IN EPS BLOCK OR MOLDED FOAM!
I hope I haven’t bored you with all the technical stuff, but I get really tired of bad info being passed around. In my opinion, good EPS is an alternative to pu/pe stuff and should be considered all the time by shapers. I shape stuff out of it, give it a shot!
Sincerely,
Brian
surfteach, you did not bore me at all. I enjoyed your talk. Thanks very much, I was just worried since I have waited for over 2 months to get my blank cut from this stuff, and thought I had done my home work. Then last night when I heard this guy talking about people were/are having problems with the EPS because it was not compressed. I almost died. You have brought hope back into my life. Thanks again. Bagman
Hey Brian, not intending to hijack the thread but I was wondering about off-gassing of block EPS manufactured outside the U.S. I machined some “blanks” from overseas that gave off a sweet odor for about a day. I figured this was pentane. Perhaps regulations allow for more agent thus the residue?
I have other questions so I will PM you…
Hey Bags;
Glad it helped! I hope you have a lot of fun shaping up that blank. Don’t forget to post some pics when you are done. Everyone here always like to see how stuff comes out, good or bad.
George: I pm’ed you earlier for your other questions and I hope it helped. I wouldn’t be a bit surprized if the pentane level was higher out of country. I do know that the TJ EPS comes from the same bead we get here in the custom plants (like who I worked for, Foam Fab. Inc.) We molded by pulling a vacuum after the steam then shot the back of the mold with water for only a few seconds. We had to recoup the vacuum system to remove the pentane which was then burnt up in the boiler. The out of country molders can’t afford this type of system and arn’t required to so they just want to make the product the cheapest way which would be to to use more pentane and less steam/energy.