Materials makers are coming up with a variety of ways to make structural composites, from recycled plastic bottles that become weight-bearing elements of heavy load bridges to substituting coconut fibers for traditional ceramic fibers in biocomposite tiles for walls and floors. Now a thermoplastic-mineral composite replicates wood's fibrous structure and is contending with wood, wood plastic composites, plastics, and metal in a range of structural applications.
The material is a fully fiberized, molecularly oriented, lineal composite system from Eovations, which is licensing the technology, said Claude Brown, vice president of technology & innovation for Eovations, in an interview. At present, structural applications include marine uses for docks, pier, seawalls, and pontoons, as well as the cargo decks of vehicles and truck liners. One of the company's primary near-term focuses is the building industry, where it can be used as a Trex replacement for structural framing, as well as for non-structural uses.
Eovations's mineral/thermoplastic composite has a modulus of elasticity between 500,000 psi and 800,000 psi, but a modulus of rupture of zero. It can flex extremely well, but does not have a catastrophic failure mode. (Source: Eovations)
But it's a bit different from other wood and polymer composites like Trex. The company uses a proprietary extrusion/drawing process to combine mineral particles with a thermoplastic matrix. It's a composite because it combines two distinct materials and phases, Brown told us. Half of the composite consists of polymer, mostly polypropylene, and the other 50 percent is a mineral filler. The process first creates a small-scale fiber matrix, and then orients polymer chains within the individual fibers into a composite structure.
Eovations uses several mineral fillers. These are present primarily as a physical nucleation site, not a chemical nucleation site, since their chemistry is less important than the right size and aspect ratio, Brown said. The material also replicates the structure of wood with an internal closed cell structure that reduces the weight of the material without sacrificing its strength. Open spaces are included as capillary-like structures between the strands, so that about 56 percent of the composite's volume is air.
The new composite has a much higher modulus of elasticity at 500,000 psi to 800,000 psi than Trex, for example, which is typically 300,000 psi, and it costs about the same as similar synthetic decking products for construction uses. It does not have a catastrophic failure mode: the modulus of rupture is zero. That means it can be valuable as a hurricane-proof material, said Brown.
"A piece of it 5/16 inches thick can pass all the hurricane standards by itself, not including any other structure. A 55 mph wind leaves only a small impression, about 3/8 inches, but it bounces off of the structure," he told us. The composite's moisture absorption is less than 0.2 percent and densities are between 0.5g/cc and 1.0 g/cc (you can access the technical data sheet here).
The material's wide processing window means that properties of the finished composite, such as density, can be customized. It can be worked like wood with common woodworking tools, including cutting, sawing, machining, and drilling. Conventional fasteners such as nails, screws, and staples can be used, and their acceptance and hold is even better than wood's.
The technology was originally developed at Dow Chemical, but never commercialized, according to Brown. Eovations's parent company, Universal Forest Products, bought the technology from Dow in 2010.
Ann, this is an interesting material. It is impressive that it can be used like wood, using the same tools and fasteners. That should make acceptance easier. The hurricane resistance should be of much interest in areas where that is a problem. I know someone with a place in Florida, and although the structure is concrete and quite resistant, they had to replace windows with bullet proof ones. Other structures, those with conventional roofs, are a real problem. This material would help.
The modulus of elasticity is about one-third that of Douglas fir, so I don't imagine it could be a one-to-one replacement for wood in critical structural components, such as bridge beams. So does anyone know which wood components might be replaced using this material?
A material thyat bends instead of breaking will have uses, but not the same as for some of the more common materials, unless it is also adequately stiff to begin with. One immediate application would be as a decking material for bridges, where the ability to flex with an overload would be very useful. Likewise for stair step tops, which get damage from varied kinds of abuse. In fact it would probably be useful for any application that had only intermittant loading.
I would offer a concern about the porous structure possibly allowing the penetration of a variety of undesireable elements including molds and asorted contamination. But possibly the spaces are small enough that it would not be much of an issue.
The report did not mention anything about flamability, which could also wind up being a show-stopper concern. Perhaps that information is available for addition to the writeup.
Interesting development. Nice to see these sort of efforts moving forward. They may not always be the most cost effective, but it's a step in the right direction. I wonder if this is one of those "we can do it in the lab, so let's see if we can sell it" sort of things or if they actually had a specific market in mind.
Lou, I thought the hurricane-resistance use was one of the most intriguing and unique about this material, aside from the more mundane uses like deck replacement. Chuck, this is not aimed at high load-bearing structural components such as bridge beams: as we state, it's for lighter construction uses such as decks and pontoons.
Okay, I'm pretty sure that "the modulus of rupture is zero" is not a correct statement. "Modulus of rupture" is a measure of the load-carrying capacity of a beam. A material with a load-carrying capacity of zero would not be very useful.
The modulus of rupture formula is only correct up to the elastic limit, so presumably the meaning of the statement is that it yields before it breaks. That's also how I'd interpret the rather amazing statement that "it does not have a catastrophic failure mode." If it doesn't fracture under any circumstances, it's be a miracle material, and they should be contacting physics journals rather than Design News. But I think they are just saying that it yields before it breaks.
That being said, this sounds like a pretty neat material. Mineral-filled polypropylene is a fairly common (and reliable) engineering material. However, making it into an open-cell foam, and drawing it so that the polymer chains are oriented, is an interesting innovation.
Which is worse for the environment, manufacturing these composite materials or logging the equivelent amount of wood?
I like the idea of composite bridges and buildings though. Perhaps people would not have lost that much with Hurricanes Katrina or Sandy. I'm sure the current cost differences will keep the materials out of construction for years to come.
"Which is worse for the environment, manufacturing these composite materials or logging the equivelent amount of wood?"
Logging industry is careful to point out the renewable resource that is lumber, and that they plant a large number of trees every year to replace what was cut. I don't think it's as easy to make that statement with regard to polypropylene.
Dave, the absence of a catastrophic failure mode (the modulus of rupture is zero) typically doesn't mean the material doesn't fail: it means it doesn't fail catastrophically, or, it bends before it breaks as you said. TJ, I agree about your comparison with plastic--anyone planted any plastic trees lately?
Ann, I wasn't talking about plastic trees; I was thinking about the renewable feedstocks we'd discussed several months ago. You mentioned that such feedstocks are no longer food-based such as corn, but still organic based.
The original question was worse for the environment - structural members made from wood or the composites described in the article.
The lumber industry sells itself as renewable because the companies plant trees to replace the ones harvested, and the renewal process is pretty straight forward - Cut down a forest, make lumber, plant seedlings in the now-cleared area, come back in 20 years or so and repeat.
IF the composites are made from organic feedstocks, they may be the equal of wood's impact on the environment. If they're made from petrochemicals, one would probably have to say they have a larger impact.
TJ, thanks for the clarification. Determining that would probably take a detailed lifecycle analysis. Although these are now voluntary, and not nearly as common as many of us would like, I hope that someday they'll be required as an item on the data sheet.
@Ann: The fact that something bends before it breaks doesn't mean that it doesn't have a catastrophic failure mode -- it just means that it bends first. If you continue to load it, it will fail catastrophically, sooner or later. (Steel bends before it breaks, too, but you can point to any number of catastrophic failures of steel structures).
And "the modulus of rupture is zero" is just plain wrong. As I said, modulus of rupture is a measure of the load-carrying capacity of a beam. If the load-carrying capacity were zero, it would be useless.
Modulus of rupture just isn't a useful number for something that yields before it breaks, since the equation assumes no yielding.
@Ann: Okay, apparently you learned some highly non-standard definitions. According to Instron's glossary of materials testing, modulus of rupture is synonymous with flexural strength. If you Google "modulus of rupture," you'll see that this is the most commonly used definition. Clearly, "the flexural strength is zero" would not be a correct statement.
The derivation of the most widely-used modulus of rupture formula assumes that the material deforms in a linear and elastic way, so the formula no longer applies after the yield point. However, this doesn't mean that "the modulus of rupture is zero"; it just means that the formula no longer correctly predicts the stress.
As far as "catastrophic failure" goes, the most common definition seems to be "(sudden) failure from which recovery is impossible."
Give me any material, and I guarantee I can find a way to make it fail such that you'll never get it back into its original shape. Hit it hard enough, and it will fail catastrophically.
The article stated the pores are closed cells but create open space between the fibers. I interpret this as closed cell foam which could perhaps be used in floating applications. Trex is pretty heavy and floppy (and expensive) but weathers better than wood. At the same price as Trex, this would seem to offer some attractive advantages. I wonder the size of the pores as cut edges would expose them. Perhaps they could be "ironed" to smooth them or even textured with heat. You may also be able to form them into hollow structural members to gain stiffness without weight (steel i-beams do this, a web with flanges on the top / bottom, or rectangular tubing (some plastic decking is formed like this). Enough mineral filler or water releasing filler (i.e. alumina tri-hydrate) might help improve fire resistance.
1. Universal Forest Products is behind this. They sell lumber and engineered lumber products. Are they researching less expensive alternatives? Better performing doesn't matter if there is not a cost savings.
2. Price same as building composites already on the market.
In my industry we saw a breif excited period of composites being used in commercial buildings (residential is a different market). This period has past with more use of conventional wood products and fiber cement sidings and trim. The choice always comes down to cost. Even in fire rated construction heavy timber remains an option where milk jug lumber may not be used. The timber industry is sustainable and the total energy used to mill and transport timber is less than the energy required to create synthetic lumber. So will this product become something more than a competitor for Trex when we don't even use Trex now?
When the "true cost" is calculated, are the prices still the same? We seemed to have an unlimited supply of everything 100 years ago. We know that's no longer true.
It seems brilliant for a lumber company to back this development.
Here in California, bending and swaying is preferred over breaking and crumbling. Mold can very likely be abated with additives.
Many abandoned developments from the early 20th century are being revived and commercialized today. It's exciting. Industrial Revolution 2.0. Hopefully we'll do a better job this time.
I've also noticed that some earlier ideas and technologies are being revived,and given another chance. Some may have been inventions that were in advance of their time.
I think it's certainly commendable a company is looking at prospects of recycling what would otherwise be waste materials into a usable product. I do agree that if the material is to be used for building purposes, flammability, tensile and compression strength, rupture strength and mold retention could be problems. Fortunately, these are characteristics that can be tested for and quantified. One question I have, do we know if there are UL standards that govern the usage of products such as these?
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