High Noon for Small High-Barrier Gas Tanks

By Jan H. Schut

New nano barrier materials are finally stepping up to meet the challenge of permeation standards for the gas tanks for golf carts, snow mobiles, boats, lawn mowers and other recreational equipment. The standards from CARB, California’s Air Resources Board, and the U.S. Environmental Protection Agency shouldn’t have taken the recreational vehicle industry by surprise. The first regulation passed in California nearly 10 years ago, but starting January 1, the California limits get a lot tougher.

From 2007 through 2011, CARB phased in permeation limits of 2.5 g/m2/day for different off-road engine sizes. In 2012-2013 CARB’s permeation limits will drop to only 1.5 g/m2/day at 40 degrees C—considerably tougher than EPA limits. On January 1, CARB’s new permeation level will apply to tanks for equipment with >80 to <225 cc engines and in 2013 to tanks for engines over 225 cc.

‘INNOVATIVE’ GAS TANKS APPROVED BY CARB

If CARB in California issues an Executive Order approving a barrier gas tank design, any tank made the same way complies in California. The EPA also certifies tanks by design, but EPA certified tanks still need permeation testing in California. 

Manufacturer              Executive Order            Tank Description

Arkema Inc.                C-U-05-005                    PetroSeal rotomolded fuel tank

Centro Inc.                  C-U-06-027                    “P” family fuel tanks w/ barrier layer

Centro Inc.                  C-U-06-028A                 “Q” family fuel tanks w/ barrier layer

Centro Inc.                  C-U-06-029                    “R” family fuel tanks w/ barrier layer

GE Plastics                 C-U-07-007                      Xenoy 6620U-1001GT or Xenoy 6620-

(SABIC Innovative     (C-U-07-007a)               BK1066GT injection molded fuel Tank Plastics)

Cyclics Corp.              Q-08-001                          CBT injection molded fuel tank

SABIC Innovative      Q-08-006                         Xenoy X6800BM-1001, Plastics                                                                    BK1066, Xenoy X6800BM-RD6D122     

Arkema Inc.                Q-08-012                         “One Shot” Petroseal for California Phase II

Solvay Advanced        Q-08-025                         Ixef BXT-2000 Polyarylamide (PARA) for Polymers LLC                                                        CE 10 test fuel

Centro Inc.                  Q-08-027                          Roto LO Perm material for CE 10 test fuel

Centro Inc.                  Q-08-027a                        Roto LO Perm with XLPE material for CE

Custom Resins            Q-08-028                         Nylene 494 BLK for Calif. Phase II fuel

LG Chem America     Q-08-041                          Hyperier-IP-1105 for Calif. Phase II fuel

LG Chem America     Q-11-017                           Hyperier-IP-1106 for natural & colored

LG Chem America     Q-11-020                         Hyperier-IP-1106 for black blow molded

Source: CARB

The EPA started regulating gas tanks for RVs in 2008, added hand-held “spark-ignited” engines in 2009 for models already certified in California and 2010 for all other models. The EPA added tanks for engines over 225 cc like ride mowers and portable marine tanks in 2011 and will add tanks for engines under 225 cc and installed marine tanks in 2012. But the EPA standards are only <1.5 g/m2/day at 28 degrees C or <2.5 g/m2/day at 40 degrees C. (Permeation rate generally doubles for every 10 degree rise in temperature.)

California approves gas tank barrier construction by “executive order.” Between 2006 and 2009 California approved an average of 10 barrier fuel tank constructions a year; none in 2010; and six in 2011. Confusingly, some tanks were tested with regular gasoline (Phase II California Reformulated Certification fuel) and some with 10% ethanol (E10 fuel). The EPA certifies tanks by design, but EPA certified tanks still need permeation testing in California.

The timing for a sweeping, somewhat confusing and inconsistent revision of small gas tank production was unfortunate, coming with a recession. “OEMs initially tried to fight the regulations, and then were behind the 8 ball on compliance,” notes one material supplier to the small tank market. Some gas tanks already complied. Small lawn mower tanks injection molded out of nylon in two halves and welded together met the permeation limits. But many larger gas tanks of diverse shapes were blow molded or rotationally molded out of HDPE, with no barrier.

Five years ago the choices for blow molded tanks to meet the new barrier standards were limited to six-layer coextrusion with EVOH or off-site barrier treatment with fluorination or sulfonation. Six-layer coex, the gas tank pioneered by the auto industry 20 years ago, is a wonderful barrier, but wasn’t considered economical for parts with low annual production. Fluorination and sulfonation add cost and transportation and don’t hold up well in durable applications.

Another possible solution was new nano barrier materials. Several were presented at the SPE Annual Blow Molding Conferences and at marine and outdoor equipment conferences, but they were untried. The big market for barrier materials has always been food packaging, which has very different requirements. It doesn’t have to contain VOCs under high pressure through cold temperature drop tests.

Finally at SPE’s Annual Blow Molding Conference last October 12-13 in Chicago (www.blowmoldingdivision.com), the first successes with the new barriers appeared. Industrial blow molder Mergon Corp. of Anderson, S.C. (www.mergon.com), presented “Alternative Solutions for Barrier Materials,” a remarkable  report of processing experience with five new barrier materials.  Mergon, which specializes in short production runs across a broad size range of 1- 60 liter blow molded parts, conducted up to three years of Design of Experiments tests on the new materials, solved processing problems, developed new quality control procedures, and qualified some for production. Mergon’s report is also the first public mention of some of the new materials themselves.

NANO, NANO

In 2007 Mergon began testing Hyperier (hyper barrier), a nano barrier made by LG Chem Ltd. in Korea with U.S. offices in Englewood Cliffs, N.J. (www.lgchem.com). Introduced at NPE 2006, Hyperier is a composite of nylon with exfoliated Montmorillonite clay platelets with an aspect ratio of 200-300, compatiblized with HDPE for blow molding. It’s blended into monolayer HDPE tanks at loadings of 16% to 24% to meet both the EPA and new CARB permeation limits. Mergon worked with Hyperier for four years, solving numerous problems, and can run Hyperier on both continuous extrusion and accumulator head blow molding machines with different set points, but without modification of machine or extrusion screws.

Blow molder Mergon blends Hyperier, a new nano barrier material, into monolayer HDPE gas tanks for high barrier. On startup the first six parts are scrapped. Before the barrier mixture reaches the right temperature, nylon-based pellets are visible in the HDPE.

Melt temperatures and pressures have to be very tightly controlled and alarmed, Mergon found.  “You have to overheat the HDPE and under heat the Hyperier,” says Steve Thompson, engineering specialist at Mergon. “Hyperier has to be heated to where the nylon starts to break down, or it doesn’t mix properly. If it’s heated too much, the barrier breaks down. Plus or minus 5 degrees C makes the difference between very good, good, or poor barrier. If you hit an alarm, you have a breakdown in barrier.”  Mergon scraps the first six parts on startup while temperature and pressure come under control. Mergon tests barrier in production every two hours by cutting a tank open, measuring wall thickness, and physically measuring and counting the nano stripes. California Executive Order Q-11-017, approving fuel tanks made with Hyperier IP1106, requires a minimum barrier thickness of 1.8 mm with a nominal wall thickness of 2.8 mm.

Molds for Hyperier also have to be modified to make a good weld. “They need a dam and bead placed in the flash pockets parallel to the pinch-off to force the melted material into the mold cavity as the mold is being closed,” Mergon’s Thompson notes. Otherwise there can be gaps in the weld seam. Mergon reports trials with eight different formulations, including black material and black material with regrind, which all met permeation levels of <1.5 g/sq m per day. Mergon has used Hyperier commercially in up to six-gallon tanks with up to 30% regrind. LG makes Hyperier in three grades for small (1-10 liter), medium (5-20 liter) and large (20-220 liter) containers. Grades for larger parts have lower specific gravity and higher impact strength, but the distinction doesn’t seem critical because LG’s website shows a 5-gallon portable fuel can and a 2-liter gas tank both made with Hyperier IP1105.

In November 2009, Mergon started trials with Enbarr 2020BN, made by Nano Polymer Composites in Taiwan (www.nanopolymer.com), and distributed in the U.S. by Enbarr LLC in Merritt Island, Fla. (www.enbarr.com). Enbarr 2020 is a nanocomposite made of nylon 6.6 and volcanic ash, or pumice, developed originally for the heat shield on the space shuttle. Enbarr isn’t a blending material, but is used at 100% and can get extremely low permeation levels of <0.1g/m2/day with a 5 mm thick wall. Enbarr has a more forgiving temperature profile than Hyperier, but is hard to deflash. Mergon needed a larger blow molding machine to have enough clamp force to get flash off. Nano Polymer is making a new formulation for better deflashing, which Mergon hopes to test early next year. Historically Enbarr 2020 cost $4-$5/lb, which is too expensive for most gas tanks. Being nylon it also has a problem with cold temperature drop tests.

Mergon, which has up to three-layer coex capability, also tested new barrier materials for coextrusion.  In 2007 Mergon began testing Ixef BXT, then a developmental blow molding grade of polyarylamide (PARA) from Solvay Advanced Polymers LLC in Alpharetta, Ga. (www.solvay.com). Solvay received CARB approval for Ixef in gas tanks in 2008, presented it at blow molding conferences in 2009 and 2010, and commercialized it this year. It can be used as a barrier layer with HDPE either with tie layers or by blending adhesive into the HDPE. Solvay has tested it in a three-layer sandwich and in two layers with Ixef as the inner layer. Mergon plans three-layer trials with it next year.

Six months ago Mergon began testing TIEVOH, a custom compound made by Enbarr,  combining EVOH and tie layer adhesive. TIEVOH bonds directly to HDPE without a tie layer, so a three-layer coex machine can make EVOH barrier tanks. Enbarr recommends 3-5% TIEVOH because tanks with over 2% EVOH overall can be certified by design by the EPA. They would still, however, require soak, durability and permeation testing in California. Mergon is developing three-layer TIEVOH marine gas tanks for a sister company of Enbarr, BluSkies International LLC in St. Charles, Ill. (www.bluskies.us). TIEVOH is already commercial in a rotomolding formulation for large three-layer installed marine gas tanks.

In 2012 Mergon has scheduled trials with Hostaform LP CKX5622, a grade of POM (polyoxymethylene) from Ticona Engineering Polymers, Florence, Ky. (www.ticona.com) also for coextrusion. Hostaform POM is an acetal copolymer (originally Celcon from Celanese), which needs to be dried. Mergon has also scheduled tests with Nylene 764B, a barrier material from Gulf View Plastics Inc., Hudson, Fla. (www.gulfviewplastics.com), which is approved in California. “We may never go into production with a lot of these materials,” Mergon’s Thompson says, “but we will have proven out the materials, and we’ll know how to use them.”

Mold designs for monolayer barrier gas tanks made with Hyperier/HDPE blends have to be modified at the pinch off to force more melt into the mold cavity. Otherwise there can be gaps in the weld line.

NEW FLEXIBILITY FOR SIX LAYER BARRIER

Six-layer EVOH barrier is also expanding for high-barrier blow molded gas tanks. Agri-Industrial Plastics Co., Fairfield, Ia., an exhibitor at the blow molding conference (www.agriindustrialplastics.com), announced a major investment in new six-layer barrier capacity. Agri currently operates three six-layer blow molding machines from Kautex Maschinenbau GmbH in Germany (www.kautex-group.com), making barrier gas tanks for a variety of non-automotive applications in the 3-50 gallon size range. It’s buying two new six-layer continuous coextrusion blow molding machines—a KBS241 with 900 kg/hr throughput and a KBS61 Smart with 750 kg/hr throughput, both for delivery next summer. The new machines will have six-axis robots and quick head and mold change capability “for more flexibility in shorter runs of gas tanks for all-terrain vehicles, snow mobiles, personal watercraft, golf carts, and lawn equipment,” says Agri sales manager Mick Stielow.

Blow molder Agri-Industrial is expanding its six-layer coex blow molding capacity from three machines to five to make high-barrier gas tanks for off-road engines. Kautex is building the new machines with six-axis robots and fast tool change for flexibility for shorter production runs.

Compliance whether with new CARB or old EPA levels is essential.  The EPA can, afterall, take any lawnmower or power boat out of a dealer’s showroom, and if the gas tanks aren’t certified, or the information on the certification turns out to be false, the penalties can be stiff—up to a maximum of $37,500 per gas tank model!

Addendum- March 7, 2012:

When this blog was posted, Fluoro-Seal, a large provider of off-site fluorination barrier treatment, took strong exception to having fluorinated tanks described as not passing the latest permeation levels for California (1.5 g/m2 at 40 degrees C). This was indeed incorrect and misleading. In 2002 CARB ran a durability test on fluorinated and sulfonated tanks to simulate wear over the life of a tank and published the results as “Durability Testing of Barrier Treated High-Density Polyethylene Small Off-Road Engine Fuel Tanks,” June 21, 2002. The fluorinated tanks performed poorly, with barrier degrading 10% vs 5% for sulfonated tanks because of a chemical interaction between the fluorinated surface and a HALS UV inhibitor used in the HDPE.

After determining that the (2002) results were biased because of the HALS UV inhibitor, CARB ran another durability test on another set of small gas tanks a year later, this time using tanks with 2% carbon black UV inhibitor. CARB measured permeability before and after 1.2 million sloshes, using a diurnal temperature profile for 24 hour SHED (Sealed Housing for Evaporative Emission) testing, which averages 29 degrees C. The results, published March 7, 2003, showed fluorinated tanks with astonishingly low permeation levels of 0.01 g/m2 before 1.2 million sloshes and 0.08 g/m2 after sloshing. The same tanks were then tested for permeation at a constant higher temperature of 40 degrees C (except when the SHED malfunctioned and hit 53 C), averaging 0.33 g/m2 of permeation, as published in an addendum March 27, 2003.

The two stress tests in 2002 and 2003, however, were done differently, so direct comparisons are difficult. The tanks were different sizes—one quart in 2002, two quarts in 2003. Tanks in 2002 were presoaked for one month, in 2003 for three months. The larger tank size and longer soak used in 2003 should have made permeation levels worse for all samples, untreated, sulfonated and fluorinated. Instead, permeation for untreated and sulfonated tanks was worse, as expected, but for fluorinated tanks was dramatically better. Untreated control tanks with 2% carbon black in 2003 averaged higher permeation of 12 g/m2 vs 10.4 g/m2 “determined by previous testing” in 2002. Sulfonated tanks also averaged higher permeation before sloshing of 1.51 g/m2 in 2003 vs 1.11 g/m2 in 2002. Only fluorinated tanks showed dramatically lower permeation in 2003 than in 2002.
The two reports simply show fluorinated 5 level treated tanks had better permeation results after undergoing pressure/vacuum and slosh durability testing when the fuel tank plastics were not manufactured with a HALS UV inhibitor.  The EPA reconciled the two tests and also concluded that it is important to “match the barrier treatment process to the fuel tank material” (www.epa.gov/otaq/regs/toxics/420r07002chp7.pdf). (Appropriate formulation, which is often proprietary, is the responsibility of the processor.)

A year and a half after CARB’s 2003 test, the EPA took the same tanks from California to Michigan and tested them again for permeation.  “During the intervening period, the fuel tanks had remained sealed with California certification fuel in them. We drained the fuel tanks and filled them with fresh California certification fuel. We then measured the permeation rate at 29 degrees C. Because this is roughly the average temperature of the California variable temperature test, similar permeation rates would be expected,” the EPA wrote. “The untreated fuel tanks showed slightly lower permeation (than in 2003) over the constant temperature test. This difference was likely due to the difference in the temperature used for the testing.” Fluorinated fuel tanks, however, showed sharply higher average permeation of 0.47 g/m2– nine times higher than when CARB tested the same tanks in 2003. The EPA then tested the tanks with a blend of gasoline and 10% ethanol and found even higher permeation of 0.56 g/m2 at 29 degrees.

For more information, please see the following reports:

“Durability Testing of Barrier Treated High-Density Polyethylene Small Off-Road Engine Fuel Tanks”, CARB, June 2002: www.arb.ca.gov/msprog/…/durability-test-HDPE-SORE-tanks.pdf

“Addendum to Durability Testing of Barrier Treated High-Density Polyethylene Small Off-Road Engine Fuel Tanks”, CARB, March 2003: www.arb.ca.gov/msprog/offroad/sore/40-degree-soak-rev2.doc

“Control of Hazardous Air Pollutants from Mobile Sources”, EPA Regulatory Impact Analysis, February 2007: www.epa.gov/otag/regs/toxics/420r07002.pdf

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4 Responses to High Noon for Small High-Barrier Gas Tanks

  1. Very intreresting blog. It was very relavant. I was searching exaxtly for this. Thank you for your effort. I hope you will write more such useful posts.

  2. Christopher K. Quick says:

    It is nice to see continued material science and technology, however much of the efforts have been trialed and abandoned in the automotive industry over the years; there are a lot of lessons learned with vigorous validation and testing to prove viable and long term durability requirements. The same trend can now be witnessed with years of field compliance (End of Life requirements) now in the SORE market. This is also critical in ensuring a technology decision that goes beyond 10 to 20 weeks lab testing. The stakes for in field use non-compliance are high even with a lower cost fuel tank that is integrated into a hand held product, the initial purchase price and investment is nothing compared to enforceable actions as highlighted in the article.

    The regulation shift driven technology is similar to what the automotive business has witnessed for over two decades. Since 1992, the initial rollout of strict evaporative emission reductions the automotive industry has had to deal with multiple emission reduction regulations. To-date multilayer fuel tanks have been the key enabling technology to realize successful reduction of hydrocarbon emissions and continued regulation reductions.

    Walbro was a pioneer in both automotive and SORE market tanks with 9 multilayer clamps installed globally to-date to support the SORE market. Walbro is a leader in multilayer with extensive experience over two decades. The larger tanks integrated in the recreation and marine classes are for the most part already converted to multilayer with a significant transition underway in the LG markets.

    There had been many attempts with new materials with every regulation shift in the auto industry; however new integration methods were developed to keep the mainstream plastic growth with multilayer as the technology of choice. Today there are approximately 30 to 35 million multilayer plastic fuel tanks installed in vehicles globally.

    One must also think to the future and prepare for continued ‘tightening” of regulations and changing fuel compositions in the market (increased Ethanol as an example). The multilayer material package is superior in the sense in protects all fuel components (polar and non-polar from defusing through the wall) from permeating into atmosphere, additionally the HDPE which is 85% of the structure provides for superior low temperature impact resistance, durability and cost effective material prices. The technology has been tested for many fuel compositions including up to 85% ethanol with little to no impact.

    I enjoyed being a part of the automotive market for over three decades, It is now nice to be a part of the SORE market and having the opportunity of being involved with implementing low permeation solutions now in two markets. Thanks and hope you enjoy the read. Of course, comments welcome.

  3. Nick Chotta says:

    This information seems very comprehensive and I hope that it is. However, its not clear to me about the timing….In the first paragraph it states that “The first regulation passed in California nearly 10 years ago, but starting January 1, the California limits get a lot tougher.” Does that mean January 1, 2012 or 2013?

  4. Michael Brown says:

    Anyone have any idea of the selling price of Hyperier resin?

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