PFA annual meeting 2016: Technical Papers

Technical presentations featured at this year’s spring meeting of the Polyurethane Foam Association looked at how the the US foam industry reduce its environmental burden. Sarah Houlton reports.

They covered a wide range of subjects, including how to manage waste foam to minimise environmental impact; the need for changes to anti-microbial testing; improving the environmental profile of foams and retaining or improving flame retardancy; and finally, the opportunities which natural polyols can offer in polyurethane formulations.

Utilising waste foam

Sara Petty, a senior research scientist at the Green Science Policy Institute, reported on the April meeting of a stakeholder group in Berkeley, California, looking at how waste foam can be managed responsibly.

She explained that the 2013 update to California’s Technical Bulletin 117 made it possible for furniture made with flame retardant-free foam to comply with this smoulder standard, and it is now increasingly available. But what about the FR-filled furniture it replaces?

TB117-2013 has been much more successful in reducing flame retardant use than a ban, Petty said. “Banning chemicals doesn’t work as we just move on to another chemical, which we don’t necessarily understand,” she said. The new standard recognises that fires start in the fabric cover, not the foam, and therefore TB117-2013 focuses on smoulder-resistant upholstery fabrics, allowing flame retardants to be omitted from foams in many cases.

“We didn’t enter the workshop expecting solutions,” Petty said. “The aim was to get stakeholders together to decide where best to focus our energies.” Topics covered in the Berkeley meeting included US municipal waste management and environmental considerations, flexible PU foam and related industries, technologies for FR destruction, and the needs of technology and policy research.

In the US, waste management for old furniture is heavily reliant on landfill. Petty said that FRs such as PBDEs escape from foam into the environment, as they can leach out or form gases. The leachate often reaches water treatment facilities, where it cannot be effectively managed. Where PU foam is recycled, the FRs remain in the foam, and the aim is to mix it with post-industrial trim and other foam known to be FR free. The goal is to dilute the FR content, ideally to 0.1% or lower. This is then used to make bonded carpet cushion, she said.

“We need an end-of-life plan in place, and we should strongly consider

not placing the burden on waste facilities.”

Sara Petty, senior research scientist at the Green Science Policy Institute on end-of-life foam

Destroying FR-containing foam is problematic. Municipal waste incinerators need to be heated above 850°C to fully combust brominated FRs. This temperature is not an issue for cement kilns, but there is a history of feedstocks being incorrectly fed in, leading to lower temperatures. Plasma arc vessels are another alternative, but these cannot handle the scale required in the US, Petty added. A further approach involves supercritical water oxidation, but the pre-processing is much more involved.

Finally, there is a big problem in identifying FR-containing foams, and separating out those that are FR-free.

Petty suggested that solutions will include academic research projects, where the National Science Foundation is providing some funding. Industry will play its part, too. But there is much work still to be done. “No waste treatment options exist that will destroy or remove FRs from flexible PU foam,” she said. “We need an end-of-life plan in place, and we should strongly consider not placing the burden on waste facilities.”

PU foam pink stain problem-solving

At the other end of the foam’s life, Lonza’s global technical marketing lead for material protection, plastics and flooring Tom Robitaille, gave an update on modifications to the pink stain test method.

The ASTM E-1428 test is designed to measure how resistant a polyurethane foam formulation is to a number of key microbes which cause staining.

Robitaille said that the list of effective antimicrobials for the preservation of PU is shrinking. Tributyltin maleate and 10,10'-oxybisphenoxarsine have been used to inhibit the growth of microorganisms for many years, and both do well in microbial challenge tests, producing large zones of inhibition where bacteria cannot survive. However, newer antimicrobials do not produce this large zone, with the bacterium that produces pink stain a particular problem. They therefore have to be added at much higher levels before the zone appears, Robitaille said. The test is difficult to pass and is inconsistent, he added.

ASTM E-1428 is the standard test method for determining susceptibility to pink staining by Streptoverticillium reticulum. The pink stain is normally a result of the colour of the metabolites excreted by the bacteria; other colours are possible, Robitaille said. The main problem with the test is that the pass–fail determination is based solely on the presence of a pink stain on a sample. It does not measure the ability of the antimicrobial to protect the sample.

The standard test protocol involves the sample being placed on an agar plate that contains all the nutrients required for microbial growth, Robitaille explained. He added that if the antimicrobial leaches onto the agar it will create a large zone of inhibition around the sample. Newer antimicrobials do not leach in this way. Yet samples with new and older antimicrobials can be completely free from the organism of concern, and test results can be very inconsistent. False positives are common if pigment transference occurs during inoculation, he added.

The proposed modification to the test involves the sample being placed in a petri dish and the nutrient broth pipetted onto its surface. In the example given by Robitaille, using the old technique all the samples failed, but with the new method treated samples remained pink stain-free. Work is ongoing, and nine companies have been involved with its round-robin testing process.

FR-free foam innovation

Kurt Reimann, a technical consultant at Kurt Reimann & Associates, presented a project from Florida Institute of Technology (FIT) on the development of flexible PU foam that meets flammability demands while having an improved environmental profile. Although it is now possible for FR-free foam to be compliant with fire regulations in some applications, this is not the case for those with more stringent requirements such as transportation, packaging and mattresses, and FRs will still have to be used.

The FIT group has been looking at foam formulating techniques that can make materials that meet these requirements. “The goal is a technology that is adaptable to all PU foam technologies,” Reimann said.

“The goal is a technology that is adaptable to all PU foam technologies,”

Kurt Reimann, a technical consultant at Kurt Reimann & Associates, on FR-free foam

Initial studies to establish the basic principles used MDI, as requested by NASA, although a background study has also been done with TDI. Common base formulations were used to maintain a complete understanding of the foam’s flammability characteristics.

More than 1000 compounds have been made and tested on a 100g scale, for reactivity, density, cell structure and oxygen index. In all, 300 of these were scaled up to 1.5kg laboratory blocks to allow the testing of flammability properties, dynamic impact testing and cone calorimeter studies. Finally, 20 were made in 45kg large blocks and subjected to full-scale flammability tests, for example as mattresses and chairs, to see if they met the various different standards.

Overall, he said, it has been possible to make MDI-based foams that are highly flame retardant, with low levels of VOCs, and which are both non-migrating and non-halogen-containing. Foams that could pass a wide range of tests without barriers were possible, with advantages for both human health and the environment. “It is a versatile drop-in technology,” Reimann said.

Renewable polyols

Michael Brooks, a process chemist in Emery Oleochemicals’ research and technology development department, gave an insight into the performance of a number of renewable polyols in flexible PU foam. Castor oil and modified natural oil polyols based upon soybean oil can all be used to make foam, as can Emery’s Emerox polyols, which are made via ozonolysis to give dibasic acids, and esterification chemistry.

Castor oil has a fixed triglyceride structure, and the hydroxyl functionality needed for polymerisation occurs naturally, but the unsaturated nature of the chains can lead to degradation. Other natural oil polyols require chemical modification of the double bonds on the backbone to acquire these hydroxyl groups. This is usually done via epoxidation followed by reaction with a nucleophile.

However, Brooks said, these natural oil polyols are typically limited to the structure of the natural oil, because of the limited number of reaction sites for the insertion of hydroxyl groups. The chemical modifications are often inefficient, leading to residual unsaturation rendering them unstable to UV.

Emery’s Emerox renewable polyols use ozonolysis to convert natural oils into polyols. Although they are bio-based, Brooks said, they are structurally similar to those from petrochemical sources, and the range of sizes and chemical structures that can be made is much broader. The renewable content is typically in the 70–100% range, he added.

The goal was to produce a high-renewable content TDI foam that performs and feels like a conventional polyether foam. They looked at foams made with Emerox 14050, castor oil and soy polyols A and B, targeting a 1.8pcf (29kg/m3) foam by increasing bio-based polyol substitution levels. The foam formulation was adjusted to give a good cure profile and processing results, and the performance compared with polyether polyol.

“It gave the best overall balance of foam physical properties, and the foam feel was the same or better than conventional polyether foam.”

Michael Brooks, Emery Oleochemicals

The Emerox polyol was much closer in performance to the petrochemical-based product. “Minimal formulation adjustments were needed,” Brooks said. “It gave the best overall balance of foam physical properties, and the foam feel was the same or better than conventional polyether foam.”