Designing seat foam additives to reduce emissions

New flame retardant products for the automotive market need to function as efficient and cost-effective combustion modifiers; they must also show limited potential for migration out of foam at elevated temperatures.

The move to flatter windscreens has resulted in temperatures above 100° C being measured in the interior of cars.

High temperatures lead to the evaporation of volatile organic compounds (VOC)s used in the interior components of cars. These VOC’s subsequently condense on windows, where they cause fogging, and on other interior surfaces where they may feel waxy.

Recognising this issue, car makers have instituted strict volatility requirements to limit the types of ingredients that can be used in interior components.

For example, flame retardants with good fogging properties, such as photometric reflectance (>90%) are highly desirable.

As with any flame retardant development project, many performance characteristics need to be taken into account. These additional performance criteria may have little to do with how well a flame retardant works in a given substrate. The work we are presenting here outlines several new ICL products that have attractive HSE profiles and excellent VOC characteristics in automotive flexible foam formulations and work well as flame retardants in these systems.

MVSS 302 evaluations

We produced a number of laboratory foams using developmental products Fyrol PNX, Fyrol A710, Fyrol HF-9 and Fyrol HF-10. These were compared with the well-known TDCP flame retardant typically used in automotive seat foam applications.

Two typical formulation densities 1.5 pcf (24kg/m³) and 1.8 pcf (29kg/m³ were chosen for these evaluations. In the interests of comfort, quality and resilience, automotive foam applications usually use a higher density foam than inexpensive furniture foam products.

Though not typically used in automotive foam applications, the halogen-free Fyrol A710 was included for comparison.

The A710 product was developed by ICL as an alternative to the TDCP ((Tris (1,3-dichloro-2-propyl) phosphate)) flame retardant used in furniture foam to meet earlier versions of the California TB 117 furniture flammability standard. A710 is also used in European automotive polyester foam formulations.

Fyrol PNX is another halogen-free commercial flame retardant included as a reference to Fyrol HF-9 and Fyrol HF-10 which are newer products.

The PNX grade is an extremely efficient flame retardant, however, it has a tendency to discolour foam in low density exothermic formulations. The low VOC version (Fyrol PNX-LE) is recommended for use in automotive foam applications with the most stringent VOC criteria but it does not formulate well in polyester foam formulations.

Fyrol HF-9 and HF-10 are two new halogen-free products developed for the US and European automotive foam market. They were designed to address the demand for a common product that works across polyether and polyester formulations.

New products

The two new products show similar flame retardant efficiency to TDCP, and give producers the ability to use a common FR product in all of their formulations. In addition to FR performance, these two new products are less likely to contribute to foam discolouration.

  

The discolouration potential of the new products was evaluated on small scale using our standard Oven Scorch Methodology. This methodology has shown good correlation to commercial processes. (See box p36)

The time values shown in the graph represent the severity of the foaming conditions typically used in commercial applications. The 60 and 90 minute values represent most foaming operations, while the 120 and 150 minute values represent very severe exothermic conditions. The vertical axis shows the change in colour over time. A Delta E change below 30 is generally acceptable with little discolouration observed.

Fyrol HF-9 and HF-10 were developed to provide a good balance of FR efficiency, product stability and VOC performance. The scorch graph (Fig 4) shows that the new products have a lower tendency to scorch than the current commercial PNX and TDCP while giving good FR performance.

We measured VOC performance in comparison with di-ethyl hexyl phthalate (DOP) as a reference. This was used as a liquid and was included in all test runs to ensure limited variability and that measured values were within acceptable limits.

We used a reference foam without any flame retardant additives as a comparison.

Six commercial flame retardants products were evaluated a minimum of five times in a 1.8 pcf density foam formulation, following the automobile gravimetric test criteria (110°C/3hrs/21°C). The results show the relative fogging performance of the developmental and commercial halogen-free flame retardant additives in relation to that of the industry standard TDCP. All the testing was completed on foam samples.

 

As shown above, Fyrol PNX-LE contributes very little to the fogging potential of the blank foam sample and consequently makes a good FR product for applications where good fogging performance is needed. The normal version of Fyrol PNX performs similarly, if no worse than TDCP under the same conditions. The new products Fyrol HF-9 and HF-10 perform better than TDCP, with the HF-10 product showing considerably better results and TDCP.

Alongside fogging test evaluations, these new products were also evaluated in a typical 2.0pcf polyester foam formulation (polyether in the case of Fyrol PNX and PNX-LE) in the VDA 277 VOC test to determine how the total carbon emissions produced from the foam samples relate to the FR products. The results of these evaluations are shown in Table 1.

The emission numbers relating to the FR components shown in Table 1 are well below the limits required by Audi and VW for all of the samples analysed. It must be noted though that the maximum limits set by the car makers include all the emissions from all of the component materials in the foam.

Table 1 Fogging Test Conditions
Bath (C)	Duration (hrs)	Plate (C)	Region	Method
100	16	21	Europe	Gravimetric
110	3	21	Europe	Gravimetric
110	6	38	US	Photometric
100	3	21	US	Photometric
95	6	38	US	Photometric
90	6	21	US	Photometric
85	4	38	US	Photometric
Source: ICL

The limits of 50 and 20µg°C/g set by VW and Audi are total limits for all the foam emissions. To better understand how each FR product compares with each other, we only report and compare emission components associated with the FR products we evaluated. As confirmed earlier by gravimetric methods and further shown in the VDA 277 data, the new Fyrol HF-9 and HF-10 products provide equal or better emissions performance characteristics than the well-known industry standard flame retardant TDCP. We believe that these attributes and good FR performance make these desirable products for demanding flexible foam applications in the automotive sector for the US and European markets. Aside from using Fyrol HF-9 and HF-10 in automotive applications, the products have been shown to perform well in a range of applications. Data for the new products in the UK foam flammability standard BS 5852 are included below. Figure 7 shows the addition level of each flame retardant, co-FR (melamine) and corresponding weight loss associated with each test sample. Although Fyrol PNX is a very efficient flame retardant in automotive standards-- like the MVSS302 -- it does not work well in combination with melamine used to pass the tough UK flammability standard. The flame retardant performance of different flame retardant products varies from application to application and needs to be assessed on a case by case basis. Generally though, halogenated flame retardants have more consistent performance across product groups and non-halogenated flame retardants are more specific in performance. As the data Fig 7 shows, Fyrol HF-9 and HF-10 perform equally well to the industry standard combination of tris(chloropropyl) phosphate (TCPP) and melamine. Having evaluated a large number of commercial and developmental halogen-free products in the test, this result is surprising and interesting.

Table 2: Hand-mix PU formulations (1.5 and1.8 pcf density)
Ingredient	Brand	Maker	Foam A	Foam B
Polyether polyol	Voronol 3136	Dow	100	100
Flame retardant			Variable	Variable
Water			3.85	3.35
Catalyst	Dabco BLV	Air Products	0.25	0.25
Silicone surfactant	Niax	Momentive	1	0.8
Stannous Octoate,	Dabco T-10	Air Products	0.35	0.35
TDI index			110	110
Density (pcf/kg/m3)			1.5/24	1.8/24
Source: ICL

Very few non-halogenated products can compete on a weight to weight basis with TCPP in this application. Although it is not common to use TDCP to meet the BS 5852 standard, it was included for comparison purposes to help further illustrate how the new Fyrol HF-9 and HF-10 compare in a wider range of foam applications. Conclusion Fyrol HF-9 was commercially launched in 2013 and is finding use in automotive and furniture foams. Fyrol HF-10 is in commercial trials and is expected to be commercially launched later in 2014. ICL-IP is optimistic that the new materials’ good health and safety profile, good flame retardancy and good emission profile will make them viable alternatives to TDCP in many flexible foam applications. Jeffrey Stowel, Manny Pinxoni, Andrew Piotrowski, Joop Wuestenek, Jens Leopold authored this paper which was presented at UTECH North America, Charlotte, North Carolina 4-5 June 2014.