**4. Properties of the polyurethane flexible foam with different types of fire retardants**

Comparison between halogenated flame retardants which are mainly liquid with halogen free flame retardants ( expandable graphite and melamine powder) which both are solid can be categorized as **four** items.

Processing

108 Polyurethane

**Figure 8.** Chemical reaction between melamine and diisocyanate (MDI)

**Figure 9.** Particle size and distribution of 8% of melamine (SEM ×200)

Figure (9) shows particle size and distribution of melamine powder inside the flexible foam.


#### **4.1. Foaming process**

The best choice for the processing as it is clear will be the liquid grade which has a good dispersion inside the polyol and less side effects.

Expandable Graphite has a limit pot life (3-4 hours) and when it subjects with the polyol component, it attacks to the catalyst of the polyol and destroys the catalyst during the foaming process**. For the foam producing, the highly recommendation is the EG containing polyol should react with proper isocyanate before the EG pot life reaches or the EG should be injected by an individual stream and mix with the polyol stream in the mixing head instead of pre-mixing with polyol.** Otherwise the produced foams will be collapsed. The other disadvantage of this technology is related to the fact that EG is very corrosive and make the mixing head to be damaged and it is preferred to be used a hardened grade of mixing head, a damaged mixing head needle picture is showed in (Fig.10)[9].

The advantages of this technology is the good homogeneity of the EG particles inside the polyol.

**Figure 10.** Mixing head needle corrosion by EG

Despite the EG, melamine has the longer pot life inside the polyol, which is around 24 hours but the fast sedimentation of the melamine powder in the polyol will be the main disadvantages so we need a suitable method to disperse the melamine powder in the polyol very well to achieve a homogeneous mixture.

Polyurethane Flexible Foam Fire Behavior 111

ratio between the heat release and the weight of oxygen consumed is a constant (Huggett constant) equal to 13100 kJ/kg. It has been previously demonstrated that cone calorimeter results are in good correlation with results obtained in full scale fire test on upholstered

Samples of flexible foams (10\*10\*5cm) were exposed in a Stanton Redcroft Cone Calorimeter according to ASTM 1356-90 under a heat flux of 35kW/m2 (case of fully involved real firs). This flux was chosen because it corresponds to the evolved heat during a fire. An electrical spark igniter ignited volatile gases from the heated specimen. At least three specimens have been tested for each formulation. Data were recorded with a computer connected to the cone

calorimeter. The test gives the opportunity to evaluate:



combustion of the tar previously produced. [3]

The combustion of flexible polyurethane foams is a two steps process (Fig.11).

These two degradation steps lead to two distinct peaks of rate of heat released. The RHR1 values (the values of RHR of the first and second RHR peaks).

 The T1 and T2 values (times at which RHR1 and RHR2 occur). The Figra2 values (the two maximum peaks on the Figra curve).

**Figure 11.** Combustion of flexible polyurethane foams: a two-stage process

The first step corresponds to the melting of the foam into a tar and the second to the





furniture [3].

## **4.2. Reactivity**

Foam reactivity is determined by the following parameters:


The flame retardants would affect on the foam reactivity depend on the types of them, whether they are solid or liquid. Because they make changes in cell structure and total system heat capacity. The recession factor goes up with addition of EG and melamine but with different slopes. This is due to the increase in the average cell size of the foam. The bigger the flake size, the larger the cells and higher the recession factor. On the other hand melamine powders with small sizes are embedded on struts and joints and increase the viscosity and reduce the drainage rate which consequently, decreases the number of cells with bigger sizes [10]. Melamine powders with bigger size (bigger than struts and joints) are embedded inside the cell walls and open the cells.

Expansion factor which is related to the free rise density (FRD) reduces with addition of the EG and melamine in the foam. This is due to the increase the heat capacity of the entire system because of high heat capacity of melamine and EG. When melamine and EG content increases in the system, the heat capacity of the system increases and the system temperature reduces, therefore, the foam height and consequently expansion factor reduces [11].

#### **4.3. Fire properties**

The fire properties of the polyurethane flexible foams have been evaluated by different types of methods depends on the customer requirements. For example, the automotive, railway and airplane industries have their own standards.

The most important parameters which have been tested are: Cone calorimetry, flammability, smoke density and toxicity.

#### *4.3.1. Cone calorimetry ISO 5660*

The principle of the calorimetry by oxygen consumption (cone calorimeter) is based on the relation between the oxygen consumption and the heat release during the combustion. The ratio between the heat release and the weight of oxygen consumed is a constant (Huggett constant) equal to 13100 kJ/kg. It has been previously demonstrated that cone calorimeter results are in good correlation with results obtained in full scale fire test on upholstered furniture [3].

Samples of flexible foams (10\*10\*5cm) were exposed in a Stanton Redcroft Cone Calorimeter according to ASTM 1356-90 under a heat flux of 35kW/m2 (case of fully involved real firs). This flux was chosen because it corresponds to the evolved heat during a fire. An electrical spark igniter ignited volatile gases from the heated specimen. At least three specimens have been tested for each formulation. Data were recorded with a computer connected to the cone calorimeter. The test gives the opportunity to evaluate:


110 Polyurethane

**4.2. Reactivity** 

time

weight.

**4.3. Fire properties** 

smoke density and toxicity.

*4.3.1. Cone calorimetry ISO 5660* 

very well to achieve a homogeneous mixture.

Foam reactivity is determined by the following parameters:


embedded inside the cell walls and open the cells.


Despite the EG, melamine has the longer pot life inside the polyol, which is around 24 hours but the fast sedimentation of the melamine powder in the polyol will be the main disadvantages so we need a suitable method to disperse the melamine powder in the polyol




The flame retardants would affect on the foam reactivity depend on the types of them, whether they are solid or liquid. Because they make changes in cell structure and total system heat capacity. The recession factor goes up with addition of EG and melamine but with different slopes. This is due to the increase in the average cell size of the foam. The bigger the flake size, the larger the cells and higher the recession factor. On the other hand melamine powders with small sizes are embedded on struts and joints and increase the viscosity and reduce the drainage rate which consequently, decreases the number of cells with bigger sizes [10]. Melamine powders with bigger size (bigger than struts and joints) are

Expansion factor which is related to the free rise density (FRD) reduces with addition of the EG and melamine in the foam. This is due to the increase the heat capacity of the entire system because of high heat capacity of melamine and EG. When melamine and EG content increases in the system, the heat capacity of the system increases and the system temperature reduces,

The fire properties of the polyurethane flexible foams have been evaluated by different types of methods depends on the customer requirements. For example, the automotive,

The most important parameters which have been tested are: Cone calorimetry, flammability,

The principle of the calorimetry by oxygen consumption (cone calorimeter) is based on the relation between the oxygen consumption and the heat release during the combustion. The

therefore, the foam height and consequently expansion factor reduces [11].

railway and airplane industries have their own standards.


The combustion of flexible polyurethane foams is a two steps process (Fig.11).

The first step corresponds to the melting of the foam into a tar and the second to the combustion of the tar previously produced. [3]

These two degradation steps lead to two distinct peaks of rate of heat released.


**Figure 11.** Combustion of flexible polyurethane foams: a two-stage process

### *4.3.2. Flammability*

Flammability of the polyurethane foam is running with wide range of test methods depends on the applications and customers specification. Some fire tests standards include: FMVSS NO.302, British Standard 5852, ISO 9772 and FAA/JAA 25.853 Appendix F. as an example the airplane seat foam fire tests according to FAA/JAA 25.853 Appendix F have been investigated.

Polyurethane Flexible Foam Fire Behavior 113

Compression Load Deflection (CLD: P25/5) and Sag-Factor according to D411003

When the polyurethane flexible foam is going to be fire resisted, some fire retardants in liquid or solid forms are entered in to the foam structure and make some changes in the physical properties of the final foam part. Mostly the valuable changes have been observed

Depending on the fire retardant nature, shape and size, their addition may have some positive or negative effect on foam physical-mechanical properties. By loading the solid FR with the same amount, the foams become softer, because both additives have a similar size as cell windows and make the foam inhomogeneous. With EG, the homogeneity would be less than the foam loaded by melamine, because of its bigger size and flake shape which

Sag-factor or the comfort index [12] increasing when the percentage of EG and melamine increases. It means that by adding solid FR, the comfort index would change considerably. Compression set, which is another very important factor, has increased by rising the EG percentage, but there was almost no changes in CS by increasing the melamine content. This effect is due to destroying effect of the cells structure by both additives but mainly by the EG.

Tear strensgth of the foams has improved by increasing the EG which could be related to the

Finally, the resilience in 1st cycle is decreased for all additives but it is recovered in 5th cycle, because in 1st cycle the polymer chains have lost their flexibility due to rigid particles but after 5 cyclic movements the particles are embedded in struts and joints and the foam

Principle component analysis (PCA) is a useful method to illustrate relations between

Interpretation of the results consists first in the checking the representation of the variables in the circles of correlation. The correlations between variables are deduced from the relative position and the length of their corresponding vectors on the circle of correlation. An example of interpretation is done in (Fig.12); the angle between two vectors defines the intensity of the correlation (vectors 1 and 5). If α is=90⁰, no relation exists between the variables. The strength of the correlation is higher when the angle is close to 0⁰ or 180⁰. So, orthogonal vectors (vectors 1 and 2) mean no correlation between the variables. Data are strongly correlated if their vectors are collinear (vectors 1 and 3, and vectors 1 and 4). The nature of the correlation also depends on the direction of the vectors: if vectors have the

Compression Set according to D451046

Tear Strength according to D411048

makes the foam much softer [1].

restores its flexibility.

**5. Statistical method**

Tensile strength & Elongation at break according to

Resilience in 1st and 5th cycle according to D455128

by the solid FR addition rather than the liquid one.

rigidity of EG flakes but deteriorates when melamine is added.

different parameters by using STAT-BOX-ITCF [13, 14].

In this test 5 samples with 75mm\*305mm\*13mm dimension have been subjected with flame vertically for 12 sec and the following parameters have been investigated.

Burning time (the time that burning is continuing after removing the flame source) Burned length (the length of the foam which is damaged by the burning process) Time of dripping (the time which droplet continues to burn).

#### *Synergetic effect*

The synergetic effect of different types of FR has been observed. for instance, the fire properties of the EG loaded foams is much worse than when it is used by mixing with a liquid FR such halogenated phosphorous flame retardant. **Also when some amount of melamine is added to the TMCP and TDCP containing foams it helps to decrease total heat evolved, total smoke produced and CO emission significantly[2].** 

Also the mixing of the liquid FR could boost the fire properties of the melamine loaded foam considerably.

#### *4.3.3. Smoke density and toxicity*

Smoke density and Toxicity are measured according to Airbus Directive ABD0031 (2005) on two categories:


Samples with 76mm\*76mm\*13mm are chosen to do the above mention tests against them in flaming and non-flaming status.
