**3.4. Combustible properties of rigid PUR‐PIR foams with new polyol**

Rigid global statistical studies regarding fires in the recent years show that vast majority of fatal accidents during fires (60–80%) was caused by inhaling the products of thermal decomposition and burning, as well as limited visibility due to the generated smoke. The cause of a smoke with higher density and toxicity is incomplete burning of the gas phase. It also increases the ratio between carbon oxide and carbon dioxide, which makes the smoke more toxic. That is why the best way to lower the combustible properties of polyurethane materials is to produce them with raw materials that will help obtain a polymer with slow burning speed and low burning efficiency of flammable gas phase. Despite the obstruction of material combustion and limitation of flame spreading, the antipirene should not affect the processing and should not worsen the application properties of the product. The tendencies of boron and nitrogen atoms for supplementing and strengthening flame‐retardant properties were used to determine the boron polyol. The percentage value of those atoms in the new polyol is around 14%; hence, posi‐ tive results can be expected for the examination of non‐halogen method of lowering the burning of new foams. Boron participates in endothermic reactions, whose end result is the release of water and creation of protective glasslike layer. This layer protects the base from oxygen and heat from the flame. Nitrogen compounds, on the other hand, decompose into gas products that take part in creating foamed carbon layers in the condensed phase. After reaching the gas layer, they burn and become free radical scavengers.

In order to test the foam behaviour in flame, various tests were conducted. Cone calorimeter method helps to define burning properties of the material and to characterize the reactions that take place during the burning process. The comparison of parameters of the pyrolysis process in selected rigid polyurethane‐polyisocyanurate foams obtained with the use of new boron polyols has been presented in **Table 7**.

The produced rigid polyurethane‐polyisocyanurate foams with the new polyol (K1 and K5), as well as the K0 reference foam (containing only the petrochemical polyol), were subjected to the burning process using cone calorimeter method. For the K0 reference foam, the combus‐ tion time was very short and equalled 1.48 s. The same time is characteristic for materials with porous structure that are highly flammable. After introducing the boron polyol to the foam recipe, the combustion time was significantly longer. For the K5 foam, containing the highest amount of the new polyol, the time was 14 s. On the other hand, in the K1 foam, containing the least amount of the polyol, the combustion time was shortened to 7 s. During the burning test using cone calorimeter method, the total heat release (THR) value was also measured, which determines the total heat released by the burning foam. The largest amount of heat, equalling 14.3 MJ/m<sup>2</sup> , was released while testing the K0 reference foam. The use of the new polyol in the composition helped lowering the THR value, not exceeding 4 MJ/m<sup>2</sup> . The total heat release value was the lowest for the K5 reference foam, with the largest amount of the boron polyol. The THR value can indicate that the new polyol shows cooling properties, by lowering this parameter by around 80%.


**Table 7.** Results of flame tests in selected rigid PUR‐PIR foams.

helped determine that the addition of the boron polyol into the foam recipe causes significant decrease in the foam's brittleness. The higher the amount of boron polyol in the foams, the lower the brittleness, from 36.2% for K0 reference foam to 8% for K5 foam modified with the new polyol. Similar to the compressive strength, the brittleness examination of the obtained foams shows a correlation between this value and the apparent density of the samples. Higher

**Figure 5.** The correlation between compressive strength and apparent density, and the amount of boron polyol in the foams.

K0 K1 K2 K3 K4 K5

**Type of foam**

0

10

20

30

**Apparent density,**

 **[kg/m3]**

40

50

There is also a correlation between the compressive strength and the linear dimension stabil‐ ity. Along with the changes in the temperature, the internal pressure of the gas inside the cell changes. It creates a difference in pressure between foam cells and external atmospheric pressure. This difference of pressures needs to be lower than the foam's compressive strength to retain its dimensional stability. Foam deformation should not occur when the compressive strength is greater than 100 kPa, which is a value higher than the possible difference between atmospheric pressure and the pressure inside foam cells, which is close to zero. When com‐ paring the results of the ageing test for the produced rigid PUR‐PIR foams, it was determined that there is a strong correlation between the stability of linear dimensions, mass loss and changes in volume, and the use of the new polyol in foam recipe. During the simulated age‐ ing of the samples, it was observed that mass loss did not exceed 1% for all foams. Similarly, the changes in linear dimensions did not exceed 2%. This qualifies those products for the use

Rigid global statistical studies regarding fires in the recent years show that vast majority of fatal accidents during fires (60–80%) was caused by inhaling the products of thermal decomposition and burning, as well as limited visibility due to the generated smoke. The cause of a smoke with higher density and toxicity is incomplete burning of the gas phase. It also increases the ratio between carbon oxide and carbon dioxide, which makes the smoke more toxic. That is why the best way to lower the combustible properties of polyurethane materials is to produce

apparent density of PUR‐PIR foams enables a significant decrease in their brittleness.

**3.4. Combustible properties of rigid PUR‐PIR foams with new polyol**

in thermal insulation.

230

250

270

290

**Compressive strength, [kPa]**

124 Aspects of Polyurethanes

310

330

The path of the heat release rate (HRR) curves shows information regarding the mechanism of lowering the flammability, which depicts the maximum value of the heat release rate. It is a very important parameter and an indicator of the material's tendency to self‐extinguish in case of fire. The HRR values in **Table 8** were determined for data from the moment of combus‐ tion until the end of the test. **Figure 6** presents the curves showing the course of heat release (HRR) in the new foams.

The HRR curves of rigid PUR‐PIR foams modified with the new polyol and the non‐modified foam show subsequent stages of the burning process. It can be observed that initially the foams become warm, then the volatile parts and flammable gas products are produced. The burning of gases is the reason for creating large amounts of heat. The curves indicate that for the K0 ref‐ erence foam, the rate of released heat is very energetic. Also, the flame on this foam is sustained. However, the foams modified with the new polyol burn in less rapid manner and reach lower values of heat release. The elongation of maximum HRR time value from 10 s (K0) to 37 s (K5) also shows flame‐retardant properties of boron polyols.

The amount of exhausted CO is much higher for the reference foam than for the foams modified with the new polyol. Carbon oxide in the reference foam was emitted in the amount of 1.352 g/g. After using the boron polyol, the amount of carbon oxide was lowered almost four times, until reaching 0.243 g/g value for the K5 foam, containing 0.5 R of borane tri[N,N′‐di(methylenoxyethylentio‐2‐hydroxyethyl)urea]. Similar correlation can be seen in the carbon dioxide emission during the burning test. The conducted analysis of carbon oxide and dioxide emissions uniformly indicates that the new boron polyol is an effective addition that reduces the amount of gases produced during a fire. Rigid polyurethane‐poly‐ isocyanurate foams with the new polyol have substantially longer time value for permanent combustion than the reference foam.

The oxygen index for the reference foam is 19.6%; however, in foams with borane polyol it is in the range from 23.2% (K1 foam) to 26.4% (K5 foam). By using the oxygen index method, it has been determined that the presence of the new polyol in the PUR‐PIR foam helps reducing flammability of this material by abound 21%. During the examination in cone calorimeter, foams modified with the new polyol produced less charred residue. Also during this test, it was observed that the K5 reference foam did not burn but rather glowed. It is caused by minor mass loss of this foam (4.87 gm2 /s) during the burning test. The speed of fire spreading, flash‐ over, is an important parameter used for the comparison of different materials with regard to fire safety. It is the value opposite to time to reach flashover (1/*t* flashover) (Eq. (3)) [14]:


**Table 8.** Properties of selected rigid PUR‐PIR foams determining their behaviour during fire.

The path of the heat release rate (HRR) curves shows information regarding the mechanism of lowering the flammability, which depicts the maximum value of the heat release rate. It is a very important parameter and an indicator of the material's tendency to self‐extinguish in case of fire. The HRR values in **Table 8** were determined for data from the moment of combus‐ tion until the end of the test. **Figure 6** presents the curves showing the course of heat release

The HRR curves of rigid PUR‐PIR foams modified with the new polyol and the non‐modified foam show subsequent stages of the burning process. It can be observed that initially the foams become warm, then the volatile parts and flammable gas products are produced. The burning of gases is the reason for creating large amounts of heat. The curves indicate that for the K0 ref‐ erence foam, the rate of released heat is very energetic. Also, the flame on this foam is sustained. However, the foams modified with the new polyol burn in less rapid manner and reach lower values of heat release. The elongation of maximum HRR time value from 10 s (K0) to 37 s (K5)

The amount of exhausted CO is much higher for the reference foam than for the foams modified with the new polyol. Carbon oxide in the reference foam was emitted in the amount of 1.352 g/g. After using the boron polyol, the amount of carbon oxide was lowered almost four times, until reaching 0.243 g/g value for the K5 foam, containing 0.5 R of borane tri[N,N′‐di(methylenoxyethylentio‐2‐hydroxyethyl)urea]. Similar correlation can be seen in the carbon dioxide emission during the burning test. The conducted analysis of carbon oxide and dioxide emissions uniformly indicates that the new boron polyol is an effective addition that reduces the amount of gases produced during a fire. Rigid polyurethane‐poly‐ isocyanurate foams with the new polyol have substantially longer time value for permanent

The oxygen index for the reference foam is 19.6%; however, in foams with borane polyol it is in the range from 23.2% (K1 foam) to 26.4% (K5 foam). By using the oxygen index method, it has been determined that the presence of the new polyol in the PUR‐PIR foam helps reducing flammability of this material by abound 21%. During the examination in cone calorimeter, foams modified with the new polyol produced less charred residue. Also during this test, it was observed that the K5 reference foam did not burn but rather glowed. It is caused by minor

over, is an important parameter used for the comparison of different materials with regard to

fire safety. It is the value opposite to time to reach flashover (1/*t*

**Foam sample 1/***t* **flashover, fire hazard (kW/m2.s) RTFHCO/CO2**

**Table 8.** Properties of selected rigid PUR‐PIR foams determining their behaviour during fire.

**K0** 188.4 2.8745 **K1** 31.6 0.1655 **K5** 13.2 0.0238

/s) during the burning test. The speed of fire spreading, flash‐

flashover) (Eq. (3)) [14]:

**, relative toxic fire hazard**

(HRR) in the new foams.

126 Aspects of Polyurethanes

also shows flame‐retardant properties of boron polyols.

combustion than the reference foam.

mass loss of this foam (4.87 gm2

**Figure 6.** Heat release rate (HRR) for rigid PUR‐PIR reference foam and foams containing new polyols (chart from cone calorimeter).

$$\frac{1}{t\_{\text{flashover}}} = \frac{\text{HRR}\_{\text{max.}}}{T\_{\text{comb}}} \tag{3}$$

where HRRmax.is the maximum heat release rate; *T*comb.is the time to combustion.

Relative toxic fire hazard (RTFH) is another parameter that can help determine the fire danger rating. In this research, the determined RTFH indicators relate to carbon oxide and dioxide, because the use of cone calorimeter can measure only CO and CO<sup>2</sup> emissions. Those indica‐ tors are calculated according to Eq. (4): \_ CO2 \_

$$\text{RTFH}\_{\text{CO/CO}\_2} = \frac{\text{MLR}}{\text{TTI}} \cdot \left( \frac{\text{CO yield}}{\text{LC}\_{50}^{\text{o}} \text{CO}} + \frac{\text{CO}\_2 \text{ yield}}{\text{LC}\_{50}^{\text{o}} \text{CO}\_2} \right) \tag{4}$$

where MLR is the average mass loss rate; CO yield is the average CO emission; CO<sup>2</sup> yield is the average CO<sup>2</sup> emission; LC50 <sup>30</sup> CO and LC50 <sup>30</sup> CO<sup>2</sup> are the lethal concentration of CO and CO<sup>2</sup> , respectively, causing death of 50% of tested animals during 30‐min exposition, in accordance with PN‐88/B‐02855.

The results of examined fire hazard related to the flashover and toxicity during the burning process of selected rigid PR‐PIR foams are represented in **Table 8**.

The calculations show that the danger related to the speed of fire spread (1/*t* flashover) in the tested rigid PUR‐PIR foams can be lowered by using the new boron polyol. The value decreased from 188.4 kW/m2.s for the reference foam to around 13 kW/m2.s for the K5 foam, containing the largest amount of boron polyol. When looking at the values of carbon oxide and dioxide emissions, it can be stated that the use of the new boron polyol helps reducing the toxic fire hazard for the obtained rigid PUR‐PIR foams. The toxic fire hazard for the K0 reference foam is 2.8745; however, the use of the new polyol in the foam production decreased this value by around 99%.
