**2.1. Characteristics of raw materials**

The polyether with trade name Rokopol RF‐55 (product of oxypropylation of sorbitol LOH = 495 mg KOH/g, produced by NZPO 'Rokita', Brzeg Dolny, Poland) and Ongromat 20–30 (technical polyisocyanate whose main component is diphenylmethane 4,4′‐diisocya‐ nate, made in Hungary) were used to prepare the rigid PUR‐PIR foams. The density of Ongromat 20–30 at a temperature of 25°C was 1.23 g/cm<sup>3</sup> , its viscosity was approx. 200 mPa s. The polyisocyanate contained 31.0% of isocyanate groups. It was characterized according to the ASTM D 1638‐70 standard.

An anhydrous potassium acetate in the form of 33% solution in diethylene glycol (Catalyst‐12, POCh Gliwice, Poland) and amine catalyst in the form of 33% solution of triethyleneamine in dipropylene glycol (DABCO, Hondrt Hülls, Germany) were applied in the foam composition.

The polysiloxanepolyoxyalyleneoxydimethylene copolymer characterized by the boiling point of 150°C at 1013 hPa and ignition temperature of 90°C (Niax Silicone L 6900, Witco Corp., USA) was used as a surfactant.

The porophor was carbon dioxide formed in situ in reaction of isocyanate with distilled water.

Moreover, tri(2‐chloro‐1‐methyl‐ethyl) phosphate (Antiblaze, Albright and Wilson, UK) was introduced into foams.

Boran tri[N,N′‐di(metylenooksy‐2‐hydroksyetylo)mocznika] obtained from the Faculty of Chemistry, Technology of Polymers and Ecotechnology of Bydgoszcz Academy was applied as a modifier for the preparation of foams.

### **2.2. Synthesis of boronitrogen polyol from boric acid and di(hydroxymethyl)urea**

be widely modified. By changing the raw materials, their correlating volume ratio and by selecting appropriate processing conditions, it is possible to obtain solid, porous, composite, leather‐like and biodegradable materials, and elastomers, glues, fibres, adhesives and many more. Rigid polyurethane foams have a special place among them. They have low appar‐ ent density and excellent mechanical properties. That is why they are used in many fields, for example, construction, automotive, furniture, shoe and packaging industries [3–6]. The superb thermo‐insulating properties of the rigid foams are the main reason for their wide usage. They are the best thermo‐insulating material used in construction and refrigeration. The main drawback of the foams, and one that may limit the expansion of polyurethanes for new applications, is their flammability. It is an important issue, especially when using polyurethanes on large surfaces and in public buildings [7–20]. Lowering their flammabil‐ ity requires multidisciplinary solutions during the stage of designing the chemical struc‐ ture and antipirenes. Usually, phosphorous, nitrogen, boron and halogens compounds are introduced to polyurethane materials. Nowadays, however, there is a worldwide tendency to withdraw the antipirenes produced based on chlorine and bromine because of the high toxicity during their thermal decomposition. The addition of large amounts of antipirenes in order to obtain the desired non‐flammable effect causes technological issues and sig‐ nificantly decreases the physicomechanical properties and dimensional stability of the pro‐

Based on the conducted research, the author stated that in order to omit the inconvenience related to the use of halogen antipirenes, the foamed polyurethanes with high‐flame resis‐ tance can be produced by using the new polyurethane composition which contains the new

The polyether with trade name Rokopol RF‐55 (product of oxypropylation of sorbitol LOH = 495 mg KOH/g, produced by NZPO 'Rokita', Brzeg Dolny, Poland) and Ongromat 20–30 (technical polyisocyanate whose main component is diphenylmethane 4,4′‐diisocya‐ nate, made in Hungary) were used to prepare the rigid PUR‐PIR foams. The density of

s. The polyisocyanate contained 31.0% of isocyanate groups. It was characterized according

An anhydrous potassium acetate in the form of 33% solution in diethylene glycol (Catalyst‐12, POCh Gliwice, Poland) and amine catalyst in the form of 33% solution of triethyleneamine in dipropylene glycol (DABCO, Hondrt Hülls, Germany) were applied in the foam composition. The polysiloxanepolyoxyalyleneoxydimethylene copolymer characterized by the boiling point of 150°C at 1013 hPa and ignition temperature of 90°C (Niax Silicone L 6900, Witco

The porophor was carbon dioxide formed in situ in reaction of isocyanate with distilled water.

, its viscosity was approx. 200 mPa

duced materials [21–24].

112 Aspects of Polyurethanes

**2. Experimental part**

**2.1. Characteristics of raw materials**

to the ASTM D 1638‐70 standard.

Corp., USA) was used as a surfactant.

boron‐nitrogen polyol which decreased flammability.

Ongromat 20–30 at a temperature of 25°C was 1.23 g/cm<sup>3</sup>

The reaction for obtaining boronitrogen polyol was conducted in an oxygen atmosphere, at the temperature of 131°C, using glass equipment: three‐neck flask placed in electric heating mantle. The flask was equipped with Deana‐Stark head, thermometer and mechanical stirrer. The flask contained 61.81 g (1 mole) of boric acid (H<sup>3</sup> BO<sup>3</sup> as a white powder with a molecular mass of 61.81 g/mol, produced by POCh in Gliwice), 212 g (2 moles) of xylene (a mixture of o‐ and p‐isomers, produced by Chempur in Piekary Śląskie, with water content above 0.1% and density of around 0.860–0.866 g/cm<sup>3</sup> ), 876 g (3 moles) of N,N′‐di(methylenoxy‐5‐hydroxy‐ pentylo)urea (yellow‐brown liquid, with 1193 g/cm<sup>3</sup> density, produced in the Chemistry and Technology of Polyurethane Department in Bydgoszcz). The flask content was kept at a boil‐ ing temperature for 510 min with constant and intense stirring. When the reaction ended and the stirring stopped, the reactive mixture was separated into an upper clear layer (xylene) and a light‐blue bottom layer (new polyol). After cooling, the separated bottom layer was kept for 1 h in the temperature of 130°C in vacuum dryer under the pressure of 0.320 kPa to remove any solvent and water residue.

As a result of the conducted reaction, borane tri[N,N′‐di(methylenoxyethylentio‐2‐hydroxyethyl) urea] was produced (**Scheme 1**).

**Scheme 1.** Reaction for obtaining borane tri[N,N′‐di(methylenoxyethylentio‐2‐hydroxyethyl)urea].

Examining the physicomechanical properties of the new compound was the next step. The results of the examination helped determining the usability of the obtained borane as a polyol for the production of rigid polyurethane‐polyisocyanurate foams. A polyol is a basic compo‐ nent of the polyurethane composition and it determines the properties of produced materials in a significant way. **Table 1** describes the physical properties of the new polyol.

The viscosity of the obtained borane is 283 mPa s; however, the density is 1300 kg/m<sup>3</sup> . The viscosity value of the new polyol does not exceed the viscosity value of industrial polyols (15,000 mPa s). Higher viscosity values of the raw materials used in polyurethane production


**Table 1.** Borane properties.

are not advisable due to the technological limitations of standard equipment used for PUR processing, available on the market.

The structure of the new polyol indicated the presence of boron and nitrogen that have a signifi‐ cant influence on flammability. Based on the conducted calorimeter analysis with carminic acid, it has been noted that the boron value is 1.3% of the mass, and nitrogen value is 9.7% of the mass.

Hydroxyl number is an elementary parameter of a polyol which is important during the cal‐ culation of polyurethane composition. That is why it has been determined for the obtained boroorganic compound. The hydroxyl number is 380 mgKOH/g and is similar to its calcu‐ lated theoretical value. It also proved that the compound in an interesting material for the production of rigid PUR‐PIR foams.

The presence of water is also an important characteristic of polyols used for obtaining poly‐ urethane foams. The amount of water needs to be precisely determined in those compounds because it can have a substantial influence on the foaming process during the reaction with the polyisocyanate. The amount of water in the obtained borane is lower than 0.1%. This value does not interfere with the process of foam production and does not have to be included in the recipe. The structure of the obtained borane compound was determined based on pro‐ ton nuclear magnetic resonance spectrum 1 HNMR, using chloroform as the dissolvent. The results of 1 H NMR analysis of the polyol are represented in **Table 2** and **Figure 1**.

The presence of characteristic groups for obtained compounds was confirmed with the analy‐ sis of the spectrum of new boron compounds, using spectroscopy in infrared. The IR spec‐ trum shows bands with frequencies typical for groups present in the new polyol. The results are presented in **Figure 2**.


**Table 2.** Assigning signals in 1 H NMR spectrum to particular protons for borane tri[N,N′‐di(methylenoxyethylentio‐2‐ hydroxyethyl)urea].

**Figure 1.** <sup>1</sup> H NMR spectrum of borane tri[N,N′‐di(methylenoxyethylentio‐2‐hydroxyethyl)urea].

The IR spectrum shows, among others, characteristic bonds representing frequencies of NH‐ CO‐NH bonds, at 1648–1654 cm−1, and in the 1290–1336 cm−1 for B‐O bonds. Also, a band typical for hydroxyl group –OH appeared in the new polyol at the 2949–3556 cm−1 range which are also confirmed by the results of the determined hydroxyl groups.

### **2.3. Synthesis of rigid PUR‐PIR foams in 18‐dm3 mould**

are not advisable due to the technological limitations of standard equipment used for PUR

**Viscosity (20°C) (Pa s)**

**Mole mass (g/mole)**

430 1300 283 546 Colourless 9.7 1.3

**Colour Nitrogen** 

**volume (%mass.)** **Boron volume (%mass.)**

The structure of the new polyol indicated the presence of boron and nitrogen that have a signifi‐ cant influence on flammability. Based on the conducted calorimeter analysis with carminic acid, it has been noted that the boron value is 1.3% of the mass, and nitrogen value is 9.7% of the mass. Hydroxyl number is an elementary parameter of a polyol which is important during the cal‐ culation of polyurethane composition. That is why it has been determined for the obtained boroorganic compound. The hydroxyl number is 380 mgKOH/g and is similar to its calcu‐ lated theoretical value. It also proved that the compound in an interesting material for the

The presence of water is also an important characteristic of polyols used for obtaining poly‐ urethane foams. The amount of water needs to be precisely determined in those compounds because it can have a substantial influence on the foaming process during the reaction with the polyisocyanate. The amount of water in the obtained borane is lower than 0.1%. This value does not interfere with the process of foam production and does not have to be included in the recipe. The structure of the obtained borane compound was determined based on pro‐

H NMR analysis of the polyol are represented in **Table 2** and **Figure 1**. The presence of characteristic groups for obtained compounds was confirmed with the analy‐ sis of the spectrum of new boron compounds, using spectroscopy in infrared. The IR spec‐ trum shows bands with frequencies typical for groups present in the new polyol. The results

**Hydrogen atom position Chemical shift (ppm)] Number of hydrogen atoms**

1 3689–3609 3 2, 6, 11, 15 4693–4308 24 3, 4, 5, 12, 13, 14 1426–1294 36 8, 9 6995–6532 6

HNMR, using chloroform as the dissolvent. The

H NMR spectrum to particular protons for borane tri[N,N′‐di(methylenoxyethylentio‐2‐

processing, available on the market.

**Polyol's name Properties**

Borane tri[N,N′‐

114 Aspects of Polyurethanes

di(methylenoxyethylentio‐2‐ hydroxyethyl)urea]

**Table 1.** Borane properties.

**Hydroxyl number (mgKOH/g)** **Density (20°C) (kg/m3 )**

production of rigid PUR‐PIR foams.

ton nuclear magnetic resonance spectrum 1

results of 1

are presented in **Figure 2**.

**Table 2.** Assigning signals in 1

hydroxyethyl)urea].

Foamed polyurethanes are usually produced based on a so‐called polyurethane system which comprises two or more components that react during mixing and give the desired product. This article focuses on the examination of polyurethane‐polyisocyanurate foams produced using two‐component A+B system. The A component was obtained by mixing polyols (Rokopol RF‐55 and N,N′‐di(hydroxymethyl)urea derivative), catalysts, surface‐active agent, and porophor. Component B on the other hand was polyisocyanate. Foams produced with this system are very simple and the process is not too energy intensive. However, the development of processing technology of foamed polyurethanes encountered a serious issue regarding the requirements for environmental protection. Developing a foaming agent that would be environmentally safe and, at the same time, would help producing materials with valuable properties is a great chal‐ lenge for polyurethane manufacturers. In the presented research, carbon dioxide was used as the foaming agent which was exhausted during the reaction or water with isocyanate groups. Despite a common opinion that carbon dioxide slightly deteriorates the application properties of a polyurethane foam (heat conductivity, durability and brittleness), initial research on using the new polyol in the polyurethane composition shows a promising final product with ben‐ eficial properties. The basis for calculating the polyurethane recipe was the hydroxyl number

**Figure 2.** IR spectrum for boroorganic compound recorded by KBr technique.

of the used polyols. Then, the values of auxiliary compounds which usually do not contain hydroxyl groups were determined, for example, catalysts, non‐reactive flame retardants and surface‐active agents. They were described in weighted portions in relation to 100 weighted portions of the polyol. The amount of isocyanate was selected with regard to the ratio of isocya‐ nate groups to hydroxyl groups, which was set to 3:1 for rigid polyurethane‐polyisocyanurate foams. The calculated amount of isocyanate was increased by the isocyanate mass needed to conduct a reaction with water, as a result of which CO<sup>2</sup> was exhausted—the gas which foams the reactive mixture. The recipes for obtained foams are described in **Table 3**.

When starting with the rigid PUR‐PIR foam production based on the determined recipes (**Table 3**), polyisocyanate was measured in the first 1‐dcm<sup>3</sup> polypropylene vessel, and polyol component polyol with added auxiliary substances was measured in the second vessel. The polyol was thor‐ oughly mixed with other components using electric stirrer with 1800‐rpm rotation speed.

The polyisocyanate was combined with the polyol component, stirred for 10 s and both were poured into a mould where the foam's rising process was observed. An open mould was used for the examination which enabled a so‐called free‐rising process.

During the first stage, the reference K0 foam was obtained, which did not contain any amount of the polyol, and then foams marked from K1 to K5 were produced by adding from 0.1 to 0.5 R of the polyol, respectively.


**Table 3.** The recipes for rigid PUR‐PIR foams.

of the used polyols. Then, the values of auxiliary compounds which usually do not contain hydroxyl groups were determined, for example, catalysts, non‐reactive flame retardants and surface‐active agents. They were described in weighted portions in relation to 100 weighted portions of the polyol. The amount of isocyanate was selected with regard to the ratio of isocya‐ nate groups to hydroxyl groups, which was set to 3:1 for rigid polyurethane‐polyisocyanurate foams. The calculated amount of isocyanate was increased by the isocyanate mass needed to

When starting with the rigid PUR‐PIR foam production based on the determined recipes (**Table 3**),

polyol with added auxiliary substances was measured in the second vessel. The polyol was thor‐ oughly mixed with other components using electric stirrer with 1800‐rpm rotation speed.

The polyisocyanate was combined with the polyol component, stirred for 10 s and both were poured into a mould where the foam's rising process was observed. An open mould was used

During the first stage, the reference K0 foam was obtained, which did not contain any amount of the polyol, and then foams marked from K1 to K5 were produced by adding from 0.1 to 0.5 R

was exhausted—the gas which foams

polypropylene vessel, and polyol component

conduct a reaction with water, as a result of which CO<sup>2</sup>

**Figure 2.** IR spectrum for boroorganic compound recorded by KBr technique.

polyisocyanate was measured in the first 1‐dcm<sup>3</sup>

of the polyol, respectively.

116 Aspects of Polyurethanes

the reactive mixture. The recipes for obtained foams are described in **Table 3**.

for the examination which enabled a so‐called free‐rising process.

During the polyurethane‐polyisocyanurate foam synthesis, the foaming process of the reac‐ tive mixture was monitored, and with the help of a stopwatch, the start time, expansion time and gelation time were measured.

Start time is the time measured with a stopwatch from the moment of mixing the components, up to when the foam reached a 'cream state'. It is indicated by the increasing volume of the foam.

Rising time is the time measured with a stopwatch from the moment of mixing the compo‐ nents, up to reaching the maximum volume of the foam.

Gelation time is the time measured with a stopwatch from the moment of mixing the compo‐ nents, up to the moment when the free surface of the foam stops sticking to a clean glass rod.

### **2.4. Methodology of rigid PUR‐PIR foam production**

The examination of apparent density was conducted after 24 h of seasoning of the samples in room temperature, according to ISO 845‐1988 standard. The apparent density was determined for all the examined samples. The samples were measured with an accuracy up to 0.01 mm and weighted with an accuracy up to 0.01 g.

The brittleness of examined foams was determined according to the ASTM C‐421‐61 standard. Based on that standard, the brittleness was measured as a percentage mass loss of 12 foam cubes (square cubes with 25 mm sides), during an examination in normalized apparatus, in relation to the initial mass. The apparatus for measuring PUR foam brittleness was a cubical box made out of oak wood, with dimensions of 190 × 197 × 197 mm, rotating along its axis with the speed of 60 rounds per min. The box was filled with 24 oak cubes with the dimen‐ sions of 20 × 20 × 20 mm.

The determination of water absorption was conducted in accordance with DIN 53433 stan‐ dard. This method measures the hydrostatic buoyancy of the sample with the dimensions of 150 × 150 × 25 mm, submerged in distilled water for 24 h.

Thermo‐insulating properties of the produced foams were determined by measuring the heat conductivity coefficient *λ*. Samples with dimensions of 200 × 200 × 25 mm were used for the test. FOX 200 apparatus by Lasercomp was used during this examination. It enables the deter‐ mination of *λ*‐value in the range of 20–100 mW/(m K). The measurement chamber needs to be fully filled to conduct proper examination.

The heat conductivity coefficient measurement method measures the amount of heat trans‐ ported through the sample material in a unit of time during the determined heat flow, that is, when the temperature difference is measured on the opposite sides of the examined sample. The measurements are performed in series, in 0.5‐s intervals.

Compressive strength was determined by the use of general‐purpose strength machine (Instron 5544). The peel and flanks of foam were cut off and the cubic samples were cut out (side of 50 ± 1 mm). Then, the samples were subjected to compressive strain by 10% according to the direction of foam expansion.

The content of closed cells was determined in compliance with PN‐ISO 4590 standard, using defect‐free samples with the dimensions of 100 × 25 × 25 mm. The method utilizes the Boyle– Mariotte law. It determines a relative pressure decrease based on calibrated volume patterns, measuring the difference on the scale of a manometer with one arm opened to the atmosphere.

The retention (remains after burning) of the PUR‐PIR foams was examined according to ASTM D3014‐73 standard, by performing the vertical test. The apparatus used for the burning examination using the vertical test had a vertical chimney with 300 × 57 × 54‐mm dimensions. Three of the walls were made out of tin and one was a removable glass wall. The test was con‐ ducted on six samples with dimensions of 150 × 19 × 19 mm. Before burning, the samples were weighted with an accuracy up to 0.0001 mm and placed inside the chimney. The glass was placed in place and flame was introduced to the samples from propane‐butane burner for 10 s. Then, the burner was moved away and the times of free burning and retention were measured with a stopwatch in the vertical test. Retention was calculated using Eq. (1):

$$R\_e = \frac{m}{m\_o} \times 100\% \tag{1}$$

where *R*<sup>e</sup> is the retention; *m*<sup>0</sup> is the sample mass before burning (g), *m* is the sample mass after burning (g).

Using the cone calorimeter, the examination of flame and smoke parameters was conducted for the produced PUR‐PIR foams based on the methodology described in the ISO 5660‐1:2001 norm.

Normalized samples with dimensions of 100 × 100 mm were subjected to heat radiation. During the examination, the following parameters were recorded: the time needed to initi‐ ate the burning process, thermokinetic parameters, that is, heat exhaustion rate and the total amount of exhausted heat, and selected toxic and smokegenic properties. The thermokinetic values were measured using the theory of oxygen usage calorimetry, which states that out of 1 g of used oxygen, there are around 13.1 kJ of heat produced with accuracy up to ±5%. The examination was conducted for material samples placed horizontally and the burning reaction was initiated by combustion. The material samples were exposed to heat radiation of 30 kW/m<sup>2</sup> . The examination ended after the burning process faded completely. The tem‐ perature distribution during burning was measured using a Vigo V‐20E2‐25 thermal imag‐ ing camera equipped with HgCdTe thermoelectrically cooled detector. The measurement conditions were compliant with conditions for determining the oxygen index (OI).

The oxygen index (OI) was determined in compliance with the methodology described in the ASTM D 2863‐1970 standard. It measures the boundary concentration of oxygen in oxygen and nitrogen mixture, sufficient for sustaining burning of a sample with the dimensions of 150 × 13 × 13. The oxygen index was calculated in percentile value according to Eq. (2)

$$\text{OI} = \frac{\text{O}\_2}{\text{O}\_2 + \text{N}\_2} \times 100\% \tag{2}$$

where O<sup>2</sup> is the volumetric flow rate of oxygen for the boundary volume (m<sup>3</sup> /h), N<sup>2</sup> is the volumetric flow rate of nitrogen for the boundary oxygen volume (m<sup>3</sup> /h).

The examination of cell structure was performed using HITACHI S‐4700 scanning elec‐ tron microscope (SEM) with NORAN Vantage microanalysis system. The reference sample (containing petrochemical polyol) and the modified sample with the largest amount of boron polyol were tested.

IR spectroscopy was used to identify characteristic groups present in PUR‐PIR. The polyure‐ thane foams were milled in Janetzky's mill before they were tested with the IR method. The analysis of the milled samples was performed with KBr technique on Brucker spectrophotom‐ eter in the range from 200 to 4000 cm−1.
