*3.1. Materials*

The water-blown RPUFs used in this study were obtained from a two-component system supplied by Purinova Sp. z o. o., after mixing the polyol (Izopianol 30/10/C) and the diphenylmethane diisocyanate (Purocyn B). The polyol is a mixture of components containing polyester polyol (hydroxyl number ca. 230 −250 mgKOH/g, functionality of 2), catalyst ( *<sup>N</sup>*,*<sup>N</sup>*-Dimethylcyclohexylamine), flame retardant (Tris(2-chloro-1-methylethyl) phosphate), a chain extender (1,2-propanediol) and water as a blowing agent. PUR foams were modified with silsesquioxanes functionalized with halogen: chloropropylisobutyl-POSS (POSS-Pr-Cl), chlorobenzylisobutyl-POSS (POSS-Ar-Cl), chlorobenzylethylisobutyl-POSS (POSS-Ar-Et-Cl) from Hybrid Plastics, Inc (Hattiesburg, MS, USA). Their structural formulas are shown in Table 5. The POSS-Cl modifiers were added to the reaction system in an amount of 2 wt.% relative to the weight of the polyol.

**Table 5.** POSS-Cl compounds used for modification of PUR foams.


#### *3.2. Synthesis of PUR Composites Foams*

PUR composite foams were produced using the method described in the previous works. Briefly, the synthesis of PUR composite foams modified with POSS-Cl was as follows: polyol premix (Izopianol) was placed in a plastic cup and intensively mixed at 1000 rpm with a mechanical mixer for 60 s. The appropriate amount of POSS-Cl modifier was then added to the cup and mixed for another 60 s to obtain a homogeneous dispersion. The calculated amount of isocyanate (Purocyn) was added to the reaction mixture and thoroughly mixed for 30 s. The reaction mixture was allowed to grow freely by measuring the individual cream, growth and tack-free times, and the maximum reaction temperature (Tmax). The grown PUR foams were left at room temperature for 24 h to ensure complete curing of the composites.

#### *3.3. Methods and Instruments*

The viscosity of the polyol systems was evaluated using a Viscometer DVII+ (Brookfield, Hadamar-Steinbach, Germany) in the function of a shear rate according to ISO 2555. The measurement was performed at ambient temperature.

The apparent density of the analyzed foams was measured according to the standard ASTM D1622 (equivalent to ISO 845). The density was tested on five samples of each foam and expressed as an average.

Cell size distribution and foam morphology were examined based on the cellular structure pictures of foams taken using JEOL JSM-5500 LV scanning electron microscopy (JEOL LTD, Akishima, Japan). The microscopic research was carried out in a high-vacuum mode and at the accelerating voltage of 10 kV.

A three-point bending test was carried out accordingly to the standard ASTM D7264 (equivalent to ISO 178) using a Zwick Z100 Testing Machine (Zwick/Roell Group, Ulm, Germany). The analyzed samples were bent with a speed of 2 mm min−1. For each series of foams, at least five measurements were made. Obtained flexural stress at the break results for each sample was expressed as a mean value and averaged.

The compressive strength (σ10%) of the foams was determined according to the standard ASTM D1621 (equivalent to ISO 844). The measurement was conducted using a Zwick Z100 Testing Machine (Zwick/Roell Group, Ulm, Germany) with a load cell of 2 kN and a speed of 2 mm min−1. The compression strength was examined as a ratio of the load causing 10% deformation of samples cross-section in both parallel and perpendicular direction to the square surface. The compressive strength was measured in five samples of foam (8 cm × 8 cm × 5 cm) and expressed as an average.

Surface hydrophobicity of PUR foams was measured using contact angle goniometer OEC-15EC (DataPhysics Instruments GmbH, Filderstadt, Germany) with software module SCA 20. Water absorption of PU foams was performed according to ISO 2896:2001.

The thermal stability of the foams was analyzed using a Mettler Toledo thermogravimetric analyzer TGA/DSC1. A thermal decomposition examination was conducted in air (flow 50 mL min−1) and in the temperature range between 25 and 600 ◦C (heating rate 10 ◦C min−1). The measurement included an analysis of the mass change as a function of temperature during thermal decomposition of the polyurethane foams. The initial temperatures of the following decomposition stages were noticed and designated as T5%, T10%, T50%. These temperature values corresponded to the percentage of weight loss.

The burning behavior and flame-retardant properties of the foams were analyzed using a cone calorimeter, according to the standard ISO 5660 in S.Z.T.K. TAPS (Maciej Kowalski Company, Saugus, Poland). The measurement for each foam was repeated on three samples and averaged. Each specimen with dimensions of 10 cm × 10 cm × 5 cm was wrapped with aluminum foil and burned at an external heat flux of 35 kW m<sup>−</sup>2. The parameters were recorded during the time.
