**3.1. The influence of raw materials on the density and processing times of the obtained foams**

The process of creating PUR‐PIR foams is very complicated from the chemical point of view. Additionally, there may be technological issues which make the examination of the foam‐ ing process of the PUR composition necessary to obtain products with beneficial properties. The foaming process is an important stage in the production of polyurethanes. Here, the cell structure is formed which significantly influences the application properties of the material. During rigid PUR‐PIR foams production, processing times (start time, rising time and gela‐ tion time) have been determined. Based on the conducted research, different times can be observed of the foam surface losing its adhesiveness. It is dependent on the type of medium (air, mould wall) that the rising foam's surface is touching. The air causes the foam to lose its


**Table 4.** Processing parameters and apparent density of rigid PUR‐PIR foams.

adhesiveness the quickest. Apparent density was also measured for the rigid foams and the results of all tests are represented in **Table 4**.

The processing times of modified foams were reduced by about 50% in comparison to the reference foam. The start time for P0 reference foam was 8 s; however, for the foam containing 0.5 R of the boron polyol, it was 3 s. Similar changes were observed for rising and gelation times. This shows a higher reactiveness of the boron‐nitrogen polyol in comparison to the industrial one.

Apparent density is one of the most important factors that determine the mechanical proper‐ ties of rigid PUR foams. From the economical point of view, it is beneficial to produce materi‐ als with the lowest possible apparent density. Nevertheless, the apparent density of a PUR foam is in close correlation with its thermo‐insulation properties, mechanical properties and dimensional stability. That is why the most commonly used rigid polyurethanes have the density values in the range of 30–60 kg/m<sup>3</sup> . By using the new boron polyol, a slight increase in the density of produced PUR‐PIR foams was observed in comparison to the reference foam. Foam density is in the range from 33.4 kg/m<sup>3</sup> for K0 foam up to 41.5 kg/m<sup>3</sup> for K5 foam, containing 0.5 R of the new polyol. The decrease in the apparent density of K1–K5 PUR‐ PIR foams is related to the amount of the boron introduced to the PUR system. By replacing the petrochemical polyol (with 9200 mPa s viscosity) with the boron polyol (with viscosity 283 mPa s), the total viscosity of the premix containing the new polyol was decreased. The amount of water used as a chemical foaming agent stayed at the same level for all recipes and generates the same amount of CO<sup>2</sup> .
