INFLUENCE OF THE NATURE OF THE CROSS-LINKING AGENT ON THE STRUCTURE AND PROPERTIES OF ORGANIC XEROGELS OBTAINED FROM TANNINS OF CEDAR BARK

It was suggested for the first time to use tannins isolated from the bark of the Siberian cedar (Pinus sibirica) for synthesis of organic xerogels. The influence of the nature of the cross-linking agent on the characteristics of xerogels prepared by sol-gel by condensation of cedar tannins with formaldehyde, furfuryl alcohol or glutaraldehyde was studied. IR study shows an increase in the number of methylene -CH2- and methylene ether -CH2-O-CH2 bonds during the formation of xerogels. The use of furfuryl alcohol leads to an increase in the density of the tannin-furfuryl gel (T/FA) xerogel (0.348 g/cm3) compared to the low density of tannin-formaldehyde (T/F) and tannin-glutar (T/G) xerogels – 0.063 and 0.071 g/cm3. BET study indicates the microporous nature of T/FA xerogel, where the proportion of micropores with an average pore size of 1.42 nm reaches 70.75%. Xerogels prepared using formaldehyde and glutaral have a meso/macroporous structure with a mesopore width of about 25–75 nm and small contribution of micropores – 8.61 and 11.27%, respectively. The SEM method revealed the formation of a branched structure of interconnected spherical particles about 3 µm in size in tannin-formaldehyde and agglomerated particles (3-8 µm) in tannin-glutar xerogels. Tannin-furfuryl gel is similar in structure and morphology to cellular foam with cavities about 10 mm in size. Using the DTA method, it was established that initial temperature of thermal composition of the T/F gel is 216 °C, T/G gel is 272 °C and T/FA is 282 °C. It was found that tannin-formaldehyde xerogel has better efficiency compared to another gels in removing methylene blue from water solution (107 mg/g).