**3. Polyglucanurethane chemical and thermal resistance**

Obtained PGU networks possess advanced thermal and chemical (both alkali and acid) resistance. Chemical resistance of PGU was analyzed using standard method…[State Standart 12020-72]. Thermal resistance of initial reagents and PGU of various composition were studied with the thermogravimetry. Table 1 shows the results of PGU20 exposure in water, acid- and alkali media. Fig 4. illustrates the TGA curves: mass loss (TG), differential mass loss (DTG) and differential thermal analysis (DTA) that characterize the dependence of thermooxidative destruction character of PGU on the degree of substitution of xanthan hydroxyl groups.

As it can be seen from table 1 data the mass of PGU20 samples remains practically unchanged after the 7 and 13 days exposure in aggressive alkali end acid medium. The initial stages of PGU interaction with water, alkali- and acid media are characterized with ignificant swelling of polysaccharide component.

According to TGA data thermooxidative destruction of the systems analyzed consists of several stages. TGA curves of xanthan are typical for polysaccharides. TGA curves character for PGU networks and number of stages in temperature interval from 20 to 700oC depend on the balance of hydroxyl and urethane groups in PGU. Stage of weight loss in temperature interval 60-140°C is accompanied with endothermal peak on DTA curve and responds to absorbed water removal.


min (3), after 20 min (4) after 30 min(5)

hydroxyl groups.

absorbed water removal.

**Figure 2.** IR spectra of reactive mixture for PGU60 at temperature 130oC(1), 150оС (2), at 150оС after 10

(a) (b) (c)

According to FTIR spectra of various PGU (PGU40, PGU80 and PGU100) the number of isocyanate groups released at the initial stage of reaction correlates with the polyisocyanate content in the system. During the first 10 min the process of polyisocyanate deblocking dominates. At the same time the urethane group formation occurs via interactiom of NCO groups and polysaccharide hydroxyl groups in acid residue of glucuronic acid and/or hydroxyl groups of mannose. The time when the urethane group formation begins to

Obtained PGU networks possess advanced thermal and chemical (both alkali and acid) resistance. Chemical resistance of PGU was analyzed using standard method…[State Standart 12020-72]. Thermal resistance of initial reagents and PGU of various composition were studied with the thermogravimetry. Table 1 shows the results of PGU20 exposure in water, acid- and alkali media. Fig 4. illustrates the TGA curves: mass loss (TG), differential mass loss (DTG) and differential thermal analysis (DTA) that characterize the dependence of thermooxidative destruction character of PGU on the degree of substitution of xanthan

As it can be seen from table 1 data the mass of PGU20 samples remains practically unchanged after the 7 and 13 days exposure in aggressive alkali end acid medium. The initial stages of PGU interaction with water, alkali- and acid media are characterized with

According to TGA data thermooxidative destruction of the systems analyzed consists of several stages. TGA curves of xanthan are typical for polysaccharides. TGA curves character for PGU networks and number of stages in temperature interval from 20 to 700oC depend on the balance of hydroxyl and urethane groups in PGU. Stage of weight loss in temperature interval 60-140°C is accompanied with endothermal peak on DTA curve and responds to

dominate depends on balance of the reagents in reaction mixture.

ignificant swelling of polysaccharide component.

**3. Polyglucanurethane chemical and thermal resistance** 

Presenting mass of absorbed water in modified and non-modified samples of exopolysaccharide as mass loss at the first stage (temperature interval 45 – 150oC) we can see that amount of absorbed water correlates with balance of hydroxyl and urethane groups in the system (Fig.3). It corresponds with the fact that system hydrophilic properties correlate with amount of hydroxyl groups. Weight loss at this stage is 1,5; 2,5; 8,5 % wt. for PGU80, PGU40, PGU20, respectively.

**Figure 3.** TGA curves - TG (1), DTG (2), DTA (3) of initial reagents: xanthan (а), blocked PIC (b); curves DTG (c) and TG (d) for initial reagents and PGU of various composition: xanthan (1), 2- PGU20 (2), PGU40, PIC (4)

**Table 1.** The weight change of PGU20 exposed in deionized water, concentrated sulphuric acid (V=20 ml, 30% wt.) and concentrate alkali solution (V=20 ml, 40% NaOH).

Intensive thermal-oxidative destruction is observed in 200 – 400oC temperature interval. The characteristic temperature responding to maximum speed of weight loss at the stage shifts toward the higher temperatures with increasing of urethane groups amount in the system. Weight loss at this stage is 35, 30, 35 % wt. for PGU80, PGU40, PGU20, respectively.

Polyglucanurethanes: Cross-Linked Polyurethanes Based on Microbial Exopolysaccharide Xanthan 437

**, nm**

solution absorbance and shows copper ions concentrating. Increasing time of interaction

256

**Figure 4.** The electron spectra of phenol water solutions: 1 – initial; 2 – PGU60 after 10 min exposure;

**1 2**

**3**

**Figure 5.** The electron spectra of copper salt water solutions: 1 - initial, 2 - after 10 min of PGU exposure

Interaction of PGU40 and PGU80 with water solution of Сu2+ and Со2+ salts with concentration of 50 and 500 mg/dm3 was studied in static conditions using conductometry. Solution conductivity was fixed after 2, 12 and 74 hours of PGU exposure. Experiment conditions were as follows mPGU=1,25 g; Vsolution=50 cm3 ; permanent stirring frequency=2 Hz; room temperature. Intermediate and final concentrations were calculated from calibration curve. Fig 7 demonstrates conductivities of cobalt and copper salt solutions of various concentrations (50 and 500 mg/dm3) depending on the time of interaction with PGU40 and PGU80. In the table 2 there are the results of concentration changes of copper(2+) sulfate and cobalt(2+) chloride solutions respectively *vs* time of exposure PGU40 and PGU80. Fig 6 shows that conductivity of cobalt chloride and copper sulfate solutions grows on the initial stages of sorbent exposure for both high (500 mg/dm) and low (50 mg/dm) concentrations.

with sorbent to 60 min leads to absorbance reduction.

**I, %**

3 – PGU20 after 10 min exposure

and 3 - after 60 min of PGU exposure

Wide peak on DTG curves in temperature interval from 500 to 700oC mainly corresponds to destruction of carbon base of polymer. With growth of urethane group content in the system the carbon residual decreases.

As it can be seen thermal resistance of PGU grows with increasing of urethane group amount. For instance, for PGU40 high temperature stage is allocated 40oC lower than for the PGU 80. The degree of hydroxyl substitution also influences the system capacity of water absorbance. With growth of urethane group content in the system the amount of absorbed water declines
