**4. PGU interaction with water solutions of phenol and transition metal salts**

It is known that microbial polysaccharides are considered as prospective raw materials for obtaining effective sorbents for extracting organic compounds and metal ions from water solution (Crini, 2005). Application of water-soluble polysaccharides (eg. xanthan) as sorbents is difficult. Using of PGU allows both keep sorption properties of polysaccharide and eliminate a number of disadvantages (water solubility, low chemical resistance etc.). Study of properties of cross-linked PGU (Hubina, 2009) revealed its ability to quantitative extraction of phenol and bivalent metal ions from water solution, while controlling capacity of the material with cross-linking degree.

To analyze ability of PGU to phenol sorption from its water solution the pollutant concentration was controlled before and after exposure of PGU20 and PGU60 films in 10-4М phenol water solution during 24, 48 and 120 hours. Phenol concentration was monitored using UV electron spectroscopy by the change of band intensity near 256 nm. Experiment conditions were as follows: T=18 oC, msorbent=7 g, Vsolution=50 ml. Calibration curve was plotted for 0,05; 0,075; 0,1; 0,15 and 0,2 М phenol water solutions.

According to UV-spectroscopy data after 24 hours of exposure PGU in phenol solution increasing of phenol concentration is observed both for PGU20 and PGU60 (Fig.4). Further exposure of PGU in solution leads to essential decreasing of phenol concentration. Such phenol concentrating during PGU interaction with phenol solution can be explained by the preferable swelling of polysaccharide component of the polymer in water.

The same character of concentration change is observed while extracting Сu2+ ions from copper sulfate solution. (Fig.5). Its concentration change was controlled using electron spectroscopy in Vis-region by the change in band intensity near 810 nm. That band corresponds to d-d transitions in [Сu(H2O)6]2+aqua ion. Exposure of PGU60 sample in copper sulfate water solution during 10 min. is accompanied by sufficient growth of solution absorbance and shows copper ions concentrating. Increasing time of interaction with sorbent to 60 min leads to absorbance reduction.

436 Polyurethane

the carbon residual decreases.

of the material with cross-linking degree.

for 0,05; 0,075; 0,1; 0,15 and 0,2 М phenol water solutions.

preferable swelling of polysaccharide component of the polymer in water.

water declines

**salts** 

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.

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

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

**4. PGU interaction with water solutions of phenol and transition metal** 

It is known that microbial polysaccharides are considered as prospective raw materials for obtaining effective sorbents for extracting organic compounds and metal ions from water solution (Crini, 2005). Application of water-soluble polysaccharides (eg. xanthan) as sorbents is difficult. Using of PGU allows both keep sorption properties of polysaccharide and eliminate a number of disadvantages (water solubility, low chemical resistance etc.). Study of properties of cross-linked PGU (Hubina, 2009) revealed its ability to quantitative extraction of phenol and bivalent metal ions from water solution, while controlling capacity

To analyze ability of PGU to phenol sorption from its water solution the pollutant concentration was controlled before and after exposure of PGU20 and PGU60 films in 10-4М phenol water solution during 24, 48 and 120 hours. Phenol concentration was monitored using UV electron spectroscopy by the change of band intensity near 256 nm. Experiment conditions were as follows: T=18 oC, msorbent=7 g, Vsolution=50 ml. Calibration curve was plotted

According to UV-spectroscopy data after 24 hours of exposure PGU in phenol solution increasing of phenol concentration is observed both for PGU20 and PGU60 (Fig.4). Further exposure of PGU in solution leads to essential decreasing of phenol concentration. Such phenol concentrating during PGU interaction with phenol solution can be explained by the

The same character of concentration change is observed while extracting Сu2+ ions from copper sulfate solution. (Fig.5). Its concentration change was controlled using electron spectroscopy in Vis-region by the change in band intensity near 810 nm. That band corresponds to d-d transitions in [Сu(H2O)6]2+aqua ion. Exposure of PGU60 sample in copper sulfate water solution during 10 min. is accompanied by sufficient growth of

Weight loss at this stage is 35, 30, 35 % wt. for PGU80, PGU40, PGU20, respectively.

**Figure 4.** The electron spectra of phenol water solutions: 1 – initial; 2 – PGU60 after 10 min exposure; 3 – PGU20 after 10 min exposure

**Figure 5.** The electron spectra of copper salt water solutions: 1 - initial, 2 - after 10 min of PGU exposure and 3 - after 60 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.

Polyglucanurethanes: Cross-Linked Polyurethanes Based on Microbial Exopolysaccharide Xanthan 439

The results of PGU sorptive properties research in static conditions correspond with the research results obtained under dynamic conditions. Ability of synthesized powdered PGU materials to sorb metal ions in dynamic conditions was examined for CoCl2 and СuSO4 water solutions of various concentration. PGU60 sorbent was used. Concentration of initial and final solutions was controlled using electron spectroscopy in Vis-region by the change of band intensity responding to d-d transitions in aqua ion [Со(H2O)6]2+ and d-d transitions in aquaion [Сu(H2O)6]2+ ( near 510 nm and 810 nm respectively). Calibration graphs were plotted for 0,05; 0,075; 0,1; 0,15, 0,2 М concentrations of CоCl26H2O and CuSO45H2O. Experiment was carried out at 18 oC. Solutions of copper and cobalt salts with initial concentrations of 0,1 М and 0,05 М were pumped through the column filled with the sorbent powder. mPGU=7 g; Vsolution=50 cm3. Under dynamic conditions the time of interaction ranged from 60 to 120

After dynamic contact of copper salt with sorbent during 60 seconds absorbance of filtrate (D) falls to 1,08 in comparison with the initial solution absorbance value of 1,4. It responds to 40% decreasing of copper ions in solution. For 0,1M solution of cobalt chloride after dynamic contact with PGU40 there is observed absorbance fall from 0,52 to 0,48 that responds to extracting of 20% metal ions. For 0,05M solution of cobalt chloride is achieved 40% decreasing of cobalt ion concentration after 60 sec contact. Calculated concentration of cobalt ions in final solutions was 0,08M for initial 0,1M and 0,03M for initial 0,05M. The dynamic sorption of metal ions with PGU40 sorbent is more effective for solutions with

 (a) (b) (c) **Figure 7.** The electron spectra of water solutions of metal salts before (1) and after (2) passing through

According to (Bergmann et al., 2008) the mechanism of ion capture by water soluble polysaccharides mainly related to formation of complexes of chelate structure. Research of complex formation of PGU with metal ions allows conclude of chelate structure of formed

seconds. Fig. 7 illustrates the character of Со2+ and Cu2+ ion sorption.

lower concentration.

**<sup>D</sup> <sup>1</sup>**

the column filled with powdered PGU40

**, nm**

**2**

0 200 400 600 800

0,0

0,4

0,8

1,2

1,6

**Figure 6.** Dependence of solution conductivity *vs* time of sorbent exposure

Similar effect was observed for hot-pressed samples of PGU while interacting with water solutions of phenol and transition metal salts due to predominant swelling of polysaccharide component on the initial stages. Next 12 and 74 hours of PGU exposure result in sufficient solution concentration decreasing due to metal ions capture by the functional groups of sorbent. Equilibrium was achieved both for PGU40 and PGU80 in solutions of high cobalt salt concentration (500 mg/ dm3) while for copper salt solutions equilibrium was achieved for low concentration (50 mg/ dm3).

As table 2 and Fig 6 show the efficiency of metal ions extraction depends on both concentration of solution and the balance of hydroxyl and urethane groups in PGU. The highest concentration fall was observed for PGU80. The solutions of low concentration aren't sensible to hydroxyl and urethane balance in PGU. Besides, the best ion extraction of cobalt ions from low concentration solutions is achieved with short-time exhibition of sorbent. For cobalt salts solutions of high concentration and copper salts solutions of low concentration the best effect is achieved during 74 hours of exhibition.


**Table 2.** Concentration change of cobalt chloride and copper sulfate solutions.

The results of PGU sorptive properties research in static conditions correspond with the research results obtained under dynamic conditions. Ability of synthesized powdered PGU materials to sorb metal ions in dynamic conditions was examined for CoCl2 and СuSO4 water solutions of various concentration. PGU60 sorbent was used. Concentration of initial and final solutions was controlled using electron spectroscopy in Vis-region by the change of band intensity responding to d-d transitions in aqua ion [Со(H2O)6]2+ and d-d transitions in aquaion [Сu(H2O)6]2+ ( near 510 nm and 810 nm respectively). Calibration graphs were plotted for 0,05; 0,075; 0,1; 0,15, 0,2 М concentrations of CоCl26H2O and CuSO45H2O. Experiment was carried out at 18 oC. Solutions of copper and cobalt salts with initial concentrations of 0,1 М and 0,05 М were pumped through the column filled with the sorbent powder. mPGU=7 g; Vsolution=50 cm3. Under dynamic conditions the time of interaction ranged from 60 to 120 seconds. Fig. 7 illustrates the character of Со2+ and Cu2+ ion sorption.

438 Polyurethane

PGU С,

mg/dm3

 1 – СuSO4 500 mg/ dm3 in PGU80, 1 - СоСl2 500 mg/ dm3 in PGU80, 2 - СuSO4 500 mg/ dm3 in PGU40, 2 - СоСl2 500 mg/ dm3 in PGU40 3 - СuSO4 50 mg/ dm3 in PGU80, 3. - СоСl2 50 mg/ dm3 in PGU80, 4. - СuSO4 50 mg/ dm3 in PGU40 4. - СоСl2 50 mg/ dm3 in PGU40

Similar effect was observed for hot-pressed samples of PGU while interacting with water solutions of phenol and transition metal salts due to predominant swelling of polysaccharide component on the initial stages. Next 12 and 74 hours of PGU exposure result in sufficient solution concentration decreasing due to metal ions capture by the functional groups of sorbent. Equilibrium was achieved both for PGU40 and PGU80 in solutions of high cobalt salt concentration (500 mg/ dm3) while for copper salt solutions

As table 2 and Fig 6 show the efficiency of metal ions extraction depends on both concentration of solution and the balance of hydroxyl and urethane groups in PGU. The highest concentration fall was observed for PGU80. The solutions of low concentration aren't sensible to hydroxyl and urethane balance in PGU. Besides, the best ion extraction of cobalt ions from low concentration solutions is achieved with short-time exhibition of sorbent. For cobalt salts solutions of high concentration and copper salts solutions of low

Cu SO4 CoCl2

40 50 20,0 45,3 55,0 11,2 43,4 33,1 80 50 24,2 47,2 48,3 29,2 53,6 36,4 40 500 73,2 84,7 86,4 55,0 58,0 60,0 80 500 63,2 83,2 86,3 55,2 60,7 61,2

С2h , % С12h , % С74h, % С2h , % С12h , % С74h , %

**Figure 6.** Dependence of solution conductivity *vs* time of sorbent exposure

equilibrium was achieved for low concentration (50 mg/ dm3).

concentration the best effect is achieved during 74 hours of exhibition.

**Table 2.** Concentration change of cobalt chloride and copper sulfate solutions.

After dynamic contact of copper salt with sorbent during 60 seconds absorbance of filtrate (D) falls to 1,08 in comparison with the initial solution absorbance value of 1,4. It responds to 40% decreasing of copper ions in solution. For 0,1M solution of cobalt chloride after dynamic contact with PGU40 there is observed absorbance fall from 0,52 to 0,48 that responds to extracting of 20% metal ions. For 0,05M solution of cobalt chloride is achieved 40% decreasing of cobalt ion concentration after 60 sec contact. Calculated concentration of cobalt ions in final solutions was 0,08M for initial 0,1M and 0,03M for initial 0,05M. The dynamic sorption of metal ions with PGU40 sorbent is more effective for solutions with lower concentration.

**Figure 7.** The electron spectra of water solutions of metal salts before (1) and after (2) passing through the column filled with powdered PGU40

According to (Bergmann et al., 2008) the mechanism of ion capture by water soluble polysaccharides mainly related to formation of complexes of chelate structure. Research of complex formation of PGU with metal ions allows conclude of chelate structure of formed complexes. In particular chelate structure of copper ion (2+) complexes with PGU is confirmed in (Hubina et al., 2010). Using results of (Bergman et al., 2008; Hubina et al., 2010) we can assume that cobalt ions also form chelate structures with PGU.

Polyglucanurethanes: Cross-Linked Polyurethanes Based on Microbial Exopolysaccharide Xanthan 441

0,5

1,0

1,5

D,10-9cm2s-1

(a) (b)

Obtained data demonstrate that addition of metal salt to water and increasing of solution concentration decreases the coefficient of water molecules self diffusion in swelled xanthan

That indicates the swelled polymer density growth in presence of metal ions. Such condensation effect can be explained taking into account ability of transition metal chelates to form charge-transfer complexes with electron-donor centers of polymer resulting in creation of additional 'coordination juncs' both in swelled linear polysaccharide and in

Thus, polyglucanurethanes based on water soluble polysaccharide xanthan and blocked polyisocyanate are able to extract heavy metal ions from their salt water solutions. Variation of hydroxyl and urethane groups balance at the cross-linking stage provides effective

Used plastics utilization had become an important problem. One of the ways of polymer and in particular of polyurethane waste reclamation is biodegradation of plastic. The ability

regulation of complexing and capturing of metal ions with polyglucaneurethanes.

**Figure 9.** Dependence of energy broadening of quasi-elastic peak E *vs* squared transferred kinetic moment *q* for various polymer–metal salt ratio (а) and concentration dependencies of D, Dsingl and Dcol (b).

2,0

2,5

012345

C, %

Dcoll

Dsingl

D

For description of experimental dependences there was calculated the values of general coefficient of water self diffusion in swelled gel *D=* Dsingl *+* Dcol as well as values of its Dsingl

(single particle) component and Dcol (collective) component. (Fig 9b).

0 2 4 6 8 10 12

q, A-2

gel both for general coefficient and for its components.

 c=0 c=1% c=2,5% c=5%

0,0

chemically cross-linked PGU.

**5. Biodestruction** 

0,2

0,4

0,6

E, meV

0,8

1,0

1,2

1,4

Analysis influence of cross-linking degree of PGU on complexing metal ions with functional groups of PGU demonstrated that variation of hydroxyl and urethane groups balance in the system allows to achieve effective control over holding metal ions in PGU matrix.

Peculiarities of "PGU-copper ion" complex formation were studied using electron paramagnetic resonance method (EPR). Copper ions were introduced into PGU matrix via pumping of 0,1M water solution of CuSO4 through column filled with PGU60 (the way it described above for dynamic sorption conditions). Then metal-containing PGU sample was dried and the EPR spectra of bivalent copper were recorded. Fig. 8 demonstrates EPR spectrum of dried PGU60 after interaction with copper sulfate water solution.

Recorded spectra are characterized with anisotropy of g-factor and appearance of hyperfine structure in the region of g║ that is usually concerned to tetragonal chelate complexes of bivalent copper. Hyperfine structure components are broadened as a result of superposition of signals from tetragonal copper complexes which can differ both in symmetry distortion and in nearest chemical surrounding. Integral intensity of obtained EPR spectra depends on the balance of hydroxyl and urethane group in PGU while electron spin parameters are almost unchanged. That points on preferable interaction of metal cation with one of the components of PGU. This conclusion corresponds with the regularities of bivalent copper ion complexing with mono saccharides.

**Figure 8.** The representative EPR spectrum of copper containing PGU

Experimental analysis of influence of metal ions on water molecules self diffusion process in swelled polysaccharide gel was carried out by the method of quasi-elastic neutron scattering.

For description of experimental dependences there was calculated the values of general coefficient of water self diffusion in swelled gel *D=* Dsingl *+* Dcol as well as values of its Dsingl (single particle) component and Dcol (collective) component. (Fig 9b).

**Figure 9.** Dependence of energy broadening of quasi-elastic peak E *vs* squared transferred kinetic moment *q* for various polymer–metal salt ratio (а) and concentration dependencies of D, Dsingl and Dcol (b).

Obtained data demonstrate that addition of metal salt to water and increasing of solution concentration decreases the coefficient of water molecules self diffusion in swelled xanthan gel both for general coefficient and for its components.

That indicates the swelled polymer density growth in presence of metal ions. Such condensation effect can be explained taking into account ability of transition metal chelates to form charge-transfer complexes with electron-donor centers of polymer resulting in creation of additional 'coordination juncs' both in swelled linear polysaccharide and in chemically cross-linked PGU.

Thus, polyglucanurethanes based on water soluble polysaccharide xanthan and blocked polyisocyanate are able to extract heavy metal ions from their salt water solutions. Variation of hydroxyl and urethane groups balance at the cross-linking stage provides effective regulation of complexing and capturing of metal ions with polyglucaneurethanes.
