THERMODYNAMICS OF INTERACTION IN POLYMER SYSTEMS BASED ON CELLULOSE DERIVATIVES

ABSTRACT

On the base of sorption isotherms of water and benzole vapours in light of thermodynamical theorise of polymer solutions some thermodinamical functions of macromolecular interaction in polymer systems esters of cellulose-proteins able to interpolymer complexoformation owing of cooperative interactions of functional groups have been calculated. Obtained results have shown that such thermodinamical functions as ∆g^m, χ_is, ∆G_i, G₁₁/V₁, ∆g_x capillary-porous characteristics of initial components and also parameters of interactions polymer- polymer-solvent according to Flory-Scott,Krause and Pattersond  have indicated that investigated systems are thermodynamically compatible in all range of investigated compositions.

АННОТАЦИЯ

На основе изотерм сорбции паров воды и бензола в свете термодинамической теории растворов полимеров рассчитаны некоторые термодинамические функции макромолекулярного взаимодействия в полимерных системах сложных эфиров целлюлоза-белки, способных к интерполимерному комплексообразованию за счет кооперативного взаимодействия функциональных групп. Полученные результаты показали, что такие термодинамические функции, как ∆g^m, χ_is, DG₁₁/`V₁, ∆g_x, капиллярно-пористые характеристики исходных компонентов, а также параметры взаимодействия полимер-полимер-растворитель по Флори-Скотту, Краузе и Паттерсону имеют указали, что исследуемые системы термодинамически совместимы во всем диапазоне исследуемых составов.

Keywords: sorbtion, isotherma, Flory-Scott, Krause, Pattersond, polymer – solvent, polymer – polymer – solvent, polymer – polymer, esters of cellulose, proteins.

Ключевые слова: сорбция, изотермы, Флори-Скотт, Краузе, Паттерсон, полимер-растворитель, полимер-полимер-растворитель, полимер-полимер, эфиров целлюлозы, белок,

Introduction: At present time attention of investigators is directed towards the achievement of synergism properties and obtaining polymers with unique properties. An important role is devoted to the conformational state of molecules in solutions and intensity of intermolecular interactions in systems polymer – solvent and polymer – polymer – solvent.

Elaboration of compositional materials with the new complex of physico - chemical properties and structural features is an actual problem in solving some of practical problems related to sorption, catalysis, electronics etc. Special attention is devanted to using of natural macromolecular compounds in particular – polysaccharides such as cellulose and it’s esters as well as their biodegradable mixtures with starch [12], decstrine and polymer – polymer compositional complexes with such proteins as collagen, gelatin and albumin obtained on the base of cooperative macromolecular reactions. Important role is devoted to water – soluble cellulose ethers, which are commonly used for stabilization of suspensions, emulgation and thickening and also fibers, composites obtained from them. Cellulose ethers valuable owing to a number of their specific properties and from them by saponification hydrocellulose can be obtained and unlike ordinary ethers of cellulose they have dissolved in water. Also methods of obtaining cross – linked films by them and possibilities of using water - soluble acetates of cellulose for obtaining medicine preparates as a binding compounds, tablets and also for increasing indestructible properties of fabrics are known [7].

Application of polysaccharides in many different areas of human vital activities required investigation of the processes of their interaction with environment [8, 9]. An important place is devoted to investigation of interaction of polysaccharides with water, which had allowed to elucidate the thermodynamical causes of biocompatibility, stability and biodestruction of polysaccharides. Many polymers in the environment have decompose during a long time and so the elaboration of biodegradable materials is important task. Materials based on mixtures of natural polymers cause a great interest because they can be used in medical practice, pharmaceutics, food and chemical industries for creation of new ecologically safe materials [13].

Experimental Part. Objects of research

The objects of investigation are water-soluble acetylcellulose (WSAC), oxidized 0-WSAC synthesized at the department of chemistry of natural compounds in the chemistry faculty at National University of Uzbekistan named after Mirzo Ulugbek.

WSAC is a white powder, without odour with characteristical viscosity η =1.538.

0-WSAC is a white powder, odorless with characteristical viscosity η = 1,420.

Samples of carboxymethylcellulose (CMC), it’s sodium salt (NaCMC) with degree of substitution 70,0 and 80,0; degree of polymerization 450 were presented by prof. G. R. Rahmanberdiev and samples with degree of substitution from 5.0 to 85.0 were presented by prof. Sarymsakov A.A.

Collagen is the main fibrillar connective protein tissues that performs the most important functions in the body. Molecular mass equals 300000. Collagen was presented by prof. Kadirov T.J.

Albumin is a simple protein soluble in water and salt solutions. Albumin was presented by prof. Kasymov Sh.

Gelatin is colorless or light yellow, tasteless and odorless powder with molecular mass higher 300,000; it has swallowed in cold water and dilute acids, but does not dissolve. Gelatin is a natural biopolymer, product of destruction of collagen. Photogelatine is obtained from collagen and they are modified polypeptide chains of collagen, usually referred to α – ferment chains retain the amino acid sequence of collagen with the exception of telopeptides which are separated from polypeptide processes of collagen obtaining. Other fractions have appeared as a result of more or less random crosslinking and destruction of peptide bonds in α – chains.

The method of isothermal sorption

For investigation the sorption properties of various celluloses and their ethers a high-vacuum sorption instillation was used.

The middle free energy of polymer-solvent mixing  was calculated according to equation:

                                     (1)

By calculating the values  for all relative pressures of steams graph of dependence on =, has been constructed and by which the thermodynamic potential of Gibbs  which is a measure of affinity between solvent and polymer has been determined.

Also the values of the thermodynamical parameters of interactions in system polymer-solvent of Flory-Haggains have been calculated:

         (2)

The function of cluster formation was calculated by the equation of Zimm - Landberg:

         (3)

The quantity of equilibrium sorbed water was determined by the theory of De Bura and Zwicker applying the equation:

lglg(      (4)

Value of interaction in system polymer - polymer has been calculated by equation:

            (5)

The polymer polymer  solvent interaction parameter was calculated by the equation of FlorryScott:

    (6)

The average free energy of mixing polymer  polymer has been calculated by equation of Krause:

             (7)

or by Patterson's equation:

            (8)

Pycnometrical investigations of the samples were carried out in systems, ethalone heptane and water-solvent, which have moisted cellulose. On the base of pycnometrical studies and theoretical calculations the coefficients of molecular packing in the "walls" of pores, which are measure of density and packing of macromolecules, have been calculated.

RESULTS AND THEIR DISCUSSION

Thermodynamic analysis of interaction of water soluble ethers and esters of cellulose with water and benzene has been carried out. Sorption investigations have shown that isotherms of sorption of investigated samples have S-figured type with salient initial part characterized for frially-pahked-chain polymers which is caused by simultaneously carrying out processes of physical adsorption of sorbate in frialke fields of polymer and it’s swelling in sorbate. It is known that, sorption isotherms have given only qualitative information of interactions in system polymer-solvent and hydrophylity of investigated samples. Sample of NaCMC with the degree of substitution 70 has the highest sorption ability. Calculation of the parameter of interaction χ_is by theory Flory-Haggins also has indicated on the best interaction of water with NaCMC with degree of substitution 70 (value of χ_is is changed in limits from -0,44 to -0,25 in dependence of concentration NaCMC). This calculation was proved by calculations of the diffusional [3, 4] coefficient (γ) , concentration dependence. Deff. for NaCMC (degree of substitution 70%) by uniform increasing of volume part of solvent has changed uniformly but for sample with SD=80 charp maximum at φ_s=0,15 has been observed. Calculations by theory Zimm-Landberg have shown absence of claster-formation for these samples of NaCMC in all interval of activities of water steams.

Comparative sorption investigations of different esters of cellulose have shown that CMC and o-WSAC have possessed by smallest sorption ability and samples of WSAC and NaCMC have the highest sorption ability that is they in best degree have interacted with solvent. These results were proved by calculations of interaction parameter of polymer-solvent χ_is of Flory-Haggins (fig.) which have indicated on better interaction in system WSAC, NaCMC-water.

Theory of solutions of polymers Flory-Haggins was used at consideration of experimental data in sorption equilibrium in systems cellulose or its derivatives – water. In most cases these investigations have been limited by calculation by experimental data of the parameter of interaction χ_is from activity of water steams.

Figure 1. Dependence of parameter of thermodynamic affinity χ_is from activity of water steams for samples: WSAC (1), o-WSAC (2), CMC (3) and NaCMC (4) at 298 K

Described changes are various what is connected with deviation of structure of real solution from such in initial model about what high values of χ_is are witnessed. For quantitative value of the thermodynamic activity of system CMC, NaCMC, WSAC, o-WSAC with water and benzene the middle free energies of mixing polymer-solvent Δg^m were calculated on the base of the chemical potentials of solvent Δµ_i and polymer Δµ_r and by concentration dependence Δg^m potentials ΔG. were found. From table 1 it is shown that WCAS and NaCMC have possessed by more negative values of Gibbs energy in water, what was proved by values of parameter Flory-Haggins.

Table 1.

The middle free energies of mixing and Gibbs energies calculated by isotherms of sorption of steams of water and benzene

Calculations have shown that capacity of monolayer and specific “water” surface for sample WSAC-water [10] have a high values but radius of pores has possessed the lowest values. Real values of capillary-porous structure of samples didn’t complicated by interaction with solvent and their swelling can be obtained by sorption data of benzene. Values of X_m and S_sp for investigated samples by benzene are near but radius of pores has possessed by highest value for WSAC. Differences in values of r_middle obviously is connected with high intensity of interaction in system WSAC-water what is proved by high negative values of Δg^m and ΔG. By results of sorption investigations samples can be presented in raw by decreasing of monolayer and the specific “water” surface: WSAC, NACMC, o-WSAC, CMC and by real specific surface in raw: o-WSAC, NaCMC, CMC, WSAC. From this is followed that o-WSAC and NaCMC have possessed by microporous structure with relatively high values of capacity of monolayer and the specific surface.

It is noted that esters of cellulose are used in medical practice namely at production of medicals. Between wide class of water-soluble esters of cellulose WSAC is a base for obtaining medicals of prolonged action. Compositions on the base of WSAC and collagen also are presented interest as film and spongy resolving materials in callogenoplastics. Sorption investigations of compositions have shown that isotherms of sorption of water steams by samples of WSAC, collagen and their mixtures of different composition have S-figuratively type. Initial samples of WSAC and collagen have the most sorption ability. For mixtures of WSAC-collagen in all interval of relative pressures low sorption ability in comparison with initial polymers has been observed. In this case interaction of polymer-polymer was prevailed under interactions polymer-solvent that is it was observed the phenomenon of compatibility of macromolecules of different nature. Middle free energies of mixing polymer-solvent Δg^m and values of Δg^m_max are less negative what has indicated on decreasing interactions polymer-solvent and increasing intermacromolecular interactions of different chemical nature.

On the base of sorption isotherms of water steams values of parameter Flory-Haggins were calculated for samples WSAC-collagen of different composition, characterizing interaction of polymers with solvent. Investigation has shown that compositions have more higher values of parameter χ in comparison with initial WSAC and collagen what has indicated on worsening of interaction of solvent with mixtures of different compositions. Mixture WSAC-collagen at ratio of components 1:3 has microporous structure with relative high values of capacity of monolayer X_m and special surface S_sp and with decreasing of collagen in mixture the improvement of multysolubility of polymeric components was observed. It was shown that values of the middle free energy of mixing polymer-solvent Δg^m and Gibbs energy ΔG in the case of systems WSAC-collagen at ratio of components 1:1 and 3:1 are less negative but values of parameter of interaction polymer-solvent Flory-Haggins at middle relative pressures of water steams are more positive in comparison with initial polymers [14].

Analysis of experimental data according to theory Zimma-Landberg has been carried out and it gave information about mechanism of sorption of water steams and has allowed to value trends to formation of clusters of water molecules in process of their absorption by polymers. In corresponding with theory at DG_II/V_I³-1 molecules of water are aggregated in clusters. For systems WSAC, collagen, WSAC-collagen at ratio of components 1:3 value of function of cluster-formation has transported in positive range at activity of water steams Р_i/P_i⁰=0,2-0,6; what has indicated on the beginning of formation of clusters in field Р_i/P_i⁰=0,2. For systems WSAC-collagen-water at ratio of components 1:1 and 3:1 at middle relative pressures of water steams the negative values of function of cluster-formation have been observed witnessing about good interaction of water molecules with macromolecules. Results of investigations have witnessed that for investigated samples cluster-formation was observed only in range of middle activity of water steams what is coordinated with literature data by claster formation in hydrophilic polar polymers. Cluster formation in range of low relative pressures is connected with formation of hydrogen bonds polymer-water and water-water.

Adsorption theory [15] of De Bur and Zviker elaborated for processes interaction of polymer sorbates with polar sorbents can be used for systems WSAC-collagen-water. It can be used for processes of water bonding by adsorption and absorption mechanisms. Results of experimental checking of equation of De Bur and Zviker have shown linearization of isotherm of sorption of water steams and allowed to determine value of “true” sorption didn’t complicated by capillary condensation and clusterization of water. It is shown from them that in the field of relative pressure Р_i/P_i⁰<0,75 for system WSAC-collagen-water isotherms are linear. For systems WSAC and WSAC-collagen at ratio of components 1:1 linearization was observed and isotherms were practically linear in all range of the relative pressures. In accordance with theory of De Bur and Zviker this fact means that is stated range of activities by WSAC and WSAC-collagen (1:1) there is not “free” water that is it all sorbited by active groups of polymers. For these samples values of the parameter Zimm-Landberg are negative and cluster-formation didn’t observed in all range of the relative pressures.

Values of the middle free energy of mixing polymer-polymer Δg_x were calculated by method of Tager which for all compositions of mixtures WSAC-collagen are negative what is witnessed about thermodynamic stability of investigated systems. Conclusions obtained on the base of calculations Δg_x from composition of mixtures WSAC-collagen were proved by calculations of parameter of interaction in system polymer-polymer-solvent by theory of mixing Flory-Scott.

In medical relation system NaCMC-dextran is interested. It is known that solutions of dextran are used as thermodynamic mediums. Water-soluble CMC has promoted increasing and prolongation of dextran properties and by this reason it is important to have data about thermodynamic compatibility of this system. Thermodynamic investigations [11] has allowed to reveal of biocompatibility and biodegradation of investigated polymes systems. Also it is very important to investigate interactions such systems with water. Thermodynamic calculations on the base of modern theories of solutions have shown that system NaCMC-dextran is one-phase and compatibile in all interval of it’s compositions.

Mixtures of NaCMC and starch are very perspective because they can be used as biodegradated systems. Thermodynamic investigations NaCMC-MS have shown a compatibility of this system at low concentrations of NaCMC and with increasing of its content the system has became metastable. By this reason at elaboration of biodegradable materials optimal compositions of mixtures were prepared with small content of NaCMC.

System NaCMC-collagen can be very perspective from point of view of physiologic activity and film-forming properties of collagen. However the thermodynamic compatibility of collagen with derivatives of cellulose practically did not investigated; there are not experimental data about intermolecular interaction between polymeric components in such systems. Investigations have shown that initial polymers and compositions NaCMC-collagen (3:1) have possessed by the maximal sorption ability according to water in all range of the relative pressure that is they in better degree have interacted with solvent; compositions at others ratios of components have low sorption ability.

Interpolymeric compositions NaCMC-collagen are characterized by more high values of parameter χ_is in comparison with initial samples what has indicated of worsening interaction with solvent of mixtures of different compositions. These results are proved by calculations of the middle free energy of mixing Δg^m in systems of polymer-polymer and polymer-polymer-solvent [1].

For mixtures of different compositions Δg^m_max has possessed less negative values in comparison with initial samples of NaCMC and protein.

Explanation of so different types of concentration dependence is connected with energetic interactions of water with polar groups of polymeric matrix or molecular structure of polymer sorbent or also by formation of clusters of water molecules in polymer.

Beginning of clusterisation and value of forming aggregates is possible to determine from theory Zimm-Landberg. From the point of view of state water molecules in polymer matrix isotherms of sorption are divided on two zones: zone of solubility and zone of formation of clusters. Dimensions of clusters are determined by value 1+j G₁₁/, which equal excess of middle member moleculaes of sorbate near this molecule.

Calculations of the function of clusterization for initial polymers and IPC of different compositions have shown that practically in all cases values of function of cluster-formation have negative values <-1 what has witnessed about absence of process clusterization in system NaCMC-collagen of different compositions. Values of the middle free energy of mixing polymer-polymer Δg_x, by equation Tagger parameters of interaction χ₁₂, by Flory-Scott, Grayze and Patterson and also function of clusterization Zimm-Landberg are presented in table 2.

Table 2.

Thermodynamic parameters of interaction in systems polymer-solvent, polymer-polymer-solvent, polymer-polymer and functions of clusterization Zimm-Landberg

It is known that if Dg_x<0, than investigated system is thermodynamically compatible. As shown from table 2 values of the middle free energy of mixing polymer-polymer Dg_x and parameter of interaction polymer-polymer-solvent χ_12s depending on composition of mixture NaCMC-collagen have possessed negative values what is indicated on thermodynamical compatibility of this system.

Analysis of dependence values Dg_x on compositions of system NaCMC-collagen also has shown that at low contents one of components system is thermodynamically more stable in comparison with mixtures with approximately equal quantities of components. In this range of compositions it was observed metastable state. Dependence of the parameter χ_12s on composition of mixture and also values of parameter of interactions polymer-polymer by Patterson and Crause have proved conclusions obtained by method of Tager [2].

Also systems NaCMC-albumine and NaCMC-jelative, which at incraction can formed IPC, have been investigated. The importent value is devoted to thermodinamical compatibilits of NaCMC with blood components and also it is necessery to note that system NaCMC-jelatine can be used as hemostatic means  and also ability of jelatine to selforganisation can be used at elaboration of therapeftic systems. Thermodinamical investigation have shown compatibility of these systems in all range of compositions.

It is shown that special interest of investigators working in construction of preparates of medicine is devoted to cellulose and it’s hydrophilic water-soluble derivatives namely simple ethers and esters. High solubility in water, simplicity of obtaining and physiologic in differentation of esters of cellulose have provided their relative harmfulness. It is necessary to note that they are used in medicine practice namely at production of medicine drugs. Water soluble esters of cellulose [5, 6] WSAC and NaCMC are a base for obtaining medicine drugs of prolonged action. The special attention is devoted to multicomponent systems on their base such as their mixtures, IPC. It is caused by fact that IPC have a complex of universal properties and they can be examine as a new class of polymer materials which are perspective at using in medicine, bio- and membrane technologies. Mixtures of polymers and IPC can be perspective from the point of their biodegradation, improvement of physiologic activity and also of film-forming properties of individual natural polymers and proteins.

Thus on the base of experimental investigations of thermodynamic and physico-chemical properties optimal compositions and conditions of obtaining of mixtures of polymers, IPC an composition materials have been elaborated and fields of their application have been determined:

-biodecomposed polymer materials on the base of compositions of water-soluble ethers and esters of cellulose with such proteins as collagen, albumin and gelatin have been elaborated;

-film-forming and physico-mechanical properties of collagen have been improved by elaboration of compositions with WSAC which were proposed for using in collagenoplastic and at elaboration of properties of antiseptic action accelerating processes of regeneration of own tissues of organisms.

CONCLUSIONS

1. The “water” and “real” specific surface and porosity of different esters of cellulose were determined and also was shown that investigated samples can be disposed in following raw of decreasing by capacity of monolayer and the specific “water” surface: WSAC, NaCMC, o-WSAC, CMC and by “real” specific surface: o-WSAC, NaCMC, CMC, WSAC.

2. The thermodynamic stability and optimal composition with best film-forming properties of system WSAC-collagen were determined which has important applied importance in medicine at elaboration of increasing processes of regeneration; drugs of prolonged action. It was shown that for this system a negative values of function of cluster-forming, middle free energy of mixing polymer-polymer and parameter Flory-Scott were observed. Calculations by theory De Bur and Zviker have shown linear dependence of isotherm practically in all range of relative pressures what has indicated on absence of “free” water and that sorption didn’t complicated by process of capillary condensation and clusterization.

4. In accordance with modern thermodynamic theories of polymer solutions parameters of macromolecular interaction in polymeric systems NaCMC-collagen, NaCMC-albumine and NaCMC-gelatine able to interpolymeric complex-formation owing to cooperative interactions of functional groups and formation of nanocompositions. On the base of determination of such thermodynamic functions as ∆g^m, χ_is, ∆G_i, G₁₁/V₁, ∆g^x and also parameters of interaction polymer-polymer-solvent by Flory-Scott, Crause and Patterson the thermodynamic compatibility of investigated systems in all range of compositions has been shown.

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