Impact of adsorption of polyaspartic acid and it

Authors: Małgorzata Wiśniewska Iwona Ostolska Dariusz Sternik

Publish Date: 2016/04/28

Volume: 125, Issue: 3, Pages: 1171-1184

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Abstract

The polymer structure impact on the adsorption layer conformation formed on the chromium III oxide surface was investigated As adsorbates three macromolecular compounds were tested polylaspartic acid homopolymer and two block copolymers containing the polyamino acid segments as well as the polyethylene glycol ones in the chain structure Due to the ionic nature of the polyamino acid all measurements were carried out as a function of solution pH value The most probable polymer chain binding mechanism was determined on the basis of the values obtained from the adsorption potentiometric titration turbidimetry and thermogravimetry experiments The acquired results indicate that the solution pH has a great influence on the adsorbed macromolecule conformation Additionally in the case of the block copolymers the individual structural unit affinity for the solid particles can be modified by the pH changes Therefore a significant difference in the mass decrement measured for the systems at pH 3 and 10 can be explained by the contribution of electrostatic forces and hydrogen bond formation to the polymer adsorption mechanism Structure of the adsorbed polymer layer determines also the suspension stability The solid surface charge neutralization by the macromolecules bound to the Cr2O3 surface at pH 3 impairs the sample stability whereas the presence of the extended polymer chains in the basic solution leads to the durability improvementPolymers adsorption at the solid–liquid interface is a very sophisticated process depending on various factors but at the same time this phenomenon finds numerous applications in many industrial branches as well as in human activities 1 2 3 4 However it is a complex process depending on numerous factors related to the macromolecular compound structure nature of adsorbent surface as well as the conditions of the entire process 5 6 7 8Chromium III oxide Cr2O3 is a dark green amorphous powder forming hexagonal crystals on heating that are insoluble in water or acids It is broadly used in many industry branches Cr2O3 finds application in the metallurgical processing of ferrochromium and other metallurgical products to impart corrosion resistance chiefly stainless steel It is one of the most frequently used dyes in the industry Chromium III oxide is applied for coloring a concrete as a stable green pigment for toys plastics and leather The aqueous suspension of Cr2O3 is very popular substance in the production of banknotes and green ink It is also used in paint and ceramic industries a heterogeneous catalyst as well as a coating for providing mechanical and thermal protection Due to the light and chemical resistance chromium III oxide is required for glass ceramics and polymers Moreover Cr2O3 can be used as an ingredient in cosmetics production of eye shadows dye in bronzers lipsticks and cheek rose It is possible due to the fact that this solid is chemically stable under a wide range of solution pH conditions 9 10 11 12The presence of the polymers in aqueous medium has a significant influence on the colloidal system stability As a result of macromolecular compound adsorption the polymer chains assembled on the solid surface modify the interactions present in the system As a consequence two opposite effects can be observed First of all the presence of polymer can increase the particle suspension durability on account of steric or electrosteric stabilization mechanism In the second case the macromolecules adsorbed at the solid–liquid interface lead to a complete system destabilization bridging flocculation depletion interactions or charge neutralization 13 14 Therefore in terms of the applications involving preparation of stable aqueous suspensions as in case of coloring a concrete leather production of banknotes and magnetic composites containing Cr2O3 particles the addition of suitable polymer is necessary to obtain a stable system 15 16 17 18 19 20Searching for new stabilizers the suspensiondestabilizing agents or the surface modifiers has led to the increased interest in copolymers—the compounds consisting of two or more types of structural units connected via a covalent bond All blocks present in the copolymer macromolecules can exhibit a different spatial structure and chain length as well as the opposite ionic character polarity or affinity for the solid surface Hence these substances show considerably different properties compared with those of proper homopolymers which are their building blocks 21 In relation to the applied solution pH conditions the ionic blocks may achieve a variety of conformations at the solid–liquid interface depending on the electrostatic forces occurring in the studied sample Usually under appropriate conditions one of the polymer structural units undergoes a strong adsorption an anchor whereas the other is extended into the bulk solution a buoy 22 23 24 25 26Polyamino acids are a group of synthetic polymers whose backbone is made up of individual amino acid monomers linked by a stable peptide bond Besides the synthetic origin the prepared polymers exhibit a number of important properties relevant to medicine pharmacy and environmental protection First of all the macromolecules are characterized by complete biodegradability and biodegradability Secondly these compounds are characterized by an excellent solubility in water and resistance to pH changes As a result in the future they can replace polymeric substances currently used which are not decomposed in the environment or they are slightly biodegradable 27 28 29Since interactions between various metal oxides and polymers containing only one type of the functional groups were repeatedly tested the copolymer adsorption mechanism on the solid surface should be precisely investigated In the presented paper three different polymers were used as adsorbates the polylaspartic acid homopolymer ASP and two block copolymers containing ASP and polyethylene glycol PEG segments in the chain structure It is worth noting that polyaspartic acid is anionic watersoluble compound Because of the unique properties such as dispersing activity and biodegradability ASP can be used as a component of laundry detergents dishwashing as well as water treatment chemical 28 30 Both the anionic polyamino acid and the nonionic PEG play an important role applied as a dispersing agent not only in the industrial processes but also in biomedicine to obtain stable systems used in MRI probes 27 28 31 32 33The aim of the paper was to investigate the polymer structure impact on the adsorption layer conformation Application of the different types of measurements adsorption potentiometric titration turbidimetry thermogravimetry allows to determine the homopolymer and copolymer binding mechanism at the Cr2O3–polymer solution interface Moreover the conclusions resulting from the comparison of dependencies obtained from different techniques can be very useful due to the potential application of both the solid and the polyamino acid homopolymer or the PEGylated copolymers

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