Influences of polyacrylic acid adsorption and temperature on the alumina suspension stability
Graphical abstract
The adsorption of polyacrylic acid causes destabilization of the alumina suspension in the 15–35 °C temperature range. Such effect is the lowest at 25 °C. The presence of PAA 2 000 in the system causes its coagulation by charge neutralization while the adsorption of PAA 240 000 favors the bridging flocculation.
Introduction
The stabilization–flocculation properties of polymers find a wide practical application in many technological and ecological processes. Purification of drinking and industrial waters requires the use of high molecular weight polymer to cause the flocculation process of a dispersed suspension of contaminants. On the other hand, production of pigments, cosmetics, pharmaceuticals, and paper requires high stability of these systems, which can be obtained by the addition of low molecular weight polymer. Polyelectrolytes, including polyacrylic acid are especially appropriate for these purposes, because in this case the suspension stability can be controlled by both steric and electrostatic forces.
The stabilization and flocculation processes of colloidal suspension in the presence of macromolecules depend on their conformation both on the solid surface and in the bulk solution. Many parameters influence the polymer chain conformation. The most important are: type of polymer — ionic and nonionic, its molecular weight and polydispersity, type of adsorbent surface groups and degree of its purity as well as pH and ionic strength of the solution and temperature.
Temperature increase leads to changes in the polymer chain conformation (increase of the linear dimensions of macromolecules) and can cause changes in solid surface characteristics (changes of surface and diffuse layer charge densities, shift of pHpzc and pHiep points).
Thus, the colloidal system stability in the presence of polymer can be successfully controlled by appropriate choice of temperature conditions.
Evans [1] distinguished three types of steric stabilization. They are: entropic, enthalpic and combined enthalpic–entropic stabilizations. Stabilization–flocculation properties of the system depend on respective enthalpy and entropy contributions to the free energy. The transition from one type of stabilization to another can be obtained by the changes in temperature and the addition of the nonsolvent to the system. Even small changes in temperature lead from the stable to the unstable region and rapid flocculation takes place [2].
Nevertheless, the effect of temperature on structure of polymer adsorption layer on the solid surface has not been fully discussed in literature so far [3], [4].
The aim of this study was to determine the influence of polyacrylic acid (PAA) on the stability of Al2O3 suspension in the temperature range 15–35 °C. The stabilities of the investigated systems were measured with Turbiscan LabExpert, which simultaneously registers light transmission and light backscattering on the dispersed solid particles. Additionally, at 25 °C the suspension stability was determined using a spectrophotometer Specord M52 from the absorbance changes. This study is the continuation and kind of supplement of the previous studies concerning the temperature influence on the adsorbed amounts, polymer layer thicknesses and free energies of PAA adsorption on the alumina surface [5], [6], [7].
Both polyacrylic acid and alumina find wide practical applications in industry and environment protection. PAA is a very popular stabilizer in the production processes of pigments, paints, cosmetics, pharmaceuticals and paper. Moreover, it is often used as flocculent in recycling of hazardous wastes as well as purification of drinking and technological waters [8], [9]. Alumina also finds wide usage in water treatment technology in the removal process of dissolved hazardous organic contaminants [10]. Besides, Al2O3 is the catalyst of ozonation and wet air oxidation processes [11].
Section snippets
Materials
The samples of crystalline γ-Al2O3 (Merck) were used in the experiments. Aluminum oxide was washed with doubly distilled water to achieve the supernatant conductivity less than 2 μS/cm. The BET specific surface area of Al2O3 was equal to 155 m2/g. The average pore diameter of the alumina was 6.1 nm. The mean grain size of solid particles, obtained from the electrokinetic measurements was 496 nm. Moreover, alumina is characterized by the following physicochemical properties: minimal solubility, high
Results and discussion
Table 1 shows the parameters characterizing PAA macromolecules conformation in the solution and its adsorbed layers on the Al2O3 surface at different temperatures. These data were presented in detail in previous papers [5], [6], [7] and in the present manuscript the most important of them were compiled in the form of a table. The analysis of the data in Table 1 is very important for explanation of the obtained results from the stability measurements.
The transmission and backscattering curves at
Conclusions
The temperature effect on the stabilization–destabilization properties of the alumina (Al2O3)–polyacrylic acid (PAA) systems was studied.
The data obtained by the use of Turbiscan LabExpert and the calculated values of Turbiscan Stability Indexes (TSI) indicate that the addition of PAA causes lowering of the alumina suspension stability towards settling at both 15 and 35 °C. On the other hand, at 25 °C the polymer adsorption improves insignificantly the stability of Al2O3 suspension.
The
Acknowledgment
This work was supported by MNiSW, grant N204 071 32/1869 in the years 2007–2010.
References (20)
- et al.
J. Eur. Ceram. Soc.
(1997) - et al.
J. Colloid Interface Sci.
(2004) - et al.
J. Colloid Interface Sci.
(2009) J. Colloid Interface Sci.
(1977)- et al.
J. Colloid Interface Sci.
(1974) - et al.
Powder Technol.
(2004) - et al.
J. Colloid Interface Sci.
(2002) - et al.
Colloids Surf.
(2000) Adv. Colloid Interface Sci.
(2004)- R. Evans, PhD Thesis, University of Sydney,...
Cited by (81)
Investigation into the influence of droplet size on the stability of diesel emulsions based on multiple light scattering
2023, Journal of Molecular LiquidsPumpkin and kale fibers - A potential hydrocolloids in processed cheese sauce formulations with different fat source
2022, LWTCitation Excerpt :The exemplary results representing all the performed measurements are presented in Fig. 3. The TSI represents the measured value of stability between different samples (Wiśniewska, 2010). The higher TSI value the higher destabilization kinetics of the tested samples (Huang et al., 2021).
Experimental Study on the Effect of Nanoparticle Migration on the Convective Heat Transfer Coefficient of EG/Water-based Al<inf>2</inf>O<inf>3</inf> Nanofluids
2021, International Journal of Heat and Mass TransferPreparation and characterization of an oil-in-water microemulsion of thiamethoxam and acetamiprid without organic solvent for unmanned aerial vehicle spraying
2020, Colloids and Surfaces A: Physicochemical and Engineering AspectsInvestigating the synergetic dispersing effect of hydrolyzed biomacromolecule Cellulase and SDS on CuPc pigment
2019, Colloids and Surfaces B: Biointerfaces