Obtenção de polímeros graftizados de quitosana e estudo daspropriedades físico-químicas para aplicação na indústria do petróleo

摘要

Chitosan is a biopolymer derived from the shells of crustaceans, biodegradable,inexpensive and renewable with important physical and chemical properties. Moreover, thedifferent modifications possible in its chemical structure generate new properties, making itan attractive polysaccharide owing to its range of potential applications. Polymers have beenused in oil production operations. However, growing concern over environmental constraintshas prompted oil industry to search for environmentally sustainable materials. As such, thisstudy sought to obtain chitosan derivatives grafted with hydrophilic (poly(ethylene glycol),mPEG) and/or hydrophobic groups (n-dodecyl) via a simple (one-pot) method and evaluatetheir physicochemical properties as a function of varying pH using rheology, small-angle Xrayscattering (SAXS), dynamic light scattering (DLS) and zeta potential. The chitosanderivatives were prepared using reductive alkylation under mild reaction conditions and thechemical structure of the polymers was characterized by nuclear magnetic resonance (1HNMR) and CHN elemental analysis. Considering a constant mPEG/Chitosan molar ratio onmodification of chitosan, the solubility of the polymer across a wide pH range (acidic, neutraland basic) could only be improved when some of the amino groups were submitted toreacetylation using the one-pot method. Under these conditions, solubility is maintained evenwith the simultaneous insertion of n-dodecyl. On the other hand, the solubility of derivativesobtained only through mPEG incorporation using the traditional methodology, or with the ndodecylgroup, was similar to that of its precursor. The hydrophilic group promoted decreasedviscosity of the polymer solutions at 10 g/L in acid medium. However, at basic pH, bothviscosity and thermal stability increased, as well as exhibited a pronounced pseudoplasticbehavior, suggesting strong intermolecular associations in the alkaline medium. The SAXSresults showed a polyelectrolyte behavior with the decrease in pH for the polymer systems.DLS analyses revealed that although the dilute polymer solutions at 1 g/L and pH 3 exhibiteda high density of protonated amino groups along the polymer chain, the high degree of chargecontributed significantly to aggregation, promoting increased particle size with the decrease inpH. Furthermore, the hydrophobic group also contributed to increasing the size of aggregatesin solution at pH 3, whereas the hydrophilic group helped reduce their size across the entirepH range. Nevertheless, the nature of aggregation was dependent on the pH of the medium.Zeta potential results indicated that its values do not depend solely on the surface charge ofthe particle, but are also dependent on the net charge of the medium. In this study, water soluble associative polymers exhibit properties that can be of great interest in the petroleumindustry