In environmental applications the applied materials are required to be non-toxic and biodegradable. Carboxymethyl chitosan nanoparticles cross-linked with Ca2+ ions (CMC-Ca) fulfill these requirements, and they are also renewable. These nanoparticles were applied to oil-spill treatment in our previous study and here we focused on enhancing their properties. It was found that while the divalent Ca2+ ions are crucial for the formation of the CMC-Ca, the attractive interaction between NH3+ and COO- groups contributed significantly to the formation and stability of the CMC-Ca. The stability decreased as a function of pH due to the deprotonation of the amino groups. Therefore, the nanoparticles were found to be fundamentally pH sensitive in solution, if the pH deviated from the pH (7-9) that was used in the synthesis of the nanoparticles. The pH sensitive CMC-Ca synthesized in pH 7 and 8 were most stable in the studied conditions and could find applications in oil-spill treatment or controlled-release of substances.

Reinforcing, surface-functionalized cellulose nanocrystals (CNCs) with photoactive groups were obtained from wood cellulose fibers using sequential periodate oxidation and a “click-type” reaction between aldehyde groups and p-aminobenzoic acid in an aqueous environment, followed by mechanical disintegration. In the solution state, CNCs exhibited very high UV-absorption properties, especially in UVA and UVB regions (100% absorption was achieved with only 0.1% of CNCs) and high transparency in the visible light region (around 90% with 0.1% of CNCs). The fabricated CNCs functioned as lightweight-reinforcing fillers with high UV-absorption capability when incorporated into a poly(vinyl alcohol) (PVA) matrix. Complete UVA and UVB opacity of the nanocomposite was achieved using 10% of CNCs while simultaneously retaining over 80% transparency over the whole visible light spectrum. In addition, up to 33% and 77% higher tensile strength and modulus, respectively, were achieved using 10% of CNCs compared to pristine PVA. This result presented a unique way to produce multifunctional CNCs to be incorporated into nanocomposite structures instead of metal nanoparticles. These CNCs are supposed to be suitable for many applications requiring high visible light transparency and blocking of UV radiation.

The emulsification properties of carboxymethyl chitosan (CMChi) and hydrophobically-modified carboxymethyl chitosan (h-CMChi) were studied as a function pH of and dodecane/water ratio. The pH was varied between 6—10, and the oil/water ratio between 0.1—2.0. In CMChi solution, the emulsion stability increased as the pH was lowered from 10 to 7, and the phase inversion was shifted from oil/water ratio 1.0 to 1.8, respectively. The system behaved differently in pH 6 due to the aggregation of CMChi and the formation of nanoparticles (~200—300 nm). No phase inversion was observed and the maximum amount of emulsified oil was reached at oil/water ratio 1.2. The h-CMChi showed similar behavior as a function of pH but, due to hydrophobic modification, the phase inversion was shifted to higher values in pH 7—10. In pH 6, the behavior was similar, but the maximum amount of emulsified oil was higher compared to CMChi. The amount of adsorbed particles correlated with the emulsified amount of oil. Reversible emulsification of dodecane was demonstrated by pH adjustment using CMChi and h-CMChi solutions. The formed emulsions were gel-like, suggesting particle-particle interaction.

Oil spills are the significant sources of hydrocarbons entering in the receiving aquatic environment. An efficient method to remove hydrocarbons from water resources is adsorption. In this study, water soluble N,O-carboxymethyl chitosan (NO-CS) was synthesized by carboxymethylation of chitosan in a hydro-alcoholic medium at 50°C by chloroacetic acid. The polymer was characterized through degree of deacetylation, degree of substitution, FTIR and 1H NMR. Effectiveness of NO-CS as an adsorbent was studied as a function of dosage, salinity and pH to destabilize the Marine diesel (Oil-1), Diesel (Oil-2) and Marine-2T oil (Oil-3) into small oil droplets of less than 100μm. Optical microscope was used for studying the size of oil droplets and adsorption effect of the oils on this polymer. The destabilization of marine diesel was the most effective among the studied three oils, which showed excellent adsorption at sea water alkalinity and salinity.