Juha P. Heiskanen

Amphiphilic cellulose nanocrystals from acid-free oxidative treatment: physicochemical characteristics and use as an oil-water stabilizer.

A chemical pretreatment for producing cellulose nanocrystals (CNCs) with periodate oxidation and reductive amination is reported. This new functionalization of cellulose fibers dispenses an alternative method for fabricating individual CNCs without the widely used acid hydrolysis process. CNCs can be directly modified during the pretreatment step, and no additional post-treatments are required to tune the surface properties. Three butylamine isomers were tested to fabricate CNCs with amphiphilic features. After mechanical homogenization, CNCs occurred as individual crystallinities without aggregation where high uniformity in terms of shape and size was obtained. The elemental analysis and (1)H NMR measurement show that iso- and n-butylamine attach the highest number of butylamino groups to the cellulose fibers. Linking the alkyl groups increases the hydrophobic nature of the CNCs, where water contact angles from self-standing films up to 110.5° are reported. Since these butylamino-functionalized CNCs have hydrophobic characteristics in addition to the hydrophilic backbone of cellulose, the stabilization impact on oil/water emulsions is demonstrated as a potential application.

UV-absorbing cellulose nanocrystals as functional reinforcing fillers in polymer nanocomposite films

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 pH sensitive properties of carboxymethyl chitosan nanoparticles cross-linked with calcium ions

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.

Synthesis of Alkaline-Soluble Cellulose Methyl Carbamate Using a Reactive Deep Eutectic Solvent

This study presents the use of a reactive deep eutectic solvent (DES) for the chemical modification of wood cellulose fibers. DES based on dimethylurea and ZnCl2 was used to synthetize cellulose methyl carbamate (CMeC). This synthesis was performed at elevated temperature under solvent-free conditions. Chemical characterization based on FTIR and NMR indicated that methyl carbamate was successfully introduced to cellulose, and a degree of substitution (DS) of 0.17 was obtained after 3 h of reaction at 150 °C. The product with a DS of 0.17 exhibited good alkaline solubility (in 3 % NaOH solution) after freeze-thawing, whereas the original cellulose fibers were practically insoluble even in 9 % NaOH. As dimethylurea can be produced from CO2 , this method can be used as a sustainable way to obtain novel cellulose materials with desirable properties for use in a wide range of applications.

Synthesis of Benzothiadiazole Derivatives by Applying C–C Cross-Couplings

The benzothiadiazole moiety has been extensively exploited as a building block in the syntheses of efficient organic semiconducting materials during the past decade. In this paper, parallel synthetic routes to benzothiadiazole derivatives, inspired by previous computational findings, are reported. The results presented here show that various C-C cross-couplings of benzothiadiazole, thiophene, and thiazole derivatives can be efficiently performed by applying Xantphos as a ligand of the catalyst system. Moreover, improved and convenient methods to synthesize important chemical building blocks, e.g., 4,7-dibromo-2,1,3-benzothiadiazole, in good to quantitative yields are presented. Additionally, the feasibility of Suzuki-Miyaura and direct coupling methods are compared in the synthesis of target benzothiadiazole derivatives. The computational characterization of the prepared benzothiadiazole derivatives shows that these compounds have planar molecular backbones and the possibility of intramolecular charge transfer upon excitation. The experimental electrochemical and spectroscopic studies reveal that although the compounds have similar electronic and optical properties in solution, they behave differently in solid state due to the different alkyl side-group substitutions in the molecular backbone. These benzothiadiazole derivatives can be potentially used as building blocks in the construction of more advanced small molecule organic semiconductors with acceptor-donor-acceptor motifs.

Effectiveness of N,O-carboxymethyl chitosan on destabilization of Marine Diesel, Diesel and Marine-2T oil for oil spill treatment

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.

Spectroscopic study of a synthesized Alq3 end-capped oligothiophene applied in organic solar cells

In this paper, we report the spectroscopic properties of a synthetically tailored Alq3 end-capped oligothiophene ((Alq3)2-OT) studied by steady state and time resolved spectroscopic methods in chloroform and solid films. In chloroform a photo-induced intramolecular electron transfer from the oligothiophene backbone to the Alq3 moiety was observed. When (Alq3)2-OT was mixed with a fullerene derivative (PCBM) in chloroform, we demonstrate that (Alq3)2-OT donates an electron to PCBM. With that in mind, (Alq3)2-OT was applied as a dopant molecule to improve the efficiency of P3HT:PCBM bulk hetero junction (BHJ) solar cells.

UV-Blocking Synthetic Biopolymer from Biomass-Based Bifuran Diester and Ethylene Glycol

A furan-based synthetic biopolymer composed of a bifuran monomer and ethylene glycol was synthesized through melt polycondensation, and the resulting polyester was found to have promising thermal and mechanical properties. The bifuran monomer, dimethyl 2,2′-bifuran-5,5′-dicarboxylate, was prepared using a palladium-catalyzed, phosphine ligand-free direct coupling protocol. A titanium-catalyzed polycondensation procedure was found effective at polymerizing the bifuran monomer with ethylene glycol. The prepared bifuran polyester exhibited several intriguing properties including high tensile modulus. In addition, the bifuran monomer furnished the polyester with a relatively high glass transition temperature. Films prepared from the new polyester also had excellent oxygen and water barrier properties, which were found to be superior to those of poly(ethylene terephthalate). Moreover, the novel polyester also has good ultraviolet radiation blocking properties.

Carboxymethyl Chitosan and Its Hydrophobically Modified Derivative as pH-Switchable Emulsifiers

The emulsification properties of carboxymethyl chitosan (CMChi) and hydrophobically modified carboxymethyl chitosan (h-CMChi) were studied as a function of pH 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.