Algirdas Zemaitaitis

The role of anionic substances in removal of textile dyes from solutions using cationic flocculant

The mechanism of dye removal from textile waste water using polyquaternary ammonium salt as a flocculant has been proposed. It was shown that the cationic polymer tends to react with anionic textile finishing chemicals and auxiliaries (anionic detergents, dispersing agents, thickeners), forming intermolecular complexes of different stoichiometry. Under controlled conditions these complexes are able to incorporate the dye ions or molecules and precipitate together. Formation of triple complexes is postulated to be the only possible way for non-ionic dyes to be precipitated. The nature of forces causing the transfer of the dyes to a polymeric matrix has been revealed. The necessity of an anionic polyfunctional compound with a proper chemical structure to play the role of disperse dye carrier is emphasised. The mechanism of incorporation of dye ions into triple complexes, the possibility of competitive reactions, and the problems of stability and reduced cationic functionality of nonstoichiometric complexes are discussed.

Adsorption of hexavalent chromium on cationic cross-linked starches of different botanic origins.

The influence of origin of native starch used to obtain cationic cross-linked starch (CCS) on the adsorption of Cr(VI) onto CCS has been investigated. CCS granule size is influenced by the botanic source of native starch. The equilibrium adsorption of Cr(VI) onto CCS was described by the Langmuir, Freundlich, Dubinin-Radushkevich and Temkin models. The more equal the adsorption energy of the quaternary ammonium groups in CCS granule as indicated by low value of change of Temkin adsorption energy DeltaE(T) the greater amount of Cr(VI) was adsorbed onto CCS. The value of DeltaE(T) decreased and sorption capacity of CCS increased with the decrease of CCS granule size and with the increase of number of amorphous regions in CCS granules. The affinity of dichromate anions increases and adsorption proceeds more spontaneously when Cr(VI) is adsorbed onto more amorphous CCS. Adsorption process of Cr(VI) onto such CCS is more exothermic and order of system undergoes major changes during adsorption. After the adsorption on CCS Cr(VI) could be regenerated by incineration at temperature of 800 degrees C.

Cationic starch nanoparticles based on polyelectrolyte complexes.

Cationic starch nanoparticles were obtained by aqueous polyelectrolyte complex formation between cationic quaternary ammonium substituted starches and anionic sodium tripolyphosphate. The formation of nanosized starch particles of spherical shape was verified by dynamic light scattering and scanning electron microscopy measurements. The cationic starch nanoparticles of different constitution and containing various contents of free quaternary ammonium groups were produced and their zeta potential was modulated between +4 mV and +34 mV by varying polycation/polyanion ratio. Furthermore, the polyelectrolyte complex formation was confirmed by differential scanning calorimetry and FTIR analyses. The thermal stability of cationic starch nanoparticles increased with the introduction of polysalt into polyelectrolyte complex. The solubilization capacity of nanoparticles was varying with the concentration and composition as revealed by fluorescence probe experiments. The capability to accommodate hydrophobic pyrene quest molecule was decreasing with the increasing number of cationic groups in cationic starches and little depended on polyanion/polycation ratio in starch nanoparticles.

Preparation, stability and antimicrobial activity of cationic cross-linked starch–iodine complexes

Cationic cross-linked starch (CCS)-iodine complexes containing different amounts of quaternary ammonium groups (different degrees of substitution (DS)) and iodine have been obtained by iodine adsorption on CCS from aqueous iodine potassium iodide solution. Equilibrium adsorption studies showed that with an increase of DS the amount of iodine adsorbed on CCS and the affinity of iodine to CCS increased linearly. The influences of the DS of CCS and the amount of adsorbed iodine on the stability of CCS-iodine complexes in a solution of 0.02M sodium acetate and reactivity toward l-tyrosine have been investigated. At the same DS, the stability of CCS-iodine complexes decreased with an increase of the amount of adsorbed iodine. With increasing the DS, the stability of CCS-iodine complexes increased. The iodine consumption in the reaction with l-tyrosine increased significantly with an increase of the amount of adsorbed iodine. The influence of DS on iodine consumption was lower and depended on the amount of adsorbed iodine. The antibacterial activity of CCS-iodine complexes against Bacillus cereus, Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli was determined by the broth-dilution and spread-plate methods. The obtained results have demonstrated that an appropriate selection of the CCS-iodine complex composition (the DS of CCS and the amount of adsorbed iodine) could ensure good antimicrobial properties by keeping a low concentration of free iodine in the system. The main advantage of using CCS-iodine complexes as antimicrobial agents is the biodegradability of the polymeric matrix.

A novel way to obtain effective cationic starch flocculants

AbstractA novel way to obtain an effective flocculant based on biodegradable starch was found. The medium-substituted (DS from 0.10 to 0.54) cationic starches (CS) with preserved microgranular form was synthesised by the reaction of potato starch with 2,3-epoxypropyltrimethylammonium chloride using the semi-dry process. The cationic starch derivatives were characterised by Fourier Transform infrared spectroscopy, X-ray diffraction and 1H-NMR, and their pasting and swelling properties were investigated. High-performance flocculant was obtained using intense mechanical shearing of aqueous cationic starch slurry. Swollen CS microgranules were crushed by the applied mechanical shearing and low-viscosity, stable CS aqueous dispersions were prepared. Sheared CS have a higher accessibility to polyanions, a lower molecular weight and a markedly higher flocculation efficiency—a lower minimum dose, while maintaining wide flocculation window. The flocculation mechanism of the kaolin suspension by sheared CS was prop...

Thermal imidization peculiarities of electrospun BPDA-PDA/ODA copolyamic acid nanofibers

AbstractCopolyamic acid (coPAA) based on 4,4′-oxydianiline (ODA), p-phenylenediamine (PDA) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) was synthesized in N,N-dimethylformamide (DMF). The preparation of continuous defect-free nanofibers from BPDA-PDA/ODA coPAA was achieved by electrospinning of its DMF solution. The average fiber diameter significantly increased from 385 to 590 nm on increasing the total polymer concentration of the spinning solutions from 5 to 7 wt%. The addition of dodecylethyldimethylammonium bromide (DEDAB) salt to the spinning solution resulted in the procurement of coPAA nanofibers with a much smaller (more than 3 times) average diameter. The coPAA imidization process was investigated through FTIR spectroscopy. The chemical composition and morphology of coPI nanofibers were assessed by X-ray photoelectron spectroscopy and scanning electron microscopy. Imidization under isothermal conditions proceeded faster in the first stage. Activation energies in the first and second imidization stages were similar when DEDAB had been added into the electrospinning solution. Cylindrical or crimped defect-free nanofibers of BPDA-PDA/ODA copolyimide (coPI) were obtained by the stepped thermal imidization of coPAA. The morphology of coPI nanofibers depends on the curing temperature. The crimped coPI nanofibers were most probably due to the relief of residual stress when the curing temperature was higher than the polymer glass transition temperature.

Modification of BPDA-ODA Polyimide Films by Diimides

Diimides 4,4′-oxydiphenylene diphthalylimide (PT-ODA-PT) and diphenylbiphenyltetracarboxyimide (A-BPDA-A) of an evident affinity to polyimides have been dispersed in a matrix of poly(4,4′-oxydiphenylene biphenyltetracarboxyimide) (BPDA-ODA). Changes in thermal and mechanical properties of BPDA-ODA films modified by diimides have been found to depend on the amount of diimide added and the conditions of film preparation (stretching). It has been established that diimides can play two different roles. When dissolved in polyimide, they act as plasticizers improving the segment mobility of BPDA-ODA chains, which may be critically needed to achieve the better molecular packing. The films plasticized by diimides show lower T g and the order–disorder transition temperature; the unstretched films exhibit better tensile properties, compared to unmodified films. However, dispersed beyond the limit of solubility in polyimides, diimides have detrimental effects on mechanical properties of the films. Though changes of the thermal properties of compositions derived from BPDA-ODA polyimide and microparticular diimides are less expressed than those of polyimide films plasticized by diimides, the compositions have poorer ultimate strength and shorter elongation at break. The conclusion may be drawn that the mechanical properties of the films modified by microparticular diimide are mainly controlled not by the interfacial interaction matrix–microparticles, but more likely by the much stronger macromolecular chain–chain interaction.