The Use of Cationic Agents to Increase the Efficiency of Titanium Dioxide in Paper

Handsheets were made with a bleached sulfite pulp, titanium dioxide and cationic agents. The optical properties of these sheets were studied in order to determine and compare the efficiency of the titanium dioxide retained. The cationic agents used in this study were a quaternary ammonium salt, a polyamide, cationic starches made with these two chemicals, and a commercial cationic starch. When the optical properties of handsheets made from these substances were compared, it was found that the quaternary ammonium salt gave the highest opacity but the lowest retention. The polyamide gave lower opacities but higher retentions. The cationic starches made from these cationic chemicals showed slightly lower opacities than the cationic chemicals by themselves but they gave much higher retentions. The commercial cationic starch gave intermediate retention but lower opacity. It was concluded that the quaternary ammonium salt gave the best dispersion of the titanium dioxide but gave the lowest cationic charge to the pigment. The polymide gave a slightly poorer dispersion but gave a much higher charge to the pigment. The cationic starches gave the best retention through a combination of mechanical and physio-chemical retention, but did not disperse the pigment too well

The Application of Zeta Potential for the Effective Retention of Titanium Dioxide in Chemically Modified Systems

This study was done to determine how to obtain maximum effective filler retention in a fiber and titanium dioxide system. Retention of fillers in a fibrous system is greatly influenced through the use of high molecular weight polymers. It was found that by using cationic and anionic polymers in the same system, a synergistic effect results which yields a higher effective retention than if either polymers were used along. Furthermore, by precisely controlling the amounts of each polymer so as to obtain the isoelectric point in zeta potential; the peak effective retention is reached

Effect of Retention Aids on AKD Size Response and Permanence

Poor size response and size reversion have been major concerns with the use of an alkyl ketene dimer (AKD) sizing system. Poor retention of calcium carbonate fillers and fiber fines are believed to be the cause of poor size response. A number of materials, including carbonate fillers, promoters and retention aids are believed to contribute to size reversion. The focus of this study was to determine the effectiveness of retention aids in obtaining good size response. Size permanence was also studied The performance of the retention aides were studied by preparing handsheets at five different zeta potentials. It was determined that when no retention aid was added to the system, size response was not dependent on zeta potential. It was dependent on the amount of polyethyleneimine (PEI) present in the system. Low sizing levels in the absence of PEI indicate poor retention of the size molecules. When cationic polymers were added to the stock, sizing levels showed a dramatic increase. This increase was do to superior retention of the fiber fines. As zeta potential was increased to highly cationic, size levels dropped due to poor retention of the sizing chemical. Cationic polymer was not observed to contribute to size reversion. Size response with the addition of an anionic polymer was highly dependent on the presence of a cationic fixative. When no PEI was present in the stock, the anionic polymer was ineffective. Small amounts of PEI provided cationic sites for the anionic polymer to bridge the fibers. Contrary to previous literature studies, the anionic polymer did not contribute to size reversion. When PEI was added to the system, large increases in sizing levels were observed PEI promotes excellent retention of the fiber fines. Good fines retention will increase sizing levels. Not only did PEI promote the reaction between AKD and cellulose, no size reversion was observed when it was used

Tuning the electronic, photophysical and charge transfer properties of small D-A molecules based on Thienopyrazine-terthienyls by changing the donor fragment: A DFT study

Indexación: Scopus.Four acceptor-donor organic conjugated molecules based on thieno[3,4-b]pyrazine-terthienyls were analyzed in order to explore the effect of the donor substituent on their molecular structures, electronic and optical properties. Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD/DFT) calculations were carried out employing the B3LYP hybrid functional in combination with the 6-31G(d,p) basis set. The results suggests that the addition of electron-donating substituents to the conjugated molecules can diminish their energy gap value, which is beneficial to the photon harvesting. The lowest-lying absorption spectra of compounds substituted with electron donor groups exhibited a red-shift and a high oscillation factor compared with the unsubstituted molecule. Additionally, the ionization potential (IP), electron affinity (EA), reorganization energy (λ) and open-circuit voltage (Voc) of the molecules were evaluated. According to these values, the molecules show good photovoltaic properties, and efficient charge transfer for hole and electron and balanced charges.https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0717-97072017000303637&lng=en&nrm=iso&tlng=e

Novel "green" catalysts for controlled ring-opening polymerization of lactide

Syntéza polylaktidu (PLA) polymerací za otevření kruhu cyklického monomeru (ROP) může být uskutečněna různými způsoby. Literatura uvádí více než 100 katalytických systémů, jejichž pomocí lze polylaktid a jiné biodegradabilní alifatické polyestery získat. Například organokovové katalyzátory na bázi Sn, Zn, Al atd. se po splnění své polymerační funkce stávají kontaminanty a pro humánní implantáty je použití takového materiálu diskutabilní. V současné době jsou v centru výzkumné pozornosti nové N-heterocyklické karbenové katalyzátory. Tyto „metal-free“ katalytické struktury jsou schopné reprodukovatelně řídit syntézu polymerů předem definované molekulové hmotnosti s definovanými koncovými skupinami a nízkou polydisperzitou, která je charakteristická pro živý průběh polymerace. Nabízí se možnost syntézy blokových kopolymerů a různorodých makromolekulárních architektur. Předložená diplomová práce se zabývá studiem polymerace cyklického monomeru D,L-laktidu katalyzované N-heterocyklickým karbenem. Polymerace byly vedeny v přítomnosti benzylalkoholu jako iniciátoru v roztoku THF. Byl sledován vliv složení reakčního systému monomer – iniciátor – katalyzátor. Dále byly připraveny polymery opticky čistého L-laktidu s makroiniciátory PEG s Mn = 1000 a 2000 g/mol. Střední číselná molekulová hmotnost (Mn) a polydisperzita (PDI) byly stanoveny pomocí GPC. Definovatelnost koncových skupin vybraných polymerů byla prokázána pomocí 1H NMR.The synthesis of polylactide (PLA) by ring-opening polymerization (ROP) of cyclic monomer can be realized by different routes. More than 100 catalysts for the synthesis of polylactide and other biodegradable aliphatic polyesters are published in the literature. For example organometallic catalysts based on Sn, Zn, Al etc. after finishing polymerization function became contaminants and using obtained polymer material in human body is controversial. At present, the research is focused on novel N-hererocyclic carbene catalysts. These metal-free catalysts are able to produce polymers with controlled molecular weight, narrow polydispersity, end-group fidelity with high reproducibility as well as to synthesize the block copolymers and complex macromolecular architectures, which is characteristic for living polymerization system. This diploma thesis is focused on study of polymerization of cyclic monomer D,L-lactide catalyzed by N-hererocyclic carbene. Polymerizations were carried out at the presence of benzylalcohol as initiator at THF. We were focused on the influence of composition of reaction system monomer – initiator – catalyst. Polymers of optically pure L-lactide with macroinitiators PEG with Mn of 1000 a 2000 g/mol were prepared as well. Number average molecular weight (Mn) and polydispersity index (PDI) was determined by GPC. 1H NMR was used to prove end-group fidelity.

A Study of Dual Polymer Retention Aids for the Retention on Titanium Dioxide Using the Dynamic Drainage Jar, Minidrinier, and Handsheets

Two types of dual polymer retention aid systems, a low molecular weight, high charge density, cationic polyamine with a high molecular weight, low charge density, cationic polyacrylamide, and the same polyamine with a high molecular weight, highly charged anionic polyacrylamide, were studied using the Dynamic Drainage Jar, the Minidrinier, and handsheets. Both systems gave higher retention than could be achieved using any of the retention aids alone, however, formation was a problem. Contact time and shear were shown to be important variables. All three testing methods were useful, the Dynamic Drainage Jar having an advantage due to its flexibility

Relaxation Behavior by Time-Salt and Time-Temperature Superpositions of Polyelectrolyte Complexes from Coacervate to Precipitate

Complexation between anionic and cationic polyelectrolytes results in solid-like precipitates or liquid-like coacervate depending on the added salt in the aqueous medium. However, the boundary between these polymer-rich phases is quite broad and the associated changes in the polymer relaxation in the complexes across the transition regime are poorly understood. In this work, the relaxation dynamics of complexes across this transition is probed over a wide timescale by measuring viscoelastic spectra and zero-shear viscosities at varying temperatures and salt concentrations for two different salt types. We find that the complexes exhibit time-temperature superposition (TTS) at all salt concentrations, while the range of overlapped-frequencies for time-temperature-salt superposition (TTSS) strongly depends on the salt concentration (Cs) and gradually shifts to higher frequencies as Cs is decreased. The sticky-Rouse model describes the relaxation behavior at all Cs. However, collective relaxation of polyelectrolyte complexes gradually approaches a rubbery regime and eventually exhibits a gel-like response as Cs is decreased and limits the validity of TTSS.Comment: 12 pages, 5 figures, Follow Gels journal link for latest versio

Immobilized photosensitizers for antimicrobial applications

Photodynamic antimicrobial chemotherapy (PACT) is a very promising alternative to conventional antibiotics for the efficient inactivation of pathogenic microorganisms; this is due to the fact that it is virtually impossible for resistant strains to develop due to the mode of action employed. PACT employs a photosensitizer, which preferentially associates with the microorganism, and is then activated with non-thermal visible light of appropriate wavelength(s) to generate high localized concentrations of reactive oxygen species (ROS), inactivating the microorganism. The concept of using photosensitizers immobilized on a surface for this purpose is intended to address a range of economic, ecological and public health issues. Photosensitising molecules that have been immobilized on solid support for PACT applications are described herein. Different supports have been analyzed as well as the target microorganism and the effectiveness of particular combinations of support and photosensitiser