Effect of Charge Asymmetry on Adsorption and Phase Separation of Polyampholytes on Silica and Cellulose Surfaces

Physicochemical properties of electrostatically crosslinked carrageenan/chitosan hydrogels and carrageenan/chitosan/Laponite nanocomposite hydrogels

In this work physical carrageenan/chitosan (Car/Chit) hydrogels are prepared by electrostatic complexation between the two oppositely charged polysaccharides. The hydrogels have storage moduli in the order of 5-10 kPa and swelling ratios in the order of 5000-6000 %. At conditions where both polysaccharides are highly charged (pH 5) the swelling ratios are lower than the ones at conditions of lower dissociation i.e., at pH 2 and 7 and the opposite trend is found for the storage modulus. Chit appears to act as a crosslinker for Car as increasing its concentration the swelling ratio decreases and the moduli increase. The hydrogels can incorporate the nanoclay Laponite (Lap) and form hybrid nanocomposites where the intercalation by the two biopolymers leads to exfoliation of the clay nanoplatelets in the presence of both Car and Chit. The composite hydrogels retain the mechanical properties of the Car/Chit hydrogels at the studied pH range (pH 2 to pH 7). This shows the prepared hydrogels can be potentially used as multifunctional biomaterials for drug delivery, tissue engineering and bone regeneration applications.

Effect of cationic monomer structure on the aggregation behavior of amphoteric acrylic polymer around isoelectric point

Amphoteric polymer can be used as retanning agent in leather manufacture. It is particularly useful in chrome-free tanning systems since it can regulate the charge properties of chrome-free leather and enhance the fixation of anionic post-tanning chemicals in leather. However, the aggregation and precipitation of amphoteric polymer retanning agents around the isoelectric point (pI) hinder their wide application. Herein, we synthesized five amphoteric acrylic polymers (AAPs) by free radical copolymerization with acrylic acid and five different cationic acrylic monomers. The effect of cationic monomer structure on the aggregation behavior of AAPs was investigated. The aggregation of AAPs in aqueous solution showed pH and concentration dependence. Light scattering analysis showed that Poly (AA-co-MAPTAC) and Poly (AA-co-DMAPMA) were in the shape of coiled linear flexible chains with small particle size (Rg 7.6 nm and 14.8 nm, respectively) near the pI. However, Poly (AA-co-DAC), Poly (AA-co-DMC) and Poly (AA-co-DMAEMA) were in the shape of hollow spheres and exhibited serious aggregation. Quantum chemical calculations suggested that the amide groups in the cationic monomers MAPTAC and DMAPMA enhanced the nucleophilicity of AAPs. Thus the corresponding AAPs could carry a large number of cationic charges to slow their aggregation when the pH just climbed over the pI. The results are expected to provide theoretical reference for the synthesis and widespread application of AAPs.

Impacts of degree of substitution of quaternary cellulose on the strength improvement of fiber networks

The degree of substitution (DS) of cellulose derivative is significantly associated with its properties. In this paper, a series of quaternary cellulose (QC) samples with different DS (ranging from 0.16 to 0.51) were synthesized with assistance of microwave and their relationship with strength improvement of fiber networks was investigated systematically. QCs were characterized by elemental analysis, FT-IR, ¹H NMR, and TGA, etc. The results showed that the cationic quaternary ammonium salt group was successfully grafted onto the backbones of cellulose chains and the thermal stability was associated inversely with the DS of QCs. However, the results of strength test for the fiber networks from secondary fiber of old corrugated containers showed that the tensile and burst strength was enhanced by addition of QCs, and their performance was positively correlated their DS. The best result achieved in this investigation was in the case of QC with DS of 0.51, with increments of tensile and burst strength 6.17% and 11.68%, respectively, at a dosage of 1.0 wt% based on oven-dry pulp. This investigation highlights the importance of DS of QC to its application in strength improvement for fiber networks.

Binding affinity of family 4 carbohydrate binding module on cellulose films of nanocrystals and nanofibrils

The binding affinity and thermodynamics of family 4 carbohydrate-binding module (CBM4), belonging to type B CBM, on model surfaces of cellulose nanocrystals (CNC) and nanofibrils (CNF) were investigated by quartz crystal microbalance with dissipation monitoring (QCM-D) technology in real-time at different temperatures. The thermodynamic parameters associated with the interaction, such as Gibbs free energy, enthalpy change, entropy change and heat capacity were obtained using the van't Hoff analysis via a nonlinear parameter estimation. The results demonstrated CBM4 binds preferentially to both CNF and CNC, whereas the driving forces behind them were very different. The former was related to the hydrogen bonds formed in the CBM4 clefts, resulting in a favorable enthalpy but compensated by unfavorable entropy change; on the contrary, the latter was mainly driven by favorable entropy but compensated by unfavorable enthalpic change due to water rearrangement.

Revealing Adsorption Behaviors of Amphoteric Polyacrylamide on Cellulose Fibers and Impact on Dry Strength of Fiber Networks

Amphoteric polyacrylamide (AmPAM) has been widely used in a variety of industrial areas and the adsorption behavior of AmPAM plays a crucial role in its applications. In this study, a series of AmPAMs with various molecular weights (MW) were synthesized; and their impact on dry strength of fiber networks or paper was assessed. The results showed that the optimal MW of AmPAM for strength enhancement ranged between 300 and 500 k. More importantly, the adsorption behaviors of three typical AmPAM samples on silica (model substrate) and cellulose surfaces were revealed using a quartz crystal microbalance with dissipation monitoring (QCM-D) in situ and in real time. The adsorption dynamics of AmPAM and the conformation of the adlayers were further derived. The results indicated that a relatively high adsorption amount was achieved under the conditions of a high polymer concentration, a medium pH close to its isoelectric point (IEP), a mild ionic strength, and a high charged surface; whereas the MW of AmPAM had little effect on the equilibrium adsorption mass of AmPAM, but significantly affected the conformation of adsorbed layer on substrates. Based on the adsorption behaviors of AmPAM, the explanation of the best dry strength achieved in a narrow range of MW of AmPAM is proposed. It was concluded that the appropriate balance between bridging and flocculation, penetration into fiber pores, and conformation were only achieved in the optimal MW range of AmPAM. The findings obtained from in this work enable us to better understand the adsorption behaviors of polyampholyte, and provide a guideline on molecular design of AmPAM and its applications from both fundamental and practical points of view.

Effect of Lipoxygenase Oxidation on Surface Deposition of Unsaturated Fatty Acids

We studied the interactions of lipid molecules (linoleic acid, glycerol trilinoleate and a complex mixture of wood extractives) with hydrophilic and hydrophobic surfaces (cellulose nanofibrils (CNFs) and polyethylene terephthalate (PET), respectively). The effect of lipoxygenase treatment to minimize the affinity of the lipids with the given surface was considered. Application of an electroacoustic sensing technique (QCM) allowed the monitoring of the kinetics of oxidation as well as dynamics of lipid deposition on CNF and PET. The effect of the lipoxygenase enzymes (LOX) was elucidated with regards to their ability to reduce the formation of soiling lipid layers. The results pointed to the fact that the rate of colloidal oxidation depended on the type of lipid substrate. The pretreatment of the lipids with LOX reduced substantially their affinity to the surfaces, especially PET. Surface plasmon resonance (SPR) sensograms confirmed the effect of oxidation in decreasing the extent of deposition on the hydrophilic CNF. QCM energy dissipation analyses revealed the possible presence of a loosely adsorbed lipid layer on the PET surface. The morphology of the deposits accumulated on the solids was determined by atomic force microscopy and indicated important changes upon lipid treatment with LOX. The results highlighted the benefit of enzyme as a biobased treatment to reduce hydrophobic interactions, thus providing a viable solution to the control of lipid deposition from aqueous media.

Adsorption of polyelectrolytes and polyelectrolytes-surfactant mixtures at surfaces: a physico-chemical approach to a cosmetic challenge

The use of polymer and polymer - surfactant mixtures for designing and developing textile and personal care cosmetic formulations is associated with various physico-chemical aspects, e.g. detergency and conditioning in the case of hair or wool, that determine their correct performances in preserving and improving the appearance and properties of the surface where they are applied. In this work, special attention is paid to the systems combining polycations and negatively charged surfactants. The paper introduces the hair surface and presents a comprehensive review of the adsorption properties of these systems at solid-water interfaces mimicking the negative charge and surface energy of hair. These model surfaces include mixtures of thiols that confer various charge densities to the surface. The kinetics and factors that govern the adsorption are discussed from the angle of those used in shampoos and conditioners developed by the cosmetic industry. Finally, systems able to adsorb onto negatively charged surfaces regardless of the anionic character are presented, opening new ways of depositing conditioning polymers onto keratin substrates such as hair.

Role of textile substrate hydrophobicity on the adsorption of hydrosoluble nonionic block copolymers

The adsorption of polyalkylene glycols and co-polymers of ethylene oxide and propylene oxide on substrates relevant to textiles with varying surface energies (cellulose, polypropylene, nylon and polyester) was studied by using quartz crystal microgravimetry. Langmuirian-type isotherms were observed for the adsorption profiles of nonionic block polymers of different architectures. The affinity with the surfaces is discussed based on experimental observations, which highlights the role of hydrophobic effects. For a given type of block polymer, micellar and monomeric adsorption is governed by the balance of polymer structure (mainly, chain length of hydrophobic segments) and substrate's surface energy.

Effect of peptide secondary structure on adsorption and adsorbed film properties on end-grafted polyethylene oxide layers

Poly-l-lysine (PLL), in α-helix or β-sheet configuration, was used as a model peptide for investigating the effect of secondary structures on adsorption events to poly(ethylene oxide) (PEO) modified surfaces formed using θ solvents. Circular dichroism results showed that the secondary structure of PLL persisted upon adsorption to Au and PEO modified Au surfaces. Quartz crystal microbalance with dissipation (QCM-D) was used to characterize the chemisorbed PEO layer in different solvents (θ and good solvents), as well as the sequential adsorption of PLL in different secondary structures (α-helix or β-sheet). QCM-D results suggest that chemisorption of PEO 750 and 2000 from θ solutions led to brushes 3.8 ± 0.1 and 4.5 ± 0.1 nm thick with layer viscosities of 9.2 ± 0.8 and 4.8 ± 0.5 cP, respectively. The average number of H2O per ethylene oxides, while in θ solvent, was determined as ~0.9 and ~1.2 for the PEO 750 and 2000 layers, respectively. Upon immersion in good solvent (as used for PLL adsorption experiments), the number of H2O per ethylene oxides increased to ~1.5 and ~2.0 for PEO 750 and 2000 films, respectively. PLL adsorbed masses for α-helix and β-sheet on Au sensors was 231 ± 5 and 1087 ± 14 ng cm(-2), with layer viscosities of 2.3 ± 0.1 and 1.2 ± 0.1 cP, respectively; suggesting that the α-helix layer was more rigid, despite a smaller adsorbed mass, than that of β-sheet layers. The PEO 750 layer reduced PLL adsorbed amounts to ~10 and 12% of that on Au for α-helices and β-sheets respectively. The PLL adsorbed mass to PEO 2000 layers dropped to ~12% and 4% of that on Au, for α-helix and β-sheet respectively. No significant differences existed for the viscosities of adsorbed α-helix and β-sheet PLL on PEO surfaces. These results provide new insights into the fundamental understanding of the effects of secondary structures of peptides and proteins on their surface adsorption.

Adsorption of hydrophobically end-capped poly(ethylene glycol) on cellulose

Adsorption of poly(ethylene glycol), hydrophobically end-capped with octadecenylsuccinic anhydride (OSA-PEG-OSA), on an ultrathin film of cellulose has been studied by quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM). Normally, PEG does not adsorb on cellulosic surfaces, but the use of the telechelic hydrophobic modification was found to promote adsorption. The influence of the conformation of the polymer in solution prior to adsorption and the subsequent properties of the adsorbed layer were investigated. The adsorption experiments were done at concentrations below and above the critical association concentration. The adsorption of OSA-PEG-OSA on cellulose was observed to occur in four distinct stages. Because of the amphiphilic nature of cellulose, further adsorption experiments were performed on hydrophobic (polystyrene) and hydrophilic (silica) model substrates to illuminate the contribution of hydrophobic and hydrophilic factors in the adsorption phenomenon. As expected, the kinetics and the mechanism of adsorption were strongly dependent on the chemical composition of the substrate.