Improving stability of TiO2 particles in water by RF-plasma polymerization of poly(acrylic acid) on the particle surface

A Review on Reinforcements and Additives in Starch-Based Composites for Food Packaging

The research of starch as a matrix material for manufacturing biodegradable films has been gaining popularity in recent years, indicating its potential and possible limitations. To compete with conventional petroleum-based plastics, an enhancement of their low resistance to water and limited mechanical properties is essential. This review aims to discuss the various types of nanofillers and additives that have been used in plasticized starch films including nanoclays (montmorillonite, halloysite, kaolinite, etc.), poly-saccharide nanofillers (cellulose, starch, chitin, and chitosan nanomaterials), metal oxides (titanium dioxide, zinc oxide, zirconium oxide, etc.), and essential oils (carvacrol, eugenol, cinnamic acid). These reinforcements are frequently used to enhance several physical characteristics including mechanical properties, thermal stability, moisture resistance, oxygen barrier capabilities, and biodegradation rate, providing antimicrobial and antioxidant properties. This paper will provide an overview of the development of starch-based nanocomposite films and coatings applied in food packaging systems through the application of reinforcements and additives.

Preparation and Permeation Properties of a pH-Responsive Polyacrylic Acid Coated Porous Alumina Membrane

A pH-responsive membrane is expected to be used for applications such as drug delivery, controlling chemical release, bioprocessing, and water treatment. Polyacrylic acid (PAA) is a pH-responsive polymer that swells at high pH. A tubular α-alumina porous support was coated with PAA by grafting to introduce appropriate functional groups, followed by polymerization with acrylic acid. The permeances of acetic acid, lactic acid, phenol, and caffeine were evaluated by circulating water inside the membrane, measuring the concentration of species that permeated into the water, and analyzing the results with the permeation model. The permeance of all species decreased with increasing pH, and that of phenol was the largest among these species. At high pH, the PAA carboxy group in the membrane dissociated into carboxy ions and protons, causing the swelling of PAA due to electrical repulsion between the negative charges of the PAA chain, which decreased the pore size of the membrane and suppressed permeation. Furthermore, the electrical repulsion between negatively charged species and the PAA membrane also suppressed the permeation. The results of this study demonstrated that the PAA-coated α-alumina porous support functioned as a pH-responsive membrane.

A facile strategy to achieve monodispersity and stability of pigment TiO2 particles in low viscosity systems

Stable dispersion of TiO₂ particle is very desirable for its practical applications in various fields. It is a big challenge to stabilize pigment TiO₂ with relatively large size (200-300 nm) in low viscosity (~10 cP) systems. In the current work, we introduced a general strategy using a hydrophobic-hydrophilic structure to achieve single-dispersed TiO₂ particles with long storage stability in low viscosity systems. The modified TiO₂ particles (~250 nm) can be re-dispersed into water/glycol ethers mixture to form single dispersed suspension without any additives. Our study shows that the dispersion can be stable at least 60 days at room temperature and the rheological property is similar to the Newtonian fluids showing an extremely low yield stress at relatively high solid concentration. This work is expected to introduce a new strategy to improve the dispersion stability of the large size nanoparticles in low viscosity systems.

Effect of Modified Hexagonal Boron Nitride Nanoparticles on the Emulsion Stability, Viscosity and Electrochemical Behavior of Nanostructured Acrylic Coatings for the Corrosion Protection of AISI 304 Stainless Steel

In this study, the effect of pure and modified hexagonal boron nitride (h-BN) nanosheet incorporation on the stability, viscosity, and electrochemical behavior of a waterborne emulsion acrylic coating was studied. The functionalization of h-BN nanoplatelets with polyacrylic acid (PAA) plasma polymerization was performed, and the successful surface modification was determined through water dispersion testing, Fourier transform infrared spectroscopy and thermogravimetric analysis, X-ray photoelectron spectroscopy, and also by transmission electronic microscopy. Later, the stability and viscosity properties of emulsion nanostructured acrylic coatings, which were previously prepared by an ultrasound-assisted mixing system, were analyzed using zeta potential and rheometry testing, respectively. The electrochemical behavior was analyzed by electrochemical impedance spectroscopy. The results prove an effective deposition of PAA films on the h-BN surfaces, which enhanced the stability and viscosity acrylic of nanostructured coatings due to the interactions between the h-BN nanoplatelets surface and emulsion acrylic paint and also with the thickener additives. On the other hand, the electrochemical analysis demonstrated a significant increase (two orders of magnitude) in corrosion resistance in the acrylic nanostructured coatings with 1 wt.% of unmodified and modified h-BN nanoplatelets concerning pure acrylic paint due to a barrier protection mechanism of corrosion inhibition. Therefore, the results demonstrate that the surface modification of h-BN by plasma polymerization (green technology) helped to solve the low dispersibility issue of BN nanosheet surfaces in a waterborne polymer matrix to obtained green nanostructured acrylic coatings with the right balance in in-can properties and corrosion inhibition of AISI 304 stainless steel.

Plasma assisted-synthesis of magnetic TiO2/SiO2/Fe3O4-polyacrylic acid microsphere and its application for lead removal from water

Hybrid microsphere of polyacrylic acid (PAA) grafted TiO₂/SiO₂/Fe₃O₄ (TSF-PAA) was synthesized via coating polyacrylic acid on the core-shell-shell TiO₂/SiO₂/Fe₃O₄ (TSF) structure with the aid of plasma technique. The synthesized microsphere was applied to remove Pb²⁺ from water. The state-of-the techniques including TEM, FTIP, TGA, and XPS were used to characterize the morphology and the surface functionalities of the microsphere and confirmed that PAA was successfully grafted on TSF surfaces and active functional groups were introduced. A combination of the BET, VSM, and XRD results showed that plasma treatment decreased surface area of TSF by 36%, whereas its magnetic property and crystalline structure were not significantly altered. Both the Pb²⁺-sorbed magnetic TSF and TSF-PAA can be separated with a magnet from the aqueous phase. The pH and dosage changes of the microspheres exerted an intense influence on their lead removal efficiency. Compared to TSF, the removal capacity of Pb²⁺ by TSF-PAA was considerably improved from 65% to 95%, attributable to the fact that PAA coating induced by plasma treatment additionally introduced carboxylic and hydroxyl groups to TSF. Their introduction greatly enhanced the interaction between Pb²⁺ and TSF-PAA relative to that with TSF, which had hydroxyl groups only as supported by XPS analysis.

Plasma surface-modification of cellulose nanocrystals: a green alternative towards mechanical reinforcement of ABS

This article proposes a strategy to functionalize cellulose nanocrystals by means of plasma-surface modification utilizing monomers of different nature: caprolactone, styrene and farnesene. The surface characteristics of the nanocrystals were studied by different techniques including XPS, FTIR and STEM, demonstrating that this technique allows a successful functionalization, yielding homogenous functionalization which does not alter the rod-like shape of the nanocrystals, and therefore their anisotropic behavior. We have furthermore studied the employment of the modified nanocrystals as reinforcement additive of ABS, which significantly enhanced the impact resistance of the thermoplastic, which could have great implications for industrial applications.

This article deals with the plasma-surface modification of cellulose nanocrystals and their employment as reinforcement additive of ABS.

Biochar pyrolyzed from MgAl-layered double hydroxides pre-coated ramie biomass (Boehmeria nivea (L.) Gaud.): Characterization and application for crystal violet removal

A novel biochar/MgAl-layered double hydroxides composite (CB-LDH) was prepared for the removal of crystal violet from aqueous solution by pyrolyzing MgAl-LDH pre-coated ramie stem (Boehmeria nivea (L.) Gaud.). Pyrolysis played dual role for both converting biomass into biochar and calcining MgAl-LDH during the pyrolysis process. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) and zeta potential analysis were used to characterize the CB-LDH. The results of characterization suggested that the calcined LDH was successfully synthesized and coated on biochar. The resulted CB-LDH had higher total pore volume and more functional groups than the pristine biochar. Adsorption experimental data fitted well with the pseudo-second order kinetics model and the Freundlich isotherm model. The rate-controlled step was controlled by film-diffusion initially and then followed by intra-particle diffusion. Thermodynamic analysis showed that the adsorption of crystal violet was a spontaneous and endothermic process. The higher pH and temperature of the solution enhanced the adsorption performance. CB-LDH could also have excellent ability for the removal of crystal violet from the actual industrial wastewater and groundwater with high ionic strength. LDH adsorption, electrostatic attraction, pore-filling, π-π interaction and hydrogen bond might be the main mechanisms for crystal violet adsorption on CB-LDH. The results of this study indicated that CB-LDH is a sustainable and green adsorbent with high performance for crystal violet contaminated wastewater treatment and groundwater remediation.

Corrosion resistance of layer-by-layer assembled polyvinylpyrrolidone/polyacrylic acid and amorphous silica films on AZ31 magnesium alloys

A layer-by-layer (LbL)-assembled composite coating containing SiO₂ and a biocompatible polyvinylpyrrolidone (PVP) and polyacrylic acid (PAA) multi-layer, designated as SiO₂/(PVP/PAA)₅, was prepared on AZ31 Mg alloy via dip-coating.

Feasible electrochemical biosensor based on plasma polymerization-assisted composite of polyacrylic acid and hollow TiO2 spheres for sensitively detecting lysozyme

A composite made of polyacrylic acid and hollow TiO2 spheres (TiO2@PPAA) was prepared by the plasma polymerization method and subsequently used as an electrode material for detecting lysozyme. The chemical structure, surface morphology, and electrochemical performance of the TiO2@PPAA composite were mainly affected by the plasma input power used during plasma polymerization. After optimizing plasma conditions, aptamer strands exhibited high adsorption affinity toward the surface of TiO2@PPAA composite via synergistic effects between TiO2 and PPAA. Electrochemical impedance spectroscopy results showed that the developed TiO2@PPAA aptasensor presents highly sensitive detection ability toward lysozyme; the limit of detection of the proposed aptasensor is 0.015 ng mL(-1) (1.04 pM) within the range of 0.05-100 ng mL(-1) in terms of 3σ value. The film further showed excellent selectivity toward lysozyme in the presence of interfering proteins, such as thrombin, bovine serum albumin, and immunoglobulin E. Thus, this aptasensing strategy might broaden the applications of plasma polymerized nanomaterials in the field of biomedical research and early clinical diagnosis.