Volume 35, Issue 6

A series of fluorinated-siloxane protective surface coating materials (FPA/SiO 2 ) were prepared with different contents of dodecafluoroheptyl methacrylate (DFMA) and fixed content of siloxane. The properties of FPA/SiO 2 protective materials were investigated by the methods of Fourier transform infrared spectroscopy (FT-IR) spectra, UV-Vis spectrum, transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). The surface morphology and mineralogical analysis of the fresh and weathered stone samples were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The artificial ageing test, which was commonly used as a criterion for the evaluation of the protective ability of FPA/SiO 2 coating material, was performed. The results indicate that when the content of DFMA is 30 wt.% and the content of SiO 2 is 10 wt.%, the prepared coating material has good comprehensive performances. The artificial ageing test shows that the protective surface coating material has good compatibility with and similar appearance to stone relics. The effect of FPA/SiO 2 protective coating material for protection of Jiaoshan Steles Grove (China) is noticeable and it can be widely applied to the protection of stone relics.

Polyurethane prepolymer (PUP) was synthesized by polyethylene glycol (PEG) and polypropylene glycol (PPG) as the soft segments, isophorone diisocyanate (IPDI) as the hard segment and dimethylol propionic acid (DMPA) and diethylene glycol (DEG) as chain extenders. Silk fibroin (SF)-PU composite hydrogels were prepared by SF and PUP through chemical crosslinking and physical crosslinking interactions. A full factorial experimental design with four factors and four levels was applied to optimize the craft of preparing SF-PU composite hydrogels. The molecular weight of PEG, IPDI/(PEG+PPG) (molar ratio), PEG/(PEG+PPG) (molar ratio) and SF/(SF+PU) (mass ratio) were the factors. The swelling behavior of hydrogels was tested in deionized water at 30°C. The results showed that the equilibrium swelling ratio (ESR) was the largest by tuning the molecular weight of PEG to 4000, IPDI/(PEG+PPG)(molar ratio) to 3, PEG/(PEG+PPG) (molar ratio) to 40% and SF/(SF+PU) (mass ratio) to 2%. Fickian diffusion played a dominant role in the initial stage of swelling. For the whole process, the results fitted well into the Schott second-order kinetic equation.

Renewable, biodegradable, agricultural resources are gaining increasing attention of many researchers because of growing environmental awareness and their potential to replace petrochemical derivatives. Cardanol obtained from cashew nut shell liquid (CNSL) is a renewable resource of immense potential. Cardanol, obtained as a byproduct of the cashew processing industry, is an important renewable resource and a unique phenolic compound carrying a 15-carbon side chain in the meta position, with varying degrees of unsaturation. The current research work describes the synthesis of new bio-based cashew Mannich polyols via the stepwise oxazolidine route and confirmed by spectral analysis. The foaming characteristics were studied and the polyols were successfully used in making rigid polyurethane (PU) foams with good mechanical, thermal and fire properties. The foams were characterized for density, flexural strength, morphology and limiting oxygen index (LOI) properties.

The present article presents a study on the mechanical and water absorption properties of bagasse fiber-reinforced epoxy composites. Bagasse fibers are subjected to chemical treatment with 1% sodium hydroxide followed by 1% acrylic acid at ambient temperature to enhance the bonding strength between the fiber-polymer, resulting in high values of the mechanical properties and a reduction in the water absorption properties of the composites. We analyzed the optimum value of fiber treatment, and it was found that 15% treated fiber loading yields enhanced the mechanical properties together with a reduction in water absorption properties.

Degradable native low density polyethylene (LDPE) and modified LDPE films containing 5–30 wt% of sago starch, and LDPE with prodegradant additives in the form of a master batch (MB) in the amounts of 30% starch were prepared by twin screw extrusion followed by injection molding. Studies on their mechanical properties such as tensile strength and elongation at break and biodegradation were carried out by tensile test and exposure to hydrolysis, fungi environment as well as by natural weathering and burial in soil. The presence of high starch contents had an adverse effect on the tensile properties of the blend films. High starch content was also found to increase the rate of biodegradability of the films. The characteristic parameters of the environment were measured during the period of degradation and their influence on degradation of LDPE was discussed. Changes in weight, morphology, thermogravimetric analysis (TGA) and tensile properties of polymer samples were tested during the experiment performed.

Colloidal dispersions of hybrid nanoparticles with silica sol as the supporter (PKSol) were prepared by supporting aromatic phosphate on silica sol via a chemical action with γ-aminopropyltrimethylsilane (KH550) as a linker in wet process for the first time. Dynamic light scattering (DLS) demonstrated that hybrid nanoparticles with an average size of about 200 nm were formed and transmission electron microscopy (TEM) confirmed the presence of the ultrafine silica sols within the hybrid particles, which exhibited “currant-bun” particle morphologies, rather than typical “core-shell” structures for most polymer-encapsulated silica particles. Compared to aromatic phosphate alone and silane-modified silica sol, the effect of PKSol on the crystallization behavior and mechanical properties of isotactic polypropylene (iPP) was investigated using a polarized optical microscope (POM) and differential scanning calorimetry (DSC). The results demonstrated that PKSol showed superior nucleating ability on iPP than the other two. After adding 0.2 wt% PKSol, the crystallization peak temperature of iPP increased from 116.35°C to 120.81°C and the crystallinity increased from 39.6% to 50%. Correspondingly, the haze decreased from 37.6% to 23.3% and mechanical properties were improved.

Zinc oxide (ZnO) nanoparticles possess antibacterial properties. Being less toxic to humans than silver, they are attractive as antibacterial agents in biomedical applications. In this study, we focus on the influence of the size of ZnO nanoparticles on their antibacterial action against strains of three bacteria: one Gram-negative, Escherichia coli and two Gram-positive, Bacillus subtilis and Staphylococcus aureus . The antibacterial efficacy of the nanoparticles increases with decreasing particle size. A major contributor to antibacterial action is the oxidative stress induced by the ZnO. To understand the relationship between antibacterial action and induced oxidative stress, we measured the dependence of the nanoparticle diameter on H 2 O 2 concentration. Even at a fixed nanoparticle concentration, the H 2 O 2 concentration increased with decreasing nanoparticle diameter. This is qualitatively similar to the dependence of the antibacterial activity on the nanoparticle diameter. In addition, in the presence of ZnO nanoparticles, we detected increased quantities of endogenous H 2 O 2 in the E. coli . For use as antibacterial wound dressings, we fabricated nonwoven fiber mats from poly(vinyl alcohol) (PVA)/ZnO nanoparticle suspensions. The antibacterial efficacy of the PVA/ZnO electrospun fiber mats also increased with a decrease in the diameter and an increase in the concentration of the ZnO nanoparticles.

Electrospinning is an efficient, versatile, and straightforward technique involving the fabrication of very thin fibers from a rich variety of materials. Despite several promising applications, the remaining problem with electrospinning is the unpredictable deposition of the nanofibers. In this study, a mathematical model for a novel magnetic electrospinning process was established on the basis of a set of equations. Then, the model was utilized to analyze the behavior of the created polymer jet numerically using the Runge-Kutta method. The jet was assumed to consist of a number of discrete charged particles connected by viscoelastic segments. The results showed that exerting an appropriate magnetic field (MF) could significantly decrease the radius and the instability of the whipping circles. After fixing the instability as far as possible, it was demonstrated that a properly applied perpendicular MF could largely adjust the target of the polymer jet on the collector.

Emulsion nanoparticles of polyaniline (PANI) were synthesized in the aqueous media by using hydroxylpropylcellulose (HPC) as a stabilizer and ammonium persulfate as an oxidant in the presence of TiO 2 with nanometer size. New poly(vinyl acetate) (PVAc) coating over carbon steel was prepared by addition of emulsion nanoparticles in different concentrations (1%, 2% and 1.5%) in PVAc as the major matrix. The Tafel plot records were used for the definition of potential and corrosion current (Icorr). Nanoparticles were characterized and compared by X-ray diffraction (XRD), thermal gravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). By adding TiO 2 , the thermal stability of the nanocomposite increased. A small size of colloidal particles prevented the precipitation of conducting polymer particles and led to better dispersion of nanocomposites in the matrix of the PVAc binder; therefore, the paint was homogeneous and anticorrosion properties of the coating increased. According to the results, 1.5% of PANI-TiO 2 nanocomposite in PVAc has a much lower Icorr in NaCl aqueous solution and 2% of PANI-TiO 2 nanocomposite in PVAc has the best corrosion protection in HCl.

Plastics extrusion can be divided into the following types: conventional extrusion (run at low speed of the rotating screw), adiabatic extrusion (screw speed is relatively high, yet the process requires the use of heaters) and high speed extrusion (extruder barrel requires cooling due to very high screw speeds). This paper presents the results of a study undertaken to investigate the adiabatic extrusion of low density polyethylene using heads with circular cross-section nozzles and different geometries of flow channels. In the experiments, we examined the temperature and pressure of the polymer in the plasticizing unit, as well as the relationships between the output, thermal power conveyed by the plastic, total power supplied to the extruder, extrusion efficiency, unit consumption of the total energy supplied to the extruder as well as the rotational speed of the screw and the extruder’s head geometry. It was found that the most favorable energy conditions, i.e., the highest efficiency of the adiabatic extrusion of low density polyethylene in the whole range of the tested screw speeds, are ensured when the head with the highest diameter and length nozzle is applied.