The change in shape inducible in some photo-reversible molecules using light can effect powerful changes to a variety of properties of a host material. This class of reversible light-switchable molecules includes molecules that photo-dimerize, such as coumarins and anthracenes; those that allow intra-molecular photo-induced bond formation, such as fulgides, spiro-pyrans, and diarylethenes; and those that exhibit photo-isomerization, such as stilbenes, crowded alkenes, and azobenzenes. The most ubiquitous natural molecule for reversible shape change, however, and perhaps the inspiration for all artificial bio-mimics, is the rhodopsin/retinal protein system that enables vision, and this is the quintessential reversible photo-switch for performance and robustness. Here, the small retinal molecule embedded in a cage of rhodopsin helices isomerizes from a cis geometry to a trans geometry around a C=C double bond with the absorption of just a single photon. The modest shape change of just a few angstroms is quickly amplified and sets off a cascade of larger shape and chemical changes, eventually culminating in an electrical signal to the brain of a vision event, the energy of the input photon amplified many thousands of times in the process. Complicated biochemical pathways then revert the trans isomer back to cis, and set the system back up for another cascade upon subsequent absorption. The reversibility is complete, and many subsequent cycles are possible. The reversion mechanism back to the initial cis state is complex and enzymatic, hence direct application of the retinal/rhodopsin photo-switch to engineering systems is difficult. Perhaps the best artificial mimic of this strong photo-switching effect however in terms of reversibility, speed, and simplicity of incorporation, is azobenzene. Trans and cis states can be switched in microseconds with low-power light, reversibility of 105 and 106 cycles is routine before chemical fatigue, and a wide variety of molecular architectures is available to the synthetic materials chemist, permitting facile anchoring and compatibility, as well as chemical and physical amplification of the simple geometric change. This review article focuses on photo-mechanical effect taking place in various material systems incorporating azobenzene. The photo-mechanical effect can be defined as reversible change in shape by absorption of light, which results in a significant macroscopic mechanical deformation, and reversible mechanical actuation, of the host material. Thus, we exclude simple thermal expansion effects, reversible but non-mechanical photo-switching or photo-chemistry, as well as the wide range of optical and electro-optical switching effects for which good reviews exist elsewhere. Azobenzene-based material systems are also of great interest for light energy harvesting applications across much of the solar spectrum, yet this emerging field is still in an early enough stage of research output as to not yet warrant review, but we hope that some of the ideas put forward here toward promising future directions of research, will help guide the field.
In this overview, we focused on the bacterial cellulose (BC) applications, described in recently published scientific papers, in the field of skin regenerative medicine and wound care industry. Bacterial cellulose was proven to be biocompatible with living tissues. Moreover, its mechanical properties and porous structure are considered to be suitable for biomedical applications. It is due to the fact that porous structure of bacterial cellulose mimics the extracellular matrix of the skin. Moreover, it can also hold the incorporated drugs and other modifiers, which can modulate its properties improving the bacterial cellulose antimicrobial activity which is rather poor for native BC. Bacterial cellulose reveals high hydrophilic properties and never dries, which is a desired property, because it was proven that wounds heal better and faster when the wound is being constantly moisturized. This characteristic of bacterial cellulose indicates that it may successfully serve as wound dressings and skin tissue scaffolds.
In this work, the different cellulosic materials, namely cellulose and lignin are analyzed. In addition, the starch-containing matrices (isolated starch and flour) reinforced with cellulosic materials to be used in packaging applications are described. Many efforts have been exerted to develop biopackaging based on renewable polymers, since these could reduce the environmental impact caused by petrochemical resources. Special attention has had the starch as macromolecule for forming biodegradable packaging. For these reasons, shall also be subject of this review the effect of each type of cellulosic material on the starch-containing matrix-based thermoplastic materials. In this manner, this review contains a description of films based on starch-containing matrices and biocomposites, and then has a review of cellulosic material-based fillers. In the same way, this review contains an analysis of the works carried out on starch-containing matrices reinforced with cellulose and lignin. Finally, the manufacturing processes of starch/cellulose composites are provided as well as the conclusions and the outlook for future works.
In the present work, a series of cross-linked LVCS/PVA hydrogels with various feed compositions were prepared using glutaraldehyde as cross-linking agent. The prepared hydrogels were used for dynamic and equilibrium swelling studies. The swelling behavior of these hydrogels was investigated as functions of effect of pH, polymeric compositions and degree of cross-linking. Swelling studies were performed in 0.05 M USP phosphate buffer solutions of varying pH 1.2, 5.5, 6.5 and 7.5. Results showed that swelling increased by increasing PVA contents in the structure of hydrogels in solutions of higher pH values. This is due to the presence of more hydroxyl groups (–OH) in the PVA structure. On the other hand, by increasing LVCS contents, swelling increased in a solution of acidic pH and it is due to ionization of amino groups (–NH2), but this swelling was not significant. Swelling of hydrogels was decreased with increase in cross-linking ratio due to tighter hydrogel structure. Porosity and sol–gel fraction were also investigated. It was found that with increase in LVCS and PVA contents porosity and gel fraction increased, whereas by increasing glutaraldehyde content gel fraction increased and porosity decreased. Diffusion coefficient (D) and network parameters, i.e., the average molecular weight between cross-links (M C), solvent interaction parameters (χ), polymer volume fraction in swollen state (V 2S) and cross-linked density (q) were calculated using Flory–Rehner theory. Selected samples were loaded with model drug diphenhydramine HCl. The release of diphenhydramine HCl was studied for 12 h period in 0.05 M USP phosphate buffer solutions of varying pH 1.2, 5.5 and 7.5. It was observed that drug release increased with increasing PVA contents in the hydrogels, while release of drug decreased as the ratio of cross-linking agent increased in the hydrogel structure owing to strong physical entanglements between polymers. The release mechanisms were studied by fitting experimental data to model equations like zero order, first order, Higuchi and Peppas. Results showed that the kinetics of drug release from hydrogels in buffer solutions of pH 1.2, 5.5 and 7.5 was mainly non-fickian diffusion. Hydrogels were characterized by Fourier transform infrared and X-ray diffraction to confirm the structure and study the crystallinity of hydrogel, respectively.
The present work is focused on the development of binary blends from poly(hydroxybutyrate) (PHB) and poly(caprolactone) (PCL). Miscibility, mechanical and thermal properties as well as blends morphology are evaluated in terms of the blend composition. Binary PHB–PCL blends were manufactured by melt compounding in a twin screw co-rotating extruder and injection molded. The composition of PHB–PCL covered the full range between individual polymers at 25 wt% increments. The obtained results show that PCL acts as an impact modifier, thus leading to an increase in flexibility and ductility as the PCL content in the PHB–PCL blends increases with a noticeable increase in elongation at break and on the energy absorption in impact conditions. The tensile strength and the elastic modulus decrease with increasing PCL content in the PHB–PCL blends; nevertheless, the flexural strength and the flexural modulus reach the highest values for the PHB–PCL blends containing 25 wt% PCL, with a remarkable decrease over this composition. The analysis of fractured surfaces by field emission scanning electron microscopy and thermal properties obtained by differential scanning calorimetry (DSC) and TGA give clear evidences of the immiscibility of these two biodegradable polymers. Additionally, DSC results showed an increase in crystallinity of both PHB and PCL with regard to individual polymers for PHB–PCL blends containing 25 wt% PCL. Furthermore, an increase in the degradation onset (T 0) of about 30 °C higher was detected for the same blends. Dynamic mechanical thermal analysis showed slightly shifted glass transition temperatures of each individual polymer, thus indicating that although both PHB and PCL are not fully miscible, some interactions between them occur.
Commercially, polyurethanes are produced by the reaction of diisocyanates, polyols (polyester or polyether) and low molecular weight chain extender. Toxicity, moisture sensitivity and phosgene-based synthesis of diisocyanates resulted in investigations focused on obtaining the non-isocyanate polyurethanes (NIPUs). This work presents the review of synthesis and structure-properties relationship of non-isocyanate polyurethanes obtained by reacting cyclic carbonated intermediates with diamines or polyamines. Moreover, the presented methods of NIPU synthesis were analysed from the environmental point of view. Described five-membered ring cyclic carbonate intermediates were obtained by carbonation of glycidyl ethers or thiol-ene coupling of unsaturated cyclic carbonate monomers and thiols. The special interest was put on the bio-based non-isocyanate polyurethanes, obtained from chemically modified bio-based substances, e.g. carbonated vegetable oils. The mechanical and thermal properties of NIPUs are affected by functionality, structure and molecular weight of cyclic carbonate intermediates and diamines or polyamines.
In this study, the removal of copper(II) and lead(II) ions from aqueous solutions by Starch-graft-acrylic acid/montmorillonite (S-g-AA/MMT) nanocomposite hydrogels was investigated. For this purpose, various factors affecting the removal of heavy metal ions, such as treatment time with the solution, initial pH of the solution, initial metal ion concentration, and MMT content were investigated. The metal ion removal capacities of copolymers increased with increasing pH, and pH 4 was found to be the optimal pH value for maximum metal removal capacity. Adsorption data of the nanocomposite hydrogels were modeled by the pseudo-second-order kinetic equation in order to investigate heavy metal ions adsorption mechanism. The observed affinity order in competitive removal of heavy metals was found Cu2+ > Pb2+. The Freundlich equations were used to fit the equilibrium isotherms. The Freundlich adsorption law was applicable to be adsorption of metal ions onto nanocomposite hydrogel.
Polyacrylic acid grafted sodium alginate (SA-cl-PAA)-based hydrogel was synthesized by an aqueous polymerisation method. An acrylic acid (AA) monomer was grafted onto sodium alginate (SA) using N,N′-methylene-bisacrylamide (MBA) and potassium persulfate (KPS) as a crosslinker–initiator system. The impact of various parameters such as reaction time, the amount of solvent, pH, crosslinker amount, initiator concentration and monomer concentration on the swelling behavior of the synthesized hydrogel was investigated. We obtained a hydrogel with swelling percentage 41,298% which is quite high. Swelling studies were carried out under acidic (pH 2 buffer) and basic (pH 10 buffer) conditions and evaluated kinetically. The results revealed that the swelling process follows second order kinetics, and the water transport inside the hydrogel supports a Fickian mechanism. The swelling results also indicate that the swelling properties of the synthesized hydrogel showed an on- and off-switchable behavior under basic and acidic conditions, respectively. The synthesized hydrogel was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The hydrogel was used in the victoria blue R (VB) and rhodamine 6G (RG6) dye adsorption from wastewater. It was found that hydrogel adsorbed 95.8 and 99% of VB and RG6 (132 ppm), respectively, within 77 min. Adsorption of victoria blue is due to electrostatic interaction only, and removal of rhodamine 6G is explained on the basis of electrostatic interaction and hydrogen bonding.
Considerable interest has been devoted to graphene since this material has shown promising and excellent results in mechanical and thermal properties. This finding has attracted more researchers to discover the attributes of graphene due to its extensive and potential applications. This paper reviewed the recent advances in the modification of graphene and the fabrication of polylactic acid/graphene nanocomposite. The different techniques that have been employed to prepare graphene, such as reduction of graphene oxide and chemical vapor deposition, are discussed briefly. The preparations of PLA/graphene nanocomposites are described using in situ polymerization, solution, and melt blending; and the properties of these nanocomposites are reviewed. Due to the difficulties in obtaining good dispersions, modifications of nanomaterials have been the critical issues that lead to excellent mechanical properties.
Nanocomposites based on poly (n-butyl methacrylate) (PBMA) with various concentrations of titanium dioxide (TiO2) nanoparticles were synthesised by in situ free radical polymerisation method. The formation of nanocomposite was characterised by FTIR, UV, XRD, DSC, TGA, impedance analyser and flame retardancy measurements. FTIR and UV spectrum ascertained the intermolecular interaction between nanoparticles and the polymer chain. The XRD studies indicated that the amorphous region of PBMA decreased with the increase in content of metal oxide nanoparticles. The SEM revealed the uniform dispersion of nanoparticles in the polymer composite. The DSC and TGA studies showed that the glass transition temperature and thermal stability of the nanocomposites were increased with the increase in the concentration of nanoparticles. The conductivity and dielectric properties of nanocomposites were higher than pure PBMA and the maximum electrical property was observed for the sample with 7 wt% TiO2. As the concentration of nanoparticles increased above 7 wt%, the electrical property of nanocomposite was decreased owing to the agglomeration of nanoparticles in the polymer. Nanoparticles could impart better flame retardancy to PBMA/TiO2 composite and the flame resistance of the materials improved with the addition of nanoparticles in the polymer matrix.
Polyaniline (PANI)/copper oxide (CuO), poly(3,4-ethylenedioxythiophene) (PEDOT)/CuO and polypyrrole (PPy)/CuO have been synthesized electrochemically on glassy carbon electrode in sodium dodecyl sulfate in sulfuric acid solution as an electroactive material. To our best knowledge, the first report on comparison of supercapacitor behaviors of PANI/CuO, PEDOT/CuO and PPy/CuO nanocomposite films was studied by electrochemical impedance spectroscopy, related to the plots of Nyquist, Bode magnitude and Bode phase. The highest specific capacitance (C sp) was obtained as C sp = 286.35 F × g−1 at the scan rate of 20 mV × s−1 for PANI/CuO amongst the PEDOT/CuO (C sp = 198.89 F × g−1 at 5 mV × s−1) and PPy/CuO (C sp = 20.78 F × g−1 at 5 mV × s−1) by CV method. Long-term stability of the capacitor has also been tested by CV method, and the results indicated that, after 500 cycles, the specific capacitance of PANI/CuO nanocomposite film is 81.82 % of the initial capacitance. An equivalent circuit model of R s(C dl(R 1(Q(R 2 W))) has been used to fit the experimental and theoretical data.
In this study, novel kappa-carrageenan/poly(vinyl alcohol) nanocomposite hydrogels were developed by incorporating sodium montmorillonite nanoclay. The mixture of polymers and montmorillonite was crosslinked with freezing–thawing technique and subsequent with K+ ions. The structure of nanocomposite hydrogels was characterized with the FTIR, SEM, XRD, and TEM techniques. By introducing montmorillonite nanoclay, the swelling capacity of nanocomposites was decreased from 1200 to 320 % due to the crosslinking role of montmorillonite nanoclay. The adsorption of cationic crystal violet dye on nanocomposite hydrogels was studied via batch adsorption system on the subject of contact time, nanoclay content, pH of dye solution, temperature, and ion strength of dye solution. Compared with clay-free hydrogel, the nanocomposites indicated a relatively improved adsorption capacity at the same batch system. The variation in the pH of initial dye solution had no significant effect on dye adsorption capacity of hydrogels. Study on salinity of dye solutions showed that while the NaCl salt had less effect on adsorption capacity of hydrogels, in the presence of CaCl2 and AlCl3 salts, the adsorption capacity of nanocomposites was significantly decreased. The adsorption kinetics of crystal violet on hydrogels was well described by the pseudo-second-order model. Also, the equilibrium dye adsorption data were analyzed with non-linear Langmuir and Freundlich models and the equilibrium process was followed well the Langmuir model. According to the Langmuir model, the maximum adsorption capacity of nanocomposites was obtained 151 mg g−1. Thermodynamic parameters confirmed the spontaneity of the adsorption process. Therefore, the synthesized hydrogel nanocomposites could be employed as a low-cost adsorbent in the removal of dyes from aqueous solution.
In this work, polyvinyl chloride (PVC) polymer films doped with 0, 2, 4, and 6 wt% Al2O3 nanoparticles with average size of 10 nm were prepared by solution casting route. Al2O3 nanoparticles are found to possess rhombohedral crystal structure, and PVC is partly crystallized as confirmed with XRD analysis. SEM images showed that Al2O3 nanoparticles are well distributed in the PVC film surface. The direct optical energy gap (E opt) decreased from 5.05 to 3.60 eV and Urbach energy (E U) increased with increasing Al2O3 concentration. The typical excitation energy for electronic transitions (E 0), the dispersion energy (E d), refractive index, dipole strength (f), average oscillator wavelength (λ 0), oscillator strength parameter (S 0), optical conductivity, and both static and high-frequency dielectric constants are found to increase with increasing Al2O3 content. The third-order nonlinear optical susceptibility (χ (3)) and the nonlinear refractive index (n 2) were estimated. Also, the ratio of free carriers to effective mass (N/m*) increased from 2.69 × 1057 to 170.91 × 1057 m−3 kg−1 with increasing Al2O3 nanoparticles percentage. Finally, the group velocity dispersion (GVD), dispersion coefficient for material dispersion (D), and third-order dispersion (TOD) are found to increase upon increasing Al2O3 filler ratio.
Four polyurethane/polyamide copolymer dispersions (PUCON-co-APAS) were prepared from castor oil-based polyol (CON). Castor oil (CO) was firstly transesterified with triethanolamine at 210 °C for different time intervals: 30, 60, 90 and 120 min, to produce CON30, CON60, CON90 and CON120 polyols, respectively. The hydroxyl and acid values, density, viscosity, chemical structure analysis of the CON polyols were determined. The polyols were used to prepare PUCON30-co-APAS, PUCON60-co-APAS, PUCON90-co-APAS, and PUCON120-co-APAS copolymer dispersions in five steps using prepolymer self-emulsification solvent process. The first step is the prepolymer preparation step, in which CON was reacted with dimethylolpropionic acid and excess toluene diisocyanate to produce PUCON NCO . The second step is the copolymerization step, in which PUCON NCO was reacted with amino-terminated aromatic polyamide sulfone. The following processes are neutralization, chain extension and dispersion steps. The prepared copolymer dispersions were characterized using FTIR, DLS, TGA, DSC and GPC. Additionally, the physical, chemical and mechanical properties of the prepared copolymers were studied. The results showed an increase in the hydroxyl number of CON with increasing transesterification time. Stronger H-bonds and smaller particle sizes are produced using CON with higher transesterification time in the preparation of the copolymer dispersions.
The conducting polymer nanocomposites and bionanocomposites attracted greatly significant attention recently owing to their usage in diverse fields, particularly in electrical storage devices. Conducting hydrogel bionanocomposite based on magnetite nanoparticles (Fe3O4-NPs) was synthesized from chitosan/polyacrylic acid/polypyrrole. Furthermore, different ratios of Fe3O4-NPs were added to the synthesized biocomposites to improve the thermal and the electrical conductivity properties of the conducting bionanocomposites hydrogel. In addition, morphology and swelling percentage of the fabricated bionanocomposites hydrogel were investigated. The influence of the conductive polymer and the magnetite nanoparticles on enhancement the conductivity of the bionanocomposites is the main objective of this work. The broadband dielectric spectroscopy was employed to study the electrical and dielectric properties of the investigated samples. The addition of PPy increased the conductivity of the hydrogel by about four orders of magnitude. Furthermore, the effect of adding Fe3O4-NPs at ratios 1-5 wt% was at the satisfactory level.
In this work, microwave-shielding behavior of epoxy thermosetting plastic reinforced with silanized Cu and Cu–Fe3O4 compound particles were studied in frequency bands E, F, I, and J. The principal aim of this work is to evaluate the significant advantage of surface-modified magnetic and conductive fillers over as-received fillers in microwave shielding. The conductive and magnetic properties of epoxy resin were improved by additions of Cu and Fe3O4 particles. Compound particles of Cu–Fe3O4 were produced by mechanical alloying process (ball milling). The compound particles were surface treated by 3-Aminopropyltrimethoxysilane (APTMS) for better dispersion in epoxy resin matrix. Functional groups on particle’s surface after silane surface treatment were confirmed by FT-IR spectra analysis. The TEM images revealed that effective Cu–Fe3O4 particle compounding was formed at 1 h milling time. The maximum dielectric constant of 6.8 and magnetization of 675E−6 were observed for surface-modified compound particle-reinforced epoxy composite designation RCF2. Similarly, maximum microwave attenuation of 35% (44 dB) was observed for surface-modified compound particle-reinforced composite designation RCF2 in ‘J’-band frequency.
Novel superabsorbent membranes consisting of polyvinyl alcohol (PVA), cellulose nanocrystals originated from Ziziphus spina-christi fibers, nanosilica, glutaraldehyde, and glycerin (G) were manufactured by compression moulding process. Ziziphus spina-christi fibers are a new source to isolate pure cellulose nanocrystals via mechanical and chemical treatment. Ziziphus spina-christi fibers were used to improve water-saving irrigation systems. Glycerin was used to increase the elasticity of superabsorbent membranes. These membranes were characterized by FTIR, XRD, SEM, mechanical testing, and thermal analysis. Superabsorbent membranes showed greater equilibrium swelling capacity compared with neat cross-linked PVA. Moreover, water transport mechanism of all superabsorbent membranes followed Fickian diffusion type. Superabsorbent membranes exhibited good pH-dependent swelling reversibility and high-water retention capacity, making it more efficient water-saving material. The superabsorbent membranes were also investigated for antimicrobial activities against pathogenic bacteria like Candida albicans (fungus), Bacillus subtilis (G+ve), Staphylococcus aureus (G+ve), Proteus vulgaris (G−ve), and Erwinia carotovora (G−ve). The results showed that design of innovative bioactive superabsorbent membranes is promising for the water reservoir, which might be most profitable in agricultural applications.
Proton-conducting polymer blend electrolytes based on PVA–PVP–NH4NO3 were prepared for different compositions by solution cast technique. The prepared films are investigated by different techniques. The XRD study reveals the amorphous nature of the polymer electrolyte. The FTIR and laser Raman studies confirm the complex formation between the polymer and salt. DSC measurements show decrease in T g with increasing salt concentration. The ionic conductivity of the prepared polymer electrolyte was found by ac impedance spectroscopy analysis. The maximum ionic conductivity was found to be 1.41 × 10−3 S cm−1 at ambient temperature for the composition of 50PVA:50PVP:30 wt% NH4NO3 with low-activation energy 0.29 eV. The conductivity temperature plots are found to follow an Arrhenius nature. The dielectric behavior was analyzed using dielectric permittivity (ε*) and the relaxation frequency (τ) was calculated from the loss tangent spectra (tan δ). Using this maximum ionic conducting polymer blend electrolyte, the primary proton battery with configuration Zn + ZnSO4·7H2O/50PVA:50PVP:30 wt% NH4NO3/PbO2 + V2O5 was fabricated and their discharge characteristics studied.
Herein, a feasible protocol for the rapid preparation of polylactide (PLA) stereocomplex (SC) crystallite by extrusion was shown, in which a processing temperature lower than its melting point was chosen to suppress the thermal degradation and homocrystallization of PLA. Meanwhile, flexible and biodegradable poly(butylene adipate-co-terephthalate) (PBAT) was introduced to improve the processability of solid SC crystallite. The exclusive formation of SC crystallite with high crystallinity (~ 50 to 60%) was realized without further thermal treatment, which was clearly confirmed by wide-angle X-ray diffraction and different scanning calorimeter tests. It was found that certain amount of PBAT actually facilitates the stereocomplexation process, rendering the extrusion much smooth with 30 wt% more PBAT, thus making it promising to industrially achieve SC crystallite. Furthermore, the as-prepared PBAT/SC blend could be processed easily at a relatively low temperature, desirably allowing its scalable application. This work delivers a facile method for the efficient preparation and wider application of SC crystallite, which could be of great value to fabricate nucleating agents or heat-resistant PLA parts.
The synthesis of a salicylate-based poly(anhydride-ester) was optimized to improve the overall efficiency and quality of the polymer. First, a new approach for the preparation of the polymer precursor minimizes the overall number of synthetic steps and increases the overall yield. Second, the melt-polymerization apparatus was modified to include dynamic mixing, which yields polymer with increased molecular weights on both the milligram and gram scale.