Showing papers in "Reactive & Functional Polymers in 2014"

A review on lignin-based polymeric, micro- and nano-structured materials

Abstract: Next to cellulose, lignin is the second most abundant biopolymer, and the main source of aromatic structures on earth. It is a phenolic macromolecule, with a complex structure which considerably varies depending on the plant species and the isolation process. Lignin has long been obtained as a by-product of cellulose in the paper pulp production, but had rather low added-value applications. Changes in the paper market have however stimulated the need to focus on other applications for lignins. In addition, the emergence of biorefinery projects to develop biofuels, bio-based materials and chemicals from carbohydrate polymers should also generate large amounts of lignin with the potential for value addition. These developments have brought about renewed interest in the last decade for lignin and its potential use in polymer materials. This review covers both the topics of the direct use of lignin in polymer applications, and of the chemical modifications of lignin, in a polymer chemistry perspective. The future trend toward micro- and nanostructured lignin-based materials is then addressed.

Preparation and application of starch nanoparticles for nanocomposites: A review

Abstract: The increasing scientific and industrial interest for starch nanoparticles (SNP) has led to the development of numerous methods for preparing sub-micron starch fillers for nanocomposites applications. Starch nanocrystals (SNC), which constitute the focus of this review, are one type of SNP with crystalline property and platelet like morphology. SNC can be extracted from various starch botanical sources, allowing to obtain a large range of amylose content, shape, viscosity in suspension, surface reactivity and thermal resistance. To date, the most common method for extracting SNC remains the mild acid hydrolysis of the amorphous parts of native granular starch. So far, alternative methods render much lower yield. Since first publications on SNC, the principal aim is to use them as reinforcement in polymer matrices. Thanks to the reactive nature of starch, SNC surface can be modified by grafting or cross-linking which renders them more readily dispersible in the polymer matrix. The present review focus on the reinforcing effect and mechanisms of SNC, as well as on their impact of barrier properties of polymers.

Polymer-based chelating adsorbents for the selective removal of boron from water and wastewater: A review

Abstract: Boron removal from water is a highly interesting research area that has been addressed in various investigations in the recent years. This is due to the expansion of harmful effects of boron traces in water streams on the environment and human health with the rise in boron global demand in various industries that coincided with the implantation of more stringent water quality standards. Various technologies have been applied for the removal of boron from water solutions, including ion exchange technology, which has a great potential in treating varieties of boron-containing streams up to levels in parts per million using boron-selective adsorbents. This article comprehensively reviews the latest progress in the development of polymer-based boron-selective (chelating) materials and their applications for the removal of boron from water solutions, including commercial boron-selective resins (BSRs) and their researched counterparts. The emerging trends in the development of alternative adsorbents with different substrates, morphologies, and functional groups are also elucidated. The future directions to overcome the limitations of the present generation of resins are also discussed.

TEMPO-oxidized cellulose nanofibrils prepared from various plant holocelluloses

Abstract: Plant holocelluloses were prepared from softwood, gymnosperm, hardwood, and herbaceous species, and subjected to TEMPO-mediated oxidation using the TEMPO/NaBr/NaOCl and TEMPO/NaOCl/NaO2Cl systems in water at pH 10 and 6.8, respectively. Weight recovery ratios of the water-insoluble TEMPO-oxidized holocellulose (TOH) fractions and their carboxylate contents, sugar compositions, and X-ray diffraction patterns were measured. When the oxidation at pH 10 was used, the carboxylate content of the TOHs increased up to 1.4–1.7 mmol g−1. The oxidation at pH 6.8 resulted in higher weight recovery ratios of TOHs and their lower carboxylate contents (0.8–1.2 mmol g−1) than those prepared by the oxidation at pH 10. Hemicelluloses in plant holocelluloses are preferentially degraded to water-soluble fractions and removed from TOHs in the oxidation at pH 10. In contrast, the TEMPO-mediated oxidation at pH 6.8 provides hemicellulose-rich TOHs in high weight recovery ratios, although their nanofibrillation yields were low. All TEMPO-oxidized holocellulose nanofibrils (TOHNs) obtained by mechanical disintegration treatment of TOHs in water had the same average widths of ∼3 nm, when measured by atomic force microscopy in water, which were consistent with those of TOHs determined from X-ray diffraction patterns. The number-average lengths of TOHNs were 500–600 nm.

Nucleation, crystallization, self-nucleation and thermal fractionation of cyclic and linear poly(ε-caprolactone)s

Abstract: A series of low polydispersity cyclic PCL samples (C-PCLs), as well as their linear analogs (L-PCLs), were synthesized by click chemistry in a number average molecular weight ( M n ) range of 2–22 kg/mol. They were investigated by Polarized Light Optical Microscopy (PLOM) and Differential Scanning Calorimetry (DSC). The nucleation and overall crystallization kinetics were studied, as well as their self-nucleation behavior and SSA (Successive Self-nucleation and Annealing) thermal fractionation. Cyclic PCLs were found to nucleate and crystallize faster than linear PCLs due to: (a) faster diffusion of C-PCL chains and (b) larger supercoolings of C-PCLs at any given crystallization temperature, as compared to L-PCLs. A bell shape curve was obtained when the overall crystallization rate was examined as a function of M n , this effect is probably due to a competition between nucleation and diffusion. It was found for the first time, that since cyclic molecules have lower entanglement densities, they can quickly recover their pseudo-equilibrium compact coil conformations upon melting and therefore exhibit much smaller crystalline memory effects than their linear counterparts of identical chain lengths. SSA revealed that C-PCLs are more sensitive to annealing than L-PCLs because their ring topology and limited lamellar chain folding facilitates crystal thickening.

Preparation of poly(acrylic acid)/starch hydrogel and its application for cadmium ion removal from aqueous solutions

Abstract: In this paper, potassium bromate/thiourea dioxide redox system was used to initiate the graft copolymerization reaction of acrylic acid onto maize starch. The so obtained polyacrylic acid/starch graft copolymer was crosslinked by further treatment with alkaline epichlorohydrin to get three dimensional hydrogel. This crosslinked hydrogel was used for the removal of the heavy element, Cd2+ from its aqueous solution by adsorption. All factors which are expected to affect the adsorption process, like adsorbent concentration, immersion time, graft yield of the adsorbent, Cd2+ concentration and adsorption temperature were extensively studied and reported in the text. The study and investigations demonstrated that the adsorption efficiency is affected by the adsorbent graft yield and the adsorption medium temperature. In addition, on fitting the data obtained from the adsorption process, it was found that the adsorption obeys both Langmuir and Freundlich adsorption isotherms but the Langmuir isotherm shows better mathematical fitting for the equilibrium data than does Freundlich model, based on the higher R2 value for the Langmuir isotherm.

Synthesis and shape memory performance of polyurethane/graphene nanocomposites

Abstract: Small amounts of allyl isocyanate modified graphene (iG, 0–25 phr) were incorporated into acrylate terminated polyurethane (PU) by UV curing The effects of this incorporation on the morphological, mechanical, thermal and shape memory properties of the nanocomposites were examined The iG nanoparticles incorporated into the PU chains acted as both multifunctional crosslinkers and reinforcing fillers, and the effects were most pronounced at 15 phr iG Consequently, the glassy and rubbery state moduli, yield strength, glass transition temperature ( T g ), shape fixity and shape recovery ratios were increased by adding up to 15 phr iG Above the loadings, most of the above properties decreased due to aggregation and the auto-inhibition reaction of allyl compounds

ECTFE membrane preparation for recovery of humidified gas streams using membrane condenser

Abstract: Polymeric flat membranes, using Ethylene–Chlorotrifluoroethylene copolymer (ECTFE), have been made by Thermal Induced Phase Inversion (TIPS). The non-toxic solvent glycerol triacetate (GTA) has been used as solvent. The morphology of the membranes has been analyzed by scanning electron microscopy (SEM). Asymmetric microporous sponge-like membranes have been produced and their properties in terms of contact angle, mechanical properties, pore size and porosity have been compared with the commercial PVDF hollow-fibers membranes. Both types of membranes have been tested using a membrane condenser, varying the feed temperature and feed flow rate, for the selective recovery of water from gaseous streams. The data obtained have been also supported by a simulation study of the process. The results showed that in both type of polymers used, the percentage of water recovered was similar, between 35% and 55%, much higher than the amount of 20% needed to make the plant self-sufficient. The obtained results and the outstanding chemical resistance properties suggested that the ECTFE flat membranes are very promising candidates for being employed in a membrane condenser, which is a new membrane based operation for water recovery from gaseous waste streams (i.e. flue gas).

Preparation and characterization of an IPN type chelating resin containing amino and carboxyl groups for removal of Cu(II) from aqueous solutions

Abstract: A novel IPN type chelating resin, amino-functionalized poly (glycidyl methacrylate)/poly (acrylic acid), (pGMA/pAA), was synthesized by a combination of serial reactions including, conventional radical polymerization, amination and photopolymerization. To assess the efficacy and characteristics of the resin in removal of Cu (II), batch adsorption experiments were carried out, and the effects of different parameters such as contact time, adsorbent dosage, initial metal ion concentration, temperature, and pH on the adsorption process were investigated. The results showed that 0.5 g/L dosage and pH 5 are the optimum values to achieve the maximum adsorption capacity and the adsorption kinetic of Cu (II) was well represented by pseudo-second-order kinetic model. In addition, it was found that the adsorption was mainly controlled by the film diffusion mechanism, along with a considerable contribution of the intra-particle diffusion mechanism, and Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models can be used for interpreting the adsorption process. Moreover, FT-IR analysis results and the mean free energies of adsorption clearly indicate that the ion exchange and chelation mechanisms took place as dominating mechanisms simultaneously during the adsorption process. It was also found to be that IPN resin could be used at least four times without losing its original activity.

Antibacterial dental resin composites

Abstract: Resin composite materials exhibit good esthetic properties and strength, making them the most commonly used materials for restoring hard tissue, i.e., enamel and dentin. In the last 30 years these restorative materials have been widely used for both anterior and posterior restorations. Regrettably, studies have indicated numerous failures, the main reason for which is secondary caries. Resin composites were found to accumulate more dental plaque than enamel and other restorations. Thus, to increase the service life of resin composite restorations, modifications introducing antibacterial properties are required. In this review the authors discuss the advantages and disadvantages of various released and non-released antibacterial agents incorporated in resin composites. A change in strategy based on the use of antimicrobial polymeric macromolecules is suggested, focusing on polycationic antimicrobials. Polyethyleneimine nanoparticles, in particular, are presented as a possible solution to the disadvantages of released antiseptic agents. Developing agents with strong antimicrobial activity upon contact that do not diminish over time nor affect the biocompatibility of materials should be the focus of future research.

Biopolymeric matrices made of carrageenan and corn starch for the antioxidant extracts delivery of Cuban red propolis and yerba mate

Abstract: Fil: Chang Bravo, Liliam. Instituto de Investigaciones Industria Alimentaria. La Habana; Cuba

Doping of poly(o-phenylenediamine): Spectroscopy, voltammetry, conductivity and band gap energy

Abstract: In the present work, poly(o-phenylenediamine) (PoPDA) were synthesized by the chemical oxidation reaction of o-phenylenediamine (o-PDA) with ammonium persulfate ((NH 4 ) 2 S 2 O 8 ) (APS) as the oxidant. The chemical structure of the synthesized ladder type polymer was confirmed by UV–vis., FTIR, 1 H NMR and TGA measurements. The synthesized polymer was doped by HCl, Cu(II), H 3 BO 3, Fe(III), and I 2 chemical agents. The doped forms of the polymer were examined by cyclic voltammetry (CV), UV–vis. absorption and FTIR spectroscopy. The HOMO, LUMO levels and band gap energies of the doped and undoped forms of the PoPDA were calculated by using UV–vis. adsorption and CV data. The band gap energy of undoped PoPDA was found as 2.25 eV. In general the all dopants increased the band gap energy of the PoPDA. Also, the electrical conductivities of doped and undoped forms of PoPDA were measured. The electrical conductivity of undoped PoPDA was measured as 7.18 × 10 −7 S/cm. It was found that Fe(III) doping increased the electrical conductivity of PoPDA, while HCl, Cu(II), H 3 BO 3 and I 2 dopings decreased the electrical conductivity. The doped PoPDA polymer samples exhibited different optic, voltammetric and band gap behaviors.

Improving the mechanical resistance of waterborne wood coatings by adding cellulose nanofibres

Abstract: In the present study, microfibrillated cellulose (MFC) and nanocrystalline cellulose (NCC) were applied as additives for a waterborne acrylate/polyurethane-based wood coating in order to improve the mechanical resistance of coated wood surfaces. Coating mixtures containing up to 5 wt% nanocellulose were prepared by high-shear mixing and applied to wood substrates. The optical, mechanical and chemical properties of cured coatings were characterized. Surface roughness, gloss, scratch resistance, abrasion resistance and resistance against chemicals were determined according to the relevant European standards. Additionally, nanoindentation (NI) was used to assess the micromechanical properties of modified and unmodified coatings. Owing to a higher surface roughness, cellulose-filled coatings showed significantly lower levels of gloss than the unmodified coating indicating that nanocellulose acts as a matting agent. NI experiments revealed a slightly positive effect of nanocellulose addition on the hardness and modulus of the coatings. While scratch resistance improved consistently with increasing nanocellulose addition, abrasion resistance was found to improve only sporadically. Tensile tests on free-standing coating films revealed a significantly higher tensile strength and modulus for cellulose-filled coatings. Overall, the results suggest that the addition of cellulose nanofibres primarily improves the internal cohesion of the coating layer whereby MFC was more effective than NCC.

Enzyme immobilization on smart polymers: Catalysis on demand

Abstract: A new approach for the synthesis of hydrogel films with thermo-sensitive enzymatic activity is reported. Pepsin (PEP) was covalently immobilized on thermo-responsive hydrogels by radical polymerization in the presence of N-isopropylacrylamide and poly-(ethylene glycol) dimethacrylate 750, acting as functional monomer and crosslinking agent, respectively. Hydrogels showing lower critical solution temperatures between 32.9 and 36.1 °C were synthesized by UV-irradiation of reaction batches differing in the PEP/monomers ratio. The derivatization degree of the hydrogels was expressed as mg of PEP per gram of matrix and found to be in the range of 6 to 11% as assessed by Lowry method. Scanning electron microscopy analysis and water affinity evaluation allowed to highlight the porous morphology and thermo-responsivity of hydrogels as a function of temperature. Using bovine serum albumin as a substrate, kinetics parameters were determined by Lineweaver–Burk plots and the catalyst efficiency evaluated. The influence of temperature on enzyme activity, as well as the thermal stability and reusability of devices, were also investigated.

Reinforcing efficiency of nanocellulose in polymers

Abstract: Nanocellulose extracted from renewable sources, is a promising reinforcement for many polymers and is a material where strong interfibre hydrogen bonds add effects not seen in microfiber composites ...

Aligned unidirectional PLA/bacterial cellulose nanocomposite fibre reinforced PDLLA composites

Abstract: In an effort to enhance the properties of polylactide (PLA), we have developed melt-spinning techniques to produce both PLA/nanocellulose composite fibres, and a method akin to layered filament winding followed by compression moulding to produce self-reinforced PLA/nanocellulose composites. Poly( L -lactide) (PLLA) fibres were filled with 2 wt.% neat and modified bacterial cellulose (BC) in an effort to improve the tensile properties over neat PLA fibres. BC increased the viscosity of the polymer melt and reduced the draw-ratio of the fibres, resulting in increased fibre diameters. Nonetheless, strain induced chain orientation due to melt spinning led to PLLA fibres with enhanced tensile modulus (6 GPa) and strength (127 MPa), over monolithic PLLA, previously measured at 1.3 GPa and 61 MPa, respectively. The presence of BC also enhanced the nucleation and growth of crystals in PLA. We further produced PLA fibres with 7 wt.% cellulose nanocrystals (CNCs), which is higher than the percolation threshold (equivalent to 6 vol.%). These fibres were spun in multiple, alternating controlled layers onto spools, and subsequently compression moulded to produce unidirectional self-reinforced PLA composites consisting of 60 vol.% PLLA fibres reinforced with 7 wt.% CNC in a matrix of amorphous PDLLA, which itself contained 7 wt.% of CNC. We observed improvements in viscoelastic properties of up to 175% in terms of storage moduli in bending. Furthermore, strains to failure for PLLA fibre reinforced PDLLA were recorded at 17%.

Significance of xylan on the stability and water interactions of cellulosic nanofibrils

Abstract: In this paper, the significance of xylan on the behaviour of kraft birch pulp based nanofibrillated cellulose (CNF) is discussed The influence of CNF xylan content on fibril morphology, charge and stability as well as on the film formation ability was investigated, and the features detected on nanoscale and on macroscale are compared In addition to this, the ability of fibrils to uptake water molecules were investigated by bulk and surface sensitive methods which are dynamic water sorption analysis (DVS) and quartz crystal microbalance with dissipation monitoring (QCM-D) equipped with the humidity module, respectively Surface xylan plays a significant role as an electrosteric stabilizer in dilute CNF dispersions when the surface forces are dominant whereas the removal of xylan drastically changes the CNF dispersion properties The settling of the unstable CNF dispersions displays behaviour which is typical for hindered sedimentation When considering thin nanoscale layers of CNF, nanofibrillated cellulosic materials with high content of surface xylan has somewhat higher ability to bind water molecules However, it seems that in more concentrated CNF dispersions where the fibrillar network itself plays also a decisive role, especially with respect to film formation ability, the impact of xylan diminishes Solvent cast macroscale CNF films are still enough dense to maintain good oxygen barrier performance at higher humid conditions although agglomeration tendency of fibrils is higher due to the excessive xylan removal These findings are of high relevance when considering nanocellulosic materials, especially in the form of gels and films, as templates for high added value material solutions

Synthesis of soy protein–lignin nanofibers by solution electrospinning

Abstract: Nanofibers were produced by electrospinning aqueous alkaline solutions containing different mass ratios of soy protein and lignin in the presence of poly(ethylene glycol) coadjutant, all of which presented shear thinning behavior. SEM revealed that the addition of polyethylene oxide as a coadjutant indeed facilitated the formation of defect-free fibers whose diameter increased with lignin concentration, in the range between ≈ 124 and ≈ 400 nm. Favorable interactions between lignin and soy protein were identified from data provided by differential scanning calorimetry. In addition, an increased hydrogen bonding and the loss of secondary structure of the proteins as the lignin concentration increased were observed from the disappearance of amide II (∼1500 cm−1) and III (∼1400–1200 cm−1) bands and a red shift of amide I band in the FT-IR spectrum. The unfolding of the protein contributed to a better interaction with lignin macromolecules, which further improved the electrospinning process. It is concluded that mixtures of lignin and soy proteins, two major renewable resources with interesting chemical features, are suitable for the development of composite sub-micron fibers.

Synthesis and characterization of chitosan hydrogels cross-linked with dicarboxylic acids

Abstract: Chitosan hydrogels cross-linked with dicarboxylic acids were prepared. Succinic, glutaric and adipic acid were used as cross-linking agents, the goal being to compare the effect of the length of the chain on the behavior of the material obtained. The swelling properties were studied at different pHs and temperatures, and it was discovered that these properties depend particularly on the pH of the environment. Creep-recovery and stress-relaxation studies were performed to determine mechanical properties and the chitosan/succinic acid hydrogels exhibited a completely viscous behavior. Thermal studies were carried out using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC results revealed that the materials obtained are completely amorphous. Acetaminophen was used as a positive control for the release kinetics studies. Upon fitting the results to a specific mathematical model, it was determined that the release process is controlled by diffusion and relaxation of the polymer network.

Novel approach for attapulgite/poly(acrylic acid) (ATP/PAA) nanocomposite microgels as selective adsorbent for Pb(II) Ion

Abstract: A novel approach was developed for the preparation of the attapulgite/poly(acrylic acid) (ATP/PAA) nanocomposite microgels via the ‘‘one-pot’’ inverse suspension radical polymerization of acrylic acid (AA) with the multi-functionalized attapulgite nanorods (org-ATP) as the sole crosslinker. The parameters of the feeding ratio of the functional attapulgite (org-ATP) nanorods and AA (org-ATP/AA), oil (liquid paraffin)–water ratio, and feeding ratios of dispersing agent (sodium dodecyl benzene sulfonate (SDBS)) and initiator (ammonium persulfate (APS)) were optimized via 4-Variable 3-Level Orthogonal experiments. Under the optimized preparation condition, more than 85% of the monomer AA had been grafted onto the org-ATP nanorods to form the 3-dimensional network of the ATP/PAA nanocomposite microgel. The ATP/PAA nanocomposite microgel exhibited better mechanical stabilities (resistance to pressure and resistance to agitation) and selective adsorption to heavy metal ions, especially to Pb 2+ . The adsorbed Pb 2+ ion could be completely eluted with HCl solution. The better mechanical stability and regeneration make it potential adsorbent for the heavy metal contaminated water.

Glycidyl methacrylate and ethylhexyl acrylate based polyHIPE monoliths: Morphological, mechanical and chromatographic properties

Abstract: Using water-in-oil emulsions with a high volume share of aqueous (droplet) phase as precursors (High Internal Phase Emulsions; HIPEs), highly porous polymers (polyHIPEs) were prepared from glycidyl methacrylate (GMA) and ethylhexyl acrylate (EHA), their morphology investigated and mechanical and chromatographic characteristics evaluated. All polyHIPE monoliths had open cellular porous morphology with primary pores (cavities) between 4.8 μm and 26.2 μm and secondary level of interconnecting pores. Introduction of EHA into the oil phase and consequently into the polymer matrix of polyHIPEs had a significant effect on the mechanical properties; both tensile strength and elasticity were increased. On the other hand, chromatographic properties, such as protein binding capacity and back pressure, did not dramatically change.

Cyclic polymers as a building block for cyclic brush polymers and gels

Abstract: Cyclic polymers, as one of the oldest topological polymers, are undergoing resurgence. This is largely ascribed to the significant achievements in modern polymer chemistry. The novel ring-expansion techniques have conveniently produced varied cyclic polymers with highly topological purity and on large scales, which should facilitate their use in the near future. Beyond the monocyclic molecular conformations, the combination of controlled polymerization techniques and click chemistry have established a robust strategy for preparing cyclic polymers with more complex architectures, such as theta, eight, and tadpole shapes. This diversification in cyclic polymer composition and conformation significantly broadens interest in the cyclic polymers. However, compared to the synthesis achievements, the exploration of cyclic polymer property and application are lagging behind. Recently, we explored the ring-expansion metathesis polymerization on various functional ring-strained olefin monomers to produce cyclic functional polymers, which were then used as the building blocks to fabricate cyclic brush polymers and cyclic gel materials and will be discussed here.

Poly(NIPAAm-co-β-cyclodextrin) microgels with drug hosting and temperature-dependent delivery properties ☆

Abstract: One of the most important drawbacks of the thermosensitive hydrogels based on N-isopropylacrylamide (NIPAAm) is the lack of functional groups able to specifically bind drugs; moreover, these hydrogels are not biodegradable. In order to overcome these inconveniences, poly(NIPAAm-co-β-cyclodextrin) (poly(NIPAAm-co-β-CD)) microgels were obtained by cross-linking polymerization of the corresponding monomers. β-CD was first functionalized with an appropriate amount of vinyl groups, thus acting both as a co-monomer with hosting properties and as a biodegradable cross-linker. The volume phase transition temperature (VPTT) of the microgels was determined under simulated physiological conditions by measuring the swelling degree and by microcalorimetry. The microgels, due to their small size and high porosity, possess a relative rapid swelling/deswelling rate around the human body temperature. The hydrogels were loaded with the model drug diclofenac by inclusion within cyclodextrin cavity and the release studies were performed under simulated physiological conditions, below and the above the VPTT. In the presence of α-amylase (from Aspergillus Oryzae ), microgels have showed a low degradation rate (15% of initial weight after 7 days), the erosion occurring especially at the surface.

Influence of mechanical treatments on the properties of cellulose nanofibers isolated from microcrystalline cellulose

Abstract: The possibility of preparing cellulose whiskers-like materials by mechanical treatment of commercially available microcrystalline cellulose (MCC) was explored. High shear homogenization, grinding with a supermass colloider, and hammer-milling were the processes selected to disintegrate the MCC, which yielded F-MCC, G-MCC and H-MCC, respectively. Processing aqueous dispersions with high solid content allowed for the production of cellulose particles with greatly reduced dimensions. Morphological characterization revealed that homogenization and grinding reduced the particle size more effectively than hammer-milling, although the disintegration was incomplete in all cases. The reinforcing potential of the materials was evaluated against commercially available whiskers by using the various particles as fillers to mechanically reinforce hydroxypropylcellulose. Nanocomposite films containing 5, 10, or 20 wt.% of the filler were prepared and the mechanical properties were characterized. The results show that H-MCCs are just slightly better than the original MCC, whereas F-MCC and G-MCC performed similar to whiskers at 10 wt.% loading, despite the presence of a fraction of micrometer-sized particles. It is therefore reasonable to envision the use of the more easily produced F-MCC and G-MCC as replacement of cellulose whiskers in some applications.

The adsorptive extraction of oxidized sulfur-containing compounds from fuels by using molecularly imprinted chitosan materials

Abstract: An innovative approach for desulfurisation of fuels is proposed. It relies on the formation of recognition sites, complementary to oxidized sulfur-containing compounds, on cross-linked chitosan microspheres and electrospun chitosan nanofibers using the molecularly imprinted polymer technique. Benzothiophene sulfone (BTO 2 ), dibenzothiophene sulfone (DBTO 2 ) and 4,6-dimethyldibenzothiophene sulfone (4,6-DMDBTO 2 ) were used as templates for the preparation of molecularly imprinted polymers (MIPs). The possible molecular interactions between imprinted chitosan adsorbent and oxidized sulfur-containing compounds were investigated by molecular modeling using density functional theory (DFT) and results indicated that interactions took place via hydrogen bonding. The molecularly imprinted polymer adsorbents (cross-linked microspheres and electrospun nanofibers) gave better selectivity for the target sulfonated compounds and the adsorption isothermal studies followed the Freundlich model. Maximum adsorption capacities of 8.5 ± 0.6 mg/g, 7.0 ± 0.5 mg/g and 6.6 ± 0.7 mg/g were observed for model BTO 2 , DBTO 2 and 4,6-DMDBTO 2 respectively at 1 mL/h when imprinted nanofibers were employed, and the imprinted microspheres gave maximum adsorption capacity of 4.9 ± 0.5 mg/g, 4.2 ± 0.7 mg/g and 3.9 ± 0.6 mg/g for BTO 2 , DBTO 2 and 4,6-DMDBTO 2 respectively. Application of the nanofibers to oxidized hydro-treated fuel under continuous flow adsorption system at 1 mL/h indicated that 84% of sulfur was adsorbed, with adsorption capacity of 2.2 ± 0.2 mg/g.

A new polystyrene-based ionomer/MWCNT nanocomposite for wearable skin temperature sensors

Abstract: The present work outlines the fabrication and testing of a novel skin temperature sensor based on exfoliated and undamaged multi-walled carbon nanotubes (MWCNTs) dispersed in a poly(vinylbenzyl chloride) derivative with triethylamine (PVBC_Et3N). The dispersions were prepared by sonicating MWCNT/PVBC_Et3N mixtures in dimethylformamide for 5 min and the quantification of the MWCNTs dispersed was evaluated by UV–vis spectroscopy investigations and thermogravimetric analyses. The investigations demonstrated the realization of MWCNT/PVBC_Et3N sensors with a resistance sensitivity to temperature close to −0.004 K−1, an absolute value that is comparable to the highest values found in metals. The temperature dependence of the resistance was also found very reproducible in the range 20–40 °C, thus suggesting the possibility of using the MWCNT/PVBC_Et3N system for the fabrication of small wearable temperature sensors for the monitoring of chronic wounds.

Non-cytotoxic conductive carboxymethyl-chitosan/aniline pentamer hydrogels

Abstract: Cytocompatible electrically conducting hydrogels based on amphoteric carboxymethyl chitosan (CMCS) and aniline oligomers with bioactive molecule delivery properties were presented. A series of conductive CMCS hydrogels with different aniline pentamer (AP) content were synthesized by a one-pot reaction with the combination of grafting and crosslinking reaction via glutaraldehyde. The conductivities of the swollen hydrogels are between 1.14 × 10−4 and 4.23 × 10−4 S/cm by tuning the AP content. Swelling ratio was controlled by the AP content and crosslinking degree of the hydrogels. The hydrogels showed absorption capacity of diclofenac sodium (DCS) as a model molecule and released DCS in a controlled manner. Morphologies and mechanical properties of the hydrogels were characterized by SEM and rheometer, respectively. The biocompatibility of the hydrogels was confirmed by C2C12 myoblast cells using Live/Dead assay and Alamar blue assay. These conducting hydrogels with controlled release capacity as bioactive scaffolds have potential application for tissue regeneration.

Relationship between surface concentration of amphiphilic quaternary ammonium biocides in electrospun polymer fibers and biocidal activity

Abstract: Electrospinning was utilized to generate antimicrobial Nylon and polycarbonate fibers for potential applications including self-decontaminating fabrics, wound dressings, and filtration media. The effects of quaternary ammonium salt concentration on fiber morphology, diameter, and antimicrobial activity of the resulting fiber mats were investigated. Fibers were characterized utilizing scanning electron microscopy and X-ray photoelectron spectroscopy, while antimicrobial activity was evaluated against Staphylococcus aureus . The co-electrospinning of soluble quaternary ammonium biocides within polymeric solutions generated uniform fibers with diameters ranging from 91 to 278 nm for Nylon and 0.55–2.34 μm for polycarbonate. Fiber morphology and diameter of the resulting fibers were shown to be dependent on polymer type and biocide concentration. A positive correlation between surface concentration of quaternary ammonium salts and antimicrobial activity was observed as fibers loaded with biocides exhibited up to a 7 log reduction of viable bacteria.

Synthesis, curing behavior and thermal properties of fluorene-containing benzoxazines based on linear and branched butylamines

Abstract: A series of fluorene-containing benzoxazine monomers based on linear and branched butylamines were successfully synthesized in high purity and good yield through a facile one-pot procedure by the reaction of 9,9-bis-(4-hydroxyphenyl)-fluorene with paraformaldehyde and isomeric butylamines. The chemical structures of the target monomers were characterized by Fourier transform infrared (FT-IR), Elemental analysis, 1 H and 13 C nuclear magnetic resonance (NMR). The curing behavior of benzoxazine monomers was studied by differential scanning calorimetry (DSC) and FT-IR. The thermal properties of cured polybenzoxazines were measured by DSC and thermogravimetric analysis (TGA). The results reveal that the polarity of solvent and the basicity of butylamines produce clear effects on the synthesis of the butylamine-based benzoxazine monomers. Also, the basicity and steric effect of butylamines exhibit significant effects on the curing behavior of benzoxazine monomers and the thermal properties of their polymers. The glass transition temperature and thermal stability of branched butylamine-based polybenzoxazines are higher than those of the corresponding linear butylamine-based polybenzoxazine and traditional bisphenol A-based polybenzoxazines.

Preparation and characterization of p-tert-butyl thiacalix[4]arene imbedded flexible polyurethane foam: An efficient novel cationic dye adsorbent

Abstract: In this study, a new type of flexible polyurethane foam containing p-tert-butyl thiacalix[4]arene (TC4A) macrocycle was synthesized. TC4A macrocycle was incorporated into polyurethane foam as a part of crosslinking agent as well as glycerol. Structural, morphological, thermal and mechanical properties of this prepared foam were studied and compared with a polyurethane foam based on only glycerol as crosslinking agent, by Fourier transform infrared (FTIR), Scanning electron microscopy (SEM), Thermal gravimetric analysis (TGA), and dynamic mechanical thermal analysis (DMTA). The effect of introduction of TC4A crosslinker on cream time, rise time, apparent density, and water absorbency of the PU foams was evaluated. Moreover, it was shown that new TC4A-based polyurethane foam (TC-PUF) can be a high performance adsorbent for removal of malachite green from aqueous media using batch adsorption technique. The adsorption results indicated that TC-PUF has a high adsorption capacity of 58.82 mg/g for malachite green due to the presence of TC4A macrocycles in the structure of polyurethane foam. The kinetics of adsorption of malachite green was also investigated using the pseudo-first-order and pseudo-second-order kinetic models. The results of kinetic studies showed that the adsorption of malachite green onto TC-PUF followed pseudo-second-order kinetic model.