Addition Of Cross-linking Agent Research Articles

Formation and properties of cross-linked polymer films based on biocompatible polymers

Cross-linked polymer films based on polyvinyl alcohol and polyacrylamide have been prepared via radical cross-linking initiated by peroxide containing reactive copolymers. The influence of temperature, nature and concentration of cross-linking agents onto gel-fraction value and properties of polymer films has been studied. Obtained cross-linked polymer films are characterized by improved physico-mechanical properties that depend on the content of peroxide containing copolymer and on the presence of additional cross-linking agent.

A simple and green approach to the preparation of super tough IIR/SWCNTs nanocomposites with tunable and strain responsive electrical conductivity

Abstract Nanocomposites of single-wall carbon nanotubes in isobutylene isoprene rubber (IIR/SWCNTs) were successfully prepared by a simple and green wet process. The traditional melt mixing process and organic solvent dissolution suffered from unable to effectively disperse the SWCNTs of tangled structure, and degradation of polymer molecules, respectively. Our process very well avoided these two problems. The SWCNTs aqueous solutions emulsified by polyoxyethylene octyl phenol ether (OP-10) were firstly mixed and compounded with IIR rubber at a relatively high temperature, followed by the second step of melt compounding process with the addition of cross-linking agent and accelerators. The SWCNTs were dispersed uniformly, and a fine network was constructed in the matrix of the obtained IIR/SWCNTs nanocomposite with a low percolation threshold. With the concentration of SWCNTs as low as 2 phr, the IIR/SWCNTs nanocomposite received an electrical conductivity of 10−6∼10−3 S/cm, and a 71% improvement of tensile strength. By varying the loadings of SWCNTs in a certain range, the tensile strength, electrical conductivity, and dielectric property were found tunable. Besides, the nanocomposites also presented strain responsive specific resistance, excellent elongation (600–740%), and better heat resistance.

Affordable Magnetic Hydrogels Prepared from Biocompatible and Biodegradable Sources.

Magnetic hydrogels composed of poly(vinyl alcohol) (PVA)/water-soluble tricarboxy cellulose (CO)/magnetic fluids (MFs) have been prepared by a freeze–thaw cycle technique. The system designed here combines the renewability and biocompatibility aspects of PVA and CO, as well as the magnetic properties of MFs, thereby offering special properties to the final product with potential applications in medicine. In the first step, the water-soluble CO is synthesized using a one-shot oxidation procedure and then the aqueous solutions of CO are mixed with PVA solutions and magnetic fluids in the absence of any additional cross-linking agent. The magnetic hydrogels were thoroughly investigated by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), magnetometry (VSM), and thermogravimetric analysis. The morphological results show an excellent distribution of magnetic particles and CO inside the PVA matrix. The VSM results show that the magnetic hydrogels possess superparamagnetic properties.

Improved water absorption behaviour of experimental hydrophilic vinyl polysiloxane (VPS) impression materials incorporating a crosslinking agent and a novel surfactant

ObjectivesTo study the effects of incorporating a further crosslinking agent and a novel surfactant on the water absorption behaviour of experimental VPS impression materials. MethodsPart 1: The water uptake behaviour of Aquasil-Ultra-Monophase (AqM) was studied gravimetrically in three media (DW, 1%NaOCl and Perform ID), at 23 °C and 37 °C, over a period of one and four-months (n = 5) to gain information on long-term immersion. Part 2: Five experimental materials were formulated: Exp-I and II as hydrophobic and Exp-III-V as hydrophilic, containing an additional cross-linking agent (TFDMSOS) and Rhodasurf CET-2 surfactant. Their water uptake and desorption (both at 23 °C) properties (gravemetrically), solubility, pH and diffusion coefficient (DC) data were compared with three commercial, hydrophilic VPS impression materials, over seven days (n = 5). The results were analysed statistically. ResultsPart 1: Significant differences in water absorbed by AqM were observed in the three media at 23 °C. Aq M had a significantly higher uptake in 2% Perform ID, than in DW and NaOCl. At 37 °C, over four-months the uptake profiles were more enhanced and differed. Part 2: All Exp and commercial materials significantly increased in weight in both media (DW and 1% NaOCl at 23 °C), with differing uptake profiles and non-reached equilibrium. Exp-VPS absorbed significantly less water than commercial-VPS. Desorption of all VPS from both parts was faster than absorption, followed Fickian diffusion kinetics and reached equilibrium within 1–3 days. Desorption DCs for Exp-VPS were higher than commercial materials (10−10 versus 10−11 m2 s−1). The solubility was higher in 1% NaOCl compared to DW. The pH of DW after immersion of samples significantly increased compared to 1% NaOCl. SignificanceThe incorporation of novel cross-linking agent, TFDMSOS and non-ionic surfactant, Rhodasurf CET-2, (ethoxylated-cetyl-oleyl alcohol) improved the dimensional stability of hydrophilic Exp-VPS in DW and 1% NaOCl. These materials merit further research in producing accurate casts of the patient’s anatomy following disinfection.

Glucose-triggered in situ forming keratin hydrogel for the treatment of diabetic wounds

The development of protein-based in situ forming hydrogel remains a big challenge due to the limited chemical groups in proteins. Keratins are a group of cysteine-rich structural protein found abundant in skin and skin appendant. Recently, our lab has established a disulfide shuffling strategy to prepare keratin hydrogels via oxygen (O2) oxidation. However, such hydrogel still needed to be molded in advance. In this work, inspired by the fact that glucose commonly exists in body fluids, a glucose-triggered in situ forming keratin hydrogel was developed based on the disulfide shuffling strategy via a higher oxidation force of hydrogen peroxide (H2O2). The hydrogel precursor solution consisted of keratin, cysteine and glucose oxidase (GOD), which could generate H2O2 in an indirect and mild way via GOD-catalyzed oxidation of glucose in body fluids. Our findings demonstrated that the GOD-catalyzed oxidation method not only shortened the gelation time but improved the mechanical strength of the hydrogel by comparison with O2 oxidation and direct addition of H2O2 solution methods, and realized in situ gelation within 3 min on a full-thickness wound bed in normal mice. Moreover, the in situ forming keratin hydrogel was applied as a drug depot for wound repair, and the deferoxamine-loaded one accelerated healing in the full-thickness wounds of streptozotocin-induced diabetic rats, notably by promoting angiogenesis and neovascularization in wounds. Statement of SignificanceStudies show that keratin hydrogels possess tissue regeneration capacity, especially in skin wound repair. However, most of the reported keratin hydrogels needed to be molded in advance and cannot fit irregular wound shape. This work describes a glucose-triggered in situ forming keratin hydrogel via a disulfide shuffling strategy under the oxidation of hydrogen peroxide. Of note, the hydrogen peroxide was supplied indirectly by glucose oxidase-catalyzed oxidation of glucose in wound fluids, and this method needed no additional crosslinking agents or chemical modifications on keratins. Our findings showed that this hydrogel realized in situ gelation within 3 min on a full-thickness wound bed and enabled an injectable mode with good filling ability toward irregular wounds. Moreover, this hydrogel could be applied as a drug depot for the treatment of diabetic wounds.

Thepeculiaritiesofformation of cross-linked poly(2-ethyl-2-oxazoline) filmsand nanocompositeson theirbase

Cross-linked polymeric and nanocomposite films based on poly(2-ethyl-2-oxazoline) and modified mineral nanoparticles of hydroxyapatite and silica have been obtained via radical cross- linking initiated by peroxide containing reactive copolymers. The influence of temperature and additional cross-linking agents on the peculiarities of curing process has been studied. The obtained results reveal that at high temperatures the dependence of film gel-fraction values on time has the extremal character. Obtained cross-linked nanocomposite films are characterized by improved physico-mechanical properties that depend on the nature of mineral nanoparticles, content of peroxide containing copolymer and on the presence of additional cross-linking agent.

Synthesis and gas transport properties of hyperbranched network polyimides derived from Tris(4-aminophenyl)benzene

A series of carbon molecular sieve (CMS) membranes have been prepared for CO2/N2 separation based on the aromatic hyperbranched polyimides (HBPIs) synthesized by polymerizing 1,3,5-Tris(4-aminophenyl)benzene (TAPB) and three commercially available dianhydrides, including 1,2,4,5-benzenetetracarboxylic anhydride (PMDA), 2,3,3′,4′-Biphenyltetracarboxylic dianhydride (BPDA), 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA). The polymerizations were carried out at −60 °C to avoid the gelation at the critical polymerization concentration and the free-standing membranes were successfully obtained from the HBPI solution using directly solvent casting method after post thermal annealing. The hyperbranched molecules swollen, interpenetrated into the adjacent molecules and finally formed a network, when the temperature increased to 60 °C. Both the molecular entanglement and the post thermal imidization contribute to the membrane formation, without resorting to any additional crosslinking agents. The factors governing the gas separation of the HBPI membranes and the CMS ones were investigated using TGA analysis, FT-IR spectroscopy, X-ray diffraction and Raman characterization. The results confirm that the inter-chain spacing in the HBPIs provide the pathways for gas molecules crossing the membrane. The gas permeabilities of the CMS membranes have been further improved owing to the ultramicro- and micro-pores generated after pyrolyzing at 550 °C. For example, the CO2 permeability of XS13-550 significantly increased from 26.0 barrer (XS13) to 16564.4 barrer with a loss of CO2/N2 selectivity from 34.7 (XS13) to 16.6. This work provides a low-temperature process to prepare HBPI precursors without any crosslinking agents.

Fabrication of hierarchically micro/meso/macroporous silicon carbonitride ceramic using freeze casting method with a silsesquiazane precursor

Hierarchically porous silicon carbonitride (SiCN) was prepared using the freeze casting method with silsesquiazane (SSQZ) as a precursor. As SSQZ possesses a highly branched structure, it can provide a higher cross-linking degree than linear polysilazane and thereby, improve the structural stability. The porous SiCN can be produced without collapsing the pore structures by removing the organic groups during the pyrolysis process due to the high cross-linking degree. In this study, we used the freeze casting method to introduce macropores. In addition, the effects of glycidyl-POSS and 1,7-octadiene diepoxide as additional cross-linking agents on the formation of porous ceramics were investigated. The Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses showed that SSQZ with cross-linking agents demonstrated a higher cross-linking degree and was successfully converted to SiCN ceramics. As a result, the porous SiCN ceramics exhibited an improved structural stability, specific surface area, and pore volume.

100 Years of Macromolecular Science

100 Years of Macromolecular Science

Bovine serum albumin-imprinted magnetic poly(2-pyrrolidone) microparticles for protein recognition

This study reports on the synthesis and adsorption properties of molecularly imprinted porous magnetic microparticles (MIP) based on the biodegradable and sustainable poly(2-pyrrolidone) (PPD or PA4). These new PPD MIP materials were obtained via activated anionic ring-opening polymerization of 2-pyrroldone carried out at 40 °C, in the presence of iron fillers and bovine serum albumin (BSA) as a template. Neither solvent, nor additional crosslinking or porogen agents were used in the PPD MIP synthesis. Analogously, PPD particles without BSA imprinting (NIP) were also produced. Depending on the microparticles composition, their yields were in the 55–70 wt% range, the average size varying between 8 and 25 µm. After characterization of the surface topography of all samples, their adsorption capacity toward the BSA target was assessed as a function of the adsorption time, protein concentration and pH of the medium. All three PPD MIP samples displayed adsorption capacity toward BSA being up to one order of magnitude higher as compared to other BSA-imprinted polymer systems. It was found that the rebinding of BSA on MIP is best described by the Langmuir isotherm, whereas for rebinding on NIP the Freundlich isotherm was the more adequate model. On this basis, the nature of the adsorption on MIP and NIP was discussed. The adsorption toward two other proteins, namely Ovalbumin and Cytochrome C was also tested. The newly synthesized BSA-imprinted PPD MIP displayed selective adsorption for the BSA target being dependent on the pH values of the medium. The easy recovery of the Fe-containing MIP and the capacity of all MIP samples for multiple sorption/desorption cycles was demonstrated.

Bio-friendly titania-grafted chitosan film with biomimetic surface structure for photocatalytic application

A series of biomimetic chitosan (CS) films grafted with titanium dioxide (TiO2) were successfully prepared for photocatalytic reduction of carbon dioxide (CO2). The replication of the hierarchical structure of natural leaves to the surface of CS was conducted by nanocasting technique. The presence of amine and hydroxyl groups on CS matrix was able to anchor TiO2 nanoparticles. The addition of cross-linking agent, glutaraldehyde, improved the denseness of CS matrix but affected the distribution of TiO2. The existence of biomimetic structures on films enhanced the hydrophobicity, thermal stability and CO2 adsorption. Moreover, the surface patterns influenced the optical absorption edge of TiO2-grafted films. Under the illumination of UVA (8-Watt) light source, the TiO2-grafted CS films were able to convert CO2 into carbon monoxide and trace amounts of methanol. The biofriendly CS-supported photocatalysts exhibited the potential for sustainable CO2 reduction for cleaner production of chemical fuels.

Coating performance and rheological characteristics of novel soybean oil-based wax emulsions

Aqueous emulsions of soybean oil-based coating materials consist of ethylene glycol and propylene glycol mono- and di-esters of stearic acid (EGMD and PGMD, respectively) and compound emulsions (mixtures of EGMD emulsion with four commercial polymer emulsions) were formulated and tested for paperboard coating. Paper coated with compound emulsions had excellent water resistance and grease resistance. With EGMD accounting for as high as 60% of the emulsion’s solid content, 5-min Cobb value of about 1.0 gsm (gram per square meter) was achieved. Increased number of drawdowns (coating) significantly improved water and grease resistance of the coated papers. With three-drawdown and coat weight of 14.93–23.00 gsm, 5-min Cobb value of less than 2 gsm and oil penetration of less than 2% were achieved. Greater heat exposure during drying resulted in better water resistance. Increasing the drying temperature from 100 to 200 °C for 30 s reduced the 5-min Cobb value of papers coated with PGMD compound emulsions from 34.1 to 1.1 gsm. The addition of cross-linking agent, zinc ammonium carbonate (ZAC), in the emulsions improved water repellency but not grease resistance. The effect of different emulsifiers on coating performance, rheology and stability of W/O and W/O/W PGMD emulsions were also investigated. The yield stress of cetyltrimethylammonium bromide (CTAB) based emulsions (1.61–21.32 Pa) were much higher than those of Tween 80 based emulsions (0.023–0.066 Pa). Both the W/O and W/O/W emulsion had higher viscosity than the compound emulsions. The compound emulsions had comparable surface energy but lower gluability compared to the commercial emulsions.

Dielectric and flash DSC investigations on an epoxy based nanocomposite system with MgAl layered double hydroxide as nanofiller

Nanocomposites based on MgAL layered double hydroxides (LDH) and an epoxy resin were prepared and investigated by a combination of complementary methods. As epoxy resin Bisphenol A diglycidyl ether (DGEBA) was used with Diethylenetriamine as curing agent. The LDH was modified with taurine, which acts as an additional crosslinking agent due to its amine groups. The epoxy resin was cured in a presence of the nanofiller, which was added to the system in various concentrations. X-ray scattering, by combination of SAXS and WAXS was used to characterize the morphology of the obtained nanocomposites. These investigations show that the filler is distributed in the matrix as small stacks of ca. 10 layers. The molecular dynamics of the system, as probe for structure, was investigated by broadband dielectric spectroscopy. In addition to the β- and α-relaxation (dynamic glass transition), characteristic for the unfilled materials, a further process was found which was assigned to localized fluctuations of segments physically adsorbed or chemically bonded to the nanoparticles. The dielectric α-relaxation is shifted to higher temperatures for the nanocomposites in comparison to the pure material but depends weakly on the content of nanoparticles. Further, for the first time Flash DSC was employed to a thermosetting system to investigate the glass transition behavior of the nanocomposites. The heating rates were converted in to relaxation rates. For low concentrations of the nanofiller the thermal data overlap more or less with that of the pure epoxy. For higher concentrations the thermal data are shifted significantly to higher temperatures. This is discussed in terms the cooperativity approach to the glass transition.

Fabrication of green composites based on rice bran oil and anhydride cross-linkers

Petroleum-based composite materials have limitations in terms of environmental issues, and hence, research works have been going on to replace them with green composite materials. To the best of our knowledge, the synthesis of green oil as resin component and jute as reinforcement material in composites has never been explored. In the present study, epoxidized rice bran oil (ERBO) and acrylated epoxidized rice bran oil (AERBO) were used as toughening agent after blending with a diluter or copolymer, viz. polystyrene (PS) and anhydrides, i.e., maleic anhydride (MA) and phthalic anhydride (PA) as additional cross-linking agents to fabricate jute nonwoven-based composites. It was found that with the increase in copolymer content, there was an improvement in mechanical properties. But in the case of biodegradability test, the presence of additional cross-linkers showed less amount of weight loss due to the formation of compact structure. AERBO curing was optimized by varying the curing time and was characterized by FTIR, gel content and viscoelastic properties. Maximum tensile strength of 35.98 MPa was obtained with 50 wt% nonwoven jute. The composites showed improved thermal stability with anhydrides. Chemical resistance showed less deterioration with anhydrides. DMA analysis also showed an increase in storage and loss modulus with anhydrides and reduction in tanδ peak with its broadening. SEM micrographs showed good adhesion and cross-linking when anhydrides were used. These green composites have good potential to replace a large number of petroleum-based alternatives due to their inherent biodegradability and strength and can be used in automotive, constructions, water tanks and so on.

Injectable Alginate-Peptide Composite Hydrogel as a Scaffold for Bone Tissue Regeneration.

The high demand for tissue engineering scaffolds capable of inducing bone regeneration using minimally invasive techniques prompts the need for the development of new biomaterials. Herein, we investigate the ability of Alginate incorporated with the fluorenylmethoxycarbonyl-diphenylalanine (FmocFF) peptide composite hydrogel to serve as a potential biomaterial for bone regeneration. We demonstrate that the incorporation of the self-assembling peptide, FmocFF, in sodium alginate leads to the production of a rigid, yet injectable, hydrogel without the addition of cross-linking agents. Scanning electron microscopy reveals a nanofibrous structure which mimics the natural bone extracellular matrix. The formed composite hydrogel exhibits thixotropic behavior and a high storage modulus of approximately 10 kPA, as observed in rheological measurements. The in vitro biocompatibility tests carried out with MC3T3-E1 preosteoblast cells demonstrate good cell viability and adhesion to the hydrogel fibers. This composite scaffold can induce osteogenic differentiation and facilitate calcium mineralization, as shown by Alizarin red staining, alkaline phosphatase activity and RT-PCR analysis. The high biocompatibility, excellent mechanical properties and similarity to the native extracellular matrix suggest the utilization of this hydrogel as a temporary three-dimensional cellular microenvironment promoting bone regeneration.

Mussel-inspired, robust and self-healing nanocomposite hydrogels: Effective reusable absorbents for removal both anionic and cationic dyes

Polydopamine (PDA) composited LAPONITE® cross-linked hydrophobically associated (PLHA) hydrogels were facilely constructed by in situ polymerization. The PLHA hydrogel exerted improved mechanical properties and excellent stability with an additional cross-linking agent LAPONITE®, which guaranteed the hydrogel could be utilized for long-time and reusable application. Notably, the self-healing property of PLHA gels could be achieved easily by the hereinafter three factors: hydrophobic association, LAPONITE® and PDA. Compared with the pristine hydrophobic associated (HA) gel, excellent dye adsorption capacity towards both anionic and cationic dyes came out in PLHA gels owing to the negative charges on LAPONITE and abundant functional groups on PDA nanoparticles such as amine groups, catechol groups and aromatic moieties. The PLHA gels could bind organic dyes via various ways, including coordination, electrostatic interaction, hydrogen bonding or π-π stacking interaction. Compared with the reported works, our proposed method provided the opportunity to prepare a novel robust, self-healing physically dual cross-linked hydrogels, which have the potential to be applied in tissue engineering and the reusable adsorbents of organic colorants.

PMB quality problems based on its morphology and used equipment

In the first part of the study, a direct relationship is established between the influence of the morphology of PMB (polymer modified binder) on the totality of its consumer properties and its tendency to destruction. The second part of the study is devoted to the influence of technological equipment used for the production of polymer modified binder on its properties. It was experimentally established that having the same initial components, PMB of completely different quality were obtained at the output. According to the degree of increase in rigidity (penetration value at 25 °C), obtained PMBs can be conditionally positioned as follows: prepared using a paddle mixer, a colloid mill, and an extruder. It is proved that the high elastic properties of PMB can be achieved by using paddle mixers that do not damage the long polymer macromolecules during the process. However, such binders are prone to delamination. To eliminate this negative aspect, the use of additional crosslinking agents is necessary. PMB prepared using an extruder has lost its elastic abilities, has become tough, with a high rate of cohesive strength. Thus, it is noted that when designing PMB compositions, it is necessary to carefully choose not only the raw material base but also the technological equipment for its preparation.

On the in-depth density distribution of layered assemblies of Au nanoparticles on planar interfaces

The assemblies of optically active gold nanoparticles on a functionalized silicon planar substrate were considered in terms of the interface depth density distribution obtained by atomic-force microscopy, X-ray diffraction/reflectometry and neutron reflectometry. Two layers of nanoparticles were sequentially deposited using an additional cross-linking agent. First layer was made of nanoparticles being synthesized in light water while the second one in light/heavy water mixture. The isotope difference in layers observed in the neutron reflectometry experiment was related to water molecules incorporation into the organic shell around nanoparticles. The results are discussed with respect to the possibilities in resolving the structure of complex multilayer assemblies.

Photo-cross-linked Antibacterial Zein Nanofibers Fabricated by Reactive Electrospinning and its Effects against Streptococcus mutans

Native zein electrospun nanofibers have shown poor solvent resistance and low mechanical strength. Compared to other toxic cross-linkers, a safer method of stabilizing zein based fibers while retaining or with improved mechanical strength is needed to convert these materials for biomedical applications where culture media or body fluids may be present. We report here a method of fabricating non-toxic zein nanofibers using reactive electrospinning coupled with in situ photo-cross-linking. The cross-linked zein nanofibers exhibited significantly improved mechanical strength and sustained morphology against water and aqueous ethanol solution. This process doesn't require additional conventional cross-linking agents to form cross-linking network, which is advantageous for biomedical applications. Antimicrobial monomer with photo-reactive moiety was coupled with methacrylate zein nanofibers and showed strong inhibitory activity against cariogenic Streptococcus mutans. Cytotoxicity test with human gingival fibroblasts revealed high biocompatibility.

Influence of gamma irradiation on polymerization of pyrrole and glucose oxidase immobilization onto poly (pyrrole)/poly (vinyl alcohol) matrix

This paper describes the immobilization of glucose oxidase, GOx onto polymer matrix comprising of poly(pyrrole), PPy and poly(vinyl alcohol), PVA using gamma irradiation technique. Py/PVA-GOx film was prepared by spreading PVA:GOx, 1:1 solution onto dried pyrrole film and exposed to gamma irradiation from cobalt 60 source at doses ranging from 0 to 60 kGy. The films were subjected to structural and morphological analyses by using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Scanning electron microscope (SEM), Field emission scanning electron microscope (FESEM) and Atomic-force microscopy (AFM) techniques. Similar studies were also made on pristine pyrrole film which served as control. The SEM and FTIR spectra of Py/PVA-GOx film revealed that pyrrole has been successfully polymerized through irradiation-induced reactions. The results on the morphological properties of the samples characterize using FESEM, SEM and AFM further confirmed the occurrence of radiation-induced modification of Py/PVA-GOx film. The FTIR spectra showed the existence of intermolecular interaction between polymer matrix and GOx indicating that GOx had been successfully immobilized onto Ppy/PVA matrix by radiation-induced reactions. Results revealed that radiation induced reactions such as polymerization of pyrrole, crosslinking of PVA, grafting between the adjacent PVA and pyrrole molecules as well as immobilization of GOx onto Ppy/PVA matrix occurred simultaneously upon gamma irradiation. The optimum dose for GOx immobilization in the polymer matrix found to be 40 kGy. Therefore it is clear that this irradiation technique offered a simple single process to produce Py/PVA-GOx film without additional crosslinking and polymerization agents.