Free-radical Crosslinking Research Articles

Thermodynamic properties and morphology of 2D NBR/PEG-PPG-PEG networks

2D binary polymer blends are an interesting tool to obtain nanostructured coatings combining the constituting polymers properties. However, the incompatibility of most polymer blends leads to phase separation and the difficulty to optimally combine their properties. Interpenetrating polymer networks (IPN) have been developed in 3D as a strategy to limit phase separation. In this work, the synthesis of 2D IPN was performed and their morphology was investigated depending on the cross-linking reaction parameters. For this, 2D mixed films based on nitrile-butadiene rubber (NBR) and poly(ethylene glycol)- block -poly(propylene glycol)- block -poly(ethylene glycol) (PEG-PPG-PEG) triblock copolymers were studied by coupling thermodynamic characterizations, microscopy observations and sum frequency generation (SFG) spectroscopy. A complete phase separation has first been evidenced in a large composition range and attributed to the very large difference in the polymers viscosities. Next, NBR and/or PEG-PPG-PEG networks formation within the mixtures was studied through a free radical cross-linking and/or an acid-catalyzed acetalization reaction, respectively. The synthesis of the NBR network or both polymer networks within the blends did not induce significant morphological changes in terms of complete phase separation, however the simultaneous cross-linking allowed to freeze the initial structure. In contrast, the formation of only the PEG-PPG-PEG network led to a significant reorganization of the NBR-richest mixed films, resulting in the miscibility of the copolymers. • Complete phase separation in a large composition range is attributed to the very large difference in the polymers viscosities. • Cross-linking of PEG-PPG-PEG within some mixtures leads to miscibility of the linear copolymers. • Simultaneous polymer cross-linking within mixtures allowed to freeze the initial structure.

Fe3O4 embedded κ-carrageenan/sodium alginate hydrogels for the removal of basic dyes

Here, we introduce κ-carrageenan and sodium alginate based hydrogel (CAG-NaAlg-cl-polyAA) and hydrogel nanocomposite (CAG-NaAlg-cl-polyAA/Fe3O4) through a free radical crosslinking method using acrylic acid/ N,N′- methylenebisacrylamide as a monomer/crosslinker system. The hydrogel is stimuli-responsive and its water absorption efficiency is enhanced through the optimization of synthesis parameters. The synthesized superabsorbents have been sequentially characterized through HR-TEM, powder XRD, FTIR, SEM-EDS, and XPS analysis. The average particle size of Fe3O4 nanoparticles stabilized through the CAG-NaAlg-cl-polyAA hydrogel matrix is 10.7 ± 2.5 nm. The CAG-NaAlg-cl-polyAA hydrogel exhibited > 95 % dye removal efficiency for the removal of basic dyes (auramine O, crystal violet and malachite green), whereas the % dye removal potential of CAG-NaAlg-cl-polyAA/Fe3O4 is enhanced upto 99 % after the incorporation of Fe3O4 nanoparticles. Langmuir adsorption is the most favorable adsorption isotherm with R2 = 0.992 (auramine O, AU), 0.989 (malachite green, MG), and 0.974 (crystal violet, CV). Kinetic studies indicate that the adsorption of AU, CV, and MG follows pseudo 2nd order kinetics. Moreover, the reusability of the fabricated samples upto five consecutive cycles further explores its potential for the separation of basic textile dyes from industrial wastewater.

In situ formed self-healable quasi-solid hybrid electrolyte network coupled with eutectic mixture towards ultra-long cycle life lithium metal batteries

The exploration of high-performance polymer-based electrolyte have great promise for the development of next-generation lithium metal batteries. In this study, a self-healable quasi-solid hybrid electrolyte network coupled with deep eutectic solvent (X-PPS-D4) was prepared by polyaddition reaction, photo-initiated free-radical crosslinking, and physical blending. X-PPS-D4 not only possessed high ionic conductivity (σ) of 2.03✗10−4 S cm−1 at 30 ℃ but also wide electrochemical stability window (0∼5.0 V vs. Li+|Li). The enhanced lithium ion transference number (tLi+= 0.44) for X-PPS-D4 resulted from reduction of anion mobility that was proved by spectral analysis together with nuclear magnetic resonance study and theoretical calculation. Under testing temperature of 30 ℃, X-PPS-D4 could support stable long-term (>1300 h) plating/stripping tests of lithium symmetrical cell at current density of 0.1 mA cm−2. More importantly, the in situ formed X-PPS-D4 on LiFePO4 cathode within the coin cell facilitated excellent cell performance with specific capacity over 100 mA h g−1 at 5 C and ultra-long cycle life (>1000 cycles) with high delivered specific capacity at 1 C (>116.1 mA h g−1 after 1000 cycle). X-PPS-D4 also supported coin cells with high voltage cathode to perform decently. This research provides new insights into structure-property relationship of quasi-solid hybrid electrolyte with eutectic mixture and offered an effective way to develop high-performance polymer-based electrolytes for LMBs.

The effect of crosslinker contents on the up-conversion luminescence properties of CdNb2O6: Er3+ powders embedded in the polyethylmethacrylate (PEMA) networks

In this work, CdNb2O6:Er2O3(1.5 mol% Er3+) powders doped with Er3+ were embedded in bulk linear polyethylmethacrylate (PEMA) and also as a novelty embedded in bulk PEMA crosslinked networks (gels) with four different crosslinker contents by free-radical crosslinking polymerization with 0.1 EMA (weight %) at 60 °C. The Er3+ ions structures embedded in bulk linear PEMA and PEMA gels were investigated by the X-ray diffraction (XRD) technique. The crystalline particle size was found using Pielazsek particle distribution and the Scherrer equation. The average of the crystalline particle sizes was found to be decreasing from 75 nm to 12.50 nm by increasing the crosslinker contents therefore, it was shown that the distribution became more uniform. The morphology of CdNb2O6: Er3+ embedded in PEMA gel samples was monitored by scanning electron microscopy (SEM). The functional groups on linear PEMA and PEMA gels samples were monitored by Fourier transform infrared (FT-IR) spectra, and the results were consistent with XRD results. The optical properties of polymer samples were investigated by measuring luminescence spectra at room temperature. The doped Er3+ ion excited with a 975 nm diode laser achieved the up-conversion (UC) emissions by involving two or three-photon absorptions in the visible region. The effects of crosslinker contents on the UC emission, color tuning, and color quality parameters were observed. As the crosslinker contents increased, the UC emission intensities increased due to increasing the distance between Er3+- Er3+ ions. The change in color coordinates was also observed by increasing crosslinker content. The chromaticity diagram over the increasing power of the excitation source visualized the tunability of the emitted color. The improvement of the color purity was observed as a function of crosslinker concentration.

Environmentally benign approach for the efficient sequestration of methylene blue and coomassie brilliant blue using graphene oxide emended gelatin/κ-carrageenan hydrogels

Herein, we report the synthesis and characterization of gelatin/κ-carrageenan crosslinked polyacrylic acid hydrogel (GT-CAG-cl-polyAA) and graphene oxide incorporated hydrogel nanocomposite (GOHNC) through a free radical crosslinking pathway. Under optimized reaction conditions, GT-CAG-cl-polyAA displayed 486 % maximum swelling percentage. TEM image depicted wrinkled silk veil wave-type surface morphology of graphene oxide (GO), whereas, the SEM analysis indicated the porous nature of the GT-CAG-cl-polyAA and GOHNC capable of accumulating a large number of water/dye molecules. GT-CAG-cl-polyAA exhibited 96.11 % and 82.16 % dye removal potential for the adsorption of methylene blue (MB) and coomassie brilliant blue (CB), respectively under optimized conditions. GOHNC enhanced the % dye removal efficiency (98.39 % for MB and 94.50 % for CB). The maximum adsorption capacity of GOHNC for the removal of CB and MB was 312.7 mg/g and 94.9 mg/g, respectively. The adsorption of CB and MB exhibited best fitting with Flory-Huggins adsorption isotherms data. The negative values of ΔG° and positive values of ΔS° which were obtained from the adsorption isotherm plot suggested the thermodynamic feasibility of the adsorption. Also, the samples were reusable for up to five consecutive cycles without any degradation and hence suggested a considerable pathway for the separation of textile dyes.

Mechanistic insight into impact of clay on compressive elasticity of poly(N-alkyl acrylamide)/Laponite-based nanocomposite cryo-beads

Relationship between formation pathway and Hertzian elasticity of poly(N-isopropylacrylamide-co‑sodium acrylate)/Laponite® XLG, P(NIPA-NaA)/LAP, based nanocomposite cryo-beads was evaluated. Millimeter-sized nanocomposite cryo-beads were prepared by combination of dropwise freezing into cryogenic liquid (DFLC) method with sedimentation cryogelation method. pH-sensitive 3D-templete was formed by conducting free-radical crosslinking cryopolymerization of NIPA and NaA in the presence of synthetic hectorite Laponite® XLG as inorganic crosslinker and N,N′-methylenebis(acrylamide) as chemical crosslinker. The effects of network template, ionic comonomer, inorganic clay incorporation, pH- and ionic strength of swelling medium on the swelling and elasticity were evaluated as a function of bead size. The deformability of swollen cryo-beads was investigated using Hertzian elasticity. The crosslink density and Hertz modulus of nanocomposite beads vary with the droplet size and the polymer spheres with low crosslink density tend to absorb more water. In DFLC method, the desired sphere size and swelling can be adjusted by selecting the needle size used for dripping. The swelling degree increased significantly as the size of nanocomposite cryo-beads increased. At a fixed swelling ratio, the cylindrical nanocomposite cryogels exhibited greater elastic moduli and crosslink density than that of spherical gels. Correlation of elastic modulus of cryo-beads with swelling and cross-linked polymer concentration predicted a higher scaling exponent than the classical estimate for swelling in good solvents. It was investigated how the presence of 30 mol% pH-sensitive anionic comonomer NaA in the structure of all nanocomposite gels affects their pH-dependent swelling behavior. At pH < 5.7, the gels exhibited a lower swelling ratio, whereas at pH > 6.6 they tended to swell and followed second-order swelling kinetics by Fickian diffusion. When pH of swelling medium was alternately changed, all gels exhibited a pH-switch and swelling rate was two times higher than shrinkage rate. By investigating the effect of KCl, NaCl and K2CO3 on the swelling of cryobeads, it was determined how the salt cation changes the electrostatic repulsion between network charges. Nanocomposite cryo-beads showed fast pH-responsiveness and immediately reabsorbed the water they lost due to pH change, therefore, they can be designed as drug release carriers by pH-switching modulation.

2D Materials (WS2, MoS2, MoSe2) Enhanced Polyacrylamide Gels for Multifunctional Applications.

Multifunctional polymer composite gels have attracted attention because of their high thermal stability, conductivity, mechanical properties, and fast optical response. To enable the simultaneous incorporation of all these different functions into composite gels, the best doping material alternatives are two-dimensional (2D) materials, especially transition metal dichalcogenides (TMD), which have been used in so many applications recently, such as energy storage units, opto-electronic devices and catalysis. They have the capacity to regulate optical, electronic and mechanical properties of basic molecular hydrogels when incorporated into them. In this study, 2D materials (WS2, MoS2 and MoSe2)-doped polyacrylamide (PAAm) gels were prepared via the free radical crosslinking copolymerization technique at room temperature. The gelation process and amount of the gels were investigated depending on the optical properties and band gap energies. Band gap energies of composite gels containing different amounts of TMD were calculated and found to be in the range of 2.48–2.84 eV, which is the characteristic band gap energy range of promising semiconductors. Our results revealed that the microgel growth mechanism and gel point of PAAm composite incorporated with 2D materials can be significantly tailored by the amount of 2D materials. Furthermore, tunable band gap energies of these composite gels are crucial for many applications such as biosensors, cartilage repair, drug delivery, tissue regeneration, wound dressing. Therefore, our study will contribute to the understanding of the correlation between the optical and electronic properties of such composite gels and will help to increase the usage areas so as to obtain multifunctional composite gels.

Structure-Property Relationships of Shape Memory, Semicrystalline Polymers Fabricated by In Situ Polymerization and Crosslinking of Octadecyl Acrylate/Polybutadiene Blends.

The current work presents the study of a semicrystalline, shape memory polymer synthesized by simultaneous free radical polymerization and crosslinking in a blend of polybutadiene (PB) and octadecyl acrylate. Blending elastomers and phase change materials provide a modular method for new smart materials, such as shape memory polymers. In this system, grafted, side-chain crystalline poly(octadecyl acrylate) (PODA) fixes a programmed shape in the shape memory cycle, while crosslinked polybutadiene drives shape recovery. This work focuses on improving material parameters important for shape memory (crystallinity, gel fraction, melting temperature) by tuning the processing and formulation parameters (amount of crosslinker and PB weight fraction). The result is a shape memory PB-PODA copolymer that can be fabricated by melt processing and programmed without cooling below ambient temperature. It is found that good shape memory (i.e., high shape fixity and recovery) is obtained at a low PB weight fraction where a percolating PODA crystal network is formed at room temperature. The optimized sample shows excellent shape memory properties (fixity > 99%, recovery = 96%). It is shown that it is possible to mold this material into complex 3D shapes or topography with potential use in anticounterfeiting and antitampering applications.

Simultaneous One-Pot Interpenetrating Network Formation to Expand 3D Processing Capabilities.

The incorporation of a secondary network into traditional single-network hydrogels can enhance mechanical properties, such as toughness and loading to failure. These features are important for many applications, including as biomedical materials; however, the processing of interpenetrating polymer network (IPN) hydrogels is often limited by their multistep fabrication procedures. Here, a one-pot scheme for the synthesis of biopolymer IPN hydrogels mediated by the simultaneous crosslinking of two independent networks with light, namely: i) free-radical crosslinking of methacrylate-modified hyaluronic acid (HA) to form the primary network and ii) thiol-ene crosslinking of norbornene-modified HA with thiolated guest-host assemblies of adamantane and β-cyclodextrin to form the secondary network, is reported. The mechanical properties of the IPN hydrogels are tuned by changing the network composition, with high water content (≈94%) hydrogels exhibiting excellent work of fracture, tensile strength, and low hysteresis. As proof-of-concept, the IPN hydrogels are implemented as low-viscosity Digital Light Processing resins to fabricate complex structures that recover shape upon loading, as well as in microfluidic devices to form deformable microparticles. Further, the IPNs are cytocompatible with cell adhesion dependent on the inclusion of adhesive peptides. Overall, the enhanced processing of these IPN hydrogels will expand their utility across applications.

Selective and effective adsorption of malachite green and methylene blue on a non-toxic, biodegradable, and reusable fenugreek galactomannan gum coupled MnO2 mesoporous hydrogel

A new FG-g-AM-cl-MBA-MnO2 hydrogel has been synthesised via a free radical cross-linking reaction using fenugreek gum containing macromolecular galactomannan units, acrylamide, N, N′-methylenebisacrylamide, potassium persulfate, and MnO2 for removal of methylene blue and malachite green dyes from water. Surface morphology of synthesised hydrogel was porous and rough as determined by FESEM. The presence of functional groups and cross-linking mechanism were validated by FTIR spectroscopy. TGA revealed that FG-g-AM-cl-MBA-MnO2 hydrogel is thermally stable up to 700 °C and mass ratio of MnO2 was found to be 25.9%. BET technique gave surface area as 5.59 m2/g with a pore radius of 3.654 nm. The swelling ratio of FG-g-AM-cl-MBA-MnO2 hydrogel was 1862% at 313 K. To evaluate the influence of adsorbent dose, contact time, temperature, pH, and dye concentration on adsorption behaviour of hydrogel several batch experiments were conducted. The hydrogel preferentially removes MG (98.5%) and MB (96.3%) effectively following Langmuir model with 526.31 and 483.09 mg/g adsorption capacity, respectively. The adsorption process followed pseudo-second-order kinetics and thermodynamics study revealed that process is endothermic and spontaneous. The hydrogel retained more than 85% adsorption capacity even after ten cycles of dye adsorption-desorption process and thus, serves as a proficient, reusable, and eco-friendly adsorbent for wastewater remediation.

A Review on various methods for the Cross-linking of Polymers

Cross-Linking the carbon atoms suffices to transform such material intoa superior material that may be resistant to temperature, pressure, corrosion, and that can be used in a variety of applications. Cross Linking is a stabilization process in polymer chemistry which leads to multidimensional extension of polymeric chain resulting in network structure. Cross-link is a bond which links one polymer chain to other. It can be ionic or covalent. Cross Linking changes a liquid polymer into ‘solid’ or ‘gel’ by restricting the ability of movement. When polymer chains are linked together by cross-links, they lose some of their ability to move as individual polymer chains. A liquid polymer (where the chains are freely flowing) can be turned into a ‘solid’ or ‘gel’ by cross-Linking the chains together. Cross Linking increases the molecular mass of a polymer. Cross-linked polymers are important because they are mechanically strong and resistant to heat, wear and attack by solvents. Cross-link property has been used to improve the insolubility, mechanical strength, stiffness, and rigidity of polymer microbeads having potential applications in solid-phase synthesis, solid-phase extraction, and biomedical fields. Hydrogels represents a class of high-water content polymers with physical or chemical crosslinks. Their physical properties are similar to soft tissues. A popular approach to attaining controlled drug delivery from polymer-based systemsinvolves the use of cross-linkers. In order to improve the properties of polymers specific toothier applications, they can be modified by either physical cross-linkers (high pressure, irradiation) or chemical cross-linkers (glutraldehyde, genipin).Therefore, synthesis of polymer with desired cross-linker (hydrophilic/hydrophobic/rigid/flexible) and concentration of cross-linker (cross-link density) is an important.Polyethylene (PE) once cross linked is advantageously employed in the fabrication of blanket insulation for electrical and telephone wires, pipes for the transport of cold and hot liquids, prostheses for the human body. In the present review, chemical cross-Linking by free-radical, condensation, UV radiation, and small-molecule cross-Linking are discussed in details.

Polydopamine-heparin complex reinforced antithrombotic and antimicrobial activities of heparinized hydrogels for biomedical applications

Large-scale fabrication of heparinized hydrogel could be accomplished by free-radical crosslinking polymerization (FRCP), whilst its bioactivity is often partially lost. Heparinized hydrogel based implantable medical devices, therefore, frequently encounter the compelling problems of thrombosis and microbial infection. In this study, a facile FRCP approach was proposed to fabricate heparinized hydrogels by preforming polydopamine-heparin (PDA-HEP) complex, which bypassed the steps of heparin functionalization and effectively preserved the function of heparin in the meantime. Compared with heparin mixed hydrogels, heparin in PDA-HEP complex composite hydrogels augmented the antimicrobial activity of PDA by enhancing the combined bactericidal action of cations and reactive oxygen species (ROS), while still maintaining its anticoagulant function. Since its integration of extremely low hemolysis rate, remarkable anticoagulation property and efficient bactericidal performance, we believe that this universal method of preparing heparinized hydrogels based on PDA-HEP complex will speed up the versatile application of hydrogel implants in clinical medicine.

A Review on Various Methods for the Cross-linking of Polymers

Cross-Linking the carbon atoms suffices to transform such material intoa superior material that may be resistant to temperature, pressure, corrosion, and that can be used in a variety of applications. Cross Linking is a stabilization process in polymer chemistry which leads to multidimensional extension of polymeric chain resulting in network structure. Cross-link is a bond which links one polymer chain to other. It can be ionic or covalent. Cross Linking changes a liquid polymer into ‘solid’ or ‘gel’ by restricting the ability of movement. When polymer chains are linked together by cross-links, they lose some of their ability to move as individual polymer chains. A liquid polymer (where the chains are freely flowing) can be turned into a ‘solid’ or ‘gel’ by cross-Linking the chains together. Cross Linking increases the molecular mass of a polymer. Cross-linked polymers are important because they are mechanically strong and resistant to heat, wear and attack by solvents. Cross-link property has been used to improve the insolubility, mechanical strength, stiffness, and rigidity of polymer microbeads having potential applications in solid-phase synthesis, solid-phase extraction, and biomedical fields. Hydrogels represents a class of high-water content polymers with physical or chemical crosslinks. Their physical properties are similar to soft tissues. A popular approach to attaining controlled drug delivery from polymer-based systemsinvolves the use of cross-linkers. In order to improve the properties of polymers specific toothier applications, they can be modified by either physical cross-linkers (high pressure, irradiation) or chemical cross-linkers (glutraldehyde, genipin).Therefore, synthesis of polymer with desired cross-linker (hydrophilic/hydrophobic/rigid/flexible) and concentration of cross-linker (cross-link density) is an important.Polyethylene (PE) once cross linked is advantageously employed in the fabrication of blanket insulation for electrical and telephone wires, pipes for the transport of cold and hot liquids, prostheses for the human body. In the present review, chemical cross-Linking by free-radical, condensation, UV radiation, and small-molecule cross-Linking are discussed in details.

Synthesis and Characterization of Stretchable Ionic Cable

A transparent and flexible polymer with unique electric and sound signal transmission capability under highly stretchable conditions has been synthesized. In this paper the milestone achieved in the polymerization of intrinsic ionic Ω–conjugated polymer, hereinafter known as Ionic Cables (ICs), through free radical crosslinking co-polymerization process/technique and structural modifications encountered so far in our experiments are discussed. EIS and stress-strain assessments had showed that ionic conductivity and flexibility are dependent on the amount of accelerator Tetramethylethylenediamine (TEMED) and curing time (CT). By varying the amount of accelerator, in our case TEMED, and CT the ICs with ionic conductivity of 0.021 S/cm to 0.111S/cmand 350% elongation to 448% elongation conditions was synthesized with highly water absorption capability up to 78% of its total volume. The synthesized ICs with ultra-stretchability, transparency and conductivity can be used in versatile applications, including stretchable ionic cables, tissue engineering, ionic mass transport systems and bio sensors.

In Situ RheoNMR Correlation of Polymer Segmental Mobility with Mechanical Properties during Hydrogel Synthesis.

Understanding polymer gelation over multiple length‐scales is crucial to develop advanced materials. An experimental setup is developed that combines rheological measurements with simultaneous time‐domain 1H NMR relaxometry (TD‐NMR) techniques, which are used to study molecular motion (<10 nm) in soft matter. This so‐called low‐field RheoNMR setup is used to study the impact of varying degrees of crosslinking (DC) on the gelation kinetics of acrylic acid (AAc) and N,N′‐methylene bisacrylamide (MBA) free radical crosslinking copolymerization. A stretched exponential function describes the T 2 relaxation curves throughout the gelation process. The stretching exponent β decreases from 0.90 to 0.67 as a function of increasing DC, suggesting an increase in network heterogeneity with a broad T 2 distribution at higher DC. The inverse correlation of the elastic modulus G′ with T 2 relaxation times reveals a pronounced molecular rigidity for higher DC at early gelation times, indicating the formation of inelastic, rigid domains such as crosslinking clusters. The authors further correlate G′ with the polymer concentration during gelation using a T 1 filter for solvent suppression. A characteristic scaling exponent of 2.3 is found, which is in agreement with theoretical predictions of G′ based on the confining tube model in semi‐dilute entangled polymer solutions.

Direct fluorination of nanographene molecules with fluorine gas

The transformation of graphene into sp3-bonded carbon films through ultra-high pressure, hydrogenation or fluorination has been studied for years. It is considered that only few layers of graphenes on metal surfaces can realize this transformation and the electron orbitals hybridization between metal substrate and graphene layer is thought to be the drving force and stabilize the formed sp3 carbon structure. Here, we use nanographene molecule, hexa-peri-hexabenzocoronene (HBC), as the model compound to exploit the fluorination reaction between graphene and fluorine gas. MALDI-TOF mass, XPS and XRD results show that the direct fluorination realized the intermolecular cross-linking of nanographene molecules without the assistence of mental substrate. Combining with theoretical calculation and EPR test results, we proved that the fluorination of nanographene molecules with F2 follows a free-radical mechanism, and the carbon radicals formed during fluorination caused the covalent cross-linking between graphene molecules which have a tight π-π stacking. Meanwhile, the fluorination of other small nanographene molecules, pyrene and perylene, further confirmed the universality of this free-radical cross-linking mechanism. This would provide a further understanding for the chemical transformation from graphene layers to 2D diamond structure under chemical adsorption process.

Sulfasalazine/Nimesulide dual-loaded halloysite based poly (sulfobetaine methacrylate) hydrogels: Development and drug release characteristics

Co-administration of two or more drugs has recently become a viable option for treating a variety of diseases, including rheumatoid arthritis (RA). A simple method was used to encapsulate drugs with different solubilities in the same matrix. The internal space of halloysite nano tubes was increased by acid treatment prior to drug loading. Nimesulide (NIMS, an NSAID) and sulfasalazine (SLZ, a DMARD) were loaded into the halloysite lumen either individually or in combination. The halloysite-drug conjugates were then incorporated with poly [2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide (PSBMA) matrix during free radical crosslinking polymerization. Different kinetic models (zero-order, first-order, Higuchi, and Korsmeyer-Peppas) were studied to fit single and combined drug release kinetics. When compared to its sole drug formulation, the combined drug release kinetics demonstrated different release mechanisms. Both drugs were released more slowly as pH decreased, owing to their decreasing solubility. Cell culture tests revealed that the composite hydrogel was not cytotoxic.

Evolution of nC16H34-water–mineral systems in thermal capsules and geological implications for deeply-buried hydrocarbon reservoirs

Organic-inorganic interactions between hydrocarbons and most minerals in deeply buried reservoirs remain unclear. In this study, gold capsules and fused silica capillary capsules (FSCCs) with different combinations of nC16H34, water (distilled water, CaCl2 water) and minerals (quartz, feldspar, calcite, kaolinite, smectite, and illite) were heated at 340 °C for 3–10 d, to investigate the evolution and reaction pathways of the organic–inorganic interactions in different hot systems.After heating, minerals exhibited little alteration in the anhydrous systems. Mineral alterations, however, occurred obviously in the hydrous systems. Different inorganic components affected nC16H34 degradation differently. Overall, water promoted the free-radical thermal-cracking reaction and step oxidation reaction but suppressed the free-radical cross-linking reaction. The impact of CaCl2 water on the nC16H34 degradation was weaker than the distilled water as high Ca2+ concentration suppressed the formation of free radicals. The presence of different waters also affects the impact of different minerals on nC16H34 degradation, via its impact on mineral alterations. In the anhydrous nC16H34-mineral systems, calcite and clays catalyzed generation of low-molecular-weight (LMW) alkanes, particularly the clays. Quartz, feldspar, and calcite catalyzed generation of high-molecular-weight (HMW) alkanes and PAHs, whereas clays catalyzed the generation of LMW alkanes and mono-bicyclic aromatic hydrocarbons (M-BAHs). In the hydrous nC16H34-distilled water–mineral systems, all minerals but quartz promoted nC16H34 degradation to generate more LMW alkanes, less HMW alkanes and PAHs. In the nC16H34-CaCl2 water–mineral systems, the promotion impact of minerals was weaker than that in the systems with distilled water.This study demonstrated the generation of different hydrocarbons with different fluorescence colors in the different nC16H34-water–mineral systems after heating for the same time, implying that fluorescence colors need to be interpreted carefully in investigation of hydrocarbon charging histories and oil origins in deeply buried reservoirs. Besides, the organic–inorganic interactions in different nC16H34-water–mineral systems proceeded in different pathways at different rates, which likely led to preservation of liquid hydrocarbons at different depth (temperature). Thus, quantitative investigations of the reaction kinetics in different hydrocarbon-water-rock systems are required to improve the prediction of hydrocarbon evolution in deeply buried hydrocarbon reservoirs.

In situ-formed adhesive hyaluronic acid hydrogel with prolonged amnion-derived conditioned medium release for diabetic wound repair

Hydrogels have long been used for encapsulating stem cell-derived conditioned mediums to achieve skin regeneration after wounding. However, inappropriate mechanical strength, low adhesion and low elasticity limit their clinical application. To address these challenges, we engineered a hyaluronic acid-based hydrogel grafted with methacrylic anhydride and N-(2-aminoethyl)-4-[4-(hydroxymethyl)-2-methoxy-5-nitrophenoxy]-butanamide (NB) groups to encapsulate a lyophilized amnion-derived conditioned medium (AM-CM). This hydrogel can photopolymerize in situ within 3 s by photo-initiated free-radical crosslinking between methacrylate moieties. Meanwhile, the formed o-nitrosobenzaldehyde groups by photo-irradiation could covalently bond with the amino groups of tissue surface, which allowed strong tissue adhesion. Furthermore, the hydrogel possessed excellent mechanical properties, high elasticity, favorable biocompatibility and prolonged AM-CM release. Our further vitro and in vivo studies showed that the hydrogel significantly accelerated diabetic wound healing by regulating macrophage polarization and promoting angiogenesis. The engineered hydrogel with AM-CM release has high potential to treat chronic wounds in clinics.

REVIEW: APPLICATION OF IRRADIATION TECHNOLOGY IN NATURAL RUBBER VULCANIZATION PROCESS

APPLICATION OF IRRADIATION TECHNOLOGY IN NATURAL RUBBER VULCANIZATION PROCESS . A new vulcanization technology is needed in order to eliminate some potential negative impacts of conventional vulcanization such as contain nitrosamines and allergen proteins that are harmful to health, toxic residues of accelerator compound, cannot be done at room temperature, and sulfur crosslinking contribute to acidification impact. One of the advanced technologies that can be used in the processing of polymers, such as natural rubber, is irradiation using gamma rays. This study is descriptive analysis by conducting a literature search from books and journals of national and international reputation. Radiation in latex of natural rubber will cause free radical formation, crosslinking, and chain scission between polyisoprene chains, and also produce mostly H 2 gas. For crosslinking, materials with G(S):G(X) ratios &lt;1.00 are preferred. The dose increase till certain dose led to an increase in the cross-link density of the irradiated rubbers, while apparently, the degradation mechanism has occurred for doses greater than optimum doses. The tensile strength at break of radiation vulcanizate has long been presumed to be lower than that of sulfur vulcanizate or peroxide vulcanizate. The approaches for enhancing radiation crosslinking could be defined by incorporation with filler, increasing the possibility of polymer radical recombination, and increasing the amount of polymer radicals.