Effect Of Crosslinking Degree Research Articles

Molecular Dynamics Simulation on the Heat Transfer in the Cross-Linked Poly(dimethylsiloxane).

In this work, the effect of cross-linking degree and stretching on the thermal conductivity of poly(dimethylsiloxane) (PDMS) is explored by performing a molecular dynamics simulation. Our results demonstrate that the thermal conductivity of PDMS exhibits a monotonous rise with an increase in the cross-linking degree. By decomposing the total heat flux into three microscopic heat transfer modes, the high cross-linking degree improves the contribution from bonding interactions to the heat transfer more than that from the nonbonding interactions. An analysis of the vibrational density of states shows a blue-shift of the vibrational modes at low frequencies, indicating a large phonon group velocity due to the strong interchain bonding interaction. From the spectral distribution of heat flux, the spectral contributions are shifted toward the higher frequencies with the increasing cross-linking degree, which reflects more contribution from the high-frequency modes to the heat transfer. Stretching can improve the thermal conductivity parallel to the tensile direction with the increase in strain. This is mainly due to the further improved contribution of bonding interactions or high-frequency modes to heat transfer. Interestingly, the anisotropy of the thermal conductivity first decreases and then increases with the increasing cross-linking degree. Our study conducts a detailed investigation of the thermal conductivity of cross-linked PDMS, providing guidance on the application of thermal interface materials.

Effects of cross-linking degree and steric hindrance on the thermal degradation behavior of novel hybrid zirconium-silicone resin

Although silicone resins are commonly seen as popular candidates for heat-resistant applications, the severe weight loss at the temperature from 400 to 800 °C remains a challenge. Herein, we reported a strategy to enhance the thermal resistance by introducing Zr into the main chain. Molecular simulation shows the Zr atoms led to the formation of high energy Zr–O bonds and increased the cross-linking degree which in turn suppressed the formation of cyclic oligomers, the results was further supported by TG-IR. The degradation activation energy was increased from 75.26 (ZAS0) to 88.67 kJ/mol (ZAS5) for the major degradation stage. The degradation kinetics study shows the degradation of ZAS5 followed the cylindrical symmetrical three-dimensional diffusion mechanism (n = 1.5). This work could provide a systemic experimental and theoretical foundation for thermal properties enhancement through metal atoms incorporation.

Effects of Cross-Linking Degree and Characteristic Components on Mechanical Properties of Highly Cross-Linked Phenolic Resins: A Molecular Dynamics Simulation Study

Phenolic resins (PF), naphthol modified phenolic resins (NPF), and cyanate ester modified phenolic resins (CEPF) were constructed where naphthols and triazine rings act as chain reinforcing and chain-to-chain bridging roles, respectively. Then, molecular dynamics simulations were performed to predict the Young’s modulus. The results show that methylene bridges and branched phenolic rings are key factors affecting the stiffness of resin. Introducing naphthols does not provide a clear benefit in stiffness due to a counterbalance between the rise in nonbonded energies and the drop in methylene bridges. For CEPF, the chain-to-chain bridges of triazine rings increase the Young’s modulus up to 2.93 GPa and contribute significantly to stiffness compared to reinforcing chains by rigid naphthols. The trend of the three systems from plastic to the cured state can be seen in the mean squared displacement and Young’s modulus. These findings can support the study of the molecular design of PF to optimize stiffness.

PolySchiff based self-healing solid-state electrolytes for lithium ion battery

Vitrimers are novel polymeric materials consisting of dynamic covalent networks that can change their topology in response to external stimuli. Here, we reported flexible solid polymer electrolyte (SPE) with room temperature self-healing properties based on imine dynamic network. The effect of cross-linking degree, the content of succinonitrile (SN) plasticizer and lithium salt on the lithium ion conductivity (σ) was carefully studied. With the addition of the lithium salt, the Tg of pure polyschiff film is apparently enhanced and the vitrimers electrolyte with lower cross-linking degree show a lower Tg. The σ shows an obviously increasing trend with the dropping cross-linking degree and higher SN content, and it reach a maximum value of 6.43 × 10−4 S/cm at 30 wt % LiTFSI at 60 °C. Importantly, the cutted vitrimers electrolyte show 74 % recovery of its original tensile strength after self-healing at room temperature. Furthermore, the electrochemical window was widened with SN addition, up to 5.1 V vs. Li/Li+. The fabricated Li||PSFSPE@0.5SN||LiFePO4 cell also demonstrates a 100mAh/g discharge capacity at 0.05C after 50th cycles, showing its possible application of imine-based polymer electrolyte. Importantly, the SPEs membranes with imine bonds can heal damages outside or inside a battery without deterioration of discharging capacity of lithium ion battery.

Preparation of porous poly(4‐tert‐butylstyrene) based monoliths with high efficiency for oil‐water separation via high internal phase emulsion template

AbstractDeveloping low‐cost and highly efficient hydrophobic absorbents via simple and environmentally friendly method is demanded for oil‐water separation. This paper reports the preparation of hydrophobic absorbents of porous poly(4‐tert‐butylstyrene‐co‐divinylbenzene) (poly(tBS‐co‐DVB)) via high internal phase emulsion (HIPE) template method. The effects of crosslinking degree and internal phase volume fraction on the porous structure and adsorption performance of the absorbents are investigated. As the tBS/DVB molar ratio increases from 1:1 to 4:1, the adsorption performance of poly(tBS‐co‐DVB) toward hexane first increases to a maximum at a molar ratio of 3:1 and then decreases. As the internal phase volume fraction increases, the specific surface area (SSA) and porosity of the poly(tBS‐co‐DVB)s notably increase from 33.06 m2/g and 84.07% to 102.89 m2/g and 92.94%, respectively. When the internal phase fraction is 95 vol%, the obtained poly(tBS‐co‐DVB) foam with a water contact angle of 140° shows an absorbing capacity as high as 70.21 g/g for dichloromethane. After 10 consecutive adsorption‐desorption cycles, the adsorption performance of the poly(tBS‐co‐DVB) foam shows only a slight decrease, indicating an excellent recycling ability. The obtained poly(tBS‐co‐DVB) foams exhibit the advantages of facile preparation, high oil absorption capacity and satisfactory recoverability, which enable them potential as sustainable oil adsorbents.

Tissue paper-based composite separator using nano-SiO2 hybrid crosslinked polymer electrolyte as coating layer for lithium ion battery with superior security and cycle stability

In order to develop high power lithium ion batteries (LIBs), urgent requirements including adequate safety, higher current density and superior cyclic stability are proposed for separator. Tissue paper, composed of packed cellulose fibers, possesses lower production cost, easier accessibility, superior wettability together with outstanding thermostability, and is thus a candidate to be the substrate for high performance separator. To address the issue of structural failure usually encountered by single polymer as binder during long term cycling, crosslinked binder was constructed on tissue paper to adhere nano-SiO2 through chemical reactions between poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and hyperbranched polyethyleneimine (PEI) in this work. The effects of crosslinking degree on physical properties and electrochemical performance were studied thoroughly. When the feed ratio of PVDF-HFP and PEI is fixed at 10:1, the crosslinked composite separator displays excellent electrolyte uptake and wettability, superior ionic conductivity, better interfacial compatibility as well as higher Li+ transference number (0.56), thus offering battery with prominent rate capabilities. Besides, this crosslinked composite separator exhibits satisfying dimensional stability even treated at 250 °C, better flame retardancy, enhanced mechanical behavior, wider electrochemical window and outstanding cycle stability. Accordingly, tissue paper-based crosslinked composite separators can meet higher requirements put forward by high power LIBs.

Preparation and Properties of Thermally Expandable Microspheres for Foam Coating

A type of thermally expandable microspheres (TEMs) for foam coating was prepared by suspension polymerization with acrylonitrile (AN), methyl methacrylate (MMA), vinyl acetate (VAC) as shell polymer monomers and i-pentane as core foaming agent. The effects of an aqueous additive (Sodium Chloride, NaCl) on the size and distribution of TEMs, and the effects of crosslinking degree, i-pentane dosage and monomer mass ratio on the expansion property, expansion temperature and solvent-resistance of TEMs were investigated. The results showed that when the dosage of NaCl was close to the saturation solubility (30%), the dosage of crosslinking agent and alkane were about 0.09% and 7.4%, and the mass ratio of AN/MMA/VAC w rm distribution and good solvent resistance, the expansion diameter ratio was 5 times under 110~120 C, which meets the application requirements for foam coating of leather or synthetic leather.

Carboxymethyl cellulose/polyethersulfone thin-film composite membranes for low-pressure desalination

Herein, we report the fabrication of carboxymethyl cellulose (CMC)/polyethersulfone (PES) thin-film composite nanofiltration membranes using a dip-coating method with glutaraldehyde (GA) as the crosslinking agent. The effects of crosslinking degree and the dip-coating parameters, including CMC concentration and dipping time, on the performance and morphology of the fabricated membranes were investigated. The properties of the prepared membranes were analyzed by ATR-FTIR, AFM, FE-SEM, and water contact angle analysis. The optimized membrane containing 0.2 wt% CMC, crosslinking degree of 20% by the dipping time of 10 min represented a rejection efficiency of 91.90%, 68.63%, and 45.90% towards the Na2SO4, MgSO4, and NaCl solutions (100 mg/L), respectively. The pure water flux of the optimal membrane was 47.90 ± 1.77 L/m2 h under a low transmembrane pressure of 0.4 MPa. The flux recovery ratio of the nanofiltration membrane was 63% higher than the PES support membrane, indicating an improvement in fouling resistance.

Enhanced Gold(III) adsorption using glutaraldehyde-crosslinked chitosan beads: Effect of crosslinking degree on adsorption selectivity, capacity, and mechanism

Recovery of gold from electronic waste (e-waste) has received significant attention due to its high economic value. This study reports glutaraldehyde-crosslinked chitosan (GCC) beads as highly efficient bioadsorbents for the separation of auric ions (Au(III)) from acidic e-waste leaching solutions. With increasing extent of glutaraldehyde-crosslinking, the GCC beads showed enhanced adsorption selectivity and capacity toward Au(III). The Au(III) adsorption capacity, however, was saturated with a further increase in the crosslinking time due to increasing self-oligomerization of glutaraldehyde. High adsorption selectivity was also observed for other precious metals such as Pd(II), Pt(IV), Ir(III), Os(IV), and Ag(I), but negligible adsorption was found for most other metals. The high Au(III) adsorption capacity and selectivity of GCC beads was attributed to multiple mechanisms such as electrostatic attraction, chelation, and reduction of Au(III), based on a range of spectroscopic evidence (FTIR, XRD, XPS, SEM, and TEM) and Au(III) adsorption behavior. The adsorbed Au(III) was reduced to Au(I) and then to Au(0), forming Au-nanoparticles as the main Au species with increasing adsorption time. The GCC beads showed a good reusability in repeated Au(III) adsorption–desorption cycle tests and were used to successfully separate high purity gold (96.7%) from an acidic e-waste leaching solution.

Effects of different parameters on thermal and mechanical properties of aminated graphene/epoxy nanocomposites connected by covalent: A molecular dynamics study

This paper is devoted to studying the thermal and mechanical properties of aminated graphene (AG)/epoxy nanocomposites connected by covalent bond using molecular dynamics (MD) simulation. The effects of crosslinking degree, mass fraction and functionalized graphene (FG) type on AG/epoxy nanocomposites are considered. The elasticity modulus (E), the glass transition temperature (Tg), the coefficient of thermal expansion (CTE) and the interfacial energy (Eint) are also investigated. The MD simulation results indicate that, when the mass fraction of AG is between 1.2% and 3.1% and crosslinking degree reaches about 70%, the E, Tg, Eint and CTE of AG/epoxy nanocomposites are significantly improved compared with those of pure epoxy and graphene/epoxy nanocomposites. The reason is that AG not only possesses some excellent thermodynamic properties of graphene, but also has the function of curing agent to crosslink with epoxy monomer to form the carbon-nitrogen (C–N) covalent bond. A better interfacial interaction between nanoparticles and epoxy is essential in enhancing the thermal and mechanical properties of nanocomposite materials, which will provide a microscopic theoretical basis for the study of epoxy nanocomposites.

Effects of crosslinking degree on the coating properties of arabinoxylan

Arabinoxylan (AX) was extracted from sugarcane bagasse and modified through crosslinking with glutaraldehyde (GA). The effects of crosslinking degree on the rheological and coating properties of glutaraldehyde crosslinked arabinoxylan (GAX) were investigated. To better evaluate the degree of crosslinking, the crosslink index was used to represent the degree of crosslinking for the GAX in this study. The viscosity of the GAX solution increased when the degree of crosslinking increased, and the solution demonstrated non-Newtonian flow behavior. A high degree of crosslinking was detrimental to the film and coating properties of the GAX. At an optimum degree of crosslinking, the tensile strength of the GAX films increased by approximately 170% and 60% compared with that of the AX and GAX with the highest degree of crosslinking, respectively; the tensile strength of the GAX-coated paper increased by approximately 15% compared with that of the GAX with the highest degree of crosslinking. When calcium carbonate was mixed with the paper coating adhesives, the GAX showed comparable coating properties to that of polyvinyl alcohol, demonstrating its potential to substitute petroleum-based paper coating adhesives.

Preparation of Superhydrophilic Adsorbents with 3DOM Structure by Water-Soluble Colloidal Crystal Templates for Boron Removal from Natural Seawater.

Three-dimensionally ordered macroporous cross-linked poly(glycidyl methacrylate) (3DOM) was constructed by water-soluble colloidal crystal templates and further functionalized with N-methyl-d-glucamine (NMDG) to prepare superhydrophilic adsorbents for boron removal from natural seawater. 3DOM adsorbents possess features of interconnected macropore structure, ultrathin pore wall, and superhydrophilicity, making efficient adsorption possible. The effect of cross-linking degree on the adsorption capacity toward boron was investigated. The NMDG-modified 3DOM adsorbent with rich vicinal diol functional groups showed superhydrophilicity and outstanding performance of adsorption. Significantly, its adsorption effect in boron removal from natural seawater indicated that the concentration of boron in natural seawater could decline to 0.16 from 4.24 mg·L-1 when the adsorbent dosage was 1 g·L-1, whereas the boron rejection reached 96.2%. After 10 regeneration-adsorption cycles, the adsorption capacity of 3DOM adsorbent remained over 85% of the initial value and the ordered structure was hardly changed. Additionally, 3DOM adsorbent could be directly and quickly separated from the seawater by a filter mesh of 16 mesh number. Research shows that the 3DOM adsorbent exhibits an adsorption performance for practical applications in boron removal from natural seawater.

Effects of crosslinking degree and carbon nanotubes as filler on composites based on glycidyl azide polymer and propargyl‐terminated polyether for potential solid propellant application

ABSTRACTTriazole crosslinked polymers were prepared by reacting glycidyl azide polymer (GAP) with the propargyl‐terminated poly(tetramethylene oxide) (PTMP) at different molar ratios of azide versus alkyne. Based on the optimum mechanical properties of the GAP/PTMP‐2.5, a series of GAP/PTMP nanocomposites reinforced by either multi‐walled carbon nanotubes (MWCNTs) or carboxy‐functionalized multiwalled carbon nanotubes (MWCNTs‐COOH) were prepared with different mass ratios. The glass transition temperatures (Tg, PTMP) assigned to PTMP of the GAP/PTMP composites almost kept at a constant range when the molar ratio of azide versus alkyne was from 1.0 to 2.5. When the loading MWCNTs was 1.0 wt %, the tensile strength and elongation at break achieved a maximum of 1.77 MPa and 36.3%, respectively. The nanocomposites with nearly similar Tg, PTMP indicated no phase separation in the crosslinked polymers. The results revealed that the improved properties of GAP‐based materials could be achieved by changing the molar ratio of azide versus alkyne and the nanofillers content. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45359.

Molecular dynamic simulation on the state of water in poly(vinyl alcohol) hydrogel

In this paper, a molecular dynamic model for PVA hydrogel crosslinked by radiation is proposed. The rule of classification and statistical methods of water molecules in PVA hydrogel is formulated. Through molecular dynamic simulation, the content of non-freezing water, freezing water and free water in various cross-linking degree can be determined. The effect of cross-linking degree on the content of non-freezing water is also revealed by the simulation results. The results of molecular dynamic simulation show good agreements with the experimental data. Especially, it was shown that in a specific range of cross-linking degree, the content of non-freezing water in PVA hydrogel remains constant.

Improvement on Physical Properties of Pullulan Films by Novel Cross-Linking Strategy.

Pullulan based films possess several advantages, including high transparency, low toxicity, good biodegradability, good mechanical properties, and low oxygen permeability, are preferable for food packaging. The application of pullulan films on food packaging, however, has inherent disadvantage of high water solubility. In this study, glutaraldehyde and glycerol were used as the cross-linking reagent and the plasticizer respectively to improve water resistance and physical properties of the pullulan films. Effects of cross-linking degree on physical properties, including water absorptions, swelling behaviors, water vapor permeability and tensile strengths of films were evaluated. FTIR results demonstrated that the pullulan films were successfully cross-linked by glutaraldehyde. The tensile strength of pullulan films could be enhanced significantly (P < 0.05) when glutaraldehyde was between 1% and 5% (w/w); nevertheless, the amount of glutaraldehyde above 20% (w/w) led to films brittleness. With the addition of glycerol as a plasticizer enhanced the extensibility of films as well as the hydrophilicity, resulting in higher water vapor permeability.

Accelerated water tree aging of crosslinked polyethylene with different degrees of crosslinking

The effect of crosslinking degree on accelerated water tree aging in crosslinked polyethylene (XLPE) was investigated. The peroxide-crosslinking process was adopted to make XLPE specimens with different degrees of crosslinking by controlling the doping content of dicumyl peroxide (DCP) in low-density polyethylene (LDPE). The water blade electrode method was applied to accelerate water-tree aging of LDPE and XLPE specimens (hereafter referred to as the specimens), and their morphologies were observed using an optical microscope. The variation of crystalline morphology and anti-cracking performance of the amorphous region in the specimens were analyzed by differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and an electronic universal testing machine. Based on the experimental results, it was found that XLPE has great anti-water-treeing performance compared to LDPE. In addition, the higher the crosslinking degree, the better the anti-water-treeing performance. Although crystal growth is inhibited due to the crosslinking reaction, the density of tie molecular chains greatly increases in the amorphous region and exhibits significantly tighter lamellar stacking, which is the reason that water tree growth is restrained with increasing crosslinking degree.

Effect of crosslinking degree and thickness of thermosensitive imprinted layers on recognition and elution efficiency of protein imprinted magnetic microspheres

Crosslinking degree is difficult to determine on the premise of simultaneously considering response performance and recognition capability in the thermosensitive imprinted materials due to their mutually contradictory relationship. In addition, the effect of thickness of thermosensitive imprinted layers on the recognition of target protein is also difficult to evaluate quantitatively. To solve these two problems, a series of thermosensitive magnetic imprinted microspheres with different crosslinking degree and imprinted layer thickness were fabricated. The adsorption results showed that imprinted layer thickness of 17nm was the most appropriate for BSA imprinting. Crosslinking degree of 20% was determined as the balance point by simultaneously considering response performance and recognition capability. Under such conditions, the elution efficiency after once washing process was up to 78.60%, which guaranteed the satisfactory regeneration capability. The adsorption capacity and the imprinting factor could reach 42.01mg/g and 3.41, respectively, which were greatly increased compared to those imprinted materials reported previously. Furthermore, the practical separation performance of the imprinted microspheres was investigated by separating BSA from the protein mixture sample, and the results were exciting. All these results indicated that these imprinted microspheres were expected to be applied to the rapid isolation and purification of BSA.

Effect of cross-linking degree on selected properties of retrograded starch adipate

The aim of this study was to determine the effects of the concentration of paste used to produce retrograded starch, and esterification degree, on selected properties of the resultant distarch adipate.Starch paste was prepared from native potato starch (1, 4, 10, 18 or 30g/100g), frozen, defrosted and dried. Thus produced preparations of retrograded starch were cross-linked with various doses of a cross-linking agent (0.125, 0.25, 0.5, 1.0 or 2.0ml per 100g of starch).Properties of the produced adipates depended on both the concentration of paste used to produce retrograded starch and the degree of substitution with adipic acid residues. Solubility in water and swelling power of the cross-linked preparations of retrograded starch, as well as pasting temperature and viscosity of produced pastes, all decreased along with the increasing degree of substitution with adipic acid residues.

Mass transport properties of gliadin films: Effect of cross-linking degree, relative humidity, and temperature

The degree of cross-linking of gliadin films was increased by chemical treatment with cinnamaldehyde. The formation of a more reticulated network was able to achieve a simultaneous reduction of water vapor, oxygen, and carbon dioxide permeabilities, enhancing barrier properties by up to 64%, 75%, and 79%, respectively. The evaluation of solubility and diffusivity coefficients involved in water vapor permeation highlights the complexity of the mechanisms implicated in water transport through hydrophilic films. Water vapor sorption isotherms followed a non-linear profile, which was fitted with the D’Arcy and Watt model. Water vapor diffusivity was concentration-dependent, being affected by plasticization and water clustering. Temperature-dependence of water vapor permeability showed a discontinuous behavior when the Arrhenius law was applied, indicating possible changes in the matrix structure. Oxygen permeability was positively influenced by relative humidity and temperature. The higher selectivity to carbon dioxide permeation in comparison with oxygen diminished as the water content of the film increased, which is in accordance with the loss of barrier properties at high relative humidities. This study underlines the importance of the evaluation of environmental conditions during end-use applications in order to optimize the performance of biopolymer-based films.

Effect of Cross-Linking Degree on Hydrogels using Surfactant Detergent as Template

To avoid the formation of layer-pore structure and flocculation caused by the excessive introduction of nonionic surfactant detergent polyoxyethylene 20 cetyl ether (Brij58) into polyN-isopropylacrylamide/inorganic nanoclay hectorite hydrogels network (PLH hydrogels), inorganic nanoclay hectorite content, severed as physical cross-linker, was increased from 1wt% to 3wt%. The morphology, temperature- responsibility, capacity of water absorption and swelling kinetics of resulting PHL hydrogels were investigated by SEM, DSC and Gravimetric method, respectively. It was found that PLH hydrogels would keep well honeycomb-like pore with increasing hectorite content. Furthermore, PLH hydrogels exhibited good temperature sensitivity regardless of physical cross-linker content.