Influence Of Crosslinking Density Research Articles

Influence of Cross-Link Density on Electrochromic Properties of Conjugated Polymer

Influence of Cross-Link Density on Electrochromic Properties of Conjugated Polymer

Influence of Crosslink Density on Electrical Performance and Rheological Properties of Crosslinked Polyethylene.

To investigate the influence of the crosslinked polyethylene (XLPE) structure on electrical performance, various analytical methods were employed to study polyethylene structures with different degrees of crosslinking. Dynamic rheological analysis was conducted to determine material shear viscosity, dynamic viscosity, storage modulus (G'), loss modulus (G″), and other rheological parameters. Additionally, the electrical performance of the material was analyzed by studying the phenomenon of space charge accumulation under direct current voltage. The results indicate that with an increasing mass fraction of the crosslinking agent, the crosslink density of crosslinked polyethylene initially increases and then decreases. When the dicumyl peroxide (DCP) content exceeds 1.0 wt.%, there is an accumulation of like-polarity space charges. The best rheological processing performance of crosslinked polyethylene is observed when the DCP content is in the range of 1.0-1.5 wt.%.

The influence of cross-linking density on the efficiency of post-synthetic sulfonation of hyper-cross-linked polymers and their adsorption capacity for antibiotic pollutants

Hyper-cross-linked polymers (HCPs) attract increasing attention as promising adsorbents for removal of organic pollutants from water. The present work reveals for the first time that the efficiency of the post-synthetic sulfonation of HCPs-based adsorbents and their reactivity in removal of selected polar antibiotic pollutants can be simply controlled by adjusting the cross-linking density of the polymer network. The study included both the evaluation of the mechanism and kinetics of the adsorption process over sulfonated HCPs, as well as the determination of their stability, recyclability, and affinity toward various antibiotics. The latter was established based on adsorption tests using mono- and multicomponent mixtures of different structure antibiotics (ciprofloxacin, tetracycline, sulfamethoxazole and amoxicillin). The adsorption capacity of all sulfonated polymers was found to be directly proportional to the concentration of -SO3H functions and inversely proportional to the cross-linking density of the parent HCPs. The most promising sulfonated polymer had approximately 4 times higher adsorption capacity toward ciprofloxacin than commercial carbon-based adsorbent Norit (427.5 vs. 110.5 mg/g, respectively). The main adsorption mechanism over sulfonated HCPs was chemisorption of the antibiotics via ionic interactions with surface -SO3H groups. Spent adsorbent could be successfully recycled ten times without any loss in its efficiency.

Influence of Block Copolymer Concentration and Resin Crosslink Density on the Properties of UV‐Curable Methacrylate Resin Systems

AbstractAdditive manufacturing is on the verge of replacing established processes in dentistry, as it offers the possibility of manufacturing individual parts simply and cost‐effectively. Due to its suitability for a wide variety of materials and, above all, its high precision, the focus is currently on stereolithographic processes. Intrinsic brittleness of the used multifunctional acrylic monomers remains however one of the major challenges. One promising concept is the use of block copolymers (BCPs) guaranteeing minor effects on 3D‐printing processing and UV‐curing due to initially at least partial solubility, and hence low viscosity impact. A polycaprolactone‐polysiloxane (PCL‐PDMS‐PCL) triblock copolymer is synthesized via ring‐opening polymerization of caprolactone and used in radical UV‐cured methacrylic resin systems. Small angle X‐ray scattering measurements reveal the self‐assembly of the BCPs to objects of around 20 nm prior to curing. Subsequently, thermo‐mechanical characterization is carried out by dynamic mechanical analysis, flexural testing, and fracture toughness measurements (KIC). Transmission electron microscopy and scanning electron microscopy micrographs show a homogenous distribution of the BCPs and effective toughening via cavitation and shear yielding. The influence of the crosslink density on the toughness and the high effectiveness of block copolymers for improving fracture toughness is clearly shown.

Influence of crosslinking density on the mechanical and thermal properties of plant oil-based epoxy resin

Plant oil-based epoxy resins are of great interest due to their ecological and economic necessity. Previous studies suggested that the crosslinking density had a considerable influence on the mechanical and thermal properties of plant oil-based epoxy resins. However, so far, the relationship between the crosslinking density and the thermo-mechanical properties of plant oil-based epoxy resins is not clear. To address this issue, model tung oil-based epoxy resins with different crosslinking densities were fabricated to investigate the influence of crosslinking density on the mechanical and thermal properties of tung oil-based epoxy resins. Results show that the tensile strength, Young's modulus, and glass transition temperature are linearly increased with increasing crosslinking density. The elongation at break and tensile toughness show nonlinear downward trends as the crosslinking density increases. The elongation at break decreases gently at first, then dramatically, and finally slowly as the crosslinking density increases. The tensile toughness declines sharply at first and then slowly with increasing crosslinking density. The relationship between the thermostability and the crosslinking density is complex, because the thermostability is determined by both the molecular structure of the curing system and the crosslinking density. These results provide some information for designing plant oil-based epoxy resins according to the requirements of their applications.

Study on the influence of crosslinking density and free polysiloxan chain length on oxygen permeability and hydrophilicity of multicomponent silicone hydrogels

Study on the influence of crosslinking density and free polysiloxan chain length on oxygen permeability and hydrophilicity of multicomponent silicone hydrogels

Influence of Crosslinking Density on Antioxidant Nanocellulose in Bio-degradation and Mechanical Properties of Nitrile Rubber Composites

Nanocellulose antioxidant (Aox-NCC) was used as reinforcement and crosslinking agent in nitrile butadiene rubber (NBR) composites. The crosslinking density and volume of rubber bonded in the matrix were increased up to 3 phr and no significant improvement between 4 phr and 5 phr was recorded. The interactions of gallic acid and NCC was found to occur between the -OH and -COOH groups, as revealed by Fourier Transform Infra-Red (FTIR) and Nuclear Magnetic Resonance (NMR) analysis. Crystallinity index of Aox-NCC was increased more than 11 %, recorded by X-ray diffraction (XRD) analysis. Meanwhile, the thermal stability of Aox-NCC was increased 30°C, analyzed by thermogravimetry (TG). With the addition of 3 phr Aox-NCC, tensile strength and modulus at 500 % for NBR composites were increased significantly up to 20 %. There was no significant improvement on modulus at 100 %, modulus at 300 %, elongation at break and tear strength. The degradability of NBR composites within 6 months period was improved significantly at 5 phr of Aox- NCC. Increase in carbonyl group after soil burial test with the existence of cracks, voids and degradable parts of NBR composites were revealed. This demonstrated that, Aox-NCC plays a secure function to reinforce NBR composites.

Inhibiting Bacterial Adhesion by Mechanically Modulated Microgel Coatings.

Bacterial infection is a severe problem especially when associated with biomedical applications. This study effectively demonstrates that poly-N-isopropylmethacrylamide based microgel coatings prevent bacterial adhesion. The coating preparation via a spraying approach proved to be simple and both cost and time efficient creating a homogeneous dense microgel monolayer. In particular, the influence of cross-linking density, microgel size, and coating thickness was investigated on the initial bacterial adhesion. Adhesion of Staphylococcus aureus ATCC 12600 was imaged using a parallel plate flow chamber setup, which gave insights in the number of the total bacteria adhering per unit area onto the surface and the initial bacterial deposition rates. All microgel coatings successfully yielded more than 98% reduction in bacterial adhesion. Bacterial adhesion depends both on the cross-linking density/stiffness of the microgels and on the thickness of the microgel coating. Bacterial adhesion decreased when a lower cross-linking density was used at equal coating thickness and at equal cross-linking density with a thicker microgel coating. The highest reduction in the number of bacterial adhesion was achieved with the microgel that produced the thickest coating (h = 602 nm) and had the lowest cross-linking density. The results provided in this paper indicate that microgel coatings serve as an interesting and easy applicable approach and that it can be fine-tuned by manipulating the microgel layer thickness and stiffness.

Influence of cross-linking density on the structure and properties of the interphase within supported ultrathin epoxy films

Supported polymer film models based on epoxy resin networks with four different cross-linking densities and silica substrates have been established using molecular dynamics simulations. Van der Waals forces in the form of Lennard-Jones 9-6 are applied in calculating the interfacial interactions between the polymer and substrate. The existence of the interphase adjacent to the substrate surface was confirmed by carrying out density profile. Detailed analyses including mean square displacement and radial distribution functions of the structural properties of interphases for the four models were performed and compared. It was found that, with increasing the cross-linking density, the polymer sticks to the substrate more tightly, accompanied by stronger interactions arising from more hydrogen bonds formed between them. Furthermore, the mechanical properties of the interphase were found to be enhanced with the conversion by carrying out tensile deformation. This research regarding the interphase region within supported ultrathin epoxy films will be helpful in understanding the effect mechanism of nanofillers in the epoxy nanocomposites.

The Influence of Crosslink Density on the Failure Behavior in Amorphous Polymers by Molecular Dynamics Simulations.

The crosslink density plays a key role in the mechanical response of the amorphous polymers in previous experiments. However, the mechanism of the influence is still not clear. In this paper, the influence of crosslink density on the failure behavior under tension and shear in amorphous polymers is systematically studied using molecular dynamics simulations. The present results indicate that the ultimate stresses and the broken ratios (the broken bond number to all polymer chain number ratios) increase, as well as the ultimate strains decrease with increasing crosslink density. The strain concentration is clearer with the increase of crosslink density. In other words, a higher crosslink density leads to a higher strain concentration. Hence, the higher strain concentration further reduces the fracture strain. This study implies that the mechanical properties of amorphous polymers can be dominated for different applications by altering the molecular architecture.

Influence of Crosslink Density and Stiffness on Mechanical Properties of Type I Collagen Gel.

The mechanical properties of type I collagen gel vary due to different polymerization parameters. In this work, the role of crosslinks in terms of density and stiffness on the macroscopic behavior of collagen gel were investigated through computational modeling. The collagen fiber network was developed in a representative volume element, which used the inter-fiber spacing to regulate the crosslink density. The obtained tensile behavior of collagen gel was validated against published experimental data. Results suggest that the cross-linked fiber alignment dominated the strain stiffening effect of the collagen gel. In addition, the gel stiffness was enhanced approximately 40 times as the crosslink density doubled. The non-affine deformation was reduced with the increased crosslink density. A positive bilinear correlation between the crosslink density and gel stiffness was obtained. On the other hand, the crosslink stiffness had much less impact on the gel stiffness. This work could enhance our understanding of collagen gel mechanics and shed lights on designing future clinical relevant biomaterials with better control of polymerization parameters.

Effect of chemical structure and cross-link density on the heat resistance of phenolic resin

Limited by the knowledge of the structure and pyrolysis mechanism of cured phenolic resin (PR), the influence of cross-link density (CLD) on the heat resistance of PR remains unclear. The objective of this work is to characterize the structure of PR and understand the relationship between structure and heat resistance. The CLD of cured PR is characterized by theoretical and experimental approaches based on the full understanding of the chemical structure. The influence of CLD on the heat resistance is studied by analyzing the pyrolysis behavior of cured PR, and the results reveal that cross-link can improve the thermal stability and char yield of cured PR simultaneously. A novel pyrolysis mechanism and a quantitative relationship between the CLD and residual weight of PR are proposed. The results of our paper provide a theoretical basis to develop resins with good heat resistance.

Contact Creep Behavior of Polydimethylsiloxane and Influence of Load, Tip Size, and Crosslink Density

Time-dependent indentation creep behaviors of polydimethylsiloxane (PDMS) samples of different crosslink densities were studied through contact creep tests loaded with silica tips. Step loads from 0.1 to 10 mN were applied and held for 600 s. The data of penetration depth versus time were recorded during the holding period. A Hertz-type viscoelastic model was used to compute the creep compliance of the samples and the Johnson–Kendall–Roberts (JKR) theory was used to obtain the initial equivalent modulus, infinite equivalent modulus, and work of adhesion between the tested each pair of the PDMS and fused silica tip surfaces. The comparison between initial and infinite equivalent moduli obtained from the Hertz viscoelastic theory and the JKR theory shows that the adhesion between the tip and the sample surface plays an importance role in affecting the analysis results when the indentation strain is small. The influences of crosslink density, applied load, and tip size on the localized PDMS properties are discussed.

Synthesis and Characterization of Poly(acrylic acid)/modified Bentonite Superabsorbent Polymer

A novel poly(acrylic acid)/modified bentonite superabsorbent polymer (SAP) was synthesized through chemical crosslinking by a polymerization technique in a complete aqueous environment. This SAP was fabricated effectively by dispersing modified bentonite in a monomeric solution, using N,N′-methylenebisacrylamide as crosslinker and ammonium persulfate as initiator. Fourier transform infrared (FTIR) spectral analysis showed that the XG chains had intercalated into bentonite sheets. The influence of crosslinking density and XG content were investigated. Results showed modified bentonite not only effectively increases water absorbency, but also improves water retention ability. This can be further used as a carrier matrix for the development of a drug delivery system.

Influence of Crosslink Density on Mechanical Properties of Natural Rubber Vulcanizates

Crosslink density is an important structural parameter for cured rubber. Natural rubber (NR) vulcanizates with different crosslink densities were obtained through using different sulfur and accelerator amounts and different accelerator types. The crosslink density was characterized by an 1 H-NMR technique and its influence on mechanical properties, such as Shore A hardness, 300% modulus, tensile strength, and elongation at break, of NR vulcanizates was investigated. The results showed that both the sulfur amount and the accelerator type and amount had an influence on the crosslink density of the NR networks. The relationship between total crosslink density and mechanical properties was also studied. The results, by changing either the sulfur or the accelerator amount, showed that tensile strength of NR vulcanizates reached maximum value when the total crosslink density was around 13.5 × 10−5 mol/cm3, equivalently the average molecular weight of the intercrosslink chains (Mc) was around 7000 g/mol. The maximum value of tensile strength came from the balance between contributions of crosslink joints and stretch-induced orientation and/or crystallization of intercrosslink chains. The study on influence of total crosslink density on Shore A hardness and 300% modulus of NR vulcanizates showed that they both increased linearly with the crosslink density, the slopes were 2.7 ∼ 3.0 cm3/10−5 mol and 0.27 ∼ 0.31 MPa cm3/10−5 mol for Shore A hardness and 300% modulus, respectively, whether the crosslink density was varied by sulfur or accelerator.

Influence of crosslinking density on the tribological behavior of norbornene-based polymeric materials

► The tribological properties of ring opening metathesis polymerization (ROMP) thermosetting polymers have been evaluated as a function of crosslinking density. ► Both the friction and wear against a spherical Si 3 N 4 and a conical diamond probe were affected by crosslinking. ► The material without the crosslinker (CL-0) showed the highest friction coefficient against Si 3 N 4 . ► Reciprocating wear tests have confirmed that all materials, except CL-0, show resistance to wear against Si 3 N 4 under the given loading conditions. ► All samples exhibited abrasive wear by the sharp diamond probe. ► The abrasive wear depth was observed to decrease with increasing crosslinking density. In this study, the friction and the wear behavior of norbornene-based polymers prepared by ring-opening metathesis polymerization (ROMP) reaction are evaluated as a function of the crosslinking density. Tribological measurements were performed using a ball-on-flat reciprocating microtribometer. Friction and wear experiments under dry sliding were evaluated using a 1.2 mm radius Si 3 N 4 spherical probe as well as a 100 μm radius conical diamond probe with a 90° cone angle. Wear experiments were conducted at constant normal loads for 100–500 reciprocating cycles. Wear depths were estimated from wear grooves using a contact profilometer, and scanning electron microscopy was used to elucidate deformation mechanisms in the various samples. Correlation between the crosslinking density and the wear behavior were observed.

The influence of crosslinking density on the pore morphology of copolymer beads prepared with a novel pore-forming agent

Macroporous styrene–divinylbenzene (St–DVB) copolymer beads are prepared with a novel pore-forming agent, 1-chlorodecane. Copolymer beads with high specific surface area are obtained although 1-chlorodecane is a typical incompatible solvent of polystyrene. The unexpected behavior of 1-chlorodecane during preparation of copolymer beads is discussed. It is found that the excellent compatibility between the chloro substituents in 1-chlorodecane and phenyl rings in copolymer could be responsible for the unexpected behavior. In addition, the effect of crosslinking density on the pore morphology of the copolymer beads is systematically investigated. The results indicate that the specific surface area, the total pore volume and the average pore diameter of the copolymer beads strongly depend on the crosslinking agent concentration. Overall, the present study provides a novel route to prepare macroporous polymer beads with controllable pore morphology.

Influence of crosslinking density of a cataphoretic coating on initiation and propagation of filiform corrosion of AA6016

The effect of curing temperature on initiation and propagation of filiform corrosion of an epoxy cataphoretic electrocoating deposited on aluminum alloy substrate was studied. EIS measurements were used to follow the evolution of the water uptake of the intact coatings. In addition, EIS was applied to determine the performances of the systems as a result of exposure to HCl vapours. Cantilever method (stressmeter) was used to determine the stresses generated in an organic coating during a humidity cycle. Scanning Kelvin Probe (SKP) was applied in order to investigate the initiation and propagation of filiform corrosion of painted aluminum alloy. The mechanism of filiform corrosion is discussed according to the paint properties.

Physical properties and loading capacity of starch-based microparticles crosslinked with trisodium trimetaphosphate

Starch-based microparticles were prepared by emulsion crosslinking method, using trisodium trimetaphosphate (TSTP) as crosslinking agent. The prepared TSTP-crosslinked starch microparticles (TSMs) were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) technique. SEM pictures showed smooth face and spherical shape for the TSMs. XRD patterns revealed that TSMs were of amorphous structure mostly. This result was confirmed by FTIR spectra. Influence of crosslinking density on particle size, swelling degree and loading capacity of TSMs was studied by varying TSTP concentration. It was found that with increasing TSTP concentration from 0.1 to 0.4 g/g, the particle size and loading capacity increased, but swelling degrees showed a bell-shaped dependence on TSTP concentration with maximum values at the concentration of 0.2 g/g in different media. However, the changes of these three aspects became inconspicuous when TSTP concentration increased to 0.4 g/g. It is estimated that the crosslinking density had nearly reached its full extent at such concentration. The present investigated TSMs could potentially be applied in dry powder form for food ingredients delivery.

Two-Way Reversible Shape Memory in a Semicrystalline Network

Cooling-induced crystallization of cross-linked poly(cyclooctene) films under a tensile load results in significant elongation and subsequent heating to melt the network reverses this elongation (contracting), yielding a net two-way shape memory (2W-SM) effect. The influence of cross-linking density on the thermal transitions, mechanical properties, and the related 2W-SM effect was studied by varying the concentration of cross-linking agent dicumyl peroxide (DCP) and using differential scanning calorimetry (DSC), gel fraction measurements, dynamic mechanical analysis (DMA), and customized 2W-SM analysis. The latter showed that there is crystallization-induced elongation on cooling and melting-induced shrinkage on heating (2W-SM), with lower cross-link density leading to higher elongation at the same applied stress. For a given cross-link density, however, increasing the tensile stress applied during cooling resulted in greater stress-induced crystallization. We further observed that the onset temperatures...