Degree Of Chemical Crosslinking Research Articles

Rheological behavior of hydrophobic association polyacrylamides with high salt resistance and corrosion inhibition: Cross-linking modification based on trace dopamine hydrochloride derivatives

Hydrophobic association polyacrylamides (HAPAMs) have great potential for use in polymer flooding because of their unique aggregative, hygroscopic, and other compatible properties; however, their poor solubility in high-salt reservoir environments is one of the drawbacks of current polymers for enhanced oil recovery (EOR) applications. Herein, an amphipathic hydrophobic monomer (hexadecyldimethylallyl ammonium chloride, DMAAC16) and a dopamine hydrochloride-derived monomer (DAAM) were successfully introduced into HAPAM to synthesize novel dopamine hydrochloride-modified hydrophobic association polymers (HAPAMC16D). As a result, HAPAMC16D exhibited not only good comprehensive properties based on its porous network structure but also excellent viscosity due to the presence of the DAAM monomer. When the concentration of the polymer solution was greater than the critical association concentration (CAC), the apparent viscosity reached 614 mPa s at 5 g/L C16D5. Importantly, the salt resistance increased significantly in the representative sodium and calcium ion tests, which was attributed to the degree of chemical cross-linking and the intermolecular hydrophobic bonding force. The temperature and salt resistance tests simulating different environments for EOR showed that C16D4 had an apparent viscosity of 158 mPa s, a retention rate of 28.52 % at 90 °C and a total dissolved solids (TDS) greater than 30,000. Additionally, the weight loss method and electrochemical experiments indicated that the highly salt-resistant hydrophobic association polymers had favorable corrosion inhibition effects, with an inhibition efficiency of up to 99.02 % in the 1 M hydrochloric acid-Q235 carbon steel system. This hydrophobic association strategy provides a new approach for designing highly salt-resistant materials for polymer flooding in harsh reservoir environments.

Modified graphene oxide/waterborne epoxy composite coating with enhanced corrosion resistance

Waterborne epoxy (WEP) resin is drawing increasing attention due to its environmentally friendly nature. However, its application has been greatly hindered by poor corrosion resistance due to its rich inherent defects. In this work, maleic acid diamine (C4H6N2O2, MAD) modified graphene oxide (M-GO) was designed as the filler, and GO/WEP composite coatings with a high cross-linking degree, improved hydrophobicity, and high barrier properties were prepared. M-GO had a good water dispersibility and high affinity to the resin. The chemical grafting between the amino group of MAD and WEP can improve the degree of chemical cross-linking inside the coating to form a compact structure. Electrochemical impedance spectroscopy (EIS) measurements and salt spray test results indicate that the M-GO/WEP composite coating with 0.3 wt% M-GO has the best anti-corrosion performance. After being immersed in 3.5 wt% NaCl solution for 96 h, the |Z|0.01Hz value of M-GO/WEP composite coating is 1.03 × 108 Ω•cm2, corrosion current density is 0.00040 ɥA/cm2 and the protection efficiency reaches 99.99 %.

Effects of recycled carbon-based materials on tyre

This study examined the effect of recycled carbon-based material (rCBM), obtained by chemical degradation of end-of-life tires, on the mixture of tire tread (rubber composite) by comparing it with commercial carbon black (CB-N550). The new chemical degradation method was defined and the new rCBM was obtained. This newly method is more advantageous than other methods (devulcanization and pyrolysis). The rheometeric properties, mechanical properties, hardness, morphological properties, functional structures, thermal degradation behaviours of the rubber composites prepared were determined. The total number of bonds decreased as the amount of rCBM increased in the rubber composite mixture. As the vulcanized rubber network of the rCBM-filled rubber decreases, the cross-linking density of the rCBM-filled rubber was also reduced. As rCBM has a high sulfur value, the degree of chemical cross-linking of rCBM was reduced. In conclusion, rCBM will not be used in place of commercial carbon black but may be used by mixing with commercial carbon black depending on the desired properties of the end products.

Interfacial crack propagation between a rigid fiber and a hyperelastic elastomer: Experiments and modeling

The interfacial adhesion between a metal fiber and an elastomer plays a key role in maintaining the structural integrity of stretchable interconnect composites under large strains, but their interfacial adhesion mechanisms have remained elusive. To this end, the interfacial debonding behavior and physical mechanisms between a rigid metal fiber and hyperelastic elastomer matrix are investigated by means of fiber pullout tests and numerical modeling. An improved cylindrical specimen is adopted for a copper fiber pulling out from polydimethylsiloxane (PDMS). A numerical model is developed to simulate the interfacial cracking using the Yeoh hyperelastic model and cohesive damage model. We report a first-of-its-kind experimental observation on the pullout process of a rigid fiber from elastomers. The results demonstrate that there exist three stages in the fiber pullout process: elastic deformation, interfacial debonding and interfacial friction. The interfacial shear strength between the rigid fiber and the PDMS is proportional to the reciprocal of the mixing ratio of the PDMS, and the interfacial friction stress varies inversely with the 1.25 power of the mixing ratio. Enhancing the mixing ratio of the PDMS decreases the strength of both the PDMS and the interface between the PDMS and the metallic materials while increasing their ultimate stretch due to a decrease of chemical crosslinking degree within the PDMS and at the interface between the PDMS and the metallic materials. The results obtained from the numerical model agree well with the experimental data. This work can aid in the design of advanced stretchable interconnect composites.

NONLINEAR VISCOELASTIC DISSIPATION IN VULCANIZATES CONTAINING CARBON BLACK AND SILANIZED SILICA HYBRID FILLERS

ABSTRACT Different mechanisms of large-strain viscoelastic dissipation in vulcanizates containing carbon black or silanized silica and their synergistic effects in hybrid filler tread vulcanizates were investigated. In addition, the pure effects of fillers were examined while the degree of chemical cross-linking in the rubber matrix was similar in the vulcanizates. The results revealed that nonlinear viscoelastic loss modulus under strain-controlled dynamic tests, as a measure of dissipation mechanism, is high in both carbon black and silanized silica tread vulcanizates. However, a synergistic effect in reducing loss modulus was observed in the hybrid filler vulcanizates. Conversely, storage modulus in the vulcanizates containing more silanized silica is distinguishably higher and results in a lower loss factor representing load-controlled cyclic deformation of vulcanizates, such as in the heat buildup test. Both loss factor and heat build-up reduced nonlinearly as the amount of silanized silica increased in the vulcanizates, verifying the synergistic effect of hybrid carbon black–silanized silica filler in reducing dissipative mechanisms in large-strain dynamic loadings. This feature is highly favorable for the tire industry, where the lowering of viscoelastic dissipation in tread vulcanizates is of great importance.

A general method to improve 3D-printability and inter-layer adhesion in lignin-based composites

We report the utilization of a melt-stable lignin waste-stream from biorefineries as a renewable feedstock, with acrylonitrile-butadiene rubber and acrylonitrile-butadiene-styrene (ABS) polymer to synthesize a renewable matrix having excellent 3D-printability. While the initial low melt viscosity of the dispersed lignin phase induces local thermo-rheological relaxation facilitating the composite's melt flow, thermal crosslinking in both lignin and rubber phases as well as at the lignin-rubber interface decreases the molecular mobility. Consequently, interfacial diffusion and the resulting adhesion between deposited layers is decreased. However, addition of 10wt.% of discontinuous carbon fibers (CFs) within the green composites not only significantly enhances the material performance but also lowers the degree of chemical crosslinking formed in the matrix during melt-phase synthesis. Furthermore, abundant functional groups including hydroxyl (from lignin) and nitrile (from rubber and ABS) allow combinations of hydrogen bonded structures where CFs play a critical bridging role between the deposited layers. As a result, a highly interfused printed structure with 100% improved inter-layer adhesion strength was obtained. This research offers a route toward utilizing lignin for replacement of petroleum-based thermoplastics used in additive manufacturing and methods to enhance printability of the materials with exceptional mechanical performance.

Interphase Induced Dynamic Self‐Stiffening in Graphene‐Based Polydimethylsiloxane Nanocomposites

The ability to rearrange microstructures and self-stiffen in response to dynamic external mechanical stimuli is critical for biological tissues to adapt to the environment. While for most synthetic materials, subjecting to repeated mechanical stress lower than their yield point would lead to structural failure. Here, it is reported that the graphene-based polydimethylsiloxane (PDMS) nanocomposite, a chemically and physically cross-linked system, exhibits an increase in the storage modulus under low-frequency, low-amplitude dynamic compressive loading. Cross-linking density statistics and molecular dynamics calculations show that the dynamic self-stiffening could be attributed to the increase in physical cross-linking density, resulted from the re-alignment and re-orientation of polymer chains along the surface of nano-fillers that constitute an interphase. Consequently, the interfacial interaction between PDMS-nano-fillers and the mobility of polymer chain, which depend on the degree of chemical cross-linking and temperature, are important factors defining the observed performance of self-stiffening. The understanding of the dynamic self-stiffening mechanism lays the ground for the future development of adaptive structural materials and bio-compatible, load-bearing materials for tissue engineering applications.

Low-Temperature Sealing Force Behaviour of Fkm Elastomers as a Function of the Degree of Chemical Crosslinking and Differently Restricted Geometric Deformation in Static Compression

This publication first addresses the influence of an increasing chemical network density on the static sealing force behaviour and internal structural mobility of an FKM material in the cold. Cylindrical FKM test specimens were exposed to a high static surface pressure to make it easier to see thermodynamic and immobilising influences on sealing force behaviour as a function of chemical network density. Additional volume swelling trials and PVT measurements focused particularly on the compressible behaviour of the elastomer material as a function of its chemical network density. Furthermore – based on the static sealing force behaviour and mobility of the material in the cold – the loading situation of free compression with distortional strain energy was compared with the extreme case of a completely confined elastomer seal. The completely confined elastomer material was exposed to pure compression work, as in the PVT measurements.

A colourimetric method for the determination of the degree of chemical cross-linking in aspartic acid-based polymer gels

A 2,4,6-trinitrobenzenesulphonic acid (TNBS)-based assay is developed to determine the degree of chemical cross-linking in aspartic acid-based polymer gels. The conventional colourimetric method for the quantitative determina- tion of amine groups is difficult to use in polymer networks; thus, an improved method is developed to analyse polymer gels swollen in dimethyl sulfoxide (DMSO). Reaction products of the derivatizing reaction are examined by NMR. The chemical stability of the reagent is increased in DMSO, and the method shows satisfactory linearity and accuracy. The degree of chemical cross-linking in the investigated gels is close to its theoretical maximum, but the conversion of the pen- dant amine groups to cross-linking points is strongly dependent on the feed composition of the gels.

Synthesis of a co-cross-linked nanocomposite hydrogels from poly(methyl vinyl ether-co-maleic acid)-polyethylene glycol and nanofibrillated cellulose

This study demonstrates the preparation of a renewable and biocompatible co-cross-linked nanocomposite hydrogel from poly(methyl vinyl ether-co-maleic acid), poly(ethylene glycol) and nanofibrillated cellulose (NFC). The cross-linking reaction was favored by the formation of ester linkages as evidenced by Fourier transform infrared spectroscopy. The increase in gel fraction content of the treated NFC varied from 22 to 85 % which exhibited an increase in degree of chemical cross-linking to form a rigid network with the addition of varying amount of NFC (20–60 %). This increase in gel rigidity influenced gel swelling, showing relatively reduced water uptake ability above 40 % NFC. Rheological measurements indicated the formation of gels with superior mechanical properties.

Effect of chemical crosslinking degree on mechanical properties of bacterial cellulose/poly(vinyl alcohol) composite membranes

Bacterial cellulose/poly(vinyl alcohol) (BC/PVA) composite membranes using BC as the reinforcement and PVA as the matrix material were prepared in supersaturation of sodium chloride and crosslinked with glutaraldehyde, and characterized by attenuated total reflection Fourier-transform infrared spectroscopy, equilibrium swelling ratio tests, and mechanical properties tests. The chemical crosslinking degree of the membranes was determined by titration method, and it could be controlled by crosslinking time. The effects of the chemical crosslinking degree on properties of the BC/PVA composite membranes were investigated. It was demonstrated that chemical crosslinking was formed between BC/PVA and glutaraldehyde. As a result, the chemically crosslinked BC/PVA composite membranes exhibited some promising characteristics, such as appropriate equilibrium swelling ratio, good mechanical strength, and obvious effect of chemical crosslinking degree. Furthermore, the equilibrium swelling ratio and mechanical properties of the BC/PVA composite membranes were obviously affected by the BC content as well.

Chemical tailoring of gelatin to adjust its chemical and physical properties for functional bioprinting.

Double chemical functionalization of gelatin by methacrylation and acetylation of free amino groups enables control over both the viscous behavior of its solutions and the mechanical properties of the resulting hydrogels after photochemical crosslinking. The degree of methacrylation is controlled by the molar excess of methacrylic anhydride applied. Tenfold molar excess leads to highly methacrylated gelatin (GM10), resulting in solutions with low viscosities within the inkjet-printable range (10 wt%: 3.3 ± 0.5 mPa s, 37 °C) and crosslinked hydrogels with high storage moduli G' (10 wt%: 15.2 ± 6.4 kPa). Twofold excess of methacrylic anhydride leads to less methacrylated gelatin (GM2) proper for preparation of soft hydrogels (10 wt%: G' = 9.8 ± 4.6 mPa s) but its solutions are highly viscous (10 wt%: 14.2 ± 1.1 mPa s, 37 °C) and thus prone to clogging printing nozzles. Here we show that additional introduction of acetyl functionalities into GM2 results in a significant decrease in solution viscosity (10 wt%: 2.9 ± 0.2 mPa s, 37 °C) and prevention of physical gel formation. In such a manner twofold functionalized gelatin can be inkjet-printed while the degree of chemical crosslinking remains low and the resulting gels are soft. Thus, by adjustable twofold modification of gelatin, i.e. inserting photochemically reactive and inert groups, a versatile bioink for inkjet bioprinting is created, which allows for addressing ECM based hydrogel matrices with a broad range of physical properties. Moreover, bioinks are proven to be cytocompatible and proper for inkjet printing of viable mammalian cells.

Protein-selective adsorbers by molecular imprinting via a novel two-step surface grafting method.

Molecularly imprinted polymers (MIP) offer in principle a robust, cost-efficient alternative to antibodies, but it is still a challenge to develop such materials for protein recognition. Here, we report the molecular imprinting of a functional polymeric hydrogel layer with lysozyme as the template in a two-step grafting procedure by a novel initiation approach on track-etched polyethylene terephthalate membrane surface. This is based on surface functionalization with aliphatic C-Br groups which can be used as an initiator for surface-initiated atom transfer radical polymerization (SI-ATRP) and photo-initiated copolymerization. At first, the scaffold poly(methacrylic acid) (PMAA) was obtained through SI-ATRP of poly(tert-butyl methacrylate) and subsequent hydrolysis. Thereafter, it was assembled with the template to form a stable PMAA/lysozyme complex. In the second step, a polyacrylamide (PAAm) hydrogel was synthesized via UV-initiated surface grafting/crosslinking copolymerization around the scaffold/protein complex. Finally, the template was eluted to yield the grafted hydrogel layer with binding sites having complementary size, shape and appropriate arrangement of the functional groups to rebind lysozyme. The selectivity of lysozyme recognition, relative to cytochrome C with a similar size and isoelectric point, was increased by optimization of the scaffold chain length, UV grafting/crosslinking time and the chemical crosslinking degree of the PAAm-based hydrogel. The feasibility for the development of protein MIP in a straightforward way by independent optimization of crucial parameters - structures of scaffold with functional groups and of the crosslinked hydrogel matrix - have been demonstrated.

Improving the mechanical and thermal properties of gelatin hydrogels cross-linked by cellulose nanowhiskers

This study demonstrates the preparation of a renewable and biocompatible hydrogel with superior mechanical properties consisting of a gelatin matrix cross-linked with oxidized cellulose nanowhiskers. We found an increased degree of chemical cross-linking (0.14–17%) between gelatin and nanowhiskers with the increased amount of aldehyde contents (0.062–0.230mmolg−1). 1H nuclear magnetic resonance (NMR) T2 relaxation experiments on D2O swollen hydrogels demonstrated systems consisting of both gelatin and cellulose nanowhiskers displayed a higher percentage of “ridge” protons, attributed in part to increasing chemical cross-linking junction points between gelatin and nanowhiskers. This increase in hydrogel rigidity not only modified local chain dynamics but also influenced gel swelling, showing relatively reduced water uptake ability than that of the neat gelatin. Rheological measurements confirmed a 150% improvement in storage modulus (G′) of the cross-linked hydrogels compared to neat gelatin. Chemical cross-linking also increased the resistance of the gels towards thermal degradation above the melting temperature of gelatin as observed by thermal scanning experiments.

Shape‐memory polymer networks with Fe3O4 nanoparticles for remote activation

AbstractShape‐memory polymers (SMPs) have recently shown the capacity to actuate by remote heating via the incorporation of magnetic nanoparticles into the polymer matrix and exposure to an alternating magnetic field. In this study, methacrylate‐based thermoset SMP networks were synthesized through free‐radical polymerization with varying amounts of Fe3O4 magnetite (0, 1, and 2.5 wt %). Furthermore, the chemistry of the networks was controlled to maintain a constant glass transition temperature (Tg) while varying the degree of chemical crosslinking. Remote heating of the networks was shown to be a direct function of the nanoparticle concentration and independent of the chemistry. Magnetite reinforcement was shown to influence the thermomechanical properties of the networks; increasing Fe3O4 concentrations led to decreases in Tg and rubbery modulus. However, networks with a higher degree of crosslinking were more resistant to thermomechanical changes with respect to magnetite concentration. Strain to failure was shown to decrease with the addition of nanoparticles and the free‐strain shape‐memory cycle was investigated for all of the networks. Networks with lower degrees of crosslinking and high magnetite concentrations showed a significant amount of irrecoverable strain. Last, the use of remotely heated shape‐memory materials is discussed in light of potential biomedical applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Structure and properties of hybrid poly(2‐hydroxyethyl methacrylate)/SiO2 monoliths

AbstractHybrid poly(2‐hydroxyethyl methacrylate) (PHEMA)/SiO2 monoliths were synthesized via a sol–gel process of the precursor tetraethyl orthosilicate (TEOS) and the in situ free‐radical polymerization of 2‐hydroxyethyl methacrylate (HEMA). The weight ratio of the starting chemicals, TEOS to HEMA, was varied between 100/0 and 0/100. Structural analysis was performed by IR and NMR. The NMR results indicated that the introduction of PHEMA in the silica networks gave rise to a lower degree of condensation of TEOS. The resulting monoliths showed more than 75% transmittance in the visible region, that is, good transparency. Mechanical properties were studied with an Instron tester, and the monoliths exhibited better compressive strength and modulus than did bulk PHEMA. Surprisingly, thermogravimetric analysis (TGA) data showed greater than 50 wt % solid residue up to 700°C, possibly related to some degree of chemical crosslinking between the polymer and the silica moiety, which would greatly improve the thermal stability of such hybrid monoliths compared with a pure PHEMA. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3168–3175, 2003

Struktura fizyczna i topologia sieci przestrzennych elastomerow

Two groups of chosen models of elastomers networks have been discussed on the basis of literature data and own research results. The first group of models encloses: statistical theory of elasticity, Mooney-Rivlin model, model with constraints on chain and junctions, tube model by Heinrich, Straube and Helmis as well as Tschoegl model. They use simple experimental measurements of stress - strain dependence. However the concentration of chemical crosslinking joints of network, N-c, and crosslinking efficiency E-c, calculated for NR and IR cured with dicumyl peroxide (DCP) are much higher than the values resulting from the known mechanism of these elastomers; curing with a peroxide (E-ct = 2) (Table 1, Figs. 3 and 4). In the second groups of models, by Charlesby-Pinner (concerning the rubber showing M-w/M-n approximate to 2) and by Langley and Pearson (any value of M-w/M-n), there is necessary (for proper analysis) to do labour-consuming determinations of sol content as well as molecular weight and polydispersity of a rubber before curing, but this way determinated values of N-c and E-c, in case of curing NR and IR with DCP [(E-c = 1.8-2.0), agree with theoretical values (Table 1)]. These methods can be recommended to complex analysis of physical structure and topology of a network. In networks of cured elastomers there are both the chemical and permanent topological joints. Their part in total number of network joint reaches up to 80% when chemical crosslinking degree is not high. Key words: networks of elastomers, chemical and topological joints, chain entanglement, comparison of network models, crosslinking efficiency.

Relation for Solid−Liquid Coexistence Systems and Its Application to Melting Point Depression of Benzene in Natural Rubber

A relation that represents “solid−liquid coexistence” curves in binary equilibrium phase diagrams of solvent crystal−noncrystalline polymer systems is deduced on a more general theoretical basis, which is a counterpart of the Flory−Huggins equation representing a solution curve. The relation deduced is expressed as a function of concentration in terms of the interfacial free energy and crystal size. Next, on this relation basis, a melting point depression analysis is made by using certain experimental results on lightly chemically cross-linked NR−benzene systems whose degree of chemical crosslinking is so small that they can be regarded as uncross-linked systems. The relation is revised when considering an elastic term by chain entanglements in the good solvent and a certain concentration−temperature dependent polymer−solvent interaction parameter. Consequently, in the higher concentration range, part of the previous data of crystal size determined from X-ray fit fairly well within the upper and lower lim...

Preparation and properties of epoxidized natural rubber/poly(ε-caprolactone) self-vulcanizable blends

Curing behaviour as well as mechanical properties of the binary blends of epoxidized natural rubbers (ENR) with end-carboxylated telechelic poly(Iµ-caprolactone)s (XPCL) has been investigated for development of high-performance self-vulcanizable rubber blends. The binary blends of ENR with different degrees of epoxidation and XPCL of different molecular masses were prepared by using an open two-role mill and subsequently cured at 160–200 °C. It was found that the end-functional and crystallizable XPCLs cured ENR well in the absence of other additives and acted as an effective polymeric crosslinker for ENR to produce self-vulcanizable binary blends. The degree of chemical crosslinking depended on the degree of epoxidation of the ENR as well as the curing time and temperature. The relative contribution of the physical crosslinking via crystallization of poly(Iµ-caprolactone) chains to that chemical crosslinking was controlled by the molecular mass of the XPCL to give elastomeric materials with various stress–strain curves.

The effect of crosslinking on properties of polyurethane elastomers

AbstractA series of segmented polyurethanes from two polyols, 4,4′‐diphenylmethane diisocyanate (MDI) and butane diol was synthesized. The degree of chemical crosslinking was controlled by varying the ratio of poly(oxypropylene) diol to poly(oxypropylene/oxyethylene) triol. The samples were prepared at the stoichiometric ratio of NCO to OH groups and at a constant concentration of hard segments (butane diol; MDI) equal 50 wt %. At low concentrations of the triol the molecular weight of the polyurethanes increases; at higher concentrations (above 9 mol %) crosslinked products are obtained. All samples show a distinct two‐phase structure and in the region of 0–150°C the dynamic mechanical behavior is affected by the hard phase. Chemical crosslinking was found to increase the tensile strength and strain at break, but did not affect appreciably the tear strength, hardness, and soft segment glass transition. The stress relaxation rate at room temperature was found to depend both on the elongation and on the degree of crosslinking. A comparison of the sol fractions ws found for crosslinked samples with the predictions of the theory of branching processes proved that the achieved conversions of reactive groups in networks are high (∼ 0.98).