Formation Of Crosslinked Network Research Articles

Effect of benzalkonium chloride on trabecular meshwork cells in a new in vitro 3D trabecular meshwork model for glaucoma

PurposeTo validate a new culture model of primary human trabecular meshwork cells (p-hTMCs) using Matrigel®, in order to mimic in vitro 3D–TM organization, and to investigate the proinflammatory effect of benzalkonium chloride (BAK) in 3D p-hTMC cultures. Methodsp-hTMCs, seeded onto Matrigel®-coated inserts were stimulated with BAK (10−4%), dexamethasone (DEX) (10−6M) or transforming growth factor-beta 2 (TGF-β2) (5ng/ml) for 48h and observed with confocal microscopy. The BAK effect at 10−4% or 5.10−3% on the gene expressions of interleukin-6 (IL-6), interleukin-8 (IL-8) and matrix metalloproteinase (MMP-9) was investigated using qRT-PCR in 2D and 3D p-hTMC cultures. Resultsp-hTMCs seeded in Matrigel® were able to organize themselves in a 3D-spatial conformation in the different conditions tested with cross-linked actin network (CLAN) formation in presence of DEX or TGF-β2 and intercellular space contraction with TGF-β2. IL-6 and IL-8 gene expressions increased in presence of BAK in 2D and in 3D p-hTMC cultures. BAK 10−4% only showed a tendency to stimulate MMP-9 expression in p-hTMCs after 24h-recovery. ConclusionsWe investigated this new 3D–TM in vitro model in Matrigel® matrix for pathophysiological and toxicological purposes. It appears as a new promising tool for a better understanding of TM behavior in physiological and stress conditions, as well as toxicological evaluations of antiglaucoma eyedrops and preservatives.

ENGAGE compatibilized HDPE/EPDM blends: Modification of some industrially pertinent properties and morphology upon incorporation of Mg(OH)2 filler and electron beam crosslinked network

ABSTRACTTo observe the effect of ENGAGE (a poly‐olefin elastomer) on compatibilization of industrially important incompatible blend, high‐density polyethylene (HDPE)/ethylene‐propylene diene elastomer (EPDM), 15 wt % ENGAGE is incorporated into the system and the latter is found satisfactorily efficient as compatibilizer for the above system. To improve some industrially pertinent properties another strategies are also followed in addition, incorporation of magnesium hydroxide [Mg(OH)2] and electron beam (EB) crosslinking into the system. The gel content was found to increase with radiation dose, EPDM content and Mg(OH)2 dispersion. ENGAGE interestingly increases the gel content that is, promotes crosslinking. It is unique that filler dispersion and crosslinked network formation maintain the compatibility of the ternary system, which is confirmed by X‐ray diffraction, differential scanning calorimetry, mechanical properties, and scanning electron microscope. The compatibilization, Mg(OH)2 dispersion, and EB crosslinking improve the mechanical, thermo mechanical, flame retardant properties, and phase morphology considerably. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44922.

Orthogonally weaved silver nanowire networks for very efficient organic optoelectronic devices

We demonstrate a simple but effective method to control the orientation of silver nanowires (AgNWs). Shear-flow-induced AgNW preferable orientation is realized by judiciously controlling the process parameters in the bar-coating method. This controllability of the NW direction enables the formation of AgNW cross-linking networks for transparent conductive electrode (TCE) applications. We experimentally demonstrate that the orthogonally weaved AgNW networks possess predominant advantages of lower percolation limit, higher transmission, and lower sheet resistance compared with the randomly orientated AgNW counterparts. The phenomenon is also confirmed with theoretical calculation by the Monte Carlo method. These high-quality AgNW TCEs exhibit a high transmittance of ∼94% with a sheet resistance of ∼20 Ω/sq, which meet the requirements of modern optoelectronic devices. Very efficient organic light-emitting diodes (OLEDs) and organic solar cells (OSCs) prepared by these AgNW TCEs are demonstrated. The OLED exhibits exceptionally high luminance efficiency, power efficacy, and external quantum efficiency of 92 cd/A, 111 lm/W, and 26.8%, respectively. The OSCs also deliver a high power conversion efficiency of up to 7.5%.

Study on low temperature toughness and crystallization behavior of polypropylene random copolymer

Abstract This research designed a series of novel approaches aiming to tackle a long-standing problem that is the brittleness of polypropylene (PP) random copolymer (PPR) at low temperature. By introducing polyolefin elastomer (POE), the toughness of PPR was improved; talc improved the stiffness of PPR, low density polyethylene (LDPE) or high density PE (HDPE) improved the low temperature toughness of PPR, and annealing treatment also improved the low temperature toughness of PPR significantly. The addition of dicumyl peroxide (DCP) and triallyl isocyanurate (TAIC) increased its stiffness through the formation of cross-linking networks. Also, the crystallization behavior and morphology were investigated in detail. Differential scanning calorimetry (DSC) results indicated that the adoption of annealing treatment can improve the crystallinity of PPR, while a polarizing microscope revealed that the incorporation of foreign matter can facilitate the crystallization process of the matrix. X-ray diffraction (XRD) tests showed an unchanged polymorphic composition of PPR after introducing different additives, and scanning electron microscopy (SEM) indicated that annealing treatment can enhance interfacial interactions between the matrix and fillers.

Crosslinking kinetics of polyethylene with small amount of peroxide and its influence on the subsequent crystallization behaviors

Crosslinking reactions of high density polyethylene with low peroxide concentrations ranging from 0.1 wt% to 1.0 wt% at temperatures of 170, 180 and 190 °C were monitored by rheological measurements. A critical gel forms at the peroxide concentration of 0.2 wt%, where the transition from long chain branching generation to crosslinking network formation could occur. Rheokinetics of crosslinking can be fitted well by Ding-Leonov’s model. The curing rate k 2 at the earlier stage exhibits about 3 times acceleration per 10 °C with increasing temperature, while the equilibrium modulus G′ at the fully cured stage is almost independent of temperature. Influences of crosslinking on the subsequent crystallization behaviors were detected by DSC measurements. Above the critical gel concentration, crystallization is largely retarded as evidenced by the lower crystallization temperature T c and crystallinity X c due to the network formation. The secondary crystallization valley located at the temperature near 80 °C can be observed above the critical concentration, which becomes more evident with the increasing peroxide concentration and curing temperature. This phenomenon provides another evidence of crystallization retardation by the crosslinking network.

Effects of the amine/epoxy stoichiometry on the curing behavior and glass transition temperature of MWCNTs-NH2/epoxy nanocomposites

In this study, amine functionalized multi-walled carbon nanotubes (MWCNTs-NH2) with surface covalently linked ethylenediamine were prepared. The effect of amine/epoxy stoichiometry on the curing behavior, cross-linking network structure and glass transition temperature (Tg) of MWCNTs-NH2 reinforced epoxy-amine systems were investigated by using non-isothermal differential scanning calorimetry (DSC), Fourier transform infrared (FT-IR) and dynamic mechanical analysis (DMA), respectively. The results indicated the catalytic effect MWCNTs-NH2 in the curing process of epoxy was weakened with the increase of amine/epoxy stoichiometry, which can affect the formation of cross-linking network and Tg of the cured MWCNTs-NH2/epoxy nanocomposites contrasted with the corresponding neat epoxy. The MWCNTs-NH2/epoxy composites with moderate excess epoxy equivalent exhibited higher Tg than that of the neat epoxy, which was attributed to the excess epoxy groups can promote the etherification reaction as well as the interfacial interaction between MWCNTs-NH2 and epoxy resin.

The Synergistic Effect of Flame Retardants on Flammability, Thermal and Mechanical Properties of Natural Fiber Reinforced Epoxy Composite

Epoxy was effectively resin infused with 15 %wt intumescing Alumina Trihydrate (ATH) flame retardant (FR) formulations into a 10 %wt palm EFB natural fiber (NF) mat. The effects of ATH and its intumescing blend with Zinc Borate (ZB) and Ammonium Polyphosphate (APP) on flammability, thermal and mechanical properties of the composites were investigated. Compared to neat NF filled epoxy composites, specimens loaded with intumescing blend of FR formulations demonstrated an improved thermal properties, showing greater mass residual which can be attributed to the formation of cross-linked network amongst the NF, FRs and epoxy matrix upon combustion at elevated temperature tested within a TGA instrument. Incorporation of fibers drastically enhanced the mass residue and lowered the heat release compare to the pure epoxy. Addition of the intumescing blend of FR formulations also drastically reduces the combustion heat release, total mass loss and zero drip flame in the NF composites. The optimum FRs formulation with 5 %wt ATH and 10 %wt APP exhibited self-extinguishing property, achieved lowest mass loss and no drip flame under Bunsen burner tests, signifying the synergistic effects between ATH and APP within the NF epoxy composites. APP reacts with the carbonaceous network of NF throughout the ignition period, such interaction formed a thick char layer acting as gas and thermal barrier against the fire mechanism. This reaction does not take place in NF composite specimens without APP. In terms of mechanical properties, NF composites loaded with FRs broadly showed poorer tensile strength, mainly due to the existence of FRs, which acted as a nucleating agent affected the physico-mechanical characteristics of the composites. Amongst the FR rich formulations, specimens with APP or ZB blends seem to possess a more superior tensile strength compared with the neat ATH filled formulation. In addition, composites loaded with FRs showed enhanced Young’s modulus relative to those without addition of FRs.

Design of Self-Healing Supramolecular Rubbers by Introducing Ionic Cross-Links into Natural Rubber via a Controlled Vulcanization

Introducing ionic associations is one of the most effective approaches to realize a self-healing behavior for rubbers. However, most of commercial rubbers are nonpolar rubbers without now available functional groups to be converted into ionic groups. In this paper, our strategy was based on a controlled peroxide-induced vulcanization to generate massive ionic cross-links via polymerization of zinc dimethacrylate (ZDMA) in natural rubber (NR) and exploited it as a potential self-healable material. We controlled vulcanization process to retard the formation of covalent cross-link network, and successfully generated a reversible supramolecular network mainly constructed by ionic cross-links. Without the restriction of covalent cross-linkings, the NR chains in ionic supramolecular network had good flexibility and mobility. The nature that the ionic cross-links was easily reconstructed and rearranged facilitating the self-healing behavior, thereby enabling a fully cut sample to rejoin and retain to its original properties after a suitable self-healing process at ambient temperature. This study thus demonstrates a feasible approach to impart an ionic association induced self-healing function to commercial rubbers without ionic functional groups.

Performance comparison of acrylic and thiol-acrylic resins in two-photon polymerization.

Microfabrication by two-photon polymerization is investigated using resins based on thiol-ene chemistry. In particular, resins containing different amounts of a tetrafunctional acrylic monomer and a tetrafunctional thiol molecule are used to create complex microstructures. We observe the enhancement of several characteristics of two-photon polymerization when using thiol-acrylic resins. Specifically, microfabrication is carried out using higher writing velocities and it produces stronger polymeric microstructures. Furthermore, the amount of shrinkage typically observed in the production of three-dimensional microstructures is reduced also. By means of microspectrometry, we confirm that the thiol-acrylate mixture in TPP resins promote monomer conversion inducing a higher degree of cross-linked network formation.

Two-Dimensional Differential In-Gel Electrophoresis (2D-DIGE) Reveals Proteins Associated with Cross-Linked Actin Networks in Human Trabecular Meshwork Cells

Background: The primary risk factor for primary-open angle glaucoma (POAG) is increased intraocular pressure (IOP). In POAG patients, the outflow resistance through the trabecular meshwork (TM) is abnormally elevated. One of the important glaucoma-associated pathological changes in the TM is formation of excessive cross-linked actin networks (CLANs). CLANs are web-like polygonal structures found in confluent glaucoma TM cells and tissues. Glaucoma-associated factors transforming forming growth factor beta 2 (TGFβ2) and glucocorticoids induce CLAN formation in non-glaucoma TM cells (NTM). CLANs may increase cell stiffness and alter homeostasis, and thereby contribute to elevated IOP. Methods: We used a proteomic approach to identify CLAN-associated proteins. We treated confluent primary NTM cells with 0.1% ethanol (EtOH; vehicle), 100 nM dexamethasone (DEX), or 5 ng/ml TGFβ2 plus 0.1% EtOH for 7 days to induce CLANs. The Triton insoluble fraction containing cytoskeleton was extracted for two-dimensional differential in-gel electrophoresis (2D-DIGE). Mass spectrometry (MS) was used to identify the differential expressed proteins in the 2D-gels. Co-localization of identified proteins with CLANs was confirmed using immunocytofluorescence (ICF) microscopy. Results: 2D-DIGE revealed 103 differentially expressed proteins in both treatment groups. MSidentified 23 of the most enriched proteins. ICF showed that caldesmon, calponin, myosin light chain, and tropomyosin were colocalized with CLANs. Conclusions: We identified a subset of proteins differentially expressed in NTM cells with DEX or TGFβ2- induced CLAN formation. The potential involvement of these proteins in CLAN formation and/or maintenance requires further investigation. These proteins may provide new insights into the pathogenesis of glaucoma.

Rheological, mechanical and adhesion properties of two component adhesive based on modified silyl terminated polyether polymer and epoxy resin

4 types of two component adhesives based on modified silyl-terminated polyether polymer (MS Polymer) and epoxy resin are formulated. Rheological and mechanical properties as well as weathering resistance of the developed adhesives are investigated. It is shown that curing times vary in a wide range depending on the type of MS Polymer. It is also demonstrated that kinetics of cross-linked network formation of the investigated adhesives, depending on the type of MS Polymer, considerably affects mechanical characteristics of the system: Shore A hardness, tensile strength and tensile elongation. Although under the influence of UV weathering mechanical properties of the investigated systems are decreased, the remaining tensile elongation values are not less than 30%. In parallel it is revealed that adhesive formulations, developed in the framework of this research, are most suitable for bonding with stainless steel, partially suitable for bonding with aluminium and less suitable for bonding with polyvinyl chloride.

Diels-Alder based, thermo-reversible cross-linked epoxies for use in self-healing composites

Epoxy resins are functionalized with Diels-Alder based thermo-reversible crosslinks to enable the fabrication of composites that are capable of multiple self-healing-repair processes. The key challenge in realizing a structural combination of conventional epoxy amine systems with furfuryl and maleimide functional groups is to achieve a high conversion in the reversible cross-linked polymer network formation while avoiding the major side-reactions.We have developed a two-step process consisting of a bulk prepolymerization reaction followed by a network formation step. The second step is performed in an extruder to realize a good mixing at high temperatures, while keeping the residence time at that temperature short to avoid maleimide side-reactions. The obtained oligomers are characterized using NIR, NMR, DSC, GPC analyses while solvent exposure tests and rheological measurements are performed to prove the formation of a thermo-reversible network and study their behavior in relation to the cross-linker concentration.Densely cross-linked, solvent resistant polymeric networks are obtained that maintain the ability to un-crosslink and thus regaining fluid behavior at elevated temperatures for at least five subsequent heat cycles. Glass fiber reinforced polymer composite films, which are fabricated using these resins, demonstrate that the thermo-reversible effect is strong enough to achieve full self-healing of a severely cracked and delaminated test specimen.

Hot Set Characterization of Electron Beam Irradiated-Copper (II) Oxide Added LDPE Composites under Acidic Aging

In this research study, the effect of aging duration time and electron beam irradiation dosages on the hot set results of copper (II) oxide added LDPE composites have been investigated. The addition of copper (II) oxide particles in LDPE matrix has significantly reduced the formation of crosslinking networks in LDPE matrix by blocking the mobility of free radicals generated by electron beam irradiation. At lower irradiation dosages (< 100 kGy), all the copper (II) oxide added LDPE composites were immediately failed the hot set test when subjected to static load of 20 N/cm2 under high temperature. Besides, the occurrence of copper (II) oxide particles in LDPE matrix also reduced the matrix continuities of copper (II) oxide added LDPE composites and caused the matrix resistance ability of LDPE matrix to be decreased. The increasing of irradiation dosages has significantly delayed the failing time of all LDPE composites when under static load at high temperature. This is because the increasing of electron beam irradiation could further induce the generation of free radicals to form higher degree of crosslinking networks in LDPE matrix. At higher irradiation dosage up to 250 kGy, the pristine LDPE was observed able to withstand the applied static load under high temperature more than 15 minutes. This is due to higher degree of crosslinking networks formed in LDPE matrix could effectively restrict the mobility of LDPE chains under static load and thus delay the failing of sampels. When the aging duration time increased from 4 days to 14 days, the resistance ability of all LDPE has been significantly weakened due to the occurrence of chain scissioning process in LDPE matrix by delaying the failing time of samples.

Effect of Electron Beam Irradiation on Mechanical Properties of Copper (II) Oxide Added LDPE Composites Aged under Acidic Condition

In this study, the effect of aging time duration in acidic solution and electron beam irradiation on the physical and mechanical properties of copper (II) oxide added LDPE composites haven been investigated. The tensile strength of all (3 phr and 5 phr) copper (II) oxide added LDPE composites was gradually increased with increasing of electron beam irradiation dosages from 0 kGy to 200 kGy. The electron beam irradiation could induce the formation of crosslinking networks in LDPE matrix by increasing the resistance ability of LDPE matrix towards applied straining stress. The increasing of aging time duration in acidic condition up to 4 days has marginally reduced the tensile strength of all un-irradiated and irradiated all copper (II) oxide added LDPE composites. This might be attributed to the hydrochloric acid solution could degrade and breakdown the macromolecular chains in LDPE matrix and thus further reduce the tensile strength of copper (II) oxide added LDPE composites.

Moisture-Responsive Hydrogel Impregnated in Porous Polymer Foam as CO2 Adsorbent in High-Humidity Flue Gas

This work focuses on developing the adsorbent for carbon dioxide (CO2) capture from high-humidity flue gas by loading moisture-responsive polyethylenimine (PEI) hydrogel interface layer in porous polymer matrix. The chemical structure and porous morphology of the porous adsorbents are characterized. The CO2 adsorption capacity and adsorption thermodynamics are studied. Also, the factors that affect the adsorption capacity including different molecular weight of PEI, loading weight and cross-linking degree of hydrogel, and moisture are investigated. The experimental results show that the porous polymer coated with PEI hydrogel exhibits a much higher adsorption capacity for CO2 and keep a high CO2–N2 selectivity by effective utilization of moisture. The CO2 adsorption capacity as high as 4.85 mmol CO2/g of adsorbent is obtained at 40 °C, with 1,4-butanediol diacrylate (BDA)/PEI ratio of 0.25. Moreover, the formation of three-dimensional cross-linked network in hydrogel shows good regeneration stability.

Thermo-sensitive ionic microgels via post quaternization cross-linking: fabrication, property, and potential application

A post quaternized cross-linking strategy was reported to fabricate thermo-sensitive ionic microgels from thermo-sensitive linear copolymer poly(N-isopropylacrylamide-co-1-vinylimidazole) [P(NIPAm-co-VIM)] or poly(N-isopropylacrylamide-co-4-vinylpyridine) [P(NIPAm-co-4VP)] in aqueous solution at elevated temperature above its critical transition temperature (T c). 1,4-dibromobutane, 1,5-dibromopentane, or 1,6-dibromohexane were chosen as the quaternization cross-linker to quaternize the imidazole or pyridine moieties, leading to the formation of cross-linking and ionic network. Transmission electron microscopy (TEM), dynamic and static light scattering (DLS & SLS), electrophoretic light scattering (ELS), and UV-visible spectroscopy were used to systematically investigate the sizes, morphologies, and properties of the obtained microgels. The sizes, swelling properties, and uniformity of microgels could be tuned by selecting proper quaternization cross-linking reaction temperature and cross-linkers. The obtained ionic microgels showed capability to adsorb the heavy metal salts like K2Cr2O7 in aqueous solution via the anion exchange reactions. It was also demonstrated that other functional groups could be introduced into the microgel networks if the unquaternized moieties were available.

A New Strategy for Simultaneously Improved Flame Retardancy, Thermal Properties, and Scratch Resistance of Transparent Poly(methyl methacrylate)

A novel poly(methyl methacrylate) (PMMA)-based nanocomposite combined with a reactive flame retardant (tetramethyl (3-(triethoxysilyl) propyl-azanediyl) bis(methylene) diphosphonate (TMSAP)) and organo-modified layered aluminophosphate (OLAP) was synthesized by the sol–gel method. The structure of the nanocomposite achieves maximal integration of both merits of each component, such as silane cross-linking function and dehydration charring effect of TMSAP and physical barrier effect and catalytic-charring effect of OLAP, which promotes cross-linked network formation, improves the quality and quantity of char, and inhibits the heat, oxygen, and mass transfer, leading to significant enhancements of scratch resistance, thermal stability, and flame retardancy. Compared to PMMA, the nanocomposites maintain high transparency and exhibit increased shore hardness by 90%, glass transition temperature by 13 °C, and half degradation temperature by 105.1 °C; in addition, peak heat released rate decreased by 59.1%. This work demonstrates the simultaneous enhancement of flame retardancy, thermal properties, and mechanical performance of polymers.

Electron beam irradiation enhanced of Hibiscus cannabinus fiber strengthen polylactic acid composites

This paper reported the effects of increasing Hibiscus cannabinus fiber (also known as kenaf fiber) loading level on properties of electron beam irradiated polylactic acid/low density polyethylene (PLA/LDPE). PLA and LDPE were compounded with 5–20 parts per hundred resins (phr) of kenaf respectively to enhance mechanical properties. The compounded kenaf added PLA/LDPE samples were electron beam irradiated from 15 to 60 kGy. The physical properties of kenaf added PLA/LDPE samples were characterized using gel content, X-Ray diffraction and scanning electron microscopy analysis. The results showed that the increasing of irradiation dosages in PLA/LDPE have gradually increased the gel content and tensile strength due to the formation of crosslinking networks in polymer matrix. However, the higher loading level of kenaf and irradiation dosages could decrease the elongation at break of PLA/LDPE samples. This is due to the restriction of polymer chains mobility as resulted by the poor interfacial adhesion between polymer matrix and kenaf particles as well as the formation of crosslinking networks in polymer matrix limits the sliding of polymer chains. Meanwhile, the increasing of kenaf loading level also has gradually increased the crystallinity of PLA/LDPE matrix. It is concluded that the electron beam irradiation dosages and amount of kenaf fiber in PLA/LDPE matrix should be kept at maximum 45 kGy and 15 phr, respectively for better combination to enhance the properties of the composites.

Thermosensitive Ionic Microgels with pH Tunable Degradation via in Situ Quaternization Cross-Linking

Degradable thermosensitive ionic microgels were synthesized via surfactant-free emulsion polymerization (SFEP) of N-isopropylacrylamide (NIPAm) and 1-vinylimidazole (VIM) at 70 °C with degradable 1,4-phenylene bis(4-bromobutanoate) or 1,6-hexanediol bis(2-bromopropionate) as quaternized cross-linkers. VIM could be quaternized by 1,4-phenylene bis(4-bromobutanoate) or 1,6-hexanediol bis(2-bromopropionate), leading to the formation of degradable cross-linking network and ionic microgels. Combined techniques of transmission electron microscopy (TEM), dynamic light scattering (DLS), electrophoretic light scattering (ELS), UV–vis spectroscopy, FT-IR spectra, and gel permeation chromatography (GPC) were employed to systematically investigate the sizes, morphologies, and properties of the obtained microgels before and after degradation as well as the degradation mechanism. The obtained microgels were spherical in shape with narrow size distribution and exhibited thermosensitive behavior and controllable degradat...

Rheology of Poly(N-isopropylacrylamide)–Clay Nanocomposite Hydrogels

We used molecular dynamics simulations and experiments to study the rheology of polymer–clay nanocomposite hydrogels. The molecular dynamics simulations studied the formation of physical cross-linked networks as a function of the clay concentration. Simulations showed that while the local structure changed from isolated polymer–clay clusters to a percolating network with increasing clay concentration the networks were only able to sustain stress at concentrations of roughly 1.5 times the percolation transition. Experiments using poly(N-isopropylacrylamide) (PNIPA)–clay nanocomposites at different clay concentrations were compared with simulation results. Experiments showed a transition from viscous to gel like behavior at a clay concentration of 15.24g/L, in good agreement with simulations. The modulus, G′ and G″, prior to yield was observed to increase exponentially with clay concentration and G′ at yield could be fitted to the modified Mooney’s equation.