The small region may be an atom, a group of atoms, or a number of branch points connected by bonds, groups of atoms, or oligomeric chains.
In chemistry and biology a cross-link is a bond that links one polymer chain to another. These links may take the form of covalent bonds or ionic bonds and the polymers can be either synthetic polymers or natural polymers such as proteins. In polymer chemistry "cross-linking" usually refers to the use of cross-links to promote a change in the polymers' physical properties. When "crosslinking" is used in the biological field, it refers to the use of a probe to link proteins together to check for protein—protein interactionsas well as other creative cross-linking methodologies.Eso monster helm vendor
Although the term is used to refer to the "linking of polymer chains" for both sciences, the extent of crosslinking and specificities of the crosslinking agents vary greatly. As with all science, there are overlaps, and the following delineations are a starting point to understanding the subtleties.
Crosslinking is the general term for the process of forming covalent bonds or relatively short sequences of chemical bonds to join two polymer chains together. The term curing refers to the crosslinking of thermosetting resins, such as unsaturated polyester and epoxy resin, and the term vulcanization is characteristically used for rubbers.
In polymer chemistry, when a synthetic polymer is said to be "cross-linked", it usually means that the entire bulk of the polymer has been exposed to the cross-linking method. The resulting modification of mechanical properties depends strongly on the cross-link density. Low cross-link densities increase the viscosities of polymer melts. Intermediate cross-link densities transform gummy polymers into materials that have elastomeric properties and potentially high strengths. Very high cross-link densities can cause materials to become very rigid or glassy, such as phenol-formaldehyde materials.
Cross-links can be formed by chemical reactions that are initiated by heat, pressure, change in pH, or irradiation. For example, mixing of an unpolymerized or partially polymerized resin with specific chemicals called crosslinking reagents results in a chemical reaction that forms cross-links.
Cross-linking can also be induced in materials that are normally thermoplastic through exposure to a radiation source, such as electron beam exposure,  gamma radiationor UV light. For example, electron beam processing is used to cross-link the C type of cross-linked polyethylene. Other types of cross-linked polyethylene are made by addition of peroxide during extruding type A or by addition of a cross-linking agent e.
Citric-Acid-Derived Photo-cross-Linked Biodegradable Elastomers
The chemical process of vulcanization is a type of cross-linking that changes rubber to the hard, durable material associated with car and bike tires. This process is often called sulfur curing; the term vulcanization comes from Vulcanthe Roman god of fire.
This is, however, a slower process. However, the time can be reduced by the addition of accelerators such as 2-benzothiazolethiol or tetramethylthiuram disulfide. Both of these contain a sulfur atom in the molecule that initiates the reaction of the sulfur chains with the rubber.
Accelerators increase the rate of cure by catalysing the addition of sulfur chains to the rubber molecules. Cross-links are the characteristic property of thermosetting plastic materials. In most cases, cross-linking is irreversible, and the resulting thermosetting material will degrade or burn if heated, without melting.
Especially in the case of commercially used plastics, once a substance is cross-linked, the product is very hard or impossible to recycle. In some cases, though, if the cross-link bonds are sufficiently different, chemically, from the bonds forming the polymers, the process can be reversed.
Permanent wave solutions, for example, break and re-form naturally occurring cross-links disulfide bonds between protein chains in hair. Where chemical cross-links are covalent bonds, physical cross-links are formed by weak interactions.
For example, sodium alginate gels upon exposure to calcium ion, which allows it to form ionic bonds that bridge between alginate chains. Chemical covalent cross-links are stable mechanically and thermally, so once formed are difficult to break. Therefore, cross-linked products like car tires cannot be recycled easily. A class of polymers known as thermoplastic elastomers rely on physical cross-links in their microstructure to achieve stability, and are widely used in non-tire applications, such as snowmobile tracks, and catheters for medical use.
They offer a much wider range of properties than conventional cross-linked elastomers because the domains that act as cross-links are reversible, so can be reformed by heat.
The stabilizing domains may be non-crystalline as in styrene-butadiene block copolymers or crystalline as in thermoplastic copolyesters. Note: A rubber which cannot be reformed by heat or chemical treatment is called a thermoset elastomer.These metrics are regularly updated to reflect usage leading up to the last few days.
Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts. The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric. Find more information on the Altmetric Attention Score and how the score is calculated. Covalently cross-linked rubbers are renowned for their high elasticity that play an indispensable role in various applications including tires, seals, and medical implants.
Development of self-healing and malleable rubbers is highly desirable as it allows for damage repair and reprocessability to extend the lifetime and alleviate environmental pollution.
Herein, we propose a facile approach to prepare permanently cross-linked yet self-healing and recyclable diene-rubber by programming dynamic boronic ester linkages into the network. The resulted samples are covalently cross-linked and possess relatively high mechanical strength which can be readily tailored by varying boronic ester content.
Owing to the transesterification of boronic ester bonds, the samples can alter network topologies, endowing the materials with self-healing ability and malleability.
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More by Yingjun Liu. More by Siwu Wu. More by Baochun Guo.Table S1. Table S2. Table S3. Viscoelasticity dynamics of polyrotaxane cross-linked elastomers at various polyrotaxane concentrations. An elastomer is a three-dimensional network with a cross-linked polymer chain that undergoes large deformation with a small external force and returns to its original state when the external force is removed.
Dynamic ionic crosslinks enable high strength and ultrastretchability in a single elastomer
Because of this hyperelasticity, elastomers are regarded as one of the best candidates for the matrix material of soft robots. However, the comprehensive performance required of matrix materials is a special challenge because improvement of some matrix properties often causes the deterioration of others. For example, an improvement in toughness can be realized by adding a large amount of filler to an elastomer, but to the impairment of optical transparency.
Therefore, to produce an elastomer exhibiting optimum properties suitable for the desired purpose, very elaborate, complicated materials are often devised. Here, we have succeeded in creating an optically transparent, easily fabricated elastomer with good extensibility and high toughness by using a polyrotaxane PR composed of cyclic molecules and a linear polymer as a cross-linking agent.
In general, elastomers having conventional cross-linked structures are susceptible to breakage as a result of loss of extensibility at high cross-linking density.
Elastomers are used in automobiles, aircraft, buildings, and sporting goods because they flexibly deform under an applied load and further exhibit elastic recovery, such as reversible restoration.
Elastomers are also indispensable for the development of future products 1 — 4such as medical products that improve the quality of life 56flexible displays that can be used for wearable devices 7and soft robots that can coexist with people 8.
In addition to the flexibility and elasticity, toughness is another physical property of elastomers that is required to meet the needs of these products 9 — To develop elastomers suitable for the intended use, in addition to selecting appropriate materials, a new mechanism is needed to realize the required physical properties.
For a polymeric material to be used as an elastomer, it must be flexible. Even a cross-linked hard polymeric material will become supple with the addition of a plasticizer.Juniores cup 2019: rappresentativa “a” vs rappresentativa “c” per
However, over time, bleeding occurs in which the plasticizer melts, resulting in deterioration of the elastomer and contamination of the surface Some plasticizers have adverse human health effects, and when elastomers containing these plasticizers are used in applications that require direct contact with people, the safety of the elastomers must be considered A polymer having a glass transition temperature sufficiently lower than the operation temperature of the elastomer may be used to obtain an elastomer that does not suffer from bleeding.
Such an elastomer can be prepared without a plasticizer in these polymer chains with low glass transition temperature. Furthermore, the mechanical properties of the elastomer can be adjusted by changing its cross-linking density.
Generally, a simultaneous increase in the extensibility and elasticity of an elastomer having a conventional cross-linked structure requires a trade-off with other properties; thus, improving the toughness of the elastomer is difficult. Introducing a large amount of a filler such as carbon black or fine silica particles into an elastomer is known to be effective for creating an elastomer with a conventional cross-linked structure that has a high toughness However, for the large required amount of filler to be incorporated into an elastomer, the filler must be dispersible in the polymer material constituting the elastomer, and an appropriate kneading method must be applied 20yet these methods are not easily applied to all polymeric materials.
Moreover, the addition of a filler to an elastomer often impairs the transparency of the material, which may limit the use of the material in flexible displays and soft robotics.
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XLPO / Cross-Linked Polyolefin
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The item does not work. The item was damaged during shipping.Citric-acid-derived thermally cross-linked biodegradable elastomers CABEs have recently received significant attention in various biomedical applications, including tissue-engineering orthopedic devices, bioimaging and implant coatings.
However, citric-acid-derived photo-cross-linked biodegradable elastomers are rarely reported. Herein, we report a novel photo-cross-linked biodegradable elastomer, referred to as poly octamethylene maleate citrate POMCwhich preserves pendant hydroxyl and carboxylic functionalities after cross-linking for the potential conjugation of biologically active molecules. POMC is a low-molecular-mass pre-polymer with a molecular mass average between and Da.
POMC networks are soft and elastic with an initial modulus of 0. Photo-polymerized POMC films implanted subcutaneously into Sprague—Dawley rats demonstrated minimal in vivo inflammatory responses. The development of POMC enriches the family of citric-acid-derived biodegradable elastomers and expands the available biodegradable polymers for versatile needs in biomedical applications. Biodegradable elastomers have received significant attention for soft tissue-engineering applications due to their advantages in that they can sustain and recover from multiple deformations without causing irritation to the surround tissue when implanted in the body [ 1 — 6 ].
The mechanical irritation resulting from the compliance mismatch between implants and surround tissues has been recognized to cause significant inflammation and scar tissue formation, which ultimately prevents the implants from being effectively integrated with the surrounding tissues [ 7 ].
Among those biodegradable elastomers, recent focuses are heavily placed on cross-linked polyester elastomers such as poly glycerol-sebacate PGS and poly diol citrates [ 8 — 10 ].
It has been recognized that cross-linking confers elasticity to the polymers as similar to those naturally occurred cross-linked polymers such as collagen and elastin. PGS and poly diol citrates are soft and elastomeric cross-linked polyester networks and the mechanical properties of these polymers have been shown to match those of the soft tissues such as cardiac tissues and blood vessels in the body, thus considered as suitable candidate materials for soft tissue engineering [ 29 ].
Photo-cross-linkable biodegradable materials have recently attracted increased attention in tissue engineering, drug delivery and wound care applications [ 11 — 24 ]. For tissue-regeneration applications, photo-cross-linkable biodegradable materials may be used as cell or drug carriers delivered through minimally invasive procedures [ 25 ].
Photo-cross-linkable polymers are also widely used in microfabrication for various biomedical applications such as 3-D tissue construction and cell entrapment [ 2627 ]. Photo-cross-linkable systems may allow polymerization occurred directly in or on a tissue, thus provide advantages including localized delivery for site specific action, ease of application and a reduction in the dosage amount. Biodegradable elastomeric PGS has already been further developed into photo-cross-linkable polymers poly glycerol sebacate acrylate, PGSA by attaching acrylate groups into the PGS pre-polymer backbone to allow for free radical polymerization while still preserving elastic and biocompatible properties [ 2930 ].
However, the incorporation of the vinyl moiety sacrificed the pendant functionality —OH of the resulting polymer. It has been recognized that pendant chemistries in the bulk material are essential in order to further modify a biomaterial with biologically active molecules for targeted drug delivery or to illicit a particular cellular response [ 21 ].
A key feature for CABEs is that citric acid acts as a robust multifunctional monomer to provide valuable pendant functionality to give the above listed polymers their unique degradation, mechanical and optical properties over existing biomaterials.
Citric acid itself is an anticoagulant used in the hospital setting. Citric acid is mainly used to participate in the ester-cross-link formation in the biomaterials, but also enhances hemocompatibility, balances the hydrophilicity of the polymer network, provides hydrogen bonding and additional binding sites for bioconjugation to confer additional functionality such as optical properties [ 31 ]. Poly diol citrate s have demonstrated excellent biocompatibility, including hemocompatibility for soft tissue-engineering applications [ 3438 ].
Poly diol citrate s have not been developed into a photo-cross-linkable form which still demonstrates excellent biocompatibility.
The purpose of this study was to develop a novel photo-cross-linkable biodegradable elastomer, poly octamethylene maleate citrate s POMCsbased on poly ocatamethylene citrate s POC, a representative poly diol citrate. This new class of synthetic polyester is composed of 1,8-octanediol ODmaleic acid MA and citric acid CAwhich have all been successfully used in a wide range of biomedical applications [ 93339 — 42 ].
In the present paper, the chemical, physical and biocompatibility of POMC are studied and its potential in tissue engineering and in situ wound dressing formation is also demonstrated. All chemicals were purchased from Sigma-Aldrich and used as received. CA, OD and MA were added into a ml three-necked round-bottom flask fitted with an inlet adapter and outlet adapter.
Pre-POMC was dissolved in 1,4-dioxane and precipitated in de-ionized water in order to remove any un-reacted monomers. The precipitated polymer solution was freeze-dried to obtain the purified pre-POMC.Rent cloud gaming pc
To investigate the effects of the reactant ratio on the properties of the polymer, five different MA:CA molar ratios were studied,andas shown in Table 1. The ratio of the acids over the diol for the reaction was kept as Schematics of POMC synthesis.
Ratios of maleic acid and citric acid were varied as,andrespectively, whereas the ratio of overall acid to diol was kept as The chemical shifts for the 1 H-NMR spectra were recorded in parts per million ppmand were referenced relative to tetramethylsilane TMS, 0.
Pre-POMC was cross-linked by free radical polymerization. The thermoset elastomer achieved through this process is shown in Fig.The primary challenge in distinguishing an elastomer vs.
An elastomer is made from polymers joined by chemical bonds with a slightly cross-linked structure. Without the cross-linkages, applied stress to an elastomer would result in a permanent deformation. Because of it, the material is characterized by high elongation, flexibility, and elasticity.
This helps prevent the material from cracking, snapping, or breaking when deformed. Polymer is a more general term for any molecule made of a long, repeating chain of smaller, bonding molecules called monomers. There are organic polymers such as amino acids and DNA, and more familiar synthetic polymers which include plastics like thermosets and thermoplastics. Synthetic polymers are used daily in products all around us: clothing and carpets are made from polyester fibers, foam cushions and upholstery in furniture are made of polymers, polyethylene cups, pipes and valves, plastic bags, medical devices, cookware, rubber for tires and tubing, paints, electronic components, adhesives, and so on, are all examples of polymers.
As a polymer, elastomers fall into a group of pliable polymeric, or plastic, material that includes artificial and natural rubber.
They are good for molding, insulating, can withstand deformation and are formed easily into an assortment of rubbery shapes that are then hardened. Their versatility and usefulness make the application of elastomers popular in a wide variety of everyday products, from skateboard wheels and the soles of sneakers, to gaskets and electronic cabling and wire insulation.
Elastomers can have properties similar to thermosets or thermoplastics. As a thermoset, they can be used in high-heat applications. The flexibility of a thermoset elastomer, like all thermosets, is limited to a degree with regard to reprocessing and recycling.
Once a thermoset elastomer is created, it cannot be reversed. Thermoplastic elastomers are not well suited for high-heat applications. Industries working with elastomers have long praised their beneficial properties:. Physical Versatility — One of the most obvious advantages of elastomers is their custom molding in size, shape, flexibility, and color to customer specifications. Short Production Times — Elastomers can be mixed, molded, and cured or vulcanized rapidly, which makes for short production times.
Good Insulator — Its closed cell properties make for effective insulation of electronic and electrical products in a variety of home and industrial applications.
Excellent Adherence — Elastomers can easily be installed next to various other materials, such as metal, hard plastic, or different kinds of rubber, with excellent adherence. Generally they are insoluble, but will swell when exposed to certain solvents. They have lower creep resistance than thermoplastic materials.Basildon Chemicals - cross-linking liquid polymers
Some are even fire resistant which can add a measure of safety. Environmental Durability — Thermosetting plastic elastomers remain stable at very high temperatures and resist harsh environments, and will keep their shape and colors, no matter the exposure to water or atmospheric gases.
However, there is a need for more elastomers that perform at very low temperatures. Because of their flexibility and elasticity, the properties of elastomeric materials reflect its many uses.
Besides natural rubber, elastomers are polymerized for such applications as the polyurethanes used in the textile industry, polybutadienes used for wheels or tires, neoprene used for wetsuits, wire insulation, industrial belts, and silicone, which is used in a wide range of materials—medical devices, molding, lubricants, etc. The difference between elastomers and polymers is that elastomers are a unique polymer with unique characteristics and properties.
A Nature Research Journal. Maintenance-free self-healing elastomers that switch their mechanical properties on demand would be extremely useful materials for improving the functionalities, safety, energy efficiency, and lifetimes of many kinds of products and devices.
However, strength and stretchability are conflicting properties for elastomers because the inherent crosslinking density of a polymeric network is unchangeable. For example, heavily crosslinked elastomers are strong, but poorly stretchable.
Here we report an ionically crosslinked polyisoprene elastomer in which the ionic moieties are continually hopping between ionic aggregates at room temperature. Thus, the network is dynamic. This elastomer spontaneously self-heals without the input of external energy or healing agents. Furthermore, it behaves like a strong elastic material under rapid deformation, but acts like a highly stretchable and viscoelastic material under slow deformation.
Since the invention of the vulcanization of natural rubbers by Charles Goodyear in 1elastomers have made tremendous contributions to the advancement of modern technology. For example, they are applied in vehicle tires, soft and waterproof coatings, and as man-made skins in medical 2 and robotic 3 fields.
The practical advantage of elastomers is that their fracture strength, toughness, and stretchability can be easily and widely tuned by controlling the crosslinking density of the networks 4. However, the strength and stretchability of elastomers exhibit a trade-off relationship because these properties are oppositely dependent on the crosslinking density.
Heavily crosslinked elastomers are strong, but poorly stretchable. Indeed, elastomers that switch their properties from strong-to-soft and stretchable on demand are as yet unrealized, despite their enormous potential.
Furthermore, unlike human skin, conventional elastomers do not spontaneously self-heal 56. The development of elastomers that switch their mechanical properties on demand and exhibit autonomic self-healing ability at ambient temperature may have a significant impact on the improvement of functionality, safety, energy efficiency, and lifetimes of products and devices.
Recently, supramolecular elastomers comprising low glass transition temperature T g polymer chains and weak dynamic bonds, such as hydrogen bonds 7metal—ligand coordination 8910and ionic bonds 1112131415have been designed for autonomic self-healing at room temperature. In contrast to most self-healing materials, these supramolecular elastomers do not require the input of any external energy such as heat or light 1617181920healing agents such as monomers and catalysts 2122plasticizers 23or solvents 242526 When supramolecular elastomers are cut into two pieces, the weak dynamic bonds acting as crosslinks are preferentially broken.
However, upon contacting the cut faces, the broken crosslinks reform and flexible polymer chains self-diffuse. Thus, the two pieces reconnect, even at room temperature. For example, Leibler et al.
At shorter time scales than the lifetime of the dynamic crosslinks, they behave as strong crosslinks and the networks are elastic. Conversely, the chains will diffuse and viscoelastic behavior will be presented under slow deformation. Nevertheless, designing dynamic crosslinks with desired strengths and lifetimes is challenging 9 In the present study, we demonstrate a simple methodology to tune the strength and lifetime of the dynamic crosslinks in an elastomer.
In our ionically crosslinked polyisoprene PI elastomer, ionic moieties continuously hop between ionic aggregates at room temperature, and the hopping rate is controllable by the neutralization level. These dynamic ionic crosslinks allow our elastomer to spontaneously self-heal at room temperature. Moreover, our elastomer demonstrates a strong and elastic response to rapid stretching while ultrastretchable behavior is demonstrated under slow stretching.
Unlike previous self-healing elastomers, the self-healing rate, stretchability, toughness, and strength of our elastomer may be tuned by altering the neutralization level.
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