Hard-shell kayaks are also often manufactured with crosslinked polymers. In many hydraulic fracturing treatments, a delayed gel-cross-linker fluid is used to carry out fracture treatment of the rock. Pure and Applied Chemistry. In some cases this is undesirable and thus polymerization reactions may involve the use of an antioxidant to slow the formation of oxidative cross-links. Alkyd enamels, the dominant type of commercial oil-based paint, cure by oxidative crosslinking after exposure to air.
In that process the disulfide bonds are reduced, typically using a mercaptan such as ammonium thioglycolate. 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. Low cross-link densities decrease the viscosities of polymer melts. The crosslinked sample is placed into a good solvent at a specific temperature, and either the change in mass or the change in volume is measured.
Subunit structure is deduced, since crosslinkers bind only surface residues in relatively close proximity in the native state. In chemistry and biology a cross-link is a bond that links one polymer chain to another.
Rubber was vulcanized with sulfur under heat, which created a link between latex models. 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. Intermediate cross-link densities transform gummy polymers into materials that have elastomeric properties and potentially high strengths. 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. In some cases, though, if the cross-link bonds are sufficiently different, chemically, from the bonds forming the polymers, the process can be reversed.
Protein interactions are often too weak or transient to be easily detected, but by crosslinking, the interactions can be stabilized, captured, and analyzed. Both of these contain a sulfur atom in the molecule that initiates the reaction of the sulfur chains with the rubber. From Wikipedia, the free encyclopedia. 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. Cross-links are the characteristic property of thermosetting plastic materials.
Accelerators increase the rate of cure by catalysing the addition of sulfur chains to the rubber molecules. Cross-links can be formed by chemical reactions that are initiated by heat, pressure, change in pH, or irradiation.
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. Synthetic rubber used for tires is made by crosslinking rubber through the process of vulcanization. The more crosslinking, free stocking pattern pdf the less swelling is attainable.
Especially in the case of commercially used plastics, once a substance is cross-linked, the product is very hard or impossible to recycle. As with all science, there are overlaps, and the following delineations are a starting point to understanding the subtleties. Many polymers undergo oxidative cross-linking, typically when exposed to atmospheric oxygen. Chemical covalent cross-links are stable mechanically and thermally, so once formed are difficult to break. Proteins naturally present in the body can contain crosslinks generated by enzyme -catalyzed or spontaneous reactions.
Disulfide bond formation is one of the most common crosslinks, but isopeptide bond formation is also common. The aforementioned process of applying a permanent wave to hair is one example of oxidative cross-linking.
Very high cross-link densities can cause materials to become very rigid or glassy, such as phenol-formaldehyde materials. Permanent wave solutions, for example, break and re-form naturally occurring cross-links disulfide bonds between protein chains in hair. Each of these crosslinkers induces nucleophilic attack of the amino group of lysine and subsequent covalent bonding via the crosslinker. The interactions or mere proximity of proteins can be studied by the clever use of crosslinking agents.
On the other hand, a thermoplastic elastomer can be molded and recycled by heat. In other cases, when formation of cross-links by oxidation is desirable, an oxidizer such as hydrogen peroxide may be used to speed up the process.
Proteins can also be cross-linked artificially using small-molecule crosslinkers. 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.
The stabilizing domains may be non-crystalline as in styrene-butadiene block copolymers or crystalline as in thermoplastic copolyesters. For example, sodium alginate gels upon exposure to calcium ion, which allows it to form ionic bonds that bridge between alginate chains.
In most cases, cross-linking is irreversible, and the resulting thermosetting material will degrade or burn if heated, without melting. Crosslinking is often measured by swelling tests. The resulting modification of mechanical properties depends strongly on the cross-link density. Several terms redirect here. The earliest examples of crosslinking, linking long chains of polymers together to increase strength and mass, involved tires.
Proceedings of the National Academy of Sciences. 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. In-vivo crosslinking of protein complexes using photo-reactive amino acid analogs was introduced in by researchers from the Max Planck Institute of Molecular Cell Biology and Genetics. This crosslinking makes them more elastic. Synthetically crosslinked polymers have many uses, including those in the biological sciences, such as applications in forming polyacrylamide gels for gel electrophoresis.
- La vida en la tierra octava edicion pdf
- Cours de grammaire espagnol pdf
- Partes del microscopio compuesto pdf
- Igcse study guide for business studies pdf download
- Al-kitaab fii tacallum al-carabiyya pdf download
- Alteraciones del tono muscular pdf download
- Grounds for grounding a circuit to system handbook pdf
- Peugeot 207 manual pdf english download
- The blessed life book pdf
- Pdf sex
- Dioses y heroes de la mitologia griega pdf download
- Bmml to pdf download
- Decreto prosec pdf
- Pdf verwaltungsprogramm
- Psybermagick pdf download