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https://en.m.wikipedia.org/wiki/Nylon
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Nylons are condensation polymers or copolymers, formed by reacting difunctional monomers containing equal parts of amine and carboxylic acid, so that amides are formed at both ends of each monomer in a process analogous to polypeptide biopolymers. Most nylons are made from the reaction of a dicarboxylic acidwith a diamine (e.g. PA66) or a lactam or amino acid with itself (e.g. PA…
Nylons are condensation polymers or copolymers, formed by reacting difunctional monomers containing equal parts of amine and carboxylic acid, so that amides are formed at both ends of each monomer in a process analogous to polypeptide biopolymers. Most nylons are made from the reaction of a dicarboxylic acid with a diamine (e.g. PA66) or a lactam or amino acid with itself (e.g. PA6). In the first case, the "repeating unit" consists of one of each monomer, so that they alternate in the chain, similar to the so-called ABAB structure of polyesters and polyurethanes. Since each monomer in this copolymer has the same reactive group on both ends, the direction of the amide bond reverses between each monomer, unlike natural polyamide proteins, which have overall directionality: C terminal → N terminal. In the second case (so called AA), the repeating unit corresponds to the single monomer.
Nomenclature
In common usage, the prefix "PA" (polyamide) or the name "Nylon" are used interchangeably and are equivalent in meaning.
The nomenclature used for nylon polymers was devised during the synthesis of the first simple aliphatic nylons and uses numbers to describe the number of carbons in each monomer unit, including the carbon(s) of the carboxylic acid(s). Subsequent use of cyclic and aromatic monomers required the use of letters or sets of letters. One number after "PA" or "Nylon" indicates a homopolymer which is monadic or based on one amino acid (minus H2O) as monomer:
PA 6 or Nylon 6: [NH−(CH2)5−CO]n made from ε-caprolactam.
Two numbers or sets of letters indicate a dyadic homopolymer formed from two monomers: one diamine and one dicarboxylic acid. The first number indicates the number of carbons in the diamine. The two numbers should be separated by a comma for clarity, but the comma is often omitted.
PA or Nylon 6,10 (or 610): [NH−(CH2)6−NH−CO−(CH2)8−CO]n made from hexamethylenediamine and sebacic acid;
For copolymers the comonomers or pairs of comonomers are separated by slashes:
PA 6/66: [NH−(CH2)6−NH−CO−(CH2)4−CO]n−[NH−(CH2)5…
The term polyphthalamide (abbreviated to PPA) is used when 60% or more moles of the carboxylic acid portion of the repeating unit in the polymer chain is composed of a combination of terephthalic acid (TPA) and isophthalic acid (IPA).
Types of nylon
Nylon 66
Wallace Carothers at DuPont patented nylon 66 using amides. In the case of nylons that involve reaction of a diamine and a dicarboxylic acid, it is difficult to get the proportions exactly correct, and deviations can lead to chain termination at molecular weights less than a desirable 10,000 daltons (u). To overcome this problem, a crystalline, solid "nylon salt" can be formed at room temperature, using an exact 1:1 ratio of the acid and the base to neutralize each other. The salt is crystallized to purify it and obtain the desired precise stoichiometry. Heated to 285 °C (545 °F), the salt reacts to form nylon polymer with the production of water.
Nylon 6
The synthetic route using lactams (cyclic amides) was developed by Paul Schlack at IG Farben, leading to nylon 6, or polycaprolactam — formed by a ring-opening polymerization. The peptide bond within the caprolactam is broken with the exposed active groups on each side being incorporated into two new bonds as the monomer becomes part of the polymer backbone.
The 428 °F (220 °C) melting point of nylon 6 is lower than the 509 °F (265 °C) melting point of nylon 66.
Nylon 510
Nylon 510, made from pentamethylene diamine and sebacic acid, was studied by Carothers even before nylon 66 and has superior properties, but is more expensive to make. In keeping with this naming convention, "nylon 6,12" or "PA 612" is a copolymer of a 6C diamine and a 12C diacid. Similarly for PA 510 PA 611; PA 1012, etc. Other nylons include copolymerized dicarboxylic acid/diamine products that are not based upon the monomers listed above. For example, some fully aromatic nylons (known as "aramids") are polymerized with the addition of diacids like terephthalic acid (→ Kevlar, Twaron) or isophthalic acid (→ Nomex), more commonly associated with polyesters. There are copolymers of PA 66/6; copolymers of PA 66/6/12; and others. In general linear polymers are the most useful, but it is possible to introduce branches in nylon by the condensation of dicarboxylic acids with polyamines having three or more amino groups.
The general reaction is:
Two molecules of water are given off and the nylon is formed. Its properties are determined by the R and R' groups in the monomers. In nylon 6,6, R = 4C and R' = 6C alkanes, but one also has to include the two carboxyl carbons in the diacid to get the number it donates to the chain. In Kevlar, both R and R' are benzene rings.
Industrial synthesis is usually done by heating the acids, amines or lactams to remove water, but in the laboratory, diacid chlorides can be reacted with diamines. For example, a popular demonstration of interfacial polymerization (the "nylon rope trick") is the synthesis of nylon 66 from adipoyl chloride and hexamethylene diamine.
Nylon 1,6
Nylons can also be synthesized from dinitriles using acid catalysis. For example, this method is applicable for preparation of nylon 1,6 from adiponitrile, formaldehyde and water. Additionally, nylons can be synthesized from diols and dinitriles using this method as well.
Monomers
Nylon monomers are manufactured by a variety of routes, starting in most cases from crude oil but sometimes from biomass. Those in current production are described below.
Amino acids and lactams
• ε-Caprolactam: Crude oil → benzene → cyclohexane → cyclohexanone → cyclohexanone oxime → caprolactam
• 11-aminoundecanoic acid: Castor oil → ricinoleic acid → methylricinoleate → methyl-11-undecenoate → undecenoic acid → 11-undecenoic acid → 11-bromoundecanoic acid → 11-aminoundecanoic acid
• Laurolactam: Butadiene → cyclododecatriene → cyclododecane → cyclododecanone → cyclododecanone oxime → laurolactam
Diacids
• Adipic acid: Crude oil → benzene → cyclohexane → cyclohexanone + cyclohexanol → adipic acid
• Sebacic acid (decanedioic acid): Castor oil → ricinoleic acid → sebacic acid
• Dodecanedioic acid: Butadiene → Cyloclododecatriene → cyclododecane → (oxidation) → Dodecanedioic acid
• Terephthalic acid: Crude oil → p-xylene → terephthalic acid
• Isophthalic acid: Crude oil → m-xylene → isophthalic acid
Diamines
Various diamine components can be used, which are derived from a variety of sources. Most are petrochemicals, but bio-based materials are also being developed.
• Tetramethylene diamine (putrescine): Crude oil → propylene → acrylonitrile → succinonitrile → tetramethylene diamine
• Hexamethylene diamine (HMD): Crude oil → butadiene → adiponitrile → hexamethylene diamine
• 1,9-diaminononane: Crude oil → butadiene → 7-octen-1-al → 1,9-nonanedial → 1,9-diaminononane
• 2-methyl pentamethylene diamine: a by product of HMD production
• Trimethyl Hexamethylene diamine (TMD): Crude oil → propylene → acetone → isophorone → TMD
• m-xylylene diamine (MXD): Crude oil → m-xylene → isophthalic acid → isophthalonitrile → m-xylylene diamine
• 1,5-pentanediamine (cadaverine) (PMD): starch (e.g. cassava) → glucose → lysine → PMD.
Polymers
Due to the large number of diamines, diacids and aminoacids that can be synthesized, many nylon polymers have been made experimentally and characterized to varying degrees. A smaller number have been scaled up and offered commercially, and these are detailed below.
Homopolymers
Homopolymer nylons derived from one monomer
Examples of these polymers that are or were commercially available
• PA6 Lanxess Durethan B
• PA11 Arkema Rilsan
• PA12 Evonik Vestamid L
Homopolymer polyamides derived from pairs of diamines and diacids (or diacid derivatives). Shown in the table below are polymers which are or have been offered commercially either as homopolymers or as a part of a copolymer.
Examples of these polymers that are or were commercially available
• PA46 DSM Stanyl
• PA410 DSM Ecopaxx
• PA4T DSM Four Tii
• PA66 DuPont Zytel
Copolymers
It is easy to make mixtures of the monomers or sets of monomers used to make nylons to obtain copolymers. This lowers crystallinity and can therefore lower the melting point.
Some copolymers that have been or are commercially available are listed below:
• PA6/66 DuPont Zytel
• PA6/6T BASF Ultramid T (6/6T copolymer)
• PA6I/6T DuPont Selar PA
• PA66/6T DuPont Zytel HTN
• PA12/MACMI EMS Grilamid TR
Blends
Most nylon polymers are miscible with each other allowing a range of blends to be made. The two polymers can react with one another by transamidation to form random copolymers.
According to their crystallinity, polyamides can be:
• semi-crystalline:
• amorphous: PA6I made from hexamethylenediamine and isophthalic acid.
According to this classification, PA66, for example, is an aliphatic semi-crystalline homopolyamide.
Hydrolysis and degradation
All nylons are susceptible to hydrolysis, especially by strong acids, a reaction essentially the reverse of the synthetic reaction shown above. The molecular weight of nylon products so attacked drops, and cracks form quickly at the affected zones. Lower members of the nylons (such as nylon 6) are affected more than higher members such as nylon 12. This means that nylon parts cannot be used in contact with sulfuric acid for example, such as the electrolyte used in lead–acid batteries.
When being molded, nylon must be dried to prevent hydrolysis in the molding machine barrel since water at high temperatures can also degrade the polymer. The reaction is of the type:
Environmental impact, incineration and recycling
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