Formic Acid polyamide solvent

Polyamides (nylons) The main types of nylon are oil and petrol resistant, but on the other hand susceptible to high water absorption and to hydrolysis. There are a few solvents such as phenol, cresol and formic acid. Special grades include a water-soluble nylon, amorphous copolymers and low molecular weight grades used in conjunction with epoxide resins. Transparent amorphous polyamides are also now available. 

Dissolution/reprecipitation processes were evaluated for the recycling of poly-epsilon-caprolactam (PA6) and polyhexamethyleneadipamide (PA66). The process involved solution of the polyamide in an appropriate solvent, precipitation by the addition of a non-solvent, and recovery of the polymer by washing and drying. Dimethylsulphoxide was used as the solvent for PA6, and formic acid for PA66, and methylethylketone was used as the non-solvent for both polymers. The recycled polymers were evaluated by determination of molecular weight, crystallinity and grain size. Excellent recoveries were achieved, with no deterioration in the polymer properties. 33 refs. 

A few other successful 13C 1-NMR determinations should be mentioned. Hunt et al. [28] used 13C NMR to characterise fractions of extracted analytes of PAG and sorbitan ester samples and identified Irganox 1010. H and 13C NMR have been used to identify the main organic components of a breathable diaper back-sheet as LLDPE and pentaerythritol tetra-octyl ester (PETO) [233]. The equally present AOs Irganox 1010 and Irgafos 168 were not detected without extraction. Barendswaard et al. [234] have reported fully assigned 13C solution spectra of these two antioxidants. Chimas-sorb 944 in a polyamide matrix can be determined by H or 13C 1-NMR using solvents such as formic acid, trifluoroacetic acid or trifluoroethanol [235], Both H and 13C NMR have been used to follow the chemistry of a bis-phenoxidemethylaluminum complex (reaction product of BHT and trimethylaluminum) by exposure in air. Pierre and van Bree [216] also used 13C NMR to... 

A major challenge in using interactive chromatography for polyamides is to find a suitable mobile phase (Mengerink et al., 2001, 2002 Weidner et al., 2004). Polyamides form semicrystalline morphologies that limit the solubility in organic solvents. Besides hot phenol, formic acid, and trifluoroethanol (TFE) (Mori and Barth, 1999), 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) represents a suitable solvent for polyamides (Chen et al., 2002). These solvents are mainly used to analyze the molar mass distribution of polyamides by SEC. 

Many properties of polyamides are attributable to the formation of hydrogen bonds between the NH and CO groups of neighboring macromolecules. This is evidenced by their solubility in special solvents (sulfuric acid, formic acid, m-cresol), their high melting points (even when made from aliphatic components), and their resistance to hydrolysis. In addition, polyamides with a regular chain structure crystallize very readily. 

Thin-layer chromatography of dansyl-amino acids on a polyamide plate. A After solvents 1 (1.5% formic acid) and 2 (toluene-acetic acid). B After solvents 1,2, and 3 (ethyl acetate-methanol-acetic acid). See text for further details. 

Many of the remarks made in the previous section concerning fibres can be applied to the analysis of plastics. Some polymers are soluble in organic solvents and samples may be prepared for direct aspiration into a flame in this way, e.g. MIBK is a suitable solvent for polyesters, polystyrene, polysiloxanes, cellulose acetate and butyrate dimethyl formamide for polyacrylonitrile, dimethyl acetamide for polycarbonates and polyvinyl chloride cyclohexanone for polyvinyl chloride and polyvinyl acetate formic acid for polyamides and methanol for polyethers. These organic solutions may alternatively be injected into a graphite furnace. Otherwise, polymers may be wet or dry ashed and the resultant ash dissolved in acid. An approach which is attracting increasing interest is the direct insertion of solid samples into a graphite furnace. 

No solvent system resolves all the Dns-amino acids by one-dimensional chromatography and, also, TD chromatography requires more than two runs for a complete resolution. The most common used eluents on polyamide layers are benzene-acetic acid (9 1), toluene-acetic acid (9 1), toluene-ethanol-acetic acid (17 1 2), water-formic acid (200 3), water-ethanol-ammonium hydroxide (17 2 1 and 14 15 1), ethylacetate - ethanol- ammonium hydroxide... 

Dimethylformamide (DMF) has been known since 1893, but since the 1950s, it has evolved as an important solvent. Its main uses are as a solvent for spinning acrylic fibers, polyurethane and polyamide coatings and films, PVC, polyacrylonitrile, extraction of aromatics from petroleum, selective solvent for removal of acid gases from natural gas, solvent for dyes, electrolyses in galvanization processes, and paint remover and cleaner [16]. By 1980, the worldwide production of DMF had grown equal to the production of formic acid at 220,000 metric tons per year [18]. By 1993 the U.S. production of formic acid was 30 to 35 mm pounds and DMF production had grown to 60 to 65 mm pounds. 

For linear polyamides, the viscosity of dilute or moderately concentrated solution can be related closely to M . Thus, the molecular weight of polymer can be evaluated from i inh = ln reiA- This is usually measured at a concentration of 0.5 g of polymer in 100 ml of solvent, e.g., m-cresol. A typical value of T i h of nylon-6,6 is one forMn of about 15,000. Another method of characterization commonly used is to measure the relative viscosity (RV) of an 8.4% solution of polymer in 90% formic acid. Typical values of relative viscosity for nylon-6,6 are in the range of 30 to 70. An RV of 41 corresponds toMn of about 15,000, whereas an RV of 60 corresponds to about 19,000. Polymers in the lower range are used for textile yarns, and those in the higher range for industrial yarns. 

A widely employed chromatographic system is the one based on polyamide plates eluted with water-formic acid (200 3 v/v) in the first direction and benzene-acetic acid (9 1 v/v) in the second direction. A third run with 1 M ammonia-ethanol (1 1 v/v) or ethylacetate-acetic acid-methanol (20 1 1 v/v/v) in the direction of solvent 2 resolves especially basic Dns-amino acids or Glu/Asp and Thr/Ser pairs. 

All DABTH-amino acids, except the Leu/Ile pair, can be separated by 2D chromatography on layers of polyamide, with water—acetic acid (2 1 v/v) and toluene— n-hexane-acetic acid (2 1 1 v/v/v) being solvents 1 and 2, respectively. Resolution of the DABTH-Leu/Dns-Ile pair on polyamide is possible with formic acid-ethanol (10 9 v/v) and on silica plates using chloroform-ethanol (100 3 v/v) as eluent. 

Solubility. Solubility of selected aromatic polyamides in a variety of solvents has also been measnred (15). In general, PPTA is soluble only in strong acids, such as sulfuric, hydrofluoric and methanesulfonic acids (all of the polymers cited are soluble in these acids). MPDI is also soluble in the amide solvents (DMF, DMA, and NMP) and in dimethyl sulfoxide, as are most of the substituted variations of these two polymers. Solubility in the amide solvents is increased by the addition of salts such as LiCl and CaCl2. This class of poljuners is generally not soluble in formic acid or m-cresol, which are common solvents for aliphatic polyamides. 

Salo and co-workers have separated artificial sweeteners on mixed layers of acetylated cellulose and polyamide [82]. A good separation of dulcin (hi / 66), saccharin (47) and cyclamate (28) was possible using the solvent Shell Sol A-n-propanol-acetic acid-formic acid (75 + 10 + 12 + 3). Rhodamine B (Rgt. No. 220) or dichlorofluorescein (Rgt. No. 63) were used for detection. The layers were prepared from 9 g acetylated cellulose powder (MN 300 Ac, Firm 83) and 6 g polyamide powder for TLC (Firm 153). These were mechanically mixed into a homogeneous suspension with 60 ml methanol and then spread the layers were dried for 10 min at 70° C. A 10 cm run took about 25 min at chamber saturation. 

Experimental conditions I Silica gel CS solvent VII ethyl acetate-butanone-formic acid-water (50 + 30+ 10+ 10) [119]. II Polyamide solvent water-ethanol-butanone-acetylacetone (65 +15+15+5) [20]. Ill Polyamide solvent benzene-methanol-butanone (60+ 20+ 20) [25]. IV Cellulose layer solvent Partridge mixture. 

Most separation studies have used plant tissues which are extracted with warm ethanol or methanol. The extracts are then filtered and the supernatant used directly for PC or TLC analysis. Harborne (1984) has discussed the use of cellulose, silica gel, and polyamide layers for the separation of plant organic acids by TLC. Cellulose layers may be used with similar solvents as in paper chromatography. Silica gel plates should be developed with solvent systems such as methanol-5 M NH4OH (4 1) or benzene-methanol-acetic acid (79 14 7). The latter solvent system will separate maleic R,.- = 0.07) from fumaric acid (R = 0.23). Polyamide layers can be used to separate the acids of the tricarboxylic acid cycle with a solvent system of di-isopropyl ether-petroleum ether-carbon tetrachloride-formic acid-water (5 2 20 8 1). Less information on the TLC of organic acids from animal tissues is available, but some information can be found in Rasmussen (1967), Passera et al. (1964), Bleiweiss et al. (1967), Lupton (1975), and Hanai (1982). 

Two-dimensional TLC on polyamide sheets by ascending solvent flow is used to identify all DABTH-amino acids except DABTH-Ile/Leu. No phase equilibrium is necessary, and HrO-acetic acid (2 1) is used for the first dimension and toluene- -hexane-acetic acid (2 1 1, v/v) is used for the second dimension. The sheet is dried after the second run and exposed to HCl vapors when all yellow spots turn red or blue. For discrimination between DABTH-Ile/Leu, one-dimensional separation on polyamide (143) using formic acid-ethanol (10 9, v/v) or one-dimensional separation on silica gel... 

Aglycones of flavonols and flavones are easily separated on silica layers with traditional solvents (14,15). Polyamide layers are suitable for the separation of medium polar to apolar flavonoids (16), and a solvent system containing methanol-formic acid-water (58 10 16) is ideal for the separation of several aglycones on reversed-phase layers (17). For the separation of flavonoids on a preparative scale, centrifugal TLC on silica gel has been used for the final purification of flavanones with the... 

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