Base heat stabilizers

Organotin Compounds. Organotin-based heat stabilizers are the most efficient and universally used PVC stabilizers. Nearly 40% of the 75,0001 of stabilizers used in the United States dining 2000 were organotin-based products. These are all derivatives of tetravalent tin, and all have either one or two alkyl groups covalently bonded directly to the tin atom. The commercially important... 

According to their major components, common heat stabilizers can be divided into base heat stabilizers, fatty acids, organic tin compounds, composite heat stabilizers, and pure organic compounds. 

Base heat stabilizers are inorganic and organic acid lead salts combined with a base. They have excellent heat resistance, weathering resistance, and electrical insulating properties, as well as low cost, poor transparency, and a certain toxicity the concentration generally is 0.5%-5.0%. 

The air jet textured yam process is based on overfeeding a yam into a turbulent air jet so that the excess length forms into loops that are trapped in the yam stmcture. The air flow is unheated, turbulent, and asymmetrically impinges the yam. The process includes a heat stabilization zone. Key process variables include texturing speed, air pressure, percentage overfeed, filament linear density, air flow, spin finish, and fiber modulus (100). The loops create visual and tactile aesthetics similar to false twist textured and staple spun yams. 

Absorption of Hydrogen Chloride. Effective heat stabilizers have the abiHty to bind hydrogen chloride. Most stabilizer systems contain one or more metallic soaps or salts which readily undergo a simple acid—base reaction with the by-product hydrogen chloride as the PVC degrades ... 

Cost bilizers. In most cases the alkyl tin stabilizets ate particularly efficient heat stabilizers for PVC without the addition of costabilizers. Many of the traditional coadditives, such as antioxidants, epoxy compounds, and phosphites, used with the mixed metal stabilizer systems, afford only minimal benefits when used with the alkyl tin mercaptides. Mercaptans are quite effective costabilizets for some of the alkyl tin mercaptides, particularly those based on mercaptoethyl ester technology (23). Combinations of mercaptan and alkyl tin mercaptide ate currendy the most efficient stabilizers for PVC extmsion processes. The level of tin metal in the stabilizer composition can be reduced by up to 50% while maintaining equivalent performance. Figure 2 shows the two-roU mill performance of some methyl tin stabilizers in a PVC pipe formulation as a function of the tin content and the mercaptide groups at 200°C. 

Stabilizers. Heat stabilizers (qv) are included in PVC compounds to counteract the internal generation of hydrogen chloride as well as the external degradative effect of heat. Due to environmental considerations, there is a trend toward decreasing and even avoiding the use of stabilizers based on heavy metals, eg, lead. 

Organophosphoms compounds, primarily phosphonic acids, are used as sequestrants, scale inhibitors, deflocculants, or ion-control agents in oil wells, cooling-tower waters, and boiler-feed waters. Organophosphates are also used as plasticizers and flame retardants in plastics and elastomers, which accounted for 22% of PCl consumed. Phosphites, in conjunction with Hquid mixed metals, such as calcium—zinc and barium—cadmium heat stabilizers, function as antioxidants and stabilizer adjutants. In 1992, such phosphoms-based chemicals amounted to slightly more than 6% of all such plastic additives and represented 8500 t of phosphoms. Because PVC production is expected to increase, the use of phosphoms additive should increase 3% aimually through 1999. 

Coordination complexes of zinc, cobalt, and platinum show a stability similar to complexes involving copper and iron. They are stable to concentrated, nonoxidizing acids and bases. The fact that such complexes sublimate at 550 to 600°C without decomposing points to their extreme heat stability [7],... 

Similar to accelerated studies, stress tests give a general picture of the chemical stability and degradation pathways under exaggerated conditions, such as under extreme pH conditions (acids and bases), heat, oxidative or reductive conditions, hydrolysis, and light irradiation (light irradiation tests at not less than 1.2 million lux hours are formalized as described in ICH QIB). These mostly non-formalized stress tests are only evaluated over a short term, e.g., 1 month. 

Tetracycline antibiotics are generally considered relatively unstable compounds. Oxytetracycline posseses limited stability in aqueous solutions and shows specific and base catalysis, with overall hydrolysis observed to follow pseudo-first-order kinetics. The maximum stability of this drug is exhibited at pH 2, whereas the optimum stability ranges from pH 1 to 3, which accounts for the recent finding (70) that oxytetracycline has greater heat stability at pH 3 than at pH 6.9. 

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