Heat stabilizers lead-based

Lead heat stabilizers. Lead heat stabilizers are used primarily for wire and cable applications. Here they provide cost-effective stabilization while offering excellent electrical insulation properties. Most lead stabilizers are water-insoluble, an advantage in UL-approved electrical insulation applications. Lead stabilizers may be either organic- or inorganic-based products. Selected organic products consist of dibasic... 

The term unplastidzed (also spelt unplastidsed ) means that there is no plasticizer present in the injection molding material but, it does not mean that there are no additives mixed in with the polyvinyl chloride plastic or, resin (PVC). Additives are essential in PVC technology as without them the plastic is useless as it cannot be processed. Some additives enhance the properties of the base PVC and permit its use in a wider range of applications. Examples of such additives include heat stabilizers (often based on lead or tin), lubricants (for example, butyl stearate), processing aids (which may be based on acrylic polymers), impact modifiers... 

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. 

The stabilizer or stabilization system used depends on the heat and shear likely to be experienced by the polymer during processing, the end use application requirements, such as clarity or color, and the health concerns. A major health issue has been identified with the lead salts and soaps, because of their relative solubility and their corresponding potential to leach into water. For this reason, lead stabilizers currently find use only when other stabilizer systems do not provide the necessary stabilization or end use properties. Wire and cable sheathing is the only remaining application where the use of the lead stabilizer systems is widespread. Since most humans do not chew on wires (though mice, rats, and squirrels do) and lead-based stabilizers provide superior electrical properties, lead salts persist in this application. 

The most valuable property of 2-chlorotrityl esters is their high stability towards nucleophiles and bases. 2-Chlorotrityl esters have been successfully used at elevated temperatures (e.g. 80 °C, 5 h, toluene [63]), although prolonged heating can lead to cleavage [63],... 

These properties have been discussed in the text and elsewhere [5, 6], This table shows that both heat-stabilized PET (e.g. Melinex ST504) and heat stabilized PEN (TeonexQ65A) have an excellent balance of the key properties required for flexible electronics. TeonexQ65A has a higher-temperature performance than Melinex (Fig. 7.9) and as a result of this set of properties TeonexQ65A is emerging as a leading material for the base substrate of OLED displays and active matrix backplanes. 

HALS was based on the discovery that the 2,2,6,6-tetramethyl-l-piperidinyloxy, free radical (TEMPO) (1)), which already was known as an effective radical scavenger [46,47], was a very effective UV stabilizer too [48,49]. However, due to its physical and chemical properties TEMPO itself did not led to practical use. TEMPO is colored and will impart color to the to be stabilized polymer, it is thermally unstable and volatile [49]. Furthermore, it reacts with phenolic antioxidants present in many polymers leading to a reduction of processing and/or long-term heat stability. The discovery that compounds in which the /V-oxyl functionality was replaced by a N—H functionality also showed good UV stabilization activity was the key finding that led to the development of HALS stabilizers [49]. 

Metal Soaps—Barium and cadmium stabilizers are less toxic than lead and have lower cost on the basis of use levels, better sulfide stain resistance, and good clarity. They are a major class of heat stabilizers. Calcium and zinc soaps are also included in this classification because of their similar performance. The soaps used are based on a wide variety of anions such as octoates (2-ethyIhexanoic acid derived), benzoates, laurates, stearates, and substituted phenolates. 

Lead heat stabilizers are used for wire and cable applications as primary additives. They may be based on organic compounds including stearates and phthalates or inorganic salts such as sulphates, phosphates and carbonates. Although knowledge of the toxicity of lead has initiated the search for its replacement, no suitable, cost-effective material has yet been identified. 

The probable key to the continued success of the phosphorus-based additives in aromatic polyesters is their ability to take part in various processes beneficial to the non-oxidative heat stability of their host polymers. They are known hydroperoxide decomposers, and thus could safely destroy such species present in the polyester. They are, for the same reason, excellent secondary antioxidants, especially if used in conjunction with primary antioxidants such as hindered phenols, in a wide variety of polymers. Their ability to react with catalyst residues and prevent these contributing to degradation reactions of the polymer is also important. They would also appear to be capable of reacting with the polyester chain ends, leading to end-capping-and consequent reduction of the amount of volatiles such as acetaldehyde and acrolien-or even providing chain extension. 

Formulating lead-free flexible PVC containing Firebrake ZB (from Borax) with excellent heat stability is possible with Ca/Zn based stabilisers. An LOI of about 30 can be obtained with 30 phr of ATH and 6 phr of Firebrake ZB. These can be improved when part of the diisodecyl phthalate plasticiser is replaced by a phosphate plasticiser and calcium carbonate is present as an additional functional filler. 

Basic lead carbonate n. 2PbC03 Pb(0H)2. A very effective heat stabilizer, used where toxicity is of no concern as in electrical-insulating compounds. Its use is limited because of its tendency to form blisters during processing and to cause spew when exposed to weather, also by rising concern about lead in the environment. Gooch JW (1993) Lead based paint handbook. Plenum Press, New York. 

The use of lubricants with heat stabilizers, particularly lead types, in one-pack systems has not taken off in North America as it has in Europe. North America has focused more on the tin-based stabilizer systems, and customers still prefer buying the additives separately. 

PVC and Health Effects Virgin PVC is thermally and photochemically unstable and has a tendency to loose hydrogen chloride easily when heated, hence a stabiliser (a tin or a lead compound, usually heavy metal based compounds) is commonly used in the final compound to improve the heat stability. Various additives that are used to reduce various... 

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