Liquid Stabilisers

The performance of organotin mercaptides is not only based on the amount of tin metal content, but on the organotin species, mercaptide ligand chemistry and organic co-stabiliser (453). The mechanism of organothiotin stabilisation has been studied extensively (221,347, 348, 387, 388). 

In North America, the use of lower cost, reverse ester thiotins is common for PVC-U applications covering pipe, profile and sidings, and foam. Rohm and Haas are one supplier. 

Liquid mixed metal heat stabilisers are a blend of the metal soaps or salts in combination with 

Barium cadmium based systems (may also include zinc) have been available for many years due to their cost effectiveness in combination with good initial colour and long-term stability. However, in the European area, then-use was voluntarily phased out by the PVC industry in 2001, due to severe restrictions for environmental and toxicity reasons concerning cadmium. 

Cadmium based stabilisers are still used in the USA and Asia Pacific areas, but are coming under increasing health and environmental scrutiny (291). 

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One issue with liquid stabilisers is the emission of volatile components (phenol from the organophosphite, solvent, etc.) during processing and from the end use application, e.g., floor and wall coverings. Analytical techniques are now available to detect volatile organic compounds (VOCs) (151) and so influence stabiliser development. New organophosphite-zinc technology has also been introduced to improve this characteristic (75). 

An overview is presented of the analytical methods employed to detect volatile organic compounds associated with solid and liquid stabilisers in PVC used in such applications as floor coverings and wall coverings and a description is given of the ways in which these methods are being utilised to improve stabiliser performance in flexible polyvinyl chloride. 

Concerns over worker safety, processing emissions and finished product acceptability continue to drive new product development in this area. Western Europe has led these initiatives however, there are now signs that the USA marketplace is changing in order to conform with these environmental trends. Technological aspects of the replacement of cadmium in liquid stabilisers and the reduction of volatile constituents and phenol in these materials is reviewed. 7 refs. 

Scheme 6.7 In situ formation of an ionic liquid stabilised palladium complex in an imidazole-imidazolium ionic liquid and its performance in the Heck coupling of...

Liquid stabilisers are more convenient to disperse in PVC formulations. They are usually either barium-zinc or calcium-zinc with a co-stabiliser, and are used in flexible PVC. They are usually less prone to plate-out than solid ones, and often give better clarity. Sohd grades can be dissolved conveniently in the liquid phosphite co-stabilisers that are often used in the same formulation. 

All the ingredients are added except for the filler, and the blender is allowed to operate until the temperature reaches about 80 C. It is stopped to add filler, and then put to work until the temperature of the blend reaches about 110-120 "C. It is then emptied and cooled. The addition of liquid stabilisers at a higher temperature may cause the stabilisers to vaporise due to the heat. Higher-output extrudates are obtained within a temperature range of 105-125 C. Much higher speeds cause slower rates of extrusion due to the greater compactness of the particles [9]. 

L.P.G. Abbreviation for Liquefied Petroleum Gas, (propane or butane). LSP. Liquid Stabilised Plasma torch for thermally sprayed coatings. 

Allied Chemical Publication. (1968) "Sulfan, liquid stabilised sulphur trioxide". 

Interestingly, first examples can also be found in the literature describing the immobilisation of an ionic liquid in which metal nanoparticles are immobilised on solid supports. This concept follows in close analogy the idea of SILP catalysis but applies ionic liquid-stabilised nanoparticles on a support instead of in an ionic catalyst solution [104]. 

Preparation concepts for ionic liquid stabilised metal nanopartides... 

In suspension processes the fate of the continuous liquid phase and the associated control of the stabilisation and destabilisation of the system are the most important considerations. Many polymers occur in latex form, i.e. as polymer particles of diameter of the order of 1 p.m suspended in a liquid, usually aqueous, medium. Such latices are widely used to produce latex foams, elastic thread, dipped latex rubber goods, emulsion paints and paper additives. In the manufacture and use of such products it is important that premature destabilisation of the latex does not occur but that such destabilisation occurs in a controlled and appropriate manner at the relevant stage in processing. Such control of stability is based on the general precepts of colloid science. As with products from solvent processes diffusion distances for the liquid phase must be kept short furthermore, care has to be taken that the drying rates are not such that a skin of very low permeability is formed whilst there remains undesirable liquid in the mass of the polymer. For most applications it is desirable that destabilisation leads to a coherent film (or spongy mass in the case of foams) of polymers. To achieve this the of the latex compound should not be above ambient temperature so that at such temperatures intermolecular diffusion of the polymer molecules can occur. 

Somewhat better results have been obtained with octoates and benzoates but these still lead to some plate-out. The use of liquid cadmium-barium phenates has today largely resolved the problem of plate-out whilst the addition of a trace of a zinc salt helps to improve the colour. Greater clarity may often be obtained by the addition of a trace of stearic acid or stearyl alcohol. Thus a modem so-called cadmium-barium stabilising system may contain a large number of components. A typical packaged stabiliser could have the following composition ... 

Formulations for one-shot polyether systems are similar to those used for flexible foams and contain polyether, isocyanate, catalyst, surfactant and water. Trichloroethyl phosphate is also often used as a flame retardant. As with polyesters, diphenylmethane di-isocyanate is usually preferred to TDI because of its lower volatility. Tertiary amines and organo-tin catalysts are used as with the flexible foams but not necessarily in combination. Silicone oil surfactants are again found to be good foam stabilisers. Volatile liquids such as trichlorofluoro-methane have been widely used as supplementary blowing agents and give products of low density and of very low thermal conductivity. 

Cihal, V., Explanation of Intercrystalline Corrosion of Welded, Stabilised Cr-Ni Stainless Steels , Bergakademie, 15, 23 (1963) C.A., 58, 13523d Fleitman, A. H., Romano, A. J. and Kiermut, C. J., Corrosion of Carbon Steel by High Temperature Liquid Mercury , J. Electrochem. Soc., 110, 964 (1963)... 

P.V.C. plastisols P.V.C. plastisols are liquids which contain little or no solvent/diluent. They consist of a blend of polyvinyl chloride (p.v.c.) resins, plasticisers, stabilisers, viscosity depressants, pigments and sometimes fillers. 

Borgstedt and Freeshave shown that for the corrosion of both stabilised and unstabilised austenitic stainless steels in flowing liquid sodium at 700°C there is an almost linear dependence of the corrosion constant, k, on the oxygen content of the sodium, as follows ... 

The effect of carbon on the corrosion of stainless steels in liquid sodium depends upon the test conditions and the composition of the steels . Stabilised stainless steels tend to pick up carbon from sodium, leading to a degree of carburisation which corresponds to the carbon activity in the liquid metal. Conversely, unstabilised stainless steels suffer slight decarburisation when exposed to very pure sodium. The decarburisation may promote corrosion in the surface region of the material and, under creep rupture conditions, can lead to cavity formation at the grain boundaries and decreased strength. 

In a reactor at low pressure (0.2-0.3 MPa) and moderate temperature (375 °C) the PVC is chemically and thermally degraded. A particular feature of the process is that the chlorine in the PVC reacts in part with the fillers in PVC and is neutralised with the formation of CaCl2. In similar vein, metal stabilisers in PVC are converted into the respective metal chlorides (lead, cadmium, zinc and/or barium). At current PVC waste compositions these chlorides consist of 60% lead which can be purified and re-used. The reaction in the end results in the following solid, liquid and gaseous products. 

When the same [NiI (NHC)2] complexes are employed as alkene dimerisation catalysts in ionic liquid (IL) solvent [l-butyl-3-methylimidazolium chloride, AICI3, A-methylpyrrole (0.45 0.55 0.1)] rather than toluene, the catalysts were found to be highly active, with no evidence of decomposition. Furthermore, product distributions for each of the catalyst systems studied was surprisingly similar, indicating a common active species may have been formed in each case. It was proposed that reductive elimination of the NHC-Ni did indeed occur, as outlined in Scheme 13.8, however, the IL solvent oxidatively adds to the Ni(0) thus formed to yield a new Ni-NHC complex, 15, stabilised by the IL solvent, and able to effectively catalyse the dimerisation process (Scheme 13.9) [25-27],... 

This is hardly stable and it was not until suitable conditions of dilution were found that it was possible to handle it in industry. Even at low temperatures it detonates easily, when it is in the solid or liquid state. Detonations occurred during attempts at liquefaction. Ite dilution in nitrogen at -181° stabilises it, but there was an accident under these conditions, which was due to the presence of carborundum that makes it sensitive to impact. In the gaseous state, it detonates at a pressure of 1.4 bar and above. It can only be kept under pressure when it is in a solution of acetone in which it is highly soluble. Alcohols to C4, ketones to C4, diols C3 and C4, and carboxylic acids to C4 all play the same stabilising role as acetone. 

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