Stability colourants

Ice-cream is a product which has been developed since mechanical refrigeration became available. Ice-cream mixes comprise fats (not always dairy), milk protein, sugar and additives such as emulsifiers, stabilizers, colourings, together with extra items such as fruit, nuts, pieces of chocolate, etc., according to the particular type and flavour. The presence of this mixture of constituents means that the freezing... 

Polyvinyl chloride window profile formulations containing organic-based and calcium-zinc stabilisers were produced and the performance of the stabilised PVC compounds compared. Properties evaluated included rheological properties, heat stability, colour, gloss,... 

Minor ingredients, present in small quantities (less than about 1% by weight), such as emulsifiers, stabilizers, colours and flavours. 

The melting point needs to be above service temperatures (NB medical textiles are often steam-sterilizable at 130 °C for several minutes), but too high a melting point may adversely affect the dimensional stability, colour and handle of the fabric. 

Choosing an appropriate FR, whether brominated or not, can still be difficult because even if the necessary specifications are achieved, many have unwanted side efifects. Brominated PC often shows poor flow properties and low impact strength, and the FRs currently available for polyamides and polyesters suffer from poor compatibility, poor thermal stability, colour limitations, inadequate UV resistance, processing problems or, in one or two cases, unacceptably high cost. (Sometimes the product has to be transparent as well.) Consequently new FRs are being designed not just for better flame retardancy, but to overcome as many as possible of a whole range of problems. 

Rubbers are generated by vulcanisation (crosslinking) of elastomers. Elastomers are macromolecular organic compounds that are formed from natural or synthetic substances. In the production process additives are being used as vulcanisers, catalysts, stabilizers, colourings, fillers and lubricants, see Table 24.4. 

The properties of PC s can be adjusted to the requirements of customers by copolymerization with other polymers and/or addition of additives, e.g. mould-release agents, flame retardants, light stabilizers, reinforcements, heat stabilizers, colours. 

PBT is applied in a wide range of products in the lighting industry. Well known is the lamp base of the energy saving lamp, where PBT is selected for a combination of properties heat resistance, dimensional stability, colour stability and laser markability. 

Aminoazobenzene is a member of the large class of azo-compounds, all of which contain the characteristic grouping, C-N N-C. Azo-compounds are of considerable technical importance, as they are all coloured, and the majority possess considerable stability. They may be prepared by the following methods ... 

By using an aromatic aldehyde carrying an electron-releasing group the intermediate cation can be stabilized. This is the basis of the widely-used Ehrlich colour reaction for pyrroles, indoles and furans which have a free reactive nuclear position (Scheme 21). 

MO calculations, 7, 364 Oxetene, 2-isopropylidene-polysubstituted rearrangement, 7, 377 Oxetene, tetramethyl-structure, 7, 366 Oxetenes, 7, 363-402 decomposition, 7, 375 metabolism, 1, 243 molecular dimensions, 7, 366 thermal stability, 7, 370 Oxetenyl anions aromaticity, 7, 371 Oxetenyl cations aromaticity, 7, 371 Oxichlororaphine occurrence, 3, 196 Oxichromic developers in colour photography, 1, 378-379 Oxidation... 

In accordance with these data, ionic associates (lA) can be precipitated at phosphate concentrations more than 10 M. Below this concentration stabile supersaturated solutions of lA are formed. Colour of lA appeal s immediately after mixing of the solutions and remains constant during several hours. There is a new band in spectmm at 570-590 nm. Appearance of color is caused by formation of stable solid phase in the solution. 

New stationary phases for specific purposes in chromatographic separation are being continually proposed. Charge transfer adsorption chromatography makes use of a stationary phase which contains immobilised aromatic compounds and permits the separation of aromatic compounds by virtue of the ability to form charge transfer complexes (sometimes coloured) with the stationary phase. The separation is caused by the differences in stability of these complexes (Porath and Dahlgren-Caldwell J Chromatogr 133 180 1977). 

Such a value for relative temperature index will be specific to a particular grade of a polymer, sometimes even to a specific colour. The difference between grades of a particular species of polymer can be substantial, depending both on the variation in the inherent stability of a material between differing manufacturing methods and also on the type and amount of additives used. It is possible to obtain from the Laboratories a Generic Temperature Index to cover a species of material but this will usually be considerably lower than for many of the individual grades within that species. 

The process of post-chlorinating PVC was carried out during World War II in order to obtain polymers soluble in low-cost solvents and which could therefore be used for fibres and lacquers. The derivate was generally prepared by passing chlorine through a solution of PVC in tetrachloroethane at between 50°C and 100°C. Solvents for the product included methylene dichloride, butyl acetate and acetone. These materials were of limited value because of their poor colour, poor light stability, shock brittleness and comparatively low softening point. 

Since acetal resins are degraded by ultra violet light, additives may be included to improve the resistance of the polymer. Carbon black is effective but as in the case of polyethylene it must be well dispersed in the polymer. The finer the particle size the better the ultra violet stability of the polymer but the poorer the heat stability. About 1.5% is generally recommended. For white compounds and those with pastel colours titanium dioxide is as good in polyacetals as most transparent ultraviolet absorbers, such as the benzophenone derivatives and other materials discussed in Chapter 7. Such ultraviolet absorbers may be used for compounds that are neither black, white nor pastel shade in colour. 

The stabilised nitrate may then be bleached with sodium hypochlorite, centrifuged to remove much of the water in which the polymer has been slurried and dehydrated by displacement with alcohol while under pressure in a press. It is interesting to note that in these processes approximately 35 000 gallons (160000 litres) of water are used for every ton of cellulose nitrate produced. Control of purity of the water is important in particular the iron content should be as low as 0.03 parts per million since iron can adversely affect both the colour and heat stability of the polymer. 

As already indicated, cellulose acetate is used because of its reasonable toughness, transparency and wide colour range. It is not suitable when good electrical insulation properties, heat resistance, weathering resistance, chemical resistance and dimensional stability are important. 

Compared with the phenolic resins they have a better colour range, track resistance and scratch resistance. They have a similar order of heat resistance, although their dimensional stability when exposed to hot dry conditions is not so... 

When the resin temperature drops below the boiling point of the reactive diluent (usually styrene) the resin is pumped into a blending tank containing suitability inhibited diluent. It is common practice to employ a mixture of inhibitors in order to obtain a balance of properties in respect of colour, storage stability and gelation rate of catalysed resin. A typical system based on the above polyester fomulation would be ... 

Mercaptan-inodified polychloroprenes provide lighter colour to solutions and are more resistant to discolouration than sulphur-modified polychloroprenes. Also mercaptan-modified polychloroprenes exhibit better ageing, and improved thermal and solution stability. 

On the other hand, not only initial colour but colour change (discolouration) of the resin under UV light and heat is important. Colour retention of a resin is related to the chemical stability and increases as the degree of non-aromatic conjugated unsaturation of the resin molecule decreases. Thus, for rosins a high level of abietic-type resin acids lead to relatively unstable resins. Hydrogenation and disproportionation as well as esterification provide improved stability and colour retention to rosins. 

For rosins and rosin esters, the produets having high aeid numbers are the most susceptible to oxidation and have inferior viscosity stability and colour stability in adhesive formulations. Thus, when stability properties are essential in adhesives, rosin esters rather than high aeid number rosins are used. However, the high acid number resins are polar and display better adhesion to polar elastomers and polymeric surfaces. 

Weathering. This generally occurs as a result of the combined effect of water absorption and exposure to ultra-violet radiation (u-v). Absorption of water can have a plasticizing action on plastics which increases flexibility but ultimately (on elimination of the water) results in embrittlement, while u-v causes breakdown of the bonds in the polymer chain. The result is general deterioration of physical properties. A loss of colour or clarity (or both) may also occur. Absorption of water reduces dimensional stability of moulded articles. Most thermoplastics, in particular cellulose derivatives, are affected, and also polyethylene, PVC, and nylons. 

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