Composite heat stabilizers

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. 

Composite heat stabilizers are liquid or solid compounds based on salts or metal soaps and compounds based on organic tin. Metal salts include Ca-Mg-Zn, Ba-Ca-Zn, Ba-Zn, and Ba-Cd common organic acids include organic fatty acids, naphthenic acid, oleic acid, benzoic acid, and salicylic acid. 

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. 

Polymers. In combination with various metal salts, sorbitol is used as a stabilizer against heat and light in poly(vinyl chloride) (qv) resins and, with a phenohc antioxidant, as a stabilizer in uncured styrene—butadiene mbber (qv) compositions and in polyolefins (see Heat stabilizers Olefin POLYMERS Rubbercompounding). Heat-sealable films are prepared from a dispersion of sorbitol and starch in water (255). Incorporation of sorbitol in coUagen films gready restricts their permeabiUty to carbon dioxide (256). 

The most commonly used stabilizers are barium, cadmium, zinc, calcium and cobalt salts of stearic acid phosphorous acid esters epoxy compounds and phenol derivatives. Using stabilizers can improve the heat and UV light resistance of the polymer blends, but these are only two aspects. The processing temperature, time, and the blending equipment also have effects on the stability of the products. The same raw materials and compositions with different blending methods resulted in products with different heat stabilities. Therefore, a thorough search for the optimal processing conditions must be done in conjunction with a search for the best composition to get the best results. 

Composites are also used extensively where light but very strong materials are needed such as in the construction of the new Boeing 767 where composites play a critical role in the construction of the exterior. They are also used where excessive high heat stability is needed such as in the reusable space vehicle (Figure 18.7). 

Rose, D. and Tessier, H. (1959) Composition of ultrafiltrates from milk heated at 80 to 230°F in relation to heat stability. J. Dairy Sci., 42, 969-80. 

Rose, D. 1961A. Variations in the heat stability and composition of milk from individual cows during lactation. J. Dairy Sci. 44, 430-441. 

The stabilizers chosen for evaluation include different types of heat and light stabilizers selected to represent different mechanisms of action as well as chemical compositions (ArJi). Types of stabilizers evaluated include benzotriazole and benzophenone light stabilizers [ultraviolet (UV) light absorbers], hindered amine light stabilizers (HALS, catalytic radical scavengers), hindered phenol heat stabilizers (antioxidant radical scavengers), and thioester heat stabilizers (antioxidant hydroperoxide decomposers). 

Thermal degradation of foams is not different from that of the solid polymer, except in that the foam structure imparts superior thermal insulation properties, so that the decomposition of the foam will be slower than that of the solid polymer. Almost every plastic can be produced with a foam structure, but only a few are commercially significant. Of these flexible and rigid polyurethane (PU) foams, those which have urethane links in the polymer chain are the most important. The thermal decomposition products of PU will depend on its composition that can be chemically complex due to the wide range of starting materials and combinations, which can be used to produce them and their required properties. Basically, these involve the reaction between isocyanates, such as toluene 2,4- and 2,6-diisocyanate (TDI) or diphenylmethane 4,3-diisocyanate (MDI), and polyols. If the requirement is for greater heat stability and reduced brittleness, then MDI is favored over TDI. 

Untransformed 8-10S receptors are stabilized in vitro by sodium molybdate. Several laboratories have purified native PR in both transformed and untransformed states and have examined their protein composition. Molybdate-stabilized PR contain, in addition to A- or B-proteins, a non-steroid binding of 90 kDa, which is a heat-shock protein (hsp). This has been observed for PR of different target tissues and species [55-58] and also for molybdate stabilized glucocorticoid receptors [59,60]. Since the 90 kDa hsp associates only with molybdate-stabilized receptors it has been suggested that transformation and receptor conversion from 8-10S to 4S is due to 90 kDa dissociation and unmasking of receptor DNA binding sites. If so, the 90 kDa component of 8S receptors would function to maintain receptors in an inactive state in the absence of hormone. As with other hsps, 90 kDa is a ubiquitous and abundant protein and only a small fraction is found associated with 8-10S receptors. Because of this there is concern that 90 kDa-receptor associations may be in vitro artifacts it is not known whether these associations occur in vivo and whether these interactions are of physiological relevance to receptor function. 

Sharma, R., Singh, H. 1999. Heat stability of recombined milk systems as influenced by the composition of fat globule surface layers. Milchwissenschaft. 54, 193-196. 

C. Su, Fatty Acid Composition of Oils, Their Oxidative, Flavor, and Heat Stabilities and the Resultant Quality in Foods, Ph. D. Dissertation, Parks Library, Iowa State University, Ames, Iowa, (2003). 

In 1940, Houdry Process Corporation initiated commercial manufacture of a synthetic silica-alumina catalyst at Paulsboro, New Jersey (133). The synthetic catalyst is produced in pellet form (51,265) and contains 12 to 13% alumina (221,276). It has the advantages of controlled chemical composition, higher purity, and greater heat stability, but is more expensive than the activated-clay catalyst. 

Treatment of solid wood over the years for increased utility included many chemical systems that affected the cell wall and filled the void spaces in the wood. Some of these treatments found commercial applications, while some remain laboratory curiosities. A brief description of the earlier treatments is given for heat-stabilized wood, phenol-formaldehyde-treated veneers, bulking of the cell wall with polyethylene glycol, ozone gas-phase treatment, ammonia liquid- and gas-phase treatment, and p- and y-radiation. Many of these treatments led to commercial products, such as Staybwood, Staypak, Im-preg, and Compreg. This chapter is concerned primarily with wood-polymer composites using vinyl monomers. Generally, wood-polymers imply bulk polymerization of a vinyl-type monomer in the void spaces of solid wood. 

---