Systems, stabilizer

Ciba Specialty Chemicals Light Stabilizer Systems  

TINUVIN 111 Tinuvin 123 S Tinuvin 492 Tinuvin 494 Tinuvin 783 Tinuvin 791 Tinuvin C 353 IRGASTAB FS 210 Irgastab FS 410 Irgastab FS 811 Irgastab FS 812 FIBERSTAB L 112 

Chimasorb 119 Tinuvin 622 Tinuvin 123 Polypropylene Chimassorb 119 Oxides Stearates Chimassorb 119 Oxides Stearates 

Chimassorb 944 Tinuvin 622 Chimassorb 944 Tinuvin 770 Chimassorb 119 Tinuvin 234 Irgastab FS 042 Chimassorb 119 Irgastab FS 042 Chimassorb 944 Irgastab FS 042 Tinuvin 791 Irgastab FS 042 Tinuvin 791 Tinuvin 328 HP-136 IRCAFOS 168 Tinuvin 622 

The unsaturated nature of an elastomer accounts for its unique viscoelastic properties. However, the presence of carbon-carbon double bonds renders elastomers susceptible to attack by oxygen, ozone, and thermal degradation. A comprehensive review of elastomer oxidation and the role of antioxidants and antiozonants is available (Hong, 2004). 

Oxidation of elastomers is accelerated by a number of factors including heat, heavy metal contamination, sulfur, light, moisture, swelling in oil and solvents, dynamic fatigue, oxygen, and ozone. Three variables in the compound 

Thermooxidative stability is primarily a function of the vulcanization system. Peroxide vulcanization or cure systems tend to perform best for reversion resistance as a result of the absence of sulfur and use of carbon-carbon crosslinks. Efficient vulcanization (EV) systems that feature a low sulfur level (0.0-0.3phr), a high acceleration level, and a sulfur donor similarly show good heat stability and oxidation resistance. Such systems do, however, have poor resistance to fatigue because of the presence of predominantly monosulfidic crosslinks. Conventional cure systems that feature a high sulfur level and low accelerator concentration show poor heat and oxidation resistance because the polysulfidic crosslinks are thermally unstable and readily oxidized. Such vulcanization systems do, however, have better fatigue resistance. Semi-EV cure systems, which are intermediate between EV and conventional systems, are a compromise between resistance to oxidation and required product fatigue performance. 

Crosslinking A predominantly di- or polysulfidic crosslink network breaks down into monosulfidic crosslinks. Compound hardness increases, fatigue resistance decreases, and the compound becomes much stiffer. SBR, EPDM, NBR, and polychloroprene tend to show 

Chain scission The polymer chain breaks, causing a softening of the compound and decreased abrasion resistance. Natural rubber tends to show such degradation. 

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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. 

Many stabilizer systems have been tailored to a particular industry need or for particular areas where dilution water quaUty is poor. These grades are heavily stabilized and may contain organic sequestering agents, ie, staimate, phosphates, and nitrate ions, so that the weak solutions produced by dilution from hard water retain acceptable stabihty. The nitrate is not a stabilizer, but it inhibits corrosion of aluminum storage tanks by chloride ion. 

Fig. 6. Effect of alloying elements on the phase diagram of titanium (a) a-stabilized system, (b) P-isomorphous system, and (c) P-eutectoid system.

Many different combinations of surfactant and protective coUoid are used in emulsion polymerizations of vinyl acetate as stabilizers. The properties of the emulsion and the polymeric film depend to a large extent on the identity and quantity of the stabilizers. The choice of stabilizer affects the mean and distribution of particle size which affects the rheology and film formation. The stabilizer system also impacts the stabiUty of the emulsion to mechanical shear, temperature change, and compounding. Characteristics of the coalesced resin affected by the stabilizer include tack, smoothness, opacity, water resistance, and film strength (41,42). 

Issues to be considered in selecting the best stabilizing system are polymeric chain branching which increases with high temperature and the presence of some stabilizers, polydispersity of the particles produced, and grafting copolymerization, which may occur because of the reaction of vinyl acetate with emulsifiers such as poly(vinyl alcohol) (43,44). 

A ship roll stabilization system is shown in Figure 5.21. The system parameters are Fin time constant Tf = 1.0 seconds Ship roll natural frequency LUa = 1.414rad/s... 

Fig. 5.22 Proportional control, ship roll stabilization system.

Figure 5.25 shows the step response for (a) the hull roll action without a stabilizer system, and (b) the hull roll action with a controller/compensator with a control law... 

Fig. 5.25 Ship hull step response with and without stabilizers system.

With the stabilizer system, the step response meets the performanee speeifieation. 

The ship roll stabilization system given in ease-study Example 5.11 has a forward-path transfer funetion... 

Case study Example 5.11 uses root locus to design a ship roll stabilization system. The script file exampSll.m considers a combined PD and PID (PIDD) controller of the form... 

Major categories of industrial waste solidiflcation/stabilization systems are cement-based processes, pozzolanic processes (not including cement), thermoplastic techniques, organic polymer techniques, surface encapsulation techniques, and self-cementing techniques (for high calcium sulfate sludges). Vitrification (discussed previously) can also be considered a solidification process. 

We only briefly mentioned alkaline stabilization, but in reality this is a variation of sludge pasteurization. The basic process uses elevated pH and temperature to produce a stabilized, disinfected product. The two alkaline stabilization systems most common in the U.S. are a lime pasteurization system and a cement kiln dust pasteurization system. The lime pasteurization product has a wet-cake consistency, while the kiln dust pasteurization has a moist solid like consistency. Both products can be transported to agricultural areas for ultimate use. Literature studies show that the kiln dust product can capture a marketable value of 6.60/Mg ( 6.00/ton) to offset hauling costs, while the lime product does not appear to be able to capture financial credits for product revenues at this point in time. The reasons for this are not entirely clear. 

From a hydrate melting standpoint it is possible in the winter time to have too cold a liquid temperature and thus plug the liquid outlet of the low temperature separator. It is easier for field personnel to understand and operate a line heater for hydrate control and a multistage flash or condensate stabilizer system to maximize liquids recovery. 

Figure 6-3 shows a condensate stabilizer system. The well stream flows to a high pressure, three-phase separator. Liquids containing a high fraction of light ends are cooled and enter the stabilizer tower at approxi-... 

Figure 6-4. CokJ-feed dish llation tower of condensate stabilization system.

In the stabilization of PVC, the principal mode of action of the various stabilizer systems has been explained in terms of the Frye and Horst mechanism, i.e., substitution of labile chlorines by more stable groups. Evidence for other actions, such as HCl neutralization, addition to polyene sequences, and bimetallic complex formation have also been given. Despite the wide acceptance of the Frye and Horst mechanism, researchers have frequently contended that this could not be the dominant mechanism in the stabilization of PVC. 

Kuhn s carbanion, the all-hydrocarbon anion tris(7//-dibenzo[c,g]-fluorenylidenemethyl)methanide ion [2 ] (Kuhn and Rewicki, 1967a,b), is a stabilized system with tt electrons widely spread over the sp hybridized carbon framework, and was isolated as the potassium salt. It also appears in DMSO solution by dissolving the parent hydrocarbon, resulting in a deep green colour. The pKg value of the precursor hydrocarbon [2]-H is 5.9 in aqueous HCl-DMSO (Kuhn and Rewicki, 1967a,b), and its enormous stability, as compared with cyclopentadiene [9]-H, pKa 18 in DMSO... 

In the past five years, the use of nanoparticles in this active research area has received increased attention since some homogeneous catalysts have been shown to be nanoheterogeneous [24-26]. Today, soluble noble metal nanoparticles are considered as reference in monocyclic arene catalytic hydrogenation under mild conditions and several stabilized systems have been reported [27,28]. 

The selectivity in the hydrogenation of di-substituted benzenes such as xylene, methylanisole, cresol was also reported. In all cases, the czs-compound is largely the major compound > 80%. The ratio cis/trans decreases with the position of the substituents o > m>p but the identity of the metal does not seem important with this surfactant-stabilized system [45,47]. 

Carboxypolymethylene also exerts a stabilizing effect on a cetyl alcohol-sodium lauryl sulfate emulsion containing 15% of talc. The differential in the distribution of particles at all levels of those stabilized systems discussed above can be considered negligible for all practical purposes. 

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