Polymers, burning stabilization

Maxwell et al. 177, 178) studied the deactivation of reduced Cu2+Y catalysts for butadiene cyclodimerization in some detail. This work showed that the catalyst stability could be markedly improved by using NH3 as a reducing agent and choosing the activation conditions such that excess NH3 remains selectively chemisorbed on the zeolite acidic sites. Further, the Cu2+Y-derived catalyst was thermally stable to 850°C and was therefore able to withstand a regeneration procedure which involved a polymer burn-off at 550°C. By contrast, the catalysts prepared by direct exchange with monovalent copper, i.e., Cu+Y, formed CuO irreversibly when heated above 330°C. 

The previous conflicting investigations may now be rationalized. Red phosphorus is known to thermally convert to white phosphorus, which will burn in air. If white phosphorus is formed, a fire is expected and no flame retardant activity will be observed. On the other hand, if the phosphorus reacts with the polymer as in Scheme 1, then thermal stabilization is expected. The efficacy of red phosphorus seems to be closely related to the efficiency of mixing of the additive and the polymer, when they are well-mixed the phosphorus will react with the polymer and lead to flame retardant activity, if the mixing is poor then the phosphorus will be converted to the white allotrope and burning will result. Since all of the work reported herein was carried out in sealed tubes under vacuum, the phosphorus must react and lead to stabilization of the polymer against molecular weight loss and fuel production, i.e. thermal stabilization. 

Uses. In ultraviolet stabilizers and smoke depressants for polymers to increase the burn rate of rocket propellants to prevent erosion of space capsule shields to improve the viscosity of lubricants to catalyze polymerization reactions to catalyze combustion some derivatives used as hematinic agents... 

Several of the urethane polymers are known for their thermal stability. Probably related to the thermal stability are the slow burning rates that have been obtained with some of the propellant formulations based on polyurethanes. 

At elevated temperatures will decompose to carbon tetrachloride, sulfur chloride, and heavy oily polymers Ignition Temperature (deg. F) Not pertinent Electrical Hazard Not pertinent Burning Rale Not pertinent. Chemical Reactivity Reactivity with Water Reacts only when hot to give carbon dioxide, hydrochloric acid, and sulfur Reactivity with Common Materials Reacts with iron or steel, evolving carbon tetrachloride. Corrosive to most metals Stability During Transport Stable Neutralizing Agents for Acids and Caustics Flush with water, rinse with dilute sodium bicarbonate or lime solution Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

The purpose of fire-retardant systems is to reduce the heat supplied to the polymer below the critical level for flame stability. This can be achieved by modifying (generally decreasing) the rate of chemical or physical processes taking place in one or more of the steps of the burning process. 

Kandola, B. K., Smart, G., Horrocks, A. R., Joseph, P., Zhang, S., Hull, T. R., Ebdon, J., Hunt, B., and Cook, A., Effect of different compatibilisers on nanoclay dispersion, thermal stability, and burning behavior of polypropylene-nanoclay blends, J. Appl. Polym. Sci., 2008, 108, 816-824. 

To prevent degradation and burning, small quantities of chemicals are added to the polymers. Although the ratio of these chemicals to polymers is small, their effect is decisive for the endurance and life of the polymers. 1968 s consumption of stabilizers and fire retardants is expected to pass the 350-million pounds mark for plastics and rubbers, as 1967 figures indicate (see Table I). 

Cellulose is a polymer that meets these requirements as an adhesive. However, due to its semicrystalline structure, highly hydrogen-bonded cellulose cannot be dissolved easily in conventional solvents, and it cannot be melted before it burns. This is because the attractive forces and stability of crystal structures are greater than those that result from interaction between polymer and solvent. Hence, cellulose itself is not suitable for use as an adhesive. The same can be said of regenerated cellulose. In order to make cellulose soluble or meltable, the hydrogen bonds must be broken (i.e., cellulose molecules must be more flexible and possess high entropy, so that they can be separated easily). 

Burns and co-workers (i 7) prepared a series of alkyl-, aryl-, and arylalkyl-substituted polysilazane polymers (equation 12), and a mechanistic study of pyrolysis was carried out to determine the effect of substituents on char yield, char composition, and stability of the resulting ceramic powders. 

The gas composition of smoke depends on the chemical composition, the molecular structure and polymer formulation of the burning material, which may include a variety of additives, plasticizers, stabilizers, flame retardants, cross-linking agents, fillers, and blowing agents. In addition, the conditions of... 

---