Heat-reactivation temperature

Hot melt pressure sensitive adhesive compositions have been described, based on lactic acid polymers (37-39). However, such compositions have been claimed to be not suitable for the fields of food packaging as they have the drawbacks of being rather stiff and having a heat-reactivation temperature that is too high for food packaging applications (35). Hot melt compositions are shown in Table 7.8. 

High Temperature Carbonization. When heated at temperatures in excess of 700°C (1290°F), low temperature chars lose their reactivity through devolatilization and also suffer a decrease in porosity. High temperature carbonization, at temperatures >900° C, is, therefore, employed for the production of coke (27). As for the low temperature processes, the tars produced in high temperature ovens are also sources of chemicals and chemical intemiediates (32). 

Heat-reactive resins are more compatible than oil-soluble resins with other polar-coating resins, such as amino, epoxy, and poly(vinyl butyral). They are used in interior-can and dmm linings, metal primers, and pipe coatings. The coatings have excellent resistance to solvents, acids, and salts. They can be used over a wide range of temperatures, up to 370°C for short periods of dry heat, and continuously at 150°C. Strong alkaUes should be avoided. 

Waterborne contact adhesives contain an elastomer in latex form, usually an acryflc or neoprene-based latex, and a heat-reactive, cross-linkable phenohc resin in the form of an aqueous dispersion. The phenoHc resin improves metal adhesion, green strength, and peel strength at elevated temperature. A typical formulation contains three parts latex and one part phenohc dispersion (dry weight bases). Although metal oxides may be added, reaction of the oxide with the phenohc resin does not occur readily. 

For all three diallyl phthalate isomers, gelation occurs at nearly the same conversion DAP prepolymer contains fewer reactive allyl groups than the other isomeric prepolymers (36). More double bonds are lost by cyclisation in DAP polymerisation, but this does not affect gelation. The heat-distortion temperature of cross-linked DAP polymer is influenced by the initiator chosen and its concentration (37). Heat resistance is increased by electron beam irradiation. 

Reactivity. Bromine is nonflammable but may ignite combustibles, such as dry grass, on contact. Handling bromine in a wet atmosphere, extreme heat, and temperatures low enough to cause bromine to soHdify (—6° C) should be avoided. Bromine should be stored in a cool, dry area away from heat. Materials that should not be permitted to contact bromine include combustibles, Hquid ammonia, aluminum, titanium, mercury, sodium, potassium, and magnesium. Bromine attacks some forms of plastics, mbber, and coatings (62). 

The epoxidised polybutadiene resins available to date are more viscous than the diglycidyl ethers except where volatile diluents are employed. They are less reactive with amines but have a similar reactivity with acid anhydride hardeners. Cured resins have heat distortion temperatures substantially higher than the conventional amine-cured diglycidyl ether resins. A casting made from an epoxidised polybutadiene hardened with maleic anhydride and cured for two hours at 50°C plus three hours at 155°C plus 24 hours at 200°C gave a heat... 

Since the adsorbent bed must be heated in a relatively short time to reactivation temperature, it is necessary that the reactivation steam rate calculation is increased by some factor that will correct for the nonsteady-state heat transfer. During the steaming period, condensation and adsorption will take place in the adsorbent bed, increasing the moisture content of the adsorbent. A certain portion of the adsorbate... 

The first literature report of a reaction of an isocyanate with wood is that due to Clermont and Bender (1957). In this study, DMF impregnated wood samples 1/8 in thick were suspended above phenylisocyanate liquid in a vessel heated at temperatures from 100 °C to 125 °C for various time intervals. Treated samples were washed with DMF, then water, then acetone, and dried in an oven at 105 °C. ASEs in the range of 60-80 % were reported for these samples. In view of the reactivity of DMF with isocyanates, the lack of an efficient clean-up procedure and the fact that ASE values were calculated from the first water-soak cycle only, this study is of limited value. 

It is suggested that a detailed examination of the effect of heat-treatment temperature on the gas reactivity of the carbons studied by Walker and Baumbach 143) might show a series of reactivity maxima which correspond to temperatures at which different catalytic impurities first begin to show significant solid state diffusion and reaction with the carbon matrix followed at higher temperatures by their complete volatilization from the sample. The advent of significant diffusion and reaction of the impurity with the carbon could result in a subseiiuent increase in gas reactivity. Complete volatilization of the impurity from the sample could result in a subsequent decrease in gas reactivity. 

The use of benzocyclobutene as the source of the diene in a Diels-Alder polymerization offers a unique solution to the problems described above. Benzocyclobutene containing monomers can be stored indefinitely at room temperature without concern for further advancement of the molecular weight. It is only when benzocyclobutene is heated to temperatures of approximately 200 °C that the reactive diene, o-quinodimethane, is formed at a significant rate and enters into reaction with the dienophile. The only requirement of the dienophile is that it must be stable at these temperatures and not undergo reaction with itself. The most common dienophiles that have been successfully used in the formation of polymers from AB type benzocyclobutene monomers have been acetylenes, olefins and maleimides. 

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