Resins, properties degradation

The resin must be of highest purity for optimum processing characteristics and properties. Degradation results in discoloration, bubbling, and change in melt flow rate. 

PBO polymers, 13 377. See also Poly(p-phenylene benzobisoxazole) (PBO) applications of, 13 379 degradation of, 13 379 early syntheses of, 13 378 PB resin, properties of, 20 419t PbSe photoconductors, 19 157 PbS photoconductors, 19 157 PBT molding resins, 20 62-64. See also Poly(butyleneterephthalate) (PBT) PBT polymer... 

PPS fiber has excellent chemical resistance. Only strong oxidizing agents cause degradation. As expected from inherent resin properties, PPS fiber is flame-resistant and has an autoignition temperature of 590°C as determined in tests at the Textile Research Institute. PPS fiber is an excellent electrical insulator it finds application in hostile environments such as filter bags for filtration of flue gas from coal-fired furnaces, filter media for gas and liquid filtration, electrolysis membranes, protective clothing, and composites. 

For high temperature and rubber-modified epoxy resins, thermal degradation events and the cloud point curve are included on the diagrams, respectively. Two degradation events have been assigned devitrification, or a glass-to-rubber event and revitrification, which is associated with char formation. The cloud points and depressions of Tg for different rubber-modified epoxies can be compared and related to volume fractions of the second phase and to the mechanical properties of the cured materials. 

Since these composites combine non-degradable resins with plant-based degradable fibers they can neither return to an industrial metabolism nor to a natural metabolism. Unfortunately, they cannot be food stock for either system. They can only be downcycled because of their property degradation during reprocessing or incinerated to recover the energy value. 

Keywords Epoxy resins, synthesis, degradation mechanism, structure-property, electronic packaging... 

In the area of moleculady designed hot-melt adhesives, the most widely used resins are the polyamides (qv), formed upon reaction of a diamine and a dimer acid. Dimer acids (qv) are obtained from the Diels-Alder reaction of unsaturated fatty acids. Linoleic acid is an example. Judicious selection of diamine and diacid leads to a wide range of adhesive properties. Typical shear characteristics are in the range of thousands of kilopascals and are dependent upon temperature. Although hot-melt adhesives normally become quite brittle below the glass-transition temperature, these materials can often attain physical properties that approach those of a stmctural adhesive. These properties severely degrade as the material becomes Hquid above the melt temperature. 

The packaging (qv) requirements for shipping and storage of thermoplastic resins depend on the moisture that can be absorbed by the resin and its effect when the material is heated to processing temperatures. Excess moisture may result in undesirable degradation during melt processing and inferior properties. Condensation polymers such as nylons and polyesters need to be specially predried to very low moisture levels (3,4), ie, less than 0.2% for nylon-6,6 and as low as 0.005% for poly(ethylene terephthalate) which hydrolyzes faster. 

Mechanical and Chemical Properties. Colorants, especially pigments, can affect the tensile, compressive, elongation, stress, and impact properties of a polymer (5). The colorants can act as an interstitial medium and cause microcracks to form in the polymer colorant matrix. This then leads to degradation of the physical properties of the system. Certain chemicals can attack colorants and there can be a loss of physical properties as well as a loss of the chromatic attributes of the colorant. Colorants should always be evaluated in the resin in which they will be used to check for loss of properties that ate needed for the particular appHcations. 

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