Degradation properties, degradable

A study of structural units, where a monomer is examined by physicochemical methods to determine its thermostability, its chemical and physical properties, and its sites of degradation. 

Various monomers have been studied for their physicochemical properties and electronic structures (320, 321). For example, a series of monomers can be synthesized following Mulvaney et al. (310) and then theoretical diagrams and degradation sites are studied (Table 111-61) (134). 

The recycling of engineering thermoplastics such as polyamides, ABS, and PTEE have been discussed (50). Property degradation as a result of use, recovery, and recycling is a concern. 

Acryhc polymers are fairly iasensitive to normal uv degradation siace the primary uv absorption of acryhcs occurs below the solar spectmm (59). The iacorporation of absorbers, such as i9-hydroxyben2ophenone [117-99-7] further improves the uv stabihty (59). Under normal use conditions acryhc polymers have superior resistance to degradation and show remarkable retention of their original properties. 

The properties of SAN are significantly altered by water absorption (16). The equiUbrium water content increases with temperature while the time requited decreases. A large decrease in T can result. Strong aqueous bases can degrade SAN by hydrolysis of the nittile groups (17). 

Examination of oven-aged samples has demonstrated that substantial degradation is limited to the outer surface (34), ie, the oxidation process is diffusion limited. Consistent with this conclusion is the observation that oxidation rates are dependent on sample thickness (32). Impact property measurements by high speed puncture tests have shown that the critical thickness of the degraded layer at which surface fracture changes from ductile to brittle is about 0.2 mm. Removal of the degraded layer restores ductiHty (34). Effects of embrittled surface thickness on impact have been studied using ABS coated with styrene—acrylonitrile copolymer (35). 

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 identity of the moiety (other than glycerol) esterified to the phosphoric group determines the specific phosphoHpid compound. The three most common phosphoHpids in commercial oils are phosphatidylcholine or lecithin [8002-45-5] (3a), phosphatidylethanolamine or cephalin [4537-76-2] (3b), and phosphatidjlinositol [28154-49-7] (3c). These materials are important constituents of plant and animal membranes. The phosphoHpid content of oils varies widely. Laurie oils, such as coconut and palm kernel, contain a few hundredths of a percent. Most oils contain 0.1 to 0.5%. Com and cottonseed oils contain almost 1% whereas soybean oil can vary from 1 to 3% phosphoHpid. Some phosphoHpids, such as dipaLmitoylphosphatidylcholine (R = R = palmitic R" = choline), form bilayer stmetures known as vesicles or Hposomes. The bdayer stmeture can microencapsulate solutes and transport them through systems where they would normally be degraded. This property allows their use in dmg deHvery systems (qv) (8). 

Physical Properties. Relationships between fiber properties and their textile usefulness are in many cases quite obvious. Since fibers are frequently subjected to elevated temperatures, it is necessary that they have high melting or degradation points. It is also necessary that other fiber properties be relatively constant as a function of temperature over a useful temperature range. 

These codeposits add flame- and glow-resistance properties to textile fabrics. However, some insoluble deposits may also degrade the fabrics. Codeposits frequendy improve glow resistance, but are usuaUy more soluble than the deposit responsible for dame resistance and more easily removed during the launderiag process. 

Chemical Properties. Vacuum thermal degradation of PTFE results in monomer formation. The degradation is a first-order reaction (82). Mass spectroscopic analysis shows that degradation begins at ca 440°C, peaks at 540°C, and continues until 590°C (83). 

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

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