General properties ageing

Some very important features of thermal aging cannot be easily understood without a kinetic reasoning. In the following section, a simple kinetic model is postulated, which, in spite of its oversimplification, allows us to understand most of the general properties of thermal aging. The structure-thermal stability relationships are briefly examined and then some practical aspects are presented. 

Numerous articles of a general interest have appeared on photocatalytic chemistry. These include nanoparticles, protection of buildings, antibacterial properties, ageing of pigment blends, modified titanium dioxides, photocatalytic paints, stabilization of pigmented systems, sensitization of acid dyes " and clay masterbatches. Anatase has been found to have a detri-... 

Generally speaking, aging processes change the properties and the appearance of polymers over a certain period of time, in most cases leading to a degradation of the material parameters. 

Though, most of the discussion is limited to notched izod property and its retention upon aging, several general properties might also be of interest to the reader. A few representative properties have been presented in Table 3. Clearly, the transparent copolymer material has excellent optical properties, impact retention of up to temperatures as low as -50°C. Because of the transparent nature of the starting material, this can be colored, just like polycarbonate to create numerous custom colors. Both new copolymer materials deliver an improvement on heat and hydrolytic aging resistance while retaining most of the... 

Mechanical properties of plastics can be determined by short, single-point quaUty control tests and longer, generally multipoint or multiple condition procedures that relate to fundamental polymer properties. Single-point tests iaclude tensile, compressive, flexural, shear, and impact properties of plastics creep, heat aging, creep mpture, and environmental stress-crackiag tests usually result ia multipoint curves or tables for comparison of the original response to post-exposure response. 

Physical and chemical properties of the numerous PAG products can vary considerably. PAG products are usually aqueous solutions, although soHd products are also sold. Solutions range from colodess to amber and from clear to hazy in appearance specific gravities at 25 °G vary from about 1.2 to 1.35. Product viscosities, as measured by a Brookfield viscometer at 25 °G, are generally about 10 50 mPa-s(=cP), but can be much greater than 10, 000 mPa-s(=cP) for certain aged compositions. 

Aging Properties. The main features of ethylene—acryhc elastomers are heat (177°C) and oil resistance. At elevated temperatures, ethylene—acryhc elastomers age by an oxidative cross-linking mechanism, resulting in eventual embrittlement, rather than reversion. A general heat... 

---