Aging

Name:
Aging
Detailed information:
(1) Deleterious: gradual deterioration of a material due to long exposure to the environment. Aging characteristics of various materials:(a) Vulcanized rubber and thermoplastic polymers lose strength and crack due to oxidation, sunlight, heat; this is retarded by antioxidants, e.g., phenyl-β-naphthylamine. For accelerated aging tests see Bomb.(b) Foods: spoilage and rancidity due to bacterial contamination, retarded by butylated hydroxyanisole and various propionates.(c) Paints: cracking, fading, chalking due to exposure to weather and photochemical degradation. Retarded by proper selection of vehicles and pigments. Accelerated weathering tests are used.(d) Metals: rusting, pitting, and scaling due to corrosion, especially in moist acid and alkaline environments. Avoided by use of alloys in which noncorrosive metals are incorporated (stainless steel) or by plating or cladding the base metal with chromium or nickel. See Corrosion; Exposure Testing. (2) Beneficial: improvement of flavor by long storage. Cheeses develop a “sharp” flavor on ripening for 9–12 months, wines develop a “bouquet” after two or more years of storage. Whiskeys stored in oaken casks for several years modify their flavor by extracting components of the wood. Tobacco is aged from 3 to 5 years after curing to remove unpleasant odors and improve smoking qualities.