China 
Africa 
Explore chapters and articles related to this topic
Bleaching of Cellulosic and Synthetic Fabrics
Published in Menachem Lewin, Stephen B. Sello, Handbook of Fiber Science and Technology: Volume I Chemical Processing of Fibers and Fabrics, 2018
The color in organic substances and also in unbleached fabrics is due to mobile electrons, usually in systems of conjugated double bonds, and decolorization requires the demobilization of such electrons [48]. The chemical structure of the faint, creamy-colored matter in the unbleached cotton is not exactly known, although some workers believed it to be associated with proteins containing aromatic groups in very small amounts [238–240]. It is probable that the structure of the chromophore involved consists of conjugated double bonds which can be attacked by free radicals. According to Cates [209, 210], the free radicals will be added to a double bond in the same manner as in free-radical addition polymerization of unsaturated monomers. For example a quinoid structure,
Medical textiles
Published in Textile Progress, 2020
Polyethylene is produced by free-radical addition polymerisation of ethylene, a process which is carried out under high pressure (ca 2000 atmospheres) at 200 ºC in the presence of some oxygen. Initiation of the polymerisation reaction occurs due to the presence of oxygen which forms very reactive peroxides under these reaction conditions. Free-radicals form which produce the growing length of polymer chain as each new ethylene residue becomes attached and creates a new free-radical at the chain end. Termination occurs when two of these come together, and because that is a random process, chain lengths can vary considerably. Moreover, unfortunately, unless prevented, polymer-chain growth may not simply be linear, as it may also be initiated part way along the length of the growing polymer chain. The product, when such chain branching is allowed to occur under the polymerisation conditions spelt out above, has a degree of crystallinity below 75% and is called low-density polyethylene (LDPE). When chain branching is prevented, say by the use of Ziegler-Natta catalysts at low pressure (a few atmospheres) and a reduced temperature of 60ºC, the polymer chains are linear and their packing together/crystallinity is much improved, resulting in the product known as high-density polyethylene (HDPE). Typically it is very-highly crystalline (95% or above), and hence both stiffer and stronger than LDPE, but even so, HDPE is only between 3% and 6% more dense than LDPE. A usefully brief description of the various types of polyethylene is available online [147].