Fibers environmental degradation

Most architectural fabrics are usually flexible composites comprised of glass fibers coated with fluorocarbons to resist wind, mechanical forces, and outdoor environmental degradation. The airport terminal in Saudi Arabia, and the roofs for the Hubert Humphrey Dome in Minneapolis and the Tokyo Dome Stadium are a few examples of the successful use of architectural fabrics. 

Like mechanically fastened metal structures, composites exhibit failure modes in tension, shear and bearing but, because of the complex failure mechanisms of composites, two further modes are possible, namely cleavage and puUout. Environmental degradation of a bolted joint, after exposure to hot, wet environment is most likely to occur in the shear and bearing strength properties. The evidence shows that for fiber reinforced epoxies, temperature has a more significant effect than moisture, but in the presence of both at 127°C, a strength loss of up to 40 percent is possible. 

Acetylation is mainly applied to stabilize the cell wall against moisture absorption for improving its stability and environmental degradability [48-52]. In acetylation, acetic anhydride substitutes the hydroxyl group of the cellulose with acetyl groups that modify the properties of fibers so that they become hydrophobic [50]. Moisture absorption of fiber reduces after acetylation, which is beneficial for composites application. It was reported that after acetylation reduction in moisture uptake was found to be around 50-65% [53]. 

Acetylation methods have been used for many years to improve some properties of wood cellulose such as moisture repellency, dimensional stability and resistance to environmental degradation. Their use for improving the properties of natural fibers has increased significantly in the last decade or so. The methods are based on the reaction of lignocellulosic material with acetic anhydride at elevated temperature, with or without a catalyst. The acetic anhydride reacts with the more reactive hydroxyl groups according to the equation [36],... 

Composites can also be classified on the basis of the intended application. For example, one can distinguish between two types of biocomposites. Biocomposites for ecological applications are combinations of natural fibers or particulates with polymer matrices from both nonrenewable and renewable resources and are characterized by environmental degradability. Biocomposites for biomedical applications are combinations of biostable or degradable polymers with inert or bioactive... 

Pandey JK, Ahn SH, Lee CS, Mohanty AK, Misra M (2010) Recent advances in the application of natural fiber based composites. Macromol Mater Eng 295 975-989 Pandey JK, Chu WS, Kim CS, Lee CS, Ahn SH (2009) Bio-nano reinforcement of environmentally degradable polymer matrix by cellulose whiskers from grass. Compos B 40 676-680... 

With the renewed interest in environmentally friendly products, ceUulose esters are being re-evaluated as a natural source of biodegradable thermoplastics. CeUulose acetates are potentiaUy biodegradable (152). Films prepared from a ceUulose acetate with a DS of 2.5 were shown to require only a 10—12 day incubation period for extensive degradation in an in vitro enrichment assay. Similarly, films prepared from a ceUulose acetate with a DS of 1.7 saw 70% degradation in 27 days in a wastewater treatment facUity, whereas films prepared from a ceUulose acetate with a DS of 2.5 required approximately 10 weeks for similar degradation to occur. The results of this work demonstrate that ceUulose acetate fibers and films are potentiaUy environmentally nonpersistant. 

Whichever application of natural fiber or natural fiber-reinforced plastics will be used depends on the different environmental conditions, which are likely to add to the aging and degrading effects. On the other hand, such effects are often desirable, as is the case with com-... 

Chlorine dioxide has an odd number of electrons and is a paramagnetic yellow gas. Despite the environmental damage it creates, it is often used to bleach paper pulp, because it can oxidize the various pigments in the pulp without degrading the wood fibers. 

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