Polymers strengthening processes

Thermoplastic Elastomers TABLE IV Strengthening Processes in Polymers"... 

The catalytic conversion of platform molecules produced by bioconversion of renewables into bioproducts. This is already the basis of many industrial processes, leading to important tonnages of chemicals and polymers from carbohydrates and triglycerides and fine chemicals from terpenes. This approach needs to be extended and process efficiency should be strengthened by designing more active and selective catalysts. 

Once dehydrated, the microfibrils are practically without functionality in ordinary food processing and preparation operations, because the inert microcrystallites are difficult for water to penetrate. The polymorphs, cellulose I and II (Blackwell, 1982 Coffey el al., 1995), are differentiated by their molecular orientation, hydrogen-bonding patterns, and unit-cell structure. Cellulose I is the natural orientation cellulose II results from NaOH treatment under tension of cellulose I with 18-45% alkali (mercerization). The I—II transition is irreversible. Mercerization strengthens the fibers and improves their lustre and affinity for dyes (Sisson, 1943). Sewing thread was relatively pure mercerized cotton until the advent of synthetic polymer fibers. 

Many linear polymers are too flexible to be of use in making everyday objects because they lack the strength, the rigidity, or the elasticity for the job. Linear polymers can be stiffened and strengthened by bonds between the chains. This process is known as cross-linking and we will look now at some ways in which this can be achieved. 

Other applications are found in powder technology. The cohesion in pellets formed out of dry powders can be improved by treating the powder with an appropriate polymer solution. This process is used on an enormous scale to prepare iron ore in a form suitable for blast furnaces, but also for the preparation of pharmaceutical specialty products. Polymers are applied at a large scale in paper-making where they help to strengthen the network of celluloslc fibres and to trap different kinds of particles in this network. The building of a network Is also the purpose of adding carbon black to rubber, which improves its resilience and abrasive resistance. 

It was found that the silicone polyaddition polymers are more suitable as a matrix because of the absence of by-products fi om the process of vulcanization and the formation of ethane bridges (Scheme 1) in the polymer, which significantly strengthens the end product, while high elasticity is retained. 

Thus, amorphous regions of polymer, bounded by crystals, are macroreactors in which chain process of mechanodestruction and failure of material is being developed. Hence, decrease of the amount of polymer amorphous part will lead to strengthening of the fibre and improving its physico-mechanical characteristics. 

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