Natural polymers, Mechanical Engineering

Natural Polymers

Rubber is individual natural polymer and was illustrated earlier. Specific trees exude thick liquid that solidified in brittle material termed as rosin. Shellac or lac is exudate result of animal life, parasitic insect or coccus lacca that feeds upon specific Indian trees. This material has extremely low tensile strength. While dissolved in spirit it can be utilized for polishing wooden surfaces. Wood is a naturally occurring polymer also that main constituent is cellulose. The cellulose molecule's chain is highly aligned. This alignment creates wood in mechanical properties to vary directional. The cellulose molecule is demonstrates in following figure.

                                                             271_Natural Polymers.png

                                                                       Figure: Cellulose Monomer of Wood

Wood is a living matter of cells composed that resemble long thin tubes. These tubes walls are made along with cellulose fibres that are aligned beside the axis. A complex amorphous material termed lignin binds cell walls together, and lignin makes 20 to 35 percent of wood by 50 to 60 percent cellulose. Minute percentages of resins, carbohydrates, minerals and gums are representing in wood also. Whilst the density of wood material is constant for each types of wood, the occurrence of voids and cracks of various sizes and numbers origin variation of density from one category to another. The hygroscopic nature of cell walls reasons absorption of water and swelling of wood. These water molecules behave extremely like plasticiser giving flexibility to wood. Removal of water creates wood rigid.

Organic acids do not attack wood on room temperature except the inorganic acids and alkaline solutions attack wood mostly at higher temperature and concentration. On prolonged heating at 105 to 150oC the organic matter begins to wood turns black and decomposes. Wood burns readily giving heat and thus used as like fuel. This can be mechanically and chemically treated to generate wood pulp that is employed for producing paper.

Posted Date: 2/27/2013 4:54:27 AM | Location : United States







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