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Physical properties of polymers

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Information about Physical properties of polymers
Science-Technology

Published on March 10, 2014

Author: vnt54321

Source: authorstream.com

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Product DevelopmentPhysical Properties of Polymers : Prepared by- Vineet kumar sharma m.Pharm. 1st sem. (Pharmaceutics) Azad institute of pharmacy & research lucknow Product DevelopmentPhysical Properties of Polymers Polymers : Polymers A polymer is a large molecule, or macromolecule, composed of many repeated subunits, known as monomers. Slide 3: Polymers, both natural and synthetic, are created via polymerization of many monomers. Polymerization is the process of combining many small molecules known as monomers into a covalently bonded chain or network. During the polymerization process, some chemical groups may be lost from each monomer. Physical Properties : Physical Properties Crystallinity- Synthetic polymers may consist of both crystalline and amorphous regions. Crystallinity : Crystallinity The degree of crystallinity may be expressed in terms of a weight fraction or volume fraction of crystalline material. The crystallinity of polymers is characterized by their degree of crystallinity, ranging from zero for a completely non-crystalline polymer to one for a theoretical completely crystalline polymer.  During the polymerization process, some chemical groups may be lost from each monomer. Crystallinity : Crystallinity Polymers with microcrystalline regions are generally tougher (can be bent more without breaking). Polymers with a degree of crystallinity approaching zero or one will tend to be transparent. While polymers with intermediate degrees of crystallinity will tend to be opaque due to light scattering by crystalline or glassy regions. Slide 7: Tensile strength- The tensile strength of a material quantifies how much stress the material will endure before suffering permanent deformation. This is very important in applications that rely upon a polymer's physical strength or durability. For example, a rubber band with a higher tensile strength will hold a greater weight before snapping. Slide 8: In general, tensile strength increases with polymer chain length and crosslinking of polymer chains. Young's modulus of elasticity- Young's Modulus quantifies the elasticity of the polymer. It is defined, for small strains, as the ratio of rate of change of stress to strain. Slide 9: The modulus is strongly dependent on temperature. Transport properties- Transport properties such as diffusivity relate to how rapidly molecules move through the polymer matrix. These are very important in many applications of polymers for films and membranes. Slide 10: Melting point- The term melting point, when applied to polymers, suggests not a solid–liquid phase transition but a transition from a crystalline or semi-crystalline phase to a solid amorphous phase. Among synthetic polymers, crystalline melting is only discussed with regards to thermoplastics, as thermosetting polymers will decompose at high temperatures rather than melt. Slide 11: Glass transition temperature- A parameter of particular interest in synthetic polymer manufacturing is the glass transition temperature. At which amorphous polymers undergo a transition from a rubbery, viscous liquid to a brittle, glassy amorphous solid on cooling. Slide 12: Mixing behavior- In general, polymeric mixtures are far less miscible than mixtures of small molecule materials. This effect results from the fact that the driving force for mixing is usually entropy, not interaction energy. Miscible materials usually form a solution not because their interaction with each other is more favorable than their self-interaction. Slide 13: The phase behavior of polymer solutions and mixtures is more complex than that of small molecule mixtures. Whereas most small molecule solutions exhibit only an upper critical solution temperature phase transition, at which phase separation occurs with cooling. Slide 14: In dilute solution, the properties of the polymer are characterized by the interaction between the solvent and the polymer. In a good solvent, the polymer appears swollen and occupies a large volume.   In a bad solvent or poor solvent, intramolecular forces dominate and the chain contracts. The effect of temperature on the structure and behavior of thermoplastics. : The effect of temperature on the structure and behavior of thermoplastics. Slide 16: Inclusion of plasticizers- Inclusion of plasticizers tends to lower Glass transition temperature (Tg) and increase polymer flexibility. Plasticizers are generally small molecules that are chemically similar to the polymer and create gaps between polymer chains for greater mobility and reduced interchain interactions. A good example of the action of plasticizers is related to polyvinylchlorides or PVCs. Reference : Reference Wikipedia Remington Slide 18:  Email ID-: vineet54321@hotmail.com

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