Cellular Polymers.

Cellular materials widely occur in nature such as wood, cork, corals, sponge, human bones etc.
These natural materials with cellular structure have been used for centuries.
The idea of developing and manufacturing the broad range of cellular polymers arose when these natural cellular structures exhibited excellent properties such as high strength of wood, cushioning properties of cork and straw and good insulating properties of cork and balsa.

Example of cellular polymers.
The multifunctional cellular materials are widely used structurally for cushioning, thermal insulation, energy absorption from impacts, sound absorption and vibration dampening.
The cellular polymers consist of two phase i.e solid and gas.
Cellular rubbers are cellular polymer consisting rubber matrix containing a mass of cells.
Some properties of cellular rubbers are;

1) Limited water absorption.
2) Weather resistant.
3) Resistant to chemical and acid.

Cellular rubbers are used for sealing, isolating and shock absorption etc.
Cellular polymers not only provide insulation but are usually stronger than solid polymers.
10% of plastic resins used nowadays are used for production of cellular polymers.

Comments

Determination of molecular weight of polymers by viscosity method.

Determination of molecular weight of polymers by viscosity method. It is a simple method for determining the molecular weight of polymers. Addition of polymers in the solvent increases the viscosity of the solvent, due to introduction of inhomogeneities by the polymers. If η₀ is the viscosity of the solvent and η is the viscosity of the solution at the same temperature, then the relative viscosity is given by Relative viscosity. Specific viscosity: It is defined as the relative increase in viscosity and is given as Specific viscosity. Reduced viscosity: It is defined as the relative increase in viscosity per unit concentration (C) of polymer and is given as Reduced viscosity. Intrinsic viscosity: The reduced viscosity is dependent on concentration (C). If a graph is plotted between reduced viscosity vs concentration then the extraplotation value when C=0 is called intrinsic viscosity. Intrinsic viscosity. Graph of reduced viscosity vs concentr

Determination of molecular weight by Light scattering method.

Determination of molecular weight by Light scattering method. Due to big size macromolecules in solution, turbidity is produced. The light rays get scattered, when pass through macromolecule solution due to turbidity. The turbidity T is given by Where I₀ is the intensity of incident light. Iₜ is the intensity of transmitted light after passing through a solution of length l. In case of proteins or higher polymers the turbidity is small and is determine from the intensity of light scattered at 90° to the beam. This can be done by using a simple photometer as shown in figure below. Turbidity increase with increase in concentration as well as molecular weight. The Turbidity is related to molecular weight by the equation given by Debye. Hc/T=1/M+2Bc Where B is second virial coefficient and H is a constant. If we plot a graph between Hc/T vs c we get a straight line with intercept 1/M. Thus This curve was plotted by Zimm, so is called Zimm's Curve. Thus the c

Kinetics of copolymerisation and Composition of copolymer.

Kinetics of copolymerisation and Composition of copolymer. We must know that Where r₁ and r₂ are the reactivity ratio's for the given pair of monomers. Where the above equation is called Copolymerisation equation and it gives the copolymerisation composition without using radical concentration. Types of copolymerisation ( kinetics significance) Let us take the reactivity ratio's product of monomers i.e Product of reactivity ratios. Depending on whether this product is less, greater or equal to unity copolymers are divided into three types. 1)Ideal copolymerisation Here the product of reactivity ratios is equal to unity, i.e r₁r₂=1 2) Alternating copolymerisation Here the product of reactivity ratios is equal to zero, i.e r₁r₂=0. 3)Block copolymerisation Here the product of reactivity ratios is greater than 1, i.e r₁r₂>1.

Polymers

Search This Blog