Table of Contents
What is melt viscosity of polymers?
The melt viscosity of a polymer at a given temperature is a measure of the rate at which chains can move relative to each other. This will be controlled by the ease of rotation about the backbone bonds, i.e., the chain flexibility, and on the degree of entanglement.
Why does viscosity increase with polymer concentration?
The more concentrated a polymer solution, the more large molecules you have exerting drag and interacting with each other. Higher concentration leads to a higher viscosity measurement.
How is melt viscosity related to molecular weight of a polymer?
For a specific polymer the melt viscosity is considerably dependent on the (weight average) molecular weight. The higher the molecular weight the greater the entanglements and the greater the melt viscosity.
How can you reduce the viscosity of a polymer?
Polymer viscosity is affected by water salinity and divalent ions such as calcium (Ca2+) and magnesium (Mg2+), which decrease the viscosity of the polymer solution. As the salinity increases, the distance between the polymer chain and the molecules decreases.
What is the relationship between melt index and viscosity?
MFI values are meant to be inversely proportional to the viscosity of the plastic at the given conditions of the test. The higher the MFI value, the lower the viscosity is supposed to be.
How does viscosity affect melting?
A: It’s hard to change the viscosity of a water solution without changing other properties which affect the melting rate. These properties include the total amount of solute, which affects the melting temperature, and the density, which affects whether the melted water sinks, floats, or mixes easily.
What is concentration effect on viscosity of polymer solution?
The polymer concentration is associated with solution viscosity, which increases with the increase of the polymer concentration and then leads to a larger fiber diameter. However, if the concentration is too low, continuous polymer fibers cannot be achieved, and polymer beads are obtained.
How does concentration affect viscosity?
When the solid concentration increases, the viscosity increases because of the increase in hydrogen bonding with hydroxyl groups and the distortion in the velocity pattern of the liquid by hydrated molecules of the solute.
How is viscosity and molecular weight correlated?
A High molecular weight increases the viscosity of the material – makes it harder to process the material using conventional methods. The longer the chains, the harder it is to get them to flow because they are more tangled.
How can you reduce the viscosity of a solution?
You can increase the temperature of the processing. In this way the viscosity and the surface tension will be simultaneously decreased.
Why is viscosity important in polymers?
In a very simplified definition, viscosity is the resistance to flow. Why does viscosity matter for materials? In general terms, polymers are injection molded, compression molded, or extruded– all of which require forcing a polymer into a shape. Therefore, viscosity is especially important for polymer processing.
What is the difference between MFR and MFI?
Melt flow index (MFI) or Melt Flow Rate (MFR) is a measure of a given polymers’ flow characteristics also known as the Rheological properties in the molten state under a known applied pressure.
What is the MFI of pet?
The MFI of PET samples can be determined using the method ASTM D 1238 Standard test method for flow rates of thermoplastics by extrusion plastometer [16]. Melt Indexer Dynisco–Kayeness Polymer Test Systems model LMI 4004 instrument with a heating chamber set at 285°C is used for the PET melting timings.
Does higher viscosity mean higher melting point?
The stronger the attractive forces, the higher the boiling point, viscosity and surface tension of a liquid; the higher the melting point of a solid; and the lower the vapor pressure of a liquid.
How does the viscosity of a liquid change on increasing the temperature?
The increase in temperature causes the kinetic or thermal energy to increase and the molecules become more mobile. The attractive binding energy is reduced and therefore the viscosity is reduced.
When polymer is dissolved in solvent the viscosity increase?
High molecular weight polymers greatly increase the viscosity of liquids in which they are dissolved. The increase in viscosity is caused by strong internal friction between the randomly coiled and swollen macromolecules and the surrounding solvent molecules.
Is viscosity directly proportional to concentration?
Observed values gives direct relationship between viscosity with concentration while inverse relationship between concentration and the surface tension. The intrinsic viscosity can be estimated from intercept Figure 1a and was found to be 0.696dl/g.
What are the factors that affects viscosity?
Increase in temperature decreases viscosity. Increases in pressure increase viscosity in liquids. In water, it decreases whereas, in gases, it remains the same.
- Increase in temperature decreases viscosity.
- Increases in pressure increase viscosity in liquids. In water, it decreases whereas, in gases, it remains the same.
What is relationship between intrinsic viscosity and molecular mass of polymer?
The relationship between the molecular weight of cellulose and the intrinsic viscosity tested in such dilute solutions has been established in the form of the Mark–Houwink equation, [ η ] = 0.24 × DP 1.21 .
What is the effect of molecular weight on the coefficient of viscosity of a fluid?
With the increasing molecular mass of a liquid, the viscosity increases. The flow of molecules is inversely proportional to its mass. Hence, liquids with high molecular mass possess greater viscosity.