Polymers are the hydrocarbon materials that are made from long chain of cross linking hydrogen and carbon atoms. Polymers are extensively used in the industries for manufacturing of different sort of products and materials. They various uses of polymers include packaging industries, automobile industries, industrial spare parts and many others. Due to their extensive physical attributes, the polymer materials are used even in the manufacturing of space shuttle parts. The intrinsic properties of polymers make them ideal for use for many applications. The polymers are almost inert and are inactive when come in contact with any harsh chemical or material which makes them safe for use with chemicals and food products. Also the strength of the polymeric materials is much higher than many other materials that are used for different applications hence can be used for applications where high strength of materials is required. The polymers are available in different compositions, physical properties and chemical properties that makes them versatile and available for a variety of application in both industrial as well as domestic applications. There are many different factors that affect the quality, physical properties and chemical properties of polymers. Even a slightest deviation in these factors can have a drastic change in the chemical composition and basic molecular structure of the polymers which leads to change in the physical properties such as strength, elasticity and so forth (Plastic Testing Instruments).
This is why the manufacturers of polymer products need to understand the quality assurance of the polymers and keep a close check on the properties of the materials they are using for manufacturing of their final products. One of the most important factors that affect the overall characteristics and quality of the polymers is the molecular weight. The manufacturers need to understand that any change in the molecular weight of the can have a big impact on the properties of the polymers.
Melt Flow Rate
Calculating the molecular weight of a polymer can be decisive in choosing an application for a particular polymeric material. One of the easiest ways of calculating the molecular weight of the polymers is through the melt flow rate or Melt flow index. The MFR of a polymer basically describes the velocity of a polymer as the function of a shear rate. The polymers are considered Non-Newtonian, their viscosity changes with the change in the shear rate. The MFR value of a polymer is the amount of material that is passed through an opening with a specific size under the pressure of a shear force that is applied on the materials in a melted form. With the help of melt flow rate, the manufacturers can easily calculate the molecular weight of the material being tested. With determination of molecular eight, it becomes easy to analyze the process ability of the polymer and hence changes could be done to enhance the properties of the polymer.
Importance of Molecular weight of Polymers
The MFI of any polymer is inversely proportional to the viscosity of the material. If a material has high viscosity, there will be a high resistance offered by the material when it flows in the molten state. This makes it flow more slowly under any given set of conditions. This is the reason, the materials with higher molecular weight have a lower melt flow rate and the materials with lower melt flow rate have a higher melt flow rate. Both have their applications according to the requirements of the process. For example, in the injection molding industries, the materials with higher melt flow arte are preferred as they are easy and fast to fill in the mold. On the other hand, the blow molding and extruding processes will favor the materials with lower melt flow rate as those materials will have a high molecular weight and hence have higher strength and melting point. This is a parameter that is helpful on controlling the shape of the parison. The end users also prefer to use products made from higher molecular weight as it correlates with better performance of the products. With higher molecular weight, there is improved impact resistance, ESCR, better materials fatigue endurance, and barrier properties.
Calculation of Melt Flow Index
The calculation of the melt flow index is done with the help of melt flow index test. In this test, the material to be tested is melted and the molten material is placed at the opening of a capillary tube that has a specific diameter. The material moves under a shear pressure that pushes the material through the tube. After ten minutes, the material that has flown through the capillary tube is weighed and that gives the melt flow index of the material. It is expressed in grams per 10 minutes.
Melt flow index test
The melt flow index test is performed with the help of a melt flow index tester which is a sophisticated machine that makes it very easy to perform the melt flow index test for a polymer. The instrument has a funnel that is placed at the opening of the test orifice or the capillary tube. The material is placed in the funnel. The temperature of the funnel is increased using a heating mechanism. As the temperature of the funnel increases, the material melts. There are dead weights placed on the top of the molten material to apply the shear force. Under the effect of this shear forces, the material is made to pass through the capillary tube for duration of ten minutes. After ten minutes, the material that has passed through the tube is weighed using a digital scale. This weight of the material gives the malt floe rate of the material.
Although the MFR alone cannot give the entire performance portfolio of a material, it is an important factor to consider when making the selection of a polymeric material for an application. With the help of the MFR, the molecular weight of the material can easily be analyzed which further helps in analysis of the physical and chemical attributes of the materials.
