Ensure Higher MFI Value to Increase the Quality of Polymers

Ensure Higher MFI Value to Increase the Quality of Polymers

Many polymers are filled for various reasons from cost reductions by using cheap fillers like calcium carbonate or talc to more expensive fillers to improve mechanical, electrical and thermal properties such as glass fiber, metal powders for magnet detection and so forth and let us not forget the addition of a percentage of recycled material to the virgin material. All these materials require testing to ensure conformity to agreed standards (Plastic Testing Instruments). 

Since polymers are made up of varying lengths of polymer molecular chains, the length of the chain determines the flow characteristics. It is difficult to control the exact chain length during polymerization, the resulting mix or distribution of chain lengths also known as the molecular weight distribution affects the resulting flow properties. This molecular weight distribution is also an important contributor to the physical and mechanical properties of the resulting polymer amongst other items.

When the polymer granules are introduced to the barrel, all entrapped air is removed by tampering down the granules, as any air entrapment will give inaccurate results. Once the bore is full a piston is placed in the barrel with a known dead weight on top of it. For very basic machines the Extruded samples are cut and weighed from which the MFI value is then calculated.

Why is it Important?

Variations in the MFI value on incoming material can have detrimental effects on productivity and quality. It is important to test the incoming material to ensure Quality Standards are adhered to. It is not uncommon to find that there is batch to batch variations in materials and this can have costly implications. For example, material exceeding the expected MFI can result in the flashing of an injection mold leading to an increased reject rate and hours or days of cleaning the mold resulting in lost production from that mold or machine. A Badly flashed hot runner mold could require new nozzles and tips to be replaced which are very costly items. A material with lower than expected MFI could result in parts not filling properly and again leading to an increase in the reject rate and an increase in the quality cost to the business. If the problem is not spotted on the molding lines, then it could cause problems with finishing departments downstream.

Melt Flow Index Tester is used to measure the flow rate of various Polymers. The generated values help to distinguish the different grades of Polymers. Because plastic materials are seldom manufactured without incorporating additives, which affect the processing characteristics of material like stability and flowing ability.