Home » Support & Download » Technical Articles » Technical Articles » What's the true function of melt index in plastic production?



Tel:    +86-551-66106027
Fax:    +86-551-65868499
Address: No. 8, Cuiwei Road, Hefei City, Anhui Province, P.R.C

What's the true function of melt index in plastic production?

Melt flow index testing machine factory

Firstly, it's an important part of incoming material inspection.

1. Determine whether it is within the normal melt index range by testing the melt index of the plastic product by using melt flow index tester. For example, the melt index of the product provided by the customer must be in a certain range, and the result of the test is indeed in this range, indicating that it meets the requirements. If the melt finger is too large, it means that the performance of the product processed from this material is poor and easy to process, but cracks will occur later; if the melt finger is too small, the performance will be better, but during injection molding, the flow rate will be too high. Slow, affects injection molding, at this time, increase the temperature or pressure during injection to adjust.

2. In batch production, different products of the same batch should be sampled to check whether the melt index is stable within a certain interval, so as to determine whether the batch of materials are all qualified products. For the same batch number and different batches of incoming materials, the melt index can also be compared to determine the stability of the incoming materials.


Secondly it’s the primary reference in the processing of modified plastics. 

1. After recycling waste plastics, the plastic is reprocessed and shaped. The primary reference is the melt index, because the fluidity of the plastic determines some of the properties of the material, such as tensile strength, elongation, elastic modulus and other parameters.

2. When downstream customers are looking for materials, they often refer to the supplier's physical property table, or directly indicate how much melting index is needed to meet production needs.


Thirdly, let's study a typical case of melt index testing.

After understanding the important role and practical application of melt index in plastic products, let's use cases to explain in detail the test process of melt index of plastic products!

1. Case background. 

The customer provides two samples of the same type of PA66 plastic, sample 1 is the finished product, and sample 2 is the finished product (defective product) for comparison test of melt index.

2. Test process

Detection environment: Ambient temperature 22.6℃ Humidity 52%R.H; standard test: ASTM D1238-13 Standard Test Method for Measuring Thermoplastic Melt Flow Rate by Extrusion Plastometer

3. Test results

Sample No.

Test condition

Test result (g/min)


(qualified product)

Temperature: 275℃  load 5kg



(defective product)

Temperature: 275℃  load 5kg


Remark: Test result is the average value of 5 samples.

4. Conclusion

Finally, under the same test temperature and load conditions, the melt index of the defective product is higher than that of the normal sample. Based on this result, the customer can make corresponding adjustments to the process to improve the quality of the product.


So, how to improve the performance and quality of your products by adjusting the melt index of your raw materials?

1. Blending with similar grades with different melting index can change the melting index of raw materials to a certain extent;

2. Add cross-linking agent, such as some organic peroxides, the addition amount is about one-thousandth, this method has a relatively large impact on the mechanical properties;

3. Adding a small amount of fillers, such as submicron calcium carbonate, can reduce the melt index. This method can appropriately improve the mechanical properties;

4. There is an additive called melt finger regulator, also known as polymer binder. It is a type of polyolefin product processing modifier developed for the normal molecular structure mechanism of polyolefin products. It effectively gathers polyolefin polymers through a variety of bonding technologies, thereby increasing the attractiveness between polymer segments (Van der Waals force), through such a modification process, the performance of the partially degraded polyolefin product is restored to the performance before the chain scission, and the individual performance can be greatly improved according to the amount of addition.


In summary, the melt index, which is one of the commonly used indicators in the fields of plastic processing, manufacturing, and inspection, has important guiding significance for ensuring the quality of thermoplastics and their products, and for adjusting the production process.


Textile & Garment Tester
Door & Window Hardware Tester




 Tel:         +86 188 55105986
 Fax:       +86-551-69012300
 Address: No. 8, Cuiwei Road, Hefei City, Anhui Province, P.R.C



Copyright   2017 Anytester (Hefei) Co., Ltd. All rights reserved. Site Map | XML