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Why Is There Have Such A Nasty Smell/ Odor When The POM Is Extrusion And Pelletizing?

Jan 02, 2020

[Peculiar Smell Caused By Molecular Weight Distribution Of POM Material]

Due to the limitation of synthesis process and the need of granulation, the molecular weight of POM recycled particles used for granulating POM plastic raw materials is not single, but has a normal distribution from small to large, also known as molecular weight distribution. The different normal distribution curve is different molecular weight distribution, which leads to different performance of POM regenerated particles. If the proportion of small molecules in the molecular weight distribution of POM regenerated particles is high, the high temperature will make the small molecules volatilize and produce the taste of paraffin in the process of granulation. In addition, the residue of unreacted and by-products and catalyst in the polymerization process of POM regenerated particles will also produce peculiar smell when volatilizing during granulation.

[Odor From POM Additives]

In order to improve the pelletizability of recycled POM particles or to improve and change the performance of composite POM, various additives are often added to the recycled POM particles. In addition, some functional inorganic fillers, such as calcium carbonate, kaolin, talcum powder and silicon oxide, will be added due to the cost or to improve the light blocking property of POM; in order to increase the solubility of these inorganic fillers and POM regeneration particles, some dispersants and coupling agents will be added; Then there are various organic pigment color masterbatch, Titanium White Masterbatch, etc. these kinds of miscellaneous additives with different components are also one of the main factors that cause peculiar smell. When these additives are heated, many volatile substances will be produced, which will cause peculiar smell in POM granulation. In addition, some additives react with POM regeneration particles to produce peculiar smell.

[Odor Caused By POM Aging]

All kinds of POM regeneration particles or composite good POM, if the storage time is too long, the oxygen, ozone and water in the air, under the action of ultraviolet light, will cause decomposition and oxidation, so that the material aging will produce peculiar smell. In addition, the auxiliaries in POM materials, like POM regenerated particles themselves, cause oxidation and peculiar smell under the action of oxygen and ultraviolet light.

 

[Measures To Reduce Odor]

For POM granulation, the following measures should be taken to control the most influential odor: the selection of POM regenerated particles, decomposition of POM regenerated particles and precipitation of additives.

[Selection Of POM Plastics In Granulation]

Correctly select the brand of POM regenerated particles, and understand the type and function of additives added to the purchased POM regenerated particles. If the production is normal, try not to change the brand of POM regenerated particles. If it is necessary to temporarily change the brand of POM regenerated particles due to various reasons, it is necessary to conduct a small test first, and then put into production if there is no problem. In order to avoid the return loss caused by problems. Sometimes the molecular weight distribution of POM regenerated particles of the same brand is slightly different in different production batches, so the granulating process conditions of POM regenerated particles of the same brand and different batches also need to be adjusted slightly.

[Decomposition Of POM Regenerated Particles In Granulation]

When pelletizing, the temperature of the extrusion die is very high. At such a high temperature, POM regenerated particles are easy to decompose, and at the same time, they are thermally oxidized with oxygen in the air, which will produce peculiar smell. In order to reduce the peculiar smell, when extruding, the temperature of POM regenerated particles should be properly reduced if possible, and the granulation should be carried out at a lower temperature, and the air gap can also be properly reduced, that is, the distance between the die lip and the composite pressing roller should be shortened. It can reduce the oxidation degree of POM regeneration particles, but the air gap is too small and it is easy to reduce the composite fastness, so the amount of air gap should be appropriate. Different POM regeneration particles have different odor size, which is more likely to produce odor. There are a large number of additives in POM regenerated particles, such as antioxidant, smoothing agent, etc., which are also the important reason for peculiar smell when they are formed and granulated. It is necessary to select the proper particle type and masterbatch type for POM regeneration