Why can't polytetrafluoroethylene PTFE be injection molded?

Polytetrafluoroethylene is a polymer of tetrafluoroethylene, abbreviated as PTFE, which was discovered in the late 1930s and put into industrial production in the 1940s. It is widely used in chemical, mechanical, electronic, medical, textile and other sectors.

2024-10-22

I. Introduction of polytetrafluoroethylene
Polytetrafluoroethylene is a polymer of tetrafluoroethylene, abbreviated as PTFE, which was discovered in the late 1930s and put into industrial production in the 1940s. It is widely used in chemical, mechanical, electronic, medical, textile and other sectors. The relative molecular mass of PTFE is large, the low is hundreds of thousands, the high is more than 10 million. The general crystallinity is 90-95%, and the melting temperature is 327-342℃.
Second, the molecular structure of polytetrafluoroethylene
PTFE molecule CF2 unit arranged in a serrated shape, due to the fluorine atom radius is slightly larger than the hydrogen, so adjacent CF2 unit can not be fully cross-orientation in accordance with the trans-type, but the formation of a helical twisted chain, fluorine atoms cover the surface of almost the entire polymer chain, the formation of shielding so that the smallest of the hydrogen is very difficult to enter the C - F bond. At the same time, the fluorine atom has the highest electronegativity ( 4. 0), smaller atomic radius ( 0. 135nm), shorter bond length of C - F ( 0. 138nm), higher C - F dissociation energy ( 452KJ / mol), so it is very difficult to fracture C - F. These features determine the various properties of P TF E.
Third, why PTFE can not be injection molding?
PTFE can not be injection molding the main reasons include its high melting point, large melt viscosity, and in the molten state to maintain the stability of the shape. These properties make PTFE unsuitable for conventional plastic molding processes such as injection molding.
High melting point: PTFE has a melting point of approximately 327°C and its melt viscosity is several orders of magnitude higher than that of ordinary thermoplastics. This means that at high temperatures, PTFE flows extremely poorly and is difficult to heat through an injection molding machine and then inject into the mold to form the desired shape.
Shape stability in the molten state: In the molten state, PTFE is able to maintain its original shape, similar to a jelly state that cannot flow. This characteristic makes PTFE unable to be molded by injection molding like other thermoplastics.
In addition, PTFE's processing dimensional stability is not ideal, its coefficient of linear expansion with temperature changes and very irregular changes, hot and cold shrinkage changes, which further limits its application in injection molding.
Fourth, the molding process of polytetrafluoroethylene
PTFE crystallization melting point of 327 ℃, but the resin to be above 380 ℃ to be in a molten state. In addition, PTFE has a strong solvent resistance. Therefore, it can not use the melt processing method, but also can not be used to dissolve the processing method, usually the production of its products can only be like the processing of metals and ceramics, the first powder compaction, and then sintering and mechanical processing, or through extrusion molding, isobaric molding, coating molding and calendering molding and other ways of processing.

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Why can't PTFE be injection molded?

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Is PTFE harmful to humans?

For the most part, PTFE has essentially negligible harmful effects on the human body, with a high degree of safety due to the material's high chemical stability up to temperatures of 190°C, and is often used as a tissue substitute such as a human implant material.

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What are the properties and uses of polytetrafluoroethylene

Used in electrical appliances, chemical industry, aviation, machinery and other fields instead of quartz glassware used in atomic energy, medicine, semiconductors and other industries of ultra-pure chemical analysis and storage of various acids

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