Why can't PTFE be molded through injection?

Ⅰ：Is PTFE a Good Material?

The answer is almost always yes – it is corrosion-resistant, high-temperature resistant, non-stick, low-friction, and boasts exceptional chemical stability.

Can It Be Injection Molded? Why or Why Not?

Virtually all of PTFE’s superior properties stem from its molecular structure. Its main chain is: —CF₂—CF₂—

You can envision it as a carbon chain completely encased by fluorine atoms.

Exceptionally high C–F bond energy

1，It is one of the most stable chemical bonds in organic compounds – this grants PTFE outstanding heat resistance, chemical resistance, and anti-aging properties.

Though small in atomic radius, fluorine atoms have a compact electron shell structure that effectively shields the carbon chain

2，This results in extremely weak intermolecular forces and ultra-low surface energy, giving PTFE its prominent non-stick characteristics and low friction coefficient.

3，High rigidity and high regularity of the molecular chain

Chain segments are difficult to rotate internally and tend to stack tightly, leading to a high crystallinity (typically 50%–70%) and a relatively high melting point (approximately 327°C). Overall, it is like a cluster of stiff, straight "rods".

In summary, PTFE’s core properties are:

excellent chemical inertness, high thermal stability, a low friction coefficient, and non-adhesiveness.

Ⅱ:Any material suitable for injection molding must meet one fundamental requirement: in its molten state, it must be capable of macroscopic flow, shearing, and pumping.

Extremely high melt viscosity (the core reason)

1,PTFE is not merely "too viscous" – it has no true flowable molten state at all. The melt viscosity of standard injection-moldable plastics typically ranges from 10²–10⁵ Pa·s, while PTFE’s melt viscosity above its melting point reaches approximately 10⁹–10¹¹ Pa·s. This value is millions or even tens of millions of times that of ordinary plastics, making it impossible to force PTFE into the narrow cavities of a mold under the screw pressure of an injection molding machine.

2,A "gel state" rather than a true molten state

Ordinary thermoplastics undergo a phase change when heated, transforming from a solid to a fluid. However, due to the extremely long and rigid molecular chains of PTFE, even when heated above 327°C, it retains its original shape and only becomes transparent as its crystallinity disappears.

Extreme sensitivity to shear stress (melt fracture)

3,During injection molding, the melt must pass through nozzles and runners at high speed. PTFE’s molecular chains are highly prone to fracture or so-called melt fracture under strong shear stress. Forced injection molding would result in finished products filled with cracks and defects, completely losing their physical properties.

Narrow processing window and risk of thermal decomposition

4,PTFE only "melts" at 327°C and begins to decompose noticeably at around 400°C, leaving a processing window of less than 100°C – and this is a "non-flowing melt". Furthermore, when the temperature exceeds 400°C, PTFE decomposes and releases highly toxic gases such as perfluoroisobutylene. Frictional heating during injection molding can easily cause local overheating and decomposition, corroding equipment and endangering operators.