Efficient Catalysis by Sodium Hypophosphite for Solid-State Polymerization of High-Viscosity PA6/66 Copolyamide:...

Area of Science:

• Polymer Chemistry
• Materials Science
• Chemical Engineering

Background:

• Industrial preparation of high-viscosity copolyamides 6/66 (PA6/66) faces challenges like long reaction times, high energy use, and inconsistent viscosity.
• Solid-state polymerization (SSP) is a key process for polymer modification, but optimizing it for high-viscosity materials requires efficient catalytic systems.

Purpose of the Study:

• To investigate the use of sodium hypophosphite as a catalyst for the solid-state polymerization (SSP) of PA6/66.
• To optimize the catalyst extraction process to manage catalyst loss and control extractable content.
• To establish a reliable process for the large-scale, continuous production of high-viscosity PA6/66.

Main Methods:

• Introduction of sodium hypophosphite into the PA6/66 copolymerization system.
• Systematic investigation of catalyst effects on viscosity-increasing rate and relative viscosity during SSP.
• Optimization of an extraction process to control catalyst concentration and extractables.
• Implementation of the catalyzed SSP process on a 4500 tons/year continuous polymerization line.

Main Results:

• The relative viscosity of PA6/66 increased linearly with SSP time, with a stable apparent viscosity increase rate of 0.14 h⁻¹ at 160 °C.
• Optimal catalyst concentrations (phosphorus content) were identified as 25 ppm at 150 °C and 30 ppm at 160 °C to prevent excessive viscosity increase.
• The optimized extraction process ensured catalyst concentration remained above the control level while meeting processing requirements for extractable content.
• Successful stable preparation of high-viscosity PA6/66 chips with uniform viscosity was achieved on an industrial scale.

Conclusions:

• Sodium hypophosphite is an effective catalyst for enhancing the SSP rate of PA6/66.
• Controlled addition and optimized extraction of sodium hypophosphite enable efficient large-scale production of high-viscosity PA6/66.
• This study provides a robust theoretical and process framework for manufacturing high-quality, high-viscosity PA6/66 resins.