Advanced Polymer Technologies

Radio Frequency Treatment for Improving Nylon Properties

• Objective
• Background
• How ETAC Helped
• Results/Benefits

Objective
To develop a commercial process for treating nylon materials or polymers with radio frequency (RF) energy to improve strength and other mechanical properties.

Background
Prior to coming to ETAC, Advanced Polymer Technologies (APT) discovered that continuous application of RF energy could significantly increase the rate of nylon 6-condensation polymerization in the solid phase. Since RF heats volumetrically, it takes significantly less time than convection heating. Convection heating typically takes 20 hours while RF heating takes about four hours. Based on these potential benefits, APT approached ETAC to develop a commercial process to treat nylon materials.

ETAC enabled APT to explore the use of a robust, commercial process for the continuous RF treatment of polymeric resins and polymeric parts. The results included a substantial increase in molecular weight and associated mechanical properties such as strength, toughness and temperature resistance yielding a higher product value.

The RF-driven pilot plant device is intended to solid-state polymerize and/or dry condense polymers. The operation of the RF solid phase polymerization (SPP) results in a product with a significantly lower cost than products produced by current hot gas convection techniques.

The traditional industrial convection heating methods are limited by the poor thermal conductivity coupled with slow moisture diffusion in the product. This often produces undesirable effects by yielding variations in molecular weight in the bulk of the product, as well as in individual pellets, chips or parts of a nylon product.

How ETAC Helped
ETAC developed a unique, vertical-oriented treatment system radio frequency (VRF) design suited for free-flowing, bulk granular or particulate type products. The design of the treatment system was based on a pair of nested, cylindrical electrodes where the product was heated while flowing in the annular space between them. Material was fed into the top of the unit by a mechanical method. The material then filled the free volume of the unit by gravity and was metered from the bottom by the screw feeder. This arrangement was ideal to address the unique materials handling requirements of bulk or free-flowing product.

The other aspects of the design involved an inert atmosphere that could be run co-currently or counter-currently into the flow of material, giving the required degree of control to prevent oxidation of the nylon during processing. Another benefit was the temperature-sensing by devices mounted at different locations along the vertical height and around the circumference of the unit that provided feedback control to the fifty-ohm based RF power supply.

Results/Benefits
The results of ETAC's work with APT were:

• Nylon ideally processed in a steady-state, continuous operation during the RF treatment.
• Increased degree of polymerization to values of up to n = 175.
• Increase in formic acid viscosity values significantly more rapid than by traditional convection heating methods.
• Higher product strength at a significantly lower cost than with the current SPP techniques.

For more information on the radio frequency technology used at APT, contact us.

Note: ETAC has received approval from the company above to disclose its name and specific information about its work with ETAC.