Note on Important Health and Safety Information
Safety and Health Hazards Associated with Foaming Fluoropolymers
Using Thermal Degradation Processes
Recently, certain processing techniques have come into increased use which employ the gases generated by thermal decomposition of polymers to create a foam structure in the polymer. This process, commonly referred to as "free-foaming" or "free foam extrusion," should be avoided because of the potential to release decomposition effluents as gaseous materials at hazardous levels in the initial processing, and in subsequent storage, transportation, installation, and use of semi-finished and finished products.
Extrusion foaming processes are used to manufacture wire and cable with superior electrical properties, other polymeric insulating media, and structural foams with reduced weight. In "free-foaming," the high temperatures, alone or in combination with high shear rates, can create conditions especially conducive to production of these potentially toxic gases. Under no circumstances should a foamed fluoropolymer be created without the aid of a blowing agent or at temperatures above the manufacturer’s maximum recommended processing temperature. In other words, do not use a "free-foaming" process in processing fluoropolymers, and the use of this process with other polymers should be thoroughly investigated before adopting this manufacturing practice.
Excessive temperatures and high shear rates should be avoided during all foaming processes. It is well known that incomplete degradation of nearly all polymers due to high temperatures in processing produces hazardous gases. For example, in processing fluorinated ethylene-polyethylene (FEP) under free-foaming conditions, research indicates that under the conditions in the extruder associated with free foaming, potentially hazardous levels of hydrogen fluoride (HF) and perfluoroisobutylene (PFIB) are created in significant quantities. This same research indicates that the high temperatures and shear rates used in this process tend to generate significantly higher levels of PFIB than in processes in which nitrogen or other gases are injected during the extrusion process to facilitate foaming. Under similar "free foam" processing conditions, other polymers could produce other toxic and hazardous materials, possibly in significant quantities.
In the case of FEP fluoropolymer, the two gases of most concern in anaerobic processing are HF (or its precursors, TLV of 3 ppm (C)) and PFIB (TLV of 0.01 ppm (C)).
Processing under a manufacturer’s recommended conditions, as described in the "Guide to the Safe Handling of Fluoropolymers Resins," does not produce these thermal degradation gases in hazardous quantities.
SPI has long recommended good industrial hygiene practices designed to minimize hazards associated with melt extrusion, regardless of the method of processing used. However, due to our assessment of the hazard associated with "free-foaming" and the availability of safer foaming methods, SPI is issuing this notice to fluoropolymer processors and other polymer processors. Specifically, SPI and its members do not endorse manufacture of foamed polymer products by the "free foam" process because of the potentially increased safety and health hazards involved.
SPI will soon be supplementing the "Guide to the Safe Handling of Fluoropolymers Resins" to provide more detailed information and data in support of this notice.
Contact your resin supplier if you have questions about specific products.