Evaluation of Synergistic Chemical Effects on Medical Plastics

Overview

Environmental Stress Cracking (ESC) is responsible for an estimated 25% of failures in all plastic components in use. In today’s world, the combined use of disinfectants containing various active ingredients is becoming increasingly common in the medical industry to ensure patient safety. This developing practice expands the need for Environmental Stress Crack Resistance (ESCR) testing, especially testing for synergistic effects. Synergistic effects occur when the combined effects of individual stressors are greater than the sum of the individual stressors by themselves.

Objectives

The objective of this project was to evaluate the synergistic chemical effects of 11 brand name disinfectants across four different active ingredient groups on 16 varied medical plastic materials. Using timed wipes and tensile testing, raw tensile strength, elongation, and modulus data were gathered to analyze potential synergistic effects. 

Approach

• A testing plan was developed using ASTM-D543 and D638, past testing methods, and through conversation with Americhem. 
• Between 120-200 Type I tensile specimens were injection molded to accommodate for testing needs. 
• The testing protocol involved straining 5 specimens at a 1.5% strain level for 72 hours. Every 24 hours, samples were wiped for a total of three wipes across this 72-hour span. Samples were tensile tested within 24 hours of removal from the fixture. 
• A three-point bend fixture was designed to expose samples to 1.5% strain. 
• A sample failed if it did not have at least a 70% retention of tensile strength and 90% retention of elongation, or a 90% retention of modulus (when applicable). 
• This entire process was first carried out to evaluate individual chemical effects, but then subsequently repeated to evaluate the application of multiple disinfectants on one component.  
• If a material failed any of these criteria, then it did not move on to be synergistically tested. 

Outcomes

• Amorphous materials resulted in 18% greater loss in averaged properties than semicrystalline
• Semicrystalline passed at least two of the chemicals except for the polypropylenes
• Fiber reinforced and impact modified did not have a greater retention than unmodified average
• Little evidence for synergistic effects in PPSU-2000RX and NY3-1030GFRX
• For the other synergistically tested materials, there was decreased retention of elongation and stable retention of yield strength as compared to the single chemical testing