Determination of the Cause of Mechanical Failure of Polypropylene Hollow Fibers

Siemens M9C polypropylene (PP) hollow fiber (HF) microfilters were used in water pretreatment to reverse osmosis in the Tactical Water Purification System (TWPS).  Numerous modules returning from deployment in Iraq and Afghanistan were severely degraded after even a short time of usage. The degradation was characteristic as many broken fibers. These fibers were so brittle that they could be easily crushed and broken by squeezing or stretching them.  

Various analytical tests were conducted to determine the most likely cause of the mechanical failure. Thermal, chemical, and mechanical material properties were evaluated by utilizing various Instruments including differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), fourier transform infrared spectroscopy (FT-IR), solid state nuclear magnetic resonance (NMR), melt and solution rheology, and mechanical testing system (MTS). The crashed samples showed less thermal stability than the virgin ones. In addition, the images of outer surface and cross-section were examined by scanning electronic microscopy (SEM).  The used samples showed clear cracks and larger and irregular pore size. Energy-dispersive X-ray spectroscopy (EDS) study showed significant amount of oxygen element on the used fibers outer surface and cross-section indicating possible oxidation. 

For comparison, properties of virgin PP HF samples and samples from other suppliers were evaluated. Analysis on pretreated PP HF samples under different simulated harsh environments was also performed. A novel analytical method, nano-thermal analysis (nano-TA) to examine the local thermal property at the nanoscale is under development.