Reduction of particle embedding in solid particle erosion of polymers

Particle embedding can be an unwanted consequence of abrasive jet micromachining (AJM) of polymeric materials. The embedding of aluminum oxide particles into acrylonitrile butadiene styrene (ABS), polytetrafluoroethylene (PTFE), polydimethylsiloxane (PMDS) and polymethylmethacrylate (PMMA) was studied under cryogenic and room temperature conditions. Scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX) showed the fractional area coverage by embedded Al2O3 particles after room temperature AJM to be: 16% (ABS), 19% (PTFE), 25% (PDMS) and 3.2% (PMMA). Under cryogenic conditions, however, the fractional area coverage of embedded Al2O3 was found to be significantly reduced: 10% (ABS), 0.8% (PTFE), and 1.6% (PDMS). For PMMA, it was demonstrated that the surface was shielded by the embedded particles, resulting in an erosion rate that decreased with increasing embedded particle coverage. Several methods for the removal of embedded particles were also studied. A first step of blasting with spherical glass beads dislodged some of the Al2O3 particles embedded during AJM so that the fractional area coverage by embedded Al2O3 particles was reduced to 1.1% from 3.2% for PMMA. After this glass bead blasting, a further reduction in embedded particles could not be achieved by ultrasonic cleaning the PMMA samples with distilled water or with NaOH. However, more embedded particles could be removed using a freezing technique where the samples were first dipped in NaOH mixed with detergent or distilled water and then frozen by immersion in liquid nitrogen for 5 min after which the samples were allowed to warm to room temperature. For samples machined under cryogenic conditions, this freezing technique applied after the preliminary glass bead blast, reduced the area coverage of Al2O3 to 4% for ABS, 0.5% for PDMS and to almost 0% for PTFE. Finally, for PMMA machined at room temperature, using either the freezing method or an adhesive tape to pull out the embedded particles resulted in less than 0.5% embedded Al2O3 coverage. Since it was effective for all the studied polymers, it is recommended that glass bead blasting at 45 degrees followed by the freezing technique be used to substantially reduce particle embedding after AJM. (C) 2011 Elsevier B.V. All rights reserved.