Document k97R1b1kaLGwzvp1J4qY7o1Bn

XPS Analysis of Plastic Resin Pellets For Dupont Canada Inc. Research Centre Kingston, Ontario By Surface Science Western University of Western Ontario London, Ontario August, 1989 Prepared by: Dr. R. Foerch R.D. Davidson MafL: A pew *1 -fVf t* e.^'nrr. to sae.KJ i BOR 000420 introduc n Pellets of pvc, PE and ASS containing various levels of lead chromate (PbCrO.) have teen analyzed by X-ray photoelectron spectroscopy (X?S or ESCA) to determine the levels of lead actually on the surface of the pellets. Techniques such as IR and SEM have indicated high levels of ?b present on the surface, however both these techniques probe beyond depths of several hundred Angstroms into the sample,, thus probing the bulk polymer as well as the surface. XPS, on the other hand probes the first few monolayers to an approximate depth of 30-50 Angstroms. During XPS analysis a sample is irradiated with monochromatized X-rays of known energy causing the ejection of photoelectrons from all elements (except hydrogen) within the sample. The kinetic energy (E.^) of the ejected electron is equal to = EAl Ka * eb - Where E.. _ = energy of the incident photon and gAJ. ita 3 binding energy of the electron / eV 3 work function (usually negligible) Thus, by measuring E__ of the photoelectron and knowing E, , E- can be calculated. XPS provides both qualitative afti^tuantitative information on the elemental composition of the sample. Experimental X-ray photoelectron spectroscopy was performed on the polymer pellets using an SSX-100 Surface Science Laboratory X-ray photoelectron spectrometer which utilizes monochromatic Al Ka X-rays for excitation of the samples. The elemental broad scans were recorded using a pass energy of 148.00eV and an X-ray spot size of lOOOum or 600um analyzing binding energies between 0 and lOOOeV. Samples Al, A2, Bl, B2 and C2 were analyzed on the cylindrical, the end and on a fractured surface. On Al, A2 and B2 the cylindrical surface was sputtered for 2 minutes using Argon to probe deeper into the surface. Bl was sputtered on the fractured surface. Results XPS results have been tabulated in Table 1- and values are given in atomic %. They appear to indicate that when the bulk polymer is PVC, lead is detected even at a BOR 000421 concentration by weight of 2%. On the other hand if the hulk polymer was PE, lead is detected at a concentration level by weight of 50%, but is not detected if the concentration level is 2%. However, when the bulk polymer is A3S, no lead is detected. Samples Al, A2, 31 and B2 show levels of ?b on the cylindrical surface ranging from 1.2% to 0.01% which represents the detection limit of XPS for Pb. Upon sputtering the cylindrical surface (Al, A2, B2) for 2 minutes using Argon (to roughly a depth of 100 Angstroms), the amount of Pb very noticeably decreases suggesting lesser amounts of Pb further into the surface. Other elements detected were chlorine, silicon and very low levels of chromium in Bl. Barium and cadmium were detected in sample A2. Analyzing the end surfaces of samples Al and A2, similar levels of Pb were observed as on the cylindrical surfaces. Bl shows slightly more Pb on the end surface of the pellet, while B2 shows no Pb. Fractured surfaces of Al, A2 and B2 show similar levels of lead compared to the cylindrical surfaces. Bl shows a similar level of Pb on the fractured surface as on the outside cylindrical surface. When sputtering the fractured surface, XPS indicates an increased level of both Pb and Cr being exposed from further inside sample Bl. Chromium was also be detected on Al (cylindrical surface) and Bl (end and sputtered fracture). Sample C2 was extremely "clean", showing no Pb or Cr on any surfaces examined, even after sputtering. However, it was noticed that upon sputtering the relative % of N and 0 on the surface decreased. Otherwise all surfaces showed similar amounts of O and N. SEM Results A series of secondary electron SEM micrographs were obtained from samples Bl and B2. The micrographs are identified on an attached sheet. Table 4. The micrographs clearly show the difference in the pigment loading levels between 2% and 50% PbCr04 in the PE samples. The pigment particle size is approximately 0.5 - l.Oum. The different contrast levels for the particle (frcm bright white to a faint grey) suggest that the particles are at different depths within the matrix material. Pb X-ray BOR 000422 2. mapping was carried out on the 2% PbCrO. sample. The results show Pb, as expected, associated with the pigment particles. Conclusion The XPS results indicate that lead {PbCrO.) is present in small amounts on the surface of PbCrO, doped ?VC pellets. Upon sputtering deeper into the surface less Pb is detected. The concentration of Pb on the fractured surface is very similar to that on the cylindrical side, suggesting that the lead is present on the surface. Pb is detected in very small amounts in the PbCrO4 doped PE, even for the 50% doped pellets. The fractured surface shows similar amounts of Pb, yet upon sputtering, the concentration of Pb clearly increases. This indicates that even though some Pb is present on the surface, the majority is deeper inside the sample. In the PbCrO, doped ASS, lead and chromium are not detected on any surface. . Recommendations The objective of this preliminary study was to determine if PbCrO, pigment particles were exposed at the surface of the plastic resins. Intriguing XPS results, especially for the PVC samples, suggest that the pigment is concentrated at the surface. Further characterization with XPS and SEM may result in a better understanding of the location of the pigment particles in the PVC. It may be possible to carry out further SEM examination using stereo imaging to determine whether or not the pigment particles are standing proud of the surface. Further XPS analysis on additional samples may aid in this study. For example, XPS analysis of freshly fractured (perhaps cooled to liquid N, temperatures) resin pellets would provide a good 'bulh'^analysis to compare to the extruded cylindrical surfaces. --3-- BOR 000423 Tabic 1. XPS analysis of PbCrO^ containing polymer pellets. sample__________________ 1C 1H io ICr IPb 1C1 A1 33t PbCrO. in PVC cylindrical side 82.7 10.1 0.2 cyl. side sputtered 91.5 - 8.1 - endview 86.3 - 12.4 - fractured 79.2 ' 9.7 1.2 5.0 0.1 0.4 1.3 1.1 10.0 HOTC- *. 'THese VOLOt-e. isi 111a ll!d 1.0 - A2 21 PbCrO. in PVC cylindrical Side 78.6 9.3 0.3 10.4 0.8 0.7 cyl. side sputtered 91.2 - 3.4 - 0.04 5.3 - 0.1 endview 84.3 - 9.1 - 0.2 5.4 - 0.5 0.5 fractured 72.2 ' 4.7 0.1 22.9 0.2 0.1 Dl 50t PbCrO. in PK cylindrical side 97.3 2.7 0.03 endview 96.1 1.2 2.2 0.05 0.1 fractured 98.7 - 1.3 - 0.05 frac. side sputtered 93.3 0.3 4.5 0.8 0.6 - 0.35 - 0.6 B2 2% PbCrO. in PB cylindrical Side cyl. side sputtered endview fractured 99.2 98.2 99.2 100 1.1 - 0.85 0.75 0.8 - - 0.01 - - - . - BOR 0 0 0 4 2 4 C2 2\ PbCrOt in APS cylindrical side 90.3 4.9 4.3 0.5 cyl. side sputtered 95.1 2.0 2.9 - - - " endview 92.1 4.6 3.3 - - - - fractured 89.1 5.0 4.2 - - - 1.0