665
Anal. Chem. 1986, 58,665-667
Quantitative Measurement of Hydrogen Chloride Evolved from Polyolefin Polymers William L. Brueggemann NORCHEM, Inc., Technical Center, Morris, Illinois 60450 Producers of polyolefins are concerned with the corrosion potential of the chloride residues resulting from Ziegler-Natta based polymerization catalysts. Corrosion to molds and processing equipment is primarily due to the liberation of hydrogen chloride from the polymer at processing temperatures up to 300 "C. Polymer corrosion assessment potential clue to residual chloride has been performed by contacting metal coupons with the resin at a specific temperature (up to 300 "C), humidity, and time followed by visual or microscopic inspection of the metal coupon surface for deposits, pitting, rusting, or discoloration (1-6). Resin corrosivity ratings are variously scaled and, consequently, overlap of ratings is possible. In our laboratories we perform corrosion evaluation of polyolefins in a manner similar to the techniques reported in the literature (1-6). Visual methods of polymer corrosion assessments may require an analyst's subjective interpretation of the type and amount of corrosion present. Additionally, a significant amount of elapsed time occurs between sample preparation and evaluation of the polymer's corrosivity. Since the time between polymer sample preparation and visual corrosion assessment may range from 11/, h to as long as 24 h, these techniques are therefore, usually not suited for use in a quality control laboratory when accuracy and speed are needed to maintain product quality. An instrumental method has been reported (7) to measure bromine mainly as hydrogen bromide, evolved from flameretarded glass-fiber reinforced polyethylene terephthalate resins. The technique, with some modification, should be applicable to the measurement of hydrogen chloride evolved from polyolefins. The method, as described, requires the use of expensive equipment. This article details a simple, low-cost, rapid, and reproducible technique t,o evaluate polyolefin corrosivity by the quantitation of HC1 evolved from the polymer a t 300-320 OC within 45 min. Detection and quantitation are accomplished with Matheson-Kitagawa HC1 vapor specific stain length detector tubes.
EXPERIMENTAL SECTION Detector Tubes. Detection and quantitation of hydrochloric acid vapors are performed by use of the Matheson-Kitagawa HCl vapor specific stain length detector tubes, number 173s (Matheson Safety Products, East Rutherford, NJ). Each package contains five individual sealed glass silica gel pretreat tubes, five individual sealed glass stain detector tubes, and a piece of tubing to connect the tubes together. Calibration of the HCl vapor detector tubes is performed in the following manner. A chromatographic injection port was fabricated from a stainless steel reducer--"/, in. fractional tube to a '/* in. tube stub. A -"/le in. hole was drilled through a wrench flat into the center of the reducer. A length of '/le in. 0.d. X 0.040 in. i.d. stainless steel tubing was silver soldered into the in. hole. The ' / l e in. tubing is connected to helium gas previously set at a flow rate of 20 mL/min. A septum is cut to fit the 'is in. tube nut on the reducer. Figure 1 is a drawing of the device. The pretreat tube (for absorbing small amounts of water, vapor or liquid) is scored and broken at a point that, when connected
to the l/q in. tube stub, the syringe needle tip will introduce the HC1 calibration solution approximately 1cm into the absorbent. Prior to connection t o the tube stub the paper plug is removed. The tapered end of the pretreat tube is scored and broken and the paper plug left in place to prevent the absorbent from entering the stain detector tube. The detector tube is scored and broken approximately 1cm from the starting point of the stain detection material. The tapered end of the detector tube is scored and broken. The pretreat tube is connected to the in. tube stub with the tubing in the package. The detector tube is connected as close as possible to the tapered end of the pretreat tube with tubing from another package of detector tubes. A 1.0-pL syringe (Hamilton 7101N) is used to introduce 0.25, 0.50, and 0.75 ,uL as a 0.05 N HCl solution (1.83pg of HCl/WL) through the reducer septum into the pretreat tube absorbent. Separate combinations of pretreat and indicator tubes are used for each volume of HCl solution, and the calibration is performed in duplicate. Thirty minutes after introduction of the standard the stain length detector tube is removed from the reducer and the stain length measured (h1.0 mm). Procedure. The following system was devised to utilize the HCl vapor specific detector tubes to measure the amount of HCl evolved from polyolefins at elevated temperatures. Helium, at a flow rate of 20 mL/min, was bubbled through 200 mL of distilled water in a 250-mL gas washing bottle with a coarse frit filter stick connected to one end of a Pyrex sample tube (220 mm x 12 mm 0.d. X 10 mm id.) containing from 2.5 to 3.0 g of polymer powder or pellets, accurately weighted. The polymer was retained by glass wool plugs in the sample tube, such that the polymer sample was completely within the heating area of the tube furnace (catalog number S-36400, Sargent-Welch Scientific, Co., Skokie, IL). Additionally, the polymer was evenly distributed in the sample tube by gentle tapping so that no obstruction would occur to the water-saturated helium gas flow when the polymer melted. The exit of the sample tube was connected first to the pretreat tube, the inlet of which had the paper retainer plug removed, and then to the stain detector tube. The sample was placed in the tube furnace and heated at a temperature of 300-320 "C for 30 min. After this heating time the sample tube was removed from the heating chamber and cooled for several minutes and the pink stain length measured (h1mm). Figure 2 shows the apparatus used. Early in the work, it was found necessary to remove the paper plug at the inlet to the pretreat tube. (The other plug is left in place.) Water vapor condensate and condensed polymer oligomers on the paper plug reduced the gas flow resulting in a pressure buildup in the system causing disruptive separation of the components joined together by rubber tubing. The specific heating time, temperature, and the presence of water vapor in the helium purge gas used in this work are based upon an accelerated visual polymer corrosivity evaluation technique used in our laboratories (8). Corrosion ratings in our method, involving carbon steel coated glass slides, range from 1 to 5 with 1having little or no rusting or discoloration to 5 showing total rusting or metal removed from the mild carbon steel coated glass slide.
RESULTS AND DISCUSSION Calibration of the HCl vapor specific detector tubes gave a value of 39.0 mm with a standard deviation of *2.4 mm for 1.0 kg of HC1. The calibration graph of all data points was linear and the least-squares line of best fit of the data passed through the origin of the graph.
0003-2700/86/0358-0665$01.50/00 1986 American Chemical Society
806
ANALYTICAL CHEMISTRY. VOL. 58. NO. 3, MARCH 1986
Table 1. Corrosion Rating8 and HCI Emissions of Polypropylene
C
corrosion sample identification
rating
!
HCI emission, pg of HCl/g 0.09 0.35 0.13 0.14 0.04
G
2
H I J
1 1 1 3 4
K L
F l p n 1. Tube ('I8in.) to tube stub ('I, h.)in)emon port: (A) 'I8in. tube nut: 161 reversed '1. in. beck fwuk IC1 seotum: ID1 '1.. in.
2. Apparatus sew used to measure Hci evolved from poly-
olefins.
The reproducibility of measuring HC1 emissions from a polymer was determined on a randomly selected resin sample and analyzed 12 times. The emission level for this particular sample was determined to be 0.36 pg of HCI per gram of resin with a standard deviation of *0.04 pg of HCI per gram of polymer. Our visual corrosion teat (8) on a resin chosen for a l a b ratory standard yielded a rating mean of 2 and a standard deviation of f l corrosion rating units. Table I shows the visual corrosion ratings as determined by our laboratory method and the measured amount of HCI evolved from various stahilized polymer pellet samples. The data in Table I demonstrate that the visual evaluation of corrosion may he highly subjective to an analyst's interpretation of the corrosion of the carbon steel coated glass slide and does not, therefore, completely agree with the measured HCI emissions from the resin. Unpublished data generated in our laboratories indicate that 0.154.18 pg of HCI per gram of polymer should not exceed our corrosion rating maximum of 2. A number of major diaerepancies between visual corrosion and HCI emissions on the anme polymer sample could not be attributed solely to the analyst's interpretation of the a p pearance of the carbon steel coated glass slide. Investigation indicated that several commonly used polymer additives were degrading above 250 'C with the release of hyproducts, and
0.15 0.15 0.05 0.25 0.13 0.39 0.36
not HCI, which are 88 corrosive to mild carbon steel as is HCI. Thus, based upon the above unpublished findings in our laboratory, evaluating a stabilized polyolefin for corrosivity and assuming corrosion is due only to HCI may not be a fair assessment of the polymers corrosion potential. To assess a polymer's corrosivity due only to HC1 emissions, it is, therefore, recommended to measure HCI emissions on the resin prior to compounding with stabilizers. Evaluating the corrosivity of a stabilized resin will require the application of a combination of methods to differentiate between corrosion caused by HCI emissions and corrosion caused hy temperature-degraded additive byproducts or degraded polymer byproducts. No correlation was found between total chloride content of polyolefins and corrosiveness evaluated either hy visual m e y s or by measurement of HCI emissions. Any technique to measure the total chloride content of a polymer would include bound organic chloride, inorganic chloride as well as HCI (9). Currently, many polyolefin manufacturers using ZieglerNatta based polymerization catalysts incorporate in their process a catalyst residue removal/reduction step or a dechlorination operation to reduce the corrosion potential of the chloride residue. Additionally, acid scavengers are incorporated in the polymer to minimize the corrosion potential of the resin even after dechlorination or catalyst residue reduction. Dechlorination efficiency a t steady-state conditions has been monitored by use of the HCI vapor specific detector tubes in the manner described above. Analytical data measured on a polyolefm produced over a 24-h period, showed a maximum HCI emission level of 0.08 pg of HCI per gram of polymer. This amount of evolved HCI would he equivalent to a 1 corrosion rating according to our laboratory method. Thus, dechlorination or catalyst deactivation can be monitored on a continuous basis with dechlorination excursions being rapidly detected and speedily corrected. The effectiveness of an experimental acid scavenger was demonstrated with an undechlorinated polyolefin. The resin had been compounded originally with 360 ppm (by weight) of the acid scavenger and had an HCI measured emission of 0.34 pg HCI per gram of resin. Incremental additions of the experimental acid scavenger amounting to 250,500 and lo00 ppm (by weight) were compounded in the resin. By use of the method described herein, a nearly linear decrease in HCI evolution was measured, which approached a plateau a t the 860 ppm (360 + 500 ppm) acid scavenger level. At this level the HCI emission was 0.11 pg HCI per gram of resin. A total of 1360 ppm (360 + lo00 ppm) only reduced the HCI emission to 0.08 pg HCI per gram of polymer. The above data show the effectiveness of the experimental acid scavenger and also demonstrated that any further ad-
667
Anal. Chem. 1986, 58,667-668
dition of the acid scavenger greater than the 500 ppm added increment is unnecessary for the reduction in HC1 emissions achieved. Registry No. HCl, 7647-01-0; chloride, 16887-00-6; polypropylene (homopolymer), 9003-07-0.
LITERATURE CITED (1) BASF Aktiengeseiischaft, United Kingdom Patent 1439 948, 1976. (2) Bora, J. S.Corros. Sci. 1979, 14,503-506. (3) Shigeo Miyata, Takamatsu; Masataka, Kagawa United States Patent 4 284 762, 1976. (4) Shigeo Mlyata, Takamatsu; Masataka, Kagawa United States Patent 4 347 353, 1982.
(5) Schroeder, Waiter C.; Webster, Joseph R. United Kingdom Patent 1514903, 1978. (6) Lin, Chi-Hung United States Patent 4420609, 1983. (7) Hecht, James L.; Garrison, Wiiiiam E. Polyrn-Plast. Techno/. Eng. 1982, 18 (l),109-122. (8) NORCHEM, Inc., Morris, IL, Method Number 9107.2,1983. (9) Haslam, J.; Willis, H. A,; Squirell, D.C. M. "Identification and Analysis of Plastics", 2nd ed.; Iiiffe Books: London, 1972;Chapter 6.
RECEIVEDfor review June 26,1985. Accepted October 7,1985. The author wishes to express his appreciation and thanks to the management at NORCHEM's Technical Center, Morris, IL, for permitting publication of this work.
Separation of Tracer Titanium-44 from Vanadium Munawwar Sajjad' and Richard M. Lambrecht*'
Department of Chemistry, Brookhaven National Laboratory, Upton, N e w York 11973 The trend in medical radionuclide and radiopharmaceutical research and development is toward the use of short-lived neutron-deficient nuclides. Biomedical generators ( I ) that deliver positron-emitting nuclides will be an important source (t1/2= 4 years), of these nuclides. The 4d/ri/"Sc generator ["i 44Sc (tlIz = 3.93 h)] has been suggested previously (2-4). Furthermore, w7Sc has been suggested as a potential scanning agent for tumor and bene marrow (5) and for metabolism studies (6, 7). Syed and Hosain (8) proposed %c for studying bone diseases by positron emission tomography. Titanium-44 produced by the 45S~(p,2n)44Ti reaction is commercially available only in very limited quantities. We have found that 44Ti can also be produced by the 51V(p,2p6n)44Tinuclear reaction by irradiating a vanadium target with high-energy protons. A new separation method was required in order to recover 44Tiwithout added carrier. Kanza-Kanza et al. (9) reported a procedure for the simultaneous separation of carrier-free 4sCr,45Ti,and 44Scisotopes from cyclotron-irradiated Vz05, but the recovery yield of Ti was not indicated. Nelson et al. (13)have shown that vanadium can be separated from titanium if both are in the plus four valence state. We have developed a new method for the separation of titanium from vanadium.
EXPERIMENTAL SECTION Two vanadium disks (305 mg/cm2) of 99.7% purity were irradiated at the BNL Linac Isotope production facility with 50100-yA beams of 200-MeV protons to a fluence of 7775 and 5273 yAh, respectively. A sample assayed after 1 year indicated 46Sc, 44Ti,22Na,7Be, 54Mn,and were present. 44Ti/44S~ were the main isotopes present after a 10-year cooling period as shown in Figure 1. The activity is mainly due to 4Ti/"Sc, but 22Naand @Coare also present. Gamma spectrometry was obtained by using a 45-cm3Ge(Li) detector (full width at half-maximum of 1.87 keV at 1.33-MeV photopeak of 6oCo,peak-to-compton ratio of 32:1, and an efficiency of 7.7%) in conjunction with a Canberra Series 90 pulse-height analyzer. Titanium and vanadium in the final separated samples from the nonradioactive work were analyzed by X-ray fluorescence spectrometry. Neutron activation analysis (NAA) was used for the 44Tisamples. RESULTS AND DISCUSSION The method was developed by use of nonradioactive vanadium and titanium metal. Typically, 50 mg of V and 5-13 mg of T i were dissolved in aqua regia. The solution was Present address: Radionuclide and Cyclotron Operations, King Faisal Specialist Hospital and Research Centre, Box 3354, Riyadh 11211, Kingdom of Saudi Arabia.
evaporated to dryness. Vanadium was converted to Vz05 and titanium to TiOz. It is important to use HCl-HF media for the separation, Titanium dissolves in hot HCl but tends to precipitate even in concentrated acid. The best solvent is H F or acids to which fluoride ions have been added. Such a media dissolves titanium and holds it in solution as the fluoro complex. Four milliliters of 2 M H F and 1 mL of concentrated HC1 were added to the dried Vz05and Ti02. Ti(1V) forms a strong complex with F-, Le., TiF:-. Hydroxylamine hydrogen chloride was used to reduce V(V) to V(1V). The following standard potentials have been reported ( 2 1 , 12)
VOz+ + 2H+ + e = V02+ + H20 Eo = 1.0 V (1)
+ 2H+ + e = Ti3+ + H 2 0
Ti02+(aq)
Eo = 0.1 V
(2)
The standard potential of V(V) - V(1V) is higher than the Ti(1V) - Ti(II1) standard potential; therefore V(V) will be reduced to V(1V) before Ti(1V) will be reduced to Ti(II1). As Ti is bound as TiFs2-, it will be more difficult to reduce titanium. The exact weight of the vanadium target was known. Therefore the number of moles of NH20H-HC1needed to reduce V(V) to V(1V) was calculated by using a 1:l proportion. The weighed NH20H.HC1 was dissolved in water. A solution of NH20H.HC1 was added slowly while stirring. Insoluble Vz05 will start dissolving as V(V) is reduced to V(1V) forming the blue [VO(H20)5]2+ ion. The solution was heated to boiling for 10 min after the addition of NH20H-HC1. The solution was cooled and diluted to the final acid concentration of 0.1 M HCl-1 M HF. The solution was passed through a Dowex 1X-2 (50-100 mesh) anion-exchange column (1X 10 cm). The column was prewashed with 0.1 M HC1-1 M HF. After the dissolved target solution was eluted, the column was washed with 0.1 M HCl-1 M H F till the column was visually free of the blue vanadium solution. [VO(HzO)5]2+ was passed through the column, whereas TiF:was retained on the column. Titanium was eluted with 6 M HC1-1 M HF. The solution was evaporated to dryness, and titanium was taken up in dilute HC1 for analysis. The samples were analyzed by X-ray fluorescence spectrometry. The titanium recovery was 97 2%, and the vanadium contamination was 0.02%. The vanadium concentration can be further reduced by repeating the procedure. Separation of 44Tifrom Irradiated Vanadium Target. Figure 2 depicts a flow diagram of the radiochemical scheme used for the separation of 44Ti. Nine grams of irradiated vanadium metal was reacted with aqua regia. Thirty milliliters of concentrated HF and 8 mL of concentrated HCl were added
0003-2700/86/0358-0667$01.50/00 1986 American Chemical Society
*
