417
Ind. Eng. Chem. Prod. Res. Dev. 1985, 2 4 , 417-420
Table 111. Spattering Property of Flat Paints Thickened with Various Polymers spattering thickener description of thickener rating“ 1 high molecular weight 3 hydroxyethylcellulose (HEC) 2 medium molecular weight hydrophobically 8 modified HEC 3 low molecular weight nonionic 0 hydrophobically modified polyacrylamide 4 low molecular weight anionic 1 polyacrylamide 5 low molecular weight cationic 2 hydrophobically modified polyacrylamide a Spattering rating was baaed on standard rolling method used in paint industry. Rating 10 is the best (no spattering at all), and rating 0 is the worst.
tional-rotational Brownian motion dominant regime in which G”(w) > G’(w) occurs a t a frequency w lower than 0.1 rad/s. However, the regime can appear at a much higher frequency (>lo rad/s) for low latex contents. The difference can be attributed to the larger loss of configuration entropy of steric barriers adsorbed on latices for dispersions containing higher latex concentration. The correlation between G”(w),at low w , and paint leveling was found to be excellent. However, the correlation of G’(w) with leveling does not appear to be good. This suggests that viscosity is the leveling-controllingparameter. Results confirm the validity of Murphy’s equation relating
the change of brushmark amplitude with time. Convergent flow analysis aided by photographic technique was applied to determine the extensional viscosity of paints. The accuracy of the rheological measurement with this device was found to be satisfactory. For a Newtonian fluid the determined extensional viscosity obtained from convergent flow analysis is approximately equal to 3 times the shear viscosity. For paints thickened with certain polymers, such as polyacrylamides, the extensional viscosity was found to increase with the applied stress. It was found that paints showing increasing extensional viscosity with applied stress have very poor spattering property. Literature Cited Bird, R. B.; Armstrong, R. C.; Hassager, 0.“Dynamics of Polymeric Liquids”; Why: New York, 1977; Voi. I , p 187. Cogswell, F. N. Rheol. Acta 1069, 8 , 187. Cogswell, F. N. Po/ym. Eng. Scl. 1072, 72(1), 64. Coiclough, M. L.; Smith, N. D.P.; Wright, T. A. J . Oil Colour Chem. Assoc. 1980, 63, 183. Craig, D. H., personal communication, 1983, Hercules Inc. Glass, J. E. J . Coat. Technol. 1078. 50(641), 56. Lin, 0.C. C. CHEMTECH 1075, 5 , 51. Milkie, T.; Lok, K.; Croucher, M. D. Colloid Po/ym. Scl. 1982, 260, 531. Murphy, J. PRA internal report, RS/T/31/68. Patton, T. C. “Paint Flow 8 Pigment Dispersion”, 2nd ed.; Wiiey: New York, 1979; Chapter 28. Quach, A. Ind. Eng. Chem. Prod. Res. D e v . 1073, 72, 110. Smith, N. D. P.; Orchard, S. E.; Rhind-Tutt, A. J. J . Oil Colour Chem. Assoc. 1061, 4 4 . 618. Smith, R. E. J . Coat. Technol. 1982, 54(694), 21. Van de Ven, T. 0. M.; Hunter, R. J. Rheol. Acta 1977, 76, 534. Vinogradov, G. V.; Malktn, A. Ya. “Rheology of Polymers”; Springer-Veriag: New York, 1980; Chapters 1, 7.
Received f o r review October 1, 1984 Accepted April 29, 1985
The Effects of Metals and Inhibitors on Thermal Oxidative Degradation Reactions of Unbranched Perfluoroalkyl Ethers Wllllam R. Jones, Jr.,” Kazlmlera J. and Relnhold H. Kratzert
L. Paclorek,t David H. Harris,+Mark E. Smythe,t James H. Nakahara,’
NASA Lewis Research Center, Cleveland, Ohio 44135
Thermal oxidative degradation studies were performed on unbranched perfluoroalkyl ethers at 288 O C in oxygen in the presence of metals and alloys. The pure metals, titanium and aluminum, promoted less degradation than Ti(4A1,4Mn) alloy. The two inhibkors Investigated (a (perfluoropheny1)phosphlneand a phosphatKiazine) reduced degradation rates by several orders of magnitude: both were effective for the same duration (75-100 h).
Introduction
Unbranched perfluoroalkyl ethers developed by Montedison (Sianesi et al., 1973), in view of their remarkable temperature-viscosity properties (Snyder et al., 1981), nonflammability (Snyder et al., 1982),and thermal stability (Jones et al., 1983), offer great potential as high-temperature lubricants. Unfortunately, these materials, as reported earlier (Jones et al., 1983; Snyder et d., 1981), were found to undergo decomposition in oxidizing atmospheres below 288 OC. This reaction was greatly Ultrasystems, Inc., Irvine, CA 92714. O196-4321/05/ 1224-O417$01.50/0
accelerated by the presence of alloys M-50 and Ti(4A1,4Mn). On the other hand, low concentrations of additives were found to arrest the process virtually entirely. Both for basic understanding and for practical applications, it is necessary to know the effect of different metals and alloys on the stability of these fluids. It has been established (Paciorek et al., 1979) that in the case of commercially available poly(hexafluoropropene oxide) fluids (Krytox series, product of Du Pont) additives are effective for limited time only. Thus, the objective of the current study was to evaluate the action of pure metals on the unbranched perfluoroalkyl ethers and to assess the effectiveness of the degradation inhibitors with respect to 0 1985 American Chemical Society
418
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 3, 1985 TIME, hr
10.0
+ 3 V n
za
1t
8
t
w i
m
v,
z z
W
n
8 LL
0
+ a W
E
Al CATALYST (4A1, 4Mnl
Figure 1. Effect of metals on the degradation of perfluoroalkyl ether MLO-79-196 at 288 OC, 02.(Arrows indicate sequential tests using the same fluid sample.)
concentration and test duration.
Experimental Section The degradation studies were performed by using the procedures and the apparatus described previously (Paciorek et al., 1979). Unless specifically stated, the tests were carried out neat on 3-4 g of fluid in oxygen at 288 "C over a denoted period of time. Degradation rate is calculated from the amount of liquid nitrogen condensibles formed and is reported as milligrams of condensible product per gram of original fluid per hour. Each of the individual tests in the series, presented in Figure 2, was performed for the period of time denoted in Table I. At the end of each period, the volatiles were removed, measured, and analyzed. Subsequently, fresh oxygen was introduced and the residual fluid plus coupon were heated for the next designated period. For the mass spectral investigations, a Du Pont 21-491B double-focusing mass spectrometer was employed using an ionizing voltage of 70 eV and an ion-accelerating voltage of 1400 V. The perfluoroalkyl ethers investigated were the Fomblin Z fluids, products of Montedison Co., which were obtained from the US.Air Force Materials Laboratory. The specific batches employed were MLO-72-22 and MLO-79-196. These are US.Air Force Materials Laboratory designations; the first two numbers refer to the year in which the fluid was received. The metals evaluated [M-50 steel, Al, Ti, and Ti(4A1,4Mn)] were in the form of disks, 9.5 mm o.d., 3.2 mm i.d., and 0.94-1.27 mm thick, obtained from the Metaspec Co., San Antonio, TX. Two different degradation inhibitors were used in these studies. The perfluoroalkyl ether substituted (perfluoropheny1)phosphine (designated P-3), compound I (obtained CC3F,0CF(CF3)CF,0CF(CF3)CF,
-@-l3P
I
from the U.S.Air Force Materials Laboratory), was previously reported by Snyder et al. (1979). The perfluoro-
Table I. Effect of Metals and Inhibitors on the Thermal Oxidative Behavior of Unbranched Perfluoroalkyl Ether in Oxraen at 288 "C sample degradation testa size, g metal inhibitor rate, mg/(g h) 36 3.34 M-50 1% C2PN3* 0.01 (24)' 37 3.57 M-50 1% P-3d 0.04 (24) 38 2.65 M-50 none 28.1 (15) 41 3.84 Ti(4A1,4Mn) none 72.8 (8) 42 3.67 0.047 (24) Ti(4A1,4Mn) 1% P-3 46A 3.60 Ti(4A1,4Mn) 1% P-3 0.032 (72) 46B 3.58 Ti(4A1,4Mn) 1% P-3 5.0 (48) 55A 4.94 Ti(4A1,4Mn) 1% P-3 0.026 (86) 55B 4.92 Ti(4A1,4Mn) 1% P-3 0.11 (16) 55c 4.91 Ti(4A1,4Mn) 1% P-3 0.19 (8) 55D 4.90 Ti(4A1,4Mn) 1% P-3 1.72 (16) 54A 3.81 Ti(4A1,4Mn) 1%CzPN3 0.028 (24) 54B 3.81 Ti(4A1,4Mn) 1 % CzPN3 0.014 (48) 3.80 3.37 (28) 54C Ti(4A1,4Mn) 1% C2PN3 56A 4.03 Ti(4A1,4Mn) 0.2% CzPN3 0.040 (24) 56B 4.02 Ti(4A1,4Mn) 0.2% C2PN3 0.043 (24) 56C 4.02 Ti(4A1,4Mn) 0.2% C2PN3 0.066 (24) 56D 4.01 Ti(4A1,4Mn) 0.2% C2PN3 0.13 (8) 0.10 (8) 56E 4.01 Ti(4A1,4Mn) 0.2% CzPN3 56F 4.01 Ti(4A1,4Mn) 0.2% CzPNB 0.13 (8) 56G 4.00 Ti(4A1,4Mn) 0.2% CzPN3 0.24 (8) 56H 4.00 Ti(4A1,4Mn) 0.2% C2PN3 27.2 (24) 3.15 72A' none none 0.51 (24) 3.10 72B none none 0.45 (24) Ti(4A1,4Mn) none 75.9 (8) 73' 3.67 3.56 Ti none 5.6 (8) 74A' 74B 3.42 Ti none 29.6 (16) 3.50 A1 none 75Ae 12.3 (8) 3.16 A1 none 75B 7.9 (8) 75c 2.93 A1 none 4.13 (16) 'Fluids used, unless otherwise indicated, were pretreated at 343 "C in oxygen for 24 h; in the series of runs denoted by consecutive letters of the alphabet, the residue of the preceding test was employed after removal of the volatiles and oxygen replenishment; in the experiments up to run 61, the batch MLO-72-22 was employed; starting with test no. 72, MLO-79-196 was used. *Compound 11. 'The value in parentheses corresponds to the time of exposure in h. dCompound I. eIn these tests, the MLO-79-196 fluid was used as received.
alkyl ether substituted monophospha-s-triazine (designated C,PN,), compound 11, was described by Kratzer et al. (1977). (CpsH5)2
C3F,OCF(CF3)CF,O(CF3)CFC,
'M
\T
/CCF(CF3)OCF,CF(CF3)OC3F7 N'
I1
Results and Discussion The tests performed are summarized in Table I. The two fluid batches, MLO-79-196 and MLO-72-22, exhibited essentially identical behavior as evident from the comparison of runs 41 and 73, thus allowing direct comparisons between current and past investigations. On the basis of the results presented in Table I and Figure 1,it is apparent that the pure metals yielded definitely lower degradation rates than did the alloy [Ti(4A1,4Mn)]. It is noteworthy that the degradation rate increased with time for titanium but decreased for aluminum. This is surprising since, according to Gumprecht's (1967) postulations, one would expect aluminum fluoride to be the species responsible for chain scissions, and thus the rate of degradation should increase with time or at least stay constant. Previously reported preliminary work (Jones et al., 1983) had shown that two inhibitors, a (perfluoropheny1)phosphine, (P-3), compound I, and a phosphatriazine (C2PN3), compound 11,were highly effective in arresting degradation of the fluids in the presence of alloys and oxygen at 288
Ind. Eng. chem.Rod. Res. Dev.. Vol. 24. No. 3. 1985 418
"F0
NO INHIBITOR
Figure 4. SEM of M-50 metal from test 31 (unbranched perfluoroalkyl ether, 288 'C, Of,P-3 inhibitor).
Figure 2. Effect of inhibitors on degradation of unbranched perfluoroalkyl ether at 288 "C.0 , Ti(4A1,4Mn).
Table 11. Chromium and Vanadium Concentration ( R a t i d M Fe) for M-50 Metal Determined by Energy Dispersive X-rav Andvsia test
unused M-50 36 31 38
Figure 3. SEM of M-50 metal from test 38 (unbranched perfluoroalkyl ether. 288 OC. 02,nn inhibitor).
OC in short-term tests but had only limited effectiveness at 316 'C. In the present study, a series of tests was run for a longer time duration (up to 128 h) at 288 OC in oxygen using 1and 0.2 wt % concentrations of inhibitors. These data are expressed in graphical form in Figure 2. Both series of tests employing 1% concentrations of P-3 and C,PN, afforded similar results showing the additives' effectiveness of 75-100 h. Using 0.2% of the C,PN, inhibitor under otherwise identical conditions resulted in a gradual increase in degradation rate with test duration time. Surprisingly, however, the loss of effectiveness occurred in the same exposure range as that observed for the 1% concentration test (-100 h). In the absence of inhibition, extensive corrosion of the surface occurred. This is illustrated in the scanning electron micrograph of an M-50coupon surface shown in Figure 3. In contrast, little surface corrosion occurred in the presence of the inhibitor P-3 (Figure 4) (note the change in magnification). On the basis of the results of energy dispersive X-ray analyses (EDX) of the dark spots and the larger light areas, it appears that local depletion of chromium and vanadium occurred in the light areas while an enhancement took place in the dark areas. The results for large area EDX analyses for each M-50 metal surface for tests 36 (C,PN3 inhibitor), 37 (P-3inhibitor),
inhihiinr
cr
0.105 monophwpha-s-triazine 0.103 (perfluoropheny1)phnsphine 0.104 none 0.102
v 0.043 0.045 0.044 0.045
and 38 (no inhibitor) aa well as an unused specimen appear in Table 11. It is obvious that all specimenshave the same overall chromium and vanadium surface composition, showing that at this relatively low degree of etching, material attrition is absent. lt can be deduced that prolonged exposure would result in depletion of certain elements, i.e., chromium and vanadium. Earlier work (Paciorek et al., 1977) using hexafhoropropene oxide derived fluids showed depletion of these metals on the surface. Extensive chain scisaion in the presence of metal alloys, in particular Ti(4A1,4Mn) alloy, was clearly shown in the earlier studies (Jones et al., 1983) by the quantity of low molecular fragments involatile a t -78 'C and by the ratio of oxygen consumed to volatile products formed. Attempts were made to identify components other than carbonyl fluoride, in particular since in some instances these amounted to -50% of the degradation products collected. When combined gas chromatography/mass spectrometry on methanol-treated materials is used, the latter to transform the terminal COF groups to methyl ester moieties, only the relatively low molecular weight compounds could be identified due to extensive fragmentation and absence of molecular ions. This behavior has been reported also by others (Scherer et al., 1983). The compounds identified are listed in Figure 5.
Conclusions Pure metals, titanium and aluminum, promote less degradation of unbranched pertluoroalkyl ether fluids than do alloys such as Ti(4A1,4Mn). This shows that one cannot use data obtained with pure metals to predict the behavior of fluids with alloys. In the case of steel alloy M-50, fluid degradation was found to be associated with local surface depletions of chromium and vanadium, indicating the active role the latter metals seem to play in catalyzing degradation. Both of the inhibitors investigated were found to be effective in arresting essentially totally, for up to 100 h, the fluid's decomposition at 288 OC in oxygen in the presence of Ti(4A1,4Mn) alloy. Both provided metal
Ind. Eng. Chem. Prod. Res. Dev. 1985, 2 4 , 420-425
420
bricants, and Elastomers Branch.
+-CF2
COF
1 CF3 0 C F p - - l r y G
t
I
I
CH30H
C f 5 0 C F p 0 CF3 t
Cf5OCF20CF2CFpOCF3 t
C f 5 0 CF2 0 CF2 CF2 0 CF2 0 CF3 t
CF3 0 CF2CF2 C 0 2 C H 3 i
C F 3 0 CF2CF2OCF2CF2 OCF2C02CH3
Figure 5. Products obtained on degradation of an unbranched perfluoroalkyl ether in the presence of Ti(4A1,4Mn) at 288 " C in 0%.
surface protection as compared to the absence of additives. The few products identified confirmed the structural arrangement of Fomblin Z type fluids and proved further the chain scission mechanism. Acknowledgment We acknowledge the assistance of C. E. Snyder of the Air Force Wright Aeronautical Laboratories, Fluids, Lu-
Registry No. I, 60950-97-2; 11,65288-70-2; M50 (tool steel), 12725-39-2;Al, 7429-90-5; Ti, 7440-32-6; Ti(4Al, 4Mn), 12633-21-5; Cr. 7440-47-3; V, 7440-62-2; fomblin Z, 64772-82-3.
Literature Cited Gumprecht, W. H. "The Preparation and Thermal Behavior of Hexafluoropropylene Epoxide Polymers", presented at the Fourth International Symposium on Fluorine Chemistry, Estes Park, CO, July 1967. Jones, W. R., Jr.; Paciorek, K. J. L.; Ito. T. I.;Kratzer, R . H. Ind. Eng. Chem. Prod. Res. Dev. 1983, 22, 166. Kratzer, R. H.; Paciorek, K. J. L.; Kaufman, J.; Ito, T. I.J . Fluorine Chem. 1977, 10, 231. Paciorek, K. L.; Kratzer, R. H.; Kaufman, J.; Nakahara, J. H. "Determination of Fluorocarbon Ether Autoxidative Degradatlon Mechanism", Wright-Patterson Air Force Base, OH, AFML-TR-77-150, 1977. Paciorek, K. J. L.; Kratzer, R. H.; Kaufman, J.; Nakahara, J, H. J . Appl. folym. Sci. 1979, 24, 1397. Scherer. K. V., Jr.; Yamanouchi, K.; Ono, T. "Structure Elucidation of Perfluorochemicals by Negative Chemical Ionization Mass Spectrometry: Application to F-Alkanes, Ethers and Amines, and Comparison with E1 and PCI Mass Spectra", presented at the Sixth Winter Fluorine Conference, Daytona Beach, FL, Feb 1983. Sianesi, D.; Pasetti, A,; Fontanelli, R.; Bernardi, G. C.; Caporiccio, G. C h h . Ind. (Milan) 1973, 55, 208. Snyder, C. E., Jr.: Tamborski, C.; Gopal, H.; Svisco, C. A. Lubr. Eng. 1979, 35, 451. Snyder, C. E.,Jr.; Gschwender, L. J.; Tamborski, C. Lubr. Eng. 1981, 3 7 , 344. Snyder, C. E.. Jr.; Gschwender, L. J.; Campbell, W. B. Lubr. Eng. 1982, 3 8 , 41.
Received for review September 24, 1984 Accepted April 1, 1985
Reactions of Molten Urea with Formaldehyde? Thomas P. Murray Department of Chemistry, University of North Alabama, Florence, Alabama 35630
Ernest R. Austln," Robert G. Howard, and Timothy J. Bradford International Fertilizer Development Center, Muscle Shoals, Alabama 35662
When small amounts of formaldehyde are added to molten urea during manufacture, the physical properties of the urea are improved. Several compounds resulting from the urea-formaldehyde reaction become impurities in the urea matrix. In this study, high performance liquid chromatography (HPLC) has been used to analyze the products formed as a result of this conditioning process. A new compound, biuretmethyleneurea,has been isolated from formaldehyde-conditioned urea. The reaction of molten urea with paraformaldehyde has been studied and the reaction products have been analyzed for methylenediurea, dimethylenetriurea, biuret, triuret, and biuret-
methyleneurea.
Introduction Formaldehyde has long been known to react with urea, and various commercial urea-formaldehyde condensation products have been in the marketplace for years as materials ranging from insulating foams to fertilizers. In the fertilizer industry, formaldehyde has been used to condition urea and also to prepare nitrogen fertilizers having Presented to the Fertilizer and Soil Chemistry Division a t the 188th National Meeting, of the American Chemical Society, Philadelphia, PA, Aug 1984. 0196-4321/85/1224-0420$01.50/0
controlled-release properties. The use of formaldehyde to condition fertilizer-grade urea is a common practice among urea manufacturers. The amount of formaldehyde added as a conditioning agent is usually 0.3-0.4%. The aldehyde can be added as either formalin solution, paraformaldehyde, or UF Concentrate-85, which is 60% formaldehyde and 25% urea with 15% water. In general, conditioning is used to improve the physical properties of the product. It improves the resistance to caking and also the physical strength of granules while a t the same time reducing dust problems (IFDC, 1979). 0 1985
American Chemical Society
