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the reaction. The tube was sealed with a rubber septum, and dry nitrogen was passed in at a moderate rate to exclude oxygen. The needles used for nitrogen inlet and outlet were removed, and the tube was immersed in an oil bath preset at 170 "C (or 180 O C for collecting data at this temperature), heated by a hot plate with a magnetic stirring motor. Within 5 min the low-melting-diol component had melted, and the mixture was partly homogenized. The temperature was rapidly lowered to the appropriate temperature when needed by adding cold oil into the heating bath. At selected time intervals the tube was withdrawn and wiped clean, and while it was still hot, its septum was removed, and the tube was placed in a vacuum desiccator (at mmHg) over KOH to reach room temperature and constant weight. This ensured complete removal of water at each data point. Finally, the tube's surface was dried and degreased with acetone. The difference in weight was used to calculate the extent of reaction at the particular time. Subsequent repetition of this procedure with the same sample produced additional points for the conversion vs. time plots. The reproducibility of this method was f0.02 in the determination of
P* Registry No. BTA, 4435-67-0; HDG, 7735-42-4; DMG, 11247-0; (BTA)(DMG)(copolymer), 34606-50-3; (BTA)(HDG)(copolymer), 104241-62-5.
Literature Cited Acitelli, M. A.; Prime, R. B.; Sacher, 0. Polymer 1071, 72,335. Allen, P. E. M.; Patrick, C. R. Kineflcs and Mechanisms of Polymerization Reactions; Ellls Horwood: Chichester, 1974; Chapter 2, pp 116-117. Argyropoulos, D. S.; Bolker, H. I.Polym. Prepr. ( A m . Chem. Soc., Div. Powm. Chem.) 1086, 27, 457. Aukward, J. A.; Warfield, W.;Petree, M. C. J. folym. S d . 1058, 27, 199. Barton, J. M. Polymer 1980, 21,603. Berry, R . M. Ph.D. Thesis, McGill University, 1980, Chapter 5, p 222.
Bueche, F. Physical fropertes of Polymers; Interscience: New York, 1962. Dannenberg, H. S E J. 1050, 75, 875. Dannenberg, H. SPE Trans. 1063, 3 , 78. DiMarzio, E. A.; Gibbs, J. H. J. Polym. Sei., Polym. Chem. Ed. 1983, 7 , 1417. Edwards, D. C. Rubber Chem. Technol. 1075, 48(2), 202. Flory, P. J. J. Am. Chem. SOC. 1030, 61,3334. Flory, P. J. Principles of Polymer Chemistry; Cornell University: Ithaca, NY, 1953: Chapter I X . Fox, T. G.; Loshaek, S. J. Polym. Sci. 1055, 40, 371. Gordon, M.; Roe, J. J . Polym. Sci. 1056, 21, 27, 75. Gordon, M.; Scantlebury, G. R. J. Chem. SOC. 19678, C-I. Gordon, M.; Scantlebury, G. R. J. Chem. SOC. B 1067b, 1. Gordon, M.; Parker, T. W. Proc.-R. SOC.Edinburgh, Sect. A : Math. Phys. S d . 1071, A69, 181. Gordon, M.; Temple, W.B. Makromoi. Chem. 1072. 263, 160. Harris, T. E. The Theory of Branching Processes : Sprlnger-Veriag: West Berlin, 1963. Horie, K. J. folym. Sci. folym. Chem. Ed. 1070, 8 , 1357. James, H. M.; Guth, E . J. Chem. fhys. 1947, 75, 669. Kakurai, T.; Noguchi, T. Kobunshi Kagaku 1962, 19, 547. Kamal, M. R.; Sourour, S.: Ryan, M. Annu. Tech. Conf.-Soc. fiast. Eng. 1073, 19, 187. Loshaek, S.; Fox, T. G. J. Am. Chem. SOC.1053, 75, 3544. Love, J. A. Ph.D. Thesis, Strathclyde University, 1968. Miller, 8. J. Appl. Polym. Sci. 1066. 10, 217. Minnema, L.; Staverman, A. J. J. Polym. Sci. 1058, 29, 281. Peniche-Covas, A. L. Ph.D.Thesis, University of Essex, 1973. Ryabchikov, I.D.; Novikova, 0. S. Nature (London) 1066, Piloyan, G. 0.; 212, 1229. Price, F. P.;Glbbs, J. H.; Zimm. B. H. J. Phys. Chem. 1058, 62,972. Prime, R. B. Anal. Caiorim. 1970, 2. 201. Prime, R. 6.: Sacher, E. Polymer 1072, 13,455. Prime, R . B.; Sacher, E. folym. Eng. Sci. 1073, 13, 365. Rolfe, C. N.; Hinshelwood, G. N. Trans. Faraday SOC. 1934, 3 0 , 935. Ross-Murphy, S.B. J. folym. Sci., Polym. Symp. 1975, No. 53,11. Ryan, M. E.; Dutta, A. Po/ymer 1070, 20,203. Schiraldi, A.; Wagner, V.: Samanni, G.; Rossi, P. J. Therm. Anal. 1081, 21, 299. Shen, M. C.; Eisenberg, A. Rubber Chem. Techno/. 1970, 43(1), 95. Shultr, A. R. J. Am. Chem. SOC.1058, 8 0 , 1854. Sourour, S.; Kamal, M. R. Thermochim. Acta 1076, 14, 41. Walling, C. J . Am. Chem. SOC. 1045, 67,441.
Receiued for review December 2, 1985 Accepted April 14, 1986
Nickel Powders into Sintered Structures for the Alkaline Battery: Porosity Studies Victor A. Tracey" Inco Alloy Products Ltd., Birmingham 8 1 6 OAJ, Unitecl Kingdom
INCO nickel powder type 255 is used for the production of porous struclures for the alkaline battery. Typical porosity levels obtained by processing the powder using the optimum conditions of the slurry sinter route are about 81 YO. The increase in porosity possible by varying sintering temperature, addition of spacing agents, and use of loose sintering has been explored. The increase in porosity (up to about 90%) has been related to strength and pore structure changes.
Introduction The porous nickel used for the manufacture of electrodes of alkaline batteriea is prepared from irregular INCO nickel powder types 255 and 287 (Inco, 1981a,b) through processes involving sintering. Two processes are employed, loose sintering and slurry sintering, and the latter process has been favored by many manufacturers because of its
* Address correspondence to International Nickel Inc., Saddle Brook, N J 07662.
continuous nature (Falk and Salkind, 1969). In the manufacture of the sinter, time, temperature, powder characteristics, and atmospheres are important, and an earlier paper looked at these parameters with the objective of optimizing the process (Tracey, 1982). The paper showed that sintering at 950-1000 "C gave the best strength on the basis of economic considerations. Under the conditions specified, INCO nickel powder type 255 would produce a sintered nickel porosity of about 81% (Table I).
0 196-432118611225-0582$01.50/0 0 1986 American Chemical Soclety
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 4, 1986
583
f
95
85
90
w w
G E3
G
U
G7 0 0 : 0
b
U
c,Y
0
85
P4
Ee
0 a
80
80 Time = 5 min.
S i n t e r e d 5/950oC
9 :
i
1000
800
SINTERING TEMPERATURE, OC Figure 1. Porosity levels obtained on reducing sintering temperature. Table I. Bulk Density and Equivalent Porosity Range for Inco Nickel Powder 255 calcd eauiv porosity range, % bulk densitv. e/cm3 0.50-0.65
94.4-92.7
Table 11. Decrease in Strength on Increasing Porosity by Reducing Sintering Temperature approx porosity decrease in strength, 70 reduction in sinter temp, "C ( O F ) level, 70
---
980 (1800) 980 850 (1800 980 750 (1800 650 (1800 980 980 550 (1800
---
1560) 1360) 1200) 1020)
81
0
84
33 50 60 100
84.5 85
0
600
Increased porosity is needed for some applications, and this can be achieved in a number of ways, e.g., reducing sintering temperature, using spacing agents, and using other techniques of manufacture. It is the objective of this paper to summarize several pieces of work that involve higher porosity structures from INCO nickel powder type 255.
Porosity and Strength Trends Reduction in Sintering Temperature. Although the published work has shown that the optimum sintering temperature is between 950 and 1000 "C, which provides a sinter with a porosity of about 81%, it is naturally possible to increase porosity to 8 4 4 5 % by reducing the sintering temperature to between 800 and 650 OC (Figure 1). The strength declines as sintering temperature is reduced, and the typical loss that occurs is indicated in Table 11. The sinter is very weak below 650 "C and does not hold together below 550 "C. Addition of Spacing Agents. The use of spacing agents raises the porosity well above the 85% possible with the basic powder. The typical porosities that have been obtained in making oxamide additions to the slurry can be seen in Figure 2. The volume contents of spacing agents that are necessary to achieve higher porosities, the calculated increase in powder porosity resulting from the addition of the spacing agent, and the volume shrinkage obtained at the sintering stage are given in Table 111. The increase in volume shrinkage that occurs with the spacing agent present increases the tendency toward shrinkage crack formation, and this becomes pronounced with spacing agent contents above 25 wt %.
40
20
SPACING AGENT, w t . % Figure 2. Porosity levels obtained on adding spacing agent. Table 111. Composition of Slurry, Porosity Levels, and Volume Shrinkages on Sintering with Spacing Agent Present comnosition approx wt% vol %" calcd porosity, % ..^1 spacing spacing unsinshrinkage: Ni agent Ni agent teredb sintered % 100
0
95 75 50
5 25 50
0
100 72 29 12
88 89 93 96
28 71
88
81
37 39 42 50
82 88 92
"Volume content is based on density of nickel, 8.9 g/cm3, and oxamide, 1.2 g/cm3. bCalculated from measured value to allow for weight of spacing agent. Calculated from unsintered and sintered porosity levels in columns 5 and 6. Table IV. Decrease in Strength on Increasing Porosity through Addition of a SDacing Agent
content of spacing agent" wt% vol %
porosity level, %
approx decrease in strength, %
0
0
81
0
12 20 25
50 65 71
85
33 50 66
87 89
" Up to 45 pm oxamide. Table V. Decrease in Strength on Increasing Porosity through Using the Loose-Sintering Process approx decrease in temp of strength from slurry sintering, "C sinter a t 980 "C (OF) Dorositv level. % (1800 O F ) . 70 slurry sinter 0 980 (1800) 81 loose sinter 1050 (1920) 950 (1740) 850 (1560)
86 88 89
60 70
84
The fall in strength with the increase in porosity achieved is illustrated in Table IV. Loose-Sintered Structures. The use of the slurry technique for continuous production causes the powder particles to be drawn together more closely than free packing by loose sintering. For example, a powder with bulk densities of 0.57 g/cm3 will give a loose packed porosity of about 93%, but when the powder is treated by the slurry technique, the porosity would be about 88%, i.e., a loss of about 5% porosity before sintering. The
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1p.
*H
90
H VI
0
cc 0 a
85
80 T i m e = 5 min.
850
950
1050
SINTERING TEMPERATURE,
100
OC
Figure 3. Porosity levels of loose-sintered and slurry-sinteredmaterials.
1
10
PORE DIAMETER ,urn Figure 5. Pore spectrum for slurry-sintered material containing 30 wt % spacing agent of 45-gm maximum pore size.
E
3
Ll 0
>
el
4 b
Bccw V
z
H
W + H r3 4
el
100
10
1
PORE DIAMETER Am Figure 4. Pore spectrum for slurry-sintered material (sintered for 5 min at 950 "C).
typical porosity levels achieved on loose sintering are illustrated in Figure 3 and show that the lower packing density of the loose-sintering technique provides porosities well above those from the slurry technique. The strength levels obtained, however, are below those obtained with slurry techniques (Table V).
Pore Structure Changes In the development of the nickel structures the pore size distribution is acknowledged to be an important factor, particularly when considering impregnation efficiency. The typical slurry-formed electrode from INCO nickel powder type 255 has a mean pore size of about 10 pm with a distribution shown in Figure 4. The addition of a spacing agent with particles up to 45 km in size increases the mean pore size, and with about 30 wt 5% added, the mean pore size is raised from about 10to 13-14 pm. The effect of the addition of spacing agent is to skew the distribution generally to a higher pore size range and apparently to reduce the finer group of pores present, 2-7 pm (Figure 5). Loose sintering of the powder also produces a more open structure than slurry/sintering, with a mean about 14 pm. The pore size distribution is slightly greater than the slurrv/sinter containing macine agent. and the volume of fine ;Ares was also fouidio be less significant (Figure 6). u
u
w cc
100
10
1
PORE DIAMETER pm Figure 6. Pore spectrum for loose-sintered material (sintered for 5 min at 950 "C).
90
85
80
75
POROSITY, 5
Figure 7. Strength/porosity relationships for the three types of material.
Discussion and Conclusions The porosity of the slurry-sintered INCO nickel powder type 255 can be raised from the optimum value of about 81% obtained on sintering at about 980 "C to a practical limit of 84-85 70 bv reducing the sintering temDerature to D
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Ind. Eng. Chem. Prod. Res. Dev. 1986, 25, 585-589
below 850 OC. An increase in porosity above that level necessitates more open initial structures created either by adding spacing agents or by changing the method of preparation to loose sintering. In all cases as would be expected there is a fall in strength with an increase in porosity, and the porosity/ strength characteristics achieved by the three methods are summarized in Figure 7, which shows that reasonable levels of strength can be achieved at porosities above 85%. At higher porosities Obtained with the more 'pen structures there has been a shift in mean pore size from 10 toward 15 pm, making the secondary pore size region less pronounced (Figures 4-6).
Acknowledgment I wish to thank Inco for permission to publish this paper. Registry No. Oxamide, 471-46-5; nickel, 7440-02-0. Literature Cited Falk, S. U.; Salklnd, A. J. Alkallne Storage Batteries; Wiley International: New York, 1969; Chapter 2, p 111. International Nickel Co. Inc., Product Data Sheet A1155A INCO Nickel Powder Type 255, 1981a, New York. International Nickel Co. Inc., Product Data Sheet A1234A INCO Nickel Powder Type 257, 1981b, New York. Tracey, V, A, Ind, Eng, Chem. prod, Res, De", 1982, 21,626,
Received for review January 14, 1985 Accepted April 25,1986
Controlled-Release Polymeric Herbicide Formulations with Pendent 2,4-Dichlorophenoxyacetic Acid Shukla Bhattacharya, Shyamal K. Sanyal, and Ram N. Mukherjea" Process Engineering and Technology Laboratory, Chemical Engineering Department, Jadavpur University, Calcutta 700 032, India
Controlled-release pesticide formulations in which the pesticide is covalently bound to a polymer, either as a pendent group or as a part of the polymer backbone through a hydrolyticallylabile bond, are gaining increasing importance. As part of an ongoing project on slow-release formulations of 2,4dichlorophenoxyaceticacid (2,4-D), the herbicide was initially converted to a polymerizable derivative, a diolamide of 2,4-D. This diolamide was copolymerized with a number of dicarboxylic acid/anhydrides to give polymeric herbicide formulations in which the backbones are completely biodegradable by hydrolysis. Cross-linking reaction of these polymers with vinyl and acrylic monomers gave partially degradable polymeric herbicides. Release characteristics of these formulations have been studied in neutral, alkaline, and acidic media.
Polymeric controlled-release (CR) pesticide formulations have been introduced in response to growing concern for ecological problems associated with increased use of plant protection chemicals required for intensive agricultural practices. The toxicant is delivered from such formulations at a controlled rate, increasing the period of effectiveness of the biologically active component and obviating the need for overdose. There are basically two approaches for preparing such controlled-release pesticides. The active agent may be covalently bound on a preformed synthetic or natural polymer macromolecule (Neogi, 1970; Allan et al., 1977; Bhattacharya et al., 1985). Another approach is to polymerize a herbicide containing monomer. The second method has the advantage that it gives a much higher weight percentage of herbicide, and the activity of the polymeric herbicide can be varied by introducing comonomers into polymer or by changing the molecular weight. The work on control-activity polymers with pendently bound herbicides has been extensively reviewed by McCormick et al. (1982/1983). Herbicide monomers so far prepared are acryl and vinyl monomers containing hydrolyzable herbicide moieties (Harris et al., 1976). These monomers provide polymeric pesticide systems in which the polymer backbone is stable to hydrolytic degradation. A number of these controlled-release systems, however, failed to show biological activity in bioassay studies, implying no hydrolytic release of the pesticides. The release pattern becomes satisfactory
* Author to whom correspondence should be addressed. 0196-4321/86/1225-0585$01.50/0
when these are copolymerized with hydrophilic comonomers (Harris and Arah, 1980). Only limited studies have been done on the synthesis of biodegradable polymeric pesticides. Desmareta and Bogaerts (Schacht et al., 1978) acetalized diethyl tartarate with 2,4-dichlorobenzaldehyde; the acetal obtained was then polymerized with diamine and diols to give a polymeric herbicide having a biodegradable backbone. These controlled-release systems showed slow release of the aldehyde only in acidic homogeneous hydrolysis medium (dioxane/water, volume ratio = 2.9/1). The present study has been undertaken to synthesize a diolamide of the herbicide 2,4-dichlorophenoxyaceticacid (2,4-D), which on copolymerization with a number of dicarboxylic acids would give 2,4-D-releasing polymer systems. The structures of these polymers have been varied over a wide range by using a number of dicarboxylic acids and cross-linkingagents. The labile ester functions in the backbone would provide polymeric herbicides that are completely biodegradable by hydrolysis. Cross-linkingwith vinyl or acrylic monomers would provide partially degradable polymeric herbicides. Release characteristics of these polymeric herbicides have been studied in neutral, alkaline, and acidic media.
Materials and Methods 2,4-Dichlorophenoxyaceticacid was purified by crystallization from benzene. Diethanolamine (BDH) was purified by distillation under reduced pressure. Succinic acid (Sarabhai M. Chemicals), maleic anhydride (Loba0 1986 American Chemical Society
