Document KJ4NVGaBKyLEoOKXY66w9RRor

AN EMPIRICAL METHOD FOR EVALUATING THE SPRAY CHARACTERISTICS OF AEROSOL PRODUCTS By Paul Sanders E. I. du Pont de Nemours & Company "Freon" Products Division Wilmington, Delaware 19898 A-6S EID11453 Reproduced by permission from AEROSOL AGE Vol. II, Nos. 1 & 2, January and February 1966 *Reg. U.$. Pat. Off. for Du Pont's fluorocarbon product Better things for better living . through chemistry The spray characteristics of aerosol either with high-boiling solvents such products vary from wet, streamy as kerosene or odorless mineral spirits, sprays to very fine sprays, depending or lower boiling solvents, such as c upon the application for which the aerosol was designed. Wet or coarse ethyl alcohol. Data which illustrate this method for evaluating the spray sprays are desirable for residual prod characteristics of aerosol products are ucts such as residual insecticides, given in the present paper and the while sprays with a fine particle size potential applications and limitations are necessary for space aerosols, such of the method are discussed. as room deodorants. The type of spray produced by an aerosol product is one General Discussion of its most important properties. The method presented in this The aerosol chemist has a wide paper for comparing the variety of propellants, propellant spray characteristics of aerosol prod blends, and solvents available for the ucts is based upon a modification and formulation of aerosol products. Some extension of the "Tentative Method times this profusion of propellants for Determining Pickup Efficiency of and solvents presents a problem to Residual Aerosol Insecticides", which the formulator who must attempt to was adopted by the Scientific Com achieve the desired spray character mittee of the Aerosol Division of the istics while keeping in mind such CSMA (Reference 2). The tentative factors as pressure, compatibility, method for determining pickup effi flammability, and cost. Quite often, ciencies was developed originally to for various reasons, it is desirable to evaluate the efficiencies of residual replace the original propellant that insecticides as far as deposition on a was used in an aerosol product with target was concerned. Although the a different propellant, while maintain amount of product that is deposited ing the original spray properties of by a residual insecticide depends the aerosol. upon the particle size, an actual par Up to the present time there has ticle size measurement of the products been no simple method for comparing is considered to be impractical and c the spray properties of an aerosol product that has been formulated difficult (Reference 3). The pickup efficiency, which is defined as the with different propellants. A method percentage of the low volatile com for determining the particle size dis ponents that are deposited on a sur tribution of space insecticides has face, is a function of the particle size been published (Reference 1), but and is much easier to determine. this procedure is applicable only for The assumption upon which the products formulated with high-boil present method for comparison of ing solvents, such as deodorized kero spray properties of aerosol products sene. In addition, the method is time is based is that within certain limits, consuming and requires expensive different propellants appear to give equipment. approximately the same spray char A comparatively simple method has acteristics with the same solvent when been developed for comparing the the propellant/solvent ratios are ad spray characteristics of an aerosol justed so that the pickup efficiencies product when the concentrate has are the same. The basic assumption been formulated either with different includes not only residual aerosol propellants or with different concen products but also other aerosol trations of the same propellant. One products with much finer sprays. As of the most practical applications of an example, it was determined that the method is that it may be used to mixtures of 72% "Freon - 12"/28% determine what concentrations of dif odorless mineral spirits and 87 % ferent propellants will produce about "Freon - 12"/"Freon- 11" (50/50)/ the same spray properties. The method 13% odorless mineral spirits both is useful for products formulated had pickup efficiencies of 60%. Both EID11454 OF AEROSOL PRODUCTS by Dr. Paul A. Sanders, "Freon" Products Division, E. I. du Pont de Nemours Cr Company % P ickupE llicim ci EID11455 mixtures had about the same spray characteristics, judging by visual ob servation. The work presented in this report consisted of determining the pickup efficiencies of mixtures of odorless mineral spirits or ethyl alcohol with different propellants. The measure ments were carried out with a variety of propellant/solvent ratios and the results were illustrated graphically by plotting the pickup efficiency as a function of the propellant, solvent ratio for each of the propellants. From these graphs, it was possible to determine the propellant/solvent ra tios for different propellants that gave the same pickup efficiencies. Propelant 'solvent mixtures having compo sitions that gave the same pickup efficiencies were then prepared and the sprays were compared visually. It was judged, that at the same effi ciencies, the spray characteristics of the different mixtures were approxi mately the same. Although the data presented in this report were obtained only with pro pellant/solvent mixtures, the method and data should be applicable to many aerosol products. ence 2. Basically, it consists of a wooden box with a triple-beam bal ance mounted on top of the box. A sheet of aluminum, 12" x 12", is sus pended inside the box and is attached to the balance by means of a wire which passes through a hole in top of the box. The apparatus is illus trated in the accompanying photo graphs. The procedure consists of spraying the aerosol product against a blotter target, clamped to the aluminum sheet, from a distance of one foot. The amount of low volatile material sprayed from the container can be calculated from the weight of aerosol sprayed, assuming that the composi tion is known. The weight of low volatile material that reaches the blotter target can be determined by the increase in weight of the blotter tar get. The percent retention on the blotter target of the low volatile material that was sprayed is termed the pickup efficiency. The pickup effi ciency is a function of the particle size of the aerosol spray and the smaller the particles the lower will be the pickup efficiency. In carrying out a pickup efficiency determination, a 12" x 12" piece of or dinary blotting paper was clamped to the aluminum sheet and thus was in a vertical position. A second 12" x 12" piece of blotting paper was placed in a horizontal position at the base so that one edge was in contact with the bottom of the aluminum sheet. The second piece of blotting paper thus extended 12" beyond the alumi num sheet. The aerosol container with the propellant-solvent mixture to be tested was thermostated at 70 F and then placed at the outside edge of the horizontal blotter. The aerosol container therefore was 12" from the vertical blotter clamped to the aluminum sheet. The aerosol container was sprayed for 10 seconds with the spray directed at the center of the vertical blotter. Particles which were too coarse to /' !- s' Experimental Apparatus and Procedure The apparatus used for the present experiments was es sentially the same as that recom mended for the determination of the pickup efficiency of residual insecti cides. The construction of the appa ratus is described in detail in Refer reach the target were caught on the horizontal blotter. Immediately after spraying, the horizontal blotter was folded up against the vertical blotter and clamped. The weight of low' vola tile material that was deposited on the two blotters was determined using the procedure described in Reference 2. The weight of the blotter targets was determined immediately after spraying and at 3 minute intervals thereafter up to about 15 minutes. The blotters will decrease in w'eight due to evaporation of both propel lant and low volatile solvents. The decrease in weight is plotted as a function of time. Initially, a rapid decrease in weight occurs which is due mostly to loss of propellant and this is followed by a slow'er, steady decrease in weight w'hich is due to evaporation of the low volatile solvents. The straight portion of the curve, which represents the evaporation of the low volatiles, is extrapolated back to zero time to give the initial gross weight of the sprayed blotters without including the propellant. From these data, the ac tual weight of low volatile solvents deposited on the blotter can be deter if mined and the pickup efficiency can be calculated. All samples were prepared by cold filling in order to keep the air con centration low. At least five determi nations were carried out with eacli propellant/solvent ratio, using differ ent samples for each determination. The results obtained are illustrated graphically in the report, using aver ages of the separate determinations. The data were obtained with samples packaged with a widely used valve and actuator. The tw'o solvents used in the tests were odorless mineral spirits and ethyl alcohol. The propellants that were evaluated in combination with the solvents at various propellent/solvent ratios were as follows: "Freon-12" "Freon-12"/ " Freon-11" (70/30) "Freon-12"/"Freon-11" (50/70) "Freon-12"/ "Freon-11" (30/70) "Freon-12"/"Freon-114" (40/60) "Freon-12"/ "Freon-114" (15/85) "Freon-114" *0 50 60 % Odorless Mineral Spirit* % Odorle** Mineral Spirit* EID11456 Table 1 Propellant/Odorless Mineral Spirits Mixtures With Pickup Efficiencies of 70% Propellant/OMS Propellant Ratio (wt %) "Freon-12" "Freon-12"/ "Freon-11" (70/30) "Freon-12"/ "Freon-11" (50/50) 63/37 71/29 81/19 The pickup efficiencies of a variety of propellant/solvent mixtures were determined using the propellants and solvents previously mentioned. The data were first plotted as curves which illustrate the effect of a variation in the propellant/solvent ratio upon pickup efficiency. The data for the various propellant/solvent com binations are illustrated in the follow ing figures: "Freon-12"/"Freon-11"/Odorless Mineral Spirits . "Freon-12"/ "Freon-114"/ Odorless Mineral Spirits "Freon-12"/"Freon-l 1''/Ethyl Alcohol "Freon-12"/"Freon-114 ''/Ethyl Alcohol Figure 1 Figure 4 Figure 7 Figure 10 These curves are useful for deter mining the compositions of various propellant/solvent mixtures that have the same pickup efficiency. Thus, in Figure 1, a dotted line has been drawn through the curves at a pickup effi ciency of 70%. From Figure 1 it can be determined that the various propel- lant, odorless mineral spirits (oms) mixtures that have a pickup efficiency of 70% have the compositions indi cated above. The three propellant odorless min eral spirits mixtures shown in Table I should all have approximately the same spray characteristics if the basic- assumption that mixtures with the same pickup efficiencies have the same spray properties is true. The curves possibly could be extra polated to zero percent pickup with zero percent solvent present. The curves were not drawn with less than 10% solvent, however, because the variations in pickup efficiency with less than 10% solvent present were too large and the results were not reproducible. B. Variation of Pickup Efficiency With Composition of Propellant/ Solvent Mixtures The data from Figures 1. 4. 7 and 10 were transferred to triangular co ordinate charts to illustrate the varia tion in pickup efficiency with a varia tion in the composition of the propel lant solvent blends. The triangular coordinate charts are particularly use ful in obtaining the pickup efficiency of propellant/solvent combinations that were not tested experimentally. These data can be obtained by draw ing a line from the base line for the particular propellant mixture in quest ion through the solvent apex., For example, the pickup efficiencies of a "Freon-12"/'"Freon-ll" (60/40) blend with various concentrations of odor less mineral spirits were not deter mined experimentally but could be obtained from Figure 2 as indicated by the dotted line. The mixtures that are illustrated on the triangular coordinate charts and the corresponding figure numbers are as follows: EID11457 "Freon- 12"/"Freon-11 "/Odorless Mineral Spirits.........Figure 2 "Freon-12"/"Freon-114"/Odorless Mineral Spirits.........Figure 5 f "Freon-12", '"Freon-11 ''/Ethyl Alcohol ...................... Figure 8 "Freon-12" '"Fieon-114"/Ethyl Alcohol ...................... Figure 11 C. Relationship Between Pressure, Pickup Efficiency and Propellant/ Solvent Ratio Pressures were determined on a variety of propellant solvent blends so that the relationship between pres sure, pickup efficiency and propel lant solvent ratio could be estab lished. The samples were prepared by cold filling and pressure measure ments were carried out with a prepresurized gage on duplicate samples prepared without dip tubes. The data 40 50 60 % Ethyl Alcohol w M<twr 70 90 100 were plotted with the pressure as a spray characteristics, various propel E. Limitations of the Method function of the propellant,'solvent lant/odorless mineral spirits and pro As the proportion of propellant in ratio with the pickup efficiencies pellant 'ethyl alcohol mixtures having the propellant solvent mixtures is de shown by contour lines. The various the same pickup efficiencies were pre creased, the sprays become coarser propellant/solvent mixtures and the corresponding figure numbers are as follows: pared and the sprays were judged visually. and the pickup efficiency increases until a maximum pickup efficiency is reached. The maximum pickup effi "Freon-12" / "Freon-11"/ Odorless Mineral Spirits Figure 3 ciency obtained with the propellant/ "Freon-12"/ "Freon-114"/ Odorless Mineral Spirits Figure 6 odorless mineral spirits combinations n "Freon-12"/'"Freon-ir7Ethvl Alcohol ................ "Freon-12"/"Freon-114"/Ethvl Alcohol .............. Figure 9 Figure 12 was about 85%. That obtained with propellant ethyl alcohol mixtures was The data illustrated on these fig The results obtained with odorless slightly over 60%,. Once the maxi ures make it possible to select a mix mineral spirits as the solvent are listed mum pickup efficiency was reached, ture which will give a desired pickup in Table III and the results with ethyl decreasing the proportion of propel efficiency at a specified pressure. alcohol as the solvent are given in lant still altered the spray properties D. Relationship Between Pickup Effi Table II. As a general rule, the pro but not the pickup efficiency. There ciencies and Spray Characteristics pellant odorless mineral spirits mix fore. the method of matching spray In order to check the basic assump tures with the same pickup efficiencies properties by using pickup efficiencies tion that within certain limits, propel had about the same spray character is not effective after the maximum lant solvent mixtures with the same istics and the same was true with the pickup efficiency has been reached. pickup efficiencies had about the same propellant, ethyl alcohol mixtures. Fortunately, this limitation excludes Table II Relationship Between Spray Characteristics and Pickup Efficiencies--Propellant/Ethyl Alcohol Mixtures Propellant Propellant/ Ethyl Alcohol Pickup Ratio Efficiency Type of Spray "Freon-12" "Fi eon-12"/ "Freon-11" (50/50) "Freon-12"/"Freon-l 14" (40/60) "Freon- 12"/"Freon-l 14" (15/85) "Freon-12" 73/27 89/11 78/22 86/14 59/41 20 Very fine. dry spray 20 Verv fine, dry spray 20 Verv fine. dry spray 20 Very fine, dry spray 40 Medium to fine Table II (Cont.) "Freon-12"/"Freon-11" (50/50) "Freon-12"/ "Freon-114" (40/60) "Freon-12" 74/26 67/33 76/24 40 40 40 "Freon-12" "Freon-12'7 "Freon-11" (50/50) "Freon-12" / "Freon-11" (30/70) "Freon-12"/ "Freon-114" (40/60) "Freon-12"/"Freon-114" (15/85) "Freon-114" 46/54 61/39 79/21 55/45 66/36 79/21 60 60 60 60 60 60 Medium to fine Medium to fine Medium to fine Medium Medium Medium Medium Medium Medium EID11458 mostly products which have very wet to streamy sprays. The data in Table IV illustrate the variation in pickup efficiency and spray characteristics with a change in the "Freon - 12"/odorless mineral spirits ratio. The maximum pickup efficiency is reached when the "Freon12" concentration is reduced to about 40%. Decreasing the proportion of "Freon-12" below 40% changes the spray properties but not the pickup efficiency. Similar data obtained with ethyl alcohol as the solvent are shown in Table V. Maximum pickup effi ciency was again reached when the "Freon-12" concentration was re duced to about 40% in the mixture. As previously mentioned, at con centrations of the solvent below 10 % in the mixtures, the experimental error in determining the pickup efficiencies was too large for the method to be applicable. The method appears to be useful for formulations in which the solvent concentrations range from about 10% to the point where maxi mum pickup efficiency is reached. The latter point is a function of the particular propellant and solvent that are used. Comments: The present procedure for matching the spray proper ties of aerosol products is not intended to be considered as a precise method for indicating compositions having the same particle size distribution. However, the method does appear to indicate the relative proportions of the various propellants which will give spravs with the same general visual appearance. A limited number of tests were carried out using various valves. As would be expected, the pickup effi ciencies were found to be a function of the type of valve used. Therefore, the method can also be used to indi cate what effect a variation in valves has upon the spray characteristics of a formulation. The data in this report were ob tained with mixtures of the "Freon" propellants with odorless mineral Table III Relationship Between Spray Characteristics and Pickup Efficiencies--Propellant/Odorless Mineral Spirits Mixtures Propellant Propellant/ Pickup Type OMS Ratio Efficiency of Spray "Freon-12" "Freon-12"/ "Freon-114" (40/60) "Freon-12" "Freon-12"/ "Freon-11 " (50/50) "Freon-12"/ "Freon-114" (40/60) "Freon-12"/"Freon-114" (15/85) "Freon-12" "Freon-12" / "Freon-11 " (50/50) "Freon-12" / " Freon-11 " (30/70) "Freon-12"/"Freon-l 14" (40/60) "Freon-12"/ "Freon-114" (15/85) "Freon-114" 84/16 89/11 72/28 87/13 79/21 88/12 52/48 72/28 87/13 64/36 75/25 85/15 40 Very fine 40 Very fine 60 Fine 60 Fine 60 Fine 60 Fine 80 Medium 80 Medium 80 Medium 80 Medium 80 Medium 80 Medium Table IV Spray Characteristics and Pickup Efficiencies As a Function of the "Freon-12'7 Odorless Mineral Spirits Ratio "Freon-127 OMS Ratio Pickup Efficiency Type of Spray 84716 72/23 52/48 40/60 30/70 20/80 40 Verv fine 60 Fine 80 Medium 85 Coarse 85 Broken Stream 85 Stream VTable Spray Characteristics and Pickup Efficiencies As a Function of the "Freon-12"/Ethyl Alcohol Ratio "Freon-12"/Ethyl Alcohol Ratio Pickup Efficiency Type of Spray 73/27 59/41 46/54 40/60 30/70 20/80 20 Very fine 40 Medium to fine 60 Medium 66 Wet 63 Wet 64 Partial Stream EID11459 P re s s w i* fp t'O <rt 7 0 * f ) Pickup E fficie n cy (% ) spirits and ethyl alcohol. The results should be applicable to most aerosol formulations prepared with these sol vents. If similar data are desired for an aerosol concentrate containing other solvents, it might be possible to estimate the pickup efficiencies from the present data by using the boiling points of the solvents in the aerosol concentrates as a guide. There are other applications in which the determination of pickup efficiencies might be of considerable assistance. For example, the change in spray characteristics of a formula tion during complete discharge of the package could be detected by deter mining the pickup efficiencies of the products at intervals during discharge. Summary An empirical method for evaluating the spray charac teristics of aerosol products has been developed. The method provides a general indication of the relative pro portions of different propellants that will produce the same spray proper ties. It also shows the effect of vary ing the propellant concentration upon spray properties. The assumption upon which the method is based is that the spray properties of aerosols formulated with different propellants but the same concentrate, are about the same at the same pickup efficien cies. This assumption appears to be valid within certain limitations. Data are presented for a series of "Freon" propellant/odorless mineral spirits and "Freon" propellant/ethyl alcohol mixtures which illustrate the method of matching and comparing spray characteristics using the pickup efficiency method. References: 1. "A Tentative Method for Determina tion of the Particle Size Distribution of Space Insecticide Aerosols", Proceedings of the Forty-third Annual Meeting, CSMA, December 3-5, 1956. ("Freon" Technical Bulletin, A-45). 2. "A Tentative Method for Determin ing Pickup Efficiency of Residual Aerosol Insecticides", Proceedings of the Fortythird Mid-Year Meeting of the CSMA. May 1957 ("Freon" Technical Bulletin, 1 A-46). 3. Yeomans, A. H., "Particle Size De terminations of Residual Sprays", Pro ceedings, Fortieth Annual Meeting, CSMA. December 1953. EID11460 % Ethyl Alcohol in Mixturt ( EID11461 E. I. DU PONT DE NEMOURS & CO. (INC.) "FREON" PRODUCTS DIVISION WILMINGTON, DELAWARE 19898 FOR FURTHER INFORMATION Please contact one of the following offices: 701 Welch Road Palo Alto, California 94304 Phone: 326-2840 (Area Code 415; or Wilmington, Delaware 19898' Phone: 774-4410 (Area Code 302) The information contained herein is based on technical data and tests which we believe to be reliable and is intended for use by persons having technical skill, at their own discretion and risk. Since conditions of use are outside of Du Pont's control, we can assume no liability for results obtained or damages incurred through the application of the data presented. Publication of the information in this bulletin should not be understood as permission or recommendation for the use of "Freon" compounds in violation of any patents. cgMD u s pat o*f Better things for better living.. .through chemistry 4/70 PRINTED IN U. S. EID11462