AIRPLANE DOPES Relation of Tautening and Weathering Qualities to Composition FRANK W. REINHART ARTDGORDON M. KLINE National Bureau of Standards, Washington, D. C.
In a previous report on developing a fire-
hydroxyl content of cellulose mixed esters is especially critical in determining their suitability for use in airplane dopes. Solvent combinations and plasticizers which yield optimum tautness, resistance to slackening in wet weather, and least variation in tautness during exposure are indicated for various cellulose derivatives. A close correlation is shown to exist between the properties of the unsupported films and the behavior of doped fabrics; a considerable saving thus results in time, labor, and materials in evaluating new compounds and formulas.
resistant airplane dope to replace the hazardous cellulose nitrate product, formulas for experimental dopes for application to fabric-covered test panels were selected on the basis of the effect of plastic, plasticizer, solvent, and diluent components on the shrinkage and flexibility of dope films. This report describes the exposure tests of these experimental dopes and discusses the relation between the tautness and weathering properties of the doped fabrics and the composition of the dope. Evidence is presented to show that the HIS third in a series of reports (2, 4 ) on a n investigation of the formulation of airplane dopes was undertaken at the request of the Bureau of Aeronautics of the United States Navy Department, in order t o develop a satisfactory airplane dope based on comparatively nonflammable cellulose derivatives. The dependence of the flexibility and shrinkage characteristics of dope films on the solvents, diluents, and plasticizers used in the dopes was demonstrated in the previous report (4). Various compositions were selected on the basis of this work for application to airplane cloth to determine their tautening properties and weathering characteristics. This paper presents the results of the tests on these experimental dopes. The effect of the application of various flameproofing agents to the cloth on the tautening and weathering qualities of the cellulose acetopropionate and cellulose acetobutyrate dopes, which gave the best results in the tests described here, is now being investigated. Data are also being obtained on the ease of ignition and rate of burning of these doped fabrics with and without flameproofing treatment.
PREPARATION OF DOPEDPANELS.The construction of the wooden frames and the method of covering the panels with fabric (Figures 1 and 2) were the same as those used in the pre aration of the anels in group I by Kline and Malmberg &). The metal 8arnes were constructed by welding four pieces of l'/Z-inch angle iron into a frame 15l/, inches square. Two rows of 6/a,-inch holes were drilled and tapped for 3/8-inch bolts on the sides of the frame. The rows were 6/g inch apart, and the holes were l1/2 inches from center to center. Iron washers of g/ls-inch outside diameter were used with the bolts to hold the cloth. The bottom row of holes was employed only when the back of the frame was covered. The metal frames were painted with dope-proof primer (3)to protect them from rusting. Four coats of clear dope and two coats of aluminum-pigmented dope were brushed on the cloth. TESTINQ OF DOPEDFABRICS.The measurements of tautness of the doped fabrics were made with the spring-loaded instrument previously described (2). The deflection readings gjven in the tables are inversely proportional to the tautness; 1. e., the lower the reading, the greater the tautness. After drying approximately one week in the laboratory, the doped panels were latred in a conditioning room kept a t 70" F. and 65 per cent rerative humidity Measurements of tautness were made in this room at intervals until tautness equilibrium had been established. For the weathering tests the panels were exposed on the roof of the Industrial Building of the National Bureau of Standards on racks inclined at an angle of 45" and facing south (Figure 3). Brittleness of the film-i. e., tendency to "ringworm"-was determined in the tests previously reported by pressing the thumb firmly into the fabric covering at each corner. The following improved method to determine this quality of the doped fabric was devised and used on the panels described in this paper: A 12-inch length of brass pipe, lllrinches in diameter, is placed perpendicular to the doped surface (Figure 4). The doped surface is at an angle of 45' to the vertical. A half-pound steel ball is placed in the bottom of the tube, both resting on the doped fabric. Another half-pound steel ball is then dropped down the tube to strike the first steel ball. Each panel is tested in this way in two locations after tautness measurements are made. If the film cracks, breaks, or ringworms (Figure 5), it denotes brittleness and is indicated in the tables by R1 or R2, depending upon whether the film cracked in one or both locations tested. The data obtained from the measurements on the doped panels in the conditioning room and on the roof are presented
T
Materials and Measurements PROPERTIES OF PLASTICS. Data concerning the viscosity and composition of the plastic materials are given in Table I. These materials as well as data on the viscosities and percentage compositions were furnished by several manufacturers. SOLVENT FORMULAS. The solvent formulas for the various dopes are given in Table 11. The usual commercial grades of solvents were used. A concentration of 6.4 per cent by weight of plastic material was used for most of the dopes, although it was necessary to dilute several of the aluminumpigmented dopes to obtain a solution of suitable viscosity for brushing. Methyl methacrylate was used in a concentration of 10 per cent and cellulose triacetate in approximately 4 per cent. 185
INDUSTRIAL AND ENGINEERIKG CHEMISTRY
186
VOL. 32, NO. 2
ringwormed badly during exposure for 4 months. From evidence obtained in Sample Compositionb the course of the experiments with other Material Designation Viscositya Percentage basis Equivalents basis cellulose esters, it is reasonable to beCellulose acetate CA-all 25-35sec. 4 0 . 2 4 0 . 9 ac 2.50-2.57 ac, 0.50-0.43 hy lieve that a cellulose acetate having .... ..... Ca. 3 ac Cellulose triacetate CA-a10 a hydroxyl content of approximately Cellulose CAP-a2 527 0p.C 16.1 ac, 32.9 pro 1 . 1 7 ac, 1.80 pro, 0 . 0 3 hy acetopropionate CAP-a3 588 cp. 15.6 ac, 32.2 pro 1.10 ac, 1 . 7 1 pro, 0 . 1 9 hy 0.2 equivalent (which would still be CAP-a? 800 cp. 1 4 . 3 ac, 30.4 pro 0 . 9 6 ac, 1 . 5 4 pro, 0.50 h y CAP-ao 1007 cp. 13.6 ac, 28.6 pro 0.87 ac, 1 . 3 8 pro, 0.75 hy in the acetone-insoluble range) might CAP-a6 15 seo. 1 3 . 1 ac, 35.3 pro 0.94 ac, 1 . 9 1 pro, 0 . 1 5 hy yield films of more satisfactory flexiCAP-a7 22 sec. 1 2 . 8 ac, 36.1 pro 0 . 9 1 ac 1 . 8 8 pro 0 . 2 1 hy CAP-a8 28 sec. 1 3 . 2 ac 3 4 . 1 pro 0 . 9 3 BC'1 . 8 1 p r o ' 0 . 2 6 hy bility than the fully acetylated derivaCAP-a9 36 eec. 13.3 ac: 3 3 . 3 pro 0 . 9 2 ac: 1.74 pro,'0.34 hy tive and of less susceptibility to 3 2 . 0 ac, 1 5 . 4 b u Cellulose CAB-a1 300 cp. 2 . 2 5 ac 0 . 6 6 b u 0.09 hy acetobutyrate CAB-a2 380 cp. 28.9 ac, 16.5 b u 1 . 9 6 ac: 0 . 6 6 bu: 0 . 3 8 hy slackening in wet weather than the CAB-a3 595 cp. 26.8 ac, 15.9 b u 1 74 ac 0 . 6 3 bu 0 63 hv acetone-soluble cellulose acetates availCAB-a4 1055 cp. 2 4 . 8 ac, 1 4 . 5 b u 1152 ac' 0 . 5 4 bu' 0 . 9 4 h) CAB-a5 16 sec. 1 4 . 7 ac, 3fi.0 b u 1 . 6 3 ac' 1 . 1 0 bu' 0 . 2 7 hv able for this investigation. Cellulose CAB-b4 344 cp. 32.6 ac, 15.6 b u 2 , 3 1 ac: 0 , 6 7 bu: 0 . 0 2 hi. nitrate dopes, largely employed a t 1 1 . 2 s e c . 1 2 . 4 nitrogen Cellulose nitrate CN-c4 2 . 3 9 ni, 0 . 6 1 hy 40 CP. Ethylcellulose EC-d7 47.5-49.0 e t 2.43-2.54 et, 0.57-0.46 hy present, do not become slack in wet EC-dlO 84 cp. Ethylcellulose 47.5-49.0 e t 2.43-2.54 et, 0 . 5 7 - 0 46 hy weather and maintain satisfactory flexiBenzyicellulose BC-el High ..... ..... Chlorinated rubber CR-b2 1166 cp. ..... ..... bility during exposure but their ease of Methyl methacrylate resin h l M - c l Medium ..... ..... ignition and flammability make their a T h e viscosity values were obtained in t h e manufacturers' laboratories b y the following variety of use hazardous. methods (in parts b y weight unless otherwise noted): Cellulose acetate series CA-a: A. 9. T. M. falling ball method, using 20% solution in acetone There remain two film-forming, rela(A. S. T. M. Standards, P a r t 11, 1936). Cellulose acetopropionates CAP-a2, a3, a4, and a5: capillary viscometer method, using 10% solutively nonflammable plastics-cellulose tion in acetone a t 25O.C. Cellulose acetopropionates CAP-a6, a7, a8, and a9: A. S. T. M. falling ball method. acetopropionate and cellulose acetoCellulose acetobutyrate series CAB-a, except a5: capillary viscometer method, using 10 % solution butyrate-which offer promise for use i n acetone a t 25' C. Cellulose acetobutyrate CAB-a5: A. S. T. M. falling ball method. in airplane dopes. Figure 6 shows the Cellulose acetobutyrate series CAB-b: capillary viscometer method, using 10% solution in acevariation in tautness during exposure of tone a t 25' C. Cellulose nitrate CN-c4: A. S. T. M. falling ball method. selected panels covered with these two Ethylcellulose series EC-d: capillary viscometer method, usin a 5% solution in a mixture of 80 parts toluene and 20 parts absolute, ethyl alcohol b y volume a t 25$ C. materials, compared with the variation Chlorinated rubber CR-bZ:. capillary viscometer method, using a 20% solution in toluene a t 2 j o C. acetyl, pro = propionyl, hy hydroxyl, b u = butyryl, ni = nitrate, et = ethoxy. in tautness of cellulose acetate and cellub ac c Centipoises. lose nitrate doped fabrics exposed a t the same time. It will be noted that the cellulose acetopropionate and cellulose acetofor group I1 (exposed June 17, 1938) in Table I11 and for group butyrate panels did not slacken, whereas the cellulose acetate I11 (exposed November 1, 1938) in Table IV. panel, after 200 days of exposure, slackened consistently during periods of rain. The effect of approximately doubling Effect of Type of Plastic the butyryl content of cellulose acetobutyrate on the tautenThe plastic materials which gave sufficient initial tautness ing property is evident from a comparison of panels 210, to be useful for airplane dopes are cellulose acetate (acetone212, 221, and 222 covered with a compound containing 0.66 soluble), cellulose triacetate, cellulose acetopropionate, cellubutyryl equivalent, with panels 217, 218, 224, and 225, relose acetobutyrate, and cellulose nitrate. Ethylcellulose, spectively, covered with a compound containing 1.10 butyryl benzylcellulose, methyl methacrylate, isobutyl methacrylate, equivalents. The initial deflection of the fabric doped with and chlorinated rubber did not give panels of the requisite the material having the higher butyryl content is greater and initial tautness. This substantiates the conclusions drawn the difference becomes more pronounced with length of exfrom film data given in a previous report (4). posure. Doped fabrics of satisfactory flexibility can be All the panels covered with acetone-soluble cellulose aceprepared with cellulose acetopropionate and cellulose acetotate dopes except two containing plasticizer 608A (panels 101 butyrate, provided materials of suitable hydroxyl content and 102), slackened considerably in rainy weather during the are employed. This factor will be discussed in detail in the first year of exposure. Dopes of this type which contained next section. no plasticizer ringwormed after 2 to 7 months of exposure; The panels of ethylcellulose, benzylcellulose, chlorinated in general, those with 10 per cent or more of plasticizer rerubber, and methyl methacrylate were never very taut. mained flexible, All the cellulose triacetate doped fabrics TABLE I. VISCOSITY AND COMPOSITION OF PLASTIC MATERIALS
-
7
-
, FOR EXPERIMENTAL DOPES(WEIGHTPERCENTBASIS) TABLE 11. SOLVENTFORMULAS
Formula No. A65 A73 A82 CT24 AP89 AP93 AP96 AB87 AB109 AB110 AB112 x22
N47 E73 B97 CR30 MM19 I
VI1
I Acetone
35 35 20
10
.. ..
Methyl Ethyl Ketone 35 35
..
10
..
..
30 35 15
30
5
..
., .. ..
55
..
..
Toluene 20
15 50 (70% chlorofoi
n-Butanol
Butyl Acetate
Ethyl Lactate
Diacetone Alcohol
..
..
10
..
.. ..
2s (and 25%'meth>-l Cel?osolve)
..
..
..
30 32
..
30 25
.. ..
30
Ethyl Acetate (85-90%)
30 10
.. . I
20 25
22 20
..
50
20 25
.. ..
25
FEBRUARY, I940
INDUSTRIAL AND ENGINEERING CHEMISTRY
FIGURES1 AND 2 (above). FASTENING AIRPLANE CLOTHTO THE ‘ ~ B T FRAME;AND ‘rm TABLE, WEIGHTS, AND CLAMPS USEDTO APPLYAIRP I A N E CLOTH TO THE FILAME
FIGURE3 (below). ExPOSURE RACKS,WHERE: TAUTNESS MEASITREMENTS ARE BEINGMaon: O X DOPED FAUILrcs
FIGURE4 (right). APPARAI~US FOIL I)ETEBMIYlkG h E X I B I L 1 T Y OP DOFED FABRICS FIGURE5 (circle). TYPICAL nrst;WORMING OF DOPEDFABRIC
187
INDUSTRIAL AKD ENGINEERIKG CHEMISTRY
188
VOL. 32, NO. 2
TABLE 111. EXPOSURE TESTSON EXPERIMENTAL Panel number Plastic material Solvent formula Plasticizer, yo Plastic, grams -Conditions on D a y of TestRelative Days TErnp., huniidity, Prevailing on Roof F. % weather 0 70 65 Conditioning room
98 CA-all A65 None 22.3
99 (2.4-all A65 10 TPP 22.3
101 CA-all A65 10608A 25.5
102 CA-all A65 33 G O 8 4 25.5
105 CA-all A73 10 T P P 22.3
106 CA-all A73 10 T C P 22.3
107 CA-all A73 33 T C P 22.3
111 CA-all 482 10 T P P 22.3
114 Ch-a10 CT24 Kone 25.5
78
79
73
69
83
78
91
82
5 31 35 60 91
78 89 74 91 68
67 70 88 58 58
Cloudy Sunshine Rain Sunshine Cloudy
82 88 127 100 98
92 102 123 128 96
73 85 122 99 80
82 98 115 107 86
98 105 117 120 105
88 102 122 120 107
114 130 125 135 113
95 106 120 118 100
88 92 104 105 9OR1
94 123 152 171 182
70 85 46 55 37
98 45 42 95 54
Rain Sunshine Sunshine Misty, cloudy Sunshine
99 100 94R1 130 95
102 120 108 125 103
116 98 85 106 80
120 100 80 99 75
117 130 107 145 110
121 122 107 132 109
120 132 115 127 110
122 120 92 130 105
113 101R2 82R2 120 87R2
200 207 214 229 230
55 50 40 42 39
54 67 43 45 90
Sunshine Rain Sunshine Sunshine Rain
108 S 90R1 89R1
89 120 78 71 123
82 102 76 72 98
120 S 108 100
123 S 105 98 S
122 S 117 110 130
115
... ...
. s
124 S 102 107 S
257 273 286 311 333 365
50 45 43 86 64 93
44 26 93 24 52 55
Cloudy Sunshine Rain Sunshine Sunshine Sunshine
82 80R1 S 101 lOORl 106
90 90 S 120 115 118
65 67 110 91 91 95
70 62 82 86 88 98
90 94
87 93 S 128 119 136
105 98 S 130 144 155
90 91 S 102 106 121
Panel number Plastic material Solvent formula Plasticizer, Yo Plastic, grams
144 CAR-b4 AB87 None 23.9
145 CAR-b4 AB87 10 T P P 23.9
156 CAB-a1 AB109 10 T P P 25.5
9
9
123 115 123 157 CAB-a2 AB109 10 T P P 25.5
S
94
101 S
158 CAB-a3 AB109 10 T P P 25.5
159 CAB-a4 AB109 10 T P P 25.5
161 CAB-aZ AB112 10 608A 25.5
68
88R2
... ... ...
... ... ... ... ...
165 CN-c4 N47 None 25.5
0
70
65
Conditioning room
75
68
75
76
70
63
50
5 31 35 60 91
78 89 74 91 68
67 70 88 58 58
Cloudy Sunshine Rain Sunshine Cloudy
89 100 108 109R1 85
95 108 96 116 85
85 98 90 110 83
96 112 100 108 89
95 110 103 114 86
83 96 105 103 80
82 96 99 97 86
68 80 70 93 76
94 123 152 171 182
70 85 46 55 37
98 45 42 95 54
Rain Sunshine Sunshine Misty. cloudy Sunshine
110 107R1 89R1 110 94R2
108 102 83R1 98 90R1
93 103 80 95 76
93 110 85 110 92
110 107 89 116 94
108 94 83 118 85
104 90 78 122 76R1
73 87 70 85 G9
200 207 214 229 230
55 50 40 42 39
54 67 43 45 90
Sunshine Rain Sunshine Sunshine Rain
107R2 107 95R2 80R2 110
95 113 96R1 82 107
87 117 81R1 80 112
95 98 94 85 120
93 S 92 80 S
90 S 85 75 S
78 107 80R2 80R2 104
71 93 72 63 85
257 273 286 311 333 365
50 45 43 86 64 93
44 26 93 24 52 55
Cloudy Sunshine Rain Sunshine Sunshine Sunshine
....... .. ... ... ...
85R1 90R2 112
77 86 116 104 93 107
85 90 112 109 103 118
82 89
67 69
119 106 117
108 96 104
81R2 75 106
65 61 89 85 78 99
77
9
S
...
... ..I
a Tautness values are reported as the number; of mils deflection of the fabric under a 1-pound load. brittleness (i. e ringworming” of the film) is indicated by R followed ds 1 or 2 (the numerals indicate the degree of
brittleness, 2 being more brittle t h a n 1 ) ; S indicates slackness of the fabric in uhirh condition deflection values are meaningless. Symbols for plasticizers are: T P P = triphenyl phosphate; T C P = tri-o-cresyl phosphate;
Benzylcellulose, chlorinated rubber, and methyl methacrylate panels became tauter when wet, which is the reverse of the general behavior of the cellulose derivatives. This confirms a previous report ( 2 ) concerning these materials. Several panels of chlorinated rubber, benzylcellulose, and isobutyl methacrylate were prepared which were never exposed because they became slack on drying. It is difficult to prepare panels of these materials which are not slack. None of fifteen panels covered with cellulose nitrate has ringwormed or cracked. Films of ethylcellulose containing no plasticizer powdered off during exposure. The films containing 10 per cent of plasticizer 608A or a mixture of 10 per cent of Super-Beckacite Resin 2000 and 5 per cent of triphenyl phosphate were still intact and flexible after 6 months’ exposure, with the exception of panel 171, which had failed in one ringworming test. Panels of benzylcellulose (176 and 177) and chlorinated rubber (179 and 180) have not
ringwormed. The methyl methacrylate panels (182 and 183) had ringwormed a t the end of 3 mont’hs’ exposure.
Effect of Hydroxyl Content The relation of tautness and the hydroxyl content of various cellulose acetopropionates and acetobutyrates is shown in Table V. The initial tautness does not appear to be dependent upon the hydroxyl content of the material, but the tautness of the exposed panels in wet weather is considerably affected. Those samples which had a hydroxyl content in excess of about 0.4 equivalent became slack during periods of rain. Only three of the forty-two panels prepared with cellulose acetopropionates became brittle. These three were covered with cellulose acetopropionate sample CAP-a2. This compound is nearly a triester (0.03 hydroxyl equivalent), to
FEBRU-kRY, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
189
DOPESOF GROUP11," EXPOSED JUNE 17, 1938 115 CA-a10 CT24 10 T P P 25.5
119 CAP-a2 AP89 10 T P P 25.5
121 C.&P-a3 AP89 iowp 25.5
129 CAP-a4 AP89 IOTPP 25.5
130 CAP-a5 AP89 IOTPP 25.5
131 CAP-a6 AP89 ~OTPP 25.5
132 CAP-a7 AP89 10 T P P 25.5
133 CAP-a8 AP89 10 T P P 25.5
134 CAP-a9 AP89 10 T P P 25.5
139 CAP-a3 AP93 None 25.5
140 CAP-a3 AP93 10 608.4 25.5
143 CAP-a3 APD6 10 T P P 25.5
69
82
77
74
75
70
77
74
65
62
80
91 107 97 125 93
106 117 110 121 106
98 115 127 118 90
95 110 116 108 92
99 116 102 126 95
95 112 103 120 97
99 111 102 106 93
97 112
126 95
87 102 95 110 91
92 98 88 117 83
99 112 100 130 98
93 107R2 95R2 97 85R2
94 111 93Rl 102 85
103 120 105 116 105
113 127 100 118 98
115 110 95 123 99
102 122 100 99 100
97 123 101 100 104
100 124 96 95 104
100 121 08 105 108
96 110 80 100 95
92 104 79 95 85
105 122 88 98 107
114R2
107 130 91 SIR1 115
118 118 108 105 120
104 S 102 96 110
105 S 95 94
108 110 103 101 107
107 125 95 99 118
111 121 loa 103 127
108 120 102 97 124
100 110 87 90 117
90 108 84 85 101
112 103 100 103 117
94 83 114 118R1 112 142
103 99 118 135 127 147
86 90 S 117 109 117
96 92
96 90 115 128 112 126
97
110 146
1% 132 108 136
95 92 115 136 112 139
87 85 113 121 105 115
83 80 114 115 102 106
98 95 107 127 108 131
176 BC-el B97 hone 25.5
177 BC-el B97 10 T P P 25.5
179 CR-b2 CR30 None 25.5
180 CR-b2 CRB?, 10 "9 25.5
182 MM-cl MM19 None 25.5
183 MM-cl .M.M19 10 T P P 25.5
83
83
69
85 92 90 98R1 80R1
...
...
... ... ... ... ... . . ... ...
S
105 128
105
167 CN-c4 N47 10 GS 25.5
170 EC-1~7 E73 None 25.5
171 EC-d7 E73 1LO SB, 5 T P P 25.5
172 EC-d7 E73 10 608A 25.5
174 EC-dIO E73 10 SB.5 TPP 25.5
56
52
89
103
102
97
89
93
90
92
78 83 78 97 78
75 83 81 96 78
113 115 104 115 100
120 121 108 120 95
117 114 107 116 104
118 122 94 122 110
120 120 98 126 118
127 128 76 123 108
126 125 85 136 112
128 133 102 140 llOR2
125 127 100 138R1 105H2
80 91 74 83 73
81 88 73 90 66
105 125 99 110 111
101 122 102 108 98
110 127 107 115 120
105 128 110 115 92
97 126 90 103 106
107 135 111 107 109
73 133 119 78 125
80 140 118 80 112
100 l4OR2 120R2 93 107R2
100 145R2 103R1 93 97R2
77 103 76 70 90
70 95 70 64 84
12.5 S 128 786 142
113 108 113R1 95 103
122 105 118 108 114
108 114 107 81 120
126 118 127 77 108
127 113 130 130 112
125 105 136 113 75
123 107 125 114 88
122R2
115R2
71 67 96 93 88
67 62 90 90 81 96
128 130 130
96 92 115 143 130 140
106 101 120 143
105
89 84
120 108 112 135
120 122 110 123 126 152
105 112 88 155
119 118 90 12s 145 150
166 CT-c4 N47 10 T P P 25.5
100
... ... ...
... ...
137 112 140
-
608A = Dow plasticizer :,'608A" = di-(5-ter&butyl-2-xenyl) mono-(4-tertbutylphenyl) phosphate: 9" = D o w plasticizer "9" tri-o-xenyl phosphste; GS = glycol sebacate; 8 B = Super-Beckacite Resin 2000. All
which is attributed the early ringwonning. All the remaining samples of cellulose acetopropionates used in this investigation had hydroxyl contents of 0.15 equivalent or greater. All of the panels covered with cellulose acetobutyrates of less than 0.1 equivalent hydroxyl content ringwormed during 1 to 7 months of exposure, with one exception. Only one of the twenty panels covered with cellulose acetobutyrates of hydroxyl content greater than 0.1 equivalent ringwormed. This is definite evidence that the practically unhydrolyzed mixed esters of cellulose yield brittle films and are not suitable for use in airplane dopes.
Effect of Solvent Composition I n general, the solvent compositions giving the best resuits in initial tautness with the cellulose esters which might be considered for use in airplane dopes are as follows:
... ...
fabrics w-ere covered with 4 ooata of clear dope and 2 coats of aluminum pigmented dopes. The frames for these tests were wood. b Film powdering and washing off.
Plastic Cellulose acetate Cellulose aretopropionate Cell~iloseacetobutyrate Cellulose nitrate
Solvent Formula (Table 11) A65 -4P93 AB109 N47
A comparison of the initial tautnesses of the improved formulas with Nos. I and VI1 employed in preparing the first group of exposure panels ( 2 ) is presented in Table VI. Improvement in the tautening quality of the dopes is evident in every instance except for cellulose acetobutyrate. However, formula VI1 which gave a lower value than formula AB109 for the initial tautness with this derivative cannot be used because it yields films which are brittle.
Effect of Plasticizer The plasticizers, which in our previous work on the properties of the films appeared to offer most promise for use in air-
INDUSTRIAL AND ENGINEERING CHEMISTRY
190
VOL. 32, NO. 2
The marked improvement in tautness obtained with plasticizer 608A is clearly shown in Figure 7. Its specific effect is evident not only in decreasing the tendency to slacken in wet weather but also in the reduction of the mean value for the deflection of the doped fabric under load. Thus, for cellulose acetopropionate CAP-a3 in solvent formula AP93 the dope containing 10 per cent of triphenyl phosphate (panel 199) gave a tautness variation out of doors from 75 to 110, whereas the tautness of the dope containing 10 per cent of plasticizer 608A (panel 200) varied from 63 to 98. The sample of cellulose acetobutyrate CAB-a2 does not show this effect with a concentration of 10 per cent of plasticizer, probably because the hydroxyl content of this material (0.38 equivalent) is double that of BO 100 I 2 0 BO 100 120 80 100 120 80 100 the cellulose acetopropionate sample. HowDEFLECTION IN M I L S ever, when 33 per cent of plasticizer 608A is used with sample CAB-a2 (panel 214), the deOF FABRICS DOPEDWITH CELLCLOSE FIGURE 6. VARIATIONIN TAUTNESS flection values are not a t a maximum during DERIVATIVES AND EXPOSED ON THE ROOF(TABLE 111) periods of rain, as they are ordinarily, but rather during periods of hot weather. Further evidence of this favorable effect of plasticizer 608A plane dope formulation, were applied in dopes to fabricon tautness is available from the data presented in Table IV covered panels for exposure tests. The data in Tables I11 and IV indicate the variation in tautness and aging properties for panels 193, 194, and 195 which were doped with cellulose of a selected group of these doped fabrics. The results acetopropionate CAP-a3 in solvent formula AP89. The dope containing 10 per cent of triphenyl phosphate (panel 193) obtained with some of these panels are shown in graphic varied in tautness during exposure from 77 to 116, that conform in Figure 7. Plasticizer 608A was the only one which taining 10 per cent of plasticizer 608A (panel 194) varied from retarded slackening of the panels doped with acetone-soluble 61 to 105, whereas that containing 33 per cent of plasticizer cellulose acetate. None of the plasticizers used with cellulose 608A (panel 195) varied from 61 to 94. The dopes containing triacetate prevented ringworming during 2 to 4 months of exposure. Cellulose acetopropionate was definitely more plasticizer 6088 compare favorably with a dope composed of cellulose nitrate in solvent formula N22 plasticized with 10 resistant to loss of tautness in wet weather when plasticizer per cent of glycol sebacate, which had a tautness variation 608A was used. Ten per cent of triphenyl phosphate gave upon exposure of 57 to 85 (panel 240). approximately the same tautening effect with cellulose acetoThe following possible explanation is offered of the action of butyrate CAB-a2 as did plasticizer 608A, in the same concenplasticizer 608A in reducing the tautness variation of these tration. Glycol sebacate seems to be the best plasticizer of cellulose mixed esters to that observed for cellulose nitrate. those used for cellulose nitrate dopes. TABLE IV. EXPOSURE TESTS ON EXPERIMENTAL Panel number Plastic material Solvent formula Plasticizer, % -Conditions on D a y of TestRelative Days Temp., humidity, Prevailing onRoof F. $70 weather 0 70 65 Conditioning room
186 CA-all A65 10 T C P
187 CA-all A65 10 608A
188 CA-all A73 None
189 CA-all A73 10 T C P
190 CA-all A73 33 T C P
191 CA-all A73 10608A
192 CAP-a3 APS9 None
193 CAP-a3 AP89 10 T P P
194 CAP-a3 AP89 10608.4
195 CAP-a3 AP89 33 608A
70
65
73
72
98
67
65
75
62
68
15 30 34 45 63
46 44 55 37 55
42 45 95 54 54
Sunshine Sunshine Rain Sunshine Cloudy
70 70 112 70 75
64 59 100 62 65
71 66 122 72 74
72 67 115 66 72
90 95 116 88 102
65 60 112 62 65
65 71 103 79 82
77 88 101 87 96
61 67 68 87 73
61 69 77 68 77
70 77 92 93 120
50 40 42 39 50
67 44 45 90 44
Rain Sunshine Sunshine Rain Cloudy
S 72 82 S 65
97 60 67 105 57
7SR1 88
S
S 75 80 S 67
S 90 95 120 83
108 64 70 122 59
108 75 75 99 72
113 91 90 110 86
97 73 67 95 70
85 72 69 81
136 149 174 196 228
45 43 86 64 93
26 93 24 52 55
Sunshine Rain Sunshine Sunshine Sunshine
66 S 89 78 93
58 100 77 70 85
69 S 82 76 82
65 127 81
86 113 73
59 100 77 71 82
71 98 90 81 95
83
99 114 96 116
67 89 86 78 93
67 78 82 73 94
272 314 335 356 364 366
86 69 45 59 50 54
53 38 94 36 91 35
Sunshine Sunshine Rain Sunshine Rain Sunshine
80 80 S 80 S 71
70 71 S 63 112 56R1
74 80R2 S 85R2 S 70R2
72 71 S
88 88 97 82 S 70
112 104 112 91 116 83
89 86 103 73 105
S
66
Tautness values are reported as the numb:: of mils deflection of the fabric under a 1-pound load: brittleness (i. e., ringworming” of the film) is indicated b y R followed by 1 or 2 (the numerals indicate the degree of 0
SO
111
76 81 S 83 S 67R2
120 112 78 98
90
134
S
85
71
S 60
68
70
93 84 85 74 85 63R1
brittleness, 2 being more brittle t h a n 1 ) ; S indicates slackness of the fabrio in which condition deflection values are meaningless. Symbols for plaaticizers are: T P P = triphenyl phosphate; T C P = tri-o-cresyl phosphate;
FEBRUARY, 1940
INDUSTRIAL AND ENGINEERIKG CHEMISTRY
191
FIGURE 7. EFFECTOF PLASTICIZERS ON VARIATION IX TAUTNESS OF FABRICS DOPED WITH CELLULOSEDERIVATIVES AND EXPOSED ON THE ROOF(TABLE IV) THE
Sheppard and Newsome (5) showed that the moisture-absorbing property of cellulose derivatives is related to their content of free hydroxyl groups. The cellulose nitrate used in airplane dope contains about 0.6 equivalent of hydroxyl and yet it is less affected by humidity variations than acetone-soluble cellulose acetate, CA-all, containing less hydroxyl (approximately 0.47 equivalent). It is therefore believed that the hydroxyl groups in cellulose nitrate must be partially protected in some manner by the nitrate groups. A comparison of the electronic structure of the nitrate and phosphate groups reveals the presence in both of an oxygen atom linked to the nitrogen or phosphorus by a semipolar bond, indicated in Figure 8 by arrows. These oxygen atoms may be exceptionally active in forming hydrogen bridges (1) with the hydroxyl groups of the cellulose derivatives and thus serve to reduce their attraction for moisture.
Correlation of Film Properties and Behavior of Doped Fabrics Films were made with a portion of the clear dope applied to the panels in group 11, according to the method described in a preIf a close correlation bevious report tween film properties and the behavior of
(e).
i
DOPESOF GROUPI I I , O EXPOSED NOVEMBER I, 1938 197 CAP-a3 AP93 None
199 CAP-a3 AP93 10 T P P
64
68
59
66 75 105 75 77
75 83 100 80 83
105 75 76 108 71
223 CAB-a2 AB110 10608A
224 CAB-a5 AB110 None
225 CAB-a5
59
54
68
74
49
60 65 107 63 70
63 71 109 70 78
59 65 61 98 68
83 90 98 88 96
83 99 95 91 92
59 62 76 60 64
111 95 95 102
113 72 75 109 60
112 61 68 104 61
113 91 94 102 88
106 92 88 92 88
85 60
89
108 65 68 96 59
66 75 59
84 96 103 90 119
60 95 73 67 78
65 90 84 72 87
60 94 73 62 80
94 95 108 101
85 89 115 99 113
57 78 65 70 78
120 104 107 88 108
77 68 S 65
83 76 113 75 S 67
113 101 97 75 103 80
68 67 88 64 93 59
221 222 CAB-a2 CAB-a2 AB110 AB110 None 10 T P P
212 CAB-a2 AB109 10 T P P
213 CAB-a2 AB109 1060SA
67
65
68
80
69
78
55
63 68 84 70 73
82 81 108 73 77
71 80 92 74 82
76 82 100 71 82
78 85 75 70 75
87 84 95 85 95
86 93 91 88 101
103 77 81 98 77
90 66 68 80 68
102 75 85 107 65
111
76 82 108 68
96 72 92 108 70
78 70 87 70 70
117 90 92 101 83
71 102 93 84 100
80 95 97 84 106
63
75 111 88 78 90
78 95 90 78 102
78 100 95 86 97
75 70 106 87 107
77 92 97 86
90
99
113 80 S 73
110 85 107 77
84 85 95 72 98 63
89 78 113 73 S 66
92 88 110 71 S 67
88
105
210 200 CAP-a3 CAB-a2 AP93 AB109 1060SA None
SO
80 79 95
90 82 S 82 S 75R1
214 217 CAB-a2 CAB-a5 AB109 AB109 33608.4 None
95 91 84 68 75 62R1
608A = Dow plasticizer “60SA” = cli-(5-tert-butyl-Z-xenyl) mono-(plert-butylphenyl) phosphate. GS = glycol sebacate All fabrics were covered with 4 coats of clear dope and 2 coats of aluminum-pigmented dope
... *.. *.*
... ... ... ...
218 CAB-a5 AB109 10 T P P
so
S
52Rl
72 68 103 60R1 S 53Rl
containing a total of 25.5 grams of the plastic. were metal.
... ... ... ... ... ...
...
AB110
10 T P P
240 CN-c4 N22
10GS
The frames for these testa
INDUSTRIAL AND ENGINEERING CHEMISTRY
192
TABLEV. RELATIONOF TAUTNESS TO Solvent formula Plasticizer (triphenyl phosphate) Frame material D s y s of exposure Weather on d a y of test Hydroxyl Sample Equivalent 0.03
VOL. 32, NO. 2
THE
DEGREEOF HYDROLYSIS OF
AP89
AP93
AP93
AB109
10% T P P \?. ood
Xone Wood
TPP Letal
10% TPP Wood
0
..
207 Rain
69
130
_
h
_
c
_
_
.0.
70 Rain
Tautness, M i b 65 112
65
103
..
*..
...
doped fabrics exists, then dopes can be formulated from a study of experimental films. Much less time, labor, and materials are needed to prepare films than to prepare and dope panels. Some dopes do not show as good tautness as expected from the film shrinkage. The film on the cloth is drying under tension. Any rubberlike property of the film will allow it to stretch, which reduces the fabric tautness. When the film dries on cellophane, it shrinks without restraint. Allowance must be made for this type of film when a comparison of tautness and film shrinkage is made.
PLASTIC BASEOF
Sample CAB-b4
Panel NO. 102 140 144 149 152 155 173
AN
AIRPLANEDOPE AB109
c_.__
_
207 Rain
0
..
*.
14
_
5
THE
Hydroxyl Equivalent 0.02
Plaatia Celliiloaa anstate
..0 C -
..
207 Rain
570 T P P Metal
.0.
70 Rain
Tautness, hlils60
...
112
Days of Exposure before Ringworming
Film Flexibility
Not ringwormed Not ringwormed 60
Nonflex/ble Nonflexible Flexible Flexible Flexible Flexible Flexible
77 ..
60 60 60
Effect of Panel Construction
A series of wooden and metal test panels were prepared with cellulose acetate and cellulose nitrate dopes to compare TABLEVI. EFFECTOF soLVENT c~~~~~~~~~~ ON I~~~~~~ the effect of the material of which the frame is constructed upon the tautness values which are obtained upon exposure TAUTNESS OF DOPED FABRICS of these panels out of doors. The conditions of fabric cover-Initial Tautness of Doped Fabrics, Mils--Solvent Cellulose Cellulose acetoCellulose acetoCellulose ing were also varied to include panels covered on one side only, Formula acetate propionate butyrate nitrate panels covered on both sides with a vent cut in the back I 84 92 76 86 covering, and panels covered on both sides without a vent. VI1 72 79 65 61 I n general, the coverings on the metal frames gave less deA82 71 .. .. .. AP93 .. 71 .. .. flection than those on the wooden frames. The panels covAB109 .. .. 72 .. N47 .. .. .. 56 ered on one side only and doped with cellulose nitrate showed considerably greater fluctuations in tautness than those covered on both sides. The double covering doped with cellulose acetate varied over approximately the same range Table VI1 shows the comparison of film shrinkage and of tautness as the single-covered panels, provided the measinitial tautness of doped fabrics for one hundred thirty urements were not made during the early stages of wetting or panels, The correlation is good except for seven panels drying. The presence or absence of a vent on the back of the (about 6 per cent of the total) which show better tautness panels which were covered on both sides did not have any than the film shrinkage indicates. All seven panels give good appreciable effect on the tautness readings. Since wood tautness readings but the film shrinkages are only moderate. undergoes greater dimensional changes than metal under No reason is known to account for this. varying atmospheric humidities, i t is preferable c to use all-metal frames for testing airplane dopes. TABLEVII. COMPARISON OF FILMSHRINKAGE WITH INITIAL TAUTNESS OF DOPED FABRICS Conclusions Av. tautness, mils Rsnge of tautness, mils No. Danels Av. tautness mils Range No. panels of tadtness, mils Av. tautness, mils Range of tautness, mils No. psnela Av. tautness, mils Range of tautness, mils No. psnels Total No. panels
21.0 80 66-85 5 82 69-90 8 90 84-94 12 95 86-98 5
30
Grams of Plastic 22.3 23.9 25.5 77 60 74-81 50-75 11 26 80 74 74-86 11 57-83 26 87 90 83-91 2 ... 83-97 (214 slack) 97 90-103 (5 slack) ... 10 13 11 76
.. .... ...
-
...
.... .. ... . ..
... . ..
... ... ...
I n a comparison of the film flexibility with ringworming of the doped fabric during exposure for ninety-one experimental dopes, it was observed that only seven panels (about 8 per cent of the total) failed to give a good correlation. The data concerning these seven panels may be summarized as follows:
Film Shrinkage
1. The choice of a satisfactory plastic base for a relatively nonflammable airplane dope to be used in place of the hazardous cellulose nitrate product is limited to cellulose acetopropionate Moderate and cellulose acetobutyrate. The fabrics doped with compositions containing fully acylated Slight mixed esters of cellulose become brittle rapidly during exposure out of doors and are therefore None not suitable for use in airplane dopes. Those mixed esters which have a hydroxyl content in excess of about 0.4 equivalent become slack during periods of rain. The optimum hydroxyl content of a mixed ester for use in an airplane dope is found to be about 0.2 equivalent. It is also suggested that a cellulose acetate of about this same degree of hydrolysis would be a much more satisfactory product for many purposes than the fully esterified cellulose triacetate now available commercially. Good
INDUSTRIAL AND ENGINEERING CHEMISTRY
FEBRUARY, 1940
0,O: 00
C
00 NN
00
0
I
0 N 0 ; -C-O-N+O I 00
II
00
C co
EOE 00
OP
00
I
00
op
00
I
c o o ~ p p ‘ o :-c-O-P+O 0,000
I I 0 I
-C-
0
I
G O
-C-
C
FIGURE 8. ELECTRONIC STRUCTURES OF &-ITRATE RADICAL IN CELLULOSE ; “ r T AND ~ ~ORTHOPHOSPHATE ~ ~ ~ ~ RADICAL IN ARYLPHOSPHATE PLASTICIZERS Small letters indicate electrons from the corresponding
adjacent atoms
2. Solvent combinations giving best results in the exposure tests of dopes formulated with cellulose acetate, cellulose acetopropionate, cellulose acetobutyrate, and cellulose nitrate are reported. In every instance these formulas produced marked improvement in the tautening and aging qualities of the dopes when compared with those used in the original group of exposure panels described in the first report ( 2 ) . 3. The use of aryl phosphate plasticizers with cellulose acetate, cellulose acetopropionate, and cellulose acetobutyrate produces, in general, better initial tautness, greater resistance to slackening in wet weather, and less variation in tautness during exposure than other types of plasticizers examined. Dopes formulated with cellulose acetopropionate of 0.19 equivalent hydroxyl content and plasticizer 608A compare favorably in tautening qualities with cellulose nitrate dope plasticized with glycol sebacate. A possible explanation of this effect is presented, based on the presence in both nitrate and phosphate groups of an oxygen atom, held by a semipolar
193
bond, which may have an attraction for the hydroxyl groups in the cellulose compounds and thus reduce their affinity for moisture. 4. A close correlation is shown to exist between the properties of the films and the behavior of the doped fabrics. Data on tautness of doped fabrics and shrinkage of the unsupported films agreed in about 94 per cent of the tests and data for the flexibility of the films and exposed doped fabrics agreed in about 92 per cent of the tests. The use of the film technique in place of the application of each experimental dope t o fabric-covered panels permits a considerable saving in time, labor, and material in evaluating new compounds and formulas. 5. Doped fabrics on metal frames give less deflection, in general, than those on wooden frames. Inasmuch as wood undergoes considerable dimensional changes with varying atmospheric humidities, it is preferable to use allmetal frames for testing airplane dopes.
Acknowledgment This investigation was sponsored by the Bureau of Aeronautics, United States Kavy Department, and the results are published by permission of the chief of that bureau. The authors express their appreciation of the interest and suggestions of Lieutenant Commander C. F. Cotton of the Bureau of Aeronautics during the course of this work. The plastic materials were furnished by the Dow Chemical Company, E. I. du Pont de Nemours & Company, Inc., Eastman Kodak Company, Hercules Powder Company, and Tennessee Eastman Corporation. The interest and suggestions of these firms during the course of this work are gratefully acknowledged.
Literature Cited (1) Huggins, M. L.,J. Org. Chem., 1, 407-57 (1936). (2) Kline, G. M., and Malmberg, C. G . , IND.ENG.CHEY.,30, 542-9 (1938); cf. also Kline, G. M., and Schiefer, H. F., Natl. Advisory Com. Aeronaut., Tech. Note 729 (Sept., 1939). (3) Navy Aeronautical Specification for Primer, Zinc Chromate, Naval Aircraft, P-27b. June 1. 1937, and Amendment No. 1. June 1, 1938; Naval Aircraft Factory Tentative Process Specification for Use of Primer, Zinc Chromate, Naval Aircraft Specification P-27, PF-Sa, Oct. 14, 1935, and Specifioation Change No. 3, June 28, 1937. (4) Reinhart, F. W., and Kline, G. M., IND. ENG.CHEM..31, 1522-9 (1939). (5) Sheppard, S.E., and Newsome, P. T., J. Phys. Chem.,33, 1817-36 (1929).
PRESENTED before the Diviaion of Paint and Vsmi6h Chemistry at the 98th Meeting of the American Chemical Society, Boston. Masa.
c
