Epoxy-terminated polyisobutylene polydimethylsiloxane compositions

Abstract: An antifoam composition is disclosed comprising (A) a polydimethylsiloxane having a viscosity greater than 2 mm 2 /s (cS) at 25°C.; and (B) a polyisobutylene oligomer having a number average molecular weight of 200 to 3,000 and having at least one end terminated with an epoxy-containing group, the weight ratio of said polydimethylsiloxane (A) to said polyisobutylene (B) being in the range 1:99 to 99:1.

Description: The present invention relates to an antifoaming composition comprising a blend of a polydimethylsiloxane oil and a polyisobutylene oligomer and to a defoaming method making use of the composition. Polydimethylsiloxane oils, particularly when formulated with a silica powder, are known for their ability to reduce frothing or foaming in aqueous systems. There are also examples in the art where organic formulations have been used to control foam in such systems. These antifoaming or defoaming agents find utility in many industrial processes, some of which would be highly impractical if the agent were not available. Antifoam agents containing both organic and silicone components are also known in the art. For example, US-A-3,959,175 discloses a defoamer based on a mixture of polyisobutylene and a high melting hydrophobic component, such as fatty amide, fatty acid or tri-glyceride, or a mixture of the polyisobutylene and a hydrophobic material such as treated silica powder. Combinations of the above three ingredients are also taught therein. This patent incorrectly includes silicone oil as a member of the aforementioned "high melting" component which is said to have a melt point above 40°C. Rather, the typical melting point of a polydimethylsiloxane oil is actually -40°C. This patent also includes examples wherein silicone oil is used, albeit at levels of no more than 0.5 percent. The viscosity of the silicone oil used is not stated and no criticality thereof is suggested. Likewise, the polyisobutylene taught therein is shown to have particular end groups of the formula -CH 2 C(CH 3 )=CH 2 , and there is no suggestion to alter this group. We have found that certain blends of polydimethylsiloxane (PDMS) oils and polyisobutylene (also referred to as polybutene or PIB) have antifoaming activity which is superior to either of these individual components. Our blends, wherein the polyisobutylene has at least one terminal epoxy-containing group in its molecule, have been found to be significantly better antifoams for aqueous detergent systems than comparable blends wherein both terminal groups are saturated hydrocarbon groups, such as those having the structure -C(CH 3 ) 3 or -CH 2 CH(CH 3 ) 2 . The latter structure is almost identical with that of the end group taught by US-A-3,959,175. It is surprising that such a subtle change in end groups can result in the enhanced defoaming performance of our blends wherein the polyisobutylene has an epoxy-containing end group. The synergistic antifoam activity observed when our blends are used to defoam an aqueous foaming system may be further augmented by the incorporation of a fine silica powder. This further serves to reduce the concentration of antifoam agent required to defoam a particular foaming system. The present invention therefore relates to an antifoam composition as defined in claim 1. The polydimethylsiloxane (A) used according to our invention is a homopolymer or copolymer having a viscosity at 25°C. which is greater than 2 mm 2 /s (cS) wherein up to 15 mole percent of diorganosiloxane units may be copolymerized with the dimethylsiloxane units. It has been found that when the viscosity of the polydimethylsiloxane is ≤2 mm 2 /s (cS) the antifoam activity of the instant blends is not enhanced over the corresponding polydimethylsiloxane polymer itself. On the other hand, when the viscosity of this component is more than 2 mm 2 /s (cS), a synergistic effect is obtained whereby the antifoaming activity of our composition is superior to either the pure polydimethylsiloxane or the pure PIB components. There is no critical upper limit of the polydimethylsiloxane viscosity and it is only limited by practical mixing considerations, but is preferably no more than 100,000 mm 2 /s (cS). The organic groups of the above mentioned diorganosiloxane units are independently selected from alkyl radicals having 1 to 16 carbon atoms, phenyl radical or halogenated alkyl radicals having 3 to 6 carbon atoms or alkylene oxide groups, such as ethylene oxide, propylene oxide or copolymeric combinations thereof. The nature of the terminal groups on the polydimethylsiloxane component (A) is not critical for the purposes of the present invention. These are preferably inert groups, such as trimethylsiloxy, dimethylphenylsiloxy and diethylphenylsiloxy. They may also be illustrated by groups such as dimethylvinylsiloxy, dimethylhexenylsiloxy, dimethylhydroxysiloxy, dimethylhydrogensiloxy, dimethylalkoxysiloxy, methyldialkoxysiloxy and trialkoxysiloxy, wherein the alkoxy groups are preferably methoxy. Most preferably, component (A) is a polydimethylsiloxane homopolymer having trimethylsiloxy terminal units. Component (A) is well known in the art and is generally available commercially. Component (B) of the composition according to our invention is a polyisobutylene oligomer having a number average molecular weight (MWn) of 200 to 3,000, preferably 200 to 800 and most preferably 300 to 400. For the purposes of the present invention, the polyisobutylene oligomer must have at least one terminal group in its molecule which contains an epoxy group. This epoxy group has the general structure in which R, R' and R'' independently represent radicals selected from hydrogen and alkyl radicals having 1 to 7 carbon atoms. Such oligomers are known in the art and many are available commercially in a variety of molecular weights from the Amoco Chemical Company (Chicago, IL) under the trade name Actipol™. For this invention, the weight ratio of component (A) to component (B) is such that the antifoam activity of the blend of (A) and (B) is greater than that of either (A) or (B) alone, as determined by the percent foam drop in a simple shake test, described more completely in the examples. This ratio is 1:99 to 99:1. Preferably, this ratio is 95:5 to 5:95, more preferably 90:10 to 10:90 and most preferably 90:10 to 70:30. In addition to components (A) and (B), the instant compositions preferably also contain (C), a fine powdered silica component. The addition of silica further augments the antifoam activity of our compositions. Component (C) can be a precipitated or fumed silica which is treated with, e.g., a silane or siloxane agent to render it hydrophobic as commonly practiced in the art. Examples of such treating agents include hexamethyldisiloxane, trimethylchlorosilane and low molecular weight silanol-terminated polydimethylsiloxane, preferably hexamthyldisilazane. Preferably, this component is a silica having a surface area in the range of 50 to 400 m 2 /gram, most preferably 50 to 150 m 2 /gram. The silica can be pre-treated or treated in-situ. To prepare our antifoam compositions, components (A), (B) and, optionally, component (C) are blended to form a homogeneous mixture. Any suitable means for mixing such systems may be used (e.g., low shear mixers, vortex mixer) and the order of addition is not critical. Typically, components (A) and (B) are added to component (C) and the latter is then uniformly dispersed in components (A) and (B). Our invention further relates to a method for defoaming a foaming system as defined in claim 10. In this method, the above antifoam composition is then added to a foaming system, preferably an aqueous foaming system, in an amount sufficient to reduce foaming, as determined by routine experimentation. Typically, the amount used of our antifoam composition is approximately 1 to 14,000 parts per million (ppm) based on the weight of the foaming system. Preferably, this range is 1 to 8,000 ppm, and most preferably 200 to 4,000 ppm. When silica (C) is employed in our method, it is preferably present at a level which results in a silica concentration of no more than 140 ppm (by weight), and preferably no more than 40 ppm, in the foaming system. Preferably, up to 50%, more preferably up to 35%, and most preferably up to 3%, of the total weight of components (A), (B) and (C) is present as silica. The addition of greater amounts of silica in the contemplated foaming systems does not enhance the efficiency of our antifoam composition beyond that of only polydimethylsiloxane-silica mixtures. Thus, for example, when the total concentration of our antifoam composition is more than 4,000 ppm, the silica content is preferably no more than 3% based on the combined weight of components (A) and (B) and (C). For the preferred range of antifoam concentration in a foaming system, the silica is preferably used at a level of up to 1 percent based on the total weight of (A), (B) and (C). The skilled artisan can readily determine the optimum amount of silica by routine experimentation. In a preferred embodiment, the foaming system comprises aqueous surfactant media, such as aqueous detergents encountered in laundry and dishwashing applications. Our compositions are also suitable as antifoams in pulp and paper production. Additionally, our method may also be used to defoam other foaming systems, such as found in petroleum and petrochemical processing, solvent-based inks and paints and in chemical processing. The following examples are presented to further illustrate the composition and method of this invention. All parts and percentages in the examples are on a weight basis and all measurements were obtained at a temperature of 25°C., unless indicated to the contrary. The activity of our antifoam compositions were determined by a shake test as follows. An aqueous detergent stock solution was prepared by adding 20 drops (0.45 gram) of DAWN™ Original Scent Dishwashing Liquid (Proctor & Gamble, Cincinnati, OH) to 345 ml of warm tap water and mixing thoroughly. Twenty ml (19.7 g) aliquots of the stock solution were placed into 9.5 dram (35.2 ml) vials, filling each vial about half way. An antifoam composition was added to each vial at the level indicated in the tables below. In each shake test series at least one vial did not contain antifoam agent and this served as a control for the series. In the shake test procedure a vial was lifted to a position above the operator's ear and then shaken by extending the arm in a "throwing" motion (approximately a 0.61 m (2 foot) extension), then returning to the initial position. Ten such shake cycles were used in each case, with a slight pause between cycles, all within a span of 5 seconds. After shaking, the vial was placed on a laboratory bench top and observed as a function of time, as shown in the tables. The activity of a given antifoam composition after a given time interval was obtained according to the following formula: % drop in foam height = 100 (T - F)/(T - L) wherein T = 8.4 cm = maximum height of liquid plus foam in the vial (i.e., when empty portion of vial is completely filled with foam) F = liquid plus foam height at a given time L = liquid height = 4.4 cm From this formula it is seen that, when foam fills the empty portion of the vial, as in the case of the controls immediately after shaking, T = F and the % drop is zero. Likewise, when all the foam has collapsed after a given time interval, F = L and the % drop is 100%. Thus, a larger value of the % drop (for a given time of rest after shaking) indicates improved defoaming activity. The values of F obtained herein represent an average of three measurements, each taken at a different location around the vial. Series 1 Polysynlane™ PIB and trimethylsiloxy-terminated PDMS having a viscosity of 350 cS (350 mm 2 /s) were blended in the ratios shown in the first column of Table la to form comparative antifoam agents and these were evaluated according to the above shake test. Polysynlane™ is described as a saturated polyisobutylene having a number average molecular weight of 320 (MWn = 380 by gel permeation chromatography) and having a terminal group of the formula the other terminal group being of the formula -C(CH 3 ) 3 . It is a product of Polyesther Corporation, Southhampton, NY. The measured total concentration of the antifoam blend (or pure PIB or PDMS) in the foaming system is shown in the second column of Table la (ppm = parts per million). The % drop in foam height at three different times is reported in the last three columns. For the purposes herein, the term "immediate" indicates measurement within 10 seconds. (no silica) Weight Ratio of PDMS/PIB Antifoam concentration (ppm) Drop in Foam Height (%) Immediate 5 Minute 24 Hours 0/0 (Control) -- 0 0 25 100/0 4023 22 27 60 0/100 4162 0 0 33 90/10 4112 21 22 51 70/30 4114 14 14 50 50/50 4132 22 23 49 30/70 4208 19 19 51 10/90 4036 14 15 58 From Table la it is seen that the antifoam activity of these blends is generally lower than that of the pure PDMS component (i.e., weight ratio = 100/0) for all times. This series also included evaluation of the above compositions wherein 3% of each blend was replaced with QUSO™ WR55 FG silica powder. QUSO™ WR55 FG is described as a synthetic, amorphous, precipitated silica which is treated with polydimethylsiloxane, has a typical surface area of 90 m 2 /g and is marketed by Degussa Corporation, Dublin, OH. The results are presented in Table 1b. (3% silica in antifoam composition) Weight Ratio of PDMS/PIB Antifoam concentration (ppm) Drop in Foam Height (%) Immediate 5 Minute 24 Hours 0/0 (Control) -- 0 0 25 100/0 4061 97 98 100 0/100 4086 38 40 100 90/10 4079 95 97 100 70/30 4135 95 97 100 50/50 4081 95 95 100 30/70 4137 95 95 100 10/90 4059 93 93 100 From Table 1b it is again seen that the antifoam activity of these blends is generally lower than that of the pure PDMS component. In this case, however, the introduction of silica results in good performance for most of the compositions. Series 2 The comparative evaluations using the Polysynlane™ PIB and PDMS of Series 1 were repeated wherein the total concentration of the antifoam blend was reduced, as indicated in Tables 2a and 2b. (no silica) Weight Ratio of PDMS/PIB Antifoam concentration (ppm) Drop in Foam Height (%) Immediate 5 Minute 24 Hours 0/0 (Control) -- 0 0 26 100/0 736 23 28 57 0/100 822 0 0 8 90/10 736 0 0 39 70/30 756 11 13 49 50/50 731 0 0 25 30/70 761 4 7 44 10/90 741 0 0 29 (3% silica in antifoam agent) Weight Ratio of PDMS/PIB Antifoam concentration (ppm) Drop in Foam Height (%) Immediate 5 Minute 24 Hours 0/0 (Control) -- 0 0 26 100/0 726 84 86 100 0/100 777 11 16 100 90/10 716 67 70 100 70/30 761 85 86 100 50/50 746 75 78 100 30/70 771 79 81 100 10/90 746 76 78 100 From Tables 2a and 2b it is seen that the same general trend as found in Series 1 was obtained at the lower antifoam concentrations (i.e., the addition of this PIB to PDMS generally detracts from the antifoam performance of the latter for all time intervals under consideration). Series 3 Antifoam agents of the present invention were prepared as described in Series 1 using Actipol™ E-6 PIB in place of the Polysynlane™. Actipol™ E-6 is described as an epoxy-terminated polyisobutylene having a number average molecular weight of 365 and is a product of the Amoco Chemical Company, Chicago, IL. One terminal group of this oligomer has the structure in which Me denotes a methyl radical, the other end group being of the formula -C(CH 3 ) 3 . The results of the shake test using antifoam concentrations similar to those of Series 2 are presented in Tables 3a and 3b. (no silica) Weight Ratio of PDMS/PIB Antifoam concentration (ppm) Drop in Foam Height (%) Immediate 5 Minute 24 Hours 0/0 (Control) -- 0 0 13 100/0 695 19 21 44 0/100 706 8 18 56 90/10 690 30 34 82 70/30 690 21 26 83 50/50 670 7 7 93 30/70 680 16 18 88 10/90 675 12 13 84 (with 3% silica) Weight Ratio of PDMS/PIB Antifoam concentration (ppm) Drop in Foam Height (%) Immediate 5 Minute 24 Hours 0/0 (Control) -- 0 0 13 100/0 700 75 78 100 0/100 670 68 70 100 90/10 711 95 98 100 70/30 685 93 93 100 50/50 670 90 91 100 30/70 710 90 93 100 10/90 716 88 89 100 Table 3a demonstrates that the compositions of our invention have greater antifoam activity than the pure PDMS. This enhancement is observed either immediately, or at longer time intervals. As seen from Table 3b, the improvement is even more pronounced when silica is incorporated in our antifoam formulation. Series 4 Antifoam compositions of the invention, based on the PDMS and PIB used in Series 3, were evaluated at a higher total concentration. The results are presented in Table 4. (no silica) Weight Ratio of PDMS/PIB Antifoam concentration (ppm) Drop in Foam Height (%) Immediate 5 Minute 25 Hours 0/0 (Control) -- 0 0 0 100/0 4457 16 16 48 0/100 4166 10 13 43 99/1 4469 31 32 55 90/10 4340 45 53 86 70/30 4433 48 48 85 50/50 4296 18 22 76 30/70 4340 29 32 87 10/90 4419 20 23 90 1/99 4320 24 28 89 From Table 4 it is again seen that the antifoam activity of our blends is generally enhanced, either immediately or after longer periods. Series 5 The effect of the viscosity of trimethylsiloxy-terminated PDMS component on the antifoam performance was determined using the PIB of Series 3, this PDMS viscosity is indicated in the second column of Table 5. In this series of experiments the total antifoam agent concentration was in the range of 4096 to 4455 ppm. (no silica) Weight Ratio of PDMS/PIB Viscosity of PDMS (mm 2 /s) Drop in Foam Height (%) Immediate 5 Minute 24 Hours 0/0 (Control) -- 0 0 0 100/0 2 24 28 59 90/10 2 27 30 46 100/0 350 16 18 45 90/10 350 40 43 76 100/0 1000 42 43 72 90/10 1000 58 61 93 100/0 30000 37 38 70 90/10 30000 42 46 98 From Table 5 it is seen that the antifoam activity of blends based on PDMS having a viscosity of 2 mm 2 /s (cS) is not improved by the addition of the epoxy-terminated PIB, whereas blends of our invention containing PDMS oil having a viscosity of ≥2 mm 2 /s (cS) show enhanced performance relative to the corresponding pure PDMS component. Series 6 Antifoam performance of compositions based on the PDMS and PIB used in Series 3 were evaluated as a function of total concentration in the foaming system. The results are presented in Table 6. (no silica) Weight Ratio of PDMS/PIB Antifoam concentration (ppm) Drop in Foam Height (%) Immediate 5 Minute 24 Hours 0/0 (Control) -- 0 0 28 100/0 573 17 24 55 100/0 1909 20 23 58 100/0 4671 26 32 51 100/0 6825 23 28 68 100/0 13953 37 43 74 90/10 602 46 50 84 90/10 1890 41 46 76 90/10 4957 51 54 85 90/10 7265 53 60 79 90/10 14050 54 58 82 From Table 6 it is seen that, within the range of 600 to 14,000 ppm, the antifoam activity is relatively insensitive to total antifoam concentration. Series 7 Antifoam compositions based on the PDMS, PIB and silica used in Series 3 were evaluated as a function of silica concentration. The weight ratio of PDMS/PIB is given in the first column of Table 7 and the silica content is shown in ppm based on the total antifoam system and as a percent of the total antifoam agent (i.e., % silica in the combination of polydimethylsiloxane, PIB and silica). The total antifoam concentration in this series was 188 ppm for the samples containing 1.9 ppm silica and 4,200 for the remaining samples. Weight Ratio of PDMS/PIB Immediate Drop in Foam Height (%) at Given Silica Concentration (ppm) 1.9 4.2 21 42 136 1% 0.1% 0.5% 1% 3% 100/0 55 50 80 90 95 0/100 29 35 46 65 78 90/10 82 80 93 97 97 70/30 78 83 93 97 97 50/50 65 73 93 95 97 30/70 65 69 88 93 97 10/90 61 70 85 94 97 Table 7 demonstrates that the activity of the instant compositions is not improved much when the silica content approximates 140 ppm (3%). Series 8 The effect of the viscosity of the trimethylsiloxy-terminated PDMS component on antifoam performance was again determined using the PIB of Series 3. This PDMS viscosity is indicated in the second column of Table 8a. In this series of experiments, the total antifoam agent concentration was in the range 4112 to 4162 ppm. (no silica) Weight Ratio of PDMS/PIB Viscosity of PDMS (mm 2 /s) Drop in Foam Height (%) Immediate 4 Hours 24 Hours 0/0 (Control) -- 0 0 29 0/100 -- 16 29 47 100/0 2 28 39 58 90/10 2 28 40 60 100/0 50 13 21 38 90/10 50 28 41 63 100/0 100 16 28 47 90/10 100 15 35 62 100/0 350 30 45 63 90/10 350 61 73 94 From Table 8a it is again seen that the antifoam activity of blends based on PDMS having a viscosity of 2 mm 2 /s (cS) is not improved by the addition of the epoxy-terminated PIB, whereas our blends containing PDMS oil, having a viscosity of greater than 2 mm 2 /s (cS) show enhanced performance relative to the corresponding pure PDMS component, either immediately or after longer periods. The above results were repeated using compositions containing 0.5% of the above described silica and the results of testing at a total antifoam agent concentration of 4091 to 4211 ppm are shown in Table 8b. (0.5% silica) Weight Ratio of PDMS/PIB Viscosity of PDMS (mm 2 /s) Drop in Foam Height (%) Immediate 4 Hours 24 Hours 0/0 (Control) -- 0 0 29 0/100 -- 48 99 100 100/0 2 78 100 100 90/10 2 75 100 100 100/0 50 82 98 100 90/10 50 93 100 100 100/0 100 77 96 100 90/10 100 95 100 100 100/0 350 83 98 100 90/10 350 95 100 100 It is again seen that enhanced antifoam activity is only obtained when the viscosity of the polydimethylsiloxane is greater than 2 mm 2 /s (cS).

Claims: A defoaming composition comprising: (A) a polydimethylsiloxane homo- or copolymer having a viscosity greater than about 2 mm 2 /s (cS) at 25°C., wherein up to 15 mole percent of diorganosiloxane may be copolymerised with the dimethylsiloxane units, the organic groups of the diorganosiloxane units being independently selected from alkyl radicals having 1 to 16 carbon atoms, phenyl radicals or halogenated alkyl radicals having 3-6 carbon atoms or alkylene oxide groups; and (B) a polyisobutylene oligomer having a number average molecular weight of 200 to 3,000 and having at least one terminal group in its molecule which contains an epoxy group having the general structure in which R, R'and R" independently represent radicals selected from hydrogen and alkyl radicals having 1 to 7 carbon atoms, the weight ratio of said polydimethylsiloxane (A) to said polyisobutylene (B) being in the range 1:99 to 99:1. The composition according to claim 1, further comprising up to 50 percent of a silica powder based on the combined weight of said polydimethylsiloxane, said polyisobutylene and said silica powder. The composition according to claims 1 or 2 wherein said polydimethylsiloxane (A) is a homopolymer. The composition according to claim 3 wherein the number average molecular weight of said polyisobutylene (B) is 200 to 800. The composition according to claim 4 wherein said polydimethylsiloxane (A) has trimethylsiloxy terminal groups and has a viscosity of ≥50 mm 2 /s (cS) at 25°C. The composition according to claim 2 wherein said silica is a precipitated silica. The composition according to claim 6 wherein up to 3 percent of said silica powder is present based on the combined weight of said polydimethylsiloxane, said polyisobutylene and said silica powder. The composition according to claims 1 or 2 wherein the weight ratio of said components (A) to (B) is in the range of 90:10 to 70:30. The composition according to claim 4 wherein the weight ratio of said components (A) to (B) is in the range of 90:10 to 70:30. A method for defoaming a foaming system comprising adding to said foaming system the composition of claims 1 or 9.

Inventors: GENTLE THOMAS MATTHEW, HAUENSTEIN DALE EARL, KENNAN LINDA DENISE, POPA PAUL JOSEPH, GENTLE, THOMAS MATTHEW, HAUENSTEIN, DALE EARL, KENNAN, LINDA DENISE, POPA, PAUL JOSEPH
Applicants: DOW CORNING, DOW CORNING CORPORATION
Application year: 1995
Main classification: B01D19
IPC codes: C08K5, C08L83, C08L23, B01D19