IMPROVED ALKENYL AROMATIC-OLEFINICALLY UNSATURATED ACID FOAMS AND PROCESS FOR PREPARATION

Abstract: Alkenyl aromatic-olefinically unsaturated acid copoly­ mer foams are prepared by extrusion using as a blowing agent inorganic compounds such as sodium, magnesium, zinc, or ammonium carbonate or bicarbonate, either alone or in combination with volatile fluid foaming agents.

Description: IMPROVED ALKENYL AROMATIC-OLEFINICALLY UNSATURATED ACID FOAMS AND PROCESS FOR PREPARATION Extruded plastic foams have become important items of commerce utilized as thermal insulation and decoration. One of the more popular extruded plastic foams is polystyrene foam. It has been recognized that it would be desirable to have improved styrene polymer foam having a higher heat distortion temperature, greater solvent resistance and having a wider latitude in preparation. Extruded alkenyl aromatic polymer foams generally are prepared using substantial quantities of halocarbons as volatile fluid foaming agents. Depending on the particular volatile fluid foaming agent or mixture employed, the halocarbon will sooner or later diffuse from the foam and enter the atmosphere. There has been considerable semiscientific speculation as to the long term effects of such halogens being released into the atmosphere. In view of the current energy crisis, larger and larger volumes of extruded plastic foam and thermal insulation will be desired and required. One convenient solution to the halo-hydrocarbon problem would be to employ carbon dioxide as a blowing agent. However, certain technical drawbacks exist which make the use of carbon dioxide as a blowing agent undesirable. It would be desirable if there were available an improved alkenyl aromatic polymer foam suitable for thermal insulation and decoration. It would be desirable if there were available an improved process for the preparation of alkenyl aromatic polymer foams which minimized the amount of halo-hydrocarbons released into the atmosphere. It would also be desirable if there were available an improved process for the preparation of alkenyl aromatic polymer foams which permitted an increase in latitude in the operating conditions. These benefits and other advantages in accordance with the present invention are achieved in an improved alkenyl aromatic polymer foam, the foam having a density of from 0.5 to 8 lb/ft3 (8-128 kg/m3), the foam having a synthetic resinous thermoplastic body comprised of a polymer having a weight average molecular weight of from about 100,000 to about 350,000 gram moles, the polymer having polymerized therein from abput 99 to 70 parts by weight of an alkenyl aromatic monomer and from about 1 to 30 parts by weight of an olefinically unsaturated acid selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid and mixtures thereof, the body defining a plurality of closed gas filled cells, the foam body having an ion therein, the ion being selected from a group consisting of sodium, magnesium, zinc, ammonium and mixtures thereof. Synthetic resinous thermoplastic foams suitable for the practice of the present invention are polymers containing polymers thereof alkenyl aromatic monomer and olefinically unsaturated acid wherein the alkenyl aromatic monomer is present in the proportion of from about 99 to 70 parts by weight and the acid is present in a proportion of from about 1 to 30 parts by weight. Preferable for most applications, the alkenyl aromatic monomer is present in a proportion of from about 95 parts by weight to 80 parts by weight while the acid is present in a proportion of from about 5 to 20 parts by weight. Advantageously, the weight average molecular weight of the alkenyl aromatic monomer and olefinically unsaturated acid containing polymer is from about 100,000 to 350,000 gram moles as determined by gel permeation chromatography, and preferably from about 150,000 to 300,000 gram moles. By the term "alkenyl aromatic monomer" is meant an alkenyl aromatic compound having the general formula EMI3.1 wherein Ar represents an aromatic hydrocarbon radical, or an aromatic halohydrocarbon radical of the benzene series, and R is hydrogen or the methyl radical. Examples of such alkenyl aromatic monomers are styrene, a-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, ar-ethylstyrene, ar-vinylxylene, ar-chlorostyrene or ar-bromostyrene and the like. In the preparation of foams in accordance with the present invention, the copolymers employed need not be limited only to two monomers such as styrene and acrylic acid. A portion of the styrene may readily be replaced with alkyl styrenes such as methylstyrene, t-butylstyrene, bromostyrene, chlorostyrene and the like; as well as acrylonitrile, methacrylonitrile, methylmethacrylate in a proportion generally up to about 20 weight percent of the total polymer. The acrylic acid portion may be wholly or partially replaced with methacrylic acid, itaconic acid and the like. Blowing agents useful in the practice of the present invention include sodium bicarbonate, magnesium carbonate, ammonium carbonate, and zinc carbonate in a proportion of 0.5 to 20 parts by weight per hundred parts by weight of polymer, and combinations of sodium bicarbonate with sodium methoxide with hydrocarbons or fluorocarbons. Also useful in the practice of the present invention are sodium carbonate monohydrate, zinc acetate dihydrate, zinc carbonate, ammonium carbonate, magnesium carbonate hydrates including basic magnesium carbonates. Such foaming agents again may be used alone or in combination with hydrocarbons or fluorocarbons. Suitable volatile fluid foaming agents are well known in the art. Desirably the density of the foam in accordance with the invention is from about 0.5 to about 8 pounds per cubic foot and preferably in the range of about 1 to 5 pounds per cubic foot. Desirably the cell size of the foam is from about 0.1 to about 5 millimeters and advantageously from about 0.1 to about 2.5 millimeters. Suitable styrene-acrylic acid copolymers for the practice of the present invention are provided by a coil polymerization technique set forth in U.S. Letters Patent 3,035,033 to W. K. Schweitzer. A like procedure can be used to prepare other copolymers for the practice of the present invention. Generally, preparation of foam in accordance with the present invention is accomplished by intimately admixing particulate resin with the desired particulate blowing agent, for example a styrene-acrylic acid resin having a particle diameter of about 0.1 inch (0.25 cm) and powdered sodium bicarbonate. In order to provide uniform admixture it is often desirable to apply to the resin an adhering aid such as a 1:1 by weight mixture of dibutylphthalate and alphamethylstyrene. Usually, the particulate resin if the resin is placed into a suitable dry blender, the adhering aid added, the material tumbled for a length of time generally known only to those familiar with the particular dry blender, the powdered foaming agent such as sodium bicarbonate and then the added mixture further tumbled to provide a dispersion of sodium bicarbonate over a surface of the resin and because of the presence of the adhered aid, stratification of the resin of sodium bicarbonate does not occur under normal handling conditions. The dry blend of resin and foaming agent is then passed to an extruder where it is heat plastified, usually at a temperature of about 2500C, thoroughly mixed, cooled and extruded into a zone of lower pressure where it foams and cools to a self-supporting shape. Generally, it is desirable to maintain the heat plastified foaming agent containing resinous composition under sufficient pressure that foaming is prevented until the heated mobile gel is exposed to atmospheric pressure. The preparation of foams such as foam plank is well known and is set forth in the following U.S. Letters Patents: 2,669,751; 2,740,157; 2,838,801; 3,751,377; 3,817,669; 3,954,929; 3,897,528; and 3,914,085; the preparation of foamed sheet by extrusion is disclosed in the following U.S. Letters Patent: 2,917,217; 3,151,192; 3,648,462; 3,311,681; 3,391,051; 3,560,600. All molecular weights are determined by gel permeation chromatography. The invention is further illustrated but not limited by the following examples. Employing a 3/4 inch (1.91 cm) extruder having a feed zone heated to a temperature of about 2100C, an intermediate zone heated to about 1800C, and a die heated to about 1500C, a first series of foam samples were produced utilizing a styrene-acrylic acid copolymer containing 8.0 weight percent acrylic acid and having a molecular weight of about 260,000 gram moles; varying quantities of sodium bicarbonate were employed as blowing agent and varying screw speeds were utilized. A second series of samples were prepared using styrene-acrylic acid copolymer of about 8 weight percent acrylic acid, the remainder styrene and having a molecular weight of 210,000 gram moles. Die temperature, die pressure and screw speed were recorded; foam samples were gathered, aged in air for a period of about a week and the external skin removed prior to determining the foam density which is recorded in pounds per cubic foot. Cell size was measured using the procedure ASTM D 3576 and the percentage of open cells was determined by ASTM D 2856-A and the heat distortion temperature was determined by modified ASTM Test D 2126-75. This test employs a one hour exposure at each temperature and the heat distortion temperature is the maximum temperature giving a linear dimension change of less than two percent. The results are set forth in Table I wherein the following abbreviations are employed: SAA Styrene acrylic acid copolymer pph parts by weight per hundred parts of polymer OC degrees Centigrade rpm revolutions per minute pcf pounds per cubic foot mm millimeters Temp. Temperature TABLE I PROPERTIES OF SAA COMPOLYMER (8% AA) FOAMS EXPANDED WITH SODIUM BICARBONATE oam Density PCF NaHCO3 Die Screw Foam Density PCF Cell Open Heat Level Temp. Speed Aged Aged Size Cell Distortion (pph) ( C) (rpm) With Skin Skin Off (mm) (%) Temp.( C) 260M. W. SAA 2.33 145 40 8.89 7.90 0.81 52.7 109 4.66 145 20 4.23 3.72 0.92 30.1 109 9.32 150 30 3.39 2.09 0.47 0.94 103 13.98 150 40 2.64 1.58 0.37 0.51 110 18.64 150 40 2.30 1.50 0.53 46.3 109 210M M. W. SAA 2.33 150 40 5.87 3.53 0.74 32.4 121 4.66 150 30 3.66 3.05 0.56 9.6 109 6.99 155 30 3.08 1.90 0.50 30.9 115 9.32 150 30 2.79 2.40 0.51 4.4 109 13.98 145 40 2.56 2.01 0.27 8.0 109 For purposes of comparison a polystyrene having a weight average molecular weight of about 200,000 gram moles was treated in a generally similar manner. The results are set forth in Table II. TABLE II PROPERTIES OF POLYSTYRENE FOAMS EXPANDED WITH SODIUM BICARBONATE Die Screw Foam Density (pcf) Cell Open Heat Level Temp. Speed Aged Aged Size Cell Distortion (pph) ( C) (rpm) With Skin Skin Off (mm) (%) Temp.( C) 2 135 40 8.06 6.94 0.81 49.5 96 5 133 40 7.79 6.69 0.41 69.3 92 7 121 40 6.00 5.33 0.43 54.7 92 10 115 40 4.81 4.62 0.45 67.0 92 15 115 40 5.78 5.09 0.48 72.5 89 20 115 40 5.71 5.26 0.43 70.4 89 Results show that a lower density foam having a substantially closed cell structure and a higher heat distortion temperature is achieved by expanding styrene/acrylic acid copolymer with sodium bicarbonate. On the other hand, polystyrene is not expanded to a low density foam by sodium bicarbonate and the polystyrene foam has a high open cell content over the entire range of sodium bicarbonate level. A styrene-maleic anhydride copolymer containing about 20 percent maleic anhydride polymerized therein, with a solution viscosity of 5.6 centipoise at 250C in a 10 percent methylethylketone solution was foamed employing sodium bicarbonate as well as a styrene-acrylonitrile polymer which contained about 75 weight percent styrene with 25 weight percent acrylonitrile were foamed for comparative purposes. The styrene-maleic anhydride copolymer being designated by the abbreviations SMA and styrene-acrylonitrile polymer, by SAN. These styrene copolymers do not produce a low-density closed cell foam as shown in Table III. From the results, it appears that the response of the styrene-acrylic acid copolymer to the sodium bicarbonate blowing agent is unique. TABLE III PROPERTIES OF OTHER POLYMER FOAMS EXPANDED WITH SODIUM BICARBONATE NaHCO3 Die Screw Foam Density Cell Open Heat Polymer Level Temp. Speed Fresh With Size Cell Distortion Type (pph) ( C) (rpm) Skin (pcf) (mm) (%) Temp.( C) SMA 14 190 40 6.24 0.59 79.1 > 125 SAN 14 150 40 31.2 A series of extrusions were made using an 8 percent acrylic acid, 92 percent styrene copolymer having a molecular weight of about 210,000 gram moles and varying levels of triclorofluoromethane (F-ll) and varying levels of sodium bicarbonate. The results are set forth in Table IV. TABLE IV PROPERTIES OF SAA COPOLYMER FOAMS EXPANDED WITH F-11/NaHCO3 BINARY BLOWING AGENTS F-11 NaHCO3 Die Screw Foam Density (pcf) Cell Open Level Level Temp. Speed Aged Size Cell (pph) (pph) ( C) (rpm) Skin Off (mm) (%) Remarks 8.2 0 160 60 3.23 0.81 47.6 0.5 pph talc was added 8.2 0 158 60 2.89 0.74 57.1 1.0 pph talc was added 8.2 1 155 40 2.21 0.90 5.0 8.2 1 150 60 1.90 0.81 1.6 8.2 2 140 40 1.56 0.40 3.8 8.2 2 140 60 1.52 0.43 41.3 8.2 3 135 40 1.89 0.56 40.6 8.2 3 130 60 1.82 0.58 38.9 8.2 4 130 40 1.52 0.51 2.8 8.2 4 130 60 1.49 0.54 41.9 8.2 5 125 40 1.49 0.39 4.7 8.2 5 125 60 1.92 0.49 44.2 8.2 6 125 40 1.62 0.34 0.2 8.2 6 125 60 1.46 0.35 43.7 17.8 0 160 40 1.52 0.62 5.7 17.8 1 160 40 1.46 0.90 0 17.8 2 134 60 1.22 0.43 7.9 17.8 3 128 60 1.22 0.40 0.3 17.8 4 120 60 1.36 0.35 3.1 17.8 5 120 60 1.43 0.45 5.9 17.8 6 116 80 0.88 0.25 1.0 A similar experiment employing a volatile fluid foaming agent was performed for comparative purposes utilizing polystyrene and an 80/20 parts by weight mixture of trichlorofluoromethane/pentane with varying levels of sodium bicarbonate. The results are set forth in Table V. TABLE V PROPERTIES OF POLYSTYRENE FOAM EXPANDED WITH COMBINED BLOWING AGENTS OF 80/20 F-11/PENTANE AND NaHCO3 F-11/ Pentane NaHCO3 Die Screw Foam Density (pcf) Cell Open Level Level Temp. Speed Aged Size Cell (pph) (pph) ( C) (rpm) Skin Off (mm) (%) Remarks 9.8 0 110 40 3.31 0.56 3.1 1 pph talc was added 9.8 0 110 60 2.83 0.48 0.8 1 pph talc was added 9.8 0 110 80 2.67 0.68 0.1 1 pph talc was added 9.8 1 110 40 2.64 0.74 0.2 9.8 1 110 60 2.29 0.68 1.7 9.8 1 110 80 2.52 0.65 0.2 9.8 2 110 40 2.52 0.51 0 9.8 2 110 60 2.21 0.58 7.3 9.8 2 110 80 2.29 0.62 10.6 9.8 3 110 40 2.22 0.51 0 9.8 3 110 60 2.22 0.39 7.6 9.8 3 110 80 2.52 0.48 0 9.8 3 110 100 2.54 0.54 50.3 9.8 4 110 (Frozen at the die) 9.8 5 125 40 -- 0.60 80.8 9.8 6 120 40 2.01 0.70 59.9 9.8 6 120 60 1.82 0.58 49.9 9.8 6 120 80 2.08 0.65 38.9 A number of mixtures containing varying quantities of sodium methoxide and sodium bicarbonate were extruded to form foams with a copolymer of 8 weight percent acrylic acid and the remainder being styrene having a weight average molecular weight of about 210,000 gram moles. The results are set forth in Table VI. TABLE VI PROPERTIES OF SAA COPOLYMER FOAMS EXPANDED WITH NaOCH3/NaHCO3 MIXED BLOWING AGENTS NaOCH3 NaHCO3 Die Screw Conversion Foam Density (pcf) Cell Open Heat Level Level Temp. Speed To Salt Aged Size Cell Distortion (pph) (pph) ( C) (rpm) (mole %) Skin Off (mm) (%) Temp.( C) 3 0 155 40 46 2.32 1.81 0.5 115 1.5 4.66 160 40 43 1.98 0.63 0.8 115 1.5 6.99 155 40 68 2.28 0.45 0 115 1.0 6.99 155 60 51 1.86 0.54 2.4 115 0.6 6.99 160 40 48 1.73 0.48 0 115 A variety of other materials were extruded with a copolymer of 8 weight percent of acrylic acid and the remainder being styrene. The polymer had a molecular weight of about 210,000 gram moles. The results are set forth in Table VII. TABLE VII PROPERTIES OF SAA COPOLYMER FOAMS EXPANDED WITH OTHER METAL COMPOUNDS Compound F-11 Die Screw Conversion Level Level Temp. Speed To Salt Type (pph) (pph) ( C) (rpm) (mole %) Na2CO3 2 180 30 5 170 30 7 165 30 9 150 40 54 Na2CO3#H2O 2 158 40 5 150 30 7 150 30 9 150 30 ZnCO3 2 160 30 5 160 30 7 160 30 9 160 30 12.66 150 40 25 Zn(CH3COO)2#2H2O 3 155 30 45 ZnO 8.2 160 40 CaCO3 10 190 40 20 210 30 Talc 0.5 7.5 135 40 Na2CO3 7.5 7.5 135 40 Na2CO3#H2O 7 7.5 135 40 ZnCO3 7 7.5 135 40 TABLE VII (Continued PROPERTIES OF SAA COPOLYMER FOAMS EXPANDED WITH OTHER METAL COMPOUNDS Cell Open Heat Foam Density (pcf) Size Cell Distortion Type With Skin Skin Off (mm) (%) Temp. ( C) Na2CO3 23.1 16.8 2.03 5.29 17.2 1.62 52.3 7.38 0.63 54.0 115 Na2CO3#H2O 11.6 13.7 1.35 67.6 4.77 3.28 1.01 55.5 3.60 2.78 0.81 6.2 3.10 2.28 0.54 2.8 ZnCO3 34.6 25.9 24.8 15.4 17.5 0.54 29.4 113 Zn(CH3COO)2#2H2O 3.82 1.35 31.8 108 ZNO 61.8 CaCO3 52.6 57.4 Talc 5.03 3.81 0.49 44.5 Na2CO3 3.71 2.52 0.26 0.8 Na2CO3#H2O 2.45 1.66 0.77 0 ZnCO3 4.11 3.27 0.81 46.0 Note that of the sodium carbonate, sodium carbonate monohydrate and zinc carbonate, sodium carbonate and sodium carbonate monohydrate gave satisfactory foams while with the addition of 7.5 parts per hundred of trichlorofluoromethane, all three compounds work as an effective secondary blowing agent. A series of extrusions were performed employing styrene-acrylic acid copolymers of varying acrylic acid content and varying sodium bicarbonate content. The results are set forth in Table VIII which establishes that good foams of low density and reasonable open cell content can be obtained over a wide range of compositions. TABLE VIII EFFECT OF ACRYLIC ACID LEVEL ON THE PROCESSABILITY AND PROPERTIES OF SAA COPOLYMER FOAMS EXPANDED WITH NaHCO3 NaHCO3 Die Screw Foam Density (pcf) Cell Open Heat Level Temp. Speed Aged Aged Size Cell Distortion (pph) ( C) (rpm) With Skin Skin Off (mm) (%) Temp. ( C) 5%AA SAA Copolymer 2 150 30 6.93 4.62 0.68 60.8 113 5 145 20 4.52 3.66 0.58 5.6 107 10 145 20 3.78 2.40 0.54 5.9 107 15 145 25 3.74 2.40 0.37 6.5 106 10%AA SAA Copolymer 2 148 30 6.67 4.74 0.65 37.8 118 5 145 30 3.70 3.09 0.60 15.7 118 10 147 30 3.74 2.92 0.49 2.9 113 15 148 30 4.16 2.83 0.40 3.1 113 15%AA SAA Copolymer 2 150 30 5.88 4.23 0.77 28.8 124 5 150 30 4.17 2.61 0.62 23.4 121 10 150 30 3.57 2.01 0.40 4.5 124 15 152 30 4.31 3.21 0.30 1.0 124 20%AA SAA Copolymer 2 170 30 3.67 2.63 0.81 4.7 133 5 170 30 3.28 2.40 0.68 5.6 133 10 170 30 2.93 2.01 0.51 6.4 135 15 170 30 2.30 2.01 0.40 7.9 133 A 8 weight percent acrylic acid styrene copolymer was foamed under a variety of conditions and ammonium bicarbonate levels with trichlorofluoromethane and ethyl chloride. The results are set forth in Table IX, from which it can be seen that very little bicarbonate is equivalent to a substantial quantity of the volatile fluid foaming agent. TABLE IX PROPERTIES OF SAA COPOLYMER FOAMS EXPANDED WITH AMMONIUM BICARBONATE AND MIXTURES WITH PHYSICAL BLOWING AGENTS Physical Blowing NH4'HCO3 Die Screw Cell Open Agent Level Temp. Speed Foam Density (pcf) Size Cell (Type) (pph) (pph) ( C) (rpm) With Skin Skin Off (mm) (%) 3/4" Extruder None 2 150 40 8.35 2.70 66.8 5 145 20 4.46 3.24 71.6 7 150 20 5.12 3.24 62.4 F-11 7.5 0 135 40 9.78 4.23 1.36 10.2 7.5 0 135 40 5.14 3.24 0.6 62.6* 7.5 1 135 40 3.21 2.13 1.35 6.2 7.5 2 135 40 2.52 1.79 1.47 3.0 7.5 3 135 40 2.36 1.36 1.35 17.5 16.1 0 140 40 3.07 2.00 2.31 3.7 16.1 1 135 40 2.24 1.92 1.01 2.9 16.1 2 135 40 1.93 1.59 0.71 0 16.1 5 135 40 (Collapsed due to over expansion) 1 1/4" Extruder C2H5Cl 8.2 0 142.5 4.21 2.75 4.05 0 8.3 1 142.5 2.96 2.33 1.08 0.5 8.3 2 142.5 3.12 2.03 1.47 0 8.3 4 143 2.64 1.56 1.80 1.7 13.0 0 142 1.98 1.73 2.70 10.3 * 0.5 pph talc was added for cell size contyrol. In a manner similar to the foregoing illustration, varying quantities of hydrated magnesium carbonate were evaluated alone and in combination with trichlorofluoromethane, (8 weight percent acrylic acid resin, the remaining being styrene). The results are set forth in Table X. TABLE X PROPERTIES OF SAA COPOLYMER FOAMS EXPANDED WITH MAGNESIUM CARBONATE AND ITS MIXTURES WITH F-11 F-11 Magnesium Die Screw Cell Open Level Carbonate Temp. Speed Foam Density (pcf) Size Cell (pph) (pph) ( C) (rpm) With Skin Skin Off (mm) (%) 2 165 30 21.5 15.1 0.51 5.8 5 160 30 14.6 13.4 0.58 38.5 7 155 30 11.6 10.8 0.54 47.7 10 150 30 9.93 8.76 0.49 45.3 8.0 0 150 40 3.66 3.21 0.46 47.0* 8.0 1 145 40 3.46 2.75 0.54 41.8 8.0 2 135 40 3.19 2.59 0.58 56.1 8.0 3 130 60 3.21 2.40 0.54 60.5 8.0 4 130 40 3.53 2.86 0.49 46.2 8.0 5 130 40 3.46 2.77 0.58 37.2 8.0 6 128 60 3.09 2.30 0.60 50.2 * 1 pph talc was added for cell size control. Foamed sheet was prepared using a one-inch extruder and tubing die wherein the tube was inflated with air to provide a foamed sheet of a desired thickness. The die diameter was 1-1/4 inches and the die gap was 0.025 inch. The blowing agent used was varying amounts of sodium bicarbonate. The copolymer employed was of styrene and acrylic acid which contained about 8 weight percent acrylic acid, the remainder being styrene. The polymer was extruded at about nine pounds per hour. The screw speed and temperatures were adjusted for optimum results. The results are set forth in Table XI. TABLE XI PROPERTIES SAA FOAM SHEET PREPARED ON A ONE INCH BLOWN FILM LINE USING SODIUM BICARBONATE AS THE BLOWING AGENT Foam NaHCO3 Gel Screw Foam Thick- Foam Cell Open Tensile Percent Level Temp. Speed Width ness Density Size Cell Str.(M psi) Elongation (pph) (%) (rpm) (in) (in (pcf) (mm) (%) (MD) (CD) (MD) (CD) 1.0 203 28 15.2 0.023 9.15 0.81 7.8 2.02 5.68 4.68 1.54 2.0 203 30 8.4 0.034 12.2 1.16 17.6 7.43 4.17 1.67 1.51 3.0 210 44 7.4 0.030 6.85 0.68 24.5 6.48 4.58 2.01 1.70 4.0 213 48 10.5 0.053 8.29 0.95 29.7 3.63 3.88 1.88 2.46 5.0 209 48 11.5 0.027 7.56 0.90 31.2 8.17 4.31 3.21 3.27 7.0 213 60 8.6 0.036 6.11 0.81 51.1 4.45 1.56 1.68 3.36 Notes: MD stands for machine direction and CD for cross direction. Employing the apparatus of the previous illustration, foam was prepared from a copolymer of 92 weight percent vinyl toluene and 8 weight percent acrylic acid. The vinyl toluene was about 60 weight percent meta-isomer and 40 weight percent para-isomer. The polymer had a molecular weight of about 180,000 gram moles; 7 parts by weight of sodium bicarbonate were employed as blowing agent to 100 parts by weight of the resin. The die temperature was 1500C, screw speed was 30 revolutions per minute. The resultant foam had a density of 4.54 pounds per cubic foot; the cell size was about 0.45 millimeters and was 21.2 percent open cell. For a comparison, a homopolymer of paravinyl toluene having a molecular weight of about 300,000 gram moles was similarly treated. The foam with skin had a density of 6.11 pounds per cubic foot; cell size of 0.62 millimeters, and was 37.8 percent open cell. In a manner similar to the foregoing illustrations, other foams are readily prepared employing sodium bicarbonate, hydrated magnesium carbonate, zinc diacetate monohydrate alone or in combination with a volatile fluid foaming agent to prepare foam plank or foam sheet when the hereinbefore described styrene-acrylic acid, styrene-methacrylic acid or styrene-itaconic acid vinyl toluene acrylic acid copolymers are utilized.

Claims: 1. A process for the preparation of an alkenyl aromatic polymer having a density of 8-128 kg/m3 by blending heat plastified polymer and blowing agent under sufficient pressure to prevent foaming and subsequently extruding the blended mixture into a zone of lower pressure characterized in that (1) the polymer has a weight average molecular weight of about 100,000 to 350,000 and has polymerized therein 99 to 70 parts by weight of alkenylaromatic monomer and 1 to 30 parts by weight of acrylic, methacrylic or itaconic acid or mixtures thereof, (2) the blowing agent is sodium, magnesium, zinc, or ammonium carbonate or bicarbonate or mixtures thereof in a proportion of 0.5 to 20 parts per hundred parts polymer by weight, (3) the polymer is heat plastified under pressure sufficient to prevent foaming and blended with the blowing agent a temperature sufficiently high to decompose the carbonate or bicarbonate blowing agent prior to extrusion to form a polymeric foam having a density of 8-128 kg/m3. 2. The process of Claim 1 wherein the molecular weight of the polymer is about 150,000 to 300,000. 3. The process of Claim 1 wherein the alkenyl aromatic monomer is styrene. 4. The process of Claim 1 wherein the alkenyl aromatic monomer is vinyl toluene. 5. The process of Claim 1 wherein the acid is present in a proportion of 5 to 20 parts by weight based on weight of polymer. 6. The foam of Claim 1 wherein the polymer is a polymer of styrene and acrylic acid. 7. The process of Claim 1 employing sodium bicarbonate as blowing agent. 8. The process of Claim 1 wherein the foam has a density of 16-90 kg/m3 and an average cell size of about 0.1 to 2.5 millimeters. 9. A styrene acrylic acid polymer foam having a density of 16-90 kg/m3 and characterized by having a synthetic resinous thermoplastic body comprised of a polymer having a weight average molecular weight of from about 150,000 to 300,000 and having polymerized therein from 95 to 80 parts by weight of styrene and 5 to 20 parts by weight of acrylic acidr the foam body defining a plurality of closed gas filled cells having a cell size of about 0.1 to 2.5 millimeters and having sodium ions therein. 10. An alkenyl aromatic polymer foam preprared by the process of Claim 1.

Inventors: PARK, CHUNG POO, SUH, KYUNG WON
Applicants: THE DOW CHEMICAL COMPANY
Application year: 1981
Main classification: C08J9
IPC codes: C08J9