PAGE 1 OF 37
`
`BOREALIS EXHIBIT 1017
`
`BOREALIS EXHIBIT 1017
`
`PAGE 1 OF 37
`
`

`
`
`
`ENCYCLOPEDIA
`
`OF POLYMER
`
`S CI E NC E
`
`AND
`
`TECHNOLOGY
`
`Plastics, Resins, Rubbers, Fibers
`
`Casein
`
`PAGE 2 OF 37
`
`

`
`
`
`Copyreight © 1965 hy Jelm Wiley d’c Sons, Inc
`
`All liights 1i(=:ev1‘\-ml. This hunk-ur any purl.
`t.l1e-.1'euf must nni. he repnnluc.-ml in any l'ur1n
`without pe1'1:1is~.aiu ’
`If Lhc [n1hli.~;hc1's in \vritin;,_-;-
`This applies; ape-.1-.i%‘I|_\,' to ;1hu|..u.~at:u.i¢: and
`l:I1i(:1'0fiIm rt:prnrl1|ct.iuI1, as wail :L.~: tn L1'un:=1:1t-inns
`into foreign languages.
`
`Librztry of C0ng1'ess C-.-1.|;a1ng Card Number: 64-22188
`
`Printed in the IT11it.er.l States of America
`
`...__...;._._....-_._-.
`
`PAGE 3 OF 37
`
`PAGE 3 OF 37
`
`

`
`532
`
`Blowing Agents
`
`BLOWING AGENTS
`The term blowing agents applies to substances that can produce pores or cells
`in polymeric compositions.
`If the cells are formed through a change in the physical
`state of the substanceL~i_e, through an expansion of a compressed gas, an evapora-
`tion of a liquid, or by the dissolving of a solid-—the material is called a physical blowing
`agent.
`If the cells are formed by liberation of gases as products of the thermal de-
`composition of the material, the material is called a chemical blowing agent. The
`methods of using‘ the blowing agents described in this article are discussed under
`CELLULAR MATERIALS.
`
`Historical Background
`
`The use of blowing agents to produce cellular bodies based on high polymers goes
`back to the early days of rubber technology.
`In 1846, just a few years after the
`discovery of vulcanization, Hancock and others received several patents (1) covering
`the process of making natural rubber sponge using‘ _amn1onium carbonate and volatile
`liquids as blowing agents. Not until 1856, however, was rubber sponge produced on
`a limited scale in England (2) and offered commci-cially for a variety of end uses.
`In the United States, large-scale production of rubber sponge for household use began
`around 1902. A. C.'Squi1'cs of B.F. Goo'_(lricl1 Co. (3) developed a_ rubber compound
`containing aunnonium carbonate that yielded sponge with large, interconnected cells.
`In the 19203 the introduction of officient rubber .accelerators- and antioxidants signi-
`ficantly contributed to the rapid growth of sponge—rubber goods for industrial and
`household applications. At that time the carboI'1at'es in various physical forms (4)
`were the most popular chemical blowing agents.
`Early attempts to produce open-cell sponge by means of physical blowing agents
`(cg, alcohol, benzene, and other volatile liquids) met with limited success (5). Even-
`tually, blowing techniques which utilize volatile liquids, either aliphatic l_1ydrocar-
`bone or halogenated hydrocarbons, were perfected; these have attained considerable
`importance in the manufacture of cellular thermoplastic structures.
`Parallel to the development of atmospherically blown sponge, experimental
`work was carried out with the aim of producing closed-cell. rubber by gassing with
`elemental nitrogen under high pressure.
`In the early 1930s the Rubatcx process (6),
`based on patents of Pfleumer (7), Marshall (8), Denton (9), and others (10), became
`commercially well established. Between 1930 and 1950 large quantities of expanded
`rubber were produced by the Rubatcx and similar processes throughout the world.
`In‘ the last fifteen years the availability of efficient and easily handled organic blowing
`_ agents has made the Rubatex process virtually obsolete.
`Diazoaminobenzene (DAB), br 1,3—d.iphe.nyltriazcno, was the first commercially
`available organic blowing agent.
`Introduced as Unicel in 1940 by E. I. du Pont do
`Nemours & Co., Inc.
`(11), the compound was found extremely useful despite its
`toxicity and staining properties. For the first time it was possible to make cellular
`polgruerswith closed cells by conventional compounding and processing methods (12).
`As
`o’on as the advantages derived from the use of diazoaminobenzene became ap-
`parent, on intensive search began for better organic blowing agents.
`In the early
`1940s, a group of nonstaining aliphatic compounds, the aconitriles, was placed on the
`market (13), and of these, 2,2’-acobisisobutyronitrile was used on a large scale in the
`1/4* production of flexible and rigid poly(vinyl chloride) compounds during World War
`
`-J
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`PAGE 4 OF 37
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`PAGE 4 OF 37
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`
`Vol. 2
`
`Blowing Agents
`
`533
`
`II. Later, 2,2 ’-azobisisobutyronitrile, due to the toxicity of its residue, was abandoned
`in favor of nontoxic organic blowing agents. Neither the azonitriles nor the later-
`suggested derivatives of azodicarboxylic acid (14) could satisfy the need for a ver-
`satile,
`inexpensive blowing agent that would make the chemical blowing method
`competitive with the Rubatex process. The breakthrough came in 1946 with the
`introduction of dinitrosopentamethylenetetramine, one of the dinitrosoamines sug-
`gested earlier by Briggs and Scharfi (15).
`In the past forty years over a thousand chemicals have been suggested as blowing
`agents for high polymers. Some of the enjoyed a. short period of c0111ll1I3l'Gl
`ac-
`ceptance but were later replaced by better products; many others never reach
`full-'
`scale industrial application, while yet others remained nothinjg but laboratdry curiosi-
`ties. Today no more than ten chemically d.iiierent blowing agents are efiectively used
`throughout the
`orld. Presently, the main development effort in this field is directed
`toward extendingthe temperature spectrum of the cliemical blowing agents by provid-
`ing compounds with either higher or lower decomposition temperatures than already
`attainable.
`I
`
`,
`
`”
`
`Physical Blowing Agents
`The scope of this article is limited to those physical blowing agents which develop
`a cellular structure by passing from a liquid to a gaseous phase during the blowing
`operation. These compounds are liquids with boiling points ranging from room tem-
`perature to 110°C.
`Ideally, they should be odorless, nontoxic, noncorrosive, and
`nonflammable. At low temperatures, the liquids may have some swelling eiicct on
`the polymer to be expanded, or it may be desirable that they be soluble in the mono-
`mer, but they must possess no solvnting power or otherwise affect the physical and
`chemical properties of the polymer.
`In the gaseous state, the physical blowing agents
`must be thermally stable and chemically inert at the temperature employed in the
`blowing process. The efliciency of physical blowing agents depends upon a complete
`vaporization of the compound and is directly related to the ratio of the volume oc-
`cupied by equal weights of the vapor and the liquid. From the standpoint of the
`effective utilization of the blowing agent, a high specific gravity combined with a low
`molecular weight is most desirable.
`The change from the liquid to the gaseous state is a reversible and endothermic
`process. When the expanded polymer is cooled, a condensation of the physical
`blowing agent does not occur, inasmuch as the vapor is either under reduced pres-
`sure or diluted with air. The heat of vaporization can be utilized to control the tem-
`perature of the expanding polymer as the latter undergoes a chain extension or cross-
`linking. This permits the preparation of large cellular bodies without the danger of
`thermal degradation of the polymer. The addition of nucleating agents (eg, silica,
`silicates, sulfides) which serve as sites of bubble formation facilitates the develop-
`ment of small and uniform vapor-filled cells (16). Furthermore, chemical blowing
`agents, eg, a bicarbonate—acid system, can be used in conjunction with volatile liquids
`(17) to develop low-density cellular polymers.
`Physical blowing agents are efficient and inexpensive gas-forming compounds
`but, in general, their use requires specialized equipment designed specifically for a
`predetermined blowing operation. The most widely used physical blowing agents
`are the aliphatic hydrocarbons, as well as the chloro- and fluoro-derivatives of ali-
`phatic hydrocarbons. Of lesser importance are low-boiling alcohols (18), ethers (19),
`
`.
`'
`
`PAGE 5 OF 37
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` h
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`PAGE 5 OF 37
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`

`
`534-
`
`Blowing Agents
`
`I
`
`Table 1. Properties of Physical Blowit-ng Agents
`
`Blowing
`'
`"fi‘”°”°"
`Heat of
`vapofimtion,“-5 At
`At
`Bp,
`d“‘,°
`M01
`Blowing agent
`Wt“
`g/ml
`°C“
`cal (15°)/g
`bp
`100°C
`.
`
`1:
`
`
`
`.....-...._.x-.....-.\..-w..r.-um:
`
`E
`
`"'
`
`l
`
`I
`
`261.
`261
`260
`280
`323
`.
`
`232
`
`232
`234
`233
`229
`243
`281
`
`pentunea
`n-pentane
`2-methylbutane
`2,2—dimethylp1'opa.ne
`1-pentene
`cyclopentane
`hexanes
`
`-n-hexane
`
`'
`
`72.15
`72.15
`72 . 15
`70. 15
`70. 15
`
`0. 616"
`0.615
`0 . 613
`0. 641“
`0. 740
`
`36 .1
`27. 8
`9 . 5
`30 . 0
`49 . 2
`
`86. 0
`81.5“
`
`99 . 6“
`
`216
`210
`196
`227
`279
`
`86.17
`
`86. 17
`86.17
`86. 17
`86 . 17
`84.17
`84.17
`
`0.655
`
`0. 6531‘
`0.660
`0 . 657
`0 . 645
`0.669
`0 . 774
`
`68.7
`
`60.2
`63.3
`58 . 0
`49 . 7
`63.5
`80.8 _
`
`212
`
`207
`211
`207
`204
`219
`266
`
`80.4“
`
`76.5
`
`75 . 0
`73 . 8
`
`94 . 325
`
`77 . 09°
`
`77. 3“
`81 .7“
`78. 4“
`
`69. 0
`
`94. 1
`98. 6“
`
`66 . 7“
`
`2-methylpentane
`3-methylpentane
`2, 3-dimethylbutane
`2,2-climethylbutane
`1-hexene
`cyclohexane
`heptanea
`207
`206
`98 . 4
`0.679
`100.20
`n—hept.a.ne
`206
`200
`90 . 0
`0 . 674
`100 . 20
`2-met.hy1hexa.ne
`204
`193
`79 . 2
`0.670
`100 . 20
`2,2-dimethylpentane
`211
`205
`89 . 7
`0. 691
`100 . 20
`2,3-dimethylpentane
`204
`193
`80 . 6
`0 . 668
`100 . 20
`2,4-dimethylpentame
`210
`202
`86 . 0
`0 . 689
`100 . 20
`3,3-dimethylpentane
`212
`204
`93 .4
`0. 694
`100.20
`3-ethylpentane
`209
`198
`80.8
`0.686
`100.20
`2,2,3-triethylbutane
`216
`212
`93 . 2
`0.693
`98.20
`1—heptene
`342
`324
`80. 1
`0. 874
`78 . 11
`benzene
`286
`294
`110.6
`0.862
`92. 13
`toluene
`482
`404
`40. 0
`1 . 325
`84. 94
`dichloromethane
`382
`342
`61 .2
`1. 489
`119 . 39
`trichloromethane
`342
`330
`87. 2
`1 . 466
`131 . 40
`trichloroethylane
`316
`296
`46 . 6
`76 . 7
`1 . 584
`153. 84
`tetrachloromethane
`9233
`370
`77.3%“
`33. 5
`1.245
`98.97
`1,2-dichloroethane
`329
`261
`43. 5
`23. S
`1 .476
`137.38
`trichlorofluoromethane
`255
`219
`35 . 1
`47. 6
`1 . 565
`187 . 39
`1, 1,2-trichlorotrifluoroathane
`752
`679
`263.0
`64. 6
`0.787
`32.04
`methyl alcohol
`521
`491
`204. 07“
`78 . 3
`0 . 785
`46 . 07
`ethyl alcohol
`397
`378
`175.6“
`82.3
`0.780
`60.09
`isopropyl alcohol
`292
`240
`89 . 8”
`34. 5
`0. 708
`74. 12
`ethyl ether
`217
`193
`68.2
`67. 5
`0 . 725
`102. 16
`isopropyl other
`413
`365
`125 . 3
`56 . 2
`0 . 785
`53. 08
`acetone
`344
`324
`103.4
`79. 6
`0 .810
`72. 10
`, methyl ethyl ketono
` ___
`“ Dam taken from '1‘i1mner111u.na, P}1.ys£co~C'kem-ical Cmwtants of Pure Organic Compounds,
`Elaevier, 1950, except that. data. for isopropyl ether is from Fife and Reid, Ind. Eng. Chem. 22, 513
`(1930).
`5 At the boiling point, unless otherwise indicated.
`° Data. computed according to the formula
`
`I
`
`_
`
`(273 + z)
`r,
`_
`22,-mo
`mulwt X (donalty at 25 C) X T73
`
`V where 1 = hailing point in "C fur the next to the lust colunm and 100°C for the last. column.
`fi1-at app1'oxima.tion vapors were Heated as ideal gases.
`
`J.
`
`/'
`
`In the
`
`PAGE 6 OF 37
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`PAGE 6 OF 37
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`

`
`Vol. 2
`
`Blowing Agents
`
`535
`
`ketoncs (20), and aromatic hydrocarbons (18,20). The physical properties of £].[]11]1"1beI'
`of selected physical blowing agents are given in Table 1.
`Aliphatic Hydrocarbons. The main source of liquid aliphatic hydrocarbons
`are low-boiling fractions of petroleum, variously called “petroleum ether,” “ligroin,”
`or “light spirits.” The low-boiling solvents contain mainly isomers of pentane, hexane,
`and heptane, and are available in distillation ranges closely corresponding to the
`boiling points of the various hydrocarbon isomers. These inexpensive liquids possess
`a high blowing efficiency and a comparatively low order of toxicity. Their value
`as blowing agents for polymers is limited by the high degree of flammability. The
`low-boiling pentanes are used extensively in production of expanded polystyrene (21).
`Halogenated Aliphatic Hydrocarbons. The main advantage of chlorinated
`hydrocarbons is their nonflammability. Because of this property, these materialsrcan
`be used as blowing agents in making fire-resistant cellular polymers. Chlorinated
`hydrocarbon blowing agents are more expensive than aliphatic hydrocarbons and
`present a serious toxicity problem in handling. Among the most commonly used
`compounds of this group are methylene chloride and tri- and perchlorethylene.
`Methylene chloride has been used for manufacturing flame-resistant cellular poly-
`styrene, and the chlorinated ethylenes have been suggested as auxiliary blowing agents
`in making cellular poly (vinyl chloride) (22) and epoxy resins (18).
`Fluorinated aliphatic hydrocarbons combine several desirable properties which
`make these organic liquids ideally suited for use as blowing agents. Among their
`most significant characteristics are nonflammability, an extremely low level of toxicity,
`excellent thermal and chemical stability, low thermal conductivity, and good dielec-
`tric properties. The high density of fluorocarbon liquids contributes to a favorable
`blowing efficiency. Of the many commercially available aliphatic fluorocarbons,
`only two of the common ones are liquid at room temperature——trichlorofiuoromethane
`(available as Freon 11, Du Pont; Genetron 11, Allied Chemical; Isotron 11, Penn-
`salt Chemicals; and Ucon Propellant 11, Union Carbide Chemicals) and 1,1,2-
`trichlorotrifluoroethane (available as Freon 113, Du Pont; Genetron 112, Allied
`Chemical; and Ucon Propellant 113, Union Carbide Chemicals). Both products are
`presently used on a large scale as blowing agents for flexible and rigid polyurethan
`foam (23). Their use has been suggested in the preparation of cellular structures
`based on polyolefin resins (24), poly(vinyl chloride) compositions (25), epoxy resins
`(26), and phenol~ and urea-—formaldehyde resins (27).
`
`Chemical Blowing Agents
`
`Chemical blowing agents (28) decompose upon heating with liberation of gaseous
`products. This is usually an irreversible, exothermic reaction which occurs over a
`definite and short temperature range. Certain compounds such as bicarbonates,
`which decompose through thermal dissociation, evolve gas in a reversible and endother-
`mic reaction.
`
`The choice of a chemical blowing agent is dependent upon and limited by its
`rate of decomposition at elevated temperatures. A rapid rate of decomposition is
`desirable, but a violent breakdown of the compound must be avoided. The rate of
`decomposition should not be afiected by pressure if the compound is to be used in the
`expansion process involving high pressures. To be useful commercially, the blowing
`agent must be stable over an extended period of time at temperatures encountered
`under ordinary storage conditions.
`
`PAGE 7 OF 37
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`PAGE 7 OF 37
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`

`
`536
`
`Blowing Agents
`
`Chemical blowing agents preferably decompose with liberation of nitrogen, but
`other gaseous products such as carbon dioxide, carbon monoxide, and hydrogen are
`frequently encountered. Corrosive gases (eg, nitrogen dioxide, sulfur dioxide, and
`hydrogen chloride) should be absent from the decomposition products. Also, the
`generated gas should be virtually insoluble in the polymer.
`To obtain homogeneous distribution in the polymer, the blowing agent should
`be either easily dispersible by conventional methods of mixing, or should be soluble
`in the polymer. Furthermore, it is important that the blowing agent and its de-
`composition products exert no adverse effects on the physical and chemical properties
`of the polymer. For example, the rate of fusion (ie, intimate blending of resin and
`plasticizer under the influence of heat) or crosslinking should not be impaired, the
`electrical properties should not deteriorate, and the thermal and chemical resistance
`of the polymer should not be decreased by the presence of the residue.
`
` ”
`
`20
`
`40
`
`so
`
`so
`Time. min
`
`100
`
`120
`
`140
`
`Fig. 1. Gas development curves of ldinitrosopentamethylenetetramine (30).
`Courtesy Plastics Progress.
`
`The commercial acceptance of a chemical blowing agent quite often hinges on
`the properties of the residue.
`Ideally, the residue should be colorless, nonstaining,
`nondiscoloring, nonflammable, compatible with the polymer, and should impart no
`objectionable odor.
`It is also essential that both the blowing agent and the residue
`be nontoxic and relatively harmless to the skin.
`The efficiency of chemical blowing agents can be measured by the quantity of
`gas given off upon decomposition and is usually expressed as ml/g of blowing agent
`under given conditions. An inexpensive blowing agent is not nee
`ily the most
`economical if its gas yield is low. A gas yield based on unit cost b ter characterizes
`the efficiency of a blowing agent than does a. gas yield computed on the basis of unit
`weight.
`The major advantage derived from the use of chemical blowing agents is their
`case of handling and their adaptability to processes requiring conventional equipment.
`Testing Methods. The thermal behavior of chemical blowing agents has been
`a subject of many investigations, and numerous methods have been proposed for the
`determination of the decomposition rate, temperature, and gas yield.
`
`/
`
`'4
`
`PAGE 8 OF 37
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`PAGE 8 OF 37
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`

`
`Vol. 2
`
`Blowing Agents
`
`537
`
`i’ Endothermal
`
`T Exothermal
`
`100
`
`120
`
`180
`160
`140
`Temperature. ‘C
`
`200
`
`220
`
`Fig. 2. Typical dilferential thermal analysis graph of 4,4’-oxybis»
`(benaenesulfonyl hydi-aside) (31). Rate of heating:
`approx 10°C/min;
`reference: Al«,»0a. Courtesy SPE Journal.
`
`Temperature
`rise 6.5‘ Cfmin
`
`weight loss
`(azo group)
`
`Percentweight
`
`loss
`
`160
`
`180
`
`220
`200
`Temperature. ‘C
`
`240
`
`-
`
`260
`
`Fig. 3. Typical thiermogravimetrie analysis graph of azodioarbonamide (31).
`Courtesy SPE Journal.
`
`To compare the efliciency of blowing agents, Cooper (29) used an oil-heated,
`high-pressure gas bomb connected with a manometer which allowed the observation
`of pressure rise as the decomposition of the agent progressed.
`In another method,
`the relative performance of blowing agents and their behavior in various liquids was
`studied by measuring the volume of the evolved gas as a function of the heating time
`at several temperature levels (30). Typical results obtained by this method are
`shown in Figure 1.
`In recent years difierential thermal analysis (qv) and thermogravimetric analysis
`(qv) have been employed to investigate blowing agents (31). Differential thermal
`analysis permits the determination of the exotherm which is generated at the de-
`composition point of the blowing agent. A typical differential thermal analysis curve
`of the decomposition of a blowing agent is illustrated in Figure 2. Using thermogravi-
`metric analysis, the decomposition of a blowing agent can be followed by measuring
`
`PAGE 9 OF 37
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` m
`
`PAGE 9 OF 37
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`

`
`538
`
`Blowing Agents
`
`the weight loss of a sample heated at a constant rate. Figure 3 depicts results that
`can be obtained with thermogravimetric analysis.
`The American Society for Testing and Materials in cooperation with the Society
`of the Plastics Industry has issued a tentative method, ASTM D 1715-6073, for de-
`termination of the total gas volume evolved from chemical blowing agents. This
`method is not applicable to measuring the rate of decomposition.
`In all methods previously discussed, the rate of decomposition of the blowing
`agent is determined under environmental and thermal conditions significantly different
`from those encountered in the preparation of cellular polymers. Meaningful infor-
`mation on the thermal behavior of blowing agents in polymers can be obtained when
`their performance is compared in a particular polymer system under controlled ther-
`mal conditions. For instance, in the absence of a crosslinking or stiffening effect of
`the decomposition products, the degree of expansion of the polymer is directly related
`to the quantity of gas given off by the blowing agent at a constant tim¢.Lten1perature
`cycle (32), provided no gas is lost by cell rupture or diffusion.
`Economics. No data are available on the production and consumption of
`chemical blowing agents. Authoritative market statistics on blowing agents have
`never been published, and market estimates of various blowing agent manufacturers
`are closely guarded secrets.
`In 1960, the US. Tariff Commission published, for the last time, figures on pro-
`duction and sales of organic chemical blowing agents under the heading of “Rubber
`Processing Chemicals.” The following figures were reported:
`Productc'cn, Eb
`3 ,650 ,000
`688,000
`
`Blowing agents, cyclic
`Blowing agents, acyclic
`
`Sales, lb
`3 ,416 ,000
`457,000
`
`At the present time, the US. Tariff Commission combines the statistical infor-
`mation on blowing agents with those on other rubber processing rnateriais, eg, pep-
`tiaers, lubricants, etc. The five blowing agents included in the survey are 4,4’~oxybis-
`(benzenesulfonyl hydraside), N,N ’—dimethyldinitrosoterephthalamide, dinitrosopen-
`tamethylenetetramine, acobisformamide, and a urea—biuret mixture.
`
`Carbonates
`
`Ammonium Carbonate. Ammonium carbonate is a white, crystalline powder
`with a strong amrnoniacal odor.
`It may be prepared by reacting carbon dioxide with
`ammonia in the presence of water. The commercially available product is actually a
`mixture (or a double salt) of ammoniurnbicarbonate and ammonium carbamate (NH20'
`CONH4). When exposed to air, the crystals of ammonium carbonate liberate am-
`monia and water and are transformed into a moist ammonium bicarbonate powder.
`The thermal dissociation of ammonium carbonate starts at 30°C and the reaction
`
`‘
`proceeds quite vigorously at 55—60°C.
`The compound is a “total” blowing agent in that it decomposes without leaving
`a residue. At 100°C the gas yield is 980 ml (STP)/g, one of the highest of all chemical
`blowing agents. The usefulness of ammonium carbonate as a blowing agent is severely
`limited by its poor storage stability, the indefinite composition of the commercial
`product, the objectionable ammonia odor, and the difficulty with which the material
`can be dispersed in high polymers. The storage stability of ammonium carbonate can
`be improved, according to patent literature, by blending it with magnesium carbonate
`.1
`
`PAGE 10 OF 37
`
`’
`'
`
`1'
`
`i
`
`'
`
`I
`
`:'
`'.
`
`.
`
`
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`PAGE 10 OF 37
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`

`
`Vol. 2
`
`Blowing Agents
`
`539
`
`(33), zinc oxide (34), or alkylamincs (35). Pastes consisting of the blowing agent and —
`processing oils have better stability as well as improved dispersibility (36). Ammo-
`nium carbonate has been used in the production of sponge rubber (37); however, it
`has been displaced by the more stable sodium bicarbonate.
`It has also been proposed
`as an auxiliary blowing agent in the preparation of polynrethan foam (38), as an
`additive to dinitrosopentamethylenetetrarnine for making poly(vinyl chloride) foam
`(39), and as a blowing agent for urea~l'orma-ldehyde glues (40) and chlorosulfonated
`polyolefim compounds (41). The 1963 price of ammonium carbonate (USP grade)
`was 23.5—%.5¢/lb.
`Ammonium Bicarbonate. Ammonium bicarbonate is more stable and easier
`to obtain in pure form than ammonium carbonate. Commercially, ammonium
`bicarbonate is prepared by passing carbon dioxide through an aqueous solution of
`ammonia. Under atmospheric pressure and in the absence of moisture,
`the salt
`decomposes
`slowly at 60"C yielding ammonia,
`carbon dioxide, and water.
`NH4HCO: w——" NH: + 002 + H20
`In
`The gas yield is 8.30 ml (STP)/g assuming water to be available as vapor.
`1963 ammonium bicarbonate sold at 7.5-8.5¢/lb. It is therefore more economical as
`a blowing agent than ammonium carbonate. Moisture accelerates the dissociation
`of the salt, and high pressure suppresses the formation of the gaseous decomposition
`products.
`Ammonium bicarbonate suffers from the same disadvantages as the carbonate
`and can be used in the same applications.
`Sodium Bicarbonate. Among the inorganic blowing agents only sodium
`bicarbonate has remained in use over the years, although the introduction of organic
`blowing agents greatly diminished its importance in the manufacture of cellular
`polymers.
`Sodium bicarbonate is an odorless nontoxic white powder (specific gravity 2.20),
`which is obtained as an intermediate in the manufacture of soda ash by the Solvay
`process, or by reacting sodium carbonate solution with. carbon dioxide. The salt
`decomposes slowly at approximately 100°C with an attendant evolution of carbon
`dioxide; at 140°C the decomposition proceeds at a rapid but still controllable rate.
`2 NaHCO. 7-: NagCOs + C0: + H20
`Assuming water to be available as vapor, the total gas yield is 267 ml (STP)/g,
`which,_ combined with a low price (2.5;£/lb in 1963), makes sodium bicarbonate the
`most economical chemical blowing agent. However, the residue of this decomposi-
`tion is strongly alkaline and thus objectionable in many applications. Also, the
`degree of dimociation of sodium bicarbonate decreases rapidly with increased pressure
`and, therefore, the blowing agent cannot be used efiectively in high-pressure-expansion
`processes.
`
`The storage stability of sodium bicarbonate is adequate but the material tends
`to pick up moisture and to cake badly. However, finely ground sodium bicarbonate
`remains free-flowing if conditioned with additives such as magnesium stearate (-Ansul-
`blo, Ansul Chemical 430.; now withdrawn) (42).
`In blowing polymers, the efficiency
`of sodium bicarbonate is significantly lower than indicated by the gas yield. This
`is due to the rapid rate of difiusion of carbon dioxide from polymers, and to the poor
`dispersibility of the salt in elastomers and plastics. A paste of finely ground sodium
`
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`bicarbonate (particle size less than 15 :4) in light process oil with lecithin as an emul-
`sifier (43) possesses improved dispersibility and can be mixed easily with elastomers.
`This product, Unicel S (Du Pont), has enjoyed commercial acceptance in the pro-
`duction of cellular rubber goods. Surface-active agents can also improve the dis-
`persibility and efficiency of sodium bicarbonate paste (44). A coprecipitated master-
`batch of sodium bicarbonate-containing rubber has been claimed (45) to facilitate the
`dispersion of the blowing agent in rubber compositions.
`In the thermal decomposition of sodium bicarbonate, only half of the theoretically
`available carbon dioxide in the molecule is evolved. A total decomposition of the
`bicarbonate can be achieved by the use of acidic materials.
`In practice, weak acids
`are used in conjunction with sodium bicarbonate to obtain a higher gas yield from
`the blowing agent. For expansion of rubber, sodium bicarbonate is activated with
`stearic acid, oleic acid, or cottonseed oil acid.
`In thermosetting resins, the acidic
`curing catalyst also acts as an activator for the blowing agent.
`Sodium bicarbonate has been extensively employed in the manufacture of open-
`cell rubber sponge (46) based on all types of natural and synthetic elastcmers.
`Phenolic resin foams can be prepared by reacting the bicarbonate with an acid hardener
`(47), and this process has become commercially important. Other polymers that
`can be expanded with sodium bicarbonate are natural and synthetic latexes (48),
`polyethylene (49), alkyd resins (50), poly(vinyl chloride) (51), epoxy resins (52),
`polyamides (53), and acrylic resins (54).
`Organic Carbon Dioxide-Generating Chemicals. Ethylene carbonate (55)
`(1) is an example of organic blowing agents which decompose in polymers in the tem-
`perature range of l20~200°C with the liberation of carbon dioxide (56). The ad-
`
`0_C/OCH:
`\OCiHs
`(1)
`
`vantage claimed for this compound is its compatibility with a wide variety of poly-
`mers, which facilitates dispersion and thus leads to the formation of very fine cells.
`
`Nit:-ites
`
`Ammonium Nitrite. Ammonium nitrite, through its thermal decomposition,
`ofiers a convenient source of elemental nitrogen. Prior to the introduction of organic
`blowing agents, this product had been suggested as an expanding agent for pressure-
`blown cellular rubber (57).
`In practice, ammonium nitrite is prepared in situ by incorporating into the rubber
`mix equimolar quantities of ammonium chloride and sodium nitrite. During the
`’heating of the rubber, nitrogen is liberated.
`
`NH.Cl -1- NaN0g —-> N2 + 2 H20 + No.01
`
`Unlike the thermal dissociation of carbonates, the decomposition of ammonium
`nitrite is an ir1'eversible, exothermic reaction which proceeds independently of external
`pressure. The reaction produces nitrogen, but small quantities of nitric oxides which
`have a cure-accelerating effect and which cause corrosion of molds and other process-
`ing equipment are also generated (58). Small quantities of water and polyhydrifl
`alcohols (59) accelerate the evolution of gas. The hygroscopic sodium nitrite intro-
`duces enough moisture into the compounded polymer to initiate the reaction as S0011
`.0
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`as it comes into contact with ammonium chloride. End results are unpredictable.
`In common with other inorganic blowing agents, both sodium nitrite and ammonium
`chloride are diflicult to disperse in polymers.
`At the present time, ammonium chloride—sodinm nitrite pills are used as an
`inflating agent during the curing of hollow rubber goods (cg, c'h'ildren-‘s balls).
`To overcome some of the disadvantages of ammonium nitrite, stabilised com-
`plexes of this compound have been proposed (60) ; however, in 1963 they had not been
`commercially exploited.
`Organic Nitrites. Various organic nitrites have been considered for use as
`blowing agents.
`Aiicyiamins nitritcs (RNH;.HNOg) represent a group of organic nitrogen-releasing‘
`blowing agents which have been suggested for use in rubber ((51) and in poly(viny1'
`chloride) (62). The compounds decompose with evolution of nitrogen and water.
`
`RNH2.HNOE -> ROI-I + N2 + H20
`
`Icrt»-Buiyteminc nitrite, which was test marketed in the United States in 1955
`as Blowing Agent X-950 -(Rohm it Haas), decomposes at around 120°C and yields
`374 ml (STP)/g (considering the evolved water as vapor).
`Amidins nritrites (R.-—C(:NH)—NHg.HNO;),
`in particular guanidine nitrite
`(clec 99-110°C), guanylurea nitrite -(doc 139°C), and acetamidine nitrite (dec I55-
`160°C), have been claimed in the patent literature as blowing agents for rubber and
`plastics (63), but have not been used for this purpose commercially.
`
`Hydrides and Peroxides
`In recent years borohydrides, in particular potassium and
`Alkali Borohydridcs.
`sodium borohydrides, have been promoted as blowing agents. These compounds are
`convenient sources of hydrogen.
`The rate of hydrolysis of alkali borohydrides is governed by the hydrogen ion
`concentration and increases rapidly with decreasing pH.
`In nonaqueous systems,
`acidic compounds (eg, phthalic anhydride, stearic acid, or glycine) are added along
`with a small quantity of water. Under these conditions the decomposition of the
`borohydricles proceeds rapidly with the evolution of hydrogen. This reaction is also
`catalyzed by certain metallic salts, notably those of iron, cobalt, or nickel.
`(H+)
`MBH4 + 2HaO—~—-——r MB02 '-|'' 41-12
`
`As a result of the decomposition of the blowing agent within the polymer matrix,
`hydrogen is entrapped in the cells; however, it diffuses rapidly and is replaced by air.
`This may create explosion hazards unless the concentration of hydrogen in and around
`processing equipment is kept below 4%.
`Potassium borohydrids is a white crystalline solid which is nonhygroscopic under
`normal storage conditions.
`In air, it ignites from a free flame and burns quietly.
`The compound is readily soluble in Water.
`Its rate of decomposition in an alkaline
`solution is very slow below 100° 0. Under acidic conditions and/or at elevated tem-
`peratures, potassium borohydride decomposes rapidly, yielding 1660 ml (STP) hy-
`drogeu/g.
`Sodium borohydrede is a hygroscopic solid which decomposes slowly in moist air.
`In acidic media the compound generates 2370 ml hydrogen (STP) /g.
`
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`Blowing Agents
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`Alkali borohydrides have been proposed as blowing agents for several polymers
`in aqueous systen1s—rubber latex (64), poly(vinyl acetate), poly(vinyl alcohol), and
`1nelamine—formaldehyde resins (65). Poly(vinyl chloride) plastisols are expanded
`at room temperature with borohydrides in the presence of water and organic acids
`(66); the reaction can be delayed by the addition of isocyanates (67). A blend con-
`taining 5% potassium borohydride extended with clay was ofi’e1-ed commercially
`(Hydri—Foam, Metal Hydrides, Inc., Beverly, Mass.) for blowing natural and syn~
`thetic elastomers in the presence of stearic acid (68), but the product failed in produc-
`tion trials (69) and was withdrawn from the market.
`In 1963 sodium borohydride
`sold at $14.00/lb and potassium borohydride at $17.00/lb. The high price, the mois-
`ture sensitivity of borohydrides, and the fire and explosion hazards of the hydrogen
`generated limit the industrial acceptance of these compounds as blowing agents.
`Silicon Oxyhydridc. Silicon oxyhydride is a white, s