CA2045901A1

CA2045901A1 - Densified and re-expanded polyurethane foam and a method for preparing same

Info

Publication number: CA2045901A1
Application number: CA002045901A
Authority: CA
Inventors: Ronald M. Herrington; Robert B. Turner; Robert M. Harnden
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1990-07-02
Filing date: 1991-06-28
Publication date: 1992-01-03
Also published as: EP0470697A2; EP0470697A3; JPH04232730A; US5032622A

Abstract

ABSTRACT

Polyurethane foams having a specified glass transition temperature are densified for transportation or other purposes by heating the foam to a temperature above its Tg, compressing the heated foam, and then cooling the compressed foam to a temperature below its Tg. The cooled foam remains in a densified state until re-heated to a temperature above its Tg, whereupon it re-expands to assume its original dimensions.

37,711-F

Description

DENSIFIED AND RE-EXPANDED POLYURETHANE FOAM
AND A METHOD FOR PREPARAING SAME

This invention relates to polyurethane foam which can be densified and thermally re-expanded.

Polyurethane foams of various types are well-known and used for a variety of applications, including thermal insulation, packaging, padding9 seat cushions and bedding. As with many low density materials, it is uqually desirable to prepare the foam relatively close to the place where it will be used, since the foam takes up a large amount of space per unit weight. Because of this low density, transportation costs per unit weight are very high, and to avoid these costs it is desirable to minimize shipping the foam.

One way to reduce the shipping costs of flexible foam is to compress it for shipping, and permitting it to re-expand upon unloading. In this way, a greater weight of foam can be loaded into a given transport vehicle. However, many foams have a substantial compression set, and thus do not completely regain their original dimenqions after unloading. In addition, because the compressed foams tend to re-37,711-F -1-, .

foam during loading and unloading procedures. The expansive force of the foam also tends to lirnit the amount of foam which can be packed into a given container, as the walls of the container must be of sufficient strength to withstand those forces. It would therefore be desirable to provide a polyurethane foam which can be easily transported at a relatively high density.

In one aspect, this invention is a densified polyurethane having a bulk density of from 30 to 900 kg/m3 and a Tg o~ at least about 35C but below the decomposition temperature of said polyurethane, which densified polyurethane is thermally expandable without the addition of a blowing agent to form a polyurethane foam having a bulk density of 5 to 25 percent of the bulk density o~ the densified polyurethane.

In another aspect, this invention is a polyurethane foam having a Tg of at least about 35C but below the decomposition temperature of said poly-urethane, which foam is the reaction product of a reaction mixture comprising as a major active hydrogen--containing component a polyol having an equivalent weight from 125 to 350~ a polyisocyanate, and at least 5 parts water per 100 parts of combined weight of aLl other active hydrogen~containing components, wherein the isocyanate index is from 50 to 110.

3 In a third aspect, this invention is a re-expanded polyurethane foam having a Tg of at least about 35C but below the decomposition temperature of said polyurethane, which has been re-expanded by heating a densified polyurethane having a bulk density of 30 to 37,711-F -2-900 kg/m3 to a temperature above its Tg under conditions such that the densified polyurethane re-expands to assume a bulk density of less than about 25 percent of the bulk density of the densified polyurethane.

In a fourth aspect, this invention is a method for densifying a polyurethane foam having a Tg of at lea~t about 35C but below the decomposition temperature of said polyurethane and an initial bulk density, comprising bringing said foam to a temperature in excess of its Tg but below its decomposition temperature, then compressing the heated foam sufficiently that the compressed foam has a bulk density from 4 to 20 times the initial bulk density of the polyurethane foam, but not greater than about 900 kg/m3, then cooling the foam to a temperature below its Tg while maintaining it in said compressed state.

This invention provides a simple and effective means for transporting low density polyurethane foam in a densified state. The densified foam is then easily re-expanded by heating to regenerate the low density foam. This invention has other advantages as wellO The densified foam can be very easily shaped into a desirable configuration which will appear in the re-expanded foam as well. Thus, this invention provides a means to simplify the shaping of polyurethane foam.

In this invention, a polyurethane Poam having a 3 specified Tg is heated to a temperature above its Tg, compressed, and while compressed, cooled to a temperature below its Tg. At a temperature above its Tg, the foam exhibits elastomeric properties, allowing it to be easily compressed. Once compressed, cooling 37,711-F -3-_ 4 _ '~ q ! '~

the foam below its Tg, preferably below about 30C
causes it to "set" in the compressed configuration, so that it retains its compressed shape with the application of little or no outside force. Thus, the densified polyurethane can be easily packed and shipped in the densified shape. By heating the densified polyurethane to a temperature above its Tg, it again exhibits elastomeric properties, and will expand in the absence of applied forces to substantially regain the dimensions of the original foam.
For the purposes of this invention, the Tg o~ a polymer refers to the temperature at which the polymer undergoes its dominant glass transition, as measured by differential scanning calorimetryO In many of the foams useful herein, the glass transition of interest is very broad, starting at a temperature as low as about -60C
and continuing until in excess of 35C. In those cases, the temperature at the high end of the glass transition range is taken as the Tg. By 'Icooling the foam below it~ Tg~l, it is meant that the foam is cooled to a temperature below the high end of such a broad thermal transition. The terms "glass transition", "glass transition temperature" and "Tg" are as defined by Alger in Polymer Science Dictionary, Elsevier Science Publishing Co., Inc. New York (1989). In certain polyurethanes) the use of more than one active hydrogen--containing material in its preparation may cause the foam to have more than one Tg. In such cases, the Tg involving the greatest change in tan delta value is the Tg referred to herein. In any case, a foam which is elastomeric above about 35C but which becomes rigid enough to maintain a compressed state at a temperature 37,711-F _l~_ -5- ~

of below about 30~C is considered to have the required Tg.

The minimum Tg of the foam is above the temperature range normally encountered during the period it exists in the densified state. Otherwise, the densified polyurethane would exhibit elastomeric properties, and no longer retain its densified state without the application of outside force. For this rea~on, the Tg of the foam is advantageously in excess of about 35C. A minimum Tg of at least about 40C, more preferably at least 45, is preferred to provide a wider range of service temperature. If a higher service temperature is contemplated 9 then the foam should have a correspondingly higher Tg. Of course, if the foam is to be used and transported primarily at relatively low temperatures, the foam may in such instances have a correspondingly lower Tg.

On the other hand, the Tg of the foam rnust be below a temperature at which significant decomposition of the foam occur~. Preferably, the Tg is up to about 120C, more preferably up to about 100C, most preferably up to about 90C, so that the foam can be easily heated above its Tg for densification, and the densified polyurethane can be easily heated above its Tg for re-expansion.

In densifying the foam, it is advantageously 3 compressed to a density of about 4, preferably about 6, more preferably about 7 times the density of the original foam, up to about 20, more preferably up to about 15, more preferably up to about 12 tirnes the density of the original foam. However, the density of 37,711-F -5-the densified polyurethane should not exceed about 900, preferably about 700, and more preferably about 500 kg/m3. When the foam is densified too greatly (in excess of the density limits set out above), it often cannot be fully re-expanded.

The force needed to compress the foam is a function of its density and physical properkies.
However, a light to moderate force of about lO lb/in2 or less, preferably 1 to 5 lb/in2 ls normally sufficient.
The density of the original foam is not especially critical, although densification for transportation purposes has little practical benefit when the original ~oam density is greater than about 500 kg/m3. In mosk instances, the density of the foam is determined by the demands of its intended application.
For most insulating and packaging applications, a denslty of from about 5, preferably about 7, more preferably about 10 kg/m3, up to about 200~ more preferably about 509 most preferably about 20 kg/m3 are suitable. It is with these low density foams that this invention is of particular benefit.

The polyurethane foam of this invention is advantageously prepared in the reaction of an active hydrogen-containing composition and a polyisocyanate in the presence of a blowing agent. The desired Tg of the foam is generally related to the equivalent weight of 3 the active hydrogen-containing materials used in said reaction. The use of a major amount, based on the number of equivalents of active hydrogen-containing materials other than water, of an active hydrogen--containing material having an equivalent weight of 125 37,711-F -6--7~

to 350, preferably 130 to 250, generally provides the foam with a glass transition temperature in the desired range. Such a material is referred to for convenience herein as a "high Tg polyol". The high Tg polyol preferably constitutes 60 to 98, more preferably 80 to 98, most preferably 90 to 95 equivalent percent of all active hydrogen-containing materials other than water.
The high Tg polyol is preferably a polyether polyol having a functionality of 2 to 8, more preferably 2 to 6, and is more preferably a polymer of propylene oxide and/or ethylene oxide.

In addition to the high Tg polyol, it is advantageous, although not critical, to employ a higher equivalent weight active hydrogen-containing material in the reaction mixture in a minor amount on an equivalents basis. Such a material typically provides the foams with a second Tg well below room temperature, so that the foam retains some elastomeric character at room temperature. This has been found to improve the foam's ability to resume its original dimensions when re-expanded. Accordingly, the active hydrogen~containing composition preferably comprises an active hydrogen--containing material having an equivalent weight in excess of 350 to 8000, preferably 800 to 3000, more preferably 1000 to 2500. This higher equivalent weight material is preferably a polyether polyol or polyester polyol nominally having 2 to 4 active hydrogen-containing groups per molecule, and most preferably is a 3 polymer of ethylene oxide and/or propylene oxide nominally having 2 to 3 hydroxyl groups per molecule.
The so-called polymer polyols such as dispersions of polyurea, polyurethane, polyurethane-urea, and vinyl polymer and copolymer particles in polyether polyols are 37,711-F -7-also suitable. Examples of such dispersions are described in U. ~. Patent Nos. 4,3749209, 4,324,716 and 4,460,715. This higher equivalent weight material advantageously constitutes 2 to 40, preferably 2 to 20, more preferably 5 to 10 percent of the total equivalents of active hydrogen-containing materials other than water.

The polyisocyanates use~ul herein include those organic compounds having an average of at least about 2.0 isocyanate groups per molecule. Those containing aliphatically bound or aromatically bound isocyanate groups are useful herein. Suitable aliphatic polyisocyanates include ethylene diisocyanate, 1,4 -tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate9 1,12-dodecane diisocyanate, cyclobutane -1,3-diisocyanate, cyclohexane-1,3- and ~ -diiso-cyanate, 1,5-diisocyanato-3,3,5-trimethylcyclohexane, hydrogenated 2,4- and/or 2,6-hexahydrotoluene diisocyanate, hydrogenated -2,4'- and/or -4,4' -diphenylmethanediisocyanate (H12MDI) and isophorone diisocyanate.

Suitable aromatic polyisocyanates include, for example, 2,4- and/or 2,6-toluene diisocyanate (TDI), 1,3- and 1,4-phenylene diisocyanate, 4,4'--diphenylmethane diisocyanate (including mixtures thereof with minor quantities of the 2,4'~isomer) (MDI), 1,5-naphthylene diisocyanate, triphenylmethane-4,4',4'1-3 -triisocyanate, polyphenylpolymethylene polyisocyanates and (PMDI).

In addition, derivatives and prepolymers of`
the foregoing polyisocyanates .such as those containing 37,711-F -8-~ . , g rf, ~

urethane, carbodiimide, allophanate, isocyanurate, acylated urea, biuret, ester and similar groups are useful herein.

Of the foregoing polyisocyanates, TDI, MDI, isophorone diisocyanate, H12MDI, hexamethylene diiso-cyanate, cyclohexane diisocyanate and derivatives thereof are preferred due to their cost, commercial availability and performance. It is also pre~erred, especially in high water formulations, that a polyisocyanate or mixture thereof having an average functionality of at least about 2.1, more preferably at least about 2.2 isocyanate groups per molecule be used.
TDI, MDI and derivatives and prepolymers of MDI are particularly preferredO Most preferred are polymeric MDT and mixtures thereof with MDI and TDI.

The polyisocyanate is advantageously used in an amount sufficient to provide an isocyanate index of 60 20 to 110, preferably 70 to 100, and in high water formulations, more preferably 70 to 90. "Isocyanate index" refers to 100 times the ratio of isocyanate groups to active hydrogen-containing groups in the reaction mixture.
A blowing agent is a material which generates a gas under the conditions of the reaction of the active hydrogen-containing composition and the polyisocyanate.
Suitable blowing agents include water, low-boiling 3 organic compounds and the so-called "azo" compounds which generate nitrogen. Among the low boiling organic compounds are the hydrocarbons and halogenated hydrocarbons such as pentane, hexane, methylene chloride, Refrigerant 11, Refrigerant 12, Refrigerant 37,711-F _g_ .

123 and and Refrigerant 142-B. Other organic blowing agents include those described in PCT Published Application WO 89/00594. Preferably, however9 water, which generates carbon dioxide upon reaction with an isocyanate, is the primary blowing agent and is most preferably the sole blowing agent.

The blowing agent is used in an amount sufficient to provide the desired density to the foam~
When used as the sole blowing agent, from 3 to 25, preferably 5 to 20, most preferably 10 to 18 parts by weight are advantageously used per 100 parts by weight of the other active hydrogen-containing materials.
Those formulations containing at least about 5 parts by weight water per 100 parts by weight of the other active hydrogen containing materials are referred to herein as "high water" formulations.

In addition to the foregoing, other components which are useful in preparing the foam include materials such as surfactants, catalysts, cell size control agents, cell opening agents, colorants, antioxidants, preservatives, mold release agents and static dissipative agents. Among these, the use of surfactants ~5 and catalysts is preferred.

Surfactants suitable f'or use herein include but are not limited to the silicone surfactants and the alkali metal salts of f'atty acids. The silicone 3 surfactants are pref'erred, especially the block copolymers of an alkylene oxide and a dimethylsiloxane.

Suitable catalysts include tertiary amine compounds and organometallic compounds. Exemplary 37,711-F -10-tertiary amine catalysts include, for example, triethylenediamine, N-methylmorpholine, N-ethyl morpholine, diethyl ethanolamine, N-coco morpholine~
1-methyl-4-d;methylaminoethyl piperazine, 3-methoxy-N-dimethylpropylamine, N,N-diethyl-3-diethylamino-propylamine, dimethylbenzyl amine and bis(2-dimethylaminoethyl)ether. Tertiary amine catalysts are adYantageously employed in an amount from 0.01 to 5, preferably 0.05 to 2 parts per 100 parts by weight of the active hydrogen--containing materials.

Exemplary organometallic catalysts include organic salts of metals such as tin, bismuth, iron, mercury, zinc and lead, with the organotin compounds being preferred. Suitable organotin catalysts include dimethyltindilaurate, dibutyltindilaurate and stannous octoate. Other suitable catalysts are taught, for example in U. S. Patent No. 2 9 846,408. Advantageously 0-001 to 0.5 part by weight of an organometallic catalyst is used per 100 parts of the active hydrogen--containing materials.

It is often desired to employ a static dissipative agent in making the foam, or to treat the finished foam with such an agent. Of particular interest are effective amounts of a non-volatile 9 ionizable metal salt, optionally in conjunction with an enhancer compound, as described in U. S. Patent Nos.
3 4,806,571, 4,618,630 and 4,617,325. Of pa~ticular interest is the use of up to about 3 weight percent of sodium tetraphenylboron or a sodium salt of a perfluorinated aliphatic carboxylic acid having up to about 8 carbon atoms.

37,711-F -11-In making the foam, either free-rise (slabstock) or molding techniques can be used. In slabstock processes, the reactants are mixed and poured onto a conveyor where the reacting mixture rises against its own weight and cures. In the molding techniques, the reactants are mixed and dispensed into a mold where they react, filling the mold and assuming the shape of the mold cavity.

The use of high water formulations in this invention leads to the production of a high exotherm during the foaming reaction. This drives the temperatures inside the forming foam quite high, so that unless good heat removal occurs, significant discoloration or ever. burning of the foam can occur.
Thus, it is preferred to restrict the use of the high water formulations to the production of smaller cross--section foams, so that removal of the heat of reaction can be effected. Preferably, foam having a cross-~ectional area of 1500 in2 (0.97 m2) or less, morepreferably about 600 in2 (0.39 m2) or less, is made.

It is often desirable to post-cure the foam after initial foaming (and demolding in the case of molded foam) to develop optimal physical properties.
Post curing can be done under ambient conditions for a period of 12 hours to seven days, or under elevated temperatures for a period of 10 minutes to 3 hours.

3 It is often desirable to mechanically open the cell walls of the foam. This is most conveniently done by crushing.

37,711-F -12-.. ~ .

.

After curing, the foam may, if desired, be fabricated by cutting it into a desired shape. This fabrication can be done either be~ore o- alter densification.

The resulting foam, due to its high Tg, is particularly use~ul in packaging applications. However, it is also useful in cushioning and other energy--absorbing applications.

The ~ollowing examples are given to illustrate the invention and are not intended to limit the scope thereof. Unless stated otherwise, all parts and percentages are given by weight.

37,711-F -13-' Example 1 A polyuretnane foatn was prepared from the components listed in Table 1.

Component Polyol A~ 50 Polyol B~ 50 Water 18 Silicone Surfactant 0.75 Amine Catalyst A~ 0.3 Amine Catalyst B~ 0.5 Amine Catalyst C~ 0.1 TDI mixture~ 131.1 PMDI~ 32.8 ~A nominally trifunctional poly (propylene oxide) of 271 equivalent weight. ~A
nominally difunctional ethylene oxide-capped poly(propylene oxide) of 2000 equivalent weight. ~33% triethylene diamine in dipropylene glycol. ~Dimethyl ethylamine. ~70% bis (dimethylaminoethyl ether) in dipropylene glycol. ~An 80/20 mixture of the 2,4- and 2,6- isomers. ~A
polymeric MDI having an average functionality of about 2.3 and an equlvalent weight of about 131.

All components except isocyanates were 3 thoroughly mixed at room temperature, and then the isocyanates were added with vigorous mixing. The resulting mixture was poured immediately into an open box and permitted to react until it fully expanded and assumed stable dimensions. The foam was then post-cured 37,711-F -14-- ', ,, i`

:

-15- 2~ 5 ~3 ' in a 120C oven for fifteen to twenty minutes and cooled. The cooled foam was crushed to break cell walls, yielding an open-celled, semi-rigid foam having a bulk density of 8 to 9.6 kg/m3.

The foam was densified by heating it to 90C to 100C until soft and compressing it to about ten times its original density. While under compression, the foam was cooled back to room temperature. The cooled foamt being below its Tg, retained its compressed dimensions.
Upon reheating to a temperature above its Tg, the foam re-expanded to assume its original dimensions.

Example 2 A polyurethane foam was prepared from the components listed in Table 2.

37,711-F -15--16~

Component Weight Polyol C~ 113 Polyol B~ 113 Copolymer Polyol~ 22.5 Water 31.5 Silicone Surfactant 2.25 Dimethylethylamine 1.13 N,N-dimethyl aminoethanol 2.25 Stannous Octoate 0.23 Amine Catalyst C 0.9 PMDI~ 59.3 ~A nominally trifunctional poly (propylene oxide) of 135 equivalent weight. ~A
nominally difunctional ethylene oxide-capped poly (propylene oxide) of 2000 equivalent weight. ~A 43% solids styrene/acrylonitrile copolymer polyo1 having an equivalent weight of about 1750.
~A polymeric MDI having a functionality of about 2.7.

The foam was prepared in the same general manner as described in Example 1. It exhibited a thermal transition beginning at about -120C and ending at about -65C, and a broader thermal transition beginning at about -65C and ending at about 40C. The tan delta changed by about 0.026 units over the lower range and about 0.032 units over the higher temperature range, indicating that the higher temperature transition was the major one for this polymer. The product had a density o~ about 0.99 pound/cubic foot (15.9 kg/m3), and 37,711-F -16--17 ~ ~`i! y was densified according to the procedure described in Example 1 to form a densified product having a density of about 8 lb/ft3 (128 kg~m3). The densified foam assumed its original dimensions upon heating to 90C to 1 OOC .

The compressive strength and modulus of the foam was determined according to ASTM D 3574-86. At 5 percent deflection, the compressive strength was about 5.8 psi (400 kPa) on first testing, and on subsequent testing, the compressive strength is about 1.6 psi ( 110 kPa). At 25 percent deflection, the compressive strength was about 5.7 psi (393 kPa) on first testing, and the compressive strength on subsequent testing was about 2.6 psi (179 kPa). Compressive modulus was about 190 psi (13,100 kPa) initially. In addition, the foam exhibited compressive creep and compressive set properties similar to polyethrlene packaging foams~

Example 3 Polyurethane foam Samples A and B were prepared from the components listed in Table 3. Sample A had a bulk density of about 13.1 kg/m3, and that of Sample B
was about 13.3 kg/m3. Both foams are readily densified according to the process described in Example 1 to form a densified product having a density of about 8 lb/ft3.
Each assumed its original dimensions upon heating to 90C to 100C.

Foam Sample A exhibited a thermal transition between -120C and -65C, and a broader thermal transition beginning at about -60C and ending at about 40C. The change in tan delta over the lower 37,711-F -17-. .

-18- , temperature transition was about 0.022 units, whereas that over the higher temperature transition was about o.o38 units. This indicates that the higher temperature transition was the major one in this polymer.

Parts by Weight Component ~ ~ -Sample A Sample Polyol D~ 150 0 Polyol E~ 0 150 Polyol B~ 150 150 Copolymer Polyol~ 30 30 Water 42 42 Silicone Surfactant 3.0 3.0 15 Dimethylethylamine 1.5 1.5 N,N-dimethyl aminoethanol3.0 3.0 Stannous Octoate 0.3 0.3 Amine Catalyst C 0.9 0.9 PMDI~ 631 619 ~A nominally trifunctional poly (propylene oxide) of 2QO equivalent weight. ~A nominally difunctional ethylene oxide-capped poly (propylene oxide) of 2000 equivalent weight. ~A 43% solids styrene/acrylonitrile copolymer polyol having an equivalent weight of about 1750. ~A polymeric MDI
having a functionality of about 2.7. ~A nominally trifunctional poly (propylene oxide) of 231 equivalent weight.

The compressive strength and modulus of the foams were determined according to ASTM D-3574-86. At 5 percent deflection, the compressive strengths of Samples A and B are about 4.0 and 3.8 psi (276 and 262 kPa), respectively, on first testing, and the compressive strengths are about 1.4 and 1.6 psi (97 and 110 kPa), respectively, on subsequent testing. At 25 percent 37,711-F -18-_19~

deflection, the compressive strengths are about 4.2 and 3.9 psi (290 and 269 kPa), respectively, on ~irst testing and the compressive strengths were about 2.2 and 2.3 psi, respectively, on subsequent testing.
Compressive moduli were about 120 and about 95 psi (8274 and 6550 kPa), respectively~ on first testing. In addition, the foams exhibited compressive creep and compressive set properties similar to polyethylene packaging foams.

3o 37t71l-F -19-

Claims

1. A densified polyurethane having a bulk density of from 30 to 900 kg/m3 and a Tg of at least about 35°C but below the decomposition temperature of said polyurethane, which densified polyurethane is thermally expandable without the addition of a blowing agent to form a polyurethane foam having a bulk density of 5 to 25 percent of the bulk density of the densified polyurethane.

2. The densified polyurethane of Claim 1 which is prepared by heating a polyurethane foam to a temperature above its Tg, compressing it and cooling it to a temperature below its Tg while in a compressed state, wherein the polyurethane foam is the reaction product of a reaction mixture comprising as a major active hydrogen-containing component, a polyol having an equivalent weight from 125 to 350, a polyisocyanate, and at least about 5 parts water per 100 parts of combined weight of all active hydrogen-containing components, wherein the isocyanate index is from 50 to 110.

37,711-F -20-

3. The densified polyurethane of Claim 2 wherein said major active hydrogen-containing component is a polyether polyol having an equivalent weight from 130 to 250.

4. The densified polyurethane of Claim 3 wherein said reaction mixture further comprises an additional active hydrogen-containing material having an equivalent weight of 800 to 3000, and wherein the number of equivalents of said major active hydrogen-containing component constitutes 60 to 98 percent of the total number of equivalents of all active hydrogen-containing materials other than water.

5. The densified polyurethane of Claim 4 wherein said polyisocyanate is MDI, polymeric MDI, TDI
or a mixture thereof.

6. A re-expanded polyurethane foam having a Tg of at least about 35°C but below the decomposition temperature of said polyurethane, which has been re-expanded by heating a densified polyurethane having a bulk density of 30 to 900 kg/m3 to a temperature above its Tg under conditions such that the densified polyurethane re-expands to assume a bulk density of less than about 25 percent of the bulk density of the densified polyurethane.

7. A method for densifying a polyurethane foam having a Tg of at least about 35°C but below the decomposition temperature of said polyurethane and an initial bulk density, comprising bringing said foam to a temperature in excess of its Tg but below said decomposition temperature, then compressing the heated 37,711-F -21-foam sufficiently that the compressed foam has a bulk density from 4 to 20 times the initial bulk density of the polyurethane foam, but not greater than about 900 kg/m3, then cooling the foam to a temperature below about 30°C while maintaining the foam in said compressed state.

8. A loose-fill packing comprising a foam of Claim 6 in a particulate form.

37,711-F -22-