METHOD FOR THE SYNTHESIS OF AN AUXETIC POLYURETHANE FOAM WITH A DEFINED CELL STRUCTURE AND AUXETIC POLYURETHANE FOAM OBTAINABLE BY THE METHOD

Abstract

A method for the synthesis of an auxetic polyurethane foam with a defined cell structure and an auxetic polyurethane foam substrate obtainable by a method according to the invention. The method includes mixing a polyol reagent and a foaming reagent, forming a reaction mixture, mixing an isocyanate with the reaction mixture, compressing and/or contracting the isocyanate/reaction mixture, and allowing the compressed and/or contracted isocyanate/reaction mixture to cure.

Claims

1. A method for the synthesis of an auxetic polyurethane foam with a defined cell structure, comprising the steps of: a. mixing a polyol reagent and a foaming reagent, forming a reaction mixture; b. mixing an isocyanate with the reaction mixture; c. compressing and/or contracting the reaction mixture of step b, by applying internal forces and/or external forces; and d. allowing to cure the compressed reaction mixture of step b, wherein the compression and/or contraction during synthesis of the auxetic polyurethane foam results in polyurethane foam cells that have ribs which are protruding inwards and/or outwards, and wherein steps c and d are performed in a mould thereby providing an auxetic polyurethane foam.

2. The method according to claim 1, wherein the foaming reagent is one or more selected from the group of a blowing catalyst, a blowing agent, a gelling catalyst, a surfactant, a chain extender, a cross-linker.

3. The method according to claim 1, further comprising adding water to the reaction mixture before step b.

4. The method according to claim 1, further comprising the steps of: (i) initiating the reaction by initiating the reaction mixture of step b, wherein step (i) is performed before step c; (ii) expansion and rising of the initiated reaction mixture of step (i); and (iv) finalising of cross-linking and curing, wherein step (iv) is a sub-step of step d.

5. The method according to claim 1, further comprising the step of pouring the reaction mixture onto a moving conveyer as part of a continuous line.

6. The method according to claim 1, wherein the steps a and b are independently performed by vigorously agitating, wherein vigorously agitating comprises a rotation speed, and wherein the rotation speed for each of the steps a and b is in the range of 10 rpm to 5000 rpm.

7. (canceled)

8. The method according to claim 1, wherein step a is performed for at most 8 hour.

9. The method according to claim 1, wherein step a is performed at a temperature of less than 100° C.

10. The method according to claim 1, wherein step b is performed between 1 second to 130 seconds.

11. The method according to claim 3, wherein adding water to the reaction mixture before step b is performed under vigorously agitating between 1 second to 40 minutes.

12. The method according to claim 1, wherein the polyol reagent is one or more selected from the group of polyether polyol, polyester polyol, polyamine polyol, polyamide polyol, polythioester polyol, polythioether polyol, solid support polyol.

13. The method according to claim 1, wherein the isocyanate of formula I is provided ##STR00002## wherein R.sub.1 comprises an alkyl group and/or aromatic group.

14. The method according to claim 1, wherein the isocyanate is one or more selected from the group of tolylene-2,4-diisocyanate, tolylene-2,6-diisocyanate, methylene diphenyl diisocyanate, p-phenylene diisocyanate, dicyclohexylmethane diisocyanate, 1,5-naphthylene diisocyanate, O-tolidine diisocyanate, isophorone diisocyanate.

15. The method according to claim 2, wherein the blowing catalyst comprises a tertiary amine, wherein the tertiary amine is one or more selected from the group of triethylenediamine, 1,3,5-tris-(3-[dimethyl-amino]propyl)-hexa-hydro-1,3,5-triazine, bis(2-dimethylaminoethyl)ether, N,N-dimethylcyclohexylamine, 2,2′-dimorpholinodiethylether, N,N-dimethylethanolamine, N,N-dimethylaminoethoxyethanol, N,N,N′,N″,N″-pentamethyldiethylenetriamine, N,N-dimethylaminoethoxyethanol, 2,2′-dimorpholinodiethylether, N,N′-dimethylpiperazine; and/or wherein the blowing agent is one or more selected from the group of water, chlorofluorocarbons, hydrochlorofluorocarbons, hydrofluorocarbons, hydrocarbons, isopentane, cyclopentane, nitrogen, argon, carbon dioxide, helium, xenon, neon, air; and/or wherein the gelling catalyst comprises an organometallic catalyst, wherein the gelling catalyst is one or more selected from the group of stannous octoate, stannous neodecanoate, dibutyltindilaurate, potassium acetate; and/or wherein the surfactant is siloxane derivatives and/or oxyalkylene derivatives; and/or wherein the chain extender and/or cross-linker is one or more selected from the group of alcohols, amines, alkoxysilanes, thiols, thioesters.

16-19. (canceled)

20. The method according to claim 15, wherein the chain extender and/or cross-linker is one or more selected from the group of the glycerol, diethanolamine, triethanolamine, ethylene-oxide capped trimethylolpropane, 2-(methylamino)ethanol, ethylene glycol, methyltrimethoxysilane, dimethoxydimethylsilane.

21. An auxetic polyurethane foam substrate obtainable by a method according to claim 1, wherein the auxetic polyurethane foam comprises a Poisson's ratio in the range of −3 to 0.

22. The auxetic polyurethane foam substrate according to claim 20, comprising a total pore volume in the range of 5 to 100 cm.sup.3 g.sup.−1, and an overall average cell size in the range of 0.001 to 5.0 millimetres.

23. The auxetic polyurethane foam substrate according to claim 20, wherein the auxetic polyurethane foam substrate comprises closed cells.

24. The auxetic polyurethane foam substrate according to claim 20, wherein the auxetic polyurethane foam substrate has a glass-transition temperature of at most 180° C. or less.

25. The auxetic polyurethane foam substrate according to claim 20, wherein the auxetic polyurethane foam substrate density is in the range of 10 kg m.sup.−3 to 300 kg m.sup.−3.

Description

[0130] Further advantages, features and details of the invention are elucidated on the basis of preferred embodiments thereof, wherein reference is made to the accompanying figures, in which:

[0131] FIG. 1 shows a schematic overview of the method according to the invention;

[0132] FIG. 2 shows a micrograph of the auxetic polyurethane foam achieved by experiment 1;

[0133] FIG. 3 shows axial strain versus transverse strain of the auxetic polyurethane foam achieved by experiment 1;

[0134] FIG. 4 shows strain versus stress of the auxetic polyurethane foam achieved by experiment 1;

[0135] FIG. 5 shows a micrograph of the auxetic polyurethane foam achieved by experiment 2;

[0136] FIG. 6 shows axial strain versus transverse strain of the auxetic polyurethane foam achieved by experiment 2;

[0137] FIG. 7 shows strain versus stress of the auxetic polyurethane foam achieved by experiment 2;

[0138] FIG. 8 shows axial strain versus transverse strain of the auxetic polyurethane foam achieved by experiment 3;

[0139] FIG. 9 shows strain versus stress of the auxetic polyurethane foam achieved by experiment 3;

[0140] FIG. 10 shows axial strain versus transverse strain of the auxetic polyurethane foam achieved by experiment 9;

[0141] FIG. 11 shows a micrograph of the auxetic polyurethane foam achieved by experiment 10;

[0142] FIG. 12 shows axial strain versus transverse strain of the auxetic polyurethane foam achieved by experiment 10;

[0143] FIG. 13 shows strain versus stress of the auxetic polyurethane foam achieved by experiment 10;

[0144] FIG. 14 shows a micrograph of the auxetic polyurethane foam achieved by experiment 11;

[0145] FIG. 15 shows axial strain versus transverse strain of the auxetic polyurethane foam achieved by experiment 11;

[0146] FIG. 16 shows strain versus stress of the auxetic polyurethane foam achieved by experiment 11;

[0147] FIG. 17 shows axial strain versus transverse strain of the auxetic polyurethane foam achieved by experiment 12; and

[0148] FIG. 18 shows strain versus stress of the auxetic polyurethane foam achieved by experiment 12.

[0149] Method 10 (FIG. 1) comprises the synthesis of an auxetic polyurethane foam with a defined cell structure. Method 10 comprises step 12, also referred to as step a, wherein step 12 includes mixing a polyol reagent and a foaming reagent, forming a reaction mixture. Step 12 may be followed by step 14, wherein step 14 comprises adding water to the reaction mixture before step b.

[0150] Step 12 or step 14 is followed by step 16, also referred to as step b, wherein step 16 includes mixing an isocyanate with the reaction mixture. The reaction mixture of step 16 may rise in an appropriate mould or container. Furthermore, the reaction mixture of step 16 is compressed in step 18, also referred to as step c, wherein compressing the reaction mixture of step b is performed.

[0151] The synthesis of the auxetic polyurethane foam further comprises the step 20, also referred to as step d, which follows step 18. Step 20 comprises allowing to cure the compressed reaction mixture of step b.

[0152] For the experiments and throughout the application, Arcol 1107 comprises a trifunctional inactive propylene oxide/ethylene oxide polyether polyol with hydroxyl number of 46-50 mg KOH/g and a molecular weight of 3500 Da, Kosmos 29 comprises tin-(II)-isooctoate, tegoamine 33 comprises 33% triethylenediamine dissolved in diethylene glycol, Desmodur T80 comprises a blend of two isomers: 80% by wt. 2,4-toluene diisocyanate and 20% by wt. 2,6-toluene diisocyanate.

[0153] For the images of FIGS. 2 and 5 a ZEISS Merlin 42-16 Scanning Electron Microscope was used. Samples were cut with a razor and sputter-coated with a thin-layer of gold before observation. Magnifications used are between 70 and 80× and electron beam had an energy of 8 kV.

[0154] In a preferred embodiment according to the invention experiment 1 was performed. The used reagents and amount are provided in Table 1.

[0155] The polyol, surfactant, gelling catalyst, blowing catalyst, and chain extender were added to a 1 litre beaker at 25° C., providing a reaction mixture. The blowing agent was added to the reaction mixture and stirred for 5 minutes at 500 rpm at 25° C. To the resulting reaction mixture isocyanate was added, and the mixture was stirred for 20 seconds at 500 rpm at 25° C.

[0156] The resulting mixture was poured in a mould, wherein the mould was made of expanded polystyrene, had dimensions of 20 cm×20 cm×30 cm, and a wall thickness of 3.5 cm. The mixture was left in the mould for 24 hours and for four days to cure outside the mould. No external compression of the reaction mixture was performed and it was allowed to contract. The contraction was achieved by the formation of polymer network(s) in the foam, thus leading to shrinkage of the foam.

[0157] The obtained auxetic polyurethane foam substrate comprises foam outer dimensions after complete shrinkage and curing of 15.5 cm×15.5 cm×20 cm, a density of 145 kg m.sup.−3, a Poisson's ratio of 0.54±0.09 in compression, a tensile strip of Poisson's ratio −0.44±0.05 up to 10% strain, a Young's Modulus in tension of 15.63 kPa, a Young's Modulus in compression up to 5% strain of 17.19 kPa.

TABLE-US-00001 TABLE 1 reagents used in experiment 1 Description Amount (part Reagent of reagent by weight) polyol Arcol 1107 400.5 gram surfactant Tegostab BF 2370 10.0038 pphp* gelling catalyst Kosmos 29 0.1025 pphp* blowing catalyst Tegoamine 33 0.097 pphp* chain extender Anhydrous Glycerol 0.304 pphp* blowing agent Ultra-pure Water 1.75 pphp* isocyanate Desmodur T80 160 gram *pphp = parts per hundred grams of polyol by weight

[0158] FIG. 2 shows a micrograph of the auxetic polyurethane foam achieved by experiment 1.

[0159] FIG. 3 shows the axial strain versus transverse strain of the auxetic polyurethane foam achieved by experiment 1, and FIG. 4 shows the strain versus stress (kPa) auxetic polyurethane foam achieved by experiment 1. kPa refers to kilo Pascal.

[0160] In a preferred embodiment according to the invention experiment 2 was performed. The used reagents and amount are provided in Table 2.

[0161] The polyol, surfactant, gelling catalyst, blowing catalyst, and chain extender were added to a 1 litre beaker at 25° C., providing a reaction mixture. The blowing agent was added to the reaction mixture and stirred for 5 minutes at 500 rpm at 25° C. To the resulting reaction mixture isocyanate was added, and the mixture was stirred for 20 seconds at 500 rpm at 25° C.

[0162] The resulting mixture was poured in a mould, wherein the mould was made of expanded polystyrene, had dimensions of 20 cm×20 cm×30 cm, and a wall thickness of 3.5 cm. The mixture was left in the mould for 24 hours and for four days to cure outside the mould. No external compression of the reaction mixture was performed and it was allowed to contract. The contraction was achieved by the formation of polymer network(s) in the foam, thus leading to shrinkage of the foam.

[0163] The obtained auxetic polyurethane foam substrate comprises foam outer dimensions after complete shrinkage and curing of 12 cm×12 cm×20.5 cm, a density of 205 kg m.sup.−3, a tensile strip of Poisson's ratio −0.28±0.02 up to 10% strain, a Young's Modulus in tension of 13.66 kPa.

TABLE-US-00002 TABLE 2 reagents used in experiment 2 Description Amount (part Reagent of reagent by weight) polyol Arcol 1107 400.1 gram surfactant Tegostab BF 2370 10.00875 pphp* gelling catalyst Kosmos 29 0.10075 pphp* blowing catalyst Tegoamine 33 0.1 pphp* chain extender Anhydrous Glycerol 0.2085 pphp* blowing agent Ultra-pure Water 1.75 pphp* isocyanate Desmodur T80 172.6 gram *pphp = parts per hundred grams of polyol by weight

[0164] FIG. 5 shows a micrograph of the auxetic polyurethane foam achieved by experiment 2.

[0165] FIG. 6 shows the axial strain versus transverse strain of the auxetic polyurethane foam achieved by experiment 2, and FIG. 7 shows the strain versus stress (kPa) auxetic polyurethane foam achieved by experiment 2. kPa refers to kilo Pascal. FIG. 7 comprises a trend line with the formula of y=14.8x+0.00322 and R.sup.2=0.996.

[0166] In a preferred embodiment according to the invention experiment 3 was performed. The used reagents and amount are provided in Table 3.

[0167] The polyol, surfactant, gelling catalyst, blowing catalyst, and chain extender were added to a 1 litre beaker at 25° C., providing a reaction mixture. The blowing agent was added to the reaction mixture and stirred for 5 minutes at 500 rpm at 25° C. To the resulting reaction mixture isocyanate was added, and the mixture was stirred for 20 seconds at 500 rpm at 25° C.

[0168] The resulting mixture was poured in a mould, wherein the mould was made of expanded polystyrene, had dimensions of 20 cm×20 cm×30 cm, and a wall thickness of 3.5 cm. The mixture was left in the mould for 24 hours and for four days to cure outside the mould. No external compression of the reaction mixture was performed and it was allowed to contract. The contraction was achieved by the formation of polymer network(s) in the foam, thus leading to shrinkage of the foam.

[0169] The obtained auxetic polyurethane foam substrate comprises foam outer dimensions after complete shrinkage and curing of 15.5 cm×15.5 cm×21 cm, a density of 117 kg m.sup.−3, a Poisson's ratio of −0.43 in compression up to 15% strain, a tensile strip of Poisson's ratio −0.177±0.006 up to 10% strain, a Young's Modulus in compression of 32.72 kPa up to 5% strain, a Young's Modulus in tension of 19.36 kPa.

TABLE-US-00003 TABLE 3 reagents used in experiment 3 Description Amount (part Reagent of reagent by weight) polyol Arcol 1107 400.5 gram surfactant Tegostab BF 2370 10.0038 pphp* gelling catalyst Kosmos 29 0.1015 pphp* blowing catalyst Tegoamine 33 0.0997 pphp* chain extender Anhydrous Glycerol 0.50425 pphp* blowing agent Ultra-pure Water 1.75 pphp* isocyanate Desmodur T80 158.8 gram *pphp = parts per hundred grams of polyol by weight

[0170] FIG. 8 shows the axial strain versus transverse strain of the auxetic polyurethane foam achieved by experiment 3, and FIG. 9 shows the strain versus stress (kPa) auxetic polyurethane foam achieved by experiment 3. kPa refers to kilo Pascal. FIG. 9 comprises a trend line with the formula of y=17.034x+0.0834 and R.sup.2=0.998.

[0171] In a preferred embodiment according to the invention experiment 4 was performed. The used reagents and amount are provided in Table 4.

[0172] The polyol, surfactant, gelling catalyst, blowing catalyst, and chain extender were mixed at 50 rpm for 1 hour at a temperature between 60° C. to 70° C., providing a reaction mixture. The blowing agent was added to the reaction mixture and stirred for 2 minutes at 70 rpm at 25° C. To the resulting reaction mixture isocyanate was added, and the mixture was stirred for 20 seconds at

[0173] The resulting mixture was poured in a mould, wherein the mould was made of wood, had dimensions of 16 cm×16 cm×16 cm, and a wall thickness of 1.5 cm. The mixture was left in the mould for 10 minutes and for 24 hours to cure outside the mould. No external compression of the reaction mixture was performed and it was allowed to contract. The contraction was achieved by the formation of polymer network(s) in the foam, thus leading to shrinkage of the foam.

[0174] The obtained auxetic polyurethane foam substrate comprises foam outer dimensions after complete shrinkage and curing of 11.5 cm×11.5 cm×8 cm, a Poisson's ratio in the range of −3 to 0.

TABLE-US-00004 TABLE 4 reagents used in experiment 4 Description Amount (part Reagent of reagent by weight) polyol Arcol 1107 100 gram gelling catalyst Kosmos 29 0.31 pphp* blowing catalyst Tegoamine 33 0.21 pphp* chain extender Anhydrous Glycerol 1.11 pphp* chain extender Methyltrimethoxysilane 2.53 pphp* blowing agent Ultra-pure Water 4 pphp* isocyanate Desmodur T80 42.77 gram *pphp = parts per hundred grams of polyol by weight

[0175] In a preferred embodiment according to the invention experiment 5 was performed. The used reagents and amount are provided in Table 5.

[0176] The polyol, surfactant, gelling catalyst, blowing catalyst, and chain extender were mixed at 50 rpm for 1 hour at a temperature between 60° C. to 70° C., providing a reaction mixture. The blowing agent was added to the reaction mixture and stirred for 5 minutes at 150 rpm at 25° C. To the resulting reaction mixture isocyanate was added, and the mixture was stirred for 15 seconds at 150 rpm at 25° C.

[0177] The resulting mixture was poured in a mould, wherein the mould was made of wood, had dimensions of 16 cm×16 cm×16 cm, and a wall thickness of 3.5 cm. The mixture was left in the mould for 10 minutes and for 24 hours to cure outside the mould. No external compression of the reaction mixture was performed and it was allowed to contract. The contraction was achieved by the formation of polymer network(s) in the foam, thus leading to shrinkage of the foam.

[0178] The obtained auxetic polyurethane foam substrate comprises a Poisson's ratio in the range of −3 to 0.

TABLE-US-00005 TABLE 5 reagents used in experiment 5 Description Amount (part Reagent of reagent by weight) polyol Arcol 1107 100 gram surfactant Tegostab BF 2370 0.506 pphp* gelling catalyst Kosmos 29 0.177 pphp* blowing catalyst Tegoamine 33 0.259 pphp* chain extender Anhydrous Glycerol 1.005 pphp* chain extender Methyltrimethoxysilane 1.517 pphp* blowing agent Ultra-pure Water 4 pphp* isocyanate Desmodur T80 45.03 gram *pphp = parts per hundred grams of polyol by weight

[0179] In a preferred embodiment according to the invention experiment 6 was performed. The used reagents and amount are provided in Table 6.

[0180] The polyol, surfactant, gelling catalyst, blowing catalyst, and chain extender were mixed at 100 rpm for 1 hour at a temperature between 60° C. to 70° C., providing a reaction mixture. The blowing agent was added to the reaction mixture and stirred for 5 minutes at 150 rpm at 25° C. To the resulting reaction mixture isocyanate was added, and the mixture was stirred for 15 seconds at 150 rpm at 25° C.

[0181] The resulting mixture was poured in a mould, wherein the mould was made of wood, had dimensions of 16 cm×16 cm×16 cm, and a wall thickness of 1.5 cm. The mixture was left in the mould for 10 minutes and for 24 hours to cure outside the mould. No external compression of the reaction mixture was performed and it was allowed to contract. The contraction was achieved by the formation of polymer network(s) in the foam, thus leading to shrinkage of the foam.

[0182] The obtained auxetic polyurethane foam substrate comprises a Poisson's ratio in the range of −3 to 0.

TABLE-US-00006 TABLE 6 reagents used in experiment 6 Description Amount (part Reagent of reagent by weight) polyol Arcol 1107 100.5 gram surfactant Tegostab BF 2370 0.496 pphp* gelling catalyst Kosmos 29 0.170 pphp* blowing catalyst Tegoamine 33 0.245 pphp* chain extender Anhydrous Glycerol 1.0 pphp* chain extender Methyltrimethoxysilane 1.524 pphp* blowing agent Ultra-pure Water 4 pphp* isocyanate Desmodur T80 45.22 gram *pphp = parts per hundred grams of polyol by weight

[0183] In a preferred embodiment according to the invention experiment 7 was performed. The used reagents and amount are provided in Table 7.

[0184] The polyol, surfactant, gelling catalyst, blowing catalyst, and chain extender were mixed at 100 rpm for 1 hour at a temperature between 60° C. to 70° C., providing a reaction mixture. The blowing agent was added to the reaction mixture and stirred for 5 minutes at 150 rpm at 25° C. To the resulting reaction mixture isocyanate was added, and the mixture was stirred for 15 seconds at 150 rpm at 25° C.

[0185] The resulting mixture was poured in a mould, wherein the mould was made of wood, had dimensions of 16 cm×16 cm×16 cm, and a wall thickness of 1.5 cm. The mixture was left in the mould for 10 minutes and for 24 hours to cure outside the mould. No external compression of the reaction mixture was performed and it was allowed to contract. The contraction was achieved by the formation of polymer network(s) in the foam, thus leading to shrinkage of the foam.

[0186] The obtained auxetic polyurethane foam substrate comprises foam outer dimensions after complete shrinkage and curing of 10.5 cm×10.5 cm×7 cm, a Poisson's ratio in the range of −3 to 0.

TABLE-US-00007 TABLE 7 reagents used in experiment 7 Description Amount (part Reagent of reagent by weight) polyol Arcol 1107 100.3 gram surfactant Tegostab BF 2370 2.008 pphp* gelling catalyst Kosmos 29 0.169 pphp* blowing catalyst Tegoamine 33 0.252 pphp* chain extender Anhydrous Glycerol 1.009 pphp* chain extender Methyltrimethoxysilane 1.510 pphp* blowing agent Ultra-pure Water 4 pphp* isocyanate Desmodur T80 45.04 gram *pphp = parts per hundred grams of polyol by weight

[0187] In a preferred embodiment according to the invention experiment 8 was performed. The used reagents and amount are provided in Table 8.

[0188] The first part of polyol, surfactant, gelling catalyst, blowing catalyst, and chain extender were mixed at 100 rpm for 1 hour at a temperature between 60° C. to 70° C., providing a reaction mixture. The second part of polyol and the blowing agent were added to the reaction mixture and stirred for 5 minutes at 300 rpm at 25° C. To the resulting reaction mixture isocyanate was added, and the mixture was stirred for 15 seconds at 300 rpm at 25° C.

[0189] The resulting mixture was poured in a mould, wherein the mould was made of cardboard, and had dimensions of 21 cm×21 cm×20 cm. The mixture was left in the mould for 10 minutes and for 48 hours to cure outside the mould. No external compression of the reaction mixture was performed and it was allowed to contract. The contraction was achieved by the formation of polymer network(s) in the foam, thus leading to shrinkage of the foam.

[0190] The obtained auxetic polyurethane foam substrate comprises foam outer dimensions after complete shrinkage and curing of 12 cm×12 cm×4.5 cm, a Poisson's ratio in the range of −3 to 0.

TABLE-US-00008 TABLE 8 reagents used in experiment 8 Description Amount (part Reagent of reagent by weight) first part of polyol Arcol 1107 100 gram surfactant Tegostab BF 2370 4.0025 pphp* gelling catalyst Kosmos 29 0.1485 pphp* blowing catalyst Tegoamine 33 0.153 pphp* chain extender Anhydrous Glycerol 1.518 pphp* chain extender Methyltrimethoxysilane 2.2565 pphp* blowing agent Ultra-pure Water 3.5 pphp* second part of polyol Arcol 1107 101.8 gram isocyanate Desmodur T80 88.08 gram *pphp = parts per hundred grams of polyol by weight

[0191] In a preferred embodiment according to the invention experiment 9 was performed. The used reagents and amount are provided in Table 9.

[0192] The first part of polyol, surfactant, gelling catalyst, blowing catalyst, and chain extender were mixed at 100 rpm for 1 hour at a temperature between 60° C. to 70° C., providing a reaction mixture. The second part of polyol and the blowing agent were added to the reaction mixture and stirred for 5 minutes at 300 rpm at 25° C. To the resulting reaction mixture isocyanate was added, and the mixture was stirred for 15 seconds at 300 rpm at 25° C.

[0193] The resulting mixture was poured in a mould, wherein the mould was made of cardboard, had dimensions of 21 cm×21 cm×20 cm. The mixture was left in the mould for 30 minutes and for 48 hours to cure outside the mould. No external compression of the reaction mixture was performed and it was allowed to contract. The contraction was achieved by the formation of polymer network(s) in the foam, thus leading to shrinkage of the foam.

[0194] The obtained auxetic polyurethane foam substrate comprises foam outer dimensions after complete shrinkage and curing of 12 cm×12 cm×9.5 cm, a Poisson's ratio of −0.24 up to 20% tensile strain.

TABLE-US-00009 TABLE 9 reagents used in experiment 9 Description Amount (part Reagent of reagent by weight) first part of polyol Arcol 1107 100 gram surfactant Tegostab BF 2370 4.006 pphp* gelling catalyst Kosmos 29 0.1477 pphp* blowing catalyst Tegoamine 33 0.1493 pphp* chain extender Anhydrous Glycerol 1.518 pphp* chain extender Methyltrimethoxysilane 2.267 pphp* blowing agent Ultra-pure Water 2.667 pphp* second part of polyol Arcol 1107 202.6 gram isocyanate Desmodur T80 129.7 gram *pphp = parts per hundred grams of polyol by weight

[0195] FIG. 10 shows the axial strain versus transverse strain of the auxetic polyurethane foam achieved by experiment 9. kPa refers to kilo Pascal. FIG. 10 comprises a trend line with the formula of y=0.2414x+0.0011 and R.sup.2=0.9963.

[0196] In a preferred embodiment according to the invention experiment 10 was performed. The used reagents and amount are provided in Table 10.

[0197] The polyol, surfactant, gelling catalyst, blowing catalyst, and chain extender were added to a 600 millilitre beaker at 25° C., providing a reaction mixture. The blowing agent was added to the reaction mixture and stirred for 2 minutes at 500 rpm at 25° C. To the resulting reaction mixture isocyanate was added, and the mixture was stirred for 10 seconds at 500 rpm at 25° C.

[0198] The resulting mixture was poured in a mould, wherein the mould was made of wood, had dimensions of 16.5 cm×16.5 cm×16.5 cm, and a wall thickness of 2.5 cm. The mixture was left in the mould for 30 minutes and for 48 hours to cure outside the mould. No external compression of the reaction mixture was performed and it was allowed to contract.

[0199] The obtained auxetic polyurethane foam substrate comprises foam outer dimensions after complete shrinkage and curing of 12 cm×12 cm×7 cm, a density of 112 kg m.sup.−3, a Poisson's ratio of −0.156 in compression 50% strain and a Young's Modulus in compression up to 5% strain of 28.973 kPa when compressed on its y-axis. Alternatively, when compressed on its x-axis, the auxetic polyurethane foam exhibits a Poisson's ratio of −0.043 in compression up to 50% strain and a Young's Modulus in compression up to 5% strain of 19.50 kPa.

[0200] FIG. 11 shows a micrograph of the auxetic polyurethane foam achieved by experiment 10.

TABLE-US-00010 TABLE 10 reagents used in experiment 10 Description Amount (part Reagent of reagent by weight) polyol Arcol 1107 200 gram surfactant Tegostab BF 2370 5.031 gram gelling catalyst Kosmos 29 0.098 gram blowing catalyst Tegoamine 33 0.192 gram chain extender Anhydrous Glycerol 0.803 gram blowing agent Ultra-pure Water 3 gram isocyanate Desmodur T80 52.8 gram

[0201] FIG. 12 shows the axial strain versus transverse strain for both loading directions of the auxetic polyurethane foam achieved by experiment 10. FIG. 13 shows the strain versus axial stress (kPa) of the auxetic polyurethane foam achieved by experiment 10.

[0202] In a preferred embodiment according to the invention experiment 11 was performed. The used reagents and amount are provided in Table 11.

[0203] The polyol, surfactant, gelling catalyst, blowing catalyst, and chain extender were added to a 1 litre beaker at 25° C., providing a reaction mixture. The blowing agent was added to the reaction mixture and stirred for 5 minutes at 500 rpm at 25° C. To the resulting reaction mixture isocyanate was added, and the mixture was stirred for 20 seconds at 500 rpm at 25° C.

[0204] The resulting mixture was poured in a mould, wherein the mould was made of expanded polystyrene, had dimensions of 20 cm×20 cm×30 cm, and a wall thickness of 3.5 cm. The mixture was left in the mould for 24 hours and for four days to cure outside the mould. No external compression of the reaction mixture was performed and it was allowed to contract.

[0205] The obtained auxetic polyurethane foam substrate comprises foam outer dimensions after complete shrinkage and curing of 14.5 cm×14.5 cm×21 cm, a density of 160 kg m.sup.−3, a Poisson's ratio of −0.639 in compression up to 20% strain, a Young's Modulus in compression up to 5% strain of 23.93 kPa.

TABLE-US-00011 TABLE 11 reagents used in experiment 11 Description Amount (part Reagent of reagent by weight) polyol Arcol 1107 400.0 gram surfactant Tegostab BF 2370 10.003 pphp* gelling catalyst Kosmos 29 0.09775 pphp* blowing catalyst Tegoamine 33 0.101 pphp* chain extender Anhydrous Glycerol 0.4045 pphp* blowing agent Ultra-pure Water 1.75 pphp* isocyanate Desmodur T80 166.8 grams *pphp = parts per hundred grams of polyol by weight

[0206] FIG. 14 shows a micrograph of the auxetic polyurethane foam achieved by experiment 11.

[0207] FIG. 15 shows the axial strain versus transverse strain of the auxetic polyurethane foam achieved by experiment 11, and FIG. 16 shows the strain versus stress (kPa) auxetic polyurethane foam achieved by experiment 11.

[0208] In a preferred embodiment according to the invention experiment 12 was performed. The used reagents and amount are provided in Table 12.

[0209] The polyol, surfactant, gelling catalyst, blowing catalyst, and chain extender were added to a 1 litre beaker at 25° C., providing a reaction mixture. The blowing agent was added to the reaction mixture and stirred for 2 minutes at 900 rpm at 25° C. To the resulting reaction mixture isocyanate was added, and the mixture was stirred for 15 seconds at 900 rpm at 25° C.

[0210] The resulting mixture was poured in a mould, wherein the mould was made of expanded polystyrene, had dimensions of 20 cm×20 cm×30 cm, and a wall thickness of 5 cm. The mixture was left in the mould for 24 hours and for four days to cure outside the mould. No external compression of the reaction mixture was performed and it was allowed to contract.

[0211] The obtained auxetic polyurethane foam substrate comprises foam outer dimensions after complete shrinkage and curing of 17 cm×17 cm×27 cm, a density of 52.5 kg m.sup.−3. When loading in the y-direction, the resultant auxetic polyurethane foam sample exhibits a Poisson's ratio of −0.205 in compression up to 15% strain and a Young's Modulus in compression up to 5% strain of 21.9 kPa. When loading in the z-direction, the resultant auxetic polyurethane foam sample exhibits a Poisson's ratio of −0.253 in compression up to 35% strain and a Young's Modulus in compression up to 5% strain of 24.3 kPa.

TABLE-US-00012 TABLE 12 reagents used in experiment 12 Description Amount (part Reagent of reagent by weight) polyol Arcol 1107 400.1 gram surfactant Tegostab BF 2370 2.500 pphp* gelling catalyst Kosmos 29 0.0975 pphp* blowing catalyst Tegoamine 33 0.0245 pphp* chain extender Anhydrous Glycerol 0.4043 pphp* blowing agent Ultra-pure Water 1.85 pphp* isocyanate Desmodur T80 127.5 grams *pphp = parts per hundred grams of polyol by weight

[0212] FIG. 17 shows the axial strain versus transverse strain for both loading directions of the auxetic polyurethane foam achieved by experiment 12, and FIG. 18 shows the strain versus stress (kPa) for both loading directions auxetic polyurethane foam achieved by experiment 12. kPa refers to kilo Pascal.

[0213] The present invention is by no means limited to the above described preferred embodiments and/or experiments thereof. The rights sought are defined by the following claims within the scope of which many modifications can be envisaged.