Auxetic polyurethane and melamine foams by triaxial compression

Abstract

Described herein is a process for preparing a foam (FA) with a Poisson's ratio in the range of from −0.5 to 0.3, the method including the steps of providing a foam (F1) with a flow resistance in the range of from 3000 to 8000 Pas/m, determined according to DIN EN 29053, and subjecting the foam (F1) to thermoforming including triaxial compression, wherein the foam (F1) is not reticulated prior to step (ii). Also described herein is the foam obtained or obtainable according to the process and the use of the foam as, for example, an energy absorbing device, preferably in protective gear, furniture, cushions, in cleaning devices with improved rinse-out behavior, in shoe soles, or as sealing, insulating or anchorage providing material for example used in earphones, ear plugs or dowels, or as acoustic material.

Claims

1. A process for preparing a foam (FA) with a Poisson's ratio in the range of from −0.8 to 0.3, the method comprising the steps (i) and (ii): (i) providing a foam (F1) with a flow resistance in the range of from 3000 to 8000 Pas/m2, determined according to DIN EN 29053, and (ii) subjecting the foam (F1) to thermoforming comprising triaxial compression, wherein the foam (F1) is not reticulated prior to step (ii).

2. The process according to claim 1, wherein the thermoforming is carried out with a linear compression ratio (LCR) in all three directions in the range of from 0.33 to 0.9.

3. The process according to claim 1, wherein step (ii) comprises at least one compression step (C1) at a temperature (T1) and at least one demolding step (D).

4. The process according to claim 1, wherein the foam (F1) is a foam based on melamine and formaldehyde with a density in the range of from 3 to 20 g/l.

5. The process according to claim 1, wherein the foam (F1) is a foam based on melamine and formaldehyde in a ratio in the range of from 1:1 to 1:3.

6. The process according to claim 1, wherein the thermoforming is carried out at a temperature in the range of from 120 to 260° C.

7. The process according to claim 1, wherein the foam (F1) is a polyurethane foam with a density in the range of from 10 to 150 g/l.

8. The process according to claim 1, wherein the foam (F1) is a polyurethane foam with a water absorptivity of more than 130%.

9. The process according to claim 6, wherein the thermoforming is carried out at a temperature range of from 120 to 240° C.

10. A foam obtained or obtainable according to a process according to claim 1.

11. The foam according to claim 10, wherein the Poisson's ratio of the foam is in the range of from −0.4 to 0.

12. A method of using a foam according to claim 10, the method comprising using the foam as energy absorbing device, as sealing, insulating or anchorage providing material, or as acoustic material.

Description

EXAMPLES

(1) 1 Foam Conversion Process

(2) The thermoforming process is described for a block of foam with the a length L, a width W and a depth D.

(3) A linear compression ratio (compressed-to-uncompressed dimension) LCR was defined, based on prior experience of auxetic foam conversion, and was employed in all three directions during conversion by inserting the foam into a metallic conversion mold of internal dimensions LCR×L and LCR×W and LCR×D. Lubricant (cooking oil) and/or spatulas were used as required to minimize surface creasing during insertion of the foam into the conversion mold. End tabs were applied to the end of the mold once the foam was inserted.

(4) The mold and foam were placed in an oven at the conversion temperature for 15 minutes. The foam was then removed quickly and relaxed to avoid adhesion of ribs and to minimize surface creasing, and then reinserted into the mold at the conversion temperature for a further 10 minutes, followed by 20 min at half of conversion temperature. Finally, the foam was allowed to cool in the mold to ambient temperature prior to removal from the mold.

(5) In the thermoforming step, a block with length LCR(L), a width LCR(W) and a depth LCR(D) is obtained.

(6) 2 Conversion Conditions and Results

(7) TABLE-US-00001 Density Conversion Temp Poisson's Foam (g/l) (° C.) LCR ratio Comparative example: −0.29 reticulated PU foam* Supersoft PU foam 37 200 0.7 −0.39 Superaoft PU foam 37 n.a. 1 0.36 Comparative example: −0.07 Basotec** Basotect TG 9 180 0.6 −0.13 Basotect TG 9 n.a. 1 0.36 *C.W. Smith et al. J Mater Sci (2008) 43: 5851-5860 **C. Ge Journal of Cellular Plastics 2013 49(6) 521-533 (herein denoted as Basotec)

LITERATURE CITED

(8) WO 88/00523 A1 EP 011752 A1 U.S. Pat. No. 4,374,209 DE 3231497 A1 EP 17671 A1 EP 37470 A1 DE 1111394 A1 DE 1222669 A1 DE 1152536 A1 DE 1152537 A1 U.S. Pat. No. 3,267,050 DE 1215373 A1 EP 0351614 A1 Houben-Weyl, Methoden der organischen Chemie, Volume 14/2, 1963, pages 319 to 402 C. W. Smith et al. J Mater Sci (2008) 43:5851-5860 C. Ge Journal of Cellular Plastics 2013 49(6) 521-533