US 12,448,478 B2
Method for the synthesis of an auxetic polyurethane foam with a defined cell structure and auxetic polyurethane foam obtainable by the method
Keith Mario Azzopardi, Swieqi (MT); Matthew Anthony Xuereb, Birkirkara (MT); and Ruben Gatt, Rabat (MT)
Assigned to SMART MATERIALS LIMITED, St. Paul's Bay (MT)
Appl. No. 17/918,054
Filed by SMART MATERIALS LIMITED, St. Paul's Bay (MT)
PCT Filed Apr. 15, 2021, PCT No. PCT/EP2021/059827
§ 371(c)(1), (2) Date Oct. 10, 2022,
PCT Pub. No. WO2021/209568, PCT Pub. Date Oct. 21, 2021.
Claims priority of application No. 2025349 (NL), filed on Apr. 15, 2020.
Prior Publication US 2023/0192938 A1, Jun. 22, 2023
Int. Cl. C08G 18/38 (2006.01); C08G 18/16 (2006.01); C08G 18/20 (2006.01); C08G 18/24 (2006.01); C08G 18/32 (2006.01); C08G 18/48 (2006.01); C08G 18/66 (2006.01); C08G 18/76 (2006.01); C08J 9/02 (2006.01); C08J 9/12 (2006.01)
CPC C08G 18/3893 (2013.01) [C08G 18/165 (2013.01); C08G 18/2063 (2013.01); C08G 18/244 (2013.01); C08G 18/3206 (2013.01); C08G 18/4837 (2013.01); C08G 18/6677 (2013.01); C08G 18/7621 (2013.01); C08J 9/02 (2013.01); C08J 9/125 (2013.01); C08G 2110/0058 (2021.01); C08G 2110/0066 (2021.01); C08G 2110/0083 (2021.01); C08G 2280/00 (2013.01); C08J 2201/022 (2013.01); C08J 2203/10 (2013.01); C08J 2205/05 (2013.01); C08J 2375/08 (2013.01)] 15 Claims
 
1. A method to prepare an auxetic polyurethane foam with a defined cell structure in a single foaming process, comprising the steps of:
a. mixing a polyol reagent and a foaming reagent to form a homogeneous reaction mixture suitable for forming a homogeneous auxetic polyurethane foam, such that the foaming reagent facilitates the formation of auxetic polyurethane foam by enabling the reaction mixture to expand and polymerize;
b. mixing an isocyanate with the homogeneous reaction mixture, the isocyanate being selected and provided in an amount to cause the homogeneous reactive mixture to undergo foaming and polymerization to form a polyurethane network having closed cells and/or partially closed cells and/or pre-stressed ribs that contribute to contraction during cooling and enable the formation of a defined cellular structure with buckled ribs, delaying a cure of the reactive mixture and increasing the elasticity of the reactive mixture;
c. permitting the reactive mixture of step (b) to expand within a mold and/or on a conveyer, wherein the expansion forms a polymer network that includes closed cells that contract as the polymer network cools;
d. allowing the expanded reaction mixture at least partly to cool within the mold and/or on the conveyor to induce contraction at least partially caused by negative pressure from the trapped gases in the closed cells, and/or applying external compressive forces to the expanded mixture during or after contraction;
wherein the contraction and/or the compression promotes cell buckling and changing of the initial cellular structure to a defined cellular structure with the closed cells having cellular ribs or struts protruding inward and/or outward prior to finalization of chemical cross-linking and physical curing; and
e. after the contraction and/or the compression, allowing the compressed and/or contracted reaction mixture of step (d) to cure, wherein the curing process causes the defined cellular structure to form a defined auxetic polyurethane foam structure characterized by a Poisson's ratio in the range of −3 to 0.