Material systems and methods of manufacture for auxetic foams
A novel material for producing auxetic foams is disclosed. The material comprises a multiphase, multicomponent polymer foam with a filler polymer having a carefully selected glass transition temperature. Novel methods for producing auxetic foams from the material are also disclosed that consistently, reliably and quickly produce auxetic polyurethane foam at about room temperature (25° C.). This technology overcomes challenging issues in the large-scale production of auxetic PU foams, such as unfavorable heat-transmission problem and harmful organic solvents.
1 . An auxetic foam formed from a material system, the material system comprising:
a bulk matrix comprising:
a soft domain comprising a polymer chain and having a first glass transition temperature; and
a hard domain covalently or non-covalently linked to the polymer chain of the soft domain and having a thermal transition temperature greater than the first glass transition temperature; and
a filler polymer dispersed in the bulk matrix and having a second glass transition temperature greater than the first glass transition temperature and less than the thermal transition temperature;
the material system being a multiphase, multicomponent polymer foam having an initial volume and having a plurality of cells;
wherein the auxetic foam is produced by a method comprising:
placing the multiphase, multicomponent polymer foam into a pressure chamber and compressing the foam to a compressed volume less than the initial volume, such that the cells are deformed;
exposing the compressed foam within the pressure chamber to a compressed gas, the compressed gas comprising carbon dioxide or nitrogen, and maintaining the pressure chamber at a predetermined temperature and a predetermined pressure for a predetermined time;
dissolving at least a portion of the compressed gas into the filler polymer and reducing the second glass transition temperature of the filler polymer such that the filler polymer transitions from a glassy state to a rubbery state, wherein a shape of the filler polymer changes from generally spherical to generally ellipsoidal when the compressed gas dissolves into the filler polymer; and
allowing the foam to reach atmospheric pressure and removing the foam from the pressure chamber such that the filler polymer transitions from the rubbery state to the glassy state and the filler polymer retains the generally ellipsoidal shape, thereby fixing the cells of the foam in the deformed state, thereby forming the auxetic foam.
2 . The auxetic foam of claim 1 , wherein the filler polymer comprises styrene acrylonitrile copolymer.
3 . The auxetic foam of claim 1 , wherein the compressed volume of the foam ranges from about 15 percent to about 85 percent of the initial volume.
4 . The auxetic foam of claim 1 , wherein the predetermined pressure ranges from about 0 MPa to about 100 MPa.
5 . The auxetic foam of claim 1 , wherein the predetermined time ranges from about 1 minute to about 4 hours.
6 . The auxetic foam of claim 1 , wherein the predetermined temperature is less than about 710K.
7 . The auxetic foam of claim 1 , wherein the predetermined temperature is about 298K, the predetermined pressure is about 5 MPa, and the predetermined time is less than about 10 minutes.
8 . The auxetic foam of claim 1 , wherein the pressure chamber further comprises a mold, and the multiphase, multicomponent polymer foam conforms to a shape of the mold after removal of the foam from the pressure chamber.
9 . The auxetic foam of claim 1 , wherein the multiphase, multicomponent polymer foam comprises a polyurethane foam.
10 . The auxetic foam of claim 1 , wherein the polymer chain comprises polymeric polyols.
11 . The auxetic foam of claim 1 , wherein the filler polymer comprises styrene acrylonitrile, polyether sulfone, polysulfone, cyclic olefin copolymers, acrylonitrile-butadiene-styrene, poly(p-phenylene oxide), poly(ether ketone), poly(ether ether ketone), poly(ether ketone ketone), or combinations thereof.
12 . The auxetic foam of claim 11 , wherein the filler polymer is chosen based on the solubility of carbon dioxide or nitrogen in the filler polymer.
13 . The auxetic foam of claim 1 , wherein the bulk matrix is elastic.
14 . The auxetic foam of claim 1 , wherein the bulk matrix deforms when subjected to a mechanical compressive force.