Thermoplastic polyurethane graphene oxide nanocomposites with enhanced mechanical behavior

Abstract

A polymer nanocomposite composition, wherein nanoparticles, preferably graphene oxide, are well dispersed within a polymer matrix, preferably thermoplastic polyurethane in one embodiment. Affinity of the nanoparticles to one of the phases of the polymer matrix, preferably a hard segment of the thermoplastic polyurethane, provides enhanced mechanical properties. Processes for preparing the polymer nanocomposite compositions are described. In a preferred embodiment, an extensional dispersing element is included within the screw configuration of an extrusion process.

Claims

1. A polymer nanocomposite composition, comprising: a thermoplastic polyurethane block copolymer comprising a plurality of hard segments and a plurality of soft segments, wherein the hard segments have an aspect ratio between chain length and diameter that is below 2:1; and graphene oxide, present in an amount from about 0.05 wt. % to about 1 wt. % based on the total weight of the thermoplastic polyurethane block copolymer and graphene oxide, wherein the graphene oxide has a face surface with a lateral size between 1 and 5 microns and a thickness between 1 and 50 nanometers, wherein a face surface of a platelet of the graphene oxide is oriented substantially normal with respect to the hard segment of the thermoplastic polyurethane, and wherein the composition exhibits an increase in elongation at break and strain at break as compared to the composition without the graphene oxide.

2. The composition according to claim 1, wherein the graphene oxide is present in an amount from about 0.05 to about 0.5 wt. % based on the total weight of the thermoplastic polyurethane block copolymer.

3. The composition according to claim 1, wherein the composition has a strain at break that is increased by at least 100%, modulus is increased by up to 50% and stress at break is increased up to 50%, each as measured according to ASTM D638-14, as compared to the composition without the graphene oxide.

4. The composition according to claim 3, wherein the composition has a strain at break that is increased by at least 300%, modulus is increased by up to 100% and stress at break is increased up to 100%, each as measured according to ASTM D638-14, as compared to the composition without the graphene oxide.

5. The composition according to claim 1, wherein the composition exhibits an elongation at break of about 200% to about 1,000% percent as measured according to test ASTM D638-14.

6. The composition according to claim 5, wherein the composition has a tenacity of at least 90 J/mm.sup.2 as measured according to test ASTM D638-14 and wherein the tenacity is at least 200% greater than the tenacity of the composition not including the graphene oxide.

7. The composition according to claim 6, wherein the composition has been processed with an extensional mixing element S4 and in comparison to the composition processed with a mixing element KB has a volume loss of less than 30% as measured according to test ISO 4649.

8. A method for producing the polymer nanocomposite composition according to claim 1, comprising the steps of: obtaining the thermoplastic polyurethane and graphene oxide; and melt extruding the thermoplastic polyurethane block copolymer and graphene oxide in a twin-screw extruder without the use of a solvent and with use of at least one extensional mixing element to process the composition, wherein the at least one extensional mixing element is static and does not move with the screws.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood and other features and advantages will become apparent by reading the detailed description of the invention, taken together with the drawings, wherein:

(2) FIG. 1 is one embodiment of an extensional dispersing element employed in the process of the present invention;

(3) FIG. 2 illustrates one embodiment of a prior art mixing element;

(4) FIG. 3 is a graph including a plot of stress versus strain for various compositions; and

(5) FIG. 4 is a graph illustrating volume loss which is representative of abrasion resistance for various compositions, wherein the far right column illustrates the volume loss for a composition of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(6) The present invention includes a composition comprising a matrix polymer having both hard and soft blocks and different polarities between blocks within its constituent structure and nanoparticles that are dispersed in the polymer matrix thereby forming a polymer nanocomposite.

(7) Various polymers can be utilized as polymer matrix, for example polyurethane. The polyurethane is a thermoplastic polyurethane comprising at least one hard block and at least one soft block and preferably a plurality of hard blocks and soft blocks. The hard blocks generally comprise a diisocyanate component and short chain diols as chain extenders. The soft blocks or segments are generally polyethers or polyesters. In an important aspect of the present invention, the thermoplastic polyurethane has hard segments or blocks having an aspect ratio between chain length and diameter that is below 2:1.

(8) Thermoplastic polyurethanes are commercially available from many different sources. The maximum size of the hard block can vary, due to the degree of functionalization present.

(9) Graphene oxide is present in a composition in an amount from about 0.05 to about 1.0 wt. %, desirably from about 0.05 to about 0.5 wt. % and preferably from about 0.05 to about 0.3 wt. % based on the total weight of the thermoplastic polyurethane and graphene oxide present in the composition.

(10) The graphene oxide can be characterized as having a particular structure after processing, preferably utilizing the extrusion equipment which includes an extensional dispersing element. The graphene oxide has a face with a lateral size that is between 1 and 5 microns. The thickness of the graphene oxide is between 1 and 50 nanometers. The graphene oxide also has a particular crystalline structure that can be characterized as the presence of (002) graphitic planes at 10-12 due to the presence of oxygenated groups.

(11) Various nanoparticles can be utilized in the present invention. In a preferred embodiment graphene oxide is utilized as a nanocomposite.

(12) The polymer(s) and nanoparticle(s) are combined, along with any other desired additives, either prior to or during processing in an extrusion process, e.g. utilizing an extruder, wherein the graphene oxide is mixed with melted thermoplastic polyurethane at temperatures up to 250 C. The extrusion equipment includes an extensional dispersing element (S4), see for example FIG. 1.

(13) Analysis revealed that unexpectedly better dispersion was achieved in comparison with existing, industry standard mixing elements, see for example mixing element (KB) in FIG. 2. Structural characterization studies indicate the presence of the nanoparticles in the crystallizing phase changes the degree of crystallinity and phase separation. Tensile studies revealed that material processed utilizing the extensional dispersion element showed superior ductility of at least 800% strain, desirably at least 900% strain, and preferably at least 950% strain while compositionally equivalent polymer composite processed through standard mixing element KB displays about a 300% strain, see FIG. 3.

(14) In additional, abrasion resistance also increased for the compositions of the present invention, in spite of an increase in ductility. Upon exposure to identical abrasion, see FIG. 4, the nanocomposite composition processed through extrusion equipment including extensional dispersing element S4 showed better abrasion resistance with lesser volume loss, about 30% less in comparison to material processed utilizing standard mixing element KB, see FIG. 4.

(15) The processed composition including thermoplastic polyurethane and graphene oxide exhibits interesting structure that is believed to result in the beneficial properties of increased strength and increased ductility or strain at break due to orientation of the graphene oxide in relation to the hard segment or block of the thermoplastic polyurethane. It has been found that the graphene oxide platelets have a substantially normal orientation with respect to a hard block or segment of the thermoplastic polyurethane.

(16) Properties of the composition can be compared to the neat or virgin thermoplastic polyurethane without the graphene oxide, processed according to the present invention. Strain at break is increased by at least by 100%, desirably up to 300% and preferably up to 500% as measured according to test ASTM D638-14. Modulus is at least maintained, desirably increases by up to 50%, and preferably up to 100%, as measured according to test ASTM D638-14. Stress at break is at least maintained, desirably increased up to 50% and preferably up to 100% as measured according to test ASTM D638-14.

(17) Accordingly, the compositions of the present invention offer the combination of increases ductility and increased abrasion resistance and open the door to a development of a whole new generation of highly performing thermoplastic nanocomposites.

(18) For the avoidance of doubt, the compositions of the present invention encompass all possible combinations of the components, including various ranges of said components, disclosed herein. It is further noted that the term comprising does not exclude the presence of other elements. However, it is to also be understood that a description of a product or composition comprising certain components also discloses a product consisting of said components. Similarly, it is also to be understood that a description of a process comprising certain steps also discloses a process consisting of the steps.

(19) While in accordance with the patent statutes the best mode and preferred embodiment have been set forth, the scope of the invention is not limited thereto, but rather by the scope of the attached claims.