Patent Application
20240052134
The present invention generally relates to material science, particularly to sterilizable and reusable ultraviolet-resistant elastomer composites, fabricating methods, and applications of the same.
The background description provided herein is to present the context of the invention generally. The subject matter discussed in the background of the invention section should not be assumed to be prior art merely due to its mention in the background of the invention section. Similarly, a problem mentioned in the background of the invention section or associated with the subject matter of the background of the invention section should not be assumed to have been previously recognized in the prior art. The subject matter in the background of the invention section merely represents different approaches, which in and of themselves may also be inventions. Work of the presently named inventors, to the extent it is described in the background of the invention section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the invention.
The initial stages of the COVID-19 pandemic led to a dramatic shortage of critical personal protective equipment (PPE), including N95 masks, which offer high levels of protection against aerosol-borne pathogens. As a result, many medical personnel were forced to reuse N95 masks, oftentimes without proper sterilization. Ultraviolet germicidal irradiation (UVGI), utilizing the ultraviolet-C (UV-C) portion of the electromagnetic spectrum (200-280 nm), is a widely used sterilization technique in medical settings that has been shown to be effective at disinfecting N95 mask filters due to strong UV-C absorption by microbial nucleic acids. However, UVGI is not recommended by N95 mask manufacturers, primarily due to degradation of the elastomeric head straps, which compromises an effective fit and hence decreases filtration efficacy. Although N95 masks are no longer in short supply, aging of N95 mask straps and seals can also influence fit and effectiveness, posing challenges to long-term stockpiling of N95 masks. Therefore, to be better prepared for future pandemics, it is of high urgency to develop elastomeric materials that are resistant to UVGI irradiation, enabling decontamination and reuse of N95 masks and related PPE.
Another significant issue surrounding single-use PPE is waste generation and subsequent environmental and health impacts. During the height of the COVID-19 pandemic, it is estimated that an astounding 129 billion face masks and 65 billion gloves were being disposed monthly around the globe. Safe reuse of PPE is the preferred strategy to decrease single-use waste compared to developing biodegradable materials, which have unknown long-term environmental impacts. Furthermore, viral particles can live on plastics, including biodegradable polymers, for up to three days, which implies that discarded PPE can be vectors for viral transmission. Consequently, the development of UVGI-resistant elastomers that enable the safe reuse of PPE is of high interest from a sustainability and health perspective.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.
In one aspect, this invention relates to a composite, comprising an elastomeric matrix comprising at least one elastomer; and an UV-resistant additive incorporated into the elastomeric matrix.
In one embodiment, the at least one elastomer comprises polyurethane. Other similar substitutes include polyisoprene, polypropylene, and polybutadiene.
In one embodiment, the UV-resistant additive is adapted for absorbing UV light, thereby suppressing UV-induced degradation of the elastomeric matrix.
In one embodiment, the UV-resistant additive comprises graphene.
In one embodiment, the graphene comprises solution-exfoliated graphene.
In one embodiment, a concentration of the graphene is up to 2 wt % of the composite.
In one embodiment, the concentration of the graphene is 1 wt % of the composite.
In one embodiment, increasing the concentration of the graphene in the composite improves mechanical strength and toughness of the composite.
In one embodiment, the UV-resistant additive further comprises a cellulose polymer for providing a mechanical reinforcement to the elastomeric matrix.
In one embodiment, the cellulose polymer comprises ethyl cellulose (EC). Other similar substitutes include nitrocellulose and cellulose nanocrystals.
In one embodiment, the graphene/EC powder is adapted to increase Young's modulus, elongation at break, and toughness, with negligible changes following UV exposure.
In one embodiment, Raman spectroscopy signals for the characteristic graphene peaks comprise D, G, and 2D peaks at 1342 cm−1, 1578 cm−1, and 2700 cm−1, respectively, which are consistent with that of the graphene/EC powder, suggesting that the graphene remain intact following the composite formulation.
In one embodiment, the D/G peak ratio remains less than 1 in the composite, which confirms a relatively low graphene defect density compared to other graphene-based elastomeric composites that employ highly defective graphene oxide or reduced graphene oxide.
In one embodiment, the composites remain mechanically robust over at least 150 sterilization cycles, enabling safe reuse following ultraviolet germicidal irradiation (UVGI).
In one embodiment, the composite is UV and weathering resistant.
In one embodiment, the composite is a free-standing composite.
In one embodiment, the composite is fabricated by in-situ polymerization.
In another aspect, the invention relates to personal protective equipment (PPE), comprising at least one component formed of the above disclosed composite.
In one embodiment, the at least one component is a mask strap, or a glove. Other similar forms of PPE include medical gowns, medical bouffant caps, and related protective coverings.
In yet another aspect, the invention relates to method of fabricating a composite, comprising providing an elastomeric matrix and an UV-resistant additive; and mechanically mixing the UV-resistant additive with the elastomeric matrix.
In one embodiment, the elastomeric matrix comprises an elastomer kit including a crosslinker and a mix of elastomer polyols.
In one embodiment, said mixing step comprises: mixing various amounts of the UV-resistant additive with the elastomer polyols by bath sonicating and subsequently using a centrifugal mixer to form a first mixture thereof; adding the crosslinker into the first mixture to form a second mixture in which a weight ratio of the crosslinker to the elastomer polyols is about 1:1; and curing the second mixture at room temperature to form the composite.
In one embodiment, the method further comprises thermally treating the composite at a temperature for a period of time to further improve mechanical properties.
In one embodiment, the temperature is in a range of about 50-100° C., and the period of time is in a range of about 5-12 hrs.
In one embodiment, the elastomer comprises polyurethane. Other similar substitutes include polyisoprene, polypropylene, and polybutadiene.
In one embodiment, the UV-resistant additive is adapted for absorbing UV light, thereby suppressing UV-induced degradation of the elastomeric matrix.
In one embodiment, the UV-resistant additive comprises graphene.
In one embodiment, the graphene comprises solution-exfoliated graphene.
In one embodiment, a concentration of the graphene is up to 2 wt % of the composite.
In one embodiment, the concentration of the graphene is 1 wt % of the composite.
In one embodiment, increasing the concentration of the graphene in the composite improves mechanical strength and toughness of the composite.
In one embodiment, the UV-resistant additive further comprises a cellulose polymer for providing a mechanical reinforcement to the elastomeric matrix.
In one embodiment, the cellulose polymer comprises ethyl cellulose (EC). Other similar substitutes include nitrocellulose and cellulose nanocrystals.
These and other aspects of the present invention will become apparent from the following description of the preferred embodiment taken in conjunction with the following drawings, although variations and modifications therein may be affected without departing from the spirit and scope of the novel concepts of the invention.
The accompanying drawings illustrate one or more embodiments of the invention and together with the written description, serve to explain the principles of the invention. Wherever possible, the same reference numbers are used throughout the drawings to refer to the same or like elements of an embodiment.
The invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. However, this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this specification will be thorough and complete and fully convey the invention's scope to those skilled in the art. Like reference numerals refer to like elements throughout.
The terms used in this specification generally have their ordinary meanings in the art, within the context of the invention, and in the specific context where each term is used. Certain terms used to describe the invention are discussed below, or elsewhere in the specification, to provide additional guidance to the practitioner regarding the description. For convenience, certain terms may be highlighted, for example using italics and/or quotation marks. The use of highlighting has no influence on the scope and meaning of a term; the scope and meaning of a term are the same, in the same context, whether or not it is highlighted. It will be appreciated that same thing can be said in more than one way. Consequently, alternative language and synonyms may be used for any one or more of the terms discussed herein, nor is any special significance to be placed upon whether or not a term is elaborated or discussed herein. Synonyms for certain terms are provided. A recital of one or more synonyms does not exclude the use of other synonyms. The use of examples anywhere in this specification including examples of any terms discussed herein is illustrative only, and in no way limits the scope and meaning of the invention or of any exemplified term. Likewise, the invention is not limited to various embodiments given in this specification.
It will be understood that, as used in the description herein and throughout the claims that follow, the meaning of “a”, “an”, and “the” includes plural reference unless the context clearly dictates otherwise. Also, it will be understood that when an element is referred to as being “on” another element, it can be directly on the other element or intervening elements may be present therebetween. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
It will be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, or section without departing from the invention's teachings.
Furthermore, relative terms, such as “lower” or “bottom” and “upper” or “top,” may be used herein to describe one element's relationship to another element as illustrated in the figures. It will be understood that relative terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures. For example, if the device in one of the figures. is turned over, elements described as being on the “lower” side of other elements would then be oriented on “upper” sides of the other elements. The exemplary term “lower”, can, therefore, encompasses both an orientation of “lower” and “upper,” depending on the particular orientation of the figure. Similarly, if the device in one of the figures is turned over, elements described as “below” or “beneath” other elements would then be oriented “above” the other elements. Therefore, the exemplary terms “below” or “beneath” can encompass both an orientation of above and below.
It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including” or “has” and/or “having”, or “carry” and/or “carrying,” or “contain” and/or “containing,” or “involve” and/or “involving, and the like are to be open-ended, i.e., to mean including but not limited to. When used in this specification, they specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and this specification, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
As used in this specification, “around”, “about”, “approximately” or “substantially” shall generally mean within 20 percent, preferably within 10 percent, and more preferably within 5 percent of a given value or range. Numerical quantities given herein are approximate, meaning that the term “around”, “about”, “approximately” or “substantially” can be inferred if not expressly stated.
As used in this specification, the phrase “at least one of A, B, and C” should be construed to mean a logical (A or B or C), using a non-exclusive logical OR. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
The description below is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses. The broad teachings of the invention can be implemented in a variety of forms. Therefore, while this invention includes particular examples, the true scope of the invention should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. It should be understood that one or more steps within a method may be executed in a different order (or concurrently) without altering the principles of the invention.
Shortages of personal protective equipment (PPE) at the start of the COVID-19 pandemic caused medical workers to reuse medical supplies such as N95 masks. While ultraviolet germicidal irradiation (UVGI) is commonly used for sterilization, UVGI can also damage the elastomeric components of N95 masks, preventing effective fit and thus weakening filtration efficacy. Although PPE shortage is no longer an acute issue, the development of sterilizable and reusable UV-resistant elastomers remains of high interest from a long-term sustainability and health perspective.
Since the isolation of graphene from graphite, substantial research effort has been devoted to graphene-based materials due to their unique mechanical, thermal, and electronic properties that offer a wide range of applications. For instance, graphene has been used as an effective mechanical reinforcement in polymeric composites. Due to its zero band gap, graphene has also been shown to absorb UV radiation strongly, demonstrating promise as a UV-shielding additive or coating. For these reasons, graphene is a promising candidate to incorporate into elastomers to enable UVGI sterilization and reuse while improving overall mechanical properties, assuming that the graphene additive is produced using scalable and sustainable processing. Towards this end, we have previously reported the liquid-phase exfoliation of pristine graphene from graphite using ethyl cellulose (EC) stabilizers in ethanol. In addition to its proven scalability, this manufacturing method employs environmentally benign solvents and raw materials that can be produced from renewable bioderived sources, thus minimizing environment impact.
In this disclosure, graphene nanosheets, produced by scalable and sustainable exfoliation of graphite in ethanol using the polymer EC, are utilized as UV-resistant additives in polyurethane elastomer composites. By increasing the graphene loading up to 1 wt %, substantial UV protection is imparted by the graphene nanosheets, which strongly absorb UV light and hence suppress photo-induced degradation of the polyurethane matrix. Additionally, graphene/EC provides mechanical reinforcement, such as increasing Young's modulus, elongation at break, and toughness, with negligible changes following UV exposure. These graphene-polyurethane composites remain mechanically robust over at least 150 sterilization cycles, enabling safe reuse following UVGI. Beyond N95 masks, these UVGI-compatible graphene-polyurethane composites have potential utility in other PPE applications to address the broader issue of single-use waste.
In one aspect, this invention relates to a composite, comprising an elastomeric matrix comprising at least one elastomer; and an UV-resistant additive incorporated into the elastomeric matrix.
In one embodiment, the at least one elastomer comprises polyurethane. Other similar substitutes include polyisoprene, polypropylene, and polybutadiene.
In one embodiment, the UV-resistant additive is adapted for absorbing UV light, thereby suppressing UV-induced degradation of the elastomeric matrix.
In one embodiment, the UV-resistant additive comprises graphene.
In one embodiment, the graphene comprises solution-exfoliated graphene.
In one embodiment, a concentration of the graphene is up to 2 wt % of the composite.
In one embodiment, the concentration of the graphene is 1 wt % of the composite.
In one embodiment, increasing the concentration of the graphene in the composite improves mechanical strength and toughness of the composite.
In one embodiment, the UV-resistant additive further comprises a cellulose polymer for providing a mechanical reinforcement to the elastomeric matrix.
In one embodiment, the cellulose polymer comprises ethyl cellulose (EC). Other similar substitutes include nitrocellulose and cellulose nanocrystals.
In one embodiment, the graphene/EC powder is adapted to increase Young's modulus, elongation at break, and toughness, with negligible changes following UV exposure.
In one embodiment, Raman spectroscopy signals for the characteristic graphene peaks comprise D, G, and 2D peaks at 1342 cm−1, 1578 cm−1, and 2700 cm−1, respectively, which are consistent with that of the graphene/EC powder, suggesting that the graphene remain intact following the composite formulation.
In one embodiment, the D/G peak ratio remains less than 1 in the composite, which confirms a relatively low graphene defect density compared to other graphene-based elastomeric composites that employ highly defective graphene oxide or reduced graphene oxide.
In one embodiment, the composites remain mechanically robust over at least 150 sterilization cycles, enabling safe reuse following ultraviolet germicidal irradiation (UVGI).
In one embodiment, the composite is UV and weathering resistant.
In one embodiment, the composite is a free-standing composite.
In one embodiment, the composite is fabricated by in-situ polymerization.
In another aspect, the invention relates to personal protective equipment (PPE), comprising at least one component formed of the above disclosed composite.
In one embodiment, the at least one component is a mask strap, or a glove. Other similar forms of PPE include medical gowns, medical bouffant caps, and related protective coverings.
In yet another aspect, the invention relates to method of fabricating a composite, comprising providing an elastomeric matrix and an UV-resistant additive; and mechanically mixing the UV-resistant additive with the elastomeric matrix.
In one embodiment, the elastomeric matrix comprises an elastomer kit including a crosslinker and a mix of elastomer polyols.
In one embodiment, said mixing step comprises: mixing various amounts of the UV-resistant additive with the elastomer polyols by bath sonicating and subsequently using a centrifugal mixer to form a first mixture thereof; adding the crosslinker into the first mixture to form a second mixture in which a weight ratio of the crosslinker to the elastomer polyols is about 1:1; and curing the second mixture at room temperature to form the composite.
In one embodiment, the method further comprises thermally treating the composite at a temperature for a period of time to further improve mechanical properties.
In one embodiment, the temperature is in a range of about 50-100° C., and the period of time is in a range of about 5-12 hrs.
In one embodiment, the elastomer comprises polyurethane. Other similar substitutes include polyisoprene, polypropylene, and polybutadiene.
In one embodiment, the UV-resistant additive is adapted for absorbing UV light, thereby suppressing UV-induced degradation of the elastomeric matrix.
In one embodiment, the UV-resistant additive comprises graphene.
In one embodiment, the graphene comprises solution-exfoliated graphene.
In one embodiment, a concentration of the graphene is up to 2 wt % of the composite.
In one embodiment, the concentration of the graphene is 1 wt % of the composite.
In one embodiment, increasing the concentration of the graphene in the composite improves mechanical strength and toughness of the composite.
In one embodiment, the UV-resistant additive further comprises a cellulose polymer for providing a mechanical reinforcement to the elastomeric matrix.
In one embodiment, the cellulose polymer comprises ethyl cellulose (EC). Other similar substitutes include nitrocellulose and cellulose nanocrystals.
While primarily designed with sterilizable and reusable PPE in mind, the graphene/EC composites introduced here may also find uses in other elastomeric applications such as medical equipment, textiles and reinforcement in cyclic wear, particularly in outdoor and related contexts where UV irradiation is unavoidable. One example is automotive tires, where graphene/EC can potentially improve mechanical properties and enable UV protection, enabling longer tire life and hence waste reduction through less frequent replacement.
Among other things, the invention provides at least the following advantages.
Graphene/EC powders can be produced in a scalable and sustainable manner, as previously demonstrated by the Hersam Laboratory. Scalable production of graphene is key to industrial-scale manufacturing of graphene-elastomer composites for a variety of applications including but not limited to PPE. Here, EC not only acts as a stabilizer for exfoliating graphene sheets and obtaining a high graphene yield, but also as a mechanical reinforcement to the polyurethane matrix. EC further improves mixability of graphene in the elastomer matrix, a key factor in enabling enhanced mechanical properties.
Only relatively low amounts of graphene/EC are necessary to obtain significant improvement in mechanical properties compared to pristine polyurethane. Graphene/EC powders can be mixed uniformly with the elastomer matrix, yielding a free-standing composite elastomer, thus overcoming a roadblock to commercializing graphene-polymer composites. At 1 wt % graphene/EC loading, enhancements in Young's Modulus, toughness, and elongation at break are observed, and these improvements are sustained after at least 150 UVGI sterilization cycles. Without graphene/EC addition, pristine polyurethane experiences significant microstructural damage after UV exposure, leading to degradation of mechanical properties.
Improved mechanical properties and imparted robust UV-stability by graphene/EC addition to the elastomer matrix have further implications in waste reduction beyond single-use PPE. Targeting the challenge of single-use waste, graphene/EC elastomer composites can be extended to sterilizable and reusable medical equipment and wearable sensors. A broader application is life cycle extension of elastomeric materials that undergo cyclic wear in outdoor contexts, where UV exposure in unavoidable, such as textiles and automotive tires.
These and other aspects of the invention are further described below. Without intent to limit the scope of the invention, exemplary instruments, apparatus, methods, and their related results according to the embodiments of the invention are given below. Note that titles or subtitles may be used in the examples for convenience of a reader, which in no way should limit the scope of the invention. Moreover, certain theories are proposed and disclosed herein; however, in no way they, whether they are right or wrong, should limit the scope of the invention so long as the invention is practiced according to the invention without regard for any particular theory or scheme of action.
Shortages of personal protective equipment (PPE) at the start of the COVID-19 pandemic caused medical workers to reuse medical supplies such as N95 masks. While ultraviolet germicidal irradiation (UVGI) is commonly used for sterilization, UVGI can also damage the elastomeric components of N95 masks, preventing effective fit and thus weakening filtration efficacy. Although PPE shortage is no longer an acute issue, the development of sterilizable and reusable UV-resistant elastomers remains of high interest from a long-term sustainability and health perspective.
Since the isolation of graphene from graphite, substantial research effort has been devoted to graphene-based materials due to their unique mechanical, thermal, and electronic properties that offer a wide range of applications. For instance, graphene has been used as an effective mechanical reinforcement in polymeric composites. Due to its zero band gap, graphene has also been shown to absorb UV radiation strongly, demonstrating promise as a UV-shielding additive or coating. For these reasons, graphene is a promising candidate to incorporate into elastomers to enable UVGI sterilization and reuse while improving overall mechanical properties, assuming that the graphene additive is produced using scalable and sustainable processing. Towards this end, we have previously reported the liquid-phase exfoliation of pristine graphene from graphite using ethyl cellulose (EC) stabilizers in ethanol. In addition to its proven scalability, this manufacturing method employs environmentally benign solvents and raw materials that can be produced from renewable bioderived sources, thus minimizing environment impact.
In this exemplary example, graphene nanosheets are utilized as UV-resistant additives in polyurethane elastomer composites. By increasing the graphene loading up to 1 wt %, substantial UV protection is imparted by the graphene nanosheets, which strongly absorb UV light and hence suppress photo-induced degradation of the polyurethane matrix. Additionally, graphene/EC provides mechanical reinforcement, such as increasing Young's modulus, elongation at break, and toughness, with negligible changes following UV exposure. These graphene-polyurethane composites remain mechanically robust over at least 150 sterilization cycles, enabling safe reuse following UVGI. Beyond N95 masks, these UVGI-compatible graphene-polyurethane composites have potential utility in other PPE applications to address the broader issue of single-use waste.
Specifically, we report the formulation and testing of free-standing composites of polyurethane (PU) and graphene/EC. PU was chosen as a prototypical elastomeric matrix due to its widespread use in many applications, including N95 mask straps. While graphene and graphene-based PU composites have been studied previously for UV and weathering resistance, these previous reports have focused on graphene coatings rather than free-standing composites, only explored UV wavelengths outside the UV-C spectrum, and/or did not perform mechanical testing. In contrast, our free-standing composites are optimized to preserve their elastomeric mechanical properties following simulated UVGI conditions. In particular, we show that, unlike pristine PU that is microstructurally damaged and degrades in mechanical quality after prolonged UV-C exposure, the graphene-polyurethane (Gr-PU) composites prevent UV-induced cracking and thus preserve mechanical properties. As an added benefit, the graphene/EC additive serves as a mechanical reinforcement such that the Gr-PU composites after 30 h of UV-C exposure still possess superior mechanical properties compared to PU before any UV-C exposure. In this manner, Gr-PU composite mask straps enable sterilization and reuse of N95 masks for at least 150 UVGI decontamination cycles. Since elastomers are used in many other PPE applications (e.g., safety gloves), these UVGI-compatible Gr-PU composites can be widely utilized in other PPE contexts, thus providing an effective means of minimizing disposable PPE waste.
Graphene/EC Powder Preparation: The graphene/EC powder was prepared by adding graphite, EC, and ethanol in a 30:1:20 weight ratio and shear mixing the dispersion for 23 hours using an inline mixer (200 L, Silverson). Graphene/EC powders were obtained after centrifuging the resulting dispersion at 6500 RPM for 30 min, flocculating with a 40 mg/mL concentration of aqueous NaCl, rinsing with deionized water, and drying with an infrared lamp. Prior to incorporation into Gr-PU composites, the graphene powders were ground with a mortar and pestle. The final graphene/EC powder contains 34 wt % graphene.
Gr-PU Composite Preparation: The aforementioned graphene/EC powder was mechanically mixed with a commercially available polyurethane kit, comprised of Part A, the crosslinker, and Part B, a mix of polyurethane polyols (VytaFlex 20, Smooth-On). Various amounts of the graphene/EC powder were measured and mixed with Part B, which is the less viscous component, by bath sonicating until the graphene/EC powder was well dispersed and subsequently using a planetary centrifugal mixer (ARE-310, Thinky) with zirconia milling beads for 20 min. The 20 min cycle included 3 min steps, each followed by a 1 min pause for defoaming, which was repeated 5 times. The 5 steps varied in revolution speed as follows: 800, 1200, 1600, 2000, and 2000 rpm. Part A was then added to the well-mixed graphene/Part B so that the weight ratio of Part A to Part B was 1:1. The total weight of the sample was tuned according to the size of the molds such that the final thicknesses of the composites were about 0.75-1.0 mm. The combined components were mixed in the planetary centrifugal mixer for an additional 3 min at 2000 rpm. Subsequently, the final composite formulation was poured into the Teflon mold, degassed in a vacuum oven for 2 min to remove trapped air bubbles, and set aside to cure overnight for about 16 h at room temperature. Following the overnight cure, the composite was annealed at 65° C. in a box furnace for 8 h to further improve mechanical properties. Similarly, pristine polyurethane control samples were fabricated by hand-mixing a 1:1 weight ratio of Part A and Part B, placed in a Teflon mold, degassed, cured overnight at room temperature, and thermally treated at 65° C. for 8 h.
UVGI Exposure: Samples were placed in a reflective UV-C chamber (BioShift), equipped with four 20 W lamps at 254 nm. To ensure UV-C exposure on all sides, the samples were suspended inside the chamber at a distance of 3 in from the closest UV-C lamp. UV-C exposure was performed in 1 h increments up to a maximum of 30 h of total exposure time, which is estimated to be equivalent to 150 UVGI sterilization cycles based on literature precedent. It should be noted that the UV-C chamber manufacturer specifies that that >99.99% of bacteria and viruses on surfaces are killed within 5 min, so 150 UVGI sterilization cycles is likely to be a conservative underestimate.
Characterization: The surface morphology of the elastomer samples was characterized by a 3D laser confocal scanning microscope (LEXT OLS5000, Olympus), and the resulting scans were analyzed using the LEXT software from the manufacturer. SEM images were obtained on a Hitachi SU8030 scanning electron microscope. To characterize the chemical content of the elastomers, Raman spectroscopy (Horiba) was performed using a 532 nm laser. Mechanical data was obtained from tensile tests using an MTS Criterion Series 40 instrument.
The Gr-PU composites were fabricated by in-situ polymerization. Specifically, varying concentrations of graphene/EC powders (from 0 to 1 wt %) were mechanically mixed with commercially available polyurethane polyols, VytaFlex 20 Part B, and a crosslinker, VytaFlex Part A (panel a of
The Gr-PU composites possess a homogenously black appearance after adding as little as 0.1 wt % graphene (0.1-Gr-PU), which indicates that the graphene is well distributed throughout the PU matrix. As the graphene concentration of the Gr-PU composite is increased, the Raman spectroscopy signal for the characteristic graphene peaks commensurately becomes stronger, confirming successful incorporation of graphene into the PU matrix (panel d of
To test for compatibility with UVGI sterilization, the pristine PU control and Gr-PU composite samples were exposed to repeated UV-C cycles (254 nm), totaling 30 h or the equivalent of 150 sterilization cycles. Overall, UV-C irradiation leads to substantial microstructural damage in the pristine PU samples. In particular, after 30 h of UV-C exposure, the pristine PU sample visually appears yellow, compared to its original pink-transparent hue (panels a-b of
Unlike the pristine PU control, the 1-Gr-PU sample withstands 30 h of UV-C exposure without cracking. Visually, the 1-Gr-PU composite appears black in color before and after UV-C exposure (panels a-b of
At each graphene concentration, the surface becomes rougher after 30 h of UV-C exposure, as corroborated by a measure of root mean square height (Sq), or the standard deviation of heights throughout the area of interest. Values were obtained from confocal laser microscopy 2D scans and calculated by the LEXT software. Initial Sq values before UV exposure are similar across the various concentrations. The Sq value is greatest for the 0 wt % graphene sample after 30 h of UV-C exposure, followed by the 0.1 wt % graphene sample after the same exposure time. Sq values for the 0.5 wt % and 1 wt % graphene samples are similar after UV exposure, indicating that 0.5 wt % graphene provides adequate protection against cracking.
Improved surface morphology after UV-C exposure for the 1-Gr-PU composite is mirrored in its higher mechanical performance. Whereas tensile stress-strain curves indicate severe degradation in mechanical behavior for pristine PU after 30 h of UV-C degradation (panel a of
Increasing graphene content in the Gr-PU composites incrementally improves mechanical strength, prior to any UV-C exposure, due to increased mechanical reinforcement by graphene and EC (panel c of
Elongation at break is also improved for the 1-Gr-PU composite by 22% (from 468% to 573%), with little change after 30 h of UV-C exposure (panel d of
Toughness is also improved with increasing graphene content (panel e of
In summary, UV-resistant Gr-PU elastomeric composites have been realized based on scalably and sustainably produced graphene/EC powders. Significant mechanical property improvements as well as UV-C resistance are imparted by the incorporation of graphene/EC powders such that the mechanical properties of the 1-Gr-PU sample after 30 h of UV-C exposure even outperforms bare PU preceding UV-C exposure. This improved performance can be attributed to the suppression of UV-induced surface crack formation in the Gr-PU composites in addition to mechanical reinforcement of the PU matrix by graphene/EC. Since 30 h of UV-C exposure is equivalent to 150 UVGI sterilization cycles, these Gr-PU composites enable significant reuse of N95 masks, thus providing a pathway to substantial reductions in single-use PPE waste. While primarily designed with sterilizable and reusable PPE in mind, the Gr-PU composites introduced here may also find uses in other elastomeric applications, particularly in outdoor and related contexts where UV irradiation is unavoidable.
The foregoing description of the exemplary embodiments of the invention has been presented only for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in light of the above teaching.
The embodiments were chosen and described to explain the principles of the invention and their practical application to enable others skilled in the art to utilize the invention and various embodiments and with various modifications as are suited to the particular use contemplated. Alternative embodiments will become apparent to those skilled in the art to which the invention pertains without departing from its spirit and scope. Accordingly, the scope of the invention is defined by the appended claims rather than the foregoing description and the exemplary embodiments described therein.
Some references, which may include patents, patent applications, and various publications, are cited and discussed in the description of this invention. The citation and/or discussion of such references is provided merely to clarify the description of the invention and is not an admission that any such reference is “prior art” to the invention described herein. All references cited and discussed in this specification are incorporated herein by reference in their entireties and to the same extent as if each reference was individually incorporated by reference.
This application claims priority to and the benefit of U.S. Provisional Application No. 63/397,425, filed Aug. 12, 2022, which is incorporated herein in its entirety by reference.
This invention was made with government support under DMR-2029058, DGE-1842165, CMMI-2037026 and DMR-1720139 awarded by the National Science Foundation. The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 63397425 | Aug 2022 | US |
