Additively manufactured surface-textured polymer composites and methods of making the same

Abstract

An exemplary polymer-based composite includes one or more polymers, one or more 2D materials blended with the one or more polymers, and embedded fibers of one or more fiber types. An exemplary surface-textured composite is produced by 3D-printing an object from the blended mixture and then exposing some of the fibers embedded in the 3D-printed object.

Description

[0001] ADDITIVELY MANUFACTURED SURFACE-TEXTURED POLYMER COMPOSITES AND METHODS OF MAKING THE SAME

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims the benefit of U.S. Provisional Patent App. No. 63 / 605,091, filed December 1, 2023, the complete contents of which are herein incorporated by reference.

[0004] FIELD OF THE INVENTION

[0005] Embodiments are directed to surface-textured polymer composites and, more particularly, composites with embedded fibers and methods of making the same.

[0006] BACKGROUND

[0007] Enhancing the coefficient of friction of rubber can result in significant safety benefits for individuals and society on icy or contaminated surfaces. This includes enhancing traction for tires, braking systems, and footwear. The US Bureau of Labor Statistics reported 42,480 injuries occurring on ice, snow, or sleet at work in 2014, with projections indicating that these numbers are expected to double by 2050. Additionally, nearly half of the 1.2 million weather-related vehicle crashes in the US involved icy roads, resulting in at least 1,700 deaths. During icy weather, slipping and falling accidents of individuals and vehicles occur because of inadequate traction. This is related to forming an inherent quasi-liquid layer on the surface of ice, even at very low temperatures. This layer acts as a lubricant, making it harder to get traction on icy surfaces than non-icy ones. When the temperature rises to the melting point of ice, this layer gets thicker, reducing friction and making the ice more slippery. At these temperatures, the latent heat (approximately 80 cal / g or 1.4 kcal / mol) is sufficient to break about 10% of the dangling hydrogen bonds in polar water molecules. Furthermore, frictional heating and surface pressure at sliding speeds exceeding ~10 mm / s lead to an increase in the thickness of the quasi-liquid layer, rendering the icy surface even more slippery. In addition to outdoor icy surfaces, footwear in indoor environments encounters a different yet equally significant challenge concerning traction. One major indoor risk is slipping, often exacerbated by liquids such as oil, which significantly reduce surface friction. For instance, on ceramic surfaces lubricated with oil, friction decreases markedly due to the formation of a squeezed oil film that acts as a barrier between the outsole of the footwear and the floor. This issue is particularly evident in environments like kitchens, where grease is common and contributes to a higher incidence of falls. In British Columbia, Canada, approximately 25% of injury claims in restaurants, bars, and pubs from 2017 to 2021 were attributed to falls on oily surfaces. These statistics underscore the urgent need for footwear outsoles that can provide reliable traction in various slippery conditions, including both ice and oil, to enhance safety in real- world applications.

[0008] The surface roughness of the footwear outsole is one of the key parameters governing high ice and oil friction. Roughness refers to the irregularities or variations in the surface texture of an object. It is a measure of the deviation in surface protrusions from their average height. Higher roughness generally increases friction by expanding the surface area and allowing better contact with substrate asperities through mechanical interlocking. Recognizing the critical role of roughness in ice friction properties, recent studies have introduced surface-textured polymer composites for ice friction applications. Increasing friction on slippery surfaces provides protection against falls; however, surface-textured composites, despite their potential, remain susceptible to wear. Composite-based footwears are quite sensitive to wear and abrasion in real- world application, with a notable decrease in ice friction properties for as little as 75,000 steps. Material losses attributed to other wear mechanisms can also become significant when considering extended periods of sliding or rolling.

[0009] Polymers usually have a low modulus (=0.1 GPa), which allows them to conform to surface asperities and establish strong mechanical contact (grip). However, they are also prone to wear and abrasion. Abrasion is a predominant mode of rubber wear, particularly in the context of tire wear’.

[0010] U.S. Patent No. 11,485,057, titled “Methods of Manufacturing a High Friction Composite Material for Footwear,” disclosed a method of making high friction composite material by a compression molding technique followed by cutting to expose the embedded fibers. This approach has limitations in controlling fiber alignment, leading to random alignments visible in microscopy images of the composite materials. Besides issues of fiber alignment, the injection molding (IM) approach leads to a random distribution of fibers on the composite surface.

[0011] Therefore, there is a need for improved materials and manufacturing methods offering reproducibility, precise fiber alignment, and uniform distribution to effectively enhance the traction properties of composites.

[0012] SUMMARY

[0013] To overcome above described limitations, this disclosure introduces enhanced anti-slip composites which incorporate 2D materials and exhibit significantly improved material properties attributable at least in part by advanced manufacturing techniques, particularly additive manufacturing techniques such as fused filament fabrication (FFF) and resin 3D printing.

[0014] Exemplary composite materials comprise soft fibers and hard fibers embedded in a soft matrix. A fiber de -bonding and pull-out method may be used so that the fibers protrude out from the material’s surface. The hard fibers extending out of the surface of the material are able to penetrate hard substrates, such as ice, while the soft components (the soft fibers and soft matrix) are able to sufficiently deform and mold against hard external substrates, thereby ensuring a large contact area and very high mechanical interlocking.

[0015] Exemplary embodiments include integration of 2D materials with additive manufacturing to enhance tribological performance of composite materials. Such embodiments significantly improve friction properties for multiple reasons. First, the use of additive manufacturing such as FFF allows control over fiber orientation, alignment, and distribution at the micro-scale. Second, this enhanced control, combined with the distinct physical and chemical properties of 2D materials — such as but not limited to increased surface area, microscopic roughness, intermolecular interactions, thermal properties, flexibility, hydrophobicity, and potential electrostatic effects — enables significant improvements in friction and surface characteristics, ultimately enhancing the anti-slip performance of the composite.

[0016] Composites generated through additive manufacturing exhibited superior surface qualities compared to their injection-molded counterpails. Beyond surface performance, an additive manufacturing process such as FFF printing tends to be more affordable and flexible than injection molding, especially for smaller production runs, and generally consumes less energy overall. In contrast, injection molding is more energy-intensive initially due to the machinery and mold heating requirements but can achieve high efficiency for large-scale production, which offsets its higher upfront costs. This finding underscores the potential advantages of additive manufacturing in achieving finer surface textures and overall surface quality while also being flexible, consistent, and energy efficient.

[0017] An Example is included below providing empirical comparisons of different composites and comparisons of composites having the same constituent elements but produced by different manufacturing techniques. The results demonstrate that 2D fillers enhance both abrasionresistance and ice-friction, while FFF-fabricated composites consistently exhibit superior properties across all compositions relative to injection molding fabricated composites. Notably, hBN-reinforced samples exhibited hierarchical surface texturing, leading to enhanced abrasionresistance (FFF: 146.63±3.39%; IM: 133.83±6.8% ; p=0.036), and effective ice-traction (FFF: 0.58+0.04; IM: 0.54+0.06; p=0.043). These outperformed ice-traction properties of all other FFF-fabricated composites, including a composite consistent with U.S. Patent No. 11,485,057 (0.52±0.05) as well as composites with GNP (0.53±0.02), SEBS (0.42±0.05) and hBN+SEBS (0.45+0.02). Additionally, a combination of constituent materials disclosed by U.S. Patent No. 11,485,057 produced not by injection molding as disclosed by U.S. Patent No. 11,485,057 but instead via FFF exhibited moderate oil-traction (0.121±0.001), outperforming others. The Example shows the significant benefits of 3D printing methods like FFF and the benefits of including 2D fillers to enhance traction and durability in composites.

[0018] According to an aspect of some embodiments, an exemplary 3D printed polymer-based composite comprises one or more polymers; one or more 2D materials blended with the one or more polymers; and embedded fibers of one or more fiber types. In this disclosure, “3D printed” may be used interchangeably with “additively manufactured”. In this disclosure, “3D print” may be used interchangeably with “additively manufacture”. In this disclosure, “3D printing” may be used interchangeably with “additive manufacturing”.

[0019] According to an aspect of some embodiments, an exemplary polymer-based composite comprises carbon fiber (CF) and poly(p-phenylene-2,6-benzobisoxazole) (PBO) fiber.

[0020] According to an aspect of some embodiments, an exemplary polymer-based composite has a ratio of hard fibers (e.g., CF) to soft fibers (e.g., PBO fiber) (by weight) of 2:1. In other embodiments, the ratio of hard to soft fibers by weight may be, for example, 2:1 , 1 :1 , 1 :2, or 1 :3, or some other ratio.

[0021] According to an aspect of some embodiments, an exemplary polymer-based composite comprises 2D materials including 2D graphene nanoplatelets (GNP) and / or hexagonal boron nitride (hBN).

[0022] According to an aspect of some embodiments, an exemplary polymer-based composite comprises one or more polymers including one or more of a thermoplastic, a photocurable resin, and / or styrene-ethylene-butylene-styrene (SEBS).

[0023] According to an aspect of some embodiments, an exemplary polymer-based composite comprises one or more polymers including one or more of thermoplastic polyurethane (TPU) and / or acrylonitrile butadiene styrene (ABS).

[0024] According to an aspect of some embodiments, at least one external surface of a polymer- based composite may be configured so that some of the embedded fibers protrude out from the at least one external surface.

[0025] According to an aspect of some embodiments, at least one external surface of a polymer- based composite may be configured so that some of the embedded fibers are exposed by a fiber de-bonding and pull-out method.

[0026] According to an aspect of some embodiments, at least one external surface of a polymer- based composite may be configured so that some of the embedded fibers are exposed by cutting and / or abrading.

[0027] According to an aspect of some embodiments, an exemplary polymer-based composite has at least one external surface with a coefficient of friction that is at least 0.4, at least 0.5, or at least 0.6 when contacting external materials such as but not limited to ice. A worker skilled in the art will appreciate that the actual coefficient of friction measured may vary to an extent depending on the type of contact surface, e.g., the type of ice: melting ice (ice covered with a thin layer of liquid water) or bare ice (no liquid water present on the ice surface). An exemplary polymer-based composite has at least one external surface with a coefficient of friction that is at least 0.4, preferably at least 0.5, or more preferably at least 0.6 on any type of ice.

[0028] According to an aspect of some embodiments, an exemplary method of producing a surface-textured composite comprises blending fibers of one or more fibers types, one or more polymers, and one or more 2D materials; 3D-printing (i.e., additively manufacturing) an object from the blend material; and exposing some of the fibers embedded in the 3D-printcd object.

[0029] According to an aspect of some embodiments, an exemplary method of producing a surface-textured composite comprises blending fibers of one or more fibers types, one or more polymers including at least one thermoplastic, and one or more 2D materials; extruding the blend into a filament; 3D-printing an object from the filament; and exposing some of the fibers embedded in the 3D-printed object.

[0030] According to an aspect of some embodiments, an exemplary method of producing a surface-textured composite comprises configuring orientation settings for 3D-printing to maximize unidirectional fiber orientation of the fibers embedded in the 3D-printed object.

[0031] According to an aspect of some embodiments, an exemplary method of producing a surface-textured composite comprises fused filament fabrication (FFF).

[0032] According to an aspect of some embodiments, an exemplary method of manufacturing a surface-textured composite comprises 3D-printing an object from a mixture comprising metallic or metallic-coated fibers, one or more 2D materials, and one or more polymers including at least one photocurable polymer; manipulating fiber orientation of the metallic or metallic-coated fibers during the 3D-printing to maximize unidirectional fiber orientation of the fibers embedded in the 3D-printed object; curing the 3D-printed object; and exposing the metallic or metallic- coated fibers embedded in the 3D-printed object.

[0033] According to an aspect of some embodiments, an exemplary method of producing a surface-textured composite comprises SLA printing (3D-printing performed with a stereolithography apparatus (SLA)).

[0034] According to an aspect of some embodiments, an exemplary method of manufacturing a surface-textured composite comprises manipulating fiber orientation of metallic or metallic- coated fibers during 3D-printing by applying a magnetic field to maximize unidirectional fiber orientation of the fibers embedded in the 3D-printed object.

[0035] BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figures 1A and IB are SEM images of CF-PBO-TPU composite samples produced by fused filament fabrication (FFF) printing followed by abrasion. Figures 2A and 2B are SEM images of CF-PBO-TPU-HBN composite samples produced by fused filament fabrication (FFF) printing followed by abrasion.

[0037] Figure 3A is a simplified illustration of an exemplary surface-textured composite produced with 3D printing.

[0038] Figure 3B is a simplified illustration of a surface-textured composite produced by injection molding.

[0039] Figure 4 is an exemplary method of producing exemplary surface-textured composites.

[0040] Figure 5 is an exemplary method of producing an exemplary surface-textured composite via fused filament fabrication (FFF).

[0041] Figure 6 is an exemplary method of producing an exemplary surface-textured composite via SEA printing.

[0042] Figure 7 is an exemplary FFF printing apparatus.

[0043] Figure 8 is an exemplary SLA printing apparatus at various stages of production.

[0044] Figure 9A is a visual summary of features and factors of exemplary materials and applications where significant friction is desirable.

[0045] Figure 9B is footwear that includes exemplary composite material configured as a plurality of plugs in an outsole.

[0046] Figure 9C is a tire the tread of which is made of or at least includes one or more exemplary composites according to this disclosure.

[0047] Figure 10A is a flowchart of the fabrication and testing / characterizations of textured surface composites evaluated in Example 1.

[0048] Figure 10B is a diagram of a custom-made setup for the ice traction test of Example 1.

[0049] Figure 11: ARI value with standard deviation for different composite samples: a) CF- PBO-TPU, b) CF-PBO-TPU-hBN, c) CF-PBO-TPU-GNP, d) CF-PBO-TPU-SEBS, e) CF-PBO- TPU-hBN+SEBS, f) CF-PBO-TPU-Silica, g) CF-PBO-TPU-SiC (star indicates significant differences, p < 0.05).

[0050] Figure 12: SEM image of five different composite samples before abrasion: a) CF-PBO- TPU, b) CF-PBO-TPU-hBN, c) CF-PBO-TPU-GNP, d) CF-PBO-TPU-SEBS, e) CF-PBO-TPU hBN+SEBS.

[0051] Figure 13: SEM image of five different composite samples after abrasion: a) CF-PBO- TPU, b) CF-PBO-TPU-hBN, c) CF-PBO-TPU-GNP, d) CF-PBO-TPU-SEBS, e) CF-PBO-TPU hBN+SEBS. Circular symbols indicate the patchy distribution of the fibers, while parallel arrows indicate the uniform distribution of the fibers.

[0052] Figure 14: Relation between the COF data obtained from SATRA machine and custom setup.

[0053] Figure 15: After abrasion COF values. Error bar representing standard deviation (star indicates significant differences, p < 0.05) for composite using two different methods: a) CF- PBO-TPU, b) CF-PBO-TPU-hBN, c) CF-PBO-TPU-GNP, d) CF-PBO-TPU-SEBS, e) CF-PBO- TPU-hBN+SEBS.

[0054] Figure 16: COF value with error bar representing standard deviation for composite using FFF method on oily surface: a) CF-PBO-TPU, b) CF-PBO-TPU-hBN, c) CF-PBO-TPU-GNP, d) CF-PBO-TPU-SEBS, e) CF-PBO-TPU-hBN+SEBS.

[0055] Figure 17: Roughness values with error bar representing standard deviation (star indicates significant comparison, p < 0.05) of five different composite samples after abrasion: a) CF-PBO- TPU, b) CF-PBO-TPU-hBN, c) CF-PBO-TPU-GNP, d) CF-PBO-TPU-SEBS, e) CF-PBO-TPU- hBN+SEBS.

[0056] Figure 18: Roughness image of five different composite samples after abrasion a) CF- PBO-TPU, b) CF-PBO-TPU-hBN, c) CF-PBO-TPU-GNP, d) CF-PBO-TPU-SEBS, e) CF-PBO- TPU-hBN+SEBS.

[0057] Figure 19A: Contact angle of five different composite samples after abrasion in FFF method with respect to COF.

[0058] Figure 19B: Water droplet shape along with contact angle measurement for a) CF-PBO- TPU, b) CF-PBO-TPU-hBN, c) CF-PBO-TPU-GNP, d) CF-PBO-TPU-SEBS, e) CF-PBO-TPU- hBN+SEBS.

[0059] Figure 19C: The contact angle of five different composite samples after abrasion in FFF method with respect to roughness.

[0060] Figure 19D: The contact angle of five different composite samples based on the Wenzel model with respect to their experimental values for FFF-printed samples. DETAILED DESCRIPTION

[0061] An exemplary polymer-based composite comprises fibers of one or more fiber types, one or more polymers, and one or more 2D materials.

[0062] Exemplary types of fibers include carbon fiber (CF) and poly(p-phenylene-2,6- benzobisoxazole) (PBO) fibers. Some exemplary composites incorporable flexible PBO fibers and rigid CF microfibers within the polymer matrix. The flexible PBO fibers absorb energy generated by friction, while the rigid CF microfibers provide protection against mechanical damage to the PBO-TPU substrates. Together, these features, along with the lower elastic modulus of the polymer matrix, contribute to long-lasting slip-resistant composite properties on ice.

[0063] Fibers may be characterized as soft fibers or hard fibers. “Soft fibers” as used herein refer to fibers having a relatively lower strength in compression (e.g., compressive strength) as compared to the hard fibers. In certain embodiments, the strength in compression of the soft fibers is less than 1 GPa. In certain embodiments, the strength in compression of the soft fibers is about 0.5 GPa. Soft fibers for use in various embodiments of this disclosure include but are not limited to synthetic polymer fibers, such as poly(p-phenylene-2,6-benzobisoxazole) (PBO) fibers; aromatic polyamide fibers including but not limited to poly-p-phenylene terephthalamide fibers and poly-m-phenyleneisophthalamide fibers; polyphenylene sulfide fibers; polyurethane fibers; and nylon or ultra-high molecular weight extended chain polyethylene (UHMPE). In certain embodiments, the soft fibers include at least PBO fibers. Commercially available PBO fibers include but are not limited to Zylon™ (Toyobo Co., Japan).

[0064] “Hard fibers” as used herein refer to fibers having a relatively higher strength in compression as compared to the soft fibers. In certain embodiments, the compressive strength is between 10-20 GPa. Hard fibers for use in the methods of the present invention include but are not limited to synthetic inorganic fibers such as carbon fibers, glass fibers, asphalt fibers, graphite fibers, basalt fibers, and silicon carbide (SiC). In certain embodiments, the hard fibers include at least carbon fibers. Commercially available carbon fibers include but are not limited to Zoltek™ PX35.

[0065] In certain embodiments, the fibers for use in methods of the present disclosure have a diameter of about 10 pm to about 100 pm. In certain embodiments, the lengths of the fibers for use in the methods of the disclosure are about 1 mm to about 50 mm. A worker skilled in the art will appreciate that the fibers may be broken into smaller pieces when mixed c.g. in a compounder.

[0066] The fibers may constitute about 1 vol % to about 32 vol % of the components used in the production of an exemplary composite. In certain embodiments, the fibers are about 1 vol % to about 10 vol % of the components used in the production of the composite. In certain embodiments, the fibers are about 1 vol % to about 8 vol % of the components used in the production of the composite. In certain embodiments, the fibers are about 4 vol % to about 8 vol % of the components used in the production of the composite. In specific embodiments, the fibers are about 8 vol % of the components used in the production of the composite.

[0067] The ratio of hard to soft fibers used in the methods of the present invention may also be varied. In certain embodiments, the ratio of hard to soft fibers (by weight) is 2:1. In other embodiments, the ratio of hard to soft fibers by weight is 2:1, 1:1, 1:2, or 1:3.

[0068] The one or more polymers may include one or more of a thermoplastic, a photocurable resin, polypropylene, polyethylene, ethylvinylacetate, and styrene-ethylene -butylene- styrene (SEBS). An exemplary thermoplastic is thermoplastic polyurethane (TPU). An exemplary resin may be an acrylonitrile butadiene styrene (ABS)-like resin. Thermoplastic polyurethane (TPU) exhibits notable abrasion resistance and traction.

[0069] The incorporation of at least one 2D material with at least one polymer has been shown to provide heightened resistance to wear relative to the polymer alone. The 2D material is selected in type and amount to address the sensitivity of the polymer(s) to wear-related effects, such as indentation, abrasion, scratches, and adhesion patterns, and reduce or prevent asperities from penetrating the matrix.

[0070] The one or more 2D materials may include one or more (up to all of) the following: 2D Graphene-nanoplatelets (GNP), hexagonal-Boron-Nitride (hBN), Silica (Si), and Silicon-Carbide (SiC). Some embodiments may include, in the alternative or in addition to one or more of the forgoing materials, one or more other 2D materials which may include but are not limited to nanomaterials. In this disclosure 2D materials may also be referred to as filler materials, 2D filler materials, fillers, reinforcement materials, or 2D reinforcement materials. These terms may be used interchangeably in this disclosure. It should be appreciated that qualifying a material as a “filler” in this disclosure, as in the art more broadly, does not limit the material’s functionality and purpose to simply “filling”, that is to say adding volume and mass, to a composite. Various advantages and effects of exemplary 2D materials on exemplary composites arc discussed throughout this disclosure.

[0071] Graphene-nanoplatelets (GNP) have advantageous properties including the following: wettability reduction, hydrophobic, Van der Waals force, larger surface area. GNP has strength of 130 GPa (at -0.335 nm thickness) and flexibility due to its exceptionally high surface-to- volume ratio.

[0072] Hexagonal-Boron-Nitride (hBN) has advantageous properties including the following: wettability reduction, hydrophobic, Van der Waals force, larger surface area, hexagonal structure, and electrostatic force. hBN has the most stable crystalline structure of BN compared to cubic BN and wurtzite BN. Higher stability of crystalline structure reduces wear and material loss as a filler material. The inclusion of hBN in a TPU composite improves material properties of the composite.

[0073] The controlled inclusion of 2D fillers such as hBN and GNP has demonstrated significantly enhanced wear resistance for resulting composites, particularly when produced by an exemplary additive manufacturing process, with increases of 31% and 38% in wear resistance for hBN and GNP, respectively. While certain filler materials like hBN significantly enhance ice-friction properties of exemplary composites, their effectiveness may vary on other slippery surfaces, particularly those contaminated with oil. This variability underscores the complexity of material selection and the need for tailored solutions depending on specific environmental conditions and application requirements.

[0074] Silica filler is widely used in the top tread rubber of tires because of its exceptional performance in this use case. The inclusion of silica in rubber blends in accordance with this disclosure enhances wet grip while decreasing tire rolling resistance. Silica can improve tear strength, decrease heat buildup, improve wear resistance, and enhance adhesion during the rubber compound shaping process. However, silica may be excluded from some exemplary composites depending on the intended use of the composites.

[0075] SEBS blended with TPU modifies the performance of the TPU, offering the ability to adjust properties like abrasion resistance and enhance the friction coefficient.

[0076] SiC provides enhanced wear resistance for use with epoxy-based composites under dry and water-lubricated conditions. Figures 1 A and IB are SEM images of CF-PBO-TPU composite samples produced by fused filament fabrication (FFF) printing followed by abrasion. Figures 2A and 2B arc SEM images of CF-PBO-TPU-HBN composite samples produced by fused filament fabrication (FFF) printing followed by abrasion. The four images exhibit a considerable amount of fiber exposure to the surface following abrasion. Exposed fibers on the surface of the composites following abrasion provide significant slip-resistant properties and maintain ice frictional performance over extended use. Moreover, there is substantial uniformity / consistency in both fiber alignment and fiber distribution.

[0077] Figure 3 A is a simplified illustration of an exemplary surface-textured composite 301 produced with 3D printing (i.e., additive manufacturing). Fibers 302 exhibit generally uniform distribution and alignment with one another. When the 3D printing is FFF printing, the fibers generally align with the printing direction. For comparison, Figure 3B is a simplified illustration of a surface-textured composite 351 produced by injection molding. Though some fibers 352 align with other fibers, there is significantly greater nonuniformity in collective fiber alignment and fiber density in injection molded composite 351 compared to the 3D-printed composite 301.

[0078] Figure 4 is an exemplary method 400 of producing exemplary surface-textured composites according to this disclosure. The method 400 comprises blending fibers of one or more types, one or more polymers, and one or more 2D materials at block 401. In general, it is desirable for the blending to continue until substantially uniform distribution of the respective components in achieved. The blend is then 3D printed at block 402. In this disclosure, “3D printed” may be used interchangeably with “additively manufactured”. The 3D printing process of block 402 may vary depending on the embodiment. As exemplary non-limiting examples, the 3D printing process of block 402 may be, for example, fused filament fabrication (FFF) and / or stereolithographic printing (SEA printing).

[0079] Fibers embedded in the 3D printed object are exposed at block 403. Fibers may be exposed by, for example, cutting or abrading the 3D printed object. At least a portion of the outermost layer of a composite is removed such that the fibers protrude from the surface of the composite. The portion of the outermost layer to be removed may be dependent on the orientation of the fibers. For example, the removal of the end portion of cylindrical forms of the composite in which the fibers arc oriented in the direction of the axis of the cylinder is favorable for producing fibers which protrude substantially perpendicular from the composite surface. Any thickness of the outmost layer may be removed so long as it is sufficient to expose the fibers. In certain embodiment at least 2-3 mm is removed. A sharp cutting tool may be used to cut.

[0080] As an alternative, the method 400 may exclude block 403. In some embodiments, an outmost layer of the composite is not removed at the time of manufacture. In such embodiments, fibers are first exposed during the state of use. For instance, an exemplary composite may be used as an abrasion resistant material that shows increasingly higher friction on ice as it gets abraded from use.

[0081] Figure 5 is an exemplary method 500 of producing an exemplary surface-textured composite via fused filament fabrication (FFF). At block 501, fibers of one or more fiber types, one or more polymers, and one or more additional materials are blended together. The one or polymers include at least one thermoplastic, in other words a polymer that can be molded when heated but which solidifies when cooled. The blend is then extruded into a filament at block 502. The filament is at least one of the building materials used in the 3D printing of block 503. One or more additional building materials besides the filament produced at block 502 may be employed during the 3D printing of block 503. For example, the filament from block 502 may be ejected by a first printer nozzle, and a support material may be printed by a second FFF printer nozzle. The support material may be removed, e.g., by dissolution by chemical bath or wash, as a final or near final stage of the 3D printing process. After the 3D-printed object is finished, fibers within the 3D-printed object are exposed at at least one surface of the 3D-printed object at block 504. Exposing fibers may be achieved by, for example, abrasion and / or cutting.

[0082] The average protrusion length of the fibers may impact the coefficient of friction of the composite on ice and / or other external contact surfaces. In certain embodiments the methods of the present disclosure produce a composite in which the average protrusion length of the fibers is greater than 50 pm, greater than or equal to 100 pm, greater than or equal to 125 pm, or greater than or equal to 150 pm.

[0083] Figure 6 is an exemplary method 600 of producing an exemplary surface-textured composite via SLA printing. In this disclosure, SLA printing may be referred to interchangeably with resin 3D printing, digital light processing (DLP) printing, and liquid crystal display (LCD) resin printing. Similar to block 501 of method 500, a plurality of components are blended at block 601. In general, these components include fibers of one or more types, one or more 2D materials, and one or more polymers including at least one uncrosslinked but crosslinkable polymer (e.g., a photocurable polymer). The 3D printing process of block 603 is SLA printing. A 3D-printcd object is produced from the viscous blend by selective curing (block 632) layer by layer. In sharp contrast to known SLA printing techniques, however, the printing process 603 includes manipulation of fiber orientations at block 631. For any given layer to be printed, fiber orientations of fibers within the physical space where the layer is to be formed are manipulated into substantial alignment with one another. The blended material in this physical space is then cured while the fibers are in substantial alignment with one another. The curing sets the fibers so they remain aligned even after the means of manipulation is removed. An exemplary means of manipulating the fibers within the viscous blend is by application of a magnetic field using, e.g., one or more electromagnets. In such case, at least some of the fibers in the blend produced at block 601 are configured to react to magnetic forces. Such fibers may be or include ferromagnetic and / or paramagnetic material. For example, some fibers may be metal. Some fibers may include metal and non-metallic components. Some fibers may be metallic-coated at block 611 prior to blending at block 601. For instance, an exemplary fiber is a metallic-coated CF-PBO fiber. All or less than all of the fibers in the blend produced at block 601 may be configured to react to magnetic forces. Magnetic fibers may be included in sufficient quantity in the blend so that when the magnetic fibers move in response to an applied magnetic field, the magnetic fibers exert force on neighboring nonmagnetic fibers such that the neighboring nonmagnetic fibers are urged into substantially the same alignment as the magnetic fibers. When all layers have been cured and the 3D printing process of block 603 concluded, fibers within the 3D-printed object are exposed at at least one surface of the 3D-printed object at block 504. Exposing fibers may be achieved by, for example, abrasion and / or cutting.

[0084] Figure 7 is a diagram of an exemplary FFF printing apparatus 700. Filament material 701 is fed by a feed system 702 into a liquefier chamber 703. The liquefier chamber 703 is configured to heat the filament to a temperature that permits the composite material of which the filament is made to be formed into new shapes. The temperature is also set to be at least as high as required for the fibers embedded in the composite material to shift and change alignment relative to one another. As the feed system 702 (e.g., a pinch roller feed system) advances filament into the liquefier chamber 703, the force from adding further material into one end of the chamber forces already heated material out the other end of the chamber through the nozzle tip 704 onto the print platform 705 or else onto the scaffold 706 of already printed composite. The platform 705 may be moved in one or more of the x, y, and z directions. In addition, or in the alternative, the nozzle may be moved in or more of the x, y, and z directions. Printing parameters such as but not limited to the temperature of the liquefier chamber and the feed rate / print rate are controlled such that the fibers in the heated composite material are urged into alignment with one another as they pass through and exit the nozzle.

[0085] Figure 8 is a diagram of an exemplary SLA printing apparatus depicted at various stages of production. At stage 801 a vat 811 is filled with a viscous mixture 814 that comprises metallic or metallic-coated fibers, one or more 2D materials, and one or more polymers including at least one photocurable polymer. Filler volume percentage in the formulation is determined at least in part by a minimum viscosity required for successful SLA printing. For instance, the filler volume percentage may be less than 8%, less than 7%, less than 6%, less than 5%, less than 4%, e.g. 3%. A build platform 812 is positioned to be in contact with the viscous mixture. A magnetic force is applied, e.g., by an electromagnet 813, to manipulating fiber orientation in the viscous mixture. While the fibers are aligned with the magnetic field and therefore substantially aligned with one another, a single layer 817 of the viscous mixture is cured at stage 802 by patterned exposure 815 from radiation source 816. At stage 803 the platform is moved relative to the vat (or the vat may be moved relative to the platform) so that the previously cured layer is exposed to further uncured material. At stage 804 another layer 818 is cured. The exposure pattern may be varied from one layer to the next according to the shape of the 3D object to be printed. Stage 805 shows the progress of 3D printing the object 819 after several further layers have been printed.

[0086] Exemplary surface-textured composites may be employed in a variety of applications including but not limited to applications in which a high coefficient of friction is needed or desired. Figure 9A is a visual summary of features and factors of exemplary materials and applications where significant friction is desirable. One non-limiting application is walking and running. Figure 9A depicts a typical human gait cycle at figure-center. Exemplary surface- textured composites according to this disclosure may be employed in the outsole of footwear, such as is represented in the top-left of Figure 9A. Exemplary outsoles may be made entirely of one or more exemplary materials according to this disclosure. Alternative exemplary outsoles may be used for portions (less than all) of the outsole of footwear. For instance, Figure 9A at topleft and Figure 9B illustrate exemplary materials configured as a plurality of plugs in an outsole which may be made of a plurality of different materials. As a further nonlimiting use case, Figure 9C depicts a tire the tread of which is made of or includes one or more exemplary composites according to this disclosure.

[0087] For high friction application, exemplary composites according to this disclosure are produced so that exposed fibers have a substantial directional component which is orthogonal to the surface plane from the fibers project. This alignment tends to place the exposed fibers with a substantially orthogonal direction relative to surfaces which are contacted in a state of use. Orthogonal fiber alignment orthogonal to external surfaces promotes a high degree of mechanical interlocking with such external surfaces. This is especially advantageous on external surfaces which have low coefficients of friction, e.g., icy surfaces.

[0088] Dynamic friction between two solid surfaces is attributable to at least two mechanisms: 1) an adhesion force that induces the shear force between the contacting junctions and 2) a plowing force that occurs when a harder surface’s asperities plow through a softer surface. Figure 9A at top-right illustrates some adhesion mechanisms in nature. Figure 9A at bottom summarizes factors affecting adhesion between a shole sole and ice.

[0089] The incorporation of 2D materials (sometimes referred to in this disclosure as 2D fillers) in exemplary composites of this disclosure enhance both ice friction and abrasion resistance properties, highlighting their utility for durable winter safety applications, among other applications. These improvements stem from the unique characteristics of the 2D fillers of exemplary composites. Significant traits include hydrophobicity, wettability, increased surface area, and specific intermolecular interactions, such as electrostatic and van der Waals forces. The inherent hydrophobicity of 2D materials like hBN reduces the likelihood of droplet accumulation and ice formation. Other studies have shown that when hBN interacts with water, it exhibits the lowest wettability, resulting in high COF. Furthermore, van der Waals forces within 2D fillers initiate an adhesion mechanism akin to how frogs utilize these forces to adhere to slippery surfaces, leveraging their microscopic hexagonal array structures. As such, hBN emerges as a significant contributor to adhesion and traction on ice due to its unique combination of hydrophobicity, wettability, surface area, hexagonal structure, and van der Waals forces. This is particularly important because friction at the shoe sole-ice interface arises from the shearing effect of adhesion rather than solely from the intrinsic friction of the shoe sole. Surface forces, which facilitate contact between bodies, involve adhesion at the micro or nano level. The increased surface-to-volume ratios at these scales amplify the significance of surface and adhesion forces compared to larger bodies. Effective adhesion to the ice results in a sufficient COF, thereby promoting slip prevention. Effective adhesion to the ice results in an adequate COF, thus promoting slip prevention. Several factors, particularly on icy or snowy surfaces, play a crucial role in influencing adhesion, including temperature, contact area, normal force (body weight), surface roughness, sliding speed, surface structure, topography, and wettability as illustrated in Figure 9A.

[0090] EXAMPLE 1

[0091] This Example provides empirical evidence of the significant impact of manufacturing processes and 2D fillers on material properties of polymer-based composites and their performance in practical applications.

[0092] This Example highlights the substantial benefits of composite materials incorporating a hybrid integration of microfibers and 2D fillers for ice friction. It underscores the advantages of additive manufacturing techniques in fabricating surface-textured composites that offer enhanced durability and frictional properties. The experimental findings demonstrate that additive manufacturing allows for control over fiber distribution and alignment which are important for engineering surface characteristics such as friction.

[0093] Data is reported below as an average value followed by the standard deviation (±SD) of the samples (n > 3). Statistical analysis for COF was done by considering two-sample t-test with a significance level set at p < 0.05.

[0094] As a general overview of this Example, Figure 10A is a flowchart of the fabrication and testing / characterizations of textured surface composites evaluated in this Example. Respective composite samples were prepared by compounding a few filler materials with TPU elastomer and CF-PBO fibers in specific ratios measured with an analytical balance scale 1001 then mixed with a speed mixer 1002. Test samples were then made from the respective blended formulations by injection molding 1003a, and further test samples were made by a FFF method 1003b. Subsequently, the samples were cut 1004 and abraded 1005 with an abrasion tester machine to expose the fibers located on each sample’s outer surface. Surface roughness was measured 1006 utilizing a profilometer. Scanning Electron Microscopy (SEM) 1007 was employed for the characterization of composite surface morphology, both before and after the abrasion process, with the primary objective being the analysis of protruding fibers. Coefficient of friction (COF) on ice was evaluated 1008 using a custom-made setup (see Figure 10B), and a comparison was drawn between the obtained values from the SATRA machine. Oily COF was measured utilizing a porcelain floor tile contaminated with canola oil. A whole-shoe slip-testing device was used with standard test methods.

[0095] Composite Formulations

[0096] A CF-PBO-TPU composite material was prepared that included 2D Graphene- nanoplatelets (GNP) (Cheap Tubes Inc, USA), hexagonal-Boron-Nitride (hBN) (Panadyne Inc, USA), styrene-butadiene-styrene (SEBS) (Milagro Rubber Company, Inc., Austin, TX, USA), Silica (Si) (Milagro Rubber Company, Inc., Austin, TX, USA), and Silicon-Carbide (SiC) (Sigma- Aldrich, Massachusetts, USA). The composition had CF: PBO fibers at 8 vol%. This resulted in 92 vol% for TPU and additional filler materials. Within each composition, there was a 98:2 weight ratio of TPU to filler material. Each compound underwent thorough mixing in a speed mixer (Hauschild Speed Mixer, Germany) at 2500 rpm for two minutes.

[0097] The separately prepared compounds were as follows: a) CF-PBO-TPU, b) CF-PBO-TPU- hBN, c) CF-PBO-TPU-GNP, d) CF-PBO-TPU-SEBS, e) CF-PBO-TPU-hBN+SEBS, f) CF- PBO-TPU-Silica, g) CF-PBO-TPU-SiC.

[0098] Injection Molding (IM) of Composite Samples

[0099] A house-made cylindrical mold with a diameter of 15.87 mm and a thickness of 38.1 mm was designed as described in: Islam S, Gide K, Dutta T, et al. The effect of tread patterns on slip resistance of footwear outsoles based on composite materials in icy conditions. Journal of Safety Research [Internet], 2023 [cited 2023 Nov 23]; S0022437523001196. Each compound mixture was added through a plastic injector (AB- 100 Plastic Injector, Canada) with a controlled temperature range of 224°C-242°C and a pressure of 758.42 kPa. Cylindrical samples were produced with a 31 mm length. The samples were cut into three pieces of 8 mm thickness using a bandsaw (Anbull Portable Bandsaw) to expose the embedded fibers to the surface.

[0100] Fused Filament Fabrication (FFF) of Composite Samples

[0101] Computer-aided-design (CAD) models and slices of the models were created using appropriate software. The mixed composite compound from the previous step was extruded through a filament extruder (Noztek Pro HT, England) at 240°C, with careful attention to maintaining a consistent filament diameter. The filaments were then employed in an FFF printer (LulzBot TAZ 6, USA) to produce composite samples as shown in Figure 10A. The nozzle dimension for the printer was 1 mm. Prior to printing, precise printer setup was considered to ensure the production of high-quality samples. The printing temperature, printing speed, layer height, and bed temperature were set at 240°C, 30 mm / s, 0.23 mm, and 60°C temperature, respectively. These selections were made based on initial printing to attain the optimal quality of the sample. Once the samples were fabricated, they were cut to a thickness of 8 mm using a bandsaw, exposing embedded fibers to the surface of the composite.

[0102] Abrasion Test and Abrasion Resistance Index (ARI)

[0103] The abrasion resistance of the IM-produced composites and FFF-produced composites were tested to assess potential for degradation during everyday use. Abrasion constitutes one of the primary wear mechanisms observed in outsoles, primarily due to the sliding motion involved in walking.

[0104] The abrasion test was conducted using a rotating drum abrasion tester (DIN Abrasion Tester NextGen Material Testing, Canada). Abrasion Resistance Index (ARI) was calculated to measure the abrasiveness of our composite samples with respect to standard rubber samples employing Eq. (I):

[0105] Asl * d2ARI = — — x 100 As2 * a-L

[0106] In this equation, Asi represented the change in mass (mg) for standard rubber, As2 denoted the change in mass (mg) for the composite, di was the density of standard rubber, and do was the density of the composite. Initially, samples were weighed, then placed in the test piece holder of the abrasion tester. The samples underwent abrasion by being held against an abrasion drum covered in 60-grit sandpaper for 1.5 cycles or 126 rotations, with a 10 N load applied, following the standard operating procedure of the abrasion tester machine. Throughout this process, a paintbrush was used to brush the sandpaper, removing any excess material ingrained in the sandpaper.

[0107] The abrasion resistance index (ARI) was calculated according to ASTM standards for abrasion resistance of rubber using rotary drum abrader, where the abrasion of the surface is determined by two competing factors: i) fragmentation, which increases wear, and ii) surface saturation with the wear particles. Figure 11 illustrates the ARI scores of the IM-produced composite samples and the FFF-produced composite samples. The abrasion test was conducted on the injection molding samples of all seven composites. Notably, samples containing CF-PBO- TPU-hBN exhibited higher ARI scores (133.83 ± 6.81%), while those with CF-PBO-TPU-Silica (68.3 ± 2.15%) and CF-PBO-TPU-SiC (102.55 ± 8.09%) showed lower scores. Due to their lower ARI scores, CF-PBO-TPU-Silica and CF-PBO-TPU-SiC were excluded from the comparative analysis with the additive manufacturing method.

[0108] Significantly higher ARI values were noted for a few of compositions when manufactured with additive manufacturing methods versus when manufactured by injection moulding. Among these, CF-PBO-TPU-GNP demonstrated the highest ARI score in FFF method (FFF: 155.4 + 6.73%; IM: 113.33 ± 9.96%; p - 0.019). Following closely, CF-PBO-TPU-hBN showed the second-highest ARI score in FFF method (FFF: 146.63 ± 3.39%; IM: 133.83 ± 6.81%; p = 0.036). ARI scores for CF-PBO-TPU-SEBS (FFF: 137.7 + 6.52%; IM: 129.36 ± 9.76%; p = 0.049) and CF-PBO-TPU-hBN+SEBS (FFF: 138.95 + 5.97%; IM: 133.31 + 6.33%; p = 0.049) exhibited a comparatively smaller difference between the two manufacturing methods.

[0109] Comparing different compositions against one another, composites made of CF-PBO- TPU-hBN+SEBS demonstrated a 6.45% increase in ARI scores compared to CF-PBO-TPU- SEBS in the FFF method. The composite reinforced with hBN and GNP showed an ARI increase of 6.5% and 12.85%, respectively, compared to the composite reinforced with SEBS in the same method. The ARI score for CF-PBO-TPU was observed to be (FFF: 112 ± 15.89%; IM: 106.06 ± 12.2%; p = 0.046).

[0110] In sum, a higher level of stability is observed in the ARI scores for samples produced through the FFF 3D printing process. Notably, all the average values consistently exceeded 112% in the FFF 3D printing process and remained above 106% in the injection molding method, as depicted in Figure 11.

[0111] Surface Morphology

[0112] The topography of the composite surface of each sample was examined both before and after an abrasion test under a leol JSM-7200F Field Emission Scanning Electron Microscope (SEM) (Musashino, Akishima, Tokyo). In preparation for SEM imaging, all samples were rendered conductive by applying a thin layer of gold coating using a Denton Vacuum Desk V sputter coater (Moorestown, New Jersey, USA) in a pure argon chamber for 15 seconds. Carbon and copper tape were used to secure the coated sample and ensure a grounding connection between the sample's surface and the stub holder. The imaging used 2.0 kV with several magnifications to capture images of the sample's surface. Figures 12 and 13 show the comparison between SEM images of the various composite samples before and after abrasion using FFF method and IM method. These images exhibit a considerable amount of fiber exposure to the surface following abrasion, which can potentially lead to retaining slip-resistant properties and maintain frictional performance over extended use. The alignment of fibers appears more uniform in the FFF method compared to the injection molding method. As depicted in Figure 13, the IM samples exhibit a patchy distribution of protruded fibers, indicated by circular indicia superimposed on the images, whereas the FFF samples display a more uniform distribution of fiber protrusion, marked by parallel arrow indicia superimposed on the images.

[0113] Ice Traction Test

[0114] Ice traction experiments were carried out using a custom apparatus, illustrated in Figure 10B, which involved the utilization of a universal testing machine (Test Resource Inc, Shakopee, Minnesota, USA). Manufactured composite samples were affixed to the underside of a custom additively manufactured sample holder. This holder was designed to include embedded metal weights, replicating the normal pressure experienced during walking on the testing sample. The sample holder was attached to the testing machine's crosshead with rigid wire. The setup of the wire was configured to allow only horizontal movement of the sample holder, preventing any rotation or transverse shifts. Multiple tests were conducted for each type of sample to ensure precision in results. Actuation and force measurements were performed using the machine's crosshead in tension mode. The ice tray was generated using deionized water and a Peltier plate to prevent it from melting. The ice tray was exposed to ambient conditions with a temperature range of 22-24°C and relative humidity ranging from 24% to 50%. Prior to each test, the surface of the ice was polished using smooth aluminum foil to prevent any potential frost formation. The loaded sample holder was positioned on the ice tray, with a very brief dwell time of less than Is, before initiating a shearing motion on the ice substrate. The test was executed at a consistent velocity of 0.3 m / s for 20 s. Throughout this process, the shear force (Fs) was continuously recorded at intervals of 2 milliseconds. Simultaneously, a constant normal load denoted as FN and measuring 22.3 N (equivalent to 112 kPa) was applied to the sample. This enabled the calculation of the static COF, determined as the ratio of Fs to FN as depicted in Figure 10B. Tests were conducted on each filler type using three distinct samples for at least five runs for each sample. To assess the effectiveness of the custom setup for measuring ice-friction properties, cross-validatc results were cross-validated with a SATRA machine commonly used for analyzing ice friction in footwear. For this purpose, additional testing was performed using SATRA STM 603 slip-resistance testing machine. The COF values were measured by applying a 500 N normal force, pressing the test material onto a test surface while moving the test surface with sliding velocities of 0.5 m / s horizontally. The normal force value was recommended by SATRA for use with men's shoes above 7.5, while a sliding speed value of 0.5 m / s was selected in accordance with ASTM F2913-11, and the recommendation of the SATRA STM 603 slip testing device. Samples were tested in contact with a 5 mm thick wet ice surface maintained between 4°C and 1°C for all ice friction tests. Comparisons were made for samples from the injection molding process.

[0115] Figure 14 presents the cross-validation of COF results obtained through the custom setup compared with the results obtained using a SATRA machine for injection molding samples, using regression analysis. The R-squared value of 0.92 indicates a notably high goodness of fit, suggesting that approximately 92% of the variability in the performance of the custom setup machine can be accounted for by SATRA machine data. This high goodness of fit indicates the reliability of the COF results obtained using the custom setup, especially considering the SATRA machine's common usage in analyzing ice friction in footwear (ASTM F2913-11. Standard Test Method for Measuring the Coefficient of Friction for Evaluation of Slip Performance of Footwear and Test Surfaces / Flooring Using a Whole Shoe Tester. Annual Book of ASTM Standards. 2011).

[0116] Table 1 summarizes the COF measurements for injection molded samples and FFF produced samples before and after abrasion. The results indicated that composites with hBN filler exhibited the highest COF compared to others. Composite samples from CF-PBO-TPU- GNP showed higher wear resistance but lower COF than CF-PBO-TPU-hBN. After abrasion, an increase in COF was observed across all samples. Silica and SiC-filled IM samples had COF values after abrasion averaging below 0.40. Table 1: COF data with standard deviation for composite samples

[0117] Figure 15 compares the COF results for FFF printed and injection molded samples following abrasion. It is evident that composites containing hBN filler exhibited higher COF values (FFF: 0.58 ± 0.04; IM: 0.54 ± 0.06; p = 0.043) than others for both methods. Furthermore, CF-PBO-TPU (p = 0.047) and composites combined with GNP (p = 0.041) demonstrated a significant increase in COF in the additive manufacturing method compared to their injection molded counterparts.

[0118] These improvements may be attributed to the enhanced fiber alignment and distribution achievable through FFF, which leads to an average increase of 7.31% in the COF on ice across all samples.

[0119] Oil Traction Test

[0120] Oil traction experiments were conducted on porcelain ceramic floor tiles contaminated with canola oil, utilizing the STEPS machine (XRDS Systems, LLC, Andover, MA, USA). The COF experiments were conducted using a normal force of 250 N, a shoe-floor angle of 17°, and a sliding speed of 0.5 m / s consistent with the state of the shoe at the initiating moment of a human slip. In this test method, the shoe maintains a constant sliding speed from foot contact through the measurement period. The force level is reached within 200 ms of shoe contact and maintained during a 50 ms measurement period. These conditions have been shown to predict human slipping. The tile (Crossville Vcnho Verde, unpolished sheen, Ra = 2.7 pm, Rq = 3.5 pm, Rp = 7.1 pm) was selected because it had friction performance near the mean of a sample of 17 porcelain tiles. Canola oil was selected as a contaminant since it represents a near worst-case scenario for indoor slippery substances and is moderately correlated with friction performance of other liquid contaminants (i.e., water and soapy solutions). In these experiments, plugs of composite material (15.87 mm diameter) were adhered to a shoe surface such that only the plugs made contact with the floor surface. COF was the mean ratio of friction to normal force averaged over the 50 ms measurement period. COF was averaged across three replicate trials for each composite material.

[0121] Figure 16 depicts the comparison of COF values post-abrasion for the five compositions produced via the FFF method. These compositions were selected for their performance, evidenced by enhanced roughness, abrasion resistance, and higher COF on ice. Moderate COF values were observed for all compositions manufactured using the FFF method on oily surfaces. Notably, CF-PBO-TPU-SEBS exhibited the highest COF values (0.14 ± 0.003) among them. As a reference point, prior research that considered the same floor surface and contaminant found that a high-performing slip-resistant shoe had a COF of 0.31, a low-performing slip-resistant shoe had a COF of 0.05, a high-performing non slip-resistant shoe had a COF of 0.13 and a low- performing non slip-resistant shoe had a COF of 0.03 (Randolph AB, Reifler K, Chadha V, et al. The need for better metrics for floor-tile topography: Conventional metrics correlate only modestly with shoe-floor friction. Tribology International. 2024; 109366). While the measured values of these composite materials did not perform as well as high-performing slip-resistant shoe (one that is specifically designed for oily environments), it performed better than low- performing shoes and some of the composite materials (a, b, d, and e) performed similarly to a high performing non slip-resistant sole. Composites effective on icy surfaces did not necessarily perform well on oily surfaces, indicating that performance on one type of slippery surface does not guarantee performance on another. On the other hand, the composite sample with SEBS exhibited moderate performance on oily surfaces, surpassing all other tested samples, which can be related to the properties of SEBS, which exhibits moderate friction on oily surfaces. Roughness Test

[0122] To assess the degree of surface texturing and validate the visual observations derived from the SEM images, the surface roughness of all the composite surfaces was measured using a linear surface profilometer (DektakXT, Bruker, Billerica, USA). The profilometer was equipped with a 2-micron diamond probe tip and employed a scanning area of 1mm x 1mm for each sample. The surface roughness of all the composite surfaces was measured / quantified by the roughness (Ra) value, representing the arithmetic average of the absolute values of the roughness peaks. The Ra roughness values were recorded for the composite surface of each sample after abrasion. Table 2 summarizes the roughness results for the injection molded samples versus the FFF printed samples.

[0123] Table 2: Roughness values for composite samples

[0124] Formulation IM Sample FFF Sample

[0125] Roughness (pm) Roughness (pm)

[0126] CF-PBO-TPU 19.00 ± 1.50 21.75 ± 3.22

[0127] CF-PBO-TPU-hBN 24.50 ± 2.80 26.13 ± 2.80

[0128] CF-PBO-TPU-GNP 22.49 ± 1.43 23.68 ± 1.63

[0129] CF-PBO-TPU-SEBS 19.03 ± 3.92 20.97 ± 3.17

[0130] CF-PBO-TPU-hBN+SEBS 20.30 ± 1.26 22.15 ± 1.75

[0131] CF-PBO-TPU-Silica 14.44 + 0.31

[0132] CF-PBO-TPU-SiC 16.74 ± 1.99

[0133] Figures 17 and 18 compare the roughness results of the IM and FFF samples. Elevated Ra values were evident in additively manufactured samples manufactured through the FFF method for all types of composites. Notably, these samples displayed a lower standard deviation, signifying greater uniformity in surface roughness. It should be noted that regardless of the manufacturing method, composite samples containing hBN filler consistently displayed higher roughness values (FFF: 26.13 ± 2.80, IM: 24.5 ± 2.80) compared to others. This observation highlights the significant influence of hBN filler on the surface characteristics of composites across both fabrication techniques.

[0134] Surface Wettability Test

[0135] Hydrophobicity, measured by contact angle, depends on surface morphology and surface chemistry that may influence ice friction properties. In order to understand how hydrophobicity may affect ice friction properties and surface roughness, we measure the contact angle of the samples were measured and compared. To evaluate the contact angle, four distilled water droplets (6 pL each) were placed at different locations on the sample surfaces using an adjustable-volume pipette (Four E’S Scientific). Images of the droplets were captured within 10 seconds at room temperature. Contact angle analysis was subsequently performed using ImageJ and the contact angle plugin. The plugin procedure involves defining two baseline points and three edge points, through which the software estimates the droplet shape as an ellipse of best fit. The left and right contact angles are averaged and reported in accordance with the standard.

[0136] To further explore the effect of surface roughness on contact angles, the Wenzel model was applied. This model explains how surface roughness modifies the apparent contact angle by accounting for the increased contact area between the liquid and the rough surface. The Wenzel equation is expressed in Eq. (II): cos (0W) = r X cos (9) (II)

[0137] Where 0Wrepresents the apparent contact angle on the rough surface, 9 denotes the intrinsic contact angle on a smooth surface, and r is defined as the roughness factor, representing the ratio between the actual surface area and the projected area.

[0138] Figure 19A illustrates the contact angles of five different composites in relation to their coefficient of friction (COF), all produced through the additive manufacturing process. Notably, the hBN-reinforced composite exhibited higher contact angles compared to the other composites. Despite this, as shown in Figure 19A, no direct correlation was found between the contact angle and COF of the studied composites. Figure 19B delves deeper into the relationship between surface roughness and hydrophobicity. It was observed that increased surface roughness at the droplet-solid interface tends to enhance hydrophobicity (indicated by contact angles greater than 90 degrees). However, this increase in hydrophobicity was not entirely linear. As the contact angle rises, indicating a more hydrophobic surface, the wettability correspondingly decreases. Furthermore, Figure 19C highlights the correlation between wettability and surface characteristics, including roughness. It demonstrates that surfaces with greater roughness tend to exhibit higher contact angles, thereby reducing wettability. Lastly, Figure 19D illustrates the relationship between the contact angle of the samples after abrasion and those obtained using the Wenzel model through regression analysis. The R-squared value of 0.90 indicates a strong goodness of fit, suggesting that approximately 90% of the variability in the experimental data can be explained by the Wenzel model. This complex interplay between surface roughness, hydrophobicity, and wettability underscores the importance of surface characteristics in determining the behavior of composite materials in contact with liquids.

[0139] EXAMPLE 2

[0140] This Example details fabrication of an exemplary composite by a stereolithographic (SLA) printing process.

[0141] CF-PBO fibers, ranging from 1% to a higher percentage by volume, along with an additional filler material (2% volume), were combined with TPU and an equivalent quantity of durable Acrylonitrile Butadiene Styrene (ABS)-like resin. The ABS-like resin made the blended composition suitable for use with an SLA printer. The blended composition performed as a photopolymer resin. TPU, in its original state, is not inherently a photopolymer resin. Filler volume percentage in the formulation was 3% (less than may be used in an FFF process, e.g., an a formulation intended for FFF production may have a filler volume percentage of or about 8%). The reason for this adjustment is that having an 8 % filler inside the vat would significantly increase the viscosity, making it impractical to use with SEA. Hence, opting for a lower filler percentage became necessary. The blending of fibers, polymers, and filler(s) was thoroughly achieved using a magnetic stirrer (IKA-Werke GmbH & Co. KG) before the blended formulation was poured into a vat of the printer. The printing apparatus included means for control over fiber orientation at various angles, including 0 degrees, 90 degrees, alternating (0- 90-0 pattern, etc.), and no orientation. During the printing process, the alignment of fibers was manipulated using electromagnets. The 3D object to be printed was first prepared as a CAD model which was then sliced using commercially available slicing software.

[0142] Some of the fibers in the blend were configured to react to magnetic forces. Pure CF- PBO fibers are non-metallic, which poses a challenge when manipulating them with electromagnets. After the printing was completed, the object was immersed in alcohol for a thorough bath and then subjected to curing under UV light for a minimum of five minutes. Subsequently, the sample was precisely cut at the desired height to expose the unidirectional protruded fibers.

[0143] Where a range of values is provided in this disclosure, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges and arc also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the invention.

[0144] Unless defined otherwise, all 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. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention, representative illustrative methods and materials are described.

[0145] It is noted that, as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely,” “only” and the like in connection with the recitation of claim elements, or use of a “negative” limitation.

[0146] As will be apparent to those of skill in the ail upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present invention. Any recited method can be carried out in the order of steps recited or in any other order which is logically possible. Alternative methods may combine different elements of specific detailed methods described above and in the figures.

[0147] While exemplary embodiments of the present invention have been disclosed herein, one skilled in the ail will recognize that various changes and modifications may be made without departing from the scope of the invention as defined by the appended claims.

Claims

CLAIMSWhat is claimed is:

1. A 3D printed polymer-based composite, comprising one or more polymers; one or more 2D materials blended with the one or more polymers; and embedded fibers of one or more fiber types.

2. The 3D printed polymer-based composite of claim 1, wherein at least one external surface of the polymer-based composite is configured so that some of the embedded fibers protrude out from the at least one external surface.

3. The 3D printed polymer-based composite of claim 2, wherein the coefficient of friction of the at least one external surface is at least 0.4, at least 0.5, or at least 0.6.

4. The 3D printed polymer-based composite of any of the preceding claims, wherein the fiber types comprise carbon fiber (CF) and poly(p-phenylene-2,6-benzobisoxazole) (PBO) fiber.

5. The 3D printed polymer-based composite of any of the preceding claims, wherein the one or more 2D materials comprise one or more of 2D graphene nanoplatelets (GNP) and hexagonal boron nitride (hBN).

6. The 3D printed polymer-based composite of any of the preceding claims, wherein the one or more polymers include one or more of a thermoplastic, a photocurable resin, and styrene - ethylene-butylene-styrene (SEBS).

7. The 3D printed polymer-based composite of any of the preceding claims, wherein the one or more polymers include thermoplastic polyurethane (TPU) and / or acrylonitrile butadiene styrene (ABS).

8. A method of producing a surface-textured composite, comprising blending fibers of one or more fibers types, one or more polymers, and one or more 2D materials;3D-printing an object from the blend material; and exposing some of the fibers embedded in the 3D-printed object.

9. A polymer-based composite produced by the method of claim 8.

10. A method of producing a surface-textured composite, comprising blending fibers of one or more fibers types, one or more polymers including at least one thermoplastic, and one or more 2D materials; extruding the blend into a filament;3D-printing an object from the filament; and exposing some of the fibers embedded in the 3D-printed object.

11. The method of claim 10, further comprising configuring orientation settings for the 3D- printing to maximize unidirectional fiber orientation of the fibers embedded in the 3D-printed object.

12. The method of claim 10 or 11, wherein the fibers comprise CF-PBO fibers.

13. The method of claim 12, wherein the blending step maintains a 2:1 weight ratio of CF:PBO.

14. The method of any of claims 10-13, wherein the step of 3D-printing is fused filament fabrication (FFF).

15. The method of any of claims 10-14, wherein the step of exposing comprises one or more of cutting and abrading.

16. A surface-textured composite, produced by the method of any of claims 10-15.

17. A method of manufacturing a surface-textured composite, comprising3D-printing an object from a mixture comprising metallic or metallic-coated fibers, one or more 2D materials, and one or more polymers including at least one photocurable polymer; manipulating fiber orientation of the metallic or metallic-coated fibers during the 3D- printing to maximize unidirectional fiber orientation of the fibers embedded in the 3D-printed object; curing the 3D-printed object; and exposing the metallic or metallic-coated fibers embedded in the 3D-printed object.

18. The method of claim 17, wherein the step of 3D-printing is performed with a stereolithography apparatus (SLA).

19. The method of claim 17 or 18, wherein the step of manipulating fiber orientation comprises applying a magnetic field.

20. A surface-textured composite, produced by the method of any of claims 17-19.

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