Thermoplastic polymer-coal char composites

Abstract

Embodiments described herein generally relate to a new class of high density polyethylene (HDPE)-coal char composites. In an embodiment is provided a composite that includes HDPE and coal char. Articles of manufacture comprising such composites are also described. The coal char may be used in polymer composites as, for example, a functional filler. The coal char may significantly increase the flexural and tensile properties as well as the thermal stability of the HDPE matrix.

Description

Thermoplastic Polymer-Coal Char CompositesFIELD

[0001] Embodiments described herein generally relate to a new class of composites that include a thermoplastic polymer and coal char.BACKGROUND

[0002] There is significant interest in finding sustainable and environmental- friendly applications for coal and coal-derived products. Coal has been employed as a feedstock to prepare specialty materials, such as graphene, carbon fiber, carbon nanotubes, activated carbon, carbon electrodes, and as a feedstock in rare earth element extraction. Carbon nanotubes from pyrolysis of coal have been investigated. The development of graphene and graphene oxide from low-grade coal, such as Powder River Basin coal, as well as the coal extracts as the polyol component for polyurethane coatings, have been investigated. However, conversion of coal to these products requires several stages of treatments and different chemical reagents at high temperatures and pressures.

[0003] There is a need for new composites containing coal char. There is also a need for applications of coal with minimum treatment or processing operations.SUMMARY

[0004] Embodiments described herein generally relate to a new class of composites that include a thermoplastic polymer and coal char. Such composites are also referred to herein as thermoplastic-coal char composites. The coal char may be utilized as a functional filler for the composites. The coal char may significantly increase the flexural and tensile properties as well as the thermal stability of the thermoplastic polymer matrix, suggesting its dual role as a reinforcement and thermal stabilizer in polymeric compounds. The coal char is less processed than conventional coal-based materials. That is, unlike conventional approaches which utilize heavily processed coalbased materials requiring several treatment stages and different chemical reagents at high temperatures and pressures, embodiments described herein utilize coal char.

[0005] In an embodiment, a composite is provided. The composite comprises a thermoplastic polymer and coal char.

[0006] In another embodiment, a method of forming a thermoplastic-coal char composite is provided. The method includes extruding a mixture comprising a thermoplastic polymer and coal char to form a composite described herein.

[0007] In another embodiment is provided an article of manufacture that includes a composite described herein.

[0008] In another embodiment is provided a floor panel that includes a composite described herein.

[0009] In another embodiment is provided a decking board that includes a composite described herein.

[0010] In another embodiment is provided a pipe that includes a composite described herein.

[0011] In another embodiment is provided a plastic part that includes a composite described herein.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] So that the manner in which the above recited features of the present disclosure may be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments and are therefore not to be considered limiting of its scope, and may admit to other equally effective embodiments.

[0013] FIG. 1A shows exemplary differential scanning calorimetry (DSC) heating curves of high density polyethylene (HDPE) and example HDPE-coal char composites according to at least one embodiment of the present disclosure.

[0014] FIG. IB shows exemplary DSC cooling curves of HDPE and example HDPE-coal char composites according to at least one embodiment of the present disclosure.

[0015] FIG. 2A shows exemplary flexural strength and modulus data of HDPE and example HDPE-coal char composites according to at least one embodiment of the present disclosure.

[0016] FIG. 2B shows exemplary data for the dependency of flexural behavior on the crystallization degree of HDPE and example HDPE-coal char composites according to at least one embodiment of the present disclosure.

[0017] FIG. 2C shows exemplary tensile strength and modulus data of HDPE and example HDPE-coal char composites according to at least one embodiment of the present disclosure.

[0018] FIG. 2D shows exemplary data for the comparison of example HDPE-coal char composites with commercial wood-plastic composite boards and HDPE-coal composites according to at least one embodiment of the present disclosure.

[0019] FIG. 3 A shows exemplary data for the dependency of complex viscosity on the angular frequency of HDPE and example HDPE-coal char composites according to at least one embodiment of the present disclosure.

[0020] FIG. 3B shows exemplary data for the dependency of storage modulus on the angular frequency of HDPE and example HDPE-coal char composites according to at least one embodiment of the present disclosure.

[0021] FIG. 3C shows exemplary data for the dependency of loss modulus on the angular frequency of HDPE and example HDPE-coal char composites according to at least one embodiment of the present disclosure.

[0022] FIG. 3D shows exemplary data for the dependency of tan 5 on the angular frequency of HDPE and example HDPE-coal char composites according to at least one embodiment of the present disclosure.

[0023] FIG. 4A shows exemplary curves for the storage and loss moduli of HDPE and example HDPE-coal char composites according to at least one embodiment of the present disclosure.

[0024] FIG. 4B shows exemplary data for cross-over frequency as a function of coal char content according to at least one embodiment of the present disclosure.

[0025] FIG. 5A shows exemplary thermogravimetric analysis (TGA) curves of HDPE and example HDPE-coal char composites according to at least one embodiment of the present disclosure.

[0026] FIG. 5B shows exemplary TGA curves of HDPE and example HDPE-coal char composites according to at least one embodiment of the present disclosure.

[0027] FIG. 5C shows exemplary derivative thermogravimetric (DTG) curves of HDPE and example HDPE-coal char composites according to at least one embodiment of the present disclosure.

[0028] FIG. 5D shows exemplary DTG curves of HDPE and example HDPE-coal char composites according to at least one embodiment of the present disclosure.

[0029] FIG. 6 shows exemplary TGA curves of example HDPE-coal char composites and comparative examples according to at least one embodiment of the present disclosure.

[0030] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.DETAILED DESCRIPTION

[0031] Embodiments described herein generally relate to a new class of thermoplastic-coal char composites. Such composites may be utilized for a variety of applications including decking boards, floor panels, pipes, and plastic parts, among others.

[0032] The inventors found that coal char, which is a product of, e.g., coal pyrolysis, may be utilized in composites as, for example, a functional filler. As a functional filler in composites, the inventors found that the coal char may serve as a reinforcement and / or as a thermal stabilizer to the thermoplastic polymer.

[0033] The use of headings is for purposes of convenience only and does not limit the scope of the present disclosure. Embodiments described herein may be combined with other embodiments.

[0034] Coal is a naturally occurring, carbon-rich material that has been the engine of economic growth for many decades. Although it is employed in production processes of many products such as cement and metals, it is mainly used as an affordable source for generation of electricity. Coal consumption is continuously declining as some plants in the U.S. and Europe are retiring. For instance, combustion of coal for power in the U.S. shows a decrease of approximately 50% in the period of 2007 to 2019. This decrease is attributed to the severe impacts of coal on the environment and associated health risks. Here, coal burning is a significant contributor to global warming, contributing 40% of carbon dioxide emissions from energy use which causes more than 0.3°C of the 1°C increase in global average temperature. Coal-based power plants also emit large quantities of toxins and pollutants, including nitrogen oxides, sulfur dioxide, heavy metals (nickel, mercury, lead, cadmium, etc.), which can end up in the atmosphere, water sources, and landfills, leading to health issues such as asthma and cancer. At the same time, natural gas has become more affordable and the market share of renewable sources of energy has increased.

[0035] As a consequence, defining sustainable and environmental-friendly ways to utilize coal is of a significant interest. Coal has been employed as a feedstock to preparespecialty materials, such as graphene, carbon fiber, carbon nanotubes, activated carbon, carbon electrodes, and to extract rare earth elements. The development of graphene and graphene oxide from low-grade coal, such as Powder River Basin, as well as the coal extracts as the polyol component for the polyurethane coatings, have been investigated. However, conversion of coal to these products requires several stages of treatments and different chemical reagents at high temperatures / pressures. Therefore, there is a need for applications of coal-derived products at large scales and where the coal-derived product is made with minimum treatment or processing operations.

[0036] To this end, the inventors demonstrate use of coal-based materials as, for example, a reinforcement / filler to thermoplastic polymers. Advantageously, this novel composite — a thermoplastic-coal char composite — is free of those issues / challenges described for the conversion of coal to other coal-based products. Thermoplastic-coal char composites described herein may be utilized as a replacement for wood-plastic composites (or other composites) used for decking applications (or other applications). Here, for example, it was found that composites described herein show improved properties — such as mechanical, physical, melt viscoelastic, and thermal behavior — over conventional composites.

[0037] Embodiments of the present disclosure generally relate to composites. The composite includes a thermoplastic polymer and coal char. Optionally, composites described herein may include one or more additives. Additives may include, but are not limited to compatibilizers. When the composition includes a compatibilizer, the compatibilizer may be present in an amount that is from greater than 0 wt% to about 0.1 wt% or less of compatibilizer based on a total weight of the composite.

[0038] In some embodiments, which may be combined with other embodiments, composites described herein may be free of added compatibilizer, free of added flame retardant, or free of added compatibilizer and free of added flame retardant.

[0039] Coal char is a residue obtained from the pyrolysis of coal. Any suitable coal char may be utilized with embodiments described herein. For example, coal may be sourced from, e.g., Powder River Basin (PRB) (a subbituminous coal), and then subjected to pyrolysis at suitable temperatures such as from about 600°C to about l,000°C, such as from about 700°C to about 900°C, such as about 850°C. The coal char may be pyrolyzed for any suitable time such as about 24 hours or less, such as about 12hours or less, such as about 8 hours or less, such as about 5 hours or less, such as about 3 hours or less, such as about 2 hours or less, such as about 1 hour or less.

[0040] Others types of coal char are contemplated. For example, coal char that may be used includes, but is not limited to, coal char prepared by flash pyrolysis. Coal char produced by flash pyrolysis may be prepared by heating coal at a temperature that is from about 600°C to about l,000°C for a duration of about 1 hour or less, such as about 5 minutes or less, such as about 30 seconds or less, such as about 5 seconds or less, such as about 1 second. In some embodiments, which may be combined with other embodiments, the flash pyrolysis coal char may be made with the aforementioned flash pyrolysis in addition to a pre-pyrolysis operation. Pre-pyrolysis operations may have a duration of about 15 minutes and may be any suitable pre-pyrolysis operation.

[0041] Coal char useful for composites described herein may include flash pyrolysis coal char. Flash pyrolysis coal char is made with significantly shorter pyrolysis times than, at least, metallurgical coke and petroleum coke.

[0042] Coal char useful in composites described herein may have any suitable particle size. For example, coal char may have an average particle size that is about 100 pm or less, such as about 80 pm or less, such as about 60 pm or less, such as about 40 pm or less, such as about 20 pm or less, such as about 10 pm or less, such as about 5 pm or less, such as from about 1 pm to about 2 pm, though other sizes are contemplated. Any of the foregoing numbers may be used singly to describe an open-ended range or in combination to describe a close-ended range.

[0043] One or more types of coal char may be utilized for composites described herein. For example, the coal char used with composites of the present disclosure may be polydisperse such that particles of the coal char are not of the same size but of different sizes.

[0044] An amount of coal char in composites described herein may be from about 1 wt% to about 99 wt%, such as from about 5 wt% to about 80 wt%, such as from about 10 wt% to about 60 wt%, such as from about 15 wt% to about 55 wt%, such as from about 20 wt% to about 50 wt%, such as from about 25 wt% to about 45 wt%, such as from about 30 wt% to about 40 wt%, or from about 20 wt% to about 70 wt%, or about 40 wt% or more, such as from about 40 wt% to about 80 wt%, such as from about 40 wt% to about 60 wt%, based on a total amount of coal char and thermoplastic polymer in the composite, the total amount of coal char and thermoplastic polymer in thecomposite not to exceed 100 wt%. Other amounts are contemplated. Any of the foregoing numbers may be used singly to describe an open-ended range or in combination to describe a close-ended range.

[0045] Alternatively, coal may be utilized in composites described herein instead of coal char. Alternatively, coal char and coal may be utilized in composites.

[0046] Any suitable thermoplastic polymer may be utilized for composites described herein. Suitable thermoplastic polymers include those prepared by polymerization of olefin-containing monomers. Suitable thermoplastic polymers may include a polyethylene (such as HDPE), polypropylene (PP), acrylonitrile butadiene styrene (ABS), nylon, polyvinyl chloride, or combinations thereof.

[0047] When the thermoplastic polymer of composites described herein includes HDPE, the HDPE may have a density that is greater than about 0.940 g / cm3. HDPE utilized for embodiments described herein may have a density that is from greater than about 0.940 g / cm3to about 0.980 g / cm3or less, such as from about 0.945 g / cm3to about 0.97 g / cm3, such as from about 0.95 g / cm3to about 0.965 g / cm3, such as from about 0.955 g / cm3to about 0.96 g / cm3, or from about 0.96 g / cm3to about 0.965 g / cm3, or from about 0.96 g / cm3to about 0.97 g / cm3, such as about 0.965 g / cm3, though other densities are contemplated. Any of the foregoing numbers may be used singly to describe an open-ended range or in combination to describe a close-ended range.

[0048] When the thermoplastic polymer of composites described herein includes HDPE, the HDPE may have any suitable melt flow index (MFI, 190°C / 2.16 kg). For example, the HDPE may have a melt flow index that is from about 1 g / 10 min to about 10 g / 10 min, such as from about 2 g / 10 min to about 9 g / 10 min, such as from about 3 g / 10 min to about 8 g / 10 min, such as from about 4 g / 10 min to about 7 g / 10 min, such as from about 5 g / 10 min to about 6 g / 10 min, or from about 5 g / 10 min to about 10 g / 10 min, such as from about 7 g / 10 min to about 9 g / 10 min, such as from about 8 g / 10 min to about 8.5 g / 10 min, such as about 8.3 g / 10 min, though other MFIs are contemplated. Any of the foregoing numbers may be used singly to describe an open- ended range or in combination to describe a close-ended range.

[0049] One or more types of HDPE may be utilized for composites described herein.

[0050] The composites may include any suitable amount of thermoplastic polymer. An amount of thermoplastic polymer (such as HDPE) in composites described hereinmay be from about 40 wt% to about 90 wt%, such as from about 45 wt% to about 85 wt%, such as from about 50 wt% to about 80 wt%, such as from about 55 wt% to about 75 wt%, such as from about 60 wt% to about 70 wt%, or from about 30 wt% to about 80 wt%, or about 60 wt% or less, such as from about 20 wt% to about 60 wt%, such as from about 40 wt% to about 60 wt%, based on the total amount of coal char and thermoplastic polymer in the composite. Other amounts are contemplated. Any of the foregoing numbers may be used singly to describe an open-ended range or in combination to describe a close-ended range.

[0051] Embodiments described herein may be utilized for a variety of applications and uses. Non-limiting applications or uses of thermoplastic-coal char composites described herein may include decking boards, floor panels, pipes, and plastic parts. Other applications are contemplated. Here, for example, composites described herein may be used instead of articles conventionally manufactured using thermoplastic polymers alone, such as those articles conventionally manufactured using polyethylene, PP, ABS, or nylon alone. In addition, composites described herein may be used in applications where carbon black, carbon, and / or glass fiber are conventionally utilized, such as automotive and industrial applications.

[0052] Composites described herein may be useful for applications where strength and / or rigidity characteristics are desired, but not necessarily flexibility. However, it is contemplated that composites described herein may be useful for applications where flexibility is desired.

[0053] The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to make and use aspects of the present disclosure, and are not intended to limit the scope of aspects of the present disclosure. Efforts have been made to ensure accuracy with respect to numbers used (e.g. amounts, dimensions, etc.) but some experimental errors and deviations should be accounted for.Examples

[0054] Thermoplastic-coal char composites were made using HDPE and coal char. Properties of the thermoplastic-coal char composites were determined. Comparative examples included commercial HDPE-wood fiber composites (wood-plastic (WP) composites). These WP composites included FiberOn, Trex, and Timbertech.1. Materials1.1. HDPE

[0055] High-Density Polyethylene (HDPE) was purchased from Dow Chemical Company (USA). The Melt Flow Index (MFI) and the density of this HDPE resin are about 8.3 g / 10 min (190°C / 2.16 kg) and about 0.965 g / cm3, respectively.1.2. Coal Char

[0056] Pyrolysis coal char. Coal char used for the examples was obtained from Atlas Carbon LLC (WY, USA). This coal char was prepared via pyrolysis: by heating subbituminous coal from the Cordero Rojo mine, Wyoming, USA, in a batch process at a temperature of about 850°C for a few hours. The final process atmosphere was inert. The received coal char was ball-milled and sieved to achieve a particle size of sub 40 microns.

[0057] Flash pyrolysis coal char. One example composite was made with 60 wt% HDPE and 40 wt% flash pyrolysis coal char (HDPE / FPCC40). The coal char for this example was prepared by flash pyrolysis: heating subbituminous coal from the Cordero Rojo mine, Wyoming, USA at 1000°C for 5 s. The HDPE / FPCC40 coal char was determined to have a flexural strength of about 38.4 MPa, a flexural modulus of about 2.1 GPa, a tensile strength of about 22.4 MPa, and a tensile modulus of about 2.2 GPa. This example demonstrates the general applicability of flash pyrolysis coal char for use in thermoplastic-coal char composites.2, Processing and Molding of the Composites

[0058] Prior to melt-processing, the coal char and the HDPE were dried in a vacuum oven / oven for about 12h at about 80°C and about 4h at about 70°C, respectively. The composite components were mixed in a single screw extruder (Filabot EX6, Filabot, USA) at a barrel temperature of 190-210°C and then pelletized. Example HDPE-coal char composites containing from about 20 wt% to about 50 wt% of the filler (coal char) were prepared and designated as HDPE / CCX, where “CC” refers to coal char and “X” refers to the weight percent of the coal char. For example, HDPE / CC40 refers to an HDPE-coal char composite containing 60 wt% HDPE and 40 wt% coal char based on the total amount of HDPE and coal char in the composite.

[0059] A micro-injection molding machine (Xplore IM 12, Xplore, Netherlands) was employed to prepare dumbbell-shaped (as per ASTM D638, type V) and rectangular (125mm by 12.7mm by 3.2mm) specimens for tensile and flexural testing. Barrel / transfer mold and mold temperatures were 220°C and 40°C, respectively. Thepure HDPE sample was melt-processed, and injection molded according to the same procedure mentioned above.3. Characterization

[0060] Mechanical Testing. Mechanical performance of the samples was investigated using a universal testing machine (ZwickRoell Z020). Tensile and flexural tests were performed at a crosshead speed of 3 mm / min (according to ASTM D638) and a speed of 10 mm / min (as per ASTM D790), respectively. Five specimens were tested for each formulation and the average number was reported.

[0061] Differential scanning calorimetry (DSC). Melting and crystallization behavior of the HDPE and the HDPE / CC composites were investigated using a DSC 250 machine (TA instruments, USA). The samples (5-6 mg) were heated from ambient temperature to 180°C, subjected to an isothermal heating at 180°C for 5 minutes to eliminate any thermal history, cooled to ambient temperature, then held at this temperature for 5 minutes, and finally reheated to 180°C. DSC runs were carried out under an N2 environment at a rate of 10°C / min. The degree of crystallinity (Xc) of HDPE in the samples was calculated according to the following Equation 1 : 100 (Equation 1)wherein: Xcrefers to degree of crystallinity AHmrefers to fusion enthalpy of HDPE in the samples; AH,)) refers to fusion enthalpy of 100% crystalline HDPE (293 J / g); and COHDPE refers to weight fraction of HDPE in the composites.

[0062] Rheology. Melt viscoelastic behavior of the samples was evaluated with a TA Instruments rheometer (ARES-G2, TA instruments, USA) using a 25 mm parallel plate configuration and a gap of 1 mm at 210°C under N2 atmosphere. First, a strain sweep run was conducted at an angular frequency of 1 rad / s to determine the linear viscoelastic region (LVR). Then, angular frequency sweep (0.1-600 rad / s) measurements were performed at a strain amplitude of 0.1%. Prior to these experiments, the molten samples were heated isothermally for 5 minutes to erase any thermal and deformation history.

[0063] Thermogravimetric analysis (TGA). To analyze the thermal stability / degradation of the control polymer and the composites, a TGA Q500 thermal analyzer (TA instruments, USA) was used. The tests were conducted under two different environments at a scan rate of 10°C / min at three steps: 1) Argon: The samples were heated from ambient temperature to 900°C, held at 900°C for 2 minutes, andcooled to 750°C, followed by switching to the second gas. 2) Oxygen: heating cycle to 850°C, followed by switching back to the first gas. 3) Argon: cooling the furnace.4, Non-Limiting Results4.1. Melting / Crystallization Behavior

[0064] Studies of melting / crystallization behavior of the composite system provided insight into the influence of fillers / additives on the final performance of the composite. Heating-cooling-heating cycles were performed on pure HDPE and example HDPE-coal char composites using DSC. The obtained DSC curves are presented in FIGS. 1A and IB. Selected characteristic parameters — e.g., melting and crystallization parameters — of HDPE alone and example HDPE-coal char composites are shown in Table 1.Table 1

[0065] The melting temperature (Tm) of the pure HDPE was 134.6°C, while the composites showed a marginal change with the addition of the coal char, suggesting that the crystal morphology of the polymer matrix was not affected in the presence of the filler. The DSC cooling curves, shown in FIG. IB, clearly revealed a progressive shift of the onset temperature (Tc-onset) of crystallization and crystallization peak temperature (Tc-peak) of the HDPE phase to higher temperatures upon increase in the coal char content. In addition, the degree of crystallinity (Xc) of the HDPE was also significantly influenced by the coal char. For example, Xc of the pure HDPE polymer was 67.6%, while the degree of crystallinity increased to about 71.7%, about 77.7%, and about 84.4% as the coal char weight percent increased to about 20 wt%, about 30 wt%, and about 40 wt%, respectively. For pure HDPE, the catalyst residues are the main contributor to the nucleation, while upon incorporating of the coal char into theHDPE, the filler may increase the number of nucleation sites because it may act as a heterogeneous nucleating agent in the crystallization process. In fact, nucleation of the HDPE may be facilitated by absorbing the polymer chains on the surface of the coal char particles which lowers the crystallization free energy, leading to the growth of a large number of crystals. These results may also indicate the appropriate dispersion of the filler within the matrix as well as the strong interaction between the composite components.

[0066] The crystallization behavior of HDPE in the presence of coal char observed in this work was unexpected because reports have suggested that other common carbonbased fillers such as graphene, graphene oxide, and carbon nanotubes generally decrease the degree of crystallinity in the HDPE composites. Some have attributed this phenomenon to a hinderance effect of the nanofiller on the chain mobility, which suppresses crystal growth. Thus, the coal char particles in HDPE composites described herein may play the role of a heterogeneous nucleating agent (which means less cooling for crystallization), without any negative effect on the perfection of crystallites.4.2. Mechanical Properties

[0067] Mechanical behavior of the HDPE composites reinforced with the coal char was investigated and indicated that embodiments described herein may replace conventional wood-plastic composites. Here, flexural and tensile testing on the samples was performed.

[0068] The flexural strength and modulus of HDPE-coal char composites are shown in FIG. 2A. A noticeable increasing trend was observed in the flexural strength by adding coal char to the HDPE polymer, especially at high loadings. A similar trend was observed for the flexural modulus. For example, the example HDPE / CC50 composite showed a -60% and -178% higher strength and modulus, respectively, compared to the unfilled resin. It is surprisingly a considerable improvement in the flexural behavior of a polymer system. This result may be attributed to two contributions: First, the physical interactions between the polymer chains and the coal char. In fact, the carbon-based filler may have a fine compatibility with the non-polar HDPE, which in turn facilitates the formation of the interfacial adhesion between two phases, preventing crack propagation. Second, the role of the filler in enhancing the crystallization degree of the HDPE, as described above. In other words, higher crystallinity signifies higher mechanical properties as shown in FIG. 2B.

[0069] The tensile strength of the example composites is shown in FIG. 2C. The tensile strength was found to increase by adding up to about 40 wt% coal char, indicating that the tensile stress applied to the example HDPE-coal composite may be appropriately transferred from the HDPE phase to the coal char particles. The Young’s moduli of the example composites were much higher (about 75%) over the pure polymer, showing their high stiffness.

[0070] Comparison of the mechanical behavior of the example HDPE-coal char composites with those reported elsewhere may provide insight into the efficiency of different coal-derived materials. It has been reported that adding a low amount (10 wt%) of a bituminous coal, containing about 92 % carbon, led to a decline of 23.3% in the flexural strength of epoxy-based composites. Others have reported a slight increase in the tensile strength upon incorporating up to 10 parts of a subbituminous coal to soy protein, followed by a decrease in higher filler contents. Others have prepared polyethylene (PE) composites containing 60 wt% of two different grades of coal and reported a 29.9% and 100% improvement in the flexural strength and modulus, respectively, over virgin PE. It has also been shown that the tensile strength of the composites was inversely proportional to the weight fraction of the coals used.

[0071] These previous reports are unlike the increase in the tensile strength observed in the present study. FIG. 2D illustrates flexural properties of example HDPE- coal char composites according to embodiments described herein, comparative example HDPE-coal composites, and commercial wood-plastic composite boards (used for decking applications) reported elsewhere. As shown, the example HDPE / CC50 composite has a far better flexural strength and modulus than most commercial decking boards, including FiberOn, Veranda, Timber Tech, and Choicedek. This example HDPE / CC50 composite also shows a -47% higher strength and a comparable modulus than the best conventional decking board, Trex. These outstanding flexural properties provides a higher load and a lower deflection which may be important for decking boards according to the International Building Code (IBC), clearly confirming the potential of the HDPE-coal char composites to be employed in this application area. Furthermore, regarding the low cost of coal and its abundance, HDPE-coal char composites are very desirable from an economic standpoint.

[0072] FIG. 2D also indicates much better performance of the coal char as a reinforcement in polymers over coal. The example HDPE-coal char composite havingabout 50 wt% coal char was determined to have a -26% higher flexural strength and -64% higher modulus than the 60 wt% HDPE-coal composite reported by others, which means a better load and lower deflection for decking applications. While not wishing to be bound by any theory, this result is believed to be due to the difference in the chemical composition of these two materials.

[0073] Here, coal is composed of many chemical compounds including liquid oil (naphthalene and phenolic species), aliphatic hydrocarbons, tar, char, etc. Thus, the complexity of coal may affect its performance as a filler. In contrast, coal char is a carbon-rich and volatile-free residue from the pyrolysis of coal. The coal char used in this work was prepared by pyrolyzing a subbituminous coal from Cordero Rojo mine in the Powder River Basin (PRB), Wyoming (WY), USA at about 850°C. Since many organic compounds are decomposed or evaporated during pyrolysis, coal char is much more pure than coal. Coal and coal char also have different polarities. Upon pyrolyzing PRB coal at 900°C, the oxygen / carbon (O / C) ratio decreases from 0.40 for the coal to 0.17 for the coal char obtained at 900°C. Based on FT-IR spectra, the coal surface has ample oxygen-containing functional groups, while the structure of the coal char is more graphitic. Therefore, coal char may have more compatibility with non-polar polymers, providing a better interaction with HDPE compared to coal as a filler.

[0074] The role of coal’s chemistry in the final properties of the composites have been reported previously. In one study, polyamide-12 (PA-12) composites were filled with two different coal grades, anthracite and lignite. Although anthracite showed a high inherent modulus, addition of this coal to the PA-12caused a substantial loss in the tensile strength and modulus. In contrast, PA-12 / lignite composites had a comparable tensile strength to that of the neat polyamide polymer. This result was ascribed to the fact that there are many oxygen-containing functional groups (such as -OH) on the surface of the lignite, creating interactions with polyamide chains, while anthracite has a high carbon content (especially aromatic structures), and leading to poor dispersion within the matrix. In another study, polyamide-6 (PA-6) and HDPE composites were compared with anthracite and the authors concluded that this filler was not suitable for these thermoplastics. In fact, the unfilled PA-6 had a higher tensile strength than the composite, while the HDPE showed a marginal decrease in the presence of the filler, due to higher affinity to the coal. As another proof, the authors found that bituminous coal (P8) worked better than the sub-bituminous PRB coal in enhancing the flexuralstrength of the HDPE composites. The P8 coal possessed less polar groups which made the filler more compatible with the polyolefins. It appeared that failure to achieve appropriate flexural or tensile properties in most of the composites filled with coal was due to the limited adhesion between the filler and the polymer matrix, which causes stress concentration and crack propagation in the composite, leading to deterioration of the mechanical behavior.

[0075] In contrast, based on the results described herein, the use of coal char as a reinforcement / filler shows significant improvement in the flexural and tensile properties of polymers, which may be a result of its chemical composition and surface chemistry.4.3. Rheology

[0076] The dependency of complex viscosity on angular frequency of the HDPE and corresponding composites is illustrated in FIG. 3A. Pure HDPE showed a Newtonian region at low angular frequencies followed by a shear thinning region at higher angular frequencies. The example composites containing up to about 40 wt% coal char (HDPE / CC20, HDPE / CC30, and HDPE / CC40) exhibited similar behavior, but with a shorter Newtonian region. For the example HDPE / CC50 composite, this region almost disappeared and only a strong shear thinning region was observed, where there was a linear relationship between complex viscosity and the angular frequency. This transition has been reported for polystyrene and LDPE composites reinforced with 5 wt% of multiwalled carbon nanotube (MWNT). The rheological percolation occurs at a very low amounts of nanofillers, while the micro-composites reach this point at high filler loadings as seen in this work.

[0077] The example HDPE-coal char composites also showed a much higher complex viscosity than pure HDPE, indicating that the coal char may play a determining role in the melt behavior of the system. Further, the example composites with higher coal char content (for example, from about 40 wt% to about 50 wt%) showed a stronger shear thinning behavior. In fact, the rupture of the interface between the coal char particles and the HDPE phase may occur at higher angular frequencies. Knowing that the interactions are much stronger in these highly filled composites, a stronger shear thinning behavior may result. In fact, there may not be sufficient time for polymer chains to relax at high angular frequencies. Thus, the melt viscoelastic behavior of a polymer is determined by small polymer segments, thereby showingsimilar storage modulus in this angular frequency range as shown in FIG. 3B. In contrast, low angular frequencies may be suitable for the study of interactions between components in a composite as the modulus is significantly influenced in the presence of any filler / additive. The storage modulus (G1), shown in FIG. 3B, increased progressively with increased coal char loading, which may be due to the particle- polymer interactions along with a distinct change in the slope. A similar increasing trend was also observed for the loss modulus (G") upon adding coal char filler to the matrix and is shown in FIG. 3C.

[0078] Cross-over frequency may be utilized to track the influence of the coal char on the melt viscoelastic behavior of the example HDPE-coal char composites as shown in FIGS. 4A and 4B. For neat HDPE, loss modulus (G") was always higher than the storage modulus (G') within the frequency range investigated, suggesting the dominant viscous behavior of the polymer chains. The example HDPE-coal char composites showed a transition point at frequencies between about 300 rad / s and about 600 rad / s, after which the elastic part was dominant. Before the transition, viscous character was strong, although the difference between the G' and G" values declined upon adding more filler to the HDPE. The increase in the coal char wt% also led to a decrease in the cross-over frequency, indicating the role of the coal char particles in restricting the relaxation of the HDPE chains. The distinct viscoelastic behavior of the HDPE / CC50 example composite may originate from the formation of a solid-like network of the filler particles.

[0079] This result is further corroborated from the variations of tan 5 as a function of angular frequency as shown in FIG. 3D. Tan 5 is a useful criterion to evaluate viscoelasticity of a polymeric system because tan 5 is strongly influenced by structural changes. HDPE alone showed a peak at an angular frequency of 0.3 rad / s and a sharp loss of tan 5 was observed by incorporating coal char filler to the matrix, signifying a more solid-like behavior. This result may be attributed to the confinement of mobility of HDPE chains resulting from the coal char filler. When about 50 wt% coal char filler was added to the HDPE, tan 5 became almost frequency-independent.4.4. Thermal Stability

[0080] Thermal degradation of the HDPE-coal char composites is another parameter in determining the potential of composites described herein to be employed for, e.g., decking applications among other applications. Thermal behavior of HDPEalone, example HDPE-coal char composites, and commercial WP composites was investigated using TGA under argon (0-900°C) and oxygen (750-850°C). FIGS. 5A- 5D show TGA and DTG curves of the samples. Selected thermal stability data obtained from TGA measurements is shown in Table 2. The temperatures at which 5% mass loss and max decomposition rate occurred are designated as Ts% and Tmax, respectively in Table 2.Table 2

[0081] The HDPE sample showed a single step degradation with a Ts% of 395.4°C and a Tmax of 464.2°C due to the cleavage of carbon backbone. For the example HDPE- coal char composites, a large shift in Ts% (51-60°C) and Tmax (17-20°C) to higher temperatures was observed, indicating a significant improvement in thermal stability. An interesting finding was that the ~30 wt% coal content may be a saturation point and incorporating higher contents may marginally change Ts% and Tmax. However, the degradation rates — DTG curves, shown in FIGS. 5C and 5D — decreased as the filler content increased. The HDPE completely decomposed at 555.5°C and showed no char, while the char content at about 900°C substantially increased with an increase in the filler loading, reaching to about 41% for the HDPE / CC50 example composite.

[0082] Moreover, when the samples undergo a reheating program from 750-850°C under an O2 atmosphere, the ash content was proportional to the filler wt% as shown in Table 2 and FIG. 6. To help elucidate the role of the coal char in improving the thermal stability of the HDPE, two mechanisms may be considered: a physical aspect and a chemical aspect.

[0083] With respect to the physical aspect, the coal char — which is formed at high temperatures — may act as a protective layer hindering diffusion of oxygen. It may also slow down the transfer of heat current created during the decomposition of the influenced areas. On the other hand, coal char may show a low thermal conductivity owing to its high porosity and it has been used to develop heat-insulating building materials. Therefore, the thermal conductivity of the HDPE composites may decrease in the presence of the coal char, leading to a better thermal stability. The superior heat resistance / insulation properties of the inorganic content of the ash (silica, alumina, etc.) may also help this process.

[0084] With respect to the chemical aspect, coal and coal-derived materials may play the role of a natural antioxidant in the polymeric system. In fact, lignin structures are part of the coal composition, and the phenolic groups of these structure may trap free radicals, providing a hindered thermal degradation. In this regard, it has been reported that the efficiency of lignin as a primary stabilizer in polypropylene (PP) compounds was better than a commercial phenol antioxidant (Irganox 101).

[0085] Overall, incorporating higher amounts of coal char filler into the HDPE matrix may lead to a more effective and stronger char formation as well as a more efficient antioxidant functionality, which finally enhanced the thermal stability.

[0086] Comparison of the TGA curves clearly indicated much better thermal stability of the example HDPE-coal char composites over the commercial wood-plastic (WP) composites. The commercial WP composites even had a worse thermal behavior than pure HDPE. When the temperature reached about 255°C to about 265°C, all commercial WP composites (FiberOn, Trex, and Timbertech) lost 5% in weight, which was a much lower Ts% value than that of the HDPE alone (395°C) and the example HDPE-coal char composites (about 445°C to about 456°C). Further, Tmax of the first and the second peaks in the TGA curves of the commercial WP composites were observed in the temperature range of 350-360°C and 460-470°C, respectively. Because HDPE is used as the matrix in the commercial WP composites, this weak thermalstability may originate from the low thermal stability of the wood flour added to the HDPE polymer. The first peak may be attributed to the degradation of wood flour components, while the second one is created by the degradation of both the HDPE and the filler. In fact, the thermal degradation of the wood flour includes degradation of hemicellulose and cellulose (200-350°C) and lignin (250-500°C). It is has also been reported that free radicals are generated from wood at temperatures around 420°C, which in turn may accelerate thermal degradation of the polymer matrix by attacking HDPE chains and promoting the formation of long chain free radicals.

[0087] Because no flame retardants (active or passive) are utilized in the example HDPE-coal char composites, the thermal stability of the example HDPE-coal char composites and their exceptional performance over commercial WP composites (which usually contain flame retardants) implies a big opportunity for use of coal char in development of polymer composites. In fact, the mechanical and thermal properties of the example HDPE-coal char composites suggest that the coal char may act as both a reinforcement and a thermal stabilizer simultaneously, indicating coal char’s potential as a functional additive / filler.

[0088] Conventional technologies utilize coal, coal gangue, coal ash, petroleum coke, or metallurgical coke in composites. However, coal char has, for example, a distinct chemical structure, chemical composition, and mechanical properties, among other characteristics. For example, metallurgical coke differs from coal char used for example composites described herein because metallurgical coke is prepared from bituminous coal (which is a higher grade coal than subbituminous), and metallurgical coke is prepared using significantly longer pyrolysis times (>10 h, typically 1.5 days) at l,100°C to get sufficient mechanical strength. That is metallurgical coke is significantly more costly. Petroleum coke is similarly disadvantaged.

[0089] In contrast, the use of coal char as a filler has various advantages over conventional technologies, some of which include:

[0090] As shown in at least FIG. 2D, coal char has a higher flexural strength and modulus compared to commercial HDPE-wood fiber composites (WP composites) and HDPE-bituminous coal composites.

[0091] The use of coal char was determined to lead to an increase in tensile strength compared to the unfilled HDPE, which is not the case for coke or coal as filler.

[0092] Adding coal char led to an increase in HDPE crystallinity, as measured by DSC. Increased crystallinity may be advantageous for various applications and may be connected to the increase in strength and modulus.

[0093] Example HDPE-coal char composites of the present disclosure have significantly improved thermal stability and thermal resistance over HDPE-coal and commercial-wood plastic composites. As a result, the example HDPE-coal char composites may provide, for example, better fire resistance than wood fiber or coal.

[0094] Example HDPE-coal char composites of the present disclosure may be prepared without adding any compatibilizer. In contrast, commercial grades of HDPE / wood fiber composites require adding a compatibilizer as it improves polymer- wood fiber interaction, but increases costs and may impact polymer properties.

[0095] Coal char is less expensive than conventional fillers such as carbon black, graphite, carbon fibers, carbon nanotubes, graphene, graphene oxide, petroleum coke, and metallurgical coke.

[0096] Coal char useful for composites described herein may include flash pyrolysis coal char. Flash pyrolysis coal char is made with significantly shorter pyrolysis times than, at least, metallurgical coke and petroleum coke.

[0097] Coal char contains less hazardous volatile matter than coal as a result of it being heated to high temperatures during pyrolysis.

[0098] The inventors also determined that, although coal char has less strength than petroleum coke, metallurgical coke, among others, coal char surprisingly leads to improved HDPE composites. The lower strength of coal char relative to other fillers may be due to shorter pyrolysis times and use of lower grade coal than petroleum coke and metallurgical coke, among others.

[0099] Embodiments described herein generally relate to high density polyethylene-coal char composites. Finding new applications for coal or coal-derived materials is a major driving force that may accelerate the process of stopping use of this material as a resource for power generation and its subsequent consequences on the environment and human health. Results provided herein, demonstrate that coal char may be used in polymer composites as, for example, a functional filler. The results showed that coal char may significantly increase the flexural and tensile properties as well as the thermal stability of the HDPE matrix, suggesting its dual role as a reinforcement and thermal stabilizer in polymeric compounds. This may be attributedto HDPE’s unique structure and chemistry, which led to better performance compared to wood-plastic composites. Based on the performance and the low cost of the coal char, composites described herein may be used in a variety of applications including decking boards, floor panels, pipes, and plastic parts, among others.Embodiments Listing

[0100] The present disclosure provides, among others, the following aspects, each of which can be considered as optionally including any alternate embodiments:

[0101] Clause 1. A composite, comprising: a thermoplastic polymer; and coal char.

[0102] Clause 2. The composite of Clause 1, wherein the thermoplastic polymer comprises a thermoplastic polymers formed from polymerization of olefin-containing monomers.

[0103] Clause 3. The composite of any one of Clauses 1 or 2, wherein the thermoplastic polymer comprises high density polyethylene, polypropylene, acrylonitrile butadiene styrene (ABS), nylon, polyvinyl chloride, or combinations thereof.

[0104] Clause 4. The composite of any one of Clauses 1-3, wherein the thermoplastic polymer comprises high density polyethylene, polypropylene, or combinations thereof.

[0105] Clause 5. The composite of any one of Clauses 1-4, wherein the composite comprises: from about 20 wt% to about 70 wt% of the coal char based on a total amount of the thermoplastic polymer and the coal char in the composite, the total amount of the thermoplastic polymer and the coal char in the composite not to exceed 100 wt%.

[0106] Clause 6. The composite of any one of Clauses 1-5, wherein the composite comprises: from about 20 wt% to about 50 wt% of the coal char based on a total amount of the thermoplastic polymer and the coal char in the composite, the total amount of thermoplastic polymer and the coal char in the composite not to exceed 100 wt%; and from about 50 wt% to about 80 wt% of the thermoplastic polymer based on the total amount of the thermoplastic polymer and the coal char in the composite.

[0107] Clause 7. The composite of any one of Clauses 1-6, wherein the coal char comprises subbituminous coal char.

[0108] Clause 8. The composite of any one of Clauses 1-7, wherein the coal char comprises pyrolyzed coal, flash pyrolyzed coal, or combinations thereof.

[0109] Clause 9. The composite of any one of Clauses 1-8, wherein the coal char has an average particle size of about 40 pm or less.

[0110] Clause 10. The composite of any one of Clauses 1-9, wherein the composite further comprises from greater than 0 wt% to about 0.1 wt% or less of compatibilizer.[OHl] Clause 11. The composite of any one of Clauses 1-10, wherein the composite is free of added compatibilizer.

[0112] Clause 12. The composite of any one of Clauses 1-11, wherein the composite is free of added flame retardant.

[0113] Clause 13. The composite of any one of Clauses 1-12, wherein the composite is free of added flame retardant and free of added compatibilizer.

[0114] Clause 14. An article of manufacture, comprising the composite of any one of Clauses 1-13.

[0115] Clause 15. A floor panel, comprising the composite of any one of Clauses 1-13.

[0116] Clause 16. A decking board, comprising the composite of any one of Clauses 1-13.

[0117] Clause 17. A pipe, comprising the composite of any one of Clauses 1-13.

[0118] Clause 18. A plastic part, comprising the composite of any one of Clauses1-13.

[0119] Clause 19. A method of forming a composite, the method comprising: extruding a mixture comprising a thermoplastic polymer and coal char to form the composite of any one of Clauses 1-13.

[0120] Clause 20. A method of forming a composite, the method comprising: extruding a mixture comprising a thermoplastic polymer and coal char to form a composite comprising from about 40 wt% to about 60 wt% of the coal char based on a total weight of the composite.

[0121] Clause 21. The method of any one of Clauses 19 or 20, wherein the coal char comprises flash pyrolyzed coal char.

[0122] Clause 22. A composite, comprising: high density polyethylene; and coal char.

[0123] Clause 23. The composite of Clause 22, wherein the composite comprises: from about 10 wt% to about 60 wt% of the coal char based on a total amount of thehigh density polyethylene and the coal char in the composite, the total amount not to exceed 100 wt%.

[0124] Clause 24. The composite of any one of Clauses 22 or 23, wherein the composite comprises: from about 20 wt% to about 50 wt% of the coal char based on a total amount of the high density polyethylene and the coal char in the composite, the total amount not to exceed 100 wt%; and from about 50 wt% to about 80 wt% of the high density polyethylene based on the total amount of high density polyethylene and coal char in the composite.

[0125] Clause 25. The composite of any one of Clauses 22-24, wherein the coal char comprises subbituminous coal char.

[0126] Clause 26. The composite of any one of Clauses 22-25, wherein the coal char comprises pyrolyzed coal, flash pyrolyzed coal, or combinations thereof.

[0127] Clause 27. The composite of any one of Clauses 22-26, wherein the coal char has an average particle size of about 100 pm or less.

[0128] Clause 28. The composite of any one of Clauses 22-27, wherein the coal char has an average particle size of about 40 pm or less.

[0129] Clause 29. The composite of any one of Clauses 22-28, wherein the high density polyethylene has a density that is from about 0.94 g / cm3to about 0.98 g / cm3.

[0130] Clause 30. The composite of any one of Clauses 22-29, wherein the high density polyethylene has a density that is from about 0.96 g / cm3to about 0.97 g / cm3.

[0131] Clause 31. The composite of any one of Clauses 22-30, wherein the high density polyethylene has a melt flow index (190°C / 2.16 kg) that is from about 5 g / 10 min to about 10 g / 10 min.

[0132] Clause 32. The composite of any one of Clauses 22-31, further comprising an additive.

[0133] Clause 33. The composite of Clause 31, wherein the additive comprises a compatibilizer.

[0134] Clause 34. The composite of any one of Clauses 22-33, wherein the composite is free of added flame retardant, free of added compatibilizer, or free of both added flame retardant and added compatibilizer, or may include from greater than 0 wt% to about 0.1 wt% or less of compatibilizer.

[0135] Clause 35. An article of manufacture, comprising the composite of any one of Clauses 22-34.

[0136] Clause 36. A floor panel, comprising the composite of any one of Clauses 22-34.

[0137] Clause 37. A decking board, comprising the composite of any one of Clauses 22-34.

[0138] Clause 38. A pipe, comprising the composite of any one of Clauses 22-34.

[0139] Clause 39. A plastic part, comprising the composite of any one of Clauses22-34.

[0140] Clause 40. A method of forming a composite, the method comprising: extruding a mixture comprising a thermoplastic polymer and coal char to form the composite of any one of Clauses 22-34.

[0141] Clause 41. A method of forming a composite, the method comprising: extruding a mixture comprising high density polyethylene and coal char to form a composite.

[0142] Clause 42. The method of Clause 41, wherein the coal char comprises flash pyrolyzed coal char.

[0143] Clause 43. The method of any one of Clauses 40 or 41, wherein the composite comprises from about 40 wt% to about 60 wt% of the coal char based on a total weight of the thermoplastic and coal char in the composite.

[0144] All documents described herein are incorporated by reference herein, including any priority documents and / or testing procedures to the extent they are not inconsistent with this text. As is apparent from the foregoing general description and the specific embodiments, while forms of the embodiments have been illustrated and described, various modifications may be made without departing from the spirit and scope of the present disclosure. Accordingly, it is not intended that the present disclosure be limited thereby. Likewise, the term “comprising” is considered synonymous with the term “including.” Likewise whenever a composition, an element, a group of elements, or a method is preceded with the transitional phrase “comprising,” it is understood that we also contemplate the same composition, method, or group of elements with transitional phrases “consisting essentially of,” “consisting of,” “selected from the group of consisting of,” or “Is” preceding the recitation of the composition, element, elements, or method, and vice versa, such as the terms “comprising,” “consisting essentially of,” “consisting of’ also include the product of the combinations of elements listed after the term.

[0145] In the foregoing, reference is made to embodiments of the disclosure. However, it should be understood that the disclosure is not limited to specific described embodiments. Instead, any combination of the following features and elements, whether related to different embodiments or not, is contemplated to implement and practice the disclosure. Furthermore, although embodiments of the disclosure may achieve advantages over other possible solutions and / or over the prior art, whether or not a particular advantage is achieved by a given embodiment is not limiting of the disclosure. Thus, the foregoing aspects, features, embodiments and advantages are merely illustrative and are not considered elements or limitations of the appended claims except where explicitly recited in a claim(s). Likewise, reference to “the disclosure” shall not be construed as a generalization of any inventive subject matter disclosed herein and shall not be considered to be an element or limitation of the appended claims except where explicitly recited in a claim(s).

[0146] For purposes of this present disclosure, and unless otherwise specified, all numerical values within the detailed description and the claims herein are modified by “about” or “approximately” the indicated value, and consider experimental error and variations that would be expected by a person having ordinary skill in the art. For the sake of brevity, only certain ranges are explicitly disclosed herein. However, ranges from any lower limit may be combined with any upper limit to recite a range not explicitly recited, as well as, ranges from any lower limit may be combined with any other lower limit to recite a range not explicitly recited, in the same way, ranges from any upper limit may be combined with any other upper limit to recite a range not explicitly recited. For example, the recitation of the numerical range 1 to 5 includes the subranges 1 to 4, 1.5 to 4.5, 1 to 2, among other subranges. As another example, the recitation of the numerical ranges 1 to 5, such as 2 to 4, includes the subranges 1 to 4 and 2 to 5, among other subranges. Additionally, within a range includes every point or individual value between its end points even though not explicitly recited. For example, the recitation of the numerical range 1 to 5 includes the numbers 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, among other numbers. Thus, every point or individual value may serve as its own lower or upper limit combined with any other point or individual value or any other lower or upper limit, to recite a range not explicitly recited.

[0147] As used herein, the indefinite article “a” or “an” shall mean “at least one” unless specified to the contrary or the context clearly indicates otherwise. For example,embodiments comprising “a layer” include embodiments comprising one, two, or more layers, unless specified to the contrary or the context clearly indicates only one layer is included.

[0148] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

ClaimsWhat is claimed is:

1. A composite, comprising: a thermoplastic polymer; and coal char.

2. The composite of claim 1, wherein the thermoplastic polymer comprises a thermoplastic polymer formed from polymerization of olefin-containing monomers.

3. The composite of claim 1, wherein the thermoplastic polymer comprises high density polyethylene, polypropylene, acrylonitrile butadiene styrene (ABS), nylon, polyvinyl chloride, or combinations thereof.

4. The composite of claim 1, wherein the thermoplastic polymer comprises high density polyethylene, polypropylene, or combinations thereof.

5. The composite of claim 1, wherein the composite comprises: from about 20 wt% to about 70 wt% of the coal char based on a total amount of the thermoplastic polymer and the coal char in the composite, the total amount of the thermoplastic polymer and the coal char in the composite not to exceed 100 wt%.

6. The composite of claim 1, wherein the composite comprises: from about 40 wt% to about 60 wt% of the coal char based on a total amount of the thermoplastic polymer and the coal char in the composite, the total amount of the thermoplastic polymer and the coal char in the composite not to exceed 100 wt%; and from about 60 wt% to about 40 wt% of the thermoplastic polymer based on the total amount of the thermoplastic polymer and coal char in the composite.

7. The composite of claim 1, wherein the coal char comprises subbituminous coal char.

8. The composite of claim 1, wherein the coal char comprises pyrolyzed coal, flash pyrolyzed coal, or combinations thereof.

9. The composite of claim 1, wherein the coal char has an average particle size of about 40 pm or less.

10. The composite of claim 1, wherein the composite further comprises from greater than 0 wt% to about 0.1 wt% or less of compatibilizer.

11. The composite of claim 1, wherein the composite is free of added compatibilizer.

12. The composite of claim 1, wherein the composite is free of added flame retardant.

13. The composite of claim 1, wherein the composite is free of added flame retardant and free of added compatibilizer.

14. An article of manufacture, comprising the composite of claim 1.

15. A floor panel, comprising the composite of claim 1.

16. A decking board, comprising the composite of claim 1.

17. A pipe, comprising the composite of claim 1.

18. A plastic part, comprising the composite of claim 1.

19. A method of forming a composite, the method comprising: extruding a mixture comprising a thermoplastic polymer and coal char to form a composite comprising from about 40 wt% to about 60 wt% of the coal char based on a total weight of the thermoplastic polymer and coal char in the composite.

20. The method of claim 19, wherein the coal char comprises flash pyrolyzed coal char.