Kenaf-polyolefin composite and method for producing it

Abstract

A composition comprising woody core fibers of hemp, kenaf, jute, and / or flax, optionally coated with one or more sugars or polysaccharides and dispersed in a matrix of polyolefin.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS / INCORPORATION-BY-REFERENCE STATEMENTS] This application claims priority to U.S. Provisional Patent Application No. 62 / 943,634, filed December 4, 2019, which is expressly incorporated herein by reference in its entirety.

[0002] The inventive concepts disclosed and claimed herein relate generally to polymer composites and, more particularly, but not by way of limitation, to cellulosic fiber reinforced polymers. [Background technology]

[0003] The use of cellulosic fillers as additives in both thermoplastic and thermosetting resins has gained attention. Such fillers have included wood pulp, peanut or walnut shells, corn cobs, rice husks, vegetable fibers, and grasses. The cost advantages of cellulosic fibers were the initial motivation for their use in plastics. Natural fibers were also intended to result in lighter composites compared to glass fiber-reinforced polymers. The renewable and biodegradable qualities of natural fibers have stimulated renewed interest in cellulosic fiber-plastic composites.

[0004] Kenaf (Hibiscus cannabinus) is a plant native to South Asia. Kenaf is a bast fiber plant made up of two main components that can be utilized for industrial purposes. The first is the bast fiber, located just inside the outer layer of the plant's stem. Kenaf fiber has been used to make rope, yarn, sackcloth, and other woven products. The second useful part of the plant is the core. The core, known as kenaf hurd, is woody in nature and is typically used for animal bedding and gardening media.

[0005] The bast comprises approximately 40% of the plant and contains elongated fiber cells approximately 2-6 mm long with thick (6.3 μm) cell walls. The core comprises approximately 60% of the plant and contains relatively thick (approximately 38 μm) but short (0.5 mm) and thin-walled (3 μm) fiber cells.

[0006] To utilize kenaf as a crop, it must be incorporated into value-added products. Kenaf bast fibers are known to have potential as reinforcing fibers in thermoplastic composites due to their toughness and high aspect ratio compared to other fibers. A major disadvantage encountered when incorporating natural fibers, including kenaf bast fibers, into a polymer matrix is ​​the lack of good interfacial adhesion between the polar fiber surface and the non-polar matrix, which leads to fiber clumping and poor properties in the final product.

[0007] Kenaf wood-core fibers have not been used in plastics as reinforcing fibers, in part because of their low aspect ratio compared to kenaf bast fibers and poor interfacial adhesion between the polar fiber surface and the polymer matrix.

[0008] Because bast plants have a large amount of internal woody core, it is desirable to find a means of using woody core fibers for value-added composites. It is also desirable to improve the interfacial adhesion between plant fibers and thermoplastic resins. Summary of the Invention

[0009] Composites of wood core fibers coated with a binder and dispersed in a matrix of polyolefin can be used to make environmentally friendly extruded or molded products.

[0010] In one embodiment, kenaf wood core particles are mixed with a binder and powdered polyolefin to form a kenaf-polyolefin powder mixture. The kenaf wood core particles have a moisture content of 6% or less, and the powdered polyolefin has a particle size of -35 Tyler mesh (0.42 mm or less). Composite articles are formed from the kenaf-polyolefin powder mixture using extrusion or injection molding.

[0011] In another embodiment, kenaf wood core particles are mixed with a binder and a polyolefin to form a polyolefin-fiber mixture having a kenaf wood core content in the range of about 90% to about 98% by weight. The kenaf wood core particles have a moisture content of 6% or less. The polyolefin-fiber mixture is extruded to form masterbatch pellets. The masterbatch pellets can be used to form polyolefin-fiber composite articles.

[0012] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one or more embodiments described herein and, together with this specification, explain these embodiments. The drawings are not intended to be drawn to scale, and certain features and views of the figures may be shown exaggerated relative to scale or as schematics for clarity and conciseness. Not all components may be shown in every drawing. Like reference numbers in the figures may represent and refer to the same or similar elements or functions. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a block diagram of a process for forming a polyolefin-wood core fiber composite in accordance with the inventive concepts disclosed herein.

[0014] [Figure 2] Illustrates a 90-98% plant-based masterbatch like Example 3, which appears somewhat gritty and grainy.

[0015] [Figure 3] 1 shows the extruder used in pilot studies to make composite straws.

[0016] [Figure 4] 1 shows black, blue, and red straws of the composite material produced in Example 4.

[0017] [Figure 5] An example of mass production of a composite straw containing 80% kenaf core is shown.

[0018] [Figure 6] 1 shows an example of a straw extruded using a masterbatch produced as in Example 3 and mixed with a melt of polyethylene and polypropylene as in Example 5.

[0019] [Figure 7] An example of a composite container with a 90% kenaf core, injection molded as in Example 6 using polypropylene homopolymer, is shown.

[0020] [Figure 8] An example of a pale cream colored pellet containing a kenaf core produced as in Example 7 and subsequently used for the production of polyethylene film is shown.

[0021] [Figure 9] Light brown composite pellets of polypropylene and 80% kenaf core are shown.

[0022] [Figure 10] 1 shows a darker brown composite pellet made from recycled polypropylene and an 80% kenaf core. DETAILED DESCRIPTION OF THE INVENTION

[0023] Before describing in detail at least one embodiment of the inventive concepts disclosed herein, it is to be understood that the inventive concepts disclosed herein are not limited in their application to the details of construction and arrangement of components or steps or methodology set forth in the following description or illustrated in the drawings. The inventive concepts disclosed herein are capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.

[0024] Unless otherwise defined herein, terms used in connection with the inventive concepts disclosed herein shall have the meanings commonly understood by those of ordinary skill in the art. Further, unless otherwise required by context, singular terms shall include the plural and plural terms shall include the singular.

[0025] All of the articles and / or methods disclosed herein can be made and executed without undue experimentation in light of the present disclosure. While the articles and methods of the inventive concepts disclosed herein have been described in terms of preferred embodiments, it will be apparent to those skilled in the art that changes may be made in the articles and / or methods and in the steps or sequence of steps of the methods described herein without departing from the concept, spirit, and scope of the inventive concepts disclosed herein. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope, and concept of the inventive concepts disclosed herein.

[0026] As utilized in accordance with the present disclosure, the following terms, unless otherwise indicated, shall be understood to have the following meanings:

[0027] The use of the word "a" or "an" when used in conjunction with the word "comprising" in the claims and / or this specification may mean "one," but is also consistent with the meanings of "one or more," "at least one," and "one or more than one." The use of the word "or" in the claims is used to mean "and / or" unless expressly stated to refer to alternatives only or that the alternatives are mutually exclusive, although the present disclosure supports definitions that refer to alternatives only and "and / or."

[0028] Throughout this application, the term "about" is used to indicate that a value includes the variation of error inherent in the device or method being employed to determine the value or the variation that exists among study subjects. For example, and not as a limitation, when the term "about" is used, the specified value may vary by ±12 percent, or ±11 percent, or ±10 percent, or ±9 percent, or ±8 percent, or ±7 percent, or ±6 percent, or ±5 percent, or ±4 percent, or ±3 percent, or ±2 percent, or ±1 percent. Use of the term "at least one of X, Y, and Z" is understood to include X alone, Y alone, and Z alone, as well as any combination of X, Y, and Z. Use of ordinal terminology (i.e., "first," "second," "third," "fourth," etc.) is intended only to distinguish between two or more items and does not imply an order or sequence or importance of one item over another, or, for example, an order of addition.

[0029] As used in this specification and claims, the words "comprising" (and any form of comprising, such as "comprise" and "comprises"), "having" (and any form of having, such as "have" and "has"), "including" (and any form of including, such as "includes" and "include"), or "containing" (and any form of containing, such as "contains" and "contain") are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0030] As used herein, the term "or combinations thereof" refers to all permutations and combinations of the listed items preceding the term. For example, "A, B, C, or combinations thereof" is intended to include at least one of A, B, C, AB, AC, BC, or ABC, and, if order is important in the particular context, BA, CA, CB, CBA, BCA, ACB, BAC, or CAB. Continuing with this example, combinations including repeats of one or more items or terms are expressly included, such as BB, AAA, AAB, BBC, AAABCCCC, CBBAAA, CABABB, etc. One of ordinary skill in the art will understand that typically there is no limit to the number of items or terms in any combination, unless otherwise apparent from the context.

[0031] As used herein, the term "substantially" means that the subsequently described event or circumstance occurs completely, or that the subsequently described event or circumstance occurs to a significant extent or degree. For example, when associated with a particular event or circumstance, the term "substantially" means that the subsequently described event or circumstance occurs with at least an 80% probability, or at least an 85% probability, or at least a 90% probability, or at least a 95% probability. The term "substantially adjacent" can mean that two items are 100% adjacent to each other, or that two items are very close to each other but not 100% adjacent to each other, or that a portion of one of two items is very close to the other item but not 100% adjacent to the other item.

[0032] As used herein, the term "association" is understood to refer to a direct or indirect association between two or more items.

[0033] All percentages used herein shall be interpreted as percentages by weight unless otherwise stated.

[0034] Over the past few decades, there has been increasing interest in composites utilizing natural fibers such as hemp and kenaf. The stems of hemp, kenaf, and other fiber plants contain two primary types of fibers: bast and core. The core, also referred to herein as the woody core, inner core, or inner woody core, comprises short fibers and is located in the center of the stem. The bast comprises long fibers and is found in the outer skin (skin) of the stem. Prior art references regarding "fiber" typically refer to bast fibers. Bast fibers, also referred to as phloem fibers, are collected from the phloem or bast surrounding the stem, where they support the phloem conductance cells and provide strength to the stem. Bast fibers from plants such as flax, hemp, kenaf, and jute have been used in textile applications such as carpets, yarns, and netting. Nonwoven applications of hemp bast fibers include composite applications such as automobile door panels and headliners. Kenaf bast fibers have attracted attention for their potential use as reinforcing fibers in composite thermoplastics due to their superior toughness and high aspect ratio compared to other fibers. A single kenaf (bast) fiber can have a tensile strength and modulus as high as 11.9 GPa and 60 GPa, respectively. The fibril size and chemical content of kenaf stem are shown in Table 1 below.

[0035] [Table 1]

[0036] Other sources state that kenaf bast comprises 40% of the plant, with individual fiber cells approximately 2-6 mm long and slender, with cell walls 6.3 μm thick. Conversely, the core comprises approximately 60% of the plant, with thick (approximately 38 μm) but short (0.5 mm) and thin-walled (3 μm) fiber cells.

[0037] For thousands of years, hemp has been grown for its bast fiber, but the inner woody core or pith has been considered a waste by-product of bast production. Later, the woody core fiber found applications in products such as animal bedding, summer feed, and horticultural media. However, it has now been discovered that woody core fiber can be incorporated into plastics to create thermoplastic composites.

[0038] One embodiment of the inventive concept disclosed herein includes a composition comprising wood core fibers dispersed in a polymer matrix. The wood core fibers are coated with a binder, such as a sugar or polysaccharide, to aid in dispersing the fibers in the polymer. In one embodiment, more than 50% of the fibers in the composition are wood core fibers and less than 50% of the fibers are bast fibers. In another embodiment, 90% or more of the fibers in the composition are wood core fibers and 10% or less are bast fibers. In yet another embodiment, essentially all of the fibers in the composition are wood core fibers and essentially no bast fibers.

[0039] Wood core fibers are derived from the trunk or stem of dicotyledonous plants. Non-limiting examples of suitable plants include kenaf, hemp, jute, and flax. In one embodiment, the composition comprises kenaf wood core fibers.

[0040] The amount of wood core fiber in the composition can vary. In one embodiment, the wood core fiber is present in the composition in an amount ranging from about 25% to about 90% by weight. In another embodiment, the wood core fiber is present in the masterbatch composition in an amount ranging from about 90% to about 98% by weight.

[0041] To obtain woody core fiber, harvested kenaf, hemp, and the like are dehulled to separate the bast fibers from the core. The dehulling process varies and can be done by hand. However, a common process uses automated machines that subject the fiber plant to mechanical stress, physically breaking the bond between the inner woody core and the bast. The machine then separates the bast from the inner core. Another commonly used process for separating the bast from the inner woody core is "retting," which involves submerging the plant stems in water and soaking them for a period of time to loosen the outer fibers of the stem from the other components. Retting can also be performed by leaving cut plants outdoors to expose them to atmospheric moisture. Bacterial action affects the pectin and lignin, liberating the cellulose fibers. The stems are then removed, washed, and subjected to mechanical processing to remove the soft tissue, which is then dried. A process using a combination of retting and a dehuller can also be used to obtain bast fiber.

[0042] The wood (inner) core or pulp may be further processed by grinding to separate the wood core fibers and reduce fiber size. Grinding equipment and methods are known and understood by those skilled in the art. For example, the wood core fibers may be ground in a rotary grinder or other rotary grinding equipment.

[0043] In one embodiment, the wood core fibers in the composition have a fiber length of less than 550 μm, hi another embodiment, the wood core fibers have a weight average length in the range of about 60 μm to about 100 μm.

[0044] The wood core fibers may be derived from hemp, kenaf, jute, flax, etc. In one embodiment, the wood core fibers are kenaf wood core fibers.

[0045] One of the major disadvantages of incorporating natural fibers into a polymer matrix is ​​the lack of good interfacial adhesion between the fiber surface and the polymer, resulting in poor properties for the final product. This poor interfacial adhesion is thought to be due to polar hydroxyl groups on the fiber surface, which are actually repelled by the non-polar matrix. Regardless of the mechanism, the inherent polar and hydrophilic nature of natural fibers makes them difficult to incorporate into the hydrophobic polyolefin matrix. However, it has been found that this can be mitigated by coating the fibers with binders such as sugars or polysaccharides. For example, the fibers can be mixed with liquid starch prior to blending with polyolefin pellets, and the mixture can be extruded, resulting in excellent composite properties.

[0046] Other non-limiting examples of sugars that have been tested that have provided good processing and composite properties include cornstarch in water and clear sugar concentrate in water. Sugars and polysaccharides are hypothesized to function as coupling agents for the wood core fibers and polyolefin resins.

[0047] If the polyolefin is powdered prior to mixing with the dried wood core fiber and as described in detail below, no sugar or polysaccharide binder needs to be added. Excellent results are obtained when the wood core fiber is dried to 6% moisture or less and the polyolefin is powdered to a particle size of minus 35 mesh (Tyler) or 0.420 mm or less.

[0048] Non-limiting examples of suitable polyolefins include polyethylene, polypropylene, and blends and copolymers thereof. The polyethylene used can be high density polyethylene (HDPE), low density polyethylene (LDPE), linear low density polyethylene, and combinations thereof.

[0049] Turning now to Figure 1, in one embodiment, debarked wood core fibers are ground and mixed with a binder (e.g., a sugar or polysaccharide binder) and a polyolefin resin. The polyolefin resin may be powdered, but need not be. The addition of the binder allows for the use of the polymer in pellet form or other non-powdered form. The mixture can be extruded or injection molded using procedures known to those skilled in the art to form thermoplastic composite pellets and shapes.

[0050] In one embodiment, the mixing step is carried out at ambient temperature. In another embodiment, the mixing step is carried out at a temperature in the range of about 100°C to about 200°C. In yet another embodiment, the mixing step is carried out at a temperature in the range of about 135°C to about 165°C.

[0051] In one embodiment, prior to mixing, the polyolefin resin is powdered and the wood core fibers are dried to 6% moisture or less, eliminating the need for added binders. For example, the polyolefin resin can be powdered to form a -35 Tyler mesh (0.42 mm or less) powder. It is hypothesized that the increased surface area of ​​the powdered polyolefin, combined with the reduced hydrophilicity of the dried wood core fibers, provides ample coupling opportunities.

[0052] In one embodiment, the mixing of the dried wood core fibers with the polyolefin powder is carried out at a temperature ranging from about 100° C. to about 200° C. In another embodiment, the same mixing step is carried out at a temperature ranging from about 135° C. to about 165° C.

[0053] The heated mixture of wood core fibers, polyolefin, and optionally a sugar binder is at least partially melted and formed into composite pellets or other composite articles. Processes for forming composite shapes include, but are not limited to, extrusion processes and molding processes such as injection molding.

[0054] Once the composite pellets are formed, they can be used to form other composite shapes. [Example 1]

[0055] Kenaf core was ground to a particle size of 1 to 550 μm. 1.2 lb (approximately 0.54 kilograms) of the ground particles were mixed with 4 lb (approximately 1.81 kilograms) of polylactic acid (PLA) and extruded to form straws. The extrusion was repeated in a second test in which 1.2 lb (approximately 0.54 kilograms) of kenaf core particles were mixed with 4 lb (approximately 1.81 kilograms) of high-density polyethylene (HDPE). In a third test, 1.2 lb (approximately 0.54 kilograms) of kenaf core particles were mixed with 4 lb (approximately 1.81 kilograms) of low-density polyethylene (LDPE). Higher core concentrations were attempted; however, it was not possible to process biomaterials higher than 30%, and even when they were, they were not distributed uniformly. The tooling broke due to high backpressure from unmelted biomaterial. Redesign was required to continue testing. HDPE appeared to be the best carrier resin for consistent flow rates. However, the straws ruptured during extrusion due to aggregation of the biomaterial. [Example 2]

[0056] Kenaf core particles milled to particle sizes of 1 to 550 μm were mixed with 2% to 10% liquid starch (STA-FLO™) to coat the fiber surface, and then mixed with various amounts of LDPE and extruded to form straws. The manufacturing process was smooth; however, the resulting straws were brittle. [Example 3]

[0057] Kenaf core particles (6 lb (approximately 2.72 kilograms)) were ground to a particle size range of 1-550 μm. The ground particles, which contained 8-12% moisture, were dried to 5% moisture or less and then mixed with 2-10% liquid starch (STA-FLO™) to coat the fiber surface and then mixed with a small amount of molten polyolefin. The mixture was pelletized in an extrusion-type pelletizer to produce a 90-98% plant-based masterbatch. Figure 2 shows the masterbatch pellets, which appear somewhat gritty and grainy. [Example 4]

[0058] The masterbatches produced as in Example 3 above were mixed with polyethylene and polypropylene melts in various ratios and extruded to form straws. Figure 3 shows the extruder used in the pilot study. Composite straws with plant content (kenaf core) ranging from 20% to 85% were produced that exhibited essentially no fractures.

[0059] Different pigments or colorants were added to the mixer to produce composite black, blue, and red straws, as shown in Figure 4. These straws contained 80% kenaf core and were tested for strength and uniformity of fiber distribution. The straws produced were strong and showed good fiber distribution with slight clumping. Figure 5 shows the mass production of composite straws containing 80% kenaf core. [Example 5]

[0060] The masterbatch produced as in Example 3 above was mixed with a melt of polyethylene and polypropylene and extruded to form straws with 65% plant content (kenaf core). No colorant was added to the straw shown in Figure 6. [Example 6]

[0061] The masterbatch produced as in Example 3 above was mixed with polypropylene homopolymer and injection molded to produce the composite containers shown in Figure 7. These composite containers have a 90% plant content (kenaf core). Combinations of polypropylene homopolymer, polypropylene copolymer, and polyethylene were also molded to provide desired properties (flexibility, stiffness, etc.) for different end products. [Example 7]

[0062] Some manufacturers prefer to use pre-blended or composite plastics. To accommodate this, a masterbatch produced as in Example 3 and blended with a desired molten polymer was used to produce composite pellets. A masterbatch such as that in Example 3 blended with low-density polyethylene (LDPE) was used to produce the pale cream-colored pellets shown in Figure 8. The LDPE composite pellets contained a 70% kenaf core and could be used to make polyethylene film.

[0063] Other composite pellets were made using a masterbatch like that in Example 3 and mixed with molten polypropylene homopolymer or copolymer. Figure 9 shows a light brown polypropylene composite pellet with an 85% kenaf core. Figure 10 shows a darker brown pellet, also with an 85% kenaf core. The darker brown pellet was made using recycled polypropylene.

[0064] While the inventive concepts disclosed herein have been described in conjunction with specific language hereinabove, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications, and variations that fall within the spirit and broad scope of the inventive concepts disclosed herein. Changes may be made in the structure and operation of the various components, elements, and assemblies described herein, as well as in the steps or sequence of steps of the methods described herein, without departing from the spirit and scope of the inventive concepts disclosed herein.

Claims

1. wood core fibers at least partially coated with a sugar or polysaccharide binder and dispersed in a polyolefin matrix; The composition wherein the wood core fiber has a wood core of at least one of hemp, kenaf, jute, and flax.

2. The composition of claim 1 , essentially free of bast fibers.

3. The composition of claim 1 comprising kenaf wood core fibers.

4. The composition of claim 3 comprising 20% ​​to 90% by weight of kenaf wood core fiber.

5. The composition of claim 3 comprising 90% to 98% by weight of kenaf wood core fiber.

6. The composition of claim 3 , wherein the saccharide or polysaccharide binder comprises at least one of a starch and a sugar.

7. 4. The composition of claim 3, wherein the polyolefin is selected from the group consisting of polyethylene, polypropylene, and combinations thereof.

8. An extruded product comprising the composition of claim 7.

9. A molded product comprising the composition of claim 7.

10. 1. A process for making a composite article, comprising: mixing kenaf wood core fiber with powdered polyolefin to form a kenaf-polyolefin powder mixture, wherein the kenaf wood core fiber has a moisture content of 6% or less and the powdered polyolefin has a particle size of -35 Tyler mesh (0.42 mm or less); forming a composite article from said kenaf-polyolefin powder mixture using a process selected from extrusion and injection molding; Equipped with The kenaf-polyolefin powder mixture is the kenaf wood core fibers dispersed in a matrix of the powdered polyolefin at least partially coated with a sugar or polysaccharide binder; A process involving:

11. 11. The process of claim 10, wherein the powdered polyolefin is selected from the group consisting of polyethylene, polypropylene, and mixtures thereof.

12. 12. The process of claim 10 or claim 11, wherein the step of mixing the kenaf wood core fiber with the powdered polyolefin is carried out at a temperature in the range of 135°C to 165°C.

13. mixing the ground kenaf wood core fiber with a sugar or polysaccharide binder and a polyolefin to form a polyolefin-fiber mixture having a kenaf wood core content in the range of 90% to 98% by weight, wherein the kenaf wood core fiber has a moisture content of 6% or less; extruding the polyolefin-fiber mixture to form masterbatch pellets; Equipped with The polyolefin-fiber blend comprises kenaf wood core fibers at least partially coated with a sugar or polysaccharide binder and dispersed in the polyolefin.

14. 14. The process of claim 13, wherein the polyolefin is selected from the group consisting of polyethylene, polypropylene, and mixtures thereof.

15. 15. The process of claim 13 or claim 14, wherein the binder comprises at least one of a sugar and a starch.

16. 16. The process of claim 15, further comprising forming a composite article from the polyolefin and the masterbatch pellets using a process selected from extrusion and injection molding.

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