Patent Application
20240287709
This disclosure is directed to the processing of natural plant fibers and related equipment.
Natural fibers found in the outer bast portion of plant stems are gaining importance as a carbon-negative material for use in polymer composites that have traditionally employed glass fibers as the matrix reinforcement material. Bast fibers can be extracted as technical fibers, which are groups of single, elementary cellulosic fiber cells joined together by a pectin-rich middle lamella interphase. Bast fibers have a high specific modulus and tensile strength and are naturally produced with atmospheric CO2 as the carbon source. In addition, natural fiber extraction processes use significantly less energy than is required to make glass or other synthetic fibers. But implementing natural fibers in industry-scale structural composite applications has been limited by the high variability in fiber properties since the composite must be designed to the lower end of those properties.
The textile industry has long been the primary processor and user of bast fibers, such as processing flax fibers to make linen. While there have been widespread attempts to use naturally occurring fibers in polymer composites, decades-old fiber extraction techniques developed by the textile industry have handicapped those attempts. Problematically, there was never a need for textile fibers to have consistent and predictable mechanical properties like there is in the polymer composites industry. As a result, fiber extraction processes were never developed with any attention to fiber characteristics that are important in composite materials.
Embodiments of a stem breaking apparatus include a roller having unevenly spaced radial projections.
In various embodiments, the apparatus includes a tooth including a plurality of the radial projections.
In various embodiments, the apparatus includes a plurality of teeth, and each radial projection is provided by one of the teeth. An angular spacing between adjacent teeth is greater than an angular spacing between at least one pair of the radial projections.
In various embodiments, the apparatus includes a plurality of teeth extending from a minor diameter to a major diameter of the roller. Each radial projection is provided by one of the teeth and extends to the major diameter.
In various embodiments, each radial projection extends from a minor diameter to a major diameter of the roller, and at least one radial projection has a surface that intersects an adjacent radial projection at a diameter between the minor and major diameters.
In various embodiments, the roller is a first roller having a plurality of teeth intermeshed with a plurality of teeth of a second roller. Each roller has unevenly spaced radial projections, and each radial projection is provided by one of the teeth of the respective roller.
In various embodiments, the roller is a first roller, and the apparatus includes a second roller having radial projections intermeshed with the radial projections of the first roller such that a pair of the projections of the first roller lies between a pair of the projections of the second roller where the rollers oppose each other at a roller gap.
In various embodiments, the roller is a first roller and the unevenly spaced radial projections are arranged in an angular pattern. The apparatus includes a second roller having unevenly spaced radial projections arranged in the same angular pattern and intermeshed with the radial projections of the first roller.
In various embodiments, the roller is a first roller, and the apparatus includes a second roller having radial projections intermeshed with the radial projections of the first roller such that a plant stem passed between the rollers is subjected to four-point bending.
In various embodiments, during four-point bending in the apparatus, a plant stem spans a distance between a first radial projection and a second radial projection of the roller and additionally spans a distance between a third radial projection and a fourth radial projection of an opposing roller. The third radial projection and the fourth radial projection may extend between the first radial projection and the second radial projection. Each of the first and second radial projections may be provided by a tooth of the roller, and each of the third and fourth radial projections may provided by a respective tooth of the opposing roller.
Embodiments of a method of extracting bast fibers from a plant stem include bending the plant stem by an amount sufficiently high to break a woody core of the plant stem and sufficiently low to prevent formation of kinks in a majority of the bast fibers surrounding the woody core.
In various embodiments, the method includes subjecting the plant stem to four-point bending between a pair of rollers, during which the plant stem spans a distance between adjacent teeth of one roller and spans a distance between adjacent projections of a tooth of another roller.
In various embodiments, the method includes passing the plant stem between a pair of rollers each having unevenly spaced radial projections.
In various embodiments, the method includes compressing the plant stem before the step of passing.
In various embodiments, the method includes radially compressing the plant stem by an amount below a threshold compressive force to prevent damage to the bast fibers.
It is contemplated that any of the above-listed individual features, below-described features, and/or features depicted in the attached figures may be combined in any technically feasible combination to define a claimed invention.
Described below are an apparatus and method for extracting natural fibers from plants stems. These innovations are particularly useful with plants containing bast fibers, such as flax, hemp, ramie, jute, kenaf, and okra, to name a few examples. The bast portion of a plant stem, which contains the bast fibers, surrounds and is bound to a woody core of the stem. Extracting the fibers generally includes the steps of retting, breaking, cleaning, and refining.
Retting involves decomposition of the substances (e.g., pectin) binding the bast to the core of the stem and binding bast fiber bundles to one another. Retting can be accomplished via microbial decomposition (e.g., dew retting), enzymatic decomposition, and/or chemical decomposition. Breaking involves subjecting retted and dried stems to mechanical stresses (e.g., bending stresses) to break the woody core into small pieces referred to as shives that are allowed to fall away from the bast material after breakage. In one example, retted stems are fed through gear-like machinery to perform the breaking task. After the bulk of the woody core is separated from the surrounding bast fiber bundles during breaking, the fiber bundles may be cleaned in shaking and scutching processes, in which any residual woody material and short fibers are removed. Refining may include a hackling process, in which the cleaned bast fiber strips or bundles proceed through fine pins to be straightened and reduced to finer technical fibers.
Some of these processes can introduce defects into the fibers. For example, conventional breaking processes often result in kinks along the lengths of the fibers, which introduce weak spots along the fibers and reduce their strength accordingly. Some fibers are weakened more than others, with the result being overall weaker fibers with a high degree of variation in mechanical properties, which, while less important in the textile industry, represents a major problem with natural fibers for use as the reinforcing medium in polymer composites.
While conventional stem breaking rollers are defined by a series of evenly spaced radial projections (e.g., flutes or lobes), the illustrated rollers 12, 14 have unevenly spaced radial projections 18. That is, the angular or circumferential distance between at least one pair of adjacent radial projections 18 is different from the angular or circumferential distance between at least one other pair of adjacent radial projections 18. As used here, “adjacent” refers to the “next in sequence” along the outer perimeter of the roller. By way of example in
The illustrated rollers 12, 14 have ten evenly spaced teeth 16 and twenty unevenly spaced radial projections 18 along their respective perimeters. The number of teeth 16 per roller may be a function of the diameter of the roller, among other variables. Although the radial projections 18 are unevenly spaced, they are arranged in a repeating angular pattern with two evenly spaced projections 18 provided by each of the evenly spaced teeth 16. The angular pattern with uneven angular spacing among the radial projections may be formed by a first set of evenly spaced projections including projections 18A and 18C, and a second set of evenly spaced projections, including projection 18B, for example.
The sizes of and the spacing between the angular centers of adjacent projections 18 of the same tooth 16 is such that surfaces of the individual projections 18 of each tooth intersect at a minor projection diameter D′, which is greater than the minor diameter Dm of the rollers 12, 14 and less than the major diameter DM of the rollers. Projections 18A, 18B on roller 14 of
One result of the uneven spacing among the radial projections 18 is four-point bending of a plant stem P when passed between the rollers 12, 14, as illustrated in
With reference again to
In the illustrated example, the width w of each projection 18 is approximately twice its surface radius R (w≈2R), the width W of each tooth 16 is approximately twice the projection width w (W≈2w), the height H of each tooth and projection is half the difference between the major and minor diameters (H=(DM−Dm)/2), the support span S is approximately twice the tooth width W (S≈2W), the load span LS of each tooth is approximately twice the radius R of the radial projections (LS≈2R), and the inner span width Si is approximately the support span S minus twice the radius R of the radial projections (Si≈S−2R). The span ratio is the ratio S/LS of the support span S to the load span LS. The intermeshing clearance IC is half the difference of the inner span width Si and the tooth width W, or (Si−W)/2 and generally represents the circumferential gap between the teeth 16 of each roller where they are intermeshed.
Corresponding characteristics are labeled on the conventional stem breaking roller 12′ of
As noted above, the uneven spacing among projections 18 of the roller 12 of
Experiments confirm this desirable result. Bast fibers were extracted from flax stems having a 1.5 mm diameter and a length of 25 cm via enzymatic retting and mechanical breaking using different pairs of rollers. After retting and before breaking, the stems were water-rinsed and then dried at 100° C. for 24 hours. Two stem samples, each 5 cm in length, were taken from the middle section of single retted stems. One stem sample was passed three times through one pair of rollers having unevenly spaced projections consistent with
TABLE II lists mechanical properties of the differently processed fibers. The elastic modulus and tensile strength of the technical fibers from the flax stem sample subjected to the rollers having unevenly spaced projections are significantly higher on average than those of the technical fibers from the flax stem subjected to the conventional rollers. The effect on the strength, stiffness, and consistency of polymer composites using bast fibers processed as disclosed herein is believed to be equally as significant.
In various embodiments, the surface radius R at the distal end 22 of each of the unevenly spaced projections 18 is greater than or equal to the diameter or width of the stem. The width W of each tooth 16 may be in a range from 2R to 4R. The distal end 22 of each projection 18 is preferably a smooth and continuous surface. The span ratio may be in a range from 2.5 to 4.0, although this range may vary based on stem size and other variables. If the span ratio is too low, then stem bending will be sharper and may result in kinks near the load span location. If the span ratio is too high, then the bending will be more similar to a three-point bend causing a sharper bend at the middle of the load span.
The method may optionally include a compression step. The compression step may include passing the plant stem(s) between rollers having smooth outer surfaces or otherwise applying opposing radial forces to the plant stem. The compression step may be performed after retting and before passing the stems through the toothed rollers. The compression step may be considered a pre-breaking step or may be considered an earlier portion of the breaking step.
In image 1 of
Where the method includes a compression step, compression may be applied to the plant stems in an amount that does not exceed a threshold level CT. This threshold level can depend on several factors, including the plant species from which the stems are taken, the average diameter of the stems, etc. The not-to-exceed threshold CT can be determined via a force-compression test as in
Additional experiments indicate that the presence of the recesses 28 (
While FEA analysis indicates substantially similar compressive strain along the top side of a computer-modeled stem for both cases, the experimental data of
The effect of the above-described compression step was also evaluated using DMA and the simulated roller profile of
The plant stem processing method may thus include configuring the stem breaking rollers to subject the plant stem being processed to a threshold amount of deflection between the projections defining a support span. This threshold level can depend on several factors, including the plant species from which the stems are taken, the average diameter of the stems, the support span distance, etc. The threshold can be determined via a force-deflection test as in
It is to be understood that the foregoing is a description of one or more embodiments of the invention. The invention is not limited to the particular embodiment(s) disclosed herein, but rather is defined solely by the claims below. Furthermore, the statements contained in the foregoing description relate to particular embodiments and are not to be construed as limitations on the scope of the invention or on the definition of terms used in the claims, except where a term or phrase is expressly defined above. Various other embodiments and various changes and modifications to the disclosed embodiment(s) will become apparent to those skilled in the art. All such other embodiments, changes, and modifications are intended to come within the scope of the appended claims.
As used in this specification and claims, the terms “e.g.,” “for example,” “for instance,” “such as,” and “like,” and the verbs “comprising,” “having,” “including,” and their other verb forms, when used in conjunction with a listing of one or more components or other items, are each to be construed as open-ended, meaning that the listing is not to be considered as excluding other, additional components or items. Other terms are to be construed using their broadest reasonable meaning unless they are used in a context that requires a different interpretation.
| Number | Date | Country | |
|---|---|---|---|
| 63441617 | Jan 2023 | US |
