FR3125542A1 - Hybridization of natural fiber reinforcement for composite materials and fabrics made therefrom - Google Patents

Abstract

Hybridization of reinforcement by natural fibers for composite materials and fabrics made of the latter The present description relates to a roving or tow intended for a composite reinforced by fibers comprising: - at least one natural fiber of a first type; and - at least one additional fiber of a second type, wherein the natural and additional fibers are combed or weaved together into a single roving or tow. Figure for the abstract: Fig. 3

Description

Hybridization of natural fiber reinforcement for composite materials and fabrics made therefrom

This disclosure relates generally to the field of fiber or fabric reinforced composite materials, and, in particular, to a roving, tow, or fabric for use in a fiber reinforced composite material, and the compositions results.

Every year, millions of kilograms of carbon fibers, glass fibers, flax fibers, basalt fibers and other fibers with interesting tearing, compressive and/or flexural strengths are produced for be used as reinforcing materials in fiber-reinforced composite materials, or FRC (from the English "Fiber-Reinforced Composites" Fiber-Reinforced Plastics", fiber-reinforced plastics). These reinforcing fibers are combined with thermoset or thermoformed plastic resins (collectively referred to as the matrix) to create structural materials with properties superior to the individual components.

It is frequently desired in the manufacture of structures in which specific characteristics are required to use a hybrid reinforcement of stacking of woven layers. Those skilled in the art will be familiar with alternating layers of fabric using different fibers and/or different constructions in order to tailor the performance of the resulting composite. It is also common to make a fabric in which the tows - which are fiber bundles that are substantially aligned along the lengthwise extending axis of the roving - are alternated along at least one axis of the fabric to create a hybrid fabric. (Although the words "roving" and "tow" are generally understood to be synonymous, for the sake of clarity, we will use "roving" in this application to refer to the isolated fiber bundle, and "tow" to refer to a roving that is woven or assembled to form a fabric.)

Examples of hybrid fabrics may include a 0/90 woven fabric in which every second tow in both axes changes from a fiberglass to a basalt fiber; a +45/-45 biaxial nonwoven fabric in which 5 fiberglass tows are arranged side by side with a carbon fiber tow arranged before the 6 tow pattern is repeated along both axes; or a 0/+60/-60 triaxial fabric where the 0° axis is made of carbon fiber tow, and each of the +60/-60 axes are made of aramid fiber tow.

The hybridized constructions described above can improve the overall performance of the final composite element in terms that can include ultimate strength, bending stiffness, vibration damping, impact resistance, or cost (among others). Notably, there may also be negative effects on the overall performance of the composite structure due to hybridization which may be accentuated depending on the amount of difference between the mechanical characteristics of one hybridization fiber to another. For example, if flax tows are alternated with carbon tows in a fabric, the flax fiber can contribute positively to the overall vibration characteristics of the resulting element; however, the fact that flax fibers have both lower elongation at break and lower tensile strength means that they will tend to break under stress before carbon fibers and are less able to contribute to the ultimate strength of the formed composite. Similarly, if "E" glass fiber and HM carbon fiber tows are alternated in a fabric, the significant difference in tensile stiffness means that the HM carbon tows will support the majority of the load and lift. stress is likely to occur over a small area at the point where the tows alternate, which can cause micro-fractures in the matrix and decrease the fatigue strength of the composite.

Furthermore, the ecological impact of the production of 1 kg of carbon fibers leads to the production of 30 kg of greenhouse gases and the production of 1 kg of "E" glass generates approximately 2.8 kg of greenhouse gases. greenhouse effect. Conversely, if carbon sequestration during cultivation is taken into account, most plant fiber reinforcements are carbon negative from birth to death. As the world struggles to heed demands to meet climate impact reduction targets set by the Paris Climate Treaty, European and United Nations climate targets and other authorities nationally and internationally, the demand for creating viable solutions to sustainably manufacture high-performance composites is correspondingly increasing.

Industries that rely heavily on the use of composites for manufacturing range from the automotive or aerospace sector to sports equipment and home appliances. These different industries require correspondingly different performance characteristics as well as significant volumes of their chosen composite reinforcing fibers. In this context, additional considerations for hybridization come to the fore. Of these it will be noted that of the many fibers that show promise for use in natural fiber reinforcement only a small percentage is grown on a large enough scale to be viable for industrial use.

A second factor that should be noted is fiber variability, as natural fibers – and more specifically plant fibers – can vary significantly in terms of mechanical characteristics depending on where they are grown and how many fibers are processed. . Achieving uniform roving quality requires that the variability inherent in plant fiber cultivation be controlled well enough that predictable performance can be achieved with a natural fiber, which is an ever-increasingly difficult goal in a time of changing climate. .

Third, with the wide variety of mechanical characteristics that result in the range of reliable natural mineral and vegetable fibers it is increasingly possible to tailor the performance of a composite reinforcement very precisely; however, it is also the range of characteristics that can amplify the problems described in the previous paragraph 0005.

Although there is significant interest in hybridizing natural fiber composites with both natural and synthetic fibers, all of the published research that the inventor has been able to find focuses on hybridization that is based on fiber type tows. a single fiber. The vast majority of research involves the creation of hybrid composites based on alternating layers of fabric based on plant fibers and layers of fabric based on synthetic fibers (typically "E" glass). Far fewer projects have investigated fabric performance when tow is alternated with natural and synthetic fibers in a single fabric.

In composites, the roving exists as the "smallest divisible unit" in which the reinforcing composition is uniform.

Unlike popular synthetic reinforcing fibers such as carbon and glass fibers which are designed as continuous filaments ( ) and combined into rovings (100) when fibers are placed parallel and close together and loosely bonded with a sizing agent (102); natural fibers intended for reinforcement ( ) are often finished lengths (201) and the rovings (200) are produced in a manner similar to how yarn is prepared for use from natural fibers, but without "twisting" - the difference being that the rovings instead lay on the surface structure of the fibers "locking" in place (202) with other neighboring fibers – either with or without the use of chemical treatment or bonding agents – at the same time that the fiber sliver is made thinner/lighter by a series of combs and cylinders or drums during processing.

Thus, there is a need in the art for an improved reinforcing fiber construction and reinforced fabric composition providing effective hybridization particularly in connection with natural fiber reinforcements.

Embodiments of the present description aim to satisfy all or part of the needs of the state of the art.

An aspect of this description ( ) consists of a roving (300) consisting of at least one natural fiber (301) of one type and at least one fiber of a second type (311). The fibers of each type are oriented lengthwise and untwisted into a continuous sliver of fibers (340 and 341), and said at least two slivers of fibers are then brought into register with each other and combed or serrated into a single roving wherein said at least two types of fibers are distributed in the resulting roving which has a weight of not less than 100 g per linear kilometer and not more than 2000 g per linear kilometer. This roving of hybridized natural fibers is used wholly or in part to form the reinforcing element or a tow or an FRC.

Embodiments are claimed in the claims.

One embodiment provides a roving or tow for a fiber reinforced composite comprising:
- at least one natural fiber of a first type; And
- at least one additional fiber of a second type,
in which the natural and supplementary fibers are combed or weaved together in a single roving or tow.

According to one embodiment, the natural and additional fibers are oriented lengthwise, for example without twist, or with minimal possible twist of the fibers in the roving or tow to form a continuous fiber sliver.

According to one embodiment, the natural and supplementary fibers are distributed in the roving or tow, the roving or tow having a weight of no less than 100 g per linear kilometer and no more than 2000 g per linear kilometer.

According to one embodiment, the natural fiber is a mineral fiber, of vegetable origin or of animal origin, and in which the percentage by weight of natural fibers in the roving or the tow is at least 50%.

According to one embodiment, the additional fiber is a synthetic fiber.

According to one embodiment, the additional fiber is a natural fiber of a type different from the first type.

According to one embodiment, the natural fiber of the first type is an extracted cellulose fiber.

According to one embodiment, the roving or the tow consists only of fibers of the first and second types and unavoidable impurities.

In one embodiment, the roving or tow is made only of fibers of the first and second types and fibers that are made of a thermoplastic material that is melted during the composite's curing cycle to form the matrix of the composite.

According to one embodiment, the roving or tow is made up of more than two types of fibers.

Another embodiment provides a reinforcing tape made of at least one roving as above.

Another embodiment provides a braided reinforcement consisting of at least one roving as above.

Another embodiment provides a fabric reinforcement which is sewn, woven or glued into a form consisting of at least one roving as above.

Another embodiment provides a fiber reinforced composite comprising a reinforcing member comprising a plurality of rovings or tows as above placed in a thermoset or thermoformed matrix.

Another embodiment provides a fiber reinforced composite comprising a reinforcing member comprising a plurality of rovings or tows as above and/or any of the reinforcements as above placed in a thermoset or thermoformed matrix.

Another embodiment provides a sliding board having a structural layer comprised of the above fiber reinforced composite.

Another embodiment provides a portable pole comprising a handle made of the above fiber reinforced composite.

Another embodiment provides a method of forming roving or tow for a fiber reinforced composite comprising: combing or combing together at least one natural fiber of a first type; and at least one additional fiber of a second type to form a single roving or tow.

The same elements have been designated by the same references in the various figures. In particular, the structural and/or functional elements which are common to the different embodiments may have the same references and may have identical structural, dimensional and material properties.

In the following description, when referring to absolute position qualifiers, such as "front", "rear", "up", "down", "left", "right", etc., or relative, such as the terms "above", "below", "upper", "lower", etc., or to qualifiers of orientation, such as the terms "horizontal", "vertical", etc., it reference is made unless otherwise specified to the orientation of the figures.

Unless specified otherwise, the expressions “about”, “approximately”, “substantially”, and “of the order of” mean to within 10%, preferably within 5%.

A "natural fiber" is any fiber of mineral or vegetable or animal origin which has a prepared length which is for example greater than 50 mm and which has desirable mechanical properties for reinforcing FRCs. Examples include basalt fibers and boron fibers (both mineral fibers); flax, hemp, ramie, bamboo, pineapple leaf, sisal, kenaf, banana leaf, and coconut fibers (all plant fibers); and silk, animal hair, and serous fibers (all fibers of animal origin). In the context of the present description, mineral, vegetable and animal are considered to be "classes" of natural fibres; basalt, boron, flax, ramie, bamboo, silk, etc. are considered to be "types" of fibers.

A "continuous fiber sliver" (also known as "worsted fiber sliver" or "fiber sliver") is an untwisted, loose, flexible cord-like strand of concurrent fibers having substantially uniform thickness and constant fiber orientation along the length of the tape. It is produced by the carding process, which separates raw fibers to prepare them for roving production.

The rovings can then be used in processing such as filament winding or incorporated as a unidirectional reinforcing tape in a matrix, or can be incorporated as tows into a braided, woven or sewn fabric in a multiaxial or unidirectional construction.

The rovings can be formed using any synthetic fiber, such as carbon, glass, aramid, etc., or any natural fiber, such as extracted cellulose, ramie, of flax, basalt, etc., or any other reinforcement which is or may become commonly used in the composites industry, provided that at least 50.1 percent of the fiber comprised in the roving is a natural fiber.

Fibers which are combined to produce the roving could each have a finished length which is not less than 40 mm and not more than 1200 mm ( ). In order to adjust the performance of the roving, the different types of fibers (401 and 411) can have different overall lengths such that fibers of a first type can have a length which is between 300 mm and 400 mm, whereas fibers of a second type can have a length which is between 80 mm and 150 mm, for example.

The rovings and/or fabrics can be combined with any thermoset or thermoformed resin system to form an FRC.

Startyarns can be created having more than two types of fibers.

Tows can be incorporated into a fabric such that at least one tow in at least one axis uses the "natural fiber hybridized roving" construction.

Natural fiber hybridized rovings can be incorporated into a braided, woven or sewn fabric exclusive of other fiber tows, or a roving can be created by using a natural fiber hybridized roving and incorporated into a fabric with unhybridized reinforcing tows.

Tows, rovings, and fabrics created from rovings hybridized with natural fibers may have additions of resins, resin-based filaments (such as polylactic acid, polyolefin, or polyamide) or other additional chemicals that are added to adjust the performance of the resulting FRC.

The advantages of this solution are numerous:

1) When natural fibers with relatively similar mechanical characteristics such as hemp, flax, ramie, nettle, alpha and/or extracted cellulose are used in a single roving, it is much more possible to repeat the characteristics roving mechanics, harvest after harvest, with less likelihood of batch variance because there is a larger sample size of fiber to be drawn. As the characteristics of each type of fiber vary little, this ensures a greater ability to mix the fibers to obtain a specified set of mechanical values; and processing the extracted cellulose provides a plant-derived fiber that can mimic the repeatability of synthetic fibers.

2) Rather than exclusively using mined cellulose in rovings, which would increase the ecological impact of fiber reinforcement, combine cleaned plant fibers (i.e. flax, ramie, hemp, etc.) with the extracted cellulose reduces the overall production of greenhouse gases, and increases the biodegradability of the resulting rovings.

3) Research into the flexural strength and tensile strength of certain combinations of natural fibers shows an improvement of approximately 5-10% and in some cases more than 20% when the fibers are arranged in a unidirectional orientation and cast in an epoxy matrix when comparing the performance of alternating separate rovings made of two plant fibers to the performance of the same mass of combed fibers in hybridized rovings. The increase in the homogeneity of the fibers in the matrix allows more effective resistance to loads among the different fibers and a reduction in microfractures in the matrix where the mechanical characteristics of the variant rovings cause stress increases.

4) The extreme stiffness of high modulus carbon fibers has allowed the wall thickness of composite elements to become exceptionally thin. The density of carbon fibers is typically 1.8-2.0. Although much less stiff than HM carbon fiber, and requiring a thicker wall to achieve the same stiffness, fiberglass has a density of 2.7-3.0 making it far less efficient in terms of stiffness production . On the contrary, natural fibers lie in terms of functional density in a range between 0.9 and 1.8 and have the ability to be inserted into composites having a greater wall thickness than carbon at corresponding fiber mass. . Since the wall thickness of a composite structure influences the stiffness of the structure as a cubic function [Bending Stiffness = (Young's Modulus * Cubed Thickness)/12 * (1 - Poisson's Ratio )], the ability to increase the dimension of a wall with minimal additional mass by incorporating lower density fibers into the wall can be extremely advantageous in overcoming the difference in mechanical properties between carbon and plant fibers.

5) By hybridizing rovings with component fibers of different types and lengths, it is possible to optimize the performance of the roving for an application. If, for example, high elongational stiffness and high bending stiffness are required, then the use of a first fiber having a high elongation (such as extracted cellulose) of a greater length of fiber and hybridizing it with a second fiber having higher bending stiffness (such as basalt) of a shorter fiber length would lead to a resulting composite in which the tensile elongation of the Extracted cellulose is not excessively restricted by the tensile strength of basalt fiber, but the bending stiffness of basalt fiber can effectively increase the bending stiffness of extracted cellulose fiber. With continuous fiber rovings of a single fiber type, these characteristics would be difficult to achieve, making the hybridized roving advantageous in a range of applications where seemingly antagonistic or mutually opposing performance is desired.

Examples of fabrics comprising rovings or tows as described here are shown in Figures 5 to 13, these fabrics being for example similar to those described in the PCT application published under number WO2020/222045, but the tow or roving of this application being in this application replaced by the roving or tow described here. The contents of this PCT application as published are incorporated herein by reference to the extent permitted by law.

There represents a unidirectionally reinforced fabric made of fiber reinforced tows as previously described.

There shows a unidirectionally reinforced sewn fabric made of fiber reinforced tows using at least one tow as previously described.

There shows a multiaxial sewn fabric made of fiber reinforced tow using at least one tow as previously described.

There represents a multiaxial woven fabric made of fiber reinforced tows using at least one tow as previously described.

There represents a tubular braid made of fiber reinforced tows using at least one tow as described above.

There represents a unidirectional fabric comprising the alternation of tows of reinforcing fibers located in tows as described above.

There represents a biaxial fabric comprising the alternation of tows of reinforcing fibers located in tows as described above.

There represents a 2x1 twill fabric comprising alternating tows of reinforcing fibers located in tows as previously described.

There represents a plain weave fabric comprising alternating tows of reinforcing fibers located in tows as previously described.

In figures 5 to 13, the references designate the following elements:
- 500 unidirectional reinforced fabric;
- unidirectional stitched fabric (UD) 600;
- the tows as previously described in strips 602;
- additional thread 604;
- 700 multiaxial sewn fabric;
- cables 702;
- seam 704;
- 800 multiaxial woven fabric;
- cables in the vertical direction 802;
- cables 804 in the horizontal direction;
- 900 tubular braid;
- cable 902;
- 1000 unidirectional fabric;
- roving 1002 as described here;
- other rovings 1004 made of other materials;
- biaxial fabric 1100;
- two layers 1102, 1104 of a unidirectional fabric;
- 2x1 1200 twill fabric;
- tow 1002 as described here;
- other tows 1004;
- 1300 plain weave fabric.

Various embodiments and variants have been described. The person skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will occur to the person skilled in the art.

Finally, the practical implementation of the embodiments and variants described is within the abilities of those skilled in the art based on the functional indications given above.

Claims (18)

Roving or tow for a fiber reinforced composite comprising:
- at least one natural fiber of a first type; And
- at least one additional fiber of a second type,
in which the natural and supplementary fibers are combed or weaved together in a single roving or tow. A roving or tow according to claim 1, wherein the natural and additional fibers are oriented lengthwise, for example without twist, or with minimal possible twisting of the fibers in the roving or tow to form a sliver of fibers continued. The roving or tow according to claim 1 or 2, wherein the natural and additional fibers are distributed in the roving or tow, the roving or tow having a weight of not less than 100 g per linear kilometer and not more than 2000 g per linear kilometer. The roving or tow according to any one of claims 1 to 3, in which the natural fiber is a mineral fiber, of vegetable origin or of animal origin, and in which the percentage by weight of natural fibers in the roving or the tow is at least 50%. Roving or tow according to any one of Claims 1 to 4, in which the additional fiber is a synthetic fibre. Roving or tow according to any one of claims 1 to 4, wherein the additional fiber is a natural fiber of a type different from the first type. Roving or tow according to any one of claims 1 to 6, wherein the natural fiber of the first type is an extracted cellulose fibre. Roving or tow according to any one of Claims 1 to 7, consisting only of fibers of the first and second types and unavoidable impurities. A roving or tow according to any one of claims 1 to 7, consisting only of fibers of the first and second types and of fibers which are made of a thermoplastic material which is melted during the curing cycle of the composite to form the matrix of the composite . Roving or tow according to any one of claims 1 to 7, consisting of more than two types of fibres. Reinforcing tape consisting of at least one roving according to any one of claims 1 to 10. Braided reinforcement consisting of at least one roving according to any one of claims 1 to 10. Fabric reinforcement which is sewn, woven or glued in a form consisting of at least one roving according to any one of claims 1 to 10. A fiber reinforced composite comprising a reinforcing element comprising a plurality of rovings or tows according to any one of claims 1 to 10 placed in a thermoset or thermoformed matrix. A fiber reinforced composite comprising a reinforcing element comprising a plurality of rovings or tows according to any of claims 1 to 10 and/or any of the reinforcements according to any of claims 11 to 13 placed in a thermoset or thermoformed matrix. A sliding board having a structural layer made of the fiber reinforced composite according to claim 15. A portable pole (1500) comprising a handle made from the fiber reinforced composite of claim 15. A method of forming roving or tow for a fiber reinforced composite comprising:
- the combing or serring together of at least one natural fiber of a first type; and at least one additional fiber of a second type to form a single roving or tow.