WO2002026877A2

WO2002026877A2 - Modified cellulose acetate fibers and methods and apparatus for making the same

Info

Publication number: WO2002026877A2
Application number: PCT/JP2001/008582
Authority: WO
Inventors: Yasutaka Ebata; Atsushi Suzuki; Masamitsu Funaoka
Original assignee: Araco Kabushiki Kaisha
Priority date: 2000-09-29
Filing date: 2001-09-28
Publication date: 2002-04-04
Also published as: JP2002105746A; WO2002026877A3

Abstract

ABSTRACTCellulose acetate may be dissolved and mixed with a lignin derivative in acetone in order to form a modified cellulose acetate. The modified product of cellulose acetate is then spun to form a modified cellulose acetate fiber. A mixed fiber mat can be prepared by blending the modified cellulose acetate fiber with natural cellulose fibers and then softening the mixture. Thereafter, the mixed fiber mat can be heated and pressed to form a fiber laminate board that is, e.g., suitable for use as trim materials for automobiles.

Description

MODIFIED CELLULOSE ACETATE FIBERS AND METHODS AND APPARATUS FOR MAKING THE SAME

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to techniques for making modified cellulose acetate fibers and fiber laminate moldings, which may be suitably used s trim materials for automobiles.

Description of Related Art

A technique is generally known for manufacturing a fiber laminate board that can be used as a trim material for automobiles (e.g.- a base material far a door trim). The fiber laminate board is manufactured with cellulose acetate fibers molded from cellulose acetate and natural cellulose fibers obtained from plants. In accordance with this kno n technique, cellulose acetate fibers are kneaded with natural cellulose fibers and loosened to prepare a mixed fiber mat. The mixed fiber mat is then hot press treated. In this process, cellulose acetate serves as a binder and is softened. Further, the mixed fiber mat is molded into a board-like fib r l minate board.

Cellulose acetate, however, has poor fluidity and low thermal plasticity. Therefore the hcaLing and pressing treatment must be performed at a relatively high temperature and pressure in order to soften the cellulose acetate and improve its moldability. However, because high temperatures and pressures can easily degrade the fibers, the known method is disadvantageous.

SUMMARY OF THE INVENTION It is, accordingly, one object of the present teaching to provide improved cellulose-based materials and methods and apparatus tor making the same.

In one aspect of the present teachings, effective techniques are taught for producing modified cellulose acetate fibers and fiber laminate moldings using the modified cellulose acetate fibers. The fiber laminate moldings can be effectively utilized as trim materials for automobiles.

In another embodiment of the present teachings, cellulose acetate is modified by dissolving and mixing with a lignin derivative in an organic solvent (first step) and then spinning the modified product (second step), For example, a cellulose acetate modification product is produced by dissolving and mixing cellulose acetate and ligno-phenol (ligπin derivative) in acetone. Then, the desired modified cellulose acetate fiber can be obtained by spinning the cellulose acetate modification product into fibers.

The modified cellulose acetate fiber has a lower softening temperature than unmodified cellulose acetate fibers (i.e., fibers obtained by spinning cellulose acetate). Therefore, it is possible to make the modified cellulose acetate fibers at lower temperatures and pressure. Further, the modified cellulose acetate fibers have higher tensile strength and lower hygroscopicity than unmodified cellulose acetate fiber, which permits the production of stronger and moisture-resistance products.

The term "lignin derivatives" employed in the present specification includes products derived from lignin, for example, ligno-phenol, organosolv lignin and other similar lignin derivatives. Such lignin derivatives can be obtained by extracting lignin from lignin-containing ligno-ccllulosc materials. The term "solvent" employed in the present specification includes acetone, glacial acetic acid, phenol and other similar organic solvents. Moreover, the term "modification" employed in the present specification covers a wide range of processes resulting in changes of properties, e.g., softening temperature, tensile strength, hygroscopicily, and is not limited, for example, to any pecific -structural transformation on a molecular level. In another embodiment, kenaf is preferably used as a raw material for the ligπin derivative. Kenaf is also known as Hibiscus cannabis and is considered to be a nύn-woody source of fiber. By utilizing kenaf instead of the wood fibers from coniferous or broad-leaf trees, forest resources can be conserved.

Further, substantially the entire kenaf can be utilized in the present teachings, which minimizes waste. For example, the lignin can be extracted from the kenaf core and the natural cellulose fibers can be extracted from the kenaf bast or cortex, Ligno-phenol obtained from kenaf is particularly preferred in the present teachings.

Additional objects, features and advantages of the present invention will be readily understood after reading the following detailed description together with the accompanying drawings and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a process for manufacturing a modified cellulose acetate fiber and a fiber laminate board.

Fig. 2 shows the extraction of cellulose fibers and lignin derivatives from the core and bast of kenaf.

Fig, 3 shows a representative technique for spinning the modified cellulose acetate into fibers.

Fig. 4 shows representative press molding conditions.

Fig. 5 shows the melting points of modified cellulose acetates.

Fig. 6 shows the tensile strength of films prepared from modified cellulose acetates.

Fig, 7 shows test hygroscopicity of modified cellulose acetates.

DETAILED DESCRIPTION OF THE INVENTION

In one embodiment of the present teachings, methods are taught that include dissolving and mixing a cellulose acetate with a lignin derivative in an organic solvent. The modified cellulose acetate formed by this step is then spun in order to form modified cellulose acetate fibers. Preferably, the lignin derivative comprises a raw material generated from kenaf, more preferably the lignin derivative is a ligno-phenol and most preferably, the lignin derivative is ligno-cresol. In a preferred embodiment, the organic solvent may comprise acetone.

The weight ratio of ligπin derivative to cellulose acetate may be about 5- 20%. Further, the lignin derivative may have a relatively high ratio of syringyl units to guaiacyl units. For example, the lignin derivative may have a substantially linear molecular configuration.

Naturally, modified cellulose acetate fibers produced according to the present methods are also contemplated. In one embodiment, the modified cellulose acetate fibers preferably have a melting point between about 180-240"C, In another embodiment, the modified cellulose acetate fibers preferably have a maximum stress strength of at least about 70 Mpa. In further embodiment, the modified Cellulose acetate fibers preferably have a hygroscopicity of about 6%.

Methods are further taught for processing the above-described modified cellulose acetate fibers. For example, the modified cellulose acetate fibers may be mixed or blended with natural cellulose fibers and the mixture may be loosened in order to form a mixed fiber mat. Thereafter, the mixed fiber mat may be heated and pressed in order to form a fiber laminate molding. In one embodiment, the mixed fiber mat is heated at 160-240'C at a pressure of 10-50 kgf/c ² for about 0.5-3 minutes. In another embodiment, the mixed fiber mat is heated at 100»180^QC at a pressure of 20-100 kgf/cm² for about 0.5-3 minutes. Naturally, the present teachings further contemplated fiber laminate moldings produced by any of these methods.

In another embodiment of the present teachings, apparatus are taught for practicing the above-described methods and making the above-described modified cellulose fibers. For example, representative apparatus may include means for dissolving and mixing cellulose acetate with a lignin derivative in an organic solvent in order to form a modified cellulose acetate. Further, means may be provided for spinning the modified cellulose acetate in order to form the modified cellulose acetate fibers.

Apparatus may further include means for blending the modi ied cellulose acetate fibers with natural cellulose fibers and loosing the mixture in order to form a mixed fiber mat. Further, means may be provided for heating and pressing the mixed fiber mat in order to form a fiber laminate molding.

Each of the additional features and method steps disclosed above and below may be utilized separately or in conjunction with other features and method steps to provide improved materials, methods and apparatus. Representative examples of the present invention, which examples utilize many of these additional features and method steps in conjunction, will now be described in detail with reference to the attached drawings. This detailed description is merely intended to teach a person of skill in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the invention. Only the claims define the scope of the claimed invention. Therefore, combinations of features and steps disclosed in the following detail description may not be necessary to practice the invention in the broadest sense, and are instead taught merely to particularly describe representative examples of the invention, Moreover, various features of the representative examples and dependent claims may be combined in ways that arc not specifically enumerated in order to provide additional useful embodiments of the present teachings.

First, an embodiment will be described in which a modified cellulose acetate fiber is produced from a cellulose acetate and ligno-crcsol, which is one type of ligno-phenol that is a lignin derivative. Preferably, kenaf is utilized as a raw material for the ligno-cresol. Thereafter, an embodiment will be described in which a fiber laminate (board) is prepared for use as a trim material for automobiles. The fiber laminate is preferably prepared from a combination of the modified cellulose acetate fibers and natural cellulose fibers. Again, kenaf is preferably utilized as the raw material for the natural cellulose fibers. A representative manufacturing process is shown in Fig. 1. For example, cellulose acetate and ligno-cresol (lignin derivative) are dissolved in acetone. Thereafter, the mixture is spun to produce the modified cellulose acetate fiber. Then, a fiber laminate board may be manufactured from a combination of the modified cellulose acetate fiber and natural cellulose fibers.

As noted above, both the ligno-cresol (lignin derivative) and cellulose fibers may be prepared from a raw material that comprises kenaf. As shown in Fig. 2, ligno-cresol (lignin derivative) can be extracted from a core portion (core) of kenaf. In addition, cellulose fibers can be obtained by separating the cellulose fibers from the bast portion of kenaf. Thus, the present teachings provide an effective means for utilizing the entire kenaf in order to make modified cellulose acetate fibers and fiber laminate boards.

Dissolving and Mixing

As noted above, cellulose acetate and ligno-cresol (lignin derivative) are preferably dissolved and mixed in acetone. Acetone is one preferred solvent for use with the present teachings, although other organic solvents also can be utilized with the present teachings. Generally speaking, any lignin that is soluble in an organic solvent also can be used as the ignin derivative instead of ligno-cresol.

In a preferred embodiment, the weight ratio of lignin derivative (e.g., ligno- cresol) t respect to cellul se acetate is preferably about 5 to 20 wt,%. Such weight ratios provide modified cellulose acetate having desirable properties, as will be further described below.

As noted above, kenaf is preferably used as the raw material for the lignin derivative, such as ligno-cresol. Lignin derivatives derived from kenaf have a very high ratio of syringaldehyde (S) to vanillin (V). Furthermore, such kcnaf- dcrivcd lignin derivatives also have a molecular configuration that is more linear than other lignin derivatives. As a result, such lignin derivatives have good affinity for cellulose acetate and a highly-plastic cellulose acetate can be obtained. The S/V ratio represents a ratio of syringaldehyde (S) to vanillin (V) that are obtained as decomposition products when lignin derivatives are subjected to alkali nitrobenzene oxidation and decomposition.

Lignins generally have three types of basic units: syringyl-type, guaiacyl- type, and parahydrophenol-type. Syringyl and guaiacyl types arc radically polymerized during biosynthesis and a polymer of these basic units forms lignin. Syringyl-type basic units have two polymerization sites and guaiacyl-type basic units have three polymerization sites. As a result, when a relatively large amount of syringyl-type basic units is present, the resulting lignin polymer will have a generally linear molecular configuration. On the other hand, when a relatively large amount of guaiacyl-type basic units is present, the resulting lignin will have a substantially three-dimensionally branched molecular configuration.

Syringaldehyde is a decomposition product derived from syringyl-type basic units and vanillin is a decomposition product derived from guaiacyl-type basic units. Therefore, if the S/V ratio is relatively high, a substantially linear molecular configuration is obtained. In order for the lignin derivative to effectively serve as a softening agent for the cellulose acetate, the lignin derivative will preferably enter into gaps between cellulose acetate molecules. Thus, because generally linear .lignin derivatives (i,e, having a relatively high S/V ratio) can more efficiently enter into such gaps, generally speaking, linear lignin derivatives are preferable. Therefore, kenaf-derived lignin derivatives having a relatively high S/V ratio have a good affinity for cellulose acetate in order to soften the cellulose acetate.

Spinning

After dissolving and mixing in an organic solvent, the resulting modified cellulose acetate is preferably subjected to a spinning treatment process. In the spinning process, the modified cellulose acetate (polymer mixture) is spun using a spinning machine, as shown for example in Fig, 3. The spin machine preferably forms the modified cellulose acetate into thread and the threads can be wound around an appropriate structure. As a result, this spinning or thread formation technique produces the modified cellulose acetate fiber. Because spinning or thread formation is conducted at a low temperature, acetone is separated from the modified cellulose acetate fibers and can be easily recovered. Therefore, because acetone is substantially removed before the hot pressing process, which will be described below, working conditions during the hot pressing process can be improved.

Blending

After the spinning process, the modified cellulose acetate fibers and natural cellulose fibers (preferably derived from kenaf) are blended and softened in a defibration process. For example, the modified cellulose acetate fiber and cellulose fibers may be first cut to an appropriate length (e.g., about 70 mm). Then, the cut modified cellulose acetate fibers staple and cellulose fibers arc kneaded and softened in order to substantially uniformly mix the two fibers. A mixed fiber mat will result from this defibration process.

Heating and Pressing Treatment

Thereafter, the mixed fiber mat may be heated and pressed. As a result, the softened cellulose acetate will act as a binder for the cellulose fibers and the fiber laminate can be molded into a fiber laminate board or other form.

Fig. 4 shows preferred heating and pressing conditions using, e.g., a hot press molding method or a cold press molding method. For example, in a representative hot press molding method, the mold temperature is preferably between about 160-240°C, the pressure is preferably between about 10-50 kgf/cm*, and the lime that the heat and pressure are applied is between about 0.5-3 min. Further, in a representative cold press molding method, the furnace temperature is preferably between about 190-260°C, the mold temperature is preferably between about 100-180°C, the pressure is preferably between about 20-100 kgf/cm², and the time that the heal and pressure arc applied is between about 0.5-3 min. If such conditions are utilized, fiber laminate boards can be molded that arc suitable for use, e.g., as automobile trim materials (i.e., base materials for a door trim). In addition, as shown in Fig. 4, by using modified cellulose acetates, the heating and pressure treatments can be performed at lower temperatures and pressures for a shorter time than methods utilized with unmodified cellulose acetates. Because processing time can be shortened, the service life of the mold can be extended.

Further, the lignin derivatives used in. this representative embodiment . preferably h v a molecular weight of several thousands and a melting point of about 150°C. Therefore, the lignin derivative does not migrate to the molding surface within the range of conditions in which fiber laminate boards arc used.

In order to provide comparative testing and to determine the properties of the modified cellulose acetates of the present teachings, modified cellulose acetate A was prepared according to_t he above-described methods using ligno-cresol as the lignin derivative. Modified cellulose acetate B was prepared according to the above-described methods using an organic solvent soluble lignin as a lignin derivative. Test results concerning these two acetate products will be explained below with reference to Figs. 5-7.

Fig. 5 shows melting point data for the modified cellulose acetate A and modified cellulose acetate B, The melting point (°C) of the modified cellulose acetates changed in accordance with changes in the addition ratio (wt%) of the lignin derivative with respect to cellulose acetates. For example, as shown in Fig. 5, the melting point of both modified cellulose acetate A and modified cellulose acetate B decreased with an increase in the lignin derivative addition ration. Unmodified cellulose acetate (i.e., no lignin derivative is mixed with the cellulose acetate) has a melting point of about 250^DC. On the other hand, when the addition ratio was 5-10 wt%, modified cellulose acetate A and B had melting points of about 210°C. Further, in modified cellulose acetate A, when the ligno-cresol addition ratio reaches about 20 wt%, the melting point drops to about 180^DC. Thus, modified cellulose acetates having melting points that are lower than unmodified cellulose acetates can be obtained by utilizing a lignin derivative addition ratio, for example, of 5-20 wt%. If the melting point is reduced, the modified cellulose acetates can be molded at lower temperatures and pressures. Lower molding temperatures and pressures provide the advantageous effect of suppressing fiber degradation In the resulting fiber laminate board.

Modified cellulose acetates A and B were molded to films (width 5 mm, length 50 mm, thickness 0.2 mm) in order to measu e the tensile strength of the modified cellulose acetate films using appropriate lest equipment (i.e., an autograph). The data shown in Fig. 6 represent changes in the tensile strength (MPa) of the modified cellulose acetate films observed when the addition ratio

(wt ) of lignin derivative with respect to cellulose acetate was changed.

For example, as shown in Fig. 6, the tensile strength of the film formed from modified cellulose acetate A increased with increases in the ligno-cresol addition ratio. The maximum measured stress of the unmodified cellulose acetate film (i.e., no lignin derivative) was about 60 Mpa. On the other hand, the maximum measured stress of modified cellulose acetate film A having addition ratio of ligno-cresol of about 10-20 wt% was about 70 MPa, Further, the tensile strength of the film formed from modified cellulose acetate B decreased wjth increases in the organosolv lignin addition ratio.

Therefore, modified cellulose acetate A can be utilized to mold fiber laminate boards having increased strength as compared to fiber laminate boards molded from unmodified cellulose acetate.

Fig. 7 shows data obtained in measuring the hygroscopicity of modified cellulose acetates A and B. Hygroscopicity refers to the ability of a material to absorb and retain moisture and these data represent changes in hygroscopicity (%) of modified cellulose acetates observed when the addition ratio (wt%) of the lignin derivative with res.pect to cellulose acetate was changed. Specifically, the hygroscopicity of both modified cellulose acetates A and B decreased with increases in the lignin derivative addition ratio. For example, the hygroscopicity of the film formed from unmodified cellulose acetate (i.e., no lignin derivative) was about 11%. On the other hand, the hygroscopicity of a film formed from modified cellulose acetates having a lignin derivative addition ratio of about 10 wt% was about 6% .

Therefore, modified cellulose acetates A and B can be used to mold fiber laminate boards that are better able to resist moisture absorption and retention than fiber laminate boards molded from unmodified cellulose acetate. Reduced moisture retention is particularly advantageous for materials thai will be exposed to water or other moisture in order to avoid degradation of the material.

Thus, modified cellulose acetate fibers and fiber laminate boards are taught that have a low softening temperature, good mύldability, high tensile Strength and low hygroscopicity. Further, fiber laminate boards having high strength and resistance to water can be manufactured according to the present teachings and these fiber laminate boards may be suitably used as trim materials for automobiles.

Kenaf represents a non-woody fiber that can be effectively used for the manufacture of the modified cellulose acetate fibers and fiber laminate board. In addition, because useful lignin derivatives can be derived from kenaf are used, the lignin derivatives have high affinity for cellulose acetate and a highly plastic cellulose acetate can be obtained. In addition, cellulose acetate is a bio- decomposable material and is safer for the environment than polypropylene materials, which are typically used as a binder in the known fiber laminate board manufacturing techniques.

Various modifications are possible to the representative embodiments. For example, natural cellulose fibers and lignin derivatives derived from materials other than kenaf can also be advantageously utilized as a raw material in the present teachings. For example, non-woody fibers such as paper mulberry, Manila hemp, straw, bagasse and the like and woody fibers of coniferous trees or broad- leaf trees can be readily used as the raw materials of the present teachings.

Further, the present teachings are not limited to the use of ligno-cresol (a type of ligno-phenol) and an organosolv lignin as the lignin derivative. For example, a variety of other ligno-phenols having different types of phenols grafted (bonded) onto lignin can also be advantageously used with the present teachings. As particular representative examples, hydrophilic ligno-phenols (ligπo-catcchol and the like) in which a phenol derivative with a large number of hydroxyl groups is grafted, hydrophobic ligno-phenols (ligno-xylenol and the like) in which a phenol derivative with a large number of alkyl groups is grafted, and low- crystallinity ligno-phenols (ligno-propylphenol and the like) in which phenol derivatives with long alkyl groups are grafted can be used.

Further, although acetone is a preferred organic solvent, suitable organic solvents are not limited to acetone and various organic solvents can be selected as manufacturing conditions dictate. For example, glacial acetic acid and phenol also can be advantageously used as the organic solvent.

Finally, although fiber laminate boards prepared according to the present teachings were described as being useful as trim materials, a variety of products can be made from the methods of the present teachings. In fact, the shape of the fiber laminate molding is not limited to a board-shape and can be changed as desired. Furthermore, the present fiber laminate moldings can be utilized for a variety of applications other than automobiles.

Claims

Claims-

1. A method comprising; dissolving and mixing an cellulose acetate with a lignin derivative in an organic solvent, thereby forming a modified cellulose acetate, and spinning the modified cellulose acetate, thereby forming modified cellulose acetate fibers.

2. A method as in claim 1, wherein the lignin derivative comprises a raw material generated from kenaf.

3. A method as in claim 1 or 2, wherein the lignin derivative is a ligno-phenol.

4. A method as in claim 1, 2 or 3, wherein the lignin derivative is ligno-cresol.

5. A method as in any of claims 1-4, wherein the weight ratio of lignin derivative to cellulose acetate is about 5-20%.

6. A method as in any of claims 1-5, wherein the lignin derivative has a relatively high ratio of syringyl units to guaiacyl units.

7. A method as in any of claims 1-6, wherein the lignin derivative is substantially linear.

S. A method as in any of claims 1-7, wherein the organic -solvent comprises acetone.

9, Modified cellulose acetate fibers produced by the method of any of claims

1-8.

10. Modified cellulose acetate fibers as in claim 9, wherein the modified cellulose acetate fibers have a melting point between about 180-210°C,

11. Modified cellulose acetate fibers as in claim 9 or 10, wherein the modified cellulose acetate fibers have a maximum stress strength of at least about 70 Mpa.

12. Modified cellulose acetate fibers as in claim 9, 10 or 11, wherein the modified cellulose acetate. fibers have a hygroscopicity of about 6%.

13. A method as in any of claims 1-8, further comprising: blending the modified cellulose acetate fibers with natural cellulose fibers and loosening the mixture, thereby forming a mixed fiber mat, and heating and pressing the mixed fiber mat, thereby forming a fiber laminate molding.

14. A method comprising: blending the modified cellulose acetate fibers of any of claims 9-12 with natural cellulose fibers and loosening the mixture, thereby forming a mixed fiber mat, and heating and pressing the mixed fiber mat, thereby forming a fiber laminate molding.

15. A method as in claim 13 or 14, wherein the mixed fiber mat is heated at 160-240"C at a pressure of 10-50 kgf/cm² for about 0.5-3 minutes.

16. A method as in claim 13 or 14, wherein the fiber laminate is heated at 100- 180°C at a pressure of 20-100 kgf/cm² for about 0.5-3 minutes.

17. A fiber laminate molding produced by the method of any of claims 13-16.

18, An apparatus comprising: means for generating a modified product of cellulose acetate by dissolving and mixing an cellulose acetate with a lignin derivative in an organic solvent, and means for spinning the modified product, thereby forming modified cellulose acetate fibers.

19. An apparatus as in claim 18, further comprising; means for blending the modified cellulose acetate fibers with natural cellulose fibers and loosening the mixture, thereby forming a mixed fiber mat, and means for heating and pressing the mixed fiber mat, thereby forming a fiber laminate molding.

20, An apparatus as in claim 18 or .19, wherein the ligπin derivative comprises a raw material generated from kenaf.

21. An apparatus as in claim 18, 19 or 20, wherein the lignin derivative is ligno- cresol.