JP7766600B2 - Melt-spun cellulosic fibers - Google Patents

Description

The present invention relates to melt-spun cellulosic fibers, particularly molar mass-controlled cellulose (MMCC) esters and their use in the production of man-made continuous fibers by the melt-spinning process.

The market for biopolymers and bioplastics has enormous growth potential in the future. Estimates suggest that the production capacity of bio-based polymers will grow from 1.7 Mt in 2014 to 7.8 Mt in 2019 (a five-fold increase). Several well-known companies have announced their interest in replacing petroleum-based polymers with 100% renewable materials. Melt spinning is one of the most economical and convenient methods for producing continuous fibers in large quantities for the textile industry.

Currently, many of the man-made fibers used in clothing and furniture are derived from fossil petroleum. Burning products made from fossil petroleum increases atmospheric _CO2 levels, accelerating the effects of climate change. Thermoplastic materials used to make man-made fibers must have suitable properties from a processing perspective.

Cellulosic melt-spun fibers have previously been reported, with only a few results being prepared using cellulose acetate butyrate (CAB) (Chen et al., 2010; Hooshmand et al., 2014b, a; Wang et al., 2018). However, all of these reported short-chain cellulose derivatives require a plasticizer (e.g., triethyl citrate).

WO 2016/193542 A1 discloses a general method for improving the reactivity and processability of cellulose, providing a starting point for hydrolyzed and reactive molar mass-controlled cellulose with thermoplastic properties.

JP 2005/248354A discloses a method for producing cellulose fatty acid ester fibers that have excellent mechanical properties, particularly strength and modulus, and are highly productive. It also describes a melt spinning method for preparing continuous cellulosic fibers. However, it does not disclose how to control the molar mass and molar mass distribution of dissolving pulp raw materials through hydrolysis. Furthermore, the same document discloses the use of 5 to 25% by weight of a polyhydric alcohol-based plasticizer and a high melt spinning temperature of 260 to 340°C.

To increase the use of cellulosic materials in melt-spun fiber production, a means is needed to modify cellulosic fibers to have different thermoplastic properties, preferably by using lower melt-spinning temperatures without the addition of plasticizers.

The present invention is defined by the features of the independent claims. Some particular embodiments are defined in the dependent claims.

According to one aspect of the present invention, a melt spinning method for preparing continuous cellulosic fibers is provided.

In accordance with another aspect of the present invention, there is provided a melt-spinning method for preparing continuous cellulosic fibers from fully bio-based, controlled-molecular-mass cellulose esters and the resulting melt-spun fibers having suitable mechanical properties for various end uses, such as in the textile industry.

These and other aspects, along with the advantages thereof over known solutions, are achieved by the present invention as described and claimed below.

The melt spinning method of the present invention is primarily characterized by what is set forth in the characterizing portion of claim 1.

The melt-spun fiber of the present invention is characterized by claim 10.

The present invention offers considerable advantages. The melt spinning process is one of the most convenient methods for producing polymer fibers on an industrial scale for the textile industry. Melt spinning is a simple process and offers many advantages over solvent or wet fiber spinning, including the absence of solvents, the absence of toxic by-products, and fast production rates. The MMCC grade used is a fully biobased thermoplastic material. Furthermore, the suitability of MMCC for fiber manufacturing is demonstrated herein without the addition of plasticizers.

Next, this technology will be described in more detail with reference to specific embodiments.

This technology provides a melt-spinning process for thermoplastic cellulose esters. Molar mass-controlled cellulose esters with different side chain lengths and varying degrees of substitution (DS) were synthesized and their suitability for fiber production was evaluated. Capillary rheometer tests were performed to confirm differences in thermal behavior, and the optimal cellulose ester was selected based on the results and subjected to larger-scale melt-spinning tests.

1 is a chart showing capillary rheometer testing of cellulose hexanate and cellulose octanate compared to a polypropylene standard. 1 is an image showing melt-spun A) cellulose hexanate fiber (DS 1.5) and B) cellulose octanate fiber (DS 1.5). SEM images of A) cross section and B) surface of melt-spun cellulose octanoate fibers at 300x magnification. Scale bar = 20 μm.

In this invention, several different grades of molar mass controlled cellulose (MMCC) with various side chain lengths (C6-C16) and degrees of substitution (DS) were tested. According to one embodiment of the present invention, it was found that molar mass controlled cellulose octanate (MMCC C8) with a degree of substitution of 1.4 provides one suitable starting point for increasing the use of cellulosic starting materials in melt-spun fiber production.

According to one embodiment of the present invention, the melt spinning method of the present invention comprises preparing a continuous cellulosic fiber:
preparing a controlled molar mass cellulose ester from a cellulose feedstock having a side length of C2 to C18, a total degree of substitution of 0.7 to 3, and a molar mass distribution of 30 to 300 kDa;
melt-spinning the controlled molar mass cellulose ester using a melt-spinning apparatus;
and recovering the melt-spun fibers.

According to one embodiment, the method involves controlling (i.e., reducing) the molar mass of a cellulose feedstock through hydrolysis, except for complete hydrolysis, and performing long-chain fatty acid modification, e.g., esterification or hydroxyalkylation, to obtain a molar mass-controlled cellulose.

According to a further embodiment of the present invention, the hydrolysis is controlled so that the average molecular weight of the cellulose is reduced by at least 60% and not more than 85% from the molecular weight of the starting material. It is preferable to control the hydrolysis so that after hydrolysis, the average molecular weight of the cellulose is between 30 and 300 kDa, preferably between 40 and 200 kDa. It should be noted that the molar mass of the cellulose is actually controlled, so that the cellulose does not undergo complete hydrolysis.

According to one embodiment, the cellulose raw material is selected from natural softwood pulp, natural hardwood pulp, annual plant pulp such as bamboo pulp or straw pulp, softwood sulfite-dissolving pulp, hardwood sulfite-dissolving pulp, ozone-treated hydrolyzed pulp, or enzyme-treated pulp.

According to a further embodiment, the cellulose is hydrolyzed and subsequently activated by enzyme treatment, ozone treatment, hydrogen peroxide treatment, alkali treatment, or other chemical treatment prior to long-chain fatty acid modification, such as esterification or hydroxyalkylation.

The controlled-molecular-mass cellulose esters that can be used in this method can be prepared, for example, by homogeneous esterification of cellulose raw materials. In this method, a fatty acid chloride (C6, C8, C12, or C16, 3 or 4 equivalents per cellulose anhydroglucose unit; AGU) was added to a cellulose mixture using pyridine as a catalyst. The reaction temperature was 80°C, and the reaction time was 16 hours. The product was precipitated with ethanol and washed with ethanol and acetone.

According to one embodiment of the present invention, the controlled molar mass cellulose ester preferably has a side length of C6 to C16, e.g., C8.

According to one embodiment of the present invention, the controlled molar mass cellulose ester preferably has a total degree of substitution of 0.9 to 2.0, for example 1.4.

According to one embodiment of the present invention, melt spinning is carried out at a temperature of 120 to 150°C, more preferably 125 to 140°C, using a melt spinning apparatus equipped with a single-screw extruder, a melt pump, and a multi-strand filament die.

Therefore, one optimal method for carrying out the melt spinning process is to use a Fourne melt spinning machine (Fourne Polymertechnik GmbH, Germany) equipped with a 10 mm single-screw extruder (speed: 100 rpm), a melt pump (speed: 14 rpm), and a multi-strand filament die. In one example, a spinneret with eight holes (0.7 mm diameter) was used. Spinning was carried out at 130°C. The material was dried overnight under ambient vacuum before processing. Melt-spun fibers were collected and oriented using a draw speed range of 0 to 200 m/min, with or without brightener.

As shown in the above examples and figures, fully biobased, continuously melt-spun, controlled molar mass cellulose fibers with good mechanical properties are also within the scope of the present invention.

Throughout this specification, a reference to an embodiment means that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrase "in one embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Also, when a numerical value is referred to using terms such as "about" or "substantially," the exact numerical value is also disclosed.

While the foregoing examples illustrate the principles of the present invention in one or more particular applications, it will be apparent to those skilled in the art that numerous changes in form, application, and details of implementation can be made without the exercise of inventive faculty and without departing from the principles and concepts of the present invention. Accordingly, it is not intended that the present invention be limited except as by the claims set forth below.

The verbs "comprise" and "contain" are used in this document as open limitations which neither exclude nor require the presence of unrecited features. Features recited in dependent claims may be freely combined with each other, unless expressly stated otherwise. Furthermore, it is to be understood that the use of "a" or "an" throughout this document, i.e., the singular, does not exclude the plural.

Technical and hygiene nonwovens are the fastest growing textile materials and are typically derived from fossil synthetic polymers. Novel thermoplastic cellulose fatty acid esters possess polyolefin-like properties, and herein, the suitability of these cellulose esters for fiber production was evaluated. In this study, we demonstrate the melt spinning of textile fibers using thermoplastic, controlled-molecular-mass cellulose. The melt spinning results indicate that the novel cellulosic fibers can provide a renewable and recyclable alternative to, for example, polypropylene, in several technical and hygiene textile applications.

(material)
The cellulose material for esterification was commercial softwood dissolving pulp produced by Domsjo Fabriker AB (Sweden), which was pretreated with ozone according to the method described by Willberg-Keyrilainen et al. (2016). Polypropylene (PP) was used as the reference material, and commercially available Tallopol SLB (Bozzetto, Italy) was used as the brightener. All other reagents and solvents were purchased at the highest purity grade available from Sigma-Aldrich (Helsinki, Finland) and used as received.

(Preparation of Cellulose Ester)
Homogeneous esterification of cellulose was carried out using the method proposed by Willberg-Keyrilainen et al. (2016, 2017a). In this method, pyridine was used as a catalyst, and a fatty acid chloride (C6, C8, C12, or C16, 3 or 4 equivalents per cellulose anhydroglucose unit; AGU) was added to the cellulose mixture. The reaction temperature was 80°C, and the reaction time was 16 hours. The product was precipitated with ethanol and washed with ethanol and acetone.

(Solid state nuclear magnetic resonance (ssNMR))
The cellulose esters were analyzed using solid-state ^13C CP/MAS NMR spectroscopy (ssNMR). The analysis was carried out using an Agilent 600MHz NMR spectrometer (Agilent Technologies, USA). All ssNMR experiments were carried out at 22°C using a 10kHz MAS speed, 10,000 scans, and a 10-second recycle time.

(Capillary rheometer)
The spinnability of the prepared cellulose esters was first evaluated with a Gottfert Rheograph 6000 capillary rheometer (Gottfert, Germany). Capillary rheometry was performed using a 1/30 mm die and a shear rate range of 30 s ^-1 to 1000 s ^-1 . Tests were performed at 130 °C with a 3-minute warm-up time. Apparent values were recorded, and spinnability was evaluated manually. Prior to the experiment, the materials were dried overnight in a vacuum.

(Melt Spinning)
Melt spinning was carried out using a Fourne melt spinning machine (Fourne Polymertechnik GmbH, Germany) consisting of a 10 mm single screw extruder (speed 100 rpm), a melt pump (speed 14 rpm), and a multi-strand filament die. An 8-hole spinneret (0.7 mm diameter) was used. Spinning was carried out at 130°C. The material was dried overnight under ambient vacuum before processing. Melt-spun fibers were collected and oriented using a draw speed range of 0 to 200 m/min, with or without brightener.

(Scanning Electron Microscope (SEM))
Scanning electron microscopy of the melt-spun fibers was performed using a field emission SEM (MERLIN FE-SEM, Carl Zeiss GmbH, Germany). An accelerating voltage of 3 kV was used. Before imaging, the fibers were sputter-coated with a thin gold layer (Leica EM ACE200, Germany).

(Fiber tensile test)
The mechanical properties of the melt-spun fibers were analyzed using a Favimat+ testing system (Textechno, Germany) equipped with a 210 cN load cell and a constant crosshead speed of 20 mm/min. Twenty replicate fibers were tested, and the fibers were stored at standard conditions (23 °C, 50% relative humidity) for one week before testing. Table 1 shows the properties of melt-spun cellulose octanate fibers as an example.

(List of citations)
(Patent Documents)
WO 2016/193542 A1
JP 2005/248354A
(Non-patent literature)
1. Chen B, Zhong L, Gu L (2010) Thermal properties and chemical changes in blend melt spinning of cellulose acetate butyrate and a novel cationic dyeable copolyester. J Appl Polym Sci 116:NA-NA. doi: 10.1002/app. 30984
2. Hooshmand S, Atomaki Y, Skrifvars M, et al (2014a) All-cellulose nanocomposite fibers produced by melt spinning cellulose acetate butyrate and cellulose nanocrystals. Cellulose 21:2665-2678. doi: 10.1007/s10570-014-0269-4
3. Hooshmand S, Cho S-W, Skrifvars M, et al (2014b) Melt spun cellulose nanocomposite fibers: comparison of two dispersion techniques. Plast Rubber Compos 43:15-24. doi: 10.1179/1743289813Y. 0000000066
4. Wang X, Wang Y, Xia Y, et al (2018) Preparation, structure, and properties of melt spun cellulose acetate butyrate fibers. Text Res J 88:1491-1504. doi: 10.1177/0040517517703599
5. Willberg-Keyrilainen P, Talja R, Asikainen S, et al (2016) The effect of cellulose molar mass on the properties of palmitate esters. Carbohydr Polym 151:988-995. doi: 10.1016/j. carbpol. 2016.06.048
6. Willberg-Keyrlainen P, Vartiainen J, Harlin A, Ropponen J (2017a) The effect of side-chain length of cellulose fat acid esters on their thermal, barrier and mechanical properties. Cellulose 24:505-517. doi: 10.1007/s10570-016-1165-x

Claims (9)

1. A melt spinning process for preparing continuous cellulosic fibers, comprising:
preparing a controlled molar mass cellulose ester from a cellulose feedstock having a side length of C6 to C18, a total degree of substitution of 0.7 to 3, and a molar mass of 30 to 300 kDa;
melt-spinning the controlled molar mass cellulose ester using a melt-spinning apparatus;
and recovering the melt-spun fibers,
The molar mass of the cellulose raw material is controlled through hydrolysis except for complete hydrolysis, and the melt spinning is carried out at a temperature of 120-150°C. The method of claim 1, characterized in that the cellulose raw material is selected from natural softwood pulp, natural hardwood pulp, annual plant pulp, softwood sulfite-dissolving pulp, hardwood sulfite-dissolving pulp, ozone-treated hydrolyzed pulp, or enzyme-treated pulp. The method according to claim 1 or 2, characterized in that the hydrolysis is controlled so that the average molecular weight of the molar mass-controlled cellulose ester is reduced by 60% to 85% from the molecular weight of the cellulose raw material, thereby the molar mass of the molar mass-controlled cellulose ester after hydrolysis is in the range of 40 to 200 kDa. The method according to any one of claims 1 to 3, wherein the cellulose raw material is hydrolyzed by enzyme treatment, ozone treatment, hydrogen peroxide treatment, alkali treatment, or other chemical treatment. The method according to any one of claims 1 to 4, characterized in that the controlled-molecular-mass cellulose ester is prepared by adding a fatty acid chloride to a cellulose mixture using pyridine as a catalyst, and homogeneously esterifying the cellulose raw material at a reaction temperature of 80°C for a reaction time of 16 hours. The method according to any one of claims 1 to 5, characterized in that the melt spinning is carried out using a melt spinning apparatus equipped with a single-screw extruder, a melt pump, and a multi-strand filament die. The method of any one of claims 1 to 6, characterized in that the melt-spun fibers are recovered using a drawing speed of more than 0 m/min and not more than 200 m/min. The method according to any one of claims 1 to 7, wherein the controlled-molecular-mass cellulose ester has a side length of C6 to C16. The method according to any one of claims 1 to 8, wherein the controlled-molecular-mass cellulose ester has a total degree of substitution of 0.9 to 2.0.