Resin composition, and injection molding

Abstract

To provide a resin composition which is excellent in Charpy impact strength and is suitable for moldability while maintaining a high biomass degree, and an injection molding which is obtained using the resin composition.SOLUTION: A resin composition and an injection molding contain cellulose, lignin, polyhydroxyalkanoate and a cardanol compound.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a resin composition and an injection-molded article. [Background technology]

[0002] Due to growing awareness of global warming and environmental issues, there has been a recent trend toward reducing the use of petroleum-derived plastics, and as an alternative, interest has been growing in plastics derived from biomass resources, such as biomass plastics and biodegradable plastics. Cellulose and lignin, which are woody biomass resources (herbaceous biomass resources), are found in large quantities worldwide and are highly biodegradable in environments such as soil, activated sludge, and the ocean, making them ideal biomass resources. However, cellulose and lignin cannot be thermally melted, making them difficult to process, and thus presenting an inherent problem that their applications are extremely limited.

[0003] Under these circumstances, various studies have been conducted on the moldability of resin compositions containing cellulose or lignin. For example, Patent Document 1 proposes a resin composition comprising a cellulose ester, a non-cellulose ester thermoplastic resin, a plasticizer for the cellulose ester, and a bleed-out inhibitor for suppressing or preventing bleed-out of the plasticizer. The resin composition proposed in Patent Document 1 is said to be capable of producing molded articles with excellent stability against deformation. Patent Document 2 proposes an injection molding method in which a lignocellulosic material containing hemicellulose, lignin, and cellulose is steam-treated to produce a lignocellulosic modifier, which is then mixed with a biodegradable resin and a lubricant and injection-molded. Patent Document 3 proposes a resin composition containing a water-insoluble or organic solvent-soluble material primarily composed of cellulose fibers containing lignin, and a curing agent. The resin composition proposed in Patent Document 3 is said to be capable of producing molded articles with flame retardancy and antibacterial properties, even though the resin composition is primarily made of lignin. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-161943 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-37022 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-219722 Summary of the Invention [Problem to be solved by the invention]

[0005] As proposed in Patent Documents 1 to 3, various resin compositions containing cellulose, lignin, etc. have been proposed that take into account moldability, etc. However, there is still room for improvement in the biomass content of the resin composition and the strength of the molded articles obtained by molding the resin composition. For example, the resin composition proposed in Patent Document 1 contains a plasticizer, the injection molding method proposed in Patent Document 2 uses a mixture (resin composition) containing a lubricant, and the resin composition proposed in Patent Document 3 contains a curing agent. Therefore, the presence of these components (plasticizer, lubricant, curing agent) inherently prevents the resin composition and the molded articles obtained by molding the resin composition from having a sufficiently high biomass content. Furthermore, the resin composition proposed in Patent Document 3, which uses a curing agent, also inherently suffers from the problem of insufficient Charpy impact strength.

[0006] A main object of the present invention is to provide a resin composition that has excellent Charpy impact strength and is suitable for moldability while maintaining a high biomass content, and an injection-molded article obtained using this resin composition. [Means for solving the problem]

[0007] A resin composition according to one embodiment of the present invention contains cellulose, lignin, polyhydroxyalkanoate, and a cardanol compound.

[0008] The resin composition according to one embodiment of the present invention preferably further contains hemicellulose. The resin composition according to one embodiment of the present invention preferably contains, as the polyhydroxyalkanoate, either or both of polylactic acid and polyhydroxybutyrate hexanoate. In the resin composition of one embodiment of the present invention, the mass of the cellulose relative to the total mass of the resin composition is preferably 5% by mass or more and 90% by mass or less. In the resin composition of one embodiment of the present invention, the mass of the polyhydroxyalkanoate relative to the total mass of the resin composition is preferably 5% by mass or more and 80% by mass or less. In the resin composition according to one embodiment of the present invention, the value obtained by dividing the mass of the polyhydroxyalkanoate by the mass of the cardanol compound is preferably 0.5 or more and 10 or less. The resin composition according to one embodiment of the present invention may contain cellulose, lignin, and hemicellulose, and may use pulverized wood flour.

[0009] An injection-molded article according to one embodiment of the present invention is obtained by injection molding the above-described resin composition. [Effects of the Invention]

[0010] The resin composition of the present invention can have excellent Charpy impact strength and good moldability while maintaining a high biomass content. The injection-molded article of the present invention has excellent Charpy impact strength while maintaining a high biomass content. DETAILED DESCRIPTION OF THE INVENTION

[0011] The resin composition and injection-molded article of the present invention will be specifically described below. Note that the following embodiments do not limit the scope of the claimed invention, and not all of the elements and combinations thereof described in the embodiments are necessarily essential to the solution of the present invention.

[0012] <<Resin composition>> A resin composition according to an embodiment of the present disclosure (hereinafter referred to as a resin composition of one embodiment) contains at least cellulose, lignin, polyhydroxyalkanoate, and a cardanol compound.

[0013] According to one embodiment of the resin composition containing these components, it is possible to achieve a high biomass content, excellent Charpy impact strength, and good moldability.

[0014] The mechanism by which the resin composition of one embodiment has excellent Charpy impact strength is not necessarily clear at present, but it is presumed to be due to the following mechanism: It is clear from the results of the examples and comparative examples described below that a resin composition containing cellulose, lignin, polyhydroxyalkanoate, and a cardanol compound has extremely high Charpy impact strength, even if the mechanism is not the same.

[0015] Cellulose, lignin, and polyhydroxyalkanoate are each hard and brittle when used alone. Therefore, when a resin composition containing only cellulose, lignin, and polyhydroxyalkanoate is prepared, the Charpy impact strength of the resin composition is also low. However, when a resin composition is prepared by blending cellulose, lignin, and polyhydroxyalkanoate with a cardanol compound, the terminal hydroxyl groups of the cardanol compound interact more strongly with the hydroxyl groups of cellulose than with the hydroxyl groups of cellulose themselves. This allows the cellulose and the cardanol compound to bond together through hydrogen bonding, allowing the cellulose to exist in a bonded state. In other words, the cellulose molecules can exist in a state other than a single molecule. Furthermore, in the case of lignin, the benzene rings of the lignin stack with the benzene rings of the cardanol compound, allowing the lignin molecules to exist in a state other than a single molecule. This improves the hardness and brittleness of cellulose and lignin.

[0016] Furthermore, because the alkyl chain portions of the polyhydroxyalkanoate and the cardanol compound are incompatible, the polyhydroxyalkanoate and cellulose, and the polyhydroxyalkanoate and lignin, form a microphase-separated state. This microphase-separated state allows extremely flexible alkyl chains to be uniformly distributed among the hard and brittle structures, thereby creating flexibility between the rigid portions. This also improves the hardness and brittleness of the polyhydroxyalkanoate.

[0017] Furthermore, since the resin composition of one embodiment contains polyhydroxyalkanoate, good moldability can be achieved when molding a molded article from the resin composition of one embodiment.

[0018] Next, each component constituting the resin composition of one embodiment will be described with an example.

[0019] (cellulose) The resin composition of one embodiment contains cellulose. Various conventionally known celluloses can be used. Examples of cellulose include natural cellulose derived from plants, modified cellulose, and regenerated cellulose. Examples of natural cellulose include natural wood cellulose. Examples of modified cellulose include carboxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose.

[0020] The resin composition of one embodiment contains, for example, cellulose represented by the following formula (I).

[0021] [ka]

[0022] There is no limitation on the molecular weight of the cellulose, but it is preferably 40,000 or more and 300,000 or less. In formula (I), n is preferably 100 or more and 800 or less.

[0023] In one embodiment, the mass of cellulose relative to the total mass of the resin composition is preferably 5% by mass or more and 90% by mass or less. By setting the cellulose content within this preferred range, it is possible to suppress hydrogen bonding between cellulose molecules while ensuring a sufficient number of hydroxyl groups for hydrogen bonding with the cardanol compound, and as a result, it is possible to further increase the Charpy impact strength of the resin composition.

[0024] (lignin) The resin composition of one embodiment contains lignin. Various conventionally known lignins can be used. Examples of lignin include natural lignin and industrial lignin. Examples of natural lignin include softwood lignin, hardwood lignin, and herbaceous lignin. Examples of industrial lignin include lignosulfonic acid (salt), explosive lignin, and kraft lignin.

[0025] In one embodiment, the mass of lignin relative to the total mass of the resin composition is preferably 1% by mass or more. The upper limit may be appropriately determined taking into consideration the blending amounts of cellulose, polyhydroxyalkanoate, and cardanol compound, and, for example, the mass of lignin relative to the total mass of the resin composition is 90% by mass or less.

[0026] (Polyhydroxyalkanoate) The resin composition of one embodiment includes a polyhydroxyalkanoate. The polyhydroxyalkanoate is a polymer containing a hydroxyalkanoate as a monomer component. Examples of the polyhydroxyalkanoate include poly(α-hydroxyalkanoate) and poly(3-hydroxyalkanoate). Examples of the poly(α-hydroxyalkanoate) include polylactic acid and polyglycolic acid. Examples of poly(3-hydroxyalkanoates) include poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3-hydroxydecanoate).

[0027] A preferred embodiment of the resin composition contains either or both of polylactic acid and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) as the polyhydroxyalkanoate. Polylactic acid and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) have a curved three-dimensional structure, which easily causes microphase separation due to incompatibility with the alkyl chain of the cardanol compound, thereby enabling the resin composition to have a higher Charpy impact strength.

[0028] In one embodiment, the mass of polyhydroxyalkanoate relative to the total mass of the resin composition is preferably 5% by mass or more and 80% by mass or less. By setting the content of polyhydroxyalkanoate within a preferred range, the Charpy impact strength of the resin composition can be further increased. Specifically, by setting the content of polyhydroxyalkanoate within a preferred range, the polyhydroxyalkanoate phase in the microphase separation can be increased to a degree that sufficiently suppresses the formation of hydrogen bonds between cellulose molecules. Furthermore, the size of the polyhydroxyalkanoate phase can be optimized, suppressing the formation of a higher-order structure similar to that of polyhydroxyalkanoate alone. This allows the Charpy impact strength of the resin composition to be further increased.

[0029] (cardanol compounds) The resin composition of one embodiment includes a cardanol compound. As an example, the resin composition includes, as the cardanol compound, a cardanol compound represented by the following formula (II):

[0030] [ka]

[0031] Although there are no limitations on the mass of the cardanol compound relative to the total mass of the resin composition, it is preferable to include the cardanol compound so that the value obtained by dividing the mass of the polyhydroxyalkanoate by the mass of the cardanol compound is 0.5 or more and 10 or less. By including the cardanol compound so that the relationship between the masses of the polyhydroxyalkanoate and the cardanol compound satisfies the above-mentioned relationship, it is possible to optimize the amount of cardanol compound used for microphase separation while reducing the volume in which the cardanol compound exists alone, thereby enabling the Charpy impact strength to be further increased.

[0032] (hemicellulose) An example of the resin composition includes hemicellulose. A resin composition including hemicellulose has good flexibility.

[0033] As used herein, hemicellulose refers to a general term for cell wall-constituting polysaccharides other than cellulose in biological resources, and examples of hemicellulose include xylan, arabinoxylan, xyloglucan, and glucomannan.

[0034] (milled wood) When hemicellulose is added to the resin composition of one embodiment, pulverized wood can be used. By using pulverized wood, the resin composition can contain cellulose, lignin, and hemicellulose. When pulverized wood is used, separation processing is not required, so the production energy required for producing the resin composition can be significantly reduced, which is effective in solving environmental issues. Examples of pulverized wood include pulverized bamboo and pulverized oak.

[0035] (Biomass content of resin composition) In one embodiment, the biomass degree of the resin composition is preferably 80% or more, more preferably 90% or more, even more preferably 95% or more, and most preferably 100%. In this specification, "biomass degree" refers to a value calculated in accordance with ISO 16620-3, an international standard for calculating biomass plastic degree. Note that the biomass degree of a resin composition containing only cellulose, lignin, polyhydroxyalkanoate, a cardanol compound, and optionally added hemicellulose is 100% or a value very close to this.

[0036] The resin composition of one embodiment may contain components other than cellulose, lignin, polyhydroxyalkanoate, cardanol compound, and hemicellulose that are added as needed. When the resin composition of one embodiment contains cellulose, lignin, polyhydroxyalkanoate, and a cardanol compound, the total mass of these components relative to the total mass of the resin composition is preferably 70 mass % or more. Furthermore, when the resin composition of one embodiment contains cellulose, lignin, polyhydroxyalkanoate, a cardanol compound, and hemicellulose, the total mass of these components relative to the total mass of the resin composition is preferably 90 mass % or more.

[0037] (Molded body) The resin composition of one embodiment exhibits good moldability in any of the conventionally known molding methods, such as injection molding, extrusion molding, blow molding, inflation molding, and cast molding. The melt viscosity of the resin composition of one embodiment can be easily controlled by temperature, allowing for precise molding by injection molding. An example temperature is 100°C or higher. Furthermore, the resin composition of one embodiment has a fast solidification rate, allowing for a good cycle time in injection molding.

[0038] (injection molded product) The injection-molded article according to the embodiment of the present invention is obtained by injection molding the resin composition according to the embodiment described above. There are no limitations on the injection molding method, and any method conventionally known in the field of injection molding can be appropriately selected for molding.

[0039] Next, the present invention will be described more specifically with reference to examples and comparative examples.

[0040] (Preparation of Resin Pellets (Resin Composition Pellets)) Resin compositions containing each compound shown in Table 1 were prepared (total charge amount: 2 kg). Using a twin-screw extruder (Labo Plastomill, Toyo Seiki Co., Ltd.), the prepared resin compositions were kneaded at the cylinder temperatures shown in Table 1, extruded into strands, cooled with water in a quench pool, and cut with a pelletizer to produce each resin pellet (RP_1 to RP_26). Details of the compounds in Table 1 are as shown in Table 2. Note that resin pellet number RP_21, which does not contain polyhydroxyalkanoate, could not be kneaded, and resin pellets could not be produced. This indicates that resin compositions containing cellulose and lignin without polyhydroxyalkanoate are resin compositions that are not suitable for molding.

[0041] [Table 1]

[0042] [Table 2]

[0043] (Preparation of dumbbell test specimens) Thirty ISO527 1A dumbbell test specimens (measurement area width x thickness x gauge length = 10 x 4 x 7.5 mm) were prepared using an injection molding machine (PNX40III, Nissei Plastic Industrial Co., Ltd.) and each of the resin pellets prepared above (resin pellet numbers that cannot be kneaded (molded) (except RP_21)). The pellet numbers used to prepare the dumbbell test specimens and the molding conditions (cylinder temperature, mold temperature) are shown in Table 3.

[0044] (Charpy impact strength measurement) Each dumbbell test piece prepared above was notched using an ISO notching machine (notching tool, Toyo Seiki Seisakusho Co., Ltd.), and five pieces of each sample were measured using an impact testing device (Charpy Auto Impact Tester CHN-3, Toyo Seiki Seisakusho Co., Ltd.), and the average value was taken as the Charpy impact strength. The Charpy impact strength values ​​are also shown in Table 3.

[0045] (Biomass degree calculation) The biomass content of each resin pellet (each test piece) was calculated in accordance with ISO 16620. The calculation results are also shown in Table 3.

[0046] [Table 3]

Claims

1. Cellulose and, Industrial lignin and, Polyhydroxyalkanoates and Cardanol compounds, Resin composition.

2. Further containing hemicellulose, The resin composition according to claim 1.

3. The polyhydroxyalkanoate includes either or both of polylactic acid and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). The resin composition according to claim 1 or 2.

4. The mass of cellulose relative to the total mass of the resin composition is 5% by mass or more and 90% by mass or less. The resin composition according to claim 1 or 2.

5. The mass of the polyhydroxyalkanoate relative to the total mass of the resin composition is 5% by mass or more and 80% by mass or less. The resin composition according to claim 1 or 2.

6. The value obtained by dividing the mass of the polyhydroxyalkanoate by the mass of the cardanol compound is 0.5 or more and 10 or less. The resin composition according to claim 1 or 2.

7. A resin composition obtained by injection molding the resin composition according to claim 1 or 2, Injection molded body.

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