Resin composition and injection-molded body

Abstract

Disclosed are: a resin composition comprising cellulose, lignin, polyhydroxyalkanoate, and a cardanol compound; and an injection-molded body using the same. The resin composition may further comprise hemicellulose. The present invention provides: a resin composition that has excellent Charpy impact strength and suitable moldability while maintaining a high degree of biomass; and an injection-molded body obtained by using the resin composition.

Description

Resin composition and injection-molded article

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

[0002] In recent years, due to global warming issues and increasing awareness of environmental issues, there has been a tendency to reduce the use of plastics derived from petroleum resources. As alternatives, plastics derived from biomass resources such as biomass plastics and biodegradable plastics have been attracting growing attention. Among these, cellulose and lignin, which are woody biomass resources (herbaceous biomass resources), exist in large quantities around the world and have high biodegradability in environments such as soil, activated sludge, and oceans, so they are attracting attention as ideal biomass resources. However, since cellulose and lignin cannot be thermally melted, molding processing is difficult, and there is an inherent problem that their applications are extremely limited.

[0003] Under such 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 composed of 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. According to the resin composition proposed in Patent Document 1, it is stated that a molded article excellent in stability against deformation can be obtained. Patent Document 2 proposes an injection molding method in which a lignocellulosic material containing hemicellulose, lignin and cellulose is subjected to steam treatment to produce a lignol-based modifier, and a mixture obtained by mixing this with a biodegradable resin and a lubricant is injection-molded. Patent Document 3 proposes a resin composition containing a water-insoluble substance or an organic solvent-soluble substance mainly composed of cellulose fibers containing lignin, and a curing agent. According to the resin composition proposed in Patent Document 3, it is stated that a molded article imparted with flame retardancy and antibacterial properties can be obtained while using lignin as the main raw material.

[0004] Japanese Unexamined Patent Application Publication No. 2007-161943, Japanese Unexamined Patent Application Publication No. 2008-37022, Japanese Unexamined Patent Application Publication No. 2011-219722

[0005] As proposed in Patent Documents 1 to 3, various resin compositions containing cellulose, lignin, etc., have been proposed, taking into consideration their 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. As a result, the presence of these components (plasticizer, lubricant, curing agent) inherently presents a problem in that the biomass content of the resin composition and the molded articles obtained by molding this resin composition cannot be sufficiently high. Furthermore, resin compositions that use a curing agent, such as the one proposed in Patent Document 3, also inherently have the problem of not being able to achieve sufficient Charpy impact strength.

[0006] The primary objective of this disclosure is to provide a resin composition that maintains a high biomass content while exhibiting excellent Charpy impact strength and suitability for moldability, and an injection-molded article obtained using this resin composition.

[0007] The resin composition relating to the first aspect of this disclosure comprises cellulose, lignin, polyhydroxyalkanoate, and cardanol compound.

[0008] In one embodiment of a resin composition relating to the first aspect of this disclosure, it is shown that it further comprises hemicellulose.

[0009] In one embodiment of the resin composition relating to the first aspect of this disclosure, the polyhydroxyalkanoate is shown to include either or both of polylactic acid and polyhydroxybutyrate hexanoate.

[0010] In one embodiment of a resin composition relating to the first aspect of this disclosure, the mass of cellulose relative to the total mass of the resin composition is shown to be 5% by mass or more and 90% by mass or less.

[0011] In one embodiment of a resin composition according to the first aspect of this disclosure, the mass of the polyhydroxyalkanoate relative to the total mass of the resin composition is shown to be 5% by mass or more and 80% by mass or less.

[0012] In one embodiment of the resin composition relating to the first aspect of this disclosure, the value obtained by dividing the mass of the polyhydroxyalkanoate by the mass of the cardanol compound is shown to be 0.5 or more and 10 or less.

[0013] In one embodiment of the resin composition relating to the first aspect of this disclosure, crushed wood powder may be used as comprising the cellulose, lignin, and hemicellulose.

[0014] An injection-molded article relating to the second aspect of this disclosure is obtained by injection molding the above-mentioned resin composition.

[0015] In other words, the injection-molded article according to the second aspect of this disclosure is composed of a resin composition comprising cellulose, lignin, polyhydroxyalkanoate, and a cardanol compound.

[0016] In one embodiment of an injection-molded article according to a second aspect of the present disclosure, the injection-molded article is shown in which the resin composition further comprises hemicellulose.

[0017] In one embodiment of an injection-molded article relating to a second aspect of the present disclosure, the injection-molded article is shown in which the polyhydroxyalkanoate comprises either or both of polylactic acid and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

[0018] In one embodiment of an injection-molded article relating to a second aspect of this disclosure, an injection-molded article is shown in which 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.

[0019] In one embodiment of an injection-molded article relating to a second aspect of this disclosure, an injection-molded article is shown in which 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.

[0020] In one embodiment of an injection-molded article relating to a second aspect of this disclosure, an injection-molded article is shown in which 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.

[0021] In one embodiment of an injection-molded article relating to a second aspect of the present disclosure, the resin composition comprises ground wood powder, wherein the ground wood powder comprises cellulose, lignin, and hemicellulose.

[0022] The resin composition of this disclosure can maintain a high biomass content while exhibiting excellent Charpy impact strength and good moldability. The injection-molded article of this disclosure maintains a high biomass content while exhibiting excellent Charpy impact strength.

[0023] The resin compositions and injection-molded articles of this disclosure will be described in detail below. Note that the embodiments described below are not intended to limit the invention as defined in the claims, and not all of the elements and combinations thereof described in each embodiment are necessarily essential to the solutions of this disclosure.

[0024] <<Resin Composition>> The resin composition according to the embodiment of the present disclosure (hereinafter referred to as the resin composition of one embodiment) comprises at least cellulose, lignin, polyhydroxyalkanoate, and a cardanol compound.

[0025] According to one embodiment of the resin composition containing these components, it is possible to obtain a resin composition that has a high biomass content, excellent Charpy impact strength, and good moldability.

[0026] The mechanism by which the resin composition of one embodiment exhibits excellent Charpy impact strength is not yet fully understood, but it is presumed to be due to the following mechanism. Even if the mechanism described below is not the cause, it is clear from the results of the examples and comparative examples described later that resin compositions containing cellulose, lignin, polyhydroxyalkanoate, and cardanol compounds have extremely high Charpy impact strength.

[0027] Cellulose, lignin, and polyhydroxyalkanoates are individually hard and brittle. Therefore, a resin composition containing only cellulose, lignin, and polyhydroxyalkanoates will have a low Charpy impact strength. However, when a cardanol compound is added to the resin composition containing cellulose, lignin, and polyhydroxyalkanoates, the interaction of the terminal hydroxyl groups of the cardanol compound with the hydroxyl groups of cellulose is stronger than that between the hydroxyl groups of cellulose themselves. As a result, cellulose and the cardanol compound bond together via hydrogen bonding, allowing cellulose to exist in a bonded state. In other words, cellulose molecules can exist rather than individually. Similarly, in the case of lignin, the benzene ring of lignin stacks with the benzene ring of the cardanol compound, allowing lignin molecules to exist rather than individually. This improves the hardness and brittleness of cellulose and lignin.

[0028] Furthermore, because the alkyl chain portions of polyhydroxyalkanoates and cardanol compounds are immiscible, polyhydroxyalkanoates and cellulose, and polyhydroxyalkanoates and lignin, form a microphase separation state. This formation of a microphase separation state allows for the uniform presence of extremely flexible alkyl chains between rigid and brittle structures, resulting in flexibility between the rigid parts. This also improves the rigidity and brittleness of the polyhydroxyalkanoates.

[0029] Furthermore, since the resin composition of one embodiment contains a polyhydroxyalkanoate, the moldability of the molded article when molding from the resin composition of one embodiment can be improved.

[0030] Next, we will describe, with an example, each component constituting the resin composition of one embodiment.

[0031] (Cellulose) The resin composition of one embodiment contains cellulose. Various conventionally known celluloses can be used. Examples of cellulose include plant-derived natural cellulose, 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.

[0032] A resin composition of one embodiment includes, for example, cellulose represented by the following formula (I).

[0033]

[0034] There are no limitations on the molecular weight of cellulose, but it is preferably between 40,000 and 300,000. In formula (I), n is preferably between 100 and 800.

[0035] 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 have sufficient hydroxyl groups for hydrogen bonding with the cardanol compound while suppressing hydrogen bonding between cellulose cells, and as a result, the Charpy impact strength of the resin composition can be increased.

[0036] (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 coniferous lignin, broadleaf lignin, and herbaceous lignin. Examples of industrial lignin include lignosulfonic acid (salt), explosion lignin, and kraft lignin.

[0037] 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 can be appropriately determined by considering the amounts of cellulose, polyhydroxyalkanoate, and cardanol compound blended, and as an example, the mass of lignin relative to the total mass of the resin composition is 90% by mass or less.

[0038] (Polyhydroxyalkanoate) The resin composition of one embodiment contains a polyhydroxyalkanoate. A polyhydroxyalkanoate is a polymer containing a hydroxyalkanoate as a monomer component. Examples of polyhydroxyalkanoates include poly(α-hydroxyalkanoate) and poly(3-hydroxyalkanoate). Examples of 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).

[0039] A preferred form of the resin composition contains either or both of the following as the polyhydroxyalkanoate: polylactic acid and / or poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). Polylactic acid and / or poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) have a curved stereostructure and readily induce microphase separation due to incompatibility with the alkyl chain of the cardanol compound, thereby increasing the Charpy impact strength of the resin composition.

[0040] 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 the preferred numerical range, the Charpy impact strength of the resin composition can be further increased. Specifically, by setting the content of polyhydroxyalkanoate within the preferred numerical range, the proportion of polyhydroxyalkanoate phases in microphase separation can be increased until the occurrence of hydrogen bonding between cellulose molecules is sufficiently suppressed. In addition, the size of the polyhydroxyalkanoate phases can be optimized, and the formation of a higher-order structure such as that of polyhydroxyalkanoate alone can be suppressed. Thereby, the Charpy impact strength of the resin composition can be further increased.

[0041] (Cardanol Compound) The resin composition of one embodiment contains a cardanol compound. As an example, the resin composition includes, as the cardanol compound, a cardanol compound represented by the following formula (II).

[0042]

[0043] There is no limitation on the mass of the cardanol compound relative to the total mass of the resin composition, but it is preferable that the cardanol compound is contained such that a value obtained by dividing the mass of polyhydroxyalkanoate by the mass of the cardanol compound is 0.5 or more and 10 or less. By containing the cardanol compound such that the mass relationship between polyhydroxyalkanoate and the cardanol compound satisfies the above relationship, while optimizing the amount of the cardanol compound used for microphase separation, the volume where the cardanol compound exists alone can be reduced, and the Charpy impact strength can be further increased.

[0044] (Hemicellulose) As an example, the resin composition contains hemicellulose. A resin composition containing hemicellulose has good flexibility.

[0045] Hemicellulose as referred to in the specification of the present application is a general term for cell wall-constituting polysaccharides other than cellulose in biological resources, and examples of hemicellulose include xylan, arabinoxylan, xyloglucan, and glucomannan.

[0046] (Pulverized 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, no separation treatment is required, so the production energy for producing the resin composition can be extremely reduced, which is effective for solving environmental problems. Examples of pulverized wood include pulverized bamboo, pulverized oak, and the like.

[0047] (Biomass content of resin composition) The biomass content of the resin composition of one embodiment is preferably 80% or more, more preferably 90% or more, still more preferably 95% or more, and most preferably 100%. As used herein, the term "biomass content" refers to a value calculated in accordance with the international standard ISO 16620-3 for the method of calculating biomass plastic content. Note that when the resin composition contains only cellulose, lignin, polyhydroxyalkanoate, a cardanol compound, and optionally added hemicellulose, the biomass content of the resin composition is 100% or a value extremely close thereto.

[0048] The resin composition of one embodiment may contain components other than cellulose, lignin, polyhydroxyalkanoate, a cardanol compound, and optionally added hemicellulose. 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% by mass or more. Further, 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% by mass or more.

[0049] (Molded articles) 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 resin composition of one embodiment allows for easy control of the melt viscosity by temperature, enabling precise molding by injection molding. An example temperature is 100°C or higher. Furthermore, because the resin composition of one embodiment has a fast solidification rate, a good cycle time can be achieved in injection molding.

[0050] (Injection Molded Article) An injection molded article according to an embodiment of the present disclosure is obtained by injection molding the resin composition of one embodiment described above. There are no limitations on the injection molding method, and conventionally known methods in the field of injection molding can be appropriately selected for molding.

[0051] Next, the present disclosure will be described in more detail with reference to examples and comparative examples.

[0052] (Preparation of Resin Pellets (Pellets of Resin Composition)) Resin compositions containing each compound shown in Table 1 were prepared (total amount: 2 kg). Using a twin-screw extruder (Laboplastmill Toyo Seiki Co., Ltd.), the prepared resin compositions were kneaded at the cylinder temperatures shown in Table 1, extruded into strands, cooled in a quench pool of water, and cut with a pelletizer to produce each resin pellet (RP_1 to RP_26). Details of the compounds in Table 1 are shown in Table 2. Note that resin pellet number RP_21, which does not contain polyhydroxyalkanoate, could not be kneaded and therefore could not be produced as a resin pellet. From this, it can be seen that resin compositions containing cellulose and lignin but not polyhydroxyalkanoate are not suitable for molding.

[0053]

[0054]

[0055] (Preparation of dumbbell test specimens) Thirty IS O527 1A dumbbell test specimens (measurement section width × thickness × gauge length = 10 × 4 × 7.5 mm) were prepared using an injection molding machine (PNX40III, Nissei Plastic Industrial Co., Ltd.) and each of the resin pellets prepared as described above (excluding resin pellet numbers that could not be mixed (molded) (RP_21)). Table 3 shows the pellet numbers used to prepare the dumbbell test specimens and the molding conditions (cylinder temperature, mold temperature).

[0056] (Measurement of Charpy Impact Strength) Each dumbbell test piece prepared as described above was notched using an ISO notching machine (notching tool, Toyo Seiki Seisakusho Co., Ltd.), and five samples were measured using an impact testing device (Charpy Auto Impact Tester CHN-3, Toyo Seiki Seisakusho Co., Ltd.). The average value was taken as the Charpy impact strength. The Charpy impact strength values ​​are shown in Table 3.

[0057] (Calculation of Biomass Content) The biomass content of each resin pellet (each test piece) was calculated in accordance with ISO 16620. The calculation results are shown in Table 3.

[0058]

Claims

1. A resin composition comprising cellulose, lignin, polyhydroxyalkanoate, and cardanol compound.

2. The resin composition according to claim 1, further comprising hemicellulose.

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

4. The resin composition according to claim 1 or 2, wherein 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.

5. The resin composition according to claim 1 or 2, wherein 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.

6. The resin composition according to claim 1 or 2, wherein 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.

7. The resin composition according to claim 2, wherein the resin composition comprises crushed wood flour, and the crushed wood flour comprises the cellulose, the lignin, and the hemicellulose.

8. An injection-molded article comprising a resin composition containing cellulose, lignin, polyhydroxyalkanoate, and a cardanol compound.

9. The injection-molded article according to claim 8, wherein the resin composition further comprises hemicellulose.

10. The injection molded article according to claim 8 or 9, wherein the polyhydroxyalkanoate comprises either or both of polylactic acid and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

11. The injection molded article according to claim 8 or 9, wherein 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.

12. The injection molded article according to claim 8 or 9, wherein 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.

13. The injection molded article according to claim 8 or 9, wherein 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.

14. The injection-molded article according to claim 9, wherein the resin composition comprises crushed wood powder, and the crushed wood powder comprises the cellulose, the lignin, and the hemicellulose.

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