Development of Cardanol-Bonded Cellulose Resin with Nonfood

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Chapter 20

Development of Cardanol-Bonded Cellulose Resin with Nonfood Plant Resources: Low Energy Heterogeneous Synthesis Process Kiyohiko Toyama,* Makoto Soyama, Shukichi Tanaka, and Masatoshi Iji Smart Energy Research Laboratories, NEC Corporation, 34, Miyukigaoka, Tsukuba, Ibaraki 305-8501, Japan *E-mail: [email protected].

To synthesize a high-strength and heat-resistant novel cellulose-based bioplastic having a long side chain with low energy consumption, we developed a novel two-step heterogeneous process. The bioplastic is a cellulose ester synthesized by bonding a short side chain (acetic acid) and a long one (3-pentadecylphenoxy acetic acid, a derivative of cardanol, extracted from cashew nut shells). In conventional homogeneous processes, cellulose esters are recovered by precipitation with large quantities of poor solvents, which requires much energy consumption for their distillation. In the novel process, first, limited amounts of these chains are bonded in a heterogeneous system to achieve efficient product recovery by filtration without precipitation. Second, the short-chain acid is additionally bonded to attain good thermoplasticity of the final product, the cellulose resin, which is recovered by distilling the reaction solvent and the remaining short-chain component. The solvent usage was reduced by approximately 90% compared with a homogeneous process. The thermoplasticity of the resulting resin was comparable to that of a homogeneous one. Furthermore, the mechanical and thermal characteristics of the resin were greatly improved by adding a specific linear polyester, poly(butylene succinate adipate), and a glass fiber, achieving high target levels for durable products.

© 2015 American Chemical Society In Green Polymer Chemistry: Biobased Materials and Biocatalysis; Smith, et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


Introduction Bioplastics, which are made of plant resources, have been attracting increased attention because they help to reduce petroleum resource usage and CO2 emission. Mass-produced bioplastics such as polylactic acid (PLA) (1, 2) use starch, which is generally extracted from edible plant resources. Because of concerns over future food shortages, bioplastics derived from non-edible plant resources are desired. Cellulose is a prospective candidate for such bioplastics since it is the largest nonfood plant resource. Cellulose is a polysaccharide consisting of D-glucose units linked together by β1-4 glycosidic bonds into linear chains, and it is non-melt processable and insoluble in water and most organic solvents due to intra and intermolecular hydrogen bonding. Cellulose esters of short organic acids such as cellulose acetate have been manufactured for cellulose-based bioplastics by adding external plasticizers (3). However, because they have narrow process windows between melting and degradation temperatures, large amounts of external plasticizers were required (4), which results in insufficeient durability such as in strength, heat resistance, and exudation of plasticizers. To overcome this problem, many attempts have been made to synthesize long-chain cellulose esters (5, 6) or cellulose graft copolymers (7). In these cellulose derivatives, long chains bonded to cellulose, e.g. fatty acids, work as internal plasticizers. However, these cellulose derivatives still did not have sufficient mechanical strength, heat resistance, and water resistance for practical use in various durable products. We recently developed a novel cellulose-based bioplastic by using a cardanol derivative as a long side chain (8, 9). Cardanol is a non-edible plant resource extracted from cashew nut shells, generated in large amounts as a byproduct, and has a unique structure: a flexible and hydrophobic long side chain (carbon number: 15) with unsaturated bonds, a rigid and hydrophobic benzene ring, and a reactive phenolic hydroxyl group (10, 11). The novel bioplastic was made by esterifying cellulose diacetate (CDA) with a cardanol-derived acid, 3-pentadecylphenoxy acetic acid (PAA), which was obtained by hydrogenating unsaturated bonds in the long chain and changing the phenolic hydroxyl group to the acetyl group. The resulting cardanol-bonded cellulose resin (Figure 1) has higher heat resistance and water resistance than other cellulose derivatives, such as conventional short-chain cellulose esters and long-chain cellulose esters, because the rigid and hydrophobic benzene ring of cardanol prevents heat distortion and water absorption (5, 9). Furthermore, it has higher heat resistance and flexural strength than those of acrylonitrile-butadiene-styrene (ABS), which is petroleum-based and used in electronic products (8, 9). However, the process to produce the cardanol-bonded cellulose resin needed a lot of energy because it was a homogeneous process, in which a product dissolved in a solvent is isolated by adding large amounts of a poor solvent. The remaining reactant of PAA needed to be separated from the resin by precipitation with a poor solvent because it cannot be separated by distillation with low energy use due to its high boiling point. To cut back on poor solvents, which require large amounts of energy for distillation, another process to utilize isocyanate-modified cardanol 330 In Green Polymer Chemistry: Biobased Materials and Biocatalysis; Smith, et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


was studied (12). Although products could be isolated readily only by evaporating a reaction solvent, the starting material was also CDA, which had been produced by a conventional homogeneous process.

Figure 1. Molecular structure and schematic representation of cardanol-bonded cellulose resin.

Heterogeneous processes, in which cellulose derivatives are not dissolved in solvents, are promising in terms of energy reduction because they can cut back on poor solvents to recover the products as long as the swelling of the products in the solvents are limited. While there have been a lot of studies on bonding long chains to cellulose in heterogeneous systems (5, 6), studies have not been sufficiently made on productivity in recovery steps, which is incompatible with the thermoplasticity of the product. This incompatibility in usual heterogeneous processes is shown in Figure 2. Although a cellulose ester can be recovered easily without poor solvent in a heterogeneous process if its swelling in a solvent is limited, its thermoplasticity is low because cellulose is not modified sufficiently. Here, thermoplasticity is an index of the extent of modification, namely, the homogneity of the product. In this study, we developed a novel heterogeneous process, the “two-step heterogeneous process,” for cardanol-bonded cellulose resin to solve the above incompatibility. In the first step, cellulose is esterified with limited amounts of PAA and acetic acid in a heterogeneous system, and the resultant product is recoverd easily by filtration without poor solvent. Swelling of the product is controlled to achieve both efficient recovery of the product and sufficient amount of PAA bonded to cellulose. In the second step, the intermediate product is further acetylated to improve its thermoplasticity, i.e., homogeneity (Figure 2). The 331 In Green Polymer Chemistry: Biobased Materials and Biocatalysis; Smith, et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


resultant final product (cardanol-bonded cellulose resin) is also recovered readily without poor solvent by distilling the reaction solvent and reactant agent as these agents have relatively low boiling points. The solvent usage of the process was compared with that of a homogeneous process. We also investigated the main characteristics of the resultant cellulose resin to be used in durable products and specific additives for them to improve their characteristics.

Figure 2. Relationship between efficiency of recovery step and thermoplasticity of cellulose ester.

Results and Discussion A flow diagram of the two-step heterogeneous process is shown in Figure 3. In the first step, cellulose was esterified in a heterogeneous system by using anhydrides of PAA and acetic acid. Since the resultant intermediate product was not dissolved but moderately swollen in a solvent, it could be easily recovered by suction filtration. To control the swelling, we limited the amount of PAA and acetic acid bonded to cellulose. The degree of substitution (DS) of PAA (DSPAA) was less than or equal to 0.3, and that of acetic acid was less than 1.1. At the same time, a sufficient amount of the long chain could be bonded to cellulose. DSPAA was more than 0.2, which was found to be sufficient for the final product to attain enough thermoplasticity for injection molding. Both efficient solid-liquid separation and sufficient bonding of the long chain could be achieved by controlling the swelling of the cellulose ester. The solution obtained by the filtration was reused easily only by adding deficient comoponents, which lead to a reduction of the reaction solvent. 332 In Green Polymer Chemistry: Biobased Materials and Biocatalysis; Smith, et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


In the second step, the intermediate product was acetylated with acetic anhydride. Because this reactant and a reaction solvent are liquid components and could be distilled, the final product could also be recovered easily without poor solvent in this step. The distilled liquids could also be reused by adding defficeinet components. While thermoplasticity of the intermediate product was low, it was improved by over 10 times, as measured by melt flow rate, after the second step, reaching sufficient level for injection molding.

Figure 3. Flow diagram of two-step heterogeneous process.

The solvent usage of the two-step heterogeneous process was compared with that of a homogeneous process (12, 13) (Figure 4). Solvent usage could be reduced by about 90% mainly because of the elimination of poor solvent. The amount of solvent is important in terms of energy for production as the energy to distill solvents constitutes a major component of the total energy of a process. We believe the accomplished reduction in solvent usage will lead to a significantly lowered energy of about 1/10 compared with the homogeneous process. 333 In Green Polymer Chemistry: Biobased Materials and Biocatalysis; Smith, et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2015.

Cardanol-bonded cellulose resin Cellulose acetate + plasticizer (29 wt%)*

334


Table 1. Characteristics of Cardanol-Bonded Cellulose Resin Synthesized by Two-Step Heterogeneous Process and Its Composite

*

Homo-geneous process

Two-step heterogeneous process 1st

Intermediate product

2nd Final product

+Additives (Polyester: 27%, Glass fiber: 10%)

Amounts of side chains (DS: degree of substitution)

Short chain 2.1 Long chain -

2.1 0.33

0.90 0.23

2.4 0.24

2.4 0.27

Thermoplasticity: MFR (g/10min) 200°C, 500kgf/cm2

960

150

20

275

1330

Izod impact strength (kJ/m2)

8.8

3.5

2.5

6.6

Flexural strength (MPa)

68

84

46

50

Elastic modulus (GPa)

2.6

2.3

2.8

1.6

2

>10

Molding difficult

Breaking strain (%)

>10

>10

Glass transition temp. (°C)

109

154

140

133

Water absorption ratio (%) [Room temp. 24 hr.]

5.9

2.1

1.8

1.2

Weight ratio of long chain component of cardanol-bonded cellulose resin: 24-31 wt%.

In Green Polymer Chemistry: Biobased Materials and Biocatalysis; Smith, et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


Figure 4. Solvent usage of homogeneous and two-step heterogeneous processes. The physical properties of the cardanol-bonded cellulose resin synthesized by the two-step heterogeneous process is shown in Table 1 as well as a conventional CDA composite with an external plasticizer and the cardanol-bonded cellulose resin synthesized by a homogeneous process. While the thermoplasticity of the intermediate product of the heterogeneous process was low for injection molding, that of the final product was high enough for injection molding. Compared with the cardanol-bonded cellulose resin of the homogeneous process, the thermoplasticity, elastic modulus and water resistance of the final product of the heterogeneous process were higher, and the heat resistance (glass transition temperature) was relatively close. However, the impact strength, flexural strength, and breaking strain were lower, which is considered to be caused by inhomogeneity of the cardanol-bonded cellulose resin synthesized by the two-step heterogeneous process. On the basis of a systematic search for additives to improve the impact strength of a cardanol-bonded cellulose resin synthesized by a homogeneous process (14), we found that a specific polyester, polybutylene succinate adipate (PBSA), shows the best compatibility among various polyesters with the cellulose resin of the two-step heterogeneous process, and it is a suitable additive to improve the brittleness of the latter resin. PBSA forms an amorphous state in the cellulose resin and thus gives flexibility to the resin because of the flexible structure of its main chain. Although flexural strength was decreased by adding PBSA, it could be increased by adding a glass fiber while keeping impact strength. Finally, after adding PBSA and the glass fiber, high target levels for durable products, such as electronic products, could be reached. Compared with the CDA composite with an external plasticizer, the final product of the heterogeneous process showed higher elastic modulus, heat resistance and water resistance. Although its thermoplasticity, impact strength, flexural strength and breaking strain were lower, these properties were improved while keeping heat and water resistance by adding PBSA and the glass fiber. The resultant composite achieved high level properties for durable products as mentioned above. 335 In Green Polymer Chemistry: Biobased Materials and Biocatalysis; Smith, et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


Conclusion A novel cellulose-based bioplastic bonded with cardanol as a long side chain achieved high mechanical strength and high heat resistance, and therefore, we developed a novel two-step heterogeneous process for its practical production with low energy consumption. In the first step, a modified cardanol (PAA) and acetic acid were bonded in a heterogeneous system followed by easy recovery of the intermediate product by filtration. By controlling the swelling of the product, we could achieve both an efficient recovery step and sufficient amount of PAA bonded to cellulose. In the second step, acetic acid was additionally bonded to the intermediate product, and the final product, cardanol-bonded cellulose resin, was readily recovered only by distilling liquid components. The solvent usage was reduced by about 90% compared with a homogeneous process by elimination of poor solvent, which leads to a large reduction in energy. The thermoplasticity of the resin, which was improved by the second step, was comparable with that of a homogeneous one. The characteristics of the resin were improved by adding polybutylene succinate adipate and a glass fiber, and high target levels for durable products were reached. We therefore conclude that the novel heterogeneous process is promising for mass production of the cellulose resin, and its composites are prospective for various durable products such as electronic devices.

Acknowledgments The authors are grateful to Ms. Toshie Miyamoto and Dr. Fumi Tanabe for their support in the experiments. The work was supported by the Japan Science and Technology Agency’s Advanced Low Carbon Technology Research and Development Program (ALCA).

References Li, S.; Ernst, W.; Martin, P. Biofuels, Bioprod. Biorefin. 2010, 4, 25–40. Serizawa, S.; Inoue, K.; Iji, M. J. Appl. Polym. Sci. 2006, 100, 618–624. Zepnik, S.; Kesselring, A.; Kopitzky, R.; Michels, C. Bioplast. Mag. 2010, 5, 44–47. 4. Hwan-Man, P.; Manjusri, M.; Lawrence, T. D.; Mohanty, A. K. Biomacromolecules 2004, 5, 2281–2288. 5. Edgar, K. J.; Buchanan, C. M.; Debenham, J. S.; Rundquist, P. A.; Seiler, B. D.; Shelton, M. C.; Tindall, D. Prog. Polym. Sci. 2001, 26, 1605–1688. 6. Freire, C. S. R.; Gandini, A. Cell. Chem. Technol. 2006, 40, 691–698. 7. Roy, D.; Semsarilar, M.; Guthrie, J. T.; Perrier, S. Chem. Soc. Rev. 2009, 38, 2046–2064. 8. Iji, M.; Moon, S.; Tanaka, S. Polym. J. 2011, 43, 738–741. 9. Iji, M.; Toyama, K.; Tanaka, S. Cellulose 2013, 20, 559–569. 10. Kumar, P. P.; Parmashivappa, R.; Vithayathil, P. J.; Rao, P. V. S.; Rao, A. S. J. Agric. Food Chem. 2002, 50, 4705–4708. 11. Lubi, M. C.; Thachil, E. T. Des. Monomers Polym. 2000, 3, 123–153. 12. Tanaka, S.; Honzawa, H.; Iji, M. J. Appl. Polym. Sci. 2013, 130, 1578–1587. 1. 2. 3.

336 In Green Polymer Chemistry: Biobased Materials and Biocatalysis; Smith, et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


13. Bogan, R. T.; Brewer, R. J. In Encyclopedia of Polymer Science and Engineering; Mark, H. F., Bikales, N., Overberger, C. G., Menges, G., Kroschwitz, J. I., Eds.; John Wiley & Sons: New York, 1985, Vol. 3, pp 158−181. 14. Soyama, M.; Iji, M.; Tanaka, S.; Toyama, K. Polym. Prepr. Jpn. 2014, 63, 3683–3684.

337 In Green Polymer Chemistry: Biobased Materials and Biocatalysis; Smith, et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2015.

Development of Cardanol-Bonded Cellulose Resin with Nonfood

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