Cellulose Fiber from Coconut Coir for Development of Dental Composite Filler

(1)

Journal of International Dental and Medical ResearchISSN 1309-100X Development of Dental Composite Filler http://www.jidmr.com Twi Agnita Cevanti and et al

Cellulose Fiber from Coconut Coir for Development of Dental Composite Filler Twi Agnita Cevanti^1,2, Nur Shiyama Purnama Sari³, Steella Ilham Isnaini³, Mahardika F. Rois³,

Heru Setyawan³, Adioro Soetojo²* and Ira Widjiastuti²

1.Faculty of Dental Medicine, Universitas Airlangga, Indonesia.

2.Department of Conservation Dentistry, Faculty of Dental Medicine, Universitas Airlangga, Surabaya, Indonesia.

3.Department of Chemical Engineering, Institut Teknologi Sepuluh Nopember, Kampus ITS Sukolilo Surabaya, Indonesia.

Abstract

The aim of this study is to treat cellulose obtained from coconut coir for use as filler for flowable composites in class 2 restoration-based applications. The method of this study was bleaching using NaOH and peroxide, cross-linking using NaOH and Urea, and nucleation using ethanol as an organic antisolvent before being dried by a sublimation process. The morphology of the fibers produced and the antibacterial ability became the central point of the observation. The XRD test results formed identical C-N bonds with Nitrocellulose, and a double peak shift occurred at the main peak of cellulose. The FTIR test results showed the formation of a cross-linking bond between cellulose and Nitrogen from Urea to form fibers. The fiber morphology obtained from the SEM images showed that the cellulose from coconut coir fiber was in the form of short fibers measuring 111.95 - 155.2 micrometers with a rough surface and porous inside (hollow tube). Inhibition test results of cellulose-based on coconut coir fiber had inhibition of S. mutans bacteria where the nanocellulose had an inhibitory power. Based on these experimental results, it can be suggested that fiber coconut coir could be used as a promising alternative filler composite in dental material.

Experimental article (J Int Dent Med Res 2021; 14(4): 1401-1406) Keywords: Coconut coir, cellulose, composite, healthy lifestyle, human & heath.

Received date: 01 July 2021 Accept date: 26 October 2021

Introduction

The use of composite restorations in posterior teeth has been currently increasing due to the improvement of their physical and mechanical properties. However, compositing by the most common polymerization procedure has still some issues to be solved.

Polymerization can cause stress that may exceed the bond strength around the teeth¹. Internal contractions that occur can fail the interfacial attachment of the restoration to damage the marginal seal. This causes deformation of the tooth structure then microcracks occur and the tooth continues to fracture^2,3. Several techniques have been used to minimize this problem, one of which is the use of an elastic layer between the dentin and the composite. The layer is expected act as a

stress breaker that can absorb the stress during polymerization of the overlying restoration.

Therefore, the shrinkage pressure can be eliminated and improve the adaptation of the marginal seal^4,5. Clinicians recommend the use of flowable composites on the bottom of the cavity as the first layer. This is because flowable composites have properties of low viscosity, good elasticity and high wettability. These properties provide a better edge closing ability so that it can help reduce shrinkage stress during polymerization^5–7. Until now, the latest technology to improve the weaknesses of conventional flowable continues to be developed, especially to reduce shrinkage and polymerization stress.

Fiber-reinforced composite (FRC) technology is currently being developed as an innovative solution. The fiber in FRC plays a role in providing better transverse strength. The fibers also reduce shrinkage in a certain direction and provide lower residual stress. The use of fiber in restoration applications in dentistry is an effective option⁸. But the fiber used today is a synthetic fiber, namely E-glass fiber, which is the most widely used in dental materials because of its chemical resistance

*Corresponding author:

Adioro Soetojo,

Department of Conservation Dentistry, Faculty of Dental Medicine, Universitas Airlangga,

Surabaya 60132, Indonesia.

E-mail: [email protected]

(2)

and relatively low cost compared to other inorganic fibers. The problem with synthetic flow fiber composite today is that it still has a high viscosity. Glass fiber is required to maintain the reinforcing effect of the material. But glass fiber also makes the material more viscous and stiffer making it difficult to obtain low viscosities. E- glass fiber has a high density, the formation of the composite takes longer and is easily damaged at high pressure^9–11. That's why the potential of natural fibers is widely explored to replace synthetic fibers. Polymer products based on green materials such as agricultural and plantation crops are the basis for forming products that are eco-efficient, sustainable, and competitive with synthetic materials. On the other hand, natural fibers also have a strength that can be compared to synthetic fibers. Even for certain materials, natural fibers can outperform synthetic fibers^5,12,13.

Coir fiber, known by its Latin name Cocos nucifera L. (coir) is currently being used and developed as a raw material for composite products in the industrial sector. Coconut husk is a by-product and the largest part of the coconut fruit. Coconut coir is very abundant and has important pharmacological effects with low toxicity. The superior characteristics of coco fiber are its elastic modulus is quite low and its elongation at break is very high. The nature of the fiber is not stiff, very flexible, and the most ductile. The surface structure of the fiber is hollow like foam/sponge with a compact and strong structure^4,5,14. Another advantage is that it is strong, lightweight, heat resistant, saltwater resistant, weather-resistant, inexpensive, and easy to obtain^15–17. Looking at the characteristics, properties and structure of coir fiber, it can fulfill one of the requirements for an elastic material as a substitute for lost dentin in dental restorations. Coir has a high potential to replace synthetic fiber reinforcing materials. The fiber processing technique is an important factor that determines the structure and properties of the fiber.

An important feature that affects the strength and toughness of composite material is the strength of the adhesion between the reinforcing material and the polymer matrix. To obtain optimal adhesion strength, processing of the coir fiber must be carried out. Plant fibers cannot be used directly in their original form,

obtain more cellulose fibers as the main component to be used. The purpose of this study is to investigate the characteristics of coco fiber which can later be bonded to the polymer matrix for the manufacture of composites with low viscosity. The method used to obtain the formation of fibers from coir fibers is to modify the method of soaking coconut coir fibers with an alkaline solution mixed with urea and then nucleated using 70% ethanol.

Materials and methods

This type of research is descriptive observational research. The observation material used was cellulose fiber from coconut coir. The materials needed in this research are ethanol, aquadest, 3% w/w hydrogen peroxide (H2O2), NaOH, Urea and demineralized water.

To separate cellulose from components that are not required, extraction is carried out through a delignification process. Coconut coir powder and 60% w/w ethanol were put into the hydrothermal reactor for delignification at a temperature of 150^oC for 4 hours. Then the sample (cellulose pulp dark) was washed with demineralized water and dried in an oven. Dark colored cellulose pulp indicate that the pulp still contains lignin, so we need bleaching to dissolve.

The bleaching process is carried out by mixing dark pulp cellulose with a solution of 3%

H2O2+4% NaOH in a rotary vacuum evaporator at 50^oC for 180 min. This process is repeated 3 times to obtain a brightly colored pulp. Cellulose subsequently separated from the pulp using an alkaline solution (pulp: NaOH: urea:

demineralized water = 1g: 1g: 4g: 14ml) at room temperature. The synthesis process is carried out by adding cellulose filtrate into 70% ethanol using a sirring pump at a rate of 20 ml/min to form a slurry. After that, the sample is frozen in the freezer at -25^oC which has previously been solvent exchange by demineralized water. Finally, the frozen cellulose was freeze-dried at a temperature of -45°C and a pressure of 5 mTorr until dry particles were formed.

Characterization of cellulose fiber as composite filler includes morphology of cellulose particles and crystallinity to determine the structure of cellulose. In addition, an antibacterial test was also carried out to determine the inhibitory ability of cellulose against S. mutant

(3)

morphology of the cellulose particles was analyzed using Scanning Electron Microscopy (SEM) with Hitachi FlexSEM 1000 type. Then, the results of the SEM were processed using ImageJ software to determine the particle size of cellulose fibers. The crystallinity of the cellulose structure was analyzed using X-ray diffractometry (XRD) with the PANalytical type, X'Pert Pro.

Functional Groups to determine the presence of cellulose bonds using Fourier transform infrared spectroscopy (FTIR) analysis with the Shimadzu IRTracer-100 type over the wavenumber range of 400-4000 cm^-1. The raw fiber used to fabricate the composite is also analyzed using an antibacterial test by diffusion (wells). First, bacterial stocks were grown with an oasis on BHIB medium, and then they were incubated for 2 24 h under anaerobic conditions. Second, the turbidity of the BHIB medium was observed and then it was diluted to an equal of 0.5 McFarland's standard. Third, the stocks were planted on an agar media with a swab and distributed evenly on the surface of the agar media. Fourth, a hole was made on the media with an aluminum sterile ring of 5 mm in diameter using tweezers. Fifth, the sample was put in the well using tweezers with a probe and then incubated anaerobically for 2 24 h. Sixth, the growth of bacteria was observed and the clear zone was measured on the surface of the agar around the diameter of the well using a capillary compass.

Results

Figure 1 shows the FTIR spectra of four different samples delignified, bleached, and nanocellulose. For all samples, two main bands corresponding to cellulose can be observed. The band at 2889 cm^-1 can be attributed to C H in CH2 and the band at 1050 cm^-1 is aldehyde groups C O of cellulose compound. However, the band that appears at the sample corresponding to -cellulose changed to intermolecular hydrogen bonding 3330 cm ¹. Additional functional groups appeared because of the addition of H2O2 in the bleaching process, which is located at wavenumbers of 1420 cm ¹ and 1576 cm ¹. After the addition of NaOH-Urea, a new functional group appeared at the cellulose spectrum at 1640 cm ¹. A new band appeared at 1050 cm ¹ after nucleation with ethanol corresponding to the C O functional group.

Figure 1. FTIR spectra of Delignified, bleached, and nanocellulose from coconut coir.

To gain better insight into the transformation of cellulose structure during nanosheet formation, XRD patterns of samples after each treatment were inspected. Figure 2 shows the XRD patterns of delignifed, bleached, and nanocellulose. Where, the results of X-ray diffraction in the delignification stage, the angle of 2θ fired in the range 20,4435^o – 22,8383^o cellulose structure identical to 1-cellulose amorphous according to ICSD 00-056-1718.

Furthermore, in the bleaching stage, a 2 angle is fired in the range 8,8981^o – 62,5749^o the cellulose structure shifts the cellulose polymorph to 1∝-cellulose because there is a bond with high concentrated NaOH and 10% H2O2 which will produce Na-H-CO3 bonds as impurities by following per under ICSD 00-056-1719.

The inhibition test of Streptococcus mutant bacteria was carried out at the Research Center Laboratory of FKG UNAIR Surabaya. The results of observing and measuring the clear zone on the agar surface around the diameter of the well-using calipers showed antimicrobial properties against common oral have been proved scientifically. The results of the Independent T-Test test showed that value in the results of the independent t-test was obtained sig

= 0,000 < 0,05. In the growing media, figure 4.

shows that cellulose treated with nanocellulose bacterial inhibition with a size of 8,55 – 8,8 mm.

The control group (K) used sterile distilled water and showed no inhibition against of Streptococcus mutant bacteria.

(4)

Figure 2. X-ray diffraction patterns of delignified, bleached, and nanocellulose from coconut coir.

Figure 3. SEM images of (a) nucleated nanocellulose from coconut coir and (b) commercial composite EVER X-Flow

Figure 4. Antibacterial power of cellulose fiber.

Discussion

Fibers in fiber composites serve as the main load-bearing part. Fiber as a composite reinforcement also determines the characteristics of the composite in terms of the strength of a fiber composite. Strong adhesion between the fibers and the polymer matrix is required for efficient local transfer of the load from the matrix to the stronger fibers. So, an important factor affecting the strength and toughness of the material is the strength of the adhesion between

natural fibers that can bind well and strong, it is necessary to modify the fiber surface. The main fiber used as reinforcement in the manufacture of composites is cellulose fiber. Soaking the fiber with an alkaline solution is also known as the delignification method or the fiber cleaning method. This method is very effective in breaking down lignin and will increase the amount of cellulose released to produce pure cellulose.

Lignin and other fibers must be removed because they are stiff and brittle. Delignification also increases the surface roughness of the fiber so that it will increase the adhesion between the surface of the cellulose fiber and the matrix which can later produce a strong bond¹². The delignification process on the fiber will have two effects on the fiber, namely increasing the surface roughness of the fiber so that it will produce a better interlocking bond and will increase the amount of cellulose released¹⁸.

To obtain good fiber composite characteristics, several ways can be done such as choosing the type of fiber, fiber treatment, fiber arrangement direction, fiber composition with the matrix. Three factors significantly affect the mechanical properties of fiber composites, namely the delignification process, fiber length and fiber volume fraction^19-21. The length and diameter of the fiber also have an important role in increasing the strength of the composite. The smaller the diameter of the fiber, the better it is to use. The small diameter of the fiber will provide a larger surface area per unit weight for the same number of fibers. This helps the process of transferring stress from the matrix to the fiber more evenly. The smaller the diameter of the fiber, the stronger it is. the material, due to the lack of defects in the material.²²

In the study of extracting cellulose fibers from coconut coir fibers synthesized with 70%

ethanol anti solvent solution, cellulose-I polymorphs were produced, with a size of 6.4 µm and a length of 111.96 µm. The FTIR test resulted in the formation of fibers from the C N triple bounding functional group, which indicated that there was already a bond between cellulose and nitrogen. Triple bounding bonds are the result of cross-linking bonds that occur because urea binds to cellulose. To support the FTIR results, XRD data is needed. Where, the results of X-ray diffraction in the delignification stage, the angle of 2θ fired in the range 20,4435° –

(5)

cellulose amorphous. Cellulose 1β is dominant in higher plants including cotton cellulose, and mercerization and regeneration of cellulose 1β from cellulose II¹⁵. Furthermore, in the bleaching stage, a 2 angle is fired in the range 8,8981^o – 62,5749^o the cellulose structure shifts the cellulose polymorph to 1∝-cellulose because there is a bond with high concentrated NaOH and 10% H2O2 which will produce Na-H-CO3 bonds as impurities. Treatment of cellulose materials using a high concentration solution of sodium hydroxide causes significant swelling of the internal structure of the fiber^23,24. Furthermore, in the Nanocellulose stage, where at this stage the cellulose is dissolved in NaOH and Urea, then followed by nucleation by antisolvent using 70%

ethanol. Mixing will form C-N bonds which are identical to nitrocellulose and a double peak shift occurs in the main peak of cellulose. Lower concentrations of alkali would result in higher crystallinity index which is preferred for promoting better fiber to matrix bonding²⁵. Moreover, it can be concluded from FTIR spectra and result the XRD pattern as discussed above that the obtained coir nanocellulose is 1β-cellulose amorphous and it changes to 1∝-cellulose polymorph after added NaOH, Urea, and H2O2

treatment.

Streptococcus mutants is a gram-positive bacterium.

Coconut husk (Cocos nucifera) contains catechins and epicatechins, these are the main elements that provide antimicrobial effects. This compound inhibits Streptococcus mutants bacteria and other bacteria and microorganisms in vitro by inhibiting the isolation of bacterial glucosyltransferase in Streptococcus mutants⁶. Secondary metabolite compounds contained in coconut fiber can be used as antibacterial. The secondary metabolite compounds are tannins, flavonoids, and polyphenols. Coconut coir water extract has several compounds, including ellagic acid, gallic acid, tannins and catechins.²⁶ The results of this study showed that the diameter of the inhibition zone for Streptococcus mutants test bacteria increased in line with the increase in the use of ethanol concentration. The inhibitory power at 96% ethanol concentration was greater than the inhibitory power at 70% ethanol.

Conclusions

According to these experimental results, it can be suggested that fiber coconut coir could be used as a promising alternative filler composite in dental material.

Acknowledgements

This work was supported by the National Research and Innovation Board, Laboratory of Electrochemistry and Corrosion, Department of Chemical Engineering Institute Technology Sepuluh November, Indonesia. Authors would like to thank Universitas Airlangga, Indonesia for antibacterial test.

Declaration of Interest

The authors report no conflict of interest.

References

1. Lotfi N, Esmaeili B, Ahmadizenouz G, Bijani A, Khadem H.

Gingival microleakage in class II composite restorations using different flowable composites as liner: an in vitro evaluation.

Casp J Dent Res 2015;4(1):10–6.

2. Abouelnaga MAA. A comparison of gingival marginal adaptation and surface microhardness of class II resin based composites (conventional and bulk fill) placed in layering versus bulk fill techniques. University of Iowa 2014.

3. Stawarczyk B, Özcan M, Trottmann A, Schmutz F, Roos M, Hämmerle C. Two-body wear rate of CAD/CAM resin blocks and their enamel antagonists. J Prosthet Dent 2013;109(5):325–32.

4. Rodrigues RF, Senna SS, Soares AF, Mondelli RL, Francisconi PS, Borges AFS. Marginal adaptation in proximal cavities restored with composites and other materials. Brazilian Dent Sci 2017;20(4):63.

5. Shouha PSR, Ellakwa AE. Effect of short glass fibers on the polymerization shrinkage stress of dental composite. J Biomed Mater Res Part B Appl Biomater 2017;105(7):1930–7.

6. Soares CJ, Faria-E-Silva Al, Rodrigues M De P, Vilela Abf, Pfeifer Cs, Tantbirojn D, et al. Polymerization shrinkage stress of composite resins and resin cements – What do we need to know? Braz Oral Res 2017;31(1).

7. Zhang M, Matinlinna JP. E-Glass Fiber Reinforced Composites in Dental Applications. Silicon 2012;4(1):73–8.

8. Abouelleil H, Pradelle N, Villat C, Attik N, Colon P, Grosgogeat B. Comparison of mechanical properties of a new fiber reinforced composite and bulk filling composites. Restor Dent Endod 2015;40(4):262.

9. Segal L, Creely JJ, Martin AE, Conrad CM. An Empirical Method for Estimating the Degree of Crystallinity of Native Cellulose Using the X-Ray Diffractometer. Text Res J 1959;29(10):786–94.

10. Kondo Y, Arsyad M. Analisis Kandungan Lignin, Sellulosa, dan Hemisellulosa Serat Sabut Kelapa Akibat Perlakuan Alkali.

INTEK J Penelit 2018;5(2):94.

11. Randolph LD, Palin WM, Leloup G, Leprince JG. Filler characteristics of modern dental resin composites and their influence on physico-mechanical properties. Dent Mater 2016;32(12):1586–99.

(6)

12. Noorunnisa Khanam P, Ramachandra Reddy G, Raghu K, Venkata Naidu S. Tensile, Flexural, and Compressive Properties of Coir/Silk Fiber-reinforced Hybrid Composites. J Reinf Plast Compos 2010;29(14):2124–7.

13. Fronza B, Ayres A, Pacheco R, Rueggeberg F, Dias C, Giannini M. Characterization of Inorganic Filler Content, Mechanical Properties, and Light Transmission of Bulk-fill Resin Composites. Oper Dent 2017;42(4):445–55.

14. Arsyad M, Salam A. Analisis Pengaruh Konsentrasi Larutan Alkali Terhadap Perubahan Diameter Serat Sabut Kelapa.

INTEK J Penelit 2017 3;4(1):10.

15. Fauziyah M, Widiyastuti W, Balgis R, Setyawan H. Production of cellulose aerogels from coir fibers via an alkali–urea method for sorption applications. Cellulose 2019;26(18):9583–98.

16. Rois MF, Widiyastuti W, Setyawan H, Rahmatika AM, Ogi T.

Preparation of Activated Carbon from Alkali Lignin using Novel One-Step Process for High Electrochemical Performance Application. Arab J Chem 2021;103162.

17. Widiyastuti W, Rois MF, Setyawan H, Machmudah S, Anggoro D. Carbonization of Lignin Extracted from Liquid Waste of Coconut Coir Delignification. Indones J Chem 2020;20(4):842.

18. Karim B, Bhaskar DJ, Agali C, Gupta D, Gupta RK, Jain A, et al.

Effect of Aloe vera mouthwash on periodontal health: triple blind randomized control trial. Oral Health Dent Manag 2014;13(1):14–9.

19. Roggendorf MJ, Krämer N, Appelt A, Naumann M, Frankenberger R. Marginal quality of flowable 4-mm base vs.

conventionally layered resin composite. J Dent 2011;39(10):643–7.

20. Mahardhini S, Meidyawati R, Artiningsih DA, Amalia M.

Effects of Epoxy Resin and Calcium Silicate-Based Root Canal Sealer on Fiber Post Adhesion. Journal of International Dental and Medical Research 2021;14(1):173-9.

21. Tian W, Li H, Zhou J, Guo Y. Preparation, characterization and the adsorption characteristics of lignin/silica nanocomposites from cellulosic ethanol residue. RSC Adv 2017;7(65):41176–81.

22. Sangian HF, Kristian J, Rahma S, Agnesty SY, Gunawan S, Widjaja A. Comparative Study of the Preparation of Reducing Sugars Hydrolyzed from High-Lignin Lignocellulose Pretreated with Ionic Liquid, Alkaline Solution and Their Combination. J Eng Technol Sci 2015;47(2):137–48.

23. Chen M, Zhang X, Matharu A, Melo E, Li R, Liu C, et al.

Monitoring the Crystalline Structure of Sugar Cane Bagasse in Aqueous Ionic Liquids 2017; 5(8):7278-83.

24. Feldman D. Lignin nanocomposites. J Macromol Sci Part A Pure Appl Chem 2016;53(6):382–7.

25. Mwaikambo LY, Ansell MP. The effect of chemical treatment on the properties of hemp, sisal, jute and kapok for composite reinforcement. Die Angew Makromol Chemie 1999;272(1):108–

16.

26. Theng GW, Johari Y, Ab Rahman I, Muttlib NA, Yusuf MN, Alawi R. Mechanical Properties of Dental Composite Reinforced with Natural Fiber. Journal of International Dental and Medical Research 2019;12(4):1242-7.