The Effect of Microcrystalline Cellulose on the Physical, Thermal, and Mechanical Properties of Composites Based on Cantala Fiber and Recycled High-Density Polyethylene

ABSTRACT

This research is conducted to improve the performance of plant fiber-based composites by inserting microcrystalline cellulose (MCC). MCC was incorporated into a mixture of recycled high-density polyethylene (rHDPE) and cantala fiber at a ratio of 1, 2, 3, and 4% wt. The composites rHDPE/cantala fiber/MCC were fabricated via a twin screw extruder followed by a hot press. The composite’s mechanical, physical, and thermal properties were tested to investigate the effect of adding MCC. It was observed that the enhancement of MCC led to a significant improvement in the mechanical performance of the composite. Adding 4%wt MCC resulted in a significant improvement in mechanical properties of 50.7%, 31%, and 37.7%, respectively, in tensile strength, bending strength, and impact strength compared to rHDPE/cantala composite without MCC. Adding MCC up to 4% wt slightly increased the composite density from 0.88gr/cm³ to 0.90 gr/cm³. The enhancement of MCC did not significantly change the diffraction peak position of the composite. However, composite crystallinity increased by 6.7%. In addition, the augment of MCC increased the thermal stability of the composite, as indicated by the delay in composite degradation.

摘要

本研究旨在通过插入微晶纤维素（MCC）来提高植物纤维基复合材料的性能. 将MCC以1、2、3和4%重量的比例掺入回收高密度聚乙烯（rHDPE）和康塔拉纤维的混合物中. 采用双螺杆挤出机和热压法制备了rHDPE/康塔拉纤维/MCC复合材料. 测试了复合材料的力学、物理和热财产，以研究添加MCC的影响. 据观察，MCC的增强导致复合材料的机械性能显著提高. 与不含MCC的rHDPE/cantala复合材料相比，添加4%wt MCC后，拉伸强度、弯曲强度和冲击强度的机械财产分别显著提高50.7%、31%和37.7%. 添加高达4%wt的MCC使复合材料密度从0.88gr/cm3略微增加到0.90gr/cm3. MCC的增强并没有显著改变复合物的衍射峰位置. 然而，复合材料的结晶度增加了6.7%. 此外，MCC的增加增加了复合材料的热稳定性，复合材料降解的延迟表明了这一点.

KEYWORDS:

• rHDPE/cantala composite
• mechanical properties
• thermal properties
• physical properties
• microcrystalline cellulose, twin screw extruder, hot press

关键词:

• 康塔拉复合材料
• 力学财产
• 热财产
• 物理财产
• 微晶纤维素，双螺杆挤出机，热压

Introduction

Awareness of environmental conservation has encouraged efforts to reduce waste through increased material recycling, product reuse, and the development of eco-friendly products (Pichandi et al. 2018). Plastic is a beneficial product for human activities in modern life (Darus et al. 2020; Tamrin and Nurdiana 2021). Since commercial production in the 1930s, the consumption of plastics has increased rapidly. In 2016, the consumption was around 335 million tons, and it became 348 million tons in 2017. The demand will continue to grow and is estimated to reach 485 million tons by 2030 (Tamrin and Nurdiana 2021). However, the increase in consumption will be followed by environmental problems when its useful life runs out. Because plastic material was challenging to degrade by microorganisms. Therefore, various attempts have been made to recycle plastic and reuse it in other products (Karakus et al. 2017; Zulnazri, Dewi, and Sylvia 2020).

Polyethylene (PE) is one of the most common low-price plastic used daily. Consumption of this plastic, along with other inexpensive plastic such as polypropylene (PP) and polyvinyl chloride (PVC), accounts for 70% of the total thermoplastics used in the plastics industry (Hong and Ho Hwang 2021). Thus, the opportunity to use plastic waste as a raw material to manufacture other products was substantial.

Several researchers have introduced green materials to meet the need for eco-friendly materials. The use of green materials, such as natural fibers as biocomposites, can be found in various industrial sectors (Radzi et al. 2019). The advantages of natural fibers, such as lightweight, cheap, low density, good thermal insulation properties, excellent electrical resistance, and good specific strength, have driven the increasing application of this natural material in everyday life (Radzi et al. 2019; Rehman et al. 2019; Sullins et al. 2017). However, natural fibers have drawbacks that hinder their application. The main weakness is an inability to bond with hydrophobic polymers (Sullins et al. 2017).

Cellulose is composed of amorphous and crystalline regions. Crystal cellulose is more robust and stiffer than amorphous or native cellulose (Rehman et al. 2019). MCC is crystalline cellulose obtained from removing amorphous regions through acid hydrolysis (Mathew, Oksman, and Sain 2005). MCC has the advantage of high specific surface area compared to cellulose fibers (Bhasney et al. 2020; Kiziltas et al. 2014). MCC has been widely used in polymer composites as a binder, filling agent, and reinforcement (Boudjellal et al. 2022). MCC is added to improve the biocomposites’ mechanical properties, thermal properties, and morphology (Collazo-Bigliardi, Ortega-Toro, and Chiralt Boix 2018). (Bessa et al. 2022) observed the effect of adding silane-treated microcrystalline cellulose (MCC Si) on the bending strength of the kevlar fabrics/polybenzoxazine composites. The results showed that adding 1 wt% and 3% wt MCC increased bending strength. However, adding 5%wt MCC Si decreased the bending strength of the composite. The added MCC in a thermoplastic matrix is useful as the nucleation centers when the cooling process. The MCC network in the matrix causes an increase in the stiffness, strength, and impact resistance properties of the composite (Pichandi et al. 2018). However, excess MCC tends to agglomerate and cause a decrease in the mechanical properties of the composite. So it is necessary to control the amount of MCC distributed in the composite.

Several studies have investigated the effect of adding MCC to polymer composites. However, studies on adding MCC to natural fiber-reinforced thermoplastic composites are still minimal. Therefore, this research was conducted to study the effect of adding MCC on the mechanical, physical, and thermal properties of rHDPE/cantala composites manufactured by a twin screw extruder and hot press.

Experimental

Materials

Cantala fiber was obtained from CV Rami Kencana, Kulonprogo, Indonesia. Recycled high-density polyethylene (rHDPE) flakes with a melt flow index (MFI) of 2.43 g/10 min, a density of 1.014 kg/m³, and a melting temperature of 108.5–139.5°C were supplied by CV Vanilla Plastik, Sukoharjo, Indonesia. Microcrystalline Cellulose with an average particle size of less than 100 µm was provided by EMD Millipore Corporation, Germany.

Composite preparation

Composite made of cantala fiber, rHDPE, and MCC. Before being integrated, a crusher machine converted the cantala fiber and rHDPE into powder. Then it was sieved to get a size that passed mesh 50 and did not pass mesh 60. After that, it was heated at 110°C for 45 minutes.

In manufacturing composites, cantala fiber and rHDPE were mixed with a weight ratio of 10%: 90%. Mixing was carried out using a mixer at a speed of 75 rpm for 1 minute. Next, MCC was added to the mixture with variations in weight fraction (0, 1%, 2%, 3%, and 4%) and mixed for 1 minute at a speed of 75 rpm. Then the mixture was melted in a twin screw extruder at 150°C with a rotor speed of 100 rpm for 10 minutes. The resulting products were cut into 4-6 mm granules using a pelletizer, and a hot press converted the granules into sheets. Lastly, the specimens were taken from a sheet with their dimension following ASTM standards

Characterization

Scanning electron microscopy (SEM) analyzing

The fracture surfaces of the tensile test specimens were characterized using SEM JSM-610 PLUS/LV from JEOL. Samples were mounted on aluminum stubs and coated with platinum. The accelerating voltage was 10 kV with a 10 mm working distance (WD).

Fourier transform infrared (FTIR) analyzing

FTIR spectra for composite were recorded using a Shimadzu IR Prestige-21 in wavelengths between 500 and 4000 cm⁻¹. The sample was prepared by pressing a mixture of composite powder and potassium bromide (Kbr) at a ratio of 1:200.

X-Ray Diffraction (XRD) analyzing

The composite crystal profile was diagnosed with a Shimadzu XRD-700 operated at a voltage of 40 kV and a current of 30 mA. The diagnosis was performed using CuKα radiation (α = 1.54A). Meanwhile, scanning was carried out in the range of 10–50° at a speed of 2°/min.

Thermogravimetric analysis (TGA) analyzing

Thermal stability measurements were carried out using the Perkin Elmer Pyris Diamond TGA 6 Analyzer. Each sample weighing about 5 mg was scanned at a temperature of 30–550°C at a heating rate of 10°C/min.

Density measurement

Composite density was measured using an ACIS B-5000 digital balance with a maximum capacity of 500 grams and a sensitivity of 0.01 grams. The tests were based on the Archimedes principle and followed the ASTM D792 standard.

Stereozoom microscope

A stereo microscope was used to observe the surface of cantala/rHDPE composites. The microscope used was the Olympus stereo microscope SZX7.

Tensile strength of composite

The composite tensile test used the JTM-UTS510 universal testing machine (UTM). The device had a maximum capacity of 5000 kg, an accuracy of 0.5%, a speed of 0-1000 mm/min, and a 50–2000 kg load cell. Tensile testing followed the ASTM D638–2000 standard.

Bending strength of composite

Based on the ASTM D790 standard, the composite bending test used the three-point bending method. The test was conducted with a universal testing machine type JTM-UTS510.

Impact strength of composite

The Izod impact testing machine measured the composite impact strength referred to ASTM D-5941. The test equipment had a pendulum length of 35.7 cm, a pendulum weight of 1591 kg, a pendulum angle of 130°C, and a 3.4 m/second swing speed.

Result and discussion

SEM characterization

Figure 1 shows microcrystalline cellulose’s shape and surface morphology. The MCC structure looked like flakes with unequal lengths and widths. The effect of the MCC addition on the fracture surface morphology rHDPE/cantala fiber composite is shown in Figure 2. On composites without MCC (Figure 2(a)), voids and fiber pullouts represented the feature of poor fiber-matrix interface adhesion. The same phenomenon appears in MCC-filled rHDPE/cantala composites (Figure 2(b,e)). However, in composites with MCC, the voids were filled by MCC, which bound well to rHDPE. As a result, it reduced the holes so that stress could be transferred efficiently from the matrix to the fiber or vice versa. Thereby, it led to an increase in the tensile strength and modulus of the composite. A similar phenomenon was reported by (Kiziltas et al. 2014) in the case of microcrystalline cellulose-filled thermoplastic.

Figure 1. SEM image of MCC.

Figure 2. SEM micrograph of composite tensile fracture surface with MCC: (a) 0% wt; (b)1%wt; (c) 2%wt; (d) 3%wt; (e) 4%wt.

FTIR characterization

The spectrum of the rHDPE/cantala composite with MCC is shown in Figure 3. The infrared spectrum associated with the functional groups of the chemical bonds formed on the cantala/rHDPE/MCC composite is listed in Table 1. According to (Lazrak, Kabouchi, and Hammi 2019), in their research on rHDPE/pine wood composites, pure rHDPE showed absorption bands that matched the C-H stretching vibrations around the peak of 2923 cm⁻¹, CH₃ bending vibrations around 1475, and CH₂ rocking vibrations at 717–730 cm⁻¹. For the cantala fiber, the band appeared around 3400 cm⁻¹, 2850 cm⁻¹, the peak of 1732 cm⁻¹, which was associated with the vibration of the hydroxyl group (OH), CH2 symmetric stretching, a hemicellulose carbonyl group, respectively (Raharjo et al. 2018). The MCC spectrum pattern was similar to cantala fiber, shown by peaks around 3400 cm⁻¹, 2900 cm⁻¹, 1374 cm⁻¹, 1035–1060 cm⁻¹, and 890 cm⁻¹ (Sunardi et al. 2021).

Figure 3. FTIR spectrum of cantala/rHDPE composite with MCC: (a) 0% wt, (b) 1% wt, (c) 2% wt, (d) 3% wt, (e) 4% wt.

Table 1. Peak FTIR spectrum of the cantala/rHDPE/MCC composite.

Wavenumber (cm^−1)					Functional Group
0% MCC	1% MCC	2% MCC	3% MCC	4% MCC
721.41	720.44	721.41	721.41	719.48	C-C Stretch
1056.07	1057.04	1058.00	1058.00	1058.00	C-O Stretch
1468.86	1467.89	1468.86	1468.86	1468.86	C-H Bend
1636.67	1604.84	1637.64	1640.53	1621.24	C=C Stretch
1740.83	1738.90	1737.94	1737.94	1665.60	C=O Stretch
2849.95	2849.95	2849.95	2849.95	2849.95	C-H Stretch
2919.39	2919.39	2919.39	2919.39	2920.35	C-H Stretch
3374.61	3386.18	3398.72	3421.87	3427.65	O-H Stretch

Figure 3 shows the peak characteristics of the cantala/rHDPE fiber composite with and without MCC. The FTIR spectrum pattern of the cantala/rHDPE composite with variations of MCC looked similar. The difference was seen only in the intensity of absorption. With the addition of MCC, the peak around 3240 cm⁻¹, which indicated the presence of hydroxyl functional groups (O-H), appeared wider with increasing intensity. It showed an increase in the number of hydrogen bonds formed between MCC and rHDPE. The phenomenon was in line with the results obtained by other researchers (Chen et al. 2020; Zelaziński et al. 2020). The peak of 1740 cm⁻¹ related to the carbonyl group (C=O) stretching of hemicellulose seemed to decrease with the addition of MCC. It indicated reduced hemicellulose content due to adding MCC in the composite. Another peak that experienced a change in intensity was a small peak around 1240 cm⁻¹ associated with the C-O group in lignin. The addition of MCC caused the peak of 1240 cm⁻¹ to decrease due to the reduced lignin content in the composite. The reduction of amorphous materials (hemicellulose and lignin) encouraged the addition of composite crystallinity. The improvement had an impact on improving the mechanical properties of the composite.

XRD characterization

Figure 4 and 5 show the XRD patterns of rHDPE, MCC, and rHDPE/cantala composite. Meanwhile, the positions of the diffraction peaks and crystallinity of MCC, rHDPE, and composite rHDPE/cantala are listed in Table 2. At MCC, three prominent peaks formed at an angle of 15.6^o, 22.96^o, and 34.72^o. The peaks around 15.6^o and 34.72^o showed the amorphous regions associated with the (110) and (004) lattice planes. While the peak of 22.96^o was a crystal region associated with the lattice plane (200) (Beroual et al. 2021). Diffraction peaks from rHDPE appeared at angles of 21.62^o and 23.92^o. This angle corresponds to the planes (110) and (200) (Koniuszewska and Kaczmar 2016). Composite without and with MCC showed two peaks with prominent characters. The highest peak appears around 2θ = 21.66^o, corresponding to the crystal plane’s reflection (100). Meanwhile, the second most substantial peak occurred at 2θ = 24.12^o which corresponded to the crystal plane (200) (Lei et al. 2007). The addition of MCC in the composite did not significantly change the diffraction peak position of the composite. However, crystallinity increased by 6.7% from 48.02% in composite without MCC to 51.45% in composite with 4% MCC. Adding MCC to the composite led to an increase in peak intensity of about 22°. Therefore, composites with 4% MCC had the highest crystallinity index. MCC is crystalline, so adding the material to the composite will automatically increase its crystallinity. The addition of crystallinity will lead to an increase in the mechanical properties of the composite. It is supported by (Saiello, Kenny, and Nicolais 1990), who said that the properties of polymers and thermoplastic composites are affected by crystallinity and crystal morphology. The addition of crystallinity improved performance, such as ductility, tensile strength, and modulus of elasticity (Beroual et al. 2021; Gao and Kyo Kim 2000).

Figure 4. XRD patterns of rHDPE and MCC.

Figure 5. XRD patterns of the cantala/rHDPE composite with variations in the MCC weight fraction.

Table 2. The crystallinity of cantala fiber/rHDPE composites with variations in MCC weight fraction.

Composites	Peak Position (2θ)		Crystallinity Index (%)
	(110)	(200)
rHDPE/cantala/0%MCC	21.66	24.12	48.02
rHDPE/cantala/1%MCC	21.70	23.96	49.09
rHDPE/cantala/2%MCC	21.78	24.20	49.87
rHDPE/cantala/3%MCC	21.72	24.24	50.90
rHDPE/cantala/4%MCC	21.68	24.12	51.45

TGA characterization

Figure 6 shows the thermogravimetric (TG) and derivative thermogravimetric (DTG) curve of the rHDPE/cantala composite. On the TG curve (Figure 6(a)), weight loss due to the degradation of composite components is recorded as a temperature function. The composite without MCC underwent weight reduction in two stages. The first was a degradation of the cantala fiber and then the rHDPE. In the first stage, the degradation peak occurred around 345.8^oC with a weight loss of 6.5%. Furthermore, the peak weight loss of 62.2% would occur at 482.9^oC. The results were in line with previous studies which reported that the decomposition temperature of cantala fiber, MCC, and rHDPE was 346.5^oC, 350^oC, and 445^oC, respectively (Dou and Rodrigue 2022; Raharjo et al. 2018)

Figure 6. Curves for the thermal decomposition of cantala fiber/rHDPE composite with variations of MCC: (a). TGA; (b). DTG.

In composites with MCC up to 4%, decomposition occurred in two stages. In the first stage, degradation occurred in MCC and cantala, followed by degradation of rHDPE. The delay in composite degradation was seen after adding MCC, where the first degradation shifted to a temperature of 348–356°C. At the same time, the second degradation moved to a temperature of 474–483.6°C, as shown in Figure 6(b) and Table 3. Adding MCC enhanced the composite thermal stability, which was contributed by the presence of the MCC crystal structure and a good bond between MCC and rHDPE. This result follows the XRD test results, which showed enhanced crystallinity by adding MCC.

Table 3. Thermogravimetric of cantala fiber/rHDPE composites with MCC variations.

Composites	Peak Temperature (^oC)/%wt loss
	Stage 1	Stage 2
rHDPE/cantala/0%MCC	345.8/6.5	482.9/62.2
rHDPE/cantala/1%MCC	348.4/7.1	475.0/68.4
rHDPE/cantala/2%MCC	353.9/6.4	474.3/67.6
rHDPE/cantala/3%MCC	354.1/8.7	483.5/66.9
rHDPE/cantala/4%MCC	356.7/10	483.6/69.3

Density

The density of the cantala/rHDPE fiber composite with variations of MCC after the extrusion-hot press process is shown in Figure 7. The density test results showed the lowest value was 0.88 gr/cm³, and the highest was 0.90 gr/cm³. The addition of MCC slightly increased the composite density. The added MCC would bind to rHDPE and fill the gaps/pores between the fibers. Thereby the density of the composite was an increase. Increasing composite density encouraged improving the composite’s physical and mechanical properties.

Figure 7. Composite density with the addition of MCC.

Tensile strength

The comparison of the tensile strength of cantala fiber-reinforced rHDPE composite with and without MCC is shown in Figure 8. The tensile strength of the composite without MCC was 29.10 MPa. Adding MCC with a weight fraction of 1% to 4% could increase the tensile strength of the composite. The highest tensile strength was achieved by adding 4% MCC with a value of 43.85 MPa or an increase of 50.7%. MCC caused enhancement in composite tensile strength.

Figure 8. Tensile strength of composite with and without MCC.

During melt mixing in the double screw extruder, MCC would mix and bond with the rHDPE. Furthermore, the mixture would fill the pores or gaps between the cantala fibers, forming a good bond between the fibers, MCC, and rHDPE. When an external load was applied to the composite, MCC inhibited crack propagation and aided in transferring stresses between the fiber and the matrix. It had an impact on improving the tensile strength of the composite. The same phenomenon was found in the research conducted by (Cataldi, Deflorian, and Pegoretti 2015; Kiziltas et al. 2014; Rehman et al. 2019). In the study of (Kiziltas et al. 2014), adding 20% MCC weight fraction in Nylon 6 composites increased the tensile strength by 81% with a value of 52.7 MPa.

Figure 9 shows the effect of MCC on the tensile modulus of the rHDPE/cantala composite. The highest elastic modulus of 1.61 GPa was obtained in the composite with 4% wt MCC. At the same time, the lowest elastic modulus was obtained in the composite without MCC with a value of 0.87 GPa. The composite tensile modulus was seen to increase with the addition of MCC. Composites with 4% wt MMC showed an increase in the tensile modulus of 85.1% compared to pure composites. The increase was due to the high rigidity contributed by MCC (Haafiz et al. 2013). The modulus enhancement was also caused by MCC being evenly distributed and mixed in rHDPE, forming a good bond between the fiber, matrix, and MCC.

Figure 9. Tensile modulus of composite with and without MCC.

The addition of MCC content in the composite increased the modulus of elasticity. It followed several previous studies (Rehman et al. 2019; Reza et al. 2014). The PLA/MMT/MCC hybrid composites with the addition of MCC 1%, 3%, 5%, and 7% showed an increase in the modulus of elasticity as the MCC content increased (Reza et al. 2014). Adding MCC up to 7% increased the tensile modulus of the epoxy/Jute composite by 25.6% (Rehman et al. 2019).

Bending strength

The bending strength of the cantala/rHDPE composite with MCC is exposed in Figure 10. It was clear that the addition of MCC increased the flexural strength of the composite. The highest bending strength of 53.37 MPa was found in the composite with 4% wt MCC. The value grew by 31% compared to the bending strength of the composite without MCC. It was the contribution of MCC, which was well dispersed and bonded to rHDPE. A good interaction encouraged increased stress transfer through reinforcement-matric interfacial (Jabbar et al. 2017). In addition, the ability of MCC and rHDPE to fill pores and gaps between fibers was also one factor that increased the composite’s bending strength. Finally, when external loads were applied to the composite, a good bond between cantala, rHDPE, and MCC could transmit well stress between components in the composites.

Figure 10. Composite bending strength with and without MCC.

The graph of the relationship between the composite bending modulus and the addition of % wt MCC is depicted in Figure 11. The trend of the bending modulus graph was similar to that of the bending strength graph. Figure 11 explains that adding an MCC weight fraction encourages an increase in the value of the composite bending modulus. The highest bending modulus of 1.96 GPa was found by adding 4% wt MCC, while the lowest value of 1.1 GPa was seen in the composite without MCC. The enhancement in bending modulus was caused by the presence of MCC with high stiffness, which was evenly distributed and firmly bonded to rHDPE. In addition, an increase in the area of the reinforcement-matric interface due to the addition of MCC caused a high composite modulus (Gabr et al. 2014).

Figure 11. Bending modulus of cantala/rHDPE/MCC fiber composites.

Impact strength

The impact strength curve of the rHDPE/cantala composite in the MCC variation is shown in Figure 12. The addition of MCC led to an increase in the impact strength of the composite. The increasing trend was similar to the tendency in composites’ tensile and bending properties. With the addition of 4% wt MCC, the impact strength of the composites reached the highest value of 38.91 kJ/m². It increased by 37.7% compared to the composite impact strength without the MCC of 28.26 kJ/m². The result is in line with the findings (Mubarak and Talal Abdulsamad 2019), which reported that the impact strength of LDPE composites increased with MCC up to 20%wt but decreased for the weight fraction above it. However, it contradicted the results obtained (Mubarak 2018), where adding MCC will reduce the impact strength of polypropylene composites.

Figure 12. Impact strength of composite with and without MCC.

When an impact load was applied, the initial crack grew and propagated through the matrix. Adding MCC would inhibit crack propagation because the gap between the matrix and fiber, which was the initial crack source, filled with MCC. Besides, a good bond will form between the fiber, matrix, and MCC. Therefore, it impacted the enhancement of the impact strength of the rHDPE/cantala composite. It is in line with the results of previous studies (Pichandi et al. 2018; Rehman et al. 2019).

Conclusion

Adding 4% wt MCC resulted in a significant improvement in mechanical properties of 50.7%, 31%, and 37.7%, respectively, in tensile strength, bending strength, and impact strength compared to rHDPE/cantala composite without MCC. MCC up to 4% wt slightly increased the composite density from 0.88gr/cm³ to 0.90 gr/cm³. The enhancement of MCC did not significantly change the diffraction peak position of the composite. However, composite crystallinity increased by 6.7%. In addition, the augment of MCC increased the thermal stability of the composite.

Highlights

• Micro Crystalline Cellulose is investigated as reinforcement of cantala fiber/rHDPE composites

• The effect of MCC on the properties of the mechanical composites is investigated.

• The effectiveness of the amount of MCC is studied.

Disclosure statement

No potential conflict of interest was reported by the authors.