Fibers and Polymers 2017, Vol.18, No.1, 116-121 DOI 10.1007/s12221-017-6208-x

ISSN 1229-9197 (print version) ISSN 1875-0052 (electronic version)

Effect of Kenaf and EFB Fiber Hybridization on Physical and Thermo-Mechanical Properties of PLA Biocomposites Md. Saiful Islam1*, Irmawati Binti Ramli2, M. R. Hasan3, Md. Moynul Islam1, Kh. Nurul Islam4, Mahbub Hasan5, and Ahmad Saffian Harmaen6 1

Department of Chemistry, Faculty of Science & Humanities, Bangladesh Army University of Engineering and Technology (BAUET), Natore 6431, Bangladesh 2 Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia 3 Department of Civil Engineering, Bangladesh Army University of Engineering & Technology (BAUET), Natore 6431, Bangladesh 4 Department of Anatomy and Histology, Faculty of Veterinary Medicine, Chittagong Veterinary and Animal Science University, Chittagong 4225, Bangladesh 5 Department of Materials and Metallurgical Engineering, Bangladesh University of Engineering and Technology, Dhaka 1000, Bangladesh 6 Laboratory of Biocomposite Technology, Institute of Tropical Forestry and Forest Products (INTROP), Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia (Received February 1, 2016; Revised October 6, 2016; Accepted October 28, 2016) Abstract: Kenaf/empty fruit bunch/polylactic acid (kenaf/EFB/PLA) hybrid biocomposites were prepared using hot press technique. The ratio of fiber to polylactic acid was set at 60:40 with 1:1 ratio between kenaf and empty fruit bunch fibers. Physical, mechanical and thermal properties of hybrid biocomposites were subsequently characterized using Fourier transform infrared spectroscopy, scanning electron microscope, X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, tensile and water absorption tests. Test results indicated that mechanically stronger fiber was able to support the weaker fiber. Hybrid fiber biocomposite had higher crystallinity as compared to single fiber biocomposite. Water absorption of hybrid composite was higher as compared to single fiber composite. Thermal result revealed that hybridization of fiber was not significantly influence the thermal properties of composites. However, the presence of two different fibers proposed good wettability properties, which could reduce the formation of voids at the fibers-polymer interface and produce composites with high stiffness and strength. Keywords: EFB, Kenaf, PLA, Hybrid biocomposite, Mechanical properties, SEM, XRD, FTIR

[6]. Fiber reinforced polymer composite (FRP) is a composite materials made of a polymer matrix reinforced with fibers. FRP are usually used in the automotive, aerospace and construction industries [7]. Fiber reinforced polymer are usually added in the form of continuous or chopped fibers to polymer matrix [8]. Due to the concept of green-building, the awareness of leading natural fibers in polymer composites has been introduced. Natural fiber provides remarkable properties for composites, especially capability of recycling, renewable raw material that is less scratchy and unsafe to mankind. Green composites studies fiber reinforced polymer composite production and explains how green footprints can be reduced at every stage of the life cycle. The issues regarding to recyclability and ecofriendly are becoming very important for introduction of materials and product. Natural fibers such as jute, hemp, banana leaf, oil palm, kenaf and so on have a number of ecological and techno-economic advantages than available man-made fibers [9]. Such composites are anticipated to be a leading technology that will become important in the industries [10]. The combination of various types of natural fibers into a single matrix has led to the improvement of hybrid biocomposites. The performance of hybrid composites is a

Introduction Use of agricultural residue as filler in polymer materials are nowadays is main focus of researchers worldwide to minimizes its waste and avoid pollution as most of it been disposed by burning [1]. Natural fiber is one type of agricultural residue that can be used as a component of composite materials because it is strong, lightweight, renewable, biodegradable, less hazardous, cheaper and has high specific strength and modulus [2,3]. The attracting part about natural fibers is their effect on environment. Natural fibers will play an important role in the “green” economy based on energy proficiency. However, natural fibers are easily degraded by environmental variation. These problems can be minimized by appropriate chemical treatment and use of fiber in other applications; such as formation of fiber reinforced polymer composite [4]. The consumption of biodegradable sources in polymer products will cut the carbon emissions as a result of plastics burning [5]. The product is also non-abrasive on handling equipment and offers safer and better working environment *Corresponding author: [email protected] 116

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considered sum of the individual components in which there is a more favorable stability between the advantages and disadvantages. Other than that, the advantages of using a hybrid composite that contains two or more types of fiber are that the fiber could complement with what are lacking in the other [11]. As a result, a balance in cost and performance can be accomplished through suitable material design. The properties of a hybrid composite primarily depend on the fiber materials, length of single fibers, coordination, extent of combination of fibers, fiber to matrix bonding and arrangement of fibers. The strength of the hybrid composite is also reliant on the failure strain of specific fibers [12]. Maximum hybrid outcomes are acquired when the fibers are highly strain compatible. Polylacticacid (PLA) has attracted many researchers due to its most promising bio-based polymer, which is made from plant which is readily biodegradable [13]. PLA is straight chained polyester that is considered to be biodegradable that are from renewable sources such as sugar beets and corns [14]. The addition of fiber or filler materials to PLA is one of the ways to enhance its mechanical and thermal properties [15]. This polymer offers good strength and easy to be processed in most equipment. However, it is expensive and it needs some modification for many applied practical [16]. Therefore, an appropriate approach to improve and make it more economics material is by the addition of natural fibers, which has recently grown attention to replace synthetic fibers. Other than that, it is important to use these natural fibers and combine them into biodegradable polymer (PLA) in order to efficiently reduce the production cost by partially replacing the expensive PLA with low cost natural fibers without disturbing the biodegradation performance of the matrix polymer [17]. Kenaf fibers are increasingly becoming popular in Malaysia as natural materials that could help the development of ecofriendly resources for the food packaging, automotive, sports industries and furniture. Kenaf is obtained from the plant named Hibiscus Cannabinusbast. The main elements of kenaf are cellulose (45-57 %), hemicelluloses (21.5 %), lignin (8-13 %) and pectin (3-5 %) [18]. Kenaf fiber can generally be classified into two types. The first type is the outermost layer known as bast, while the second type is the inner part known as core. The core is very soft, hollow and suitable for application as organic filler in plastic. While bast fiber has hard properties and is suitable for blending with plastic that is used textile industry and fiberglass technology applications. Thirmizir et al. investigated that Kenaf bast fiber is the most valuable part of the plant, which is very suitable for jute fibers in some application [19]. It was also reported by Azwa et al. [6] that the addition of kenaf fibers has improved the mechanical properties of neat polymers. A palm oil plantation yields huge amount of biomass wastes in the form of empty fruit bunches (EFB). Harmaen et al. [15] reported that Malaysia and its surrounding South East Asian

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countries generates large amount of EFB fiber as waste. From the palm oil industries, huge amount of biomass wastes were gained in the form of empty fruit bunches (EFB). EFB are depending on proper handling operations at the mill. It is free from other elements such as nails, gravel, wood residues and other wastes. EFB is also abundant, versatile, renewable and cheap. It was reported that adhesion between the fiber and polymer is one of factors affecting the strength of manufactured composites [18]. Recently, demand of the natural fibers with polymers is growing in market worldwide that attracted great attention of many industries. A number of researches were carried out on natural fiber reinforced polymer composites [12-15]. However, no research was conducted on the development of green hybrid composite using Kenaf and EFB fiber and PLA. Therefore, the aim of this current study is to focus on the effect of fibers (kenaf and EFB) hybridization and filler loading on mechanical and thermal properties of kenaf/EFB/ PLA biocomposites.

Experimental Materials Kenaf and EFB fiber with ranges of 2-3 mm was purchased from National Kenaf and Tobacco Board, Kubang Kerian Kelantan and Poly Region (M) Sdn. Bhd respectively. TT Biotechnologies Sdn. Bhd, Penang, Malaysia supplied polylactic acid (PLA). Preparation of Fibers Both fibers were cut in Institute of Tropical Forestry and Forest Products (INTROP), UPM Serdang into an around length of 2 mm by using a ring knife flaker. To obtain uniform size of fiber, these jute fibers that been cut were then sieved manually using a very small size sieve (0.6 mm). Fibers were dried at open-air under direct sunlight for few days. Preparation of Hybrid Biocomposites The fibers were mixed with polylactic acid (PLA) granules using Brabender mixer machine thoroughly and homogeneously. The ratio used for fiber to PLA was 60:40 with 1:1 ratio between kenaf and EFB fibers. According to ASTM 638 and 790 standards design of mold fabrication and desire composite thickness were made. The composites were fabricated using a hot press machine. Manual hydraulic press was used to press the mold until the pressure reached 1000 psi. Temperature was set was at 160 oC for both upper and lower heater and the mold was heated for 5 minutes. The mold was cooled to room temperature in order to prevent shrinkage during extraction of the composite. Characterization of Biocomposites The machinery Industrial Co. Ltd. cutter was used to cut

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samples biocomposite into ASTM standard dumb bell shape from the flat sheet samples for tensile test. The test was conducted using ASTM D 638-03 method and INSTRON 8821S (INSTRON, USA) universal testing machine. According to ASTM D790-03, flexural test was performed using the same machine mentioned above. For impact test, notched biocomposite specimen was attached horizontally and supported unclamped at both ends. The hammer was released and allowed to strike through the specimen. The impact energy in Joules (J) was obtained from the machine. Impact strength was then calculated by dividing the impact energy with length of the notch.The water absorption test of prepared biocomposites was carried out according to ASTM D 570-99. Structural and thermal properties of composites were characterized using a Perkin-Elmer 1600 Fourier transform infrared spectrometer, JSM-5510 JEOLscanning electron microscope, thermogravimetric analyzer, differential scanning calorimeter and PAN analytical X-Ray diffractometer.

Results and Discussion Fourier Transform Infrared Spectrometric Analysis Figure 1 shows the FTIR spectra of kenaf and EFB fiber. The broad peaks at the region of 3600-3070 cm-1 for all spectra were corresponding to the presence of free -OH groups, while the peak at 2946 cm-1 attributed to C-H stretching. The absorption peak at 1740 cm-1 and 1622 cm-1 due C=O and C=C stretching band [18]. On the other hand, the peaks at 1250 cm-1 and 1030 cm-1 represent C-O stretching.

Figure 1. FTIR spectra of kenaf and EFB fiber.

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All characteristic absorption peaks as mentioned earlier confirmed the presence of polymeric constituent such as lignin, cellulose and hemicelluloses in the fiber. Scanning Electron Microscopy Figure 2 shows SEM micrographs of the tensile fractured surfaces of EFB/PLA, kenaf/PLA and EFB/kenaf/PLA composites. Surface interaction and adhesion between fiber and polymer matrix increased after fiber hybridization [20]. No significant changes were observed on the micrographs of hybrid fiber composite. However, smooth fractured surface was produced after the hybridization of two fibers, which illustrate good adhesion of fibers to polymer matrix. Good adhesion of polymer matrix and fiber plays a key role in enhancing the mechanical properties of composites. This result reflected the improvement of mechanical strength upon fiber hybridization. Therefore, it can be conclude that incorporation of two fibers proposed good wettability properties, which decreased the formation of voids at the fibers-polymer interface and formed composites with high stiffness and strength leading to high storage modulus [21]. X-ray Diffraction Analysis Figure 3 shows the XRD patterns of EFB/PLA, kenaf/PLA and hybrid EFB/kenaf/PLA biocomposites. The crystallinity values of EFB/PLA, kenaf/PLA and EFB/kenaf/PLA biocomposites were 73.14 %, 71.71 %, and 74.27 %

Figure 3. XRD patterns of (a) EFB/PLA biocomposite, (b) EFB/ kenaf/PLA hybrid biocomposite, and (c) kenaf/PLA biocomposite.

Figure 2. SEM micrographs of (a) EFB/PLA biocomposite, (b) kenaf/PLA biocomposite, and (c) EFB/kenaf/PLA hybrid biocomposite (Arrow indicates Kenaf fiber).

Kenaf and EFB Fiber Hybridized PLA Biocomposites

correspondingly. As compared to single fiber/PLA composites, the crystallinity of hybrid EFB/kenaf/PLA composites was higher. Other than that, a new peak (2θ) at 35.0 o was detected for hybrid composites. This indicates that the crystallinity and stiffness of composites was increased slightly after fiber hybridization which led to improve mechanical strength [22]. Thermal Properties Thermogravimetric Analysis Thermal stability of EFB/PLA, kenaf/PLA and EFB/ kenaf/PLA biocomposites were measured through TGA test analysis and are shown in Figure 4. It can be seen from TGA thermogram that the weight of all biocomposites slight decreased in the range 55-135 oC. This could be explained by the existence of residual water in the composites that was gradually released at above 100 oC [23]. It was also observed that the onset temperature of thermal degradation of EFB/ PLA and EFB/kenaf/PLA biocomposites was around 240 oC, however this temperature for kenaf/PLA biocomposite was at 270 oC. This is due to better interaction and dispersion of kenaf fiber into PLA matrix as compared to EFB/PLA and EFB/kenaf/PLA. This result indicates that hybridization of EFB and kenaf and composites with PLA was not influence the overall thermal stability of the developed biocomposites. Differential Scanning Calorimetric Analysis From DSC plots (Figure 5), the glass transition temperature

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(Tg) of EFB/PLA, kenaf/PLA and EFB/kenaf/PLA biocomposites was observed to be at 76 oC, 82 oC and 78 oC respectively. The polymers crystallization temperature, Tc was considered as the temperature at the lowest point of the dip [24]. The latent energy of crystallization was also determined from the area of the dip of polymer. But most essentially, the dip also indicates that the polymer was crystallized. This is because of the polymer released heat when crystallization occurred, which called crystallization an exothermic transition. The crystallization temperature of EFB/PLA, kenaf/PLA and EFB/kenaf/PLA biocomposites were observed to be at 151.4 oC, 152.9 oC and 152.1 oC respectively. The sharp peaks at 292.6 oC, 302.8 oC and 297.6 oC indicates the melting temperature of EFB/PLA, kenaf/PLA and EFB/kenaf/PLA biocomposites respectively. The results showed that there were only a small difference between the melting temperature (Tm), crystallization temperature (Tc) and glass transition temperature (Tg) between the three types of biocomposites. Thus hybridization did not have much influence on those temperatures. Mechanical Properties Tensile Properties Figures 6 and 7 represent the tensile modulus and tensile strength of EFB/PLA, kenaf/PLA and EFB/kenaf/PLA composites respectively. Figure 6 shows that the tensile

Figure 4. TGA results of (a) EFB/PLA biocomposite, (b) kenaf/ PLA biocomposite, and (c) EFB/kenaf/PLA hybrid biocomposite.

Figure 6. Tensile strength of pure PLA, EFB/PLA biocomposite, kenaf/PLA biocomposite and EFB/kenaf/PLA hybrid biocomposite.

Figure 5. DSC results of (a) EFB/PLA biocomposite, (b) kenaf/ PLA biocomposite, and (c) EFB/kenaf/PLA hybrid biocomposite.

Figure 7. Tensile modulus of pure PLA, EFB/PLA biocomposite, kenaf/PLA biocomposite and EFB/kenaf/PLA hybrid biocomposite.

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strength dramatically decreased when fiber was changed from EFB to kenaf. After hybridization of fiber, the strength of hybrid biocomposite was found to be higher as compared to that of single kenaf fiber biocomposites. However, it was still lower than single EFB fiber biocomposite. The same result was also found for the tensile modulus of the biocomposites as shown in Figure 7. The modulus was found to be decreased from 431 to 321 MPa and the modulus was increased to 345 MPa after hybridization. Both tensile strength and modulus values indicate that the hybridization of fiber was capable to produce biocomposite with optimum tensile properties. This in turn proved that the great mechanical possessions of EFB fiber were able to support the low mechanical properties of kenaf fiber. The strong bonding between the matrix and fiber will leads to improve interfacial adhesion between them and therefore a higher transfer of stress from the matrix to the fibers during tensile testing [25,26]. Flexural Properties Figures 8 and 9 represent the flexural modulus and flexural strength of EFB/PLA biocomposite, kenaf/PLA biocomposite and EFB/kenaf/PLA hybrid biocomposite. Figure 8 shows that the flexural strength was radically increased when fiber changed from EFB to kenaf. However, after hybridization of fiber, the strength of the hybrid biocomposite was found to be higher as compared to that of single BFB fiber biocomposite. However, it was still lower than single kenaf fiber biocomposite. The same result was

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found for the flexural modulus of the composites as shown in Figure 9. The modulus was found to be increased from 3.9 to 4.8 GPa and decreased to 3.6 GPa after hybridization. This rise may be described by a better fibers-matrix interaction under the compressive stresses during bending, developed in the transverse section of the flexural specimens [27]. In general, the best fiber content depends with the nature of fiber matrix interfacial, fiber aspect ratio, processing techniques, fiber and matrix adhesion, fiber agglomeration, and so on [28]. Impact Properties Figure 10 represents the impact strength of EFB/PLA biocomposite, kenaf/PLA biocomposite and EFB/kenaf/ PLA hybrid biocomposite. Impact strength sharply decreased when EFB fiber changed to kenaf. However, after hybridization of fiber, the impact strength of biocomposite was almost similar as single kenaf fiber biocomposite. This proves that hybridization of fiber was not capable to support the low impact properties of kenaf fiber. Water Absorption Characteristics Water absorption test was carried out for EFB/PLA, kenaf/ PLA and EFB/kenaf/PLA hybrid biocomposites and the results were shown in Figure 11. It was observed that water absorption of biocomposites was increased for the first 8 days, after that it almost became constant. Hybrid fiber biocomposites had the highest percentage of water absorption

Figure 10. Impact strength of pure PLA, EFB/PLA biocomposite, kenaf/PLA biocomposite and EFB/kenaf/PLA hybrid biocomposite. Figure 8. Flexural strength of pure PLA, EFB/PLA biocomposite, kenaf/PLA biocomposite and EFB/kenaf/PLA hybrid biocomposite.

Figure 9. Flexural modulus of pure PLA, EFB/PLA biocomposite, kenaf/PLA biocomposite and EFB/kenaf/PLA hybrid biocomposite.

Figure 11. Water absorption of EFB/PLA biocomposite, kenaf/ PLA biocomposite and EFB/kenaf/PLA hybrid biocomposite.

Kenaf and EFB Fiber Hybridized PLA Biocomposites

as compared to single fiber biocomposite. This might be due to the hydrophilic properties of fiber which increased upon mixed up of two different fibers. So, hybrid fiber composite absorbed more water compared to single fiber biocomposite [29].

Conclusion Present study reveals that a hybrid biocomposite with good properties could be useful and successfully improved using kenaf and EFB fibers as the filler for the PLA matrix via melt blending method. Mechanical test results indicated that high mechanical properties of one fiber were capable to support low mechanical properties of another fiber. X-ray diffraction pattern shows that the percent crystallinity of biocomposites significantly increased after hybridization. On the other hand, hybridization of fibers had no significantly influence on the thermal properties of the biocomposites. The percentage of water absorption of hybridized biocomposites was higher than the single fiber biocomposite. The morphology of biocomposites was also not much effected for fiber hybridization. The presence of two different fibers proposed good wettability properties, which decreased the development of voids at the fibers-polymer interface and created composites with high stiffness and strength.

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