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polyethylene terephthalate composites for packaging applications
Composites Communications 15 (2019) 113–119
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Short Communication
Development and study of properties of Moringa oleifera fruit fibers/ polyethylene terephthalate composites for packaging applications
T
Subhakanta Nayak*, Sujit kumar Khuntia Department of Mechanical Engineering, College of Engineering Bhubaneswar, Biju Patnaik University of Technology, Odisha, 751024, India
A R T I C LE I N FO
A B S T R A C T
Keywords: Chemical treatment Mechanical properties Thermal properties polyethylene-terephthalate Moringa oleifera fiber
Researchers are now focusing on the use of natural fiber polymer composites materials for packaging applications. It has been proposed that Moringa oleifera fruit fiber (MOF) as reinforcement can be a promising candidate for packaging applications. So in this current research, composites were fabricated by reinforcing treated moringa oleifera fruit fibers with Polyethylene terephthalate (PET) thermoplastic polymer. Its mechanical, thermal and morphological properties were investigated. Surface treatments of fibers have been carried out to have a better compatibility with PET matrix. The mechanical properties have been found to increase at the early stage with the increase in treated moringa oleifera fiber content till optimum (20 wt% of fiber) fiber loading thereafter declines. At this fiber loading the mechanical properties obtained were 65.92 MPa of tensile strength, 98.49 MPa of flexural strength, 3.78 GPa of young’s modulus and 28.09 kJ/m2 of impact strength. Thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM) have been used for analysis. The TGA inferred that the thermal stability of the composites increased as compared to neat PET matrix. It was found that composites fabricated from 20 wt% fiber content shows superior mechanical properties as well as thermal properties as compared with other fabricated composites and can be used for packaging applications.
1. Introduction Natural fiber based composites are finding expanding use in products like the interior pieces of automotives, electronic gadgets, as reinforcements in the building and construction industry, packaging etc. In particular, cellulose nanomaterials are very attractive because of their low cost, low density, high strength, high modulus and aspect ratio, lightweight, abundant availability and biodegradability [1–3]. However, conventional E-glass fibers are hazardous for human health and causes cancer. Hence, currently the research on exploring the promising and novel sustainable natural fibers as a bio-reinforcement in polymer composites for different applications is of great demand. Currently, many types of natural fibers have been investigated for use in plastics including flax, hemp, jute straw, alginate, wood, rice husk, wheat, barley, oats, kenaf, etc. Among all the natural fibers, Moringa oleifera is very useful plant and its fibers are one of the strongest natural fibers. Moringa oleifera, commonly referred to as the ‘drumstick tree’ is a member of the Moringaceae family, which grows throughout most of the tropics and is native to the sub-Himalayan tracts of north-western India, Pakistan, Bangladesh, and Afghanistan [4]. It is considered as one
*
of the most useful plant in the world because almost all its parts can be used as food, in traditional medicines and for industrial purposes [5,6]. In addition, seed and leaf flour have been used in the formulation of infant food to increase protein content [7]. The outer portion of the fruit is very hard and rough which comes out to be waste product and thrown away. It is rich in fiber and wasted from commercial industries after yielding its economic value. In the present work, Moringa oleifera fibers (MOF) is tested thoroughly for ensuring its potentiality as reinforcement in polymer matrix and find its application in packaging industries. Various research works has been done taking different parts of Moringa oleifera tree to find their respective applications. Binoj has fabricated composites taking Moringa oleifera fruit husk as reinforcement in unsaturated polyester matrix and found composites made with 20 wt% of fiber content shows the optimum properties and beyond that the fiber pull out and debonding occurred due to poor compatibility between the fiber and the matrix [8]. Prakash et al. [9] fabricated composites taking alkali treated moringa oleifera fruit fibers as reinforcement with LY556 Epoxy and found that the alkali treated fibers exhibits good mechanical properties, wear and water absorption properties when compared to untreated fibers. Nadir et al. [10] studied the mechanical and thermal properties of moringa oleifera cellulose-
Corresponding author. E-mail address: [email protected] (S. Nayak).
https://doi.org/10.1016/j.coco.2019.07.008 Received 5 June 2019; Received in revised form 6 July 2019; Accepted 25 July 2019 Available online 26 July 2019 2452-2139/ © 2019 Elsevier Ltd. All rights reserved.
Composites Communications 15 (2019) 113–119
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composite gives best performance at 20 wt % fiber loading.
based epoxy nanocomposites and found improved properties as compared to neat epoxy. Huq et al. [11] fabricated and studied the mechanical properties of jute reinforced PET composites and found tensile strength of 58 MPa. It is seen that most of the studies have been done on thermosetting polymer as matrix material in moringa oleifera fibers in order to investigate various properties while making composite material. Thermoplastic polymers have certain specific advantages such as good processability, high cost–performance ratio, low processing temperature, and high resistant to fatigue compared to thermosetting polymers. Moreover, they have an ability to resist chemical attack and offer substantial reductions in flammability, smoke, and toxicity performance. Due to the combined advantages of both natural fiber as reinforcement and thermoplastic polymer as matrix, their composites find wide applications in various places including but not limited to packaging, textiles, stationery goods, plastic parts, and reusable containers of various types, laboratory equipment and automotive components. Keeping in view the above facts, an attempt has been made to develop composite materials by reinforcing MOF in Polyethylene terephthalate (PET) thermoplastic polymer matrix. Poly(ethylene terephthalate) (PET), a low cost and high performance thermoplastic, is widely used as packaging materials, fiber, and sheet due to good rigidity, hardness, abrasion resistance, solvent resistance, and electric insulation [12,13]. The extracted fibers (Fig. 1) have been chemically modified with sodium hydroxide (NaOH) to have better compatibility with PET matrix. Different mechanical properties such as tensile strength, Young’s modulus, flexural strength, flexural modulus, and impact strengths of the composite with varying weight percentage (i.e., 10, 20, 30, and 40 wt %) of treated fibers have been studied. It has been observed that the maximum values of above mechanical properties of the composite are obtained at 20 wt % of MOF loading. The chemical interaction of polymers with fibers has been characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) at this fiber loading. The thermal properties of the composite have been studied through dynamic mechanical thermal analysis (DMTA) and thermal gravimetric analysis (TGA) at optimum fiber loading and compared with virgin matrix. From the characterization and study of properties, it is observed that PET/MOF
2. Materials and methods 2.1. Materials Poly(ethylene terephtalate (PET) was purchased from Kolkata and used as matrix. Moringa fruit fiber purchased from a local market which was disposed as waste. Sodium hydroxide (NaOH) was purchased from local market for chemical modification of the fibers. 2.2. Methods 2.2.1. Chemical modification of fibers Chemical modification of fibers is a common method for modifying the fiber surface which enhances the bonding between a natural fiber and a polymeric matrix. Natural fibers are hydrophilic in nature whereas polymeric matrix is hydrophobic, so it will result in poor fiber/ matrix adhesion. Chemical treatment helps in removing the hemicellulose, lignin, wax and oils that surround the external surface of the fiber leading to increase in the surface roughness which improves the fiber/matrix bonding. The untreated moringa fibers have been alkali treated in 5% sodium hydroxide (NaOH) solution for 1 h at a temperature of 80 °C. Then, the fibers have been cooled to room temperature and washed in running water to remove any trace of sodium hydroxide solution adhered on the surface of the fibers so that the pH level of fiber is approximately 7 (neutral). Then, they have been dried in an oven at a temperature of 60 °C for 24 h. NaOH reacts with the hydroxyl group of the natural fibres, removes the hemicellulose, lignin, wax and oils that surround the external surface of the fibre leading to increase in the surface roughness and reduction in the fiber diameter and results in a mercerized cellulose structure (as shown in Equation (1)) which improves interfacial fiber/matrix bonding.
Fiber − OH + NaOH → fiber − O − Na+ + H2 O
(1)
A typical untreated Moringa fiber appears to be surrounded by cementing materials like lignin, hemicelluloses and other impurities like wax and oils whereas the alkali-treated Moringa fiber were found to be
Fig. 1. Extraction of Moringa oleifera fruit fibers. 114
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Fig. 2. SEM of Moringa oleifera fiber (a) untreated fiber (b) alkali treated fiber.
plates under a pressure of 5 tons. Finally, the composites were cut into desired shapes. The dimensions of specimens for tensile strength and impact strength taken were 165 × 12.7 × 3.2 mm and 63.5 × 12.7 × 3.2 mm, respectively. The mechanical properties of PET/MOF composites at these fiber loadings have been measured and described in subsequent sections.
Table 1 Chemical composition of the moringa oleifera fiber before and after alkali treatment. Component %
Cellulose
Hemicellulose
Lignin
Others
Untreated Alkaline
43.44 67.12
0.25 0.11
45.84 24.57
10.47 7.7
2.2.4. Characterization and study of properties of PET/MOF composites Thermal stability of PET/MOF composites was studied by the use of thermogravimetric analysis (TGA), while the chemical composition characteristics were analyzed using FTIR and XRD spectroscopy. The thermogravimetric analysis (TGA) of PET/MOF composite has been performed with the help of Universal V4.5A TA TGA instrument at a heating rate of 10 °C min−1. FTIR of samples has been conducted by Nicolet 6700 Thermo Scientific Spectrophotometer in the absorbance range of 4000 and 400 cm−1. XRD pattern of the composites has been done through Mini Flex Diffractomer (Shimadzu, XRD-7000) operating under CuKα radiation at 40 kV and 150 mA in reflection mode, with a step of 0.05°, counting time of 1 s. Dynamic mechanical thermal analysis (DTMA) has been done in DMA Q 800 TA instruments as per ASTM D 5026 standard in shear mode. The specimen dimension is 32 × 13 × 3 mm3. The test parameters are: frequency = 1 Hz; temperature range = 33 °C–180 °C; heating rate = 2 K/ min; and maximum shear strain = 0.2 %. The surface morphology of composites was studied by using ZEISS Supra55 SEM to get a clear picture on fiber-matrix adhesion. The tensile tests of treated and untreated PET/MOF composites have been performed in servo-hydraulic static testing machine (INSTRON 3382) with a load cell of 5 kN as per ASTM D 638 standard. At each fiber loading (both treated and untreated composites), 20 samples have been tested and the average value has been recorded. The tests have been conducted at a crosshead speed of 2 mm/min at laboratory temperature and the displacement has been measured with a 50 mm extensometer. The flexural tests have been conducted on the same machine using three-point bending method at a crosshead speed of 1 mm/ min as per ASTM D 790-99 standard. Similar to tensile test, 20 samples have been tested and the average value has been noted. The bending stresses of the samples have been determined as per the following equation.
clean and rough due to the partial removal of lignin, hemicellulose and other impurities (Fig. 2). Alkaline treatment of natural fibers increases the exposure of cellulose content in the fiber surface (Table 1 where the percentage in cellulose content increases after the alkali treatment). Now the fibers were designated as alkali treated fibers henceforth. 2.2.2. Characterization of untreated and alkali treated MOF Chemical composition characteristics of untreated and alkali treated MOF were analyzed using FTIR and XRD spectroscopy. FTIR of samples has been conducted by Nicolet 6700 Thermo Scientific Spectrophotometer in the absorbance range of 4000 and 500 cm−1. XRD pattern of the composites has been done through Mini Flex Diffractomer (Shimadzu, XRD-7000) operating under CuKα radiation at 40 kV and 150 mA in reflection mode, with a step of 0.05°, counting time of 1 s. The fiber crystallinity index (C. I) of MOF was determined by using Segal empirical method [14]. It provides a simple calculation of crystallinity Index by using the following equation.
CI =
(I002 − Iam) × 100 I002
(2)
where I002 is the maximum intensity of the (0 0 2) crystalline peak and 1) Iam is the minimum intensity of the amorphous material between (10‾ and (0 0 2) peaks. 2.2.3. Fabrication of alkali-treated and untreated composites Granules of PET were heat pressed and made thin sheets (3.2 mm thickness) individually using Cipet Laboratory (INDIA) press at 200 °C. In this investigation, films of four compositions were prepared which were PET (90 wt %) plus MOF (10 wt %), PET (80 wt %) plus MOF (20 wt %), PET (70 wt %) plus MOF (30 wt %), PET (60 wt %) plus MOF (40 wt %). Firstly, the PET polymer was heat pressed taking appropriate weight of PET granules and sheets of 16.5 cm × 12.7 cm were made and kept in the desiccators until composite fabrication. Moringa fiber was dried in an oven at 105 °C to remove moisture and then cut into small pieces of dimension 16.5 cm × 12.7 cm. Secondly, composites were prepared by sandwiching two layers of moringa fibers between three layers of polymer matrix sheets according to the weight percentage displayed above and pressed at 190 °C for 5 min between two steel
3 δ = WL 48EI
115
(3)
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Table 2 Mechanical properties of PET/MOF composite. Composites
Tensile strength (MPa)
Young’s Modulus (GPa)
Elongation at break (%)
Flexural Strength (MPa)
Impact Strength (KJ/m2)
Neat PET Untreated 10 wt% 20 wt% 30 wt% 40 wt% Treated 10 wt% 20 wt% 30 wt% 40 wt%
55.26 ± 0.5
2.57 ± 0.13
19.1 ± 2.09
59.21 ± 0.86
18.79 ± 2.21
55.89 ± 3.20 58.11 ± 2.28 56.22 ± 2.01 45.16 ± 2.43
2.77 3.11 2.70 2.02
21.2 23.7 25.9 20.1
61.22 69.01 65.18 58.19
18.99 ± 2.18 21.22 ± 2.84 19.65 ± 1.26 18.01 ± 1.35
60.98 65.92 62.76 56.25
2.95 3.78 3.46 2.30
± ± ± ±
2.62 2.05 3.18 3.02
± ± ± ±
0.11 0.24 0.19 0.62
± ± ± ±
0.21 0.26 0.61 0.12
25.5 32.8 28.4 22.2
3. Result and discussion
± ± ± ±
1.88 2.61 1.18 0.98
± ± ± ±
0.15 0.14 0.10 0.06
± ± ± ±
83.11 98.49 87.70 75.34
1.28 1.00 1.99 1.16
± ± ± ±
1.66 1.89 1.79 1.20
22.50 28.09 24.20 19.98
± ± ± ±
3.31 3.47 2.20 2.02
mechanical properties are maximum, hence this weight percentage of MOF fiber has been considered for fabrication of PET/MOF composite for subsequent studies.
3.1. Mechanical properties Various mechanical properties such as tensile strength, young’s modulus, flexural strength, impact strength and elongation at break of neat PET (without fiber), PET/MOF composite at different weight percentages (10, 20, 30, and 40 wt%) of alkali-treated and untreated fiber composites have been measured and presented in Table 2. From the results, it is observed that all the above properties are higher in treated fiber composites at all fiber loadings in comparison to untreated fiber composite. Further, these properties of PET/MOF composites first increase with fiber loadings and then decrease after reaching the optimum weight percentage (i.e. 20 wt %). The measured tensile strength data of fabricated composites have been plotted against the different weight percentage of alkali-treated MOF fibers in Fig. 3. The graph shows an increasing trend in tensile strength and then the strength decreases with further fiber loadings. The untreated composites shows poor value as compared to treated composites because of presence of lignin in the untreated fibers which deteriorates the strength of the composites due to poor fiber-matrix bonding between hydrophilic fibers and hydrophobic matrix as described earlier. But after chemical treatment, the fabricated composites reveal excellent mechanical properties due to better adhesion of fiber and matrix. The maximum value has been obtained at 20 wt% of fiber loading, which gives 65.92 MPa of tensile strength, 98.49 MPa of flexural strength, 3.78 GPa of young’s modulus and 28.09 kJ/m2 of impact strength. With further increase of fiber contents, the interspaces and stress concentrations increase, which act as crack initiation points during impact that decrease the impact strength after optimum fiber loading ( 20 wt%). Since 20 wt% is the optimum fiber weight percentage at which all most all
3.2. Characterization of untreated and alkali treated MOF The FTIR results of both untreated and alkali treated fibers has been presented in Fig. 4. The spectra show various transmission bands. It is observed that the intensity of absorption band at 3275 cm−1 has been reduced in alkali-treated (Fig. 4) fiber as compared to untreated fiber due to the removal of hemicelluloses component from the fiber surface after chemical treatment. Similarly, the intensity of absorption band 2825 cm−1, attributed to the C–H stretching band structure containing groups of alkanes (cellulose), has been reduced during chemical treatment of fibers in alkali treatment. The peak observed at 1748 cm−1 is characteristic for the carbonyl stretch of carboxylic groups in hemicelluloses and pectin. The peak at 1230 cm−1 can also be readily assigned to the C–O stretching mode of acetyl groups in lignin [15]. The disappearance of the 1748 cm−1 and 1230 cm−1 peaks after alkali treatment shows the destruction of carboxylic acid and acetyl groups by the alkali treatment or the macromolecules containing these functional groups were selectively dissolved from the fibers under strong alkali conditions [16]. X-ray diffraction patterns for untreated and alkali-treated MOF are shown in Fig. 5. The crystallinity indexes (C.I) calculated for each sample from the patterns obtained from XRD are presented in Table 3. The C.I of untreated and alkali-treated MOF was approximately 52% and 58% respectively. It is interesting to know that the degree of
Fig. 3. Tensile strength of PET/MOF composite at different wt% of fiber loadings.
Fig. 4. FTIR graph of untreated and alkali-treated MOF. 116
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Fig. 7. XRD graph of neat PET and 20 wt% PET/MOF composite. Fig. 5. XRD graph of untreated and alkali-treated MOF.
Fig. 6 shows the FTIR spectra of both neat PET and PET/MOF composite at 20 wt% of fiber loading. In the spectrum of pure PET (Fig. 6), the broad band at 3375 cm−1 attributed to the symmetrical stretching vibration of –OH group [18,19], which has been shifted to 3395 cm−1 in PET/MOF composite. As a thumb rule, the –OH
stretching peak is sensitive to hydrogen bonding. The band at 2950 cm−1 is more pronounced in PET/MOF composites as compared with neat PET which is due to C–H stretching [18–20]. The stretching at 1650 cm−1 is for H–C–H bending [18,19]. The peak at 1250 cm−1 is observed in PET/MOF composite which is not observed in neat PET, this may be due to addition of MOF fibers in PET matrix. The peak 1100 cm−1 is stretched more in the composite as compared with neat PET, which is corresponds to C–H wagging [19]. Comparing the XRD of neat PET and PET/MOF (20 wt%) composite (Fig. 7), the broad XRD peak at 18° and a sharp peak at 22° may be due to the crystallinity peak of PET, whereas in case of PET/MOF composite, there is a slight left shift of peaks at 2θ values of 17.8° and 21.5°. The reason may be due to the change in crystallinity of PET in the form of composite. The interfacial adhesion between MOF and PET matrix is responsible for the change in structure of PET/MOF composite. Further, the interaction of PET with the chemically modified surface of the treated MOF is otherwise liable for change in structure of PET by the reinforcement of MOF may also be an evidence of interactive dispersion of MOF with PET matrix. Fig. 8 shows the TGA curve of neat PET and PET/MOF composite at 20 wt% of fiber loading. The composite has been degraded in three steps as shown in TGA plot. The first step is from 30 to 230 °C approximately, and it may be due to the evaporation of water molecules.
Fig. 6. FTIR graph of neat PET and 20 wt% PET/MOF composite.
Fig. 8. TGA graph of neat PET and 20 wt% PET/MOF composite.
Table 3 Crystallinity Indexes of untreated and alkali treated MOF. Fibers
Crystallinity Index (CI) %
Untreated MOF Alkali-treated MOF
52 58
crystallinity of MOF increased after alkali treatment. This is due to the fact that, alkali treatment removes non-crystalline materials from the fiber, including amorphous hemicelluloses, lignin and other non-cellulosic material, which allows the cellulose fibers the freedom to adopt a more crystalline structure [17].
3.3. Characterization and study of properties of PET/MOF composites
117
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matrix. This is due to improved stiffness of composites after addition of fibers. The loss modulus of PET/MOF composite has been found to be 160 MPa at 120 °C whereas for neat PET it was restricted to 145 MPa at 118 °C.
3.4. Scanning electron microscope analysis (SEM) Fig. 11 compares the surface texture of untreated and treated 20 wt % PET/MOF composite to have a clear idea about the fiber matrix bonding. In Fig. 11(a) it is clearly visible that, the fibers are closely packed with the matrix showing better fiber-matrix bonding in treated 20 wt% of fiber loading composite (highest mechanical properties were obtained earlier) whereas, in Fig. 11(b), the fibers are visible on the surface with a poor bonding with the matrix. Moreover, fiber pull out with some cracks are also observed which clearly explains the poor bonding in untreated 20 wt% fiber loading composite. The reason behind poor fiber-matrix bonding in untreated composite is the hydrophobic nature of the natural fibers due to presence of lignin and waxy materials that leads to fiber pull out and cracks in the fabricated composites. As discussed earlier, chemical treatment removes the unwanted materials like lignin and waxy materials which enhances the quality of the fiber and thus showing a good fiber-matrix bonding in treated composites.
Fig. 9. Tan δ (Damping factor) of PET and 20 wt% PET/MOF composite.
The second stage of degradation starts from 230 °C for composite and 250 °C for matrix, respectively, which may be attributed to weight loss. It is further observed that the PET matrix has been degraded at 480 °C, whereas the total degradation of the composite is at 540 °C. Beyond 540 °C no loss of weight is observed. It is noticed that PET/MOF composite has more thermal stability as compared to neat PET. The effect of temperature on dynamic mechanical properties in terms of damping factor (δ), storage modulus (E’) and loss modulus (E’’) of PET matrix and 20 wt% treated composite are shown in Figs. 9 and 10, respectively. Fig. 9 shows the variation of tan δ with temperature for PET matrix and PET/MOF composite. As seen from the figure the tan δ value (0.311 at 91.8 °C) for PET matrix is higher than that of PET/ MOF composite (0.297 at 100 °C). Tan δ represents the energy dissipation potential of the material. Lower tan δ value, more is the interfacial adhesion and stress transfer. In the figure, lower tan δ value indicates better interfacial adhesion between the fiber and the matrix. The storage modulus (E’) value of the treated PET/MOF composite has been found to be 1320 MPa at 30.50 °C whereas for PET matrix it is 995.6 MPa at 22.8 °C (Fig. 10(a)). A 32.58% increase in modulus has been noticed which may be due to surface modification of fibers by chemical treatment that results in good fiber matrix adhesion. Further, it has been seen that the modulus value decreases with rise in temperature in both the cases. It may be associated with the softening of the matrix at higher temperature which is less in case of composite [21]. Almost identical results have been observed in case of flax fiber reinforced high-density polyethylene (HDPE) composites [22] and PLA/ kenaf/ APP composites [23]. The change of loss modulus (E’’) with temperature for PET matrix and composite is shown in Fig. 10(b). The loss modulus of composites shows a higher value at higher temperature as compared to neat PET
4. Conclusion In the present study, natural fiber polymer composite has been developed by reinforcing sodium hydroxide (alkali treated) moringa oleifera fruit fibers with PET thermoplastic polymer. Different static and dynamic mechanical properties and thermal properties were evaluated. From the test values it has been observed that tensile strength of the composite initially increases with the increase of fiber content and decreases afterwards. 20 wt% of fiber loading was considered as optimum fiber loading for fabrication of composites as it shows highest mechanical properties (i.e 65.92 MPa of tensile strength, 98.49 MPa of flexural strength, 3.78 GPa of young’s modulus and 28.09 KJ/m2 of impact strength) as compared with other fabricated composites. Beyond this fiber loading, the mechanical properties deteriorate due to poor fiber-matrix adhesion. From the TGA, it has been found that the composite is thermally enough stable as compared with neat PET matrix. The dynamic mechanical thermal analysis suggests that the composite is extremely good in terms of dynamic mechanical properties. Moringa oleifera fruit fibers composites were found to be a good potential candidate for packaging application as it exhibits excellent mechanical as well as thermal properties.
Fig. 10. (a) Storage modulus and (b) Loss modulus of PET matrix and 20 wt% PET/MOF composite. 118
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Fig. 11. SEM of (a) 20 wt% PET/MOF composite and (b) neat PET matrix.
Declaration of interest
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None. Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.coco.2019.07.008. References [1] B. Barari, E. Omrani, D. Moghadam, A. Menezes, L. Pradeep, Pillia, M. Krishna, Mechanical, physical and tribological characterization of nanocellulose fibers reinforced bio-epoxy composites: an attempt to fabricate and scale the ‘Green’ composite, Carbohydr. Polym. 147 (2016) 282–293, https://doi.org/10.1016/j.carbpol. 2016.03.097. [2] W. Shuhua, X. Qiaoli, L. Fen, D. Jinming, J. Husheng, X. Bingshe, Preparation and properties of cellulose-based carbon microsphere/poly(lactic acid) composites, J. Compos. Mater. 48 (2014) 1297–1302, https://doi.org/10.1177/ 0021998313485263. [3] J.K. Pandey, C.S. Kim, W.S. Chu, W.Y. Choi, S.H. Ahn, C. S Lee, Preparation and structural evaluation of nano reinforced composites from cellulose whiskers of grass and biodegradable polymer matrix, J. Compos. Mater. 46 (2012) 653–663, https:// doi.org/10.1177/0021998312438174. [4] H.P.S. Makkar, K. Becker, Nutrients and antiquality factors in different morphological parts of the Moringa oleifera tree, J. Agric. Sci. 128 (1997) 311–322. [5] J. Fahey, Moringa oleifera: a review of the medical evidence for its nutritional, therapeutic, and prophylactic properties Part 1, Trees for Life J 1 (2005) 1–15, https://doi.org/10.1201/9781420039078.ch12. [6] M. Khalafalla, E. Abdellatef, Hussain Mohammed Dafalla, Amr A. Nassrallah, Khalid M. Aboul-Enein, David A. Lightfoot, Fadl E. El-Deeb, Hany A. El-Shemy, Active principle from Moringa oleifera Lam leaves effective against two leukemias and a hepatocarcinoma, Afr. J. Biotechnol. 9 (2010) 8467–8471, https://doi.org/10. 5897/AJB10.996. [7] F. Anwar, S. Latif, M. Ashraf, A.H. Gilani, Moringa oleifera: a food plant with multiple medicinal uses, Phytother Res. 21 (2007) 17–25, https://doi.org/10.1002/ ptr.2023. [8] J.S. Binoj, Characterization and optimization of mechanical properties of sustainable moringa oleifera fruit husk fiber for polymer composite applications, SAE Technical Paper 1 (2018) 1–7, https://doi.org/10.4271/2018-28-0045. [9] S. Prakash, V.S. Senthil Kumar, Mechanical and tribological behaviour of treated and untreated moringa oleifera pods fiber reinforced epoxy polymer composite for packaging applications, J. Appl. packaging Res. 11 (2019) 36–48. [10] A. Nadir, F. Ozdemir, O.B. Nazarenko, P.M. Visakh, Mechanical and thermal properties of Moringa oleifera cellulose-based epoxy nanocomposites, J. comp.
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Short Communication
Development and study of properties of Moringa oleifera fruit fibers/ polyethylene terephthalate composites for packaging applications
T
Subhakanta Nayak*, Sujit kumar Khuntia Department of Mechanical Engineering, College of Engineering Bhubaneswar, Biju Patnaik University of Technology, Odisha, 751024, India
A R T I C LE I N FO
A B S T R A C T
Keywords: Chemical treatment Mechanical properties Thermal properties polyethylene-terephthalate Moringa oleifera fiber
Researchers are now focusing on the use of natural fiber polymer composites materials for packaging applications. It has been proposed that Moringa oleifera fruit fiber (MOF) as reinforcement can be a promising candidate for packaging applications. So in this current research, composites were fabricated by reinforcing treated moringa oleifera fruit fibers with Polyethylene terephthalate (PET) thermoplastic polymer. Its mechanical, thermal and morphological properties were investigated. Surface treatments of fibers have been carried out to have a better compatibility with PET matrix. The mechanical properties have been found to increase at the early stage with the increase in treated moringa oleifera fiber content till optimum (20 wt% of fiber) fiber loading thereafter declines. At this fiber loading the mechanical properties obtained were 65.92 MPa of tensile strength, 98.49 MPa of flexural strength, 3.78 GPa of young’s modulus and 28.09 kJ/m2 of impact strength. Thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM) have been used for analysis. The TGA inferred that the thermal stability of the composites increased as compared to neat PET matrix. It was found that composites fabricated from 20 wt% fiber content shows superior mechanical properties as well as thermal properties as compared with other fabricated composites and can be used for packaging applications.
1. Introduction Natural fiber based composites are finding expanding use in products like the interior pieces of automotives, electronic gadgets, as reinforcements in the building and construction industry, packaging etc. In particular, cellulose nanomaterials are very attractive because of their low cost, low density, high strength, high modulus and aspect ratio, lightweight, abundant availability and biodegradability [1–3]. However, conventional E-glass fibers are hazardous for human health and causes cancer. Hence, currently the research on exploring the promising and novel sustainable natural fibers as a bio-reinforcement in polymer composites for different applications is of great demand. Currently, many types of natural fibers have been investigated for use in plastics including flax, hemp, jute straw, alginate, wood, rice husk, wheat, barley, oats, kenaf, etc. Among all the natural fibers, Moringa oleifera is very useful plant and its fibers are one of the strongest natural fibers. Moringa oleifera, commonly referred to as the ‘drumstick tree’ is a member of the Moringaceae family, which grows throughout most of the tropics and is native to the sub-Himalayan tracts of north-western India, Pakistan, Bangladesh, and Afghanistan [4]. It is considered as one
*
of the most useful plant in the world because almost all its parts can be used as food, in traditional medicines and for industrial purposes [5,6]. In addition, seed and leaf flour have been used in the formulation of infant food to increase protein content [7]. The outer portion of the fruit is very hard and rough which comes out to be waste product and thrown away. It is rich in fiber and wasted from commercial industries after yielding its economic value. In the present work, Moringa oleifera fibers (MOF) is tested thoroughly for ensuring its potentiality as reinforcement in polymer matrix and find its application in packaging industries. Various research works has been done taking different parts of Moringa oleifera tree to find their respective applications. Binoj has fabricated composites taking Moringa oleifera fruit husk as reinforcement in unsaturated polyester matrix and found composites made with 20 wt% of fiber content shows the optimum properties and beyond that the fiber pull out and debonding occurred due to poor compatibility between the fiber and the matrix [8]. Prakash et al. [9] fabricated composites taking alkali treated moringa oleifera fruit fibers as reinforcement with LY556 Epoxy and found that the alkali treated fibers exhibits good mechanical properties, wear and water absorption properties when compared to untreated fibers. Nadir et al. [10] studied the mechanical and thermal properties of moringa oleifera cellulose-
Corresponding author. E-mail address: [email protected] (S. Nayak).
https://doi.org/10.1016/j.coco.2019.07.008 Received 5 June 2019; Received in revised form 6 July 2019; Accepted 25 July 2019 Available online 26 July 2019 2452-2139/ © 2019 Elsevier Ltd. All rights reserved.
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composite gives best performance at 20 wt % fiber loading.
based epoxy nanocomposites and found improved properties as compared to neat epoxy. Huq et al. [11] fabricated and studied the mechanical properties of jute reinforced PET composites and found tensile strength of 58 MPa. It is seen that most of the studies have been done on thermosetting polymer as matrix material in moringa oleifera fibers in order to investigate various properties while making composite material. Thermoplastic polymers have certain specific advantages such as good processability, high cost–performance ratio, low processing temperature, and high resistant to fatigue compared to thermosetting polymers. Moreover, they have an ability to resist chemical attack and offer substantial reductions in flammability, smoke, and toxicity performance. Due to the combined advantages of both natural fiber as reinforcement and thermoplastic polymer as matrix, their composites find wide applications in various places including but not limited to packaging, textiles, stationery goods, plastic parts, and reusable containers of various types, laboratory equipment and automotive components. Keeping in view the above facts, an attempt has been made to develop composite materials by reinforcing MOF in Polyethylene terephthalate (PET) thermoplastic polymer matrix. Poly(ethylene terephthalate) (PET), a low cost and high performance thermoplastic, is widely used as packaging materials, fiber, and sheet due to good rigidity, hardness, abrasion resistance, solvent resistance, and electric insulation [12,13]. The extracted fibers (Fig. 1) have been chemically modified with sodium hydroxide (NaOH) to have better compatibility with PET matrix. Different mechanical properties such as tensile strength, Young’s modulus, flexural strength, flexural modulus, and impact strengths of the composite with varying weight percentage (i.e., 10, 20, 30, and 40 wt %) of treated fibers have been studied. It has been observed that the maximum values of above mechanical properties of the composite are obtained at 20 wt % of MOF loading. The chemical interaction of polymers with fibers has been characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) at this fiber loading. The thermal properties of the composite have been studied through dynamic mechanical thermal analysis (DMTA) and thermal gravimetric analysis (TGA) at optimum fiber loading and compared with virgin matrix. From the characterization and study of properties, it is observed that PET/MOF
2. Materials and methods 2.1. Materials Poly(ethylene terephtalate (PET) was purchased from Kolkata and used as matrix. Moringa fruit fiber purchased from a local market which was disposed as waste. Sodium hydroxide (NaOH) was purchased from local market for chemical modification of the fibers. 2.2. Methods 2.2.1. Chemical modification of fibers Chemical modification of fibers is a common method for modifying the fiber surface which enhances the bonding between a natural fiber and a polymeric matrix. Natural fibers are hydrophilic in nature whereas polymeric matrix is hydrophobic, so it will result in poor fiber/ matrix adhesion. Chemical treatment helps in removing the hemicellulose, lignin, wax and oils that surround the external surface of the fiber leading to increase in the surface roughness which improves the fiber/matrix bonding. The untreated moringa fibers have been alkali treated in 5% sodium hydroxide (NaOH) solution for 1 h at a temperature of 80 °C. Then, the fibers have been cooled to room temperature and washed in running water to remove any trace of sodium hydroxide solution adhered on the surface of the fibers so that the pH level of fiber is approximately 7 (neutral). Then, they have been dried in an oven at a temperature of 60 °C for 24 h. NaOH reacts with the hydroxyl group of the natural fibres, removes the hemicellulose, lignin, wax and oils that surround the external surface of the fibre leading to increase in the surface roughness and reduction in the fiber diameter and results in a mercerized cellulose structure (as shown in Equation (1)) which improves interfacial fiber/matrix bonding.
Fiber − OH + NaOH → fiber − O − Na+ + H2 O
(1)
A typical untreated Moringa fiber appears to be surrounded by cementing materials like lignin, hemicelluloses and other impurities like wax and oils whereas the alkali-treated Moringa fiber were found to be
Fig. 1. Extraction of Moringa oleifera fruit fibers. 114
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Fig. 2. SEM of Moringa oleifera fiber (a) untreated fiber (b) alkali treated fiber.
plates under a pressure of 5 tons. Finally, the composites were cut into desired shapes. The dimensions of specimens for tensile strength and impact strength taken were 165 × 12.7 × 3.2 mm and 63.5 × 12.7 × 3.2 mm, respectively. The mechanical properties of PET/MOF composites at these fiber loadings have been measured and described in subsequent sections.
Table 1 Chemical composition of the moringa oleifera fiber before and after alkali treatment. Component %
Cellulose
Hemicellulose
Lignin
Others
Untreated Alkaline
43.44 67.12
0.25 0.11
45.84 24.57
10.47 7.7
2.2.4. Characterization and study of properties of PET/MOF composites Thermal stability of PET/MOF composites was studied by the use of thermogravimetric analysis (TGA), while the chemical composition characteristics were analyzed using FTIR and XRD spectroscopy. The thermogravimetric analysis (TGA) of PET/MOF composite has been performed with the help of Universal V4.5A TA TGA instrument at a heating rate of 10 °C min−1. FTIR of samples has been conducted by Nicolet 6700 Thermo Scientific Spectrophotometer in the absorbance range of 4000 and 400 cm−1. XRD pattern of the composites has been done through Mini Flex Diffractomer (Shimadzu, XRD-7000) operating under CuKα radiation at 40 kV and 150 mA in reflection mode, with a step of 0.05°, counting time of 1 s. Dynamic mechanical thermal analysis (DTMA) has been done in DMA Q 800 TA instruments as per ASTM D 5026 standard in shear mode. The specimen dimension is 32 × 13 × 3 mm3. The test parameters are: frequency = 1 Hz; temperature range = 33 °C–180 °C; heating rate = 2 K/ min; and maximum shear strain = 0.2 %. The surface morphology of composites was studied by using ZEISS Supra55 SEM to get a clear picture on fiber-matrix adhesion. The tensile tests of treated and untreated PET/MOF composites have been performed in servo-hydraulic static testing machine (INSTRON 3382) with a load cell of 5 kN as per ASTM D 638 standard. At each fiber loading (both treated and untreated composites), 20 samples have been tested and the average value has been recorded. The tests have been conducted at a crosshead speed of 2 mm/min at laboratory temperature and the displacement has been measured with a 50 mm extensometer. The flexural tests have been conducted on the same machine using three-point bending method at a crosshead speed of 1 mm/ min as per ASTM D 790-99 standard. Similar to tensile test, 20 samples have been tested and the average value has been noted. The bending stresses of the samples have been determined as per the following equation.
clean and rough due to the partial removal of lignin, hemicellulose and other impurities (Fig. 2). Alkaline treatment of natural fibers increases the exposure of cellulose content in the fiber surface (Table 1 where the percentage in cellulose content increases after the alkali treatment). Now the fibers were designated as alkali treated fibers henceforth. 2.2.2. Characterization of untreated and alkali treated MOF Chemical composition characteristics of untreated and alkali treated MOF were analyzed using FTIR and XRD spectroscopy. FTIR of samples has been conducted by Nicolet 6700 Thermo Scientific Spectrophotometer in the absorbance range of 4000 and 500 cm−1. XRD pattern of the composites has been done through Mini Flex Diffractomer (Shimadzu, XRD-7000) operating under CuKα radiation at 40 kV and 150 mA in reflection mode, with a step of 0.05°, counting time of 1 s. The fiber crystallinity index (C. I) of MOF was determined by using Segal empirical method [14]. It provides a simple calculation of crystallinity Index by using the following equation.
CI =
(I002 − Iam) × 100 I002
(2)
where I002 is the maximum intensity of the (0 0 2) crystalline peak and 1) Iam is the minimum intensity of the amorphous material between (10‾ and (0 0 2) peaks. 2.2.3. Fabrication of alkali-treated and untreated composites Granules of PET were heat pressed and made thin sheets (3.2 mm thickness) individually using Cipet Laboratory (INDIA) press at 200 °C. In this investigation, films of four compositions were prepared which were PET (90 wt %) plus MOF (10 wt %), PET (80 wt %) plus MOF (20 wt %), PET (70 wt %) plus MOF (30 wt %), PET (60 wt %) plus MOF (40 wt %). Firstly, the PET polymer was heat pressed taking appropriate weight of PET granules and sheets of 16.5 cm × 12.7 cm were made and kept in the desiccators until composite fabrication. Moringa fiber was dried in an oven at 105 °C to remove moisture and then cut into small pieces of dimension 16.5 cm × 12.7 cm. Secondly, composites were prepared by sandwiching two layers of moringa fibers between three layers of polymer matrix sheets according to the weight percentage displayed above and pressed at 190 °C for 5 min between two steel
3 δ = WL 48EI
115
(3)
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Table 2 Mechanical properties of PET/MOF composite. Composites
Tensile strength (MPa)
Young’s Modulus (GPa)
Elongation at break (%)
Flexural Strength (MPa)
Impact Strength (KJ/m2)
Neat PET Untreated 10 wt% 20 wt% 30 wt% 40 wt% Treated 10 wt% 20 wt% 30 wt% 40 wt%
55.26 ± 0.5
2.57 ± 0.13
19.1 ± 2.09
59.21 ± 0.86
18.79 ± 2.21
55.89 ± 3.20 58.11 ± 2.28 56.22 ± 2.01 45.16 ± 2.43
2.77 3.11 2.70 2.02
21.2 23.7 25.9 20.1
61.22 69.01 65.18 58.19
18.99 ± 2.18 21.22 ± 2.84 19.65 ± 1.26 18.01 ± 1.35
60.98 65.92 62.76 56.25
2.95 3.78 3.46 2.30
± ± ± ±
2.62 2.05 3.18 3.02
± ± ± ±
0.11 0.24 0.19 0.62
± ± ± ±
0.21 0.26 0.61 0.12
25.5 32.8 28.4 22.2
3. Result and discussion
± ± ± ±
1.88 2.61 1.18 0.98
± ± ± ±
0.15 0.14 0.10 0.06
± ± ± ±
83.11 98.49 87.70 75.34
1.28 1.00 1.99 1.16
± ± ± ±
1.66 1.89 1.79 1.20
22.50 28.09 24.20 19.98
± ± ± ±
3.31 3.47 2.20 2.02
mechanical properties are maximum, hence this weight percentage of MOF fiber has been considered for fabrication of PET/MOF composite for subsequent studies.
3.1. Mechanical properties Various mechanical properties such as tensile strength, young’s modulus, flexural strength, impact strength and elongation at break of neat PET (without fiber), PET/MOF composite at different weight percentages (10, 20, 30, and 40 wt%) of alkali-treated and untreated fiber composites have been measured and presented in Table 2. From the results, it is observed that all the above properties are higher in treated fiber composites at all fiber loadings in comparison to untreated fiber composite. Further, these properties of PET/MOF composites first increase with fiber loadings and then decrease after reaching the optimum weight percentage (i.e. 20 wt %). The measured tensile strength data of fabricated composites have been plotted against the different weight percentage of alkali-treated MOF fibers in Fig. 3. The graph shows an increasing trend in tensile strength and then the strength decreases with further fiber loadings. The untreated composites shows poor value as compared to treated composites because of presence of lignin in the untreated fibers which deteriorates the strength of the composites due to poor fiber-matrix bonding between hydrophilic fibers and hydrophobic matrix as described earlier. But after chemical treatment, the fabricated composites reveal excellent mechanical properties due to better adhesion of fiber and matrix. The maximum value has been obtained at 20 wt% of fiber loading, which gives 65.92 MPa of tensile strength, 98.49 MPa of flexural strength, 3.78 GPa of young’s modulus and 28.09 kJ/m2 of impact strength. With further increase of fiber contents, the interspaces and stress concentrations increase, which act as crack initiation points during impact that decrease the impact strength after optimum fiber loading ( 20 wt%). Since 20 wt% is the optimum fiber weight percentage at which all most all
3.2. Characterization of untreated and alkali treated MOF The FTIR results of both untreated and alkali treated fibers has been presented in Fig. 4. The spectra show various transmission bands. It is observed that the intensity of absorption band at 3275 cm−1 has been reduced in alkali-treated (Fig. 4) fiber as compared to untreated fiber due to the removal of hemicelluloses component from the fiber surface after chemical treatment. Similarly, the intensity of absorption band 2825 cm−1, attributed to the C–H stretching band structure containing groups of alkanes (cellulose), has been reduced during chemical treatment of fibers in alkali treatment. The peak observed at 1748 cm−1 is characteristic for the carbonyl stretch of carboxylic groups in hemicelluloses and pectin. The peak at 1230 cm−1 can also be readily assigned to the C–O stretching mode of acetyl groups in lignin [15]. The disappearance of the 1748 cm−1 and 1230 cm−1 peaks after alkali treatment shows the destruction of carboxylic acid and acetyl groups by the alkali treatment or the macromolecules containing these functional groups were selectively dissolved from the fibers under strong alkali conditions [16]. X-ray diffraction patterns for untreated and alkali-treated MOF are shown in Fig. 5. The crystallinity indexes (C.I) calculated for each sample from the patterns obtained from XRD are presented in Table 3. The C.I of untreated and alkali-treated MOF was approximately 52% and 58% respectively. It is interesting to know that the degree of
Fig. 3. Tensile strength of PET/MOF composite at different wt% of fiber loadings.
Fig. 4. FTIR graph of untreated and alkali-treated MOF. 116
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Fig. 7. XRD graph of neat PET and 20 wt% PET/MOF composite. Fig. 5. XRD graph of untreated and alkali-treated MOF.
Fig. 6 shows the FTIR spectra of both neat PET and PET/MOF composite at 20 wt% of fiber loading. In the spectrum of pure PET (Fig. 6), the broad band at 3375 cm−1 attributed to the symmetrical stretching vibration of –OH group [18,19], which has been shifted to 3395 cm−1 in PET/MOF composite. As a thumb rule, the –OH
stretching peak is sensitive to hydrogen bonding. The band at 2950 cm−1 is more pronounced in PET/MOF composites as compared with neat PET which is due to C–H stretching [18–20]. The stretching at 1650 cm−1 is for H–C–H bending [18,19]. The peak at 1250 cm−1 is observed in PET/MOF composite which is not observed in neat PET, this may be due to addition of MOF fibers in PET matrix. The peak 1100 cm−1 is stretched more in the composite as compared with neat PET, which is corresponds to C–H wagging [19]. Comparing the XRD of neat PET and PET/MOF (20 wt%) composite (Fig. 7), the broad XRD peak at 18° and a sharp peak at 22° may be due to the crystallinity peak of PET, whereas in case of PET/MOF composite, there is a slight left shift of peaks at 2θ values of 17.8° and 21.5°. The reason may be due to the change in crystallinity of PET in the form of composite. The interfacial adhesion between MOF and PET matrix is responsible for the change in structure of PET/MOF composite. Further, the interaction of PET with the chemically modified surface of the treated MOF is otherwise liable for change in structure of PET by the reinforcement of MOF may also be an evidence of interactive dispersion of MOF with PET matrix. Fig. 8 shows the TGA curve of neat PET and PET/MOF composite at 20 wt% of fiber loading. The composite has been degraded in three steps as shown in TGA plot. The first step is from 30 to 230 °C approximately, and it may be due to the evaporation of water molecules.
Fig. 6. FTIR graph of neat PET and 20 wt% PET/MOF composite.
Fig. 8. TGA graph of neat PET and 20 wt% PET/MOF composite.
Table 3 Crystallinity Indexes of untreated and alkali treated MOF. Fibers
Crystallinity Index (CI) %
Untreated MOF Alkali-treated MOF
52 58
crystallinity of MOF increased after alkali treatment. This is due to the fact that, alkali treatment removes non-crystalline materials from the fiber, including amorphous hemicelluloses, lignin and other non-cellulosic material, which allows the cellulose fibers the freedom to adopt a more crystalline structure [17].
3.3. Characterization and study of properties of PET/MOF composites
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matrix. This is due to improved stiffness of composites after addition of fibers. The loss modulus of PET/MOF composite has been found to be 160 MPa at 120 °C whereas for neat PET it was restricted to 145 MPa at 118 °C.
3.4. Scanning electron microscope analysis (SEM) Fig. 11 compares the surface texture of untreated and treated 20 wt % PET/MOF composite to have a clear idea about the fiber matrix bonding. In Fig. 11(a) it is clearly visible that, the fibers are closely packed with the matrix showing better fiber-matrix bonding in treated 20 wt% of fiber loading composite (highest mechanical properties were obtained earlier) whereas, in Fig. 11(b), the fibers are visible on the surface with a poor bonding with the matrix. Moreover, fiber pull out with some cracks are also observed which clearly explains the poor bonding in untreated 20 wt% fiber loading composite. The reason behind poor fiber-matrix bonding in untreated composite is the hydrophobic nature of the natural fibers due to presence of lignin and waxy materials that leads to fiber pull out and cracks in the fabricated composites. As discussed earlier, chemical treatment removes the unwanted materials like lignin and waxy materials which enhances the quality of the fiber and thus showing a good fiber-matrix bonding in treated composites.
Fig. 9. Tan δ (Damping factor) of PET and 20 wt% PET/MOF composite.
The second stage of degradation starts from 230 °C for composite and 250 °C for matrix, respectively, which may be attributed to weight loss. It is further observed that the PET matrix has been degraded at 480 °C, whereas the total degradation of the composite is at 540 °C. Beyond 540 °C no loss of weight is observed. It is noticed that PET/MOF composite has more thermal stability as compared to neat PET. The effect of temperature on dynamic mechanical properties in terms of damping factor (δ), storage modulus (E’) and loss modulus (E’’) of PET matrix and 20 wt% treated composite are shown in Figs. 9 and 10, respectively. Fig. 9 shows the variation of tan δ with temperature for PET matrix and PET/MOF composite. As seen from the figure the tan δ value (0.311 at 91.8 °C) for PET matrix is higher than that of PET/ MOF composite (0.297 at 100 °C). Tan δ represents the energy dissipation potential of the material. Lower tan δ value, more is the interfacial adhesion and stress transfer. In the figure, lower tan δ value indicates better interfacial adhesion between the fiber and the matrix. The storage modulus (E’) value of the treated PET/MOF composite has been found to be 1320 MPa at 30.50 °C whereas for PET matrix it is 995.6 MPa at 22.8 °C (Fig. 10(a)). A 32.58% increase in modulus has been noticed which may be due to surface modification of fibers by chemical treatment that results in good fiber matrix adhesion. Further, it has been seen that the modulus value decreases with rise in temperature in both the cases. It may be associated with the softening of the matrix at higher temperature which is less in case of composite [21]. Almost identical results have been observed in case of flax fiber reinforced high-density polyethylene (HDPE) composites [22] and PLA/ kenaf/ APP composites [23]. The change of loss modulus (E’’) with temperature for PET matrix and composite is shown in Fig. 10(b). The loss modulus of composites shows a higher value at higher temperature as compared to neat PET
4. Conclusion In the present study, natural fiber polymer composite has been developed by reinforcing sodium hydroxide (alkali treated) moringa oleifera fruit fibers with PET thermoplastic polymer. Different static and dynamic mechanical properties and thermal properties were evaluated. From the test values it has been observed that tensile strength of the composite initially increases with the increase of fiber content and decreases afterwards. 20 wt% of fiber loading was considered as optimum fiber loading for fabrication of composites as it shows highest mechanical properties (i.e 65.92 MPa of tensile strength, 98.49 MPa of flexural strength, 3.78 GPa of young’s modulus and 28.09 KJ/m2 of impact strength) as compared with other fabricated composites. Beyond this fiber loading, the mechanical properties deteriorate due to poor fiber-matrix adhesion. From the TGA, it has been found that the composite is thermally enough stable as compared with neat PET matrix. The dynamic mechanical thermal analysis suggests that the composite is extremely good in terms of dynamic mechanical properties. Moringa oleifera fruit fibers composites were found to be a good potential candidate for packaging application as it exhibits excellent mechanical as well as thermal properties.
Fig. 10. (a) Storage modulus and (b) Loss modulus of PET matrix and 20 wt% PET/MOF composite. 118
Composites Communications 15 (2019) 113–119
S. Nayak and S.k. Khuntia
Fig. 11. SEM of (a) 20 wt% PET/MOF composite and (b) neat PET matrix.
Declaration of interest
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