Recent developments in sugar palm (Arenga pinnata) based biocomposites and their potential industrial applications: A review

Renewable and Sustainable Energy Reviews 54 (2016) 533–549

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Recent developments in sugar palm (Arenga pinnata) based biocomposites and their potential industrial applications: A review M.L. Sanyang a, S.M. Sapuan a,b,n, M. Jawaid c, M.R. Ishak d, J. Sahari e a

Laboratory of Advanced Materials and Nanotechnology, Institute of Advanced Technology, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia Department of Mechanical and Manufacturing Engineering, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia c Biocomposite Technology Laboratory, Institute of Tropical Forestry and Forest Products (INTROP), Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia d Department of Aerospace Engineering, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia e School of Science and Technology, Universiti Malaysia Sabah, Jalan UMS, 88400 Kota Kinabalu, Sabah, Malaysia b

art ic l e i nf o

a b s t r a c t

Article history: Received 14 November 2014 Received in revised form 27 August 2015 Accepted 20 October 2015 Available online 11 November 2015

Rapid exhaustion of petroleum resources coupled with increasing awareness of global environmental problems related to the use of conventional plastics are the main driving forces for the widespread acceptance of natural fibers and biopolymers as green materials. Natural fibers and biopolymers have attracted considerable attention of scientist and industries due to their environmentally friendly and sustainable nature. Sugar palm is a multipurpose tree grown in tropical countries and it is regarded as a potential source for natural fibers and biopolymer. Sugar palm fibers (SPF) are mainly composed of cellulose (  66.49%) which leads to their outstanding mechanical properties. The starch extracted from sugar palm tree can be plasticized, blend with other polymers or reinforced with fibers to enhance their properties. From literature review, it is clear that no comprehensive review paper published on sugar palm fibers, starch, and its biocomposites. Present review focuses on recent works related to properties of sugar palm fibers and starch, and their fabrication as green composites. The review also unveils the potential of sugar palm fibers and biopolymer for industrial applications such as automotive, packaging, bioenergy and others. & 2015 Elsevier Ltd. All rights reserved.

Keywords: Sugar palm Biopolymers Biobased materials Biocomposite

Contents 1. 2. 3. 4.

5. 6. 7.

8. 9.

n

Introduction: natural fibers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Classification of natural fibers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sugar palm (Arenga pinnata) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. Sugar palm (Arenga pinnata) in Malaysia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Properties of sugar palm fibers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1. Chemical composition of sugar palm fiber (SPF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2. Physico-mechanical properties of SPF. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sugar palm fibers as reinforcement for polymer composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Increase usage of sugar palm fibers as reinforcement in polymer composites. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Downsides of sugar palm fibers as reinforcement for polymer composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.1. Inconsistent fiber properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2. Hydrophilicity of natural fibers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3. Poor fiber–matrix adhesion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4. Low thermal stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mitigating the downsides of sugar palm fibers for better reinforcement performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sugar palm starch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.1. Extraction of sugar palm starch (SPS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.2. Properties of SPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Corresponding author. Tel: +603 89466318; Fax: +603 86567122. E-mail address: [email protected] (S.M. Sapuan).

http://dx.doi.org/10.1016/j.rser.2015.10.037 1364-0321/& 2015 Elsevier Ltd. All rights reserved.

534 534 534 535 535 535 536 537 537 538 538 538 538 538 538 539 540 540

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9.3.

Modification of SPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 540 9.3.1. Plasticization of SPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 541 9.3.2. Sugar palm starch/Chitosan blend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 542 9.3.3. Sugar palm fiber reinforced sugar palm starch composite (green biocomposites) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 542 10. Potential applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 542 10.1. Automotive. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 542 10.2. Packaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545 10.3. Renewable energy (bioethanol) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545 10.4. Other applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 546 11. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 546 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 547 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 547

1. Introduction: natural fibers Synthetic fibers are dominantly used in the composite industry for the past several decades. However, the negative environmental and health effects associated with these fibers fueled the increasing usage of natural fibers as promising alternative. Several material scientists and engineers were enticed by the numerous merits of natural fibers over man-made fibers. Table 1 [1,2] shows the comparison between natural and synthetic fibers. The escalating usage of natural fibers can be ascribed to their availability, affordability, processability, renewability, recyclability, and biodegradability [3–5]. Moreover, natural fibers demonstrated several other advantages such as comparable specific tensile properties, less health hazards, acceptable insulating properties, low density and less energy consumption during processing over synthetic fibers [5]. Generally, the properties of natural fibers vary depending on their species, growing conditions, geographical location, method of fiber preparations and many other factors [4,6]. Natural fibers extracted from plants are mainly referred to as lignocellulosic fibers because they are mostly of cellulose fibrils embedded in lignin matrix. The characteristic value for the structural parameter varies from one plant to another [7]. The structure of natural fibers normally entails complex layered structures which consist of a primary cell wall and three different secondary cell walls. Each cell wall is built of three vital components which are cellulose, hemicellulose and lignin [8]. Cellulose is a polysaccharides (C6H12O5)n and solely composed of carbon, hydrogen and oxygen; which when degraded gives only glucose (C6H12O6). Cellulose exist in the form of slender rod like crystalline microfibrils which are disorderly and helically arranged along the length of the primary cell wall and the thick middle layer of the secondary cell walls of the fiber, respectively. There are normally 30–100 cellulose molecules in extended chain conformation in each rod like crystalline microfibrils and these provide mechanical strength and stability to the fiber [9]. Cellulose is considered the most crucial structural component of cell walls as Table 1 Advantages of natural fibers compared to synthetic fibers [1,2].

Density Cost Renewability Recyclability Energy consumption Distribution CO2 neutral Health risk when inhaled Disposal

Natural fibers

Synthetic fibers

Light Low-cost Yes Yes Low Wide Yes No Biodegradable

Twice that of natural fibers Higher than natural fibers No No High High No Yes Yes, not biodegradable

compared to the other chemical constituents of any natural fiber. Mechanical properties, cost of production and various potential applications of fibers are greatly influence by the amount of cellulose in their cell walls.

2. Classification of natural fibers Natural fibers are classified depending on their origin either from plants, animals or minerals [17]. However, natural fibers from plants are the most widely used reinforcement material in biocomposites. Plant fibers are subdivided based on the type of plants or parts of the plant the fibers were extracted [10–12]. Fig. 1 shows the various classes of plant fibers which include bast, leaf, seed, fruit, stalk, and grass fibers. All these mentioned plant fibers are term as non-wood fibers. Of late, many researches focus on the usage of non-wood fibers. The utilization of such natural fibers assists in the preservation of the natural forest because deforestation is an increasing environmental threat worth tackling. Heavy consumption of wood (i.e. timber) in wood-plastic composites for construction and other applications results in deforestation which in turn cause loss of biodiversity. For instance, Malaysia is reported to have the world’s highest forest loss rate [14] from 2000 to 2012. About 14.4% of Malaysia’s forest cover for year 2000 has been loss by 2012. The loss is equivalent to 47,278 km2 [14]. Hence, resorting to non-wood natural fibers can address the ongoing forest devastation. Malaysia has rich and vast untapped natural fiber resources available as potential alternative to synthetic fibers. These indigenous existing natural fibers range from kenaf, coconut trunk fibers, sugar palm fibers, sugarcane, sago, pineapple leaf, cocoa pod husk to oil palm fruit bunches oil palm fronds, oil palm trunks and many others. Most of these natural fibers are suitable and potential to be fabricated into composite products as well as other value-added products.

3. Sugar palm (Arenga pinnata) Sugar palm is a tall and large palm with a single unbranched stem which can grow up to 20 m high and 65 cm in diameter. The trunk is covered with long black fibers and the bases of broken leaves. The trunk also acts as storage for starch. The starch is usually converted into sugars at the commencement of flowering, for the production of seeds or palm juice that is tapped [15]. However, the starch can be extracted and utilized for other purposes when the tree is unproductive in terms of sugar and fruits [16]. Sugar palm tree is a member of the Palmae family and naturally a forest species [17]. It belongs to the subfamily Arecoideae and tribe Caryoteae [18,19]. Sugar palm tree can be found in altitudes ranging from sea level up to 1400 m [20]. It grows at 1200–1500 m from sea level and in areas with rain fall of 500–1200 cm3. Sugar

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Plannt Fibeers Non nWoood Baast Flax Hemp H Kenaf

Seed Cotton Kapok Milkweed

Fruit

Woood Stalk

Coir

Leaf

Wheat Rice Barley

Pineap pple Sisaal Abacca

Grasss Bam mboo Bag gasse Esp parto

Harrd wood

Sofft Wood

Fig. 1. Classification of plant fibers [13].

palm tree grows at more humid parts of the Asian tropics. Its plantation covers from South Asia to Southeast Asia and from Taiwan to Philippines, Indonesia, Papua New Guinea, India, North Australia, Malaysia, Thailand, Burma, and Vietnam [20]. Sugar palm trees are widespread to Malaysia, Indonesia and other Southeast Asian countries. It can be found as far as The Gambia, Senegal, Guinea Bissau and other West African countries. According to Mogea et al. [21], sugar palm trees normally grow close to human settlements where anthropochoric propagation plays a major role. Otherwise it occurs preferably in secondary forest to the border of primary rainforests from the lowlands up to an altitude of about 1400 m. Its great versatility makes it one of the oldest cultivated plants, and probably a source of plant sugar long before sugarcane was cultivated for that purpose. 3.1. Sugar palm (Arenga pinnata) in Malaysia In Malaysia, sugar palm tree can be found widely along the rivers and bushes at the rural areas of Bruas-Parit, Perak; Raub, Pahang; Jasin, Melaka; Kuala Pilah, Negeri Sembilan [22]. Generally, it can be seen throughout Malaysia due to this species grows wild in many places [34]. In Tawau (Sabah, West Malaysia) around 809 ha of sugar palm plantation planted by Kebun Rimau Sdn.Bhd. and at Benta and Pahang there are 50 ha of sugar palm tree plantation [20]. However, the plantation area of this species is much less than other palm species such as oil palm and coconut. Hyene [23] reported that sugar palm have approximately around 150 local names indicating its multiple uses by the villagers. These names include, Arenga pinnata, Areng palm, Black fiber palm, Gomuti palm, Aren, Irok, Bagot and Kaong. In Malaysia, it is known as either enau or kabung. It is one of the most diverse multipurpose tree species in culture. The root, stem, fibers, leaves, sap from flowers, and fruits of the tree are all utilized for making many useful products [16]. Almost each and every part of the sugar palm tree is valuable. At least 60 different products can be generated from a single sugar palm tree, making it a real multipurpose tree [24]. Malaysia as a tropical country that has ample resources of natural fibers. One of those abundant natural fibers found in Malaysia is sugar palm fiber (locally known as ijuk fiber) but has not been widely used as reinforcement in the fabrication of polymer composites [25]. This fiber is traditionally utilized by the local people to make brooms, brushes, septic tank base filter, door mats, carpet, chair/sofa cushion, and rope. Although, the fiber is popular among locals to have high strength and stiffness, little research has been conducted to reveal the full potential of sugar palm fibers and their composites [24–28]. Another attractive potential of sugar palms is their ability to produce biopolymers (i.e. starch). The starch obtained from the trunks of sugar palm trees can be utilized to make biodegradable

Table 2 Chemical composition of fibers from different parts of the sugar palm tree [29]. Composition

Sugar palm frond

Cellulose (%) 66.49 Helocellulose (%) 81.22 Lignin (%) 18.89 Ash (%) 3.05 Moisture (%) 2.74 Extraction (%) 2.46

Sugar palm bunch

Ijuk

Sugar palm trunk

61.76 71.78 23.48 3.38 2.70 2.24

52.29 40.56 65.62 61.10 31.52 46.44 4.03 2.38 7.40 1.45 4.39 6.30

polymer which in turn can be reinforced with natural fibers to make green composites. This composite possesses the advantage of being renewable, biodegradable, inexpensive, and abundantly available (especially in tropical countries like Malaysia, Indonesia, Cambodia, Philippines, etc.). Therefore, they have a promising future in the field of biocomposite materials.

4. Properties of sugar palm fibers 4.1. Chemical composition of sugar palm fiber (SPF) Sugar palm fibers like most other natural fibers are lignocellulosic, where the cellulose and hemicellulose are reinforced in a lignin matrix [4]. SPF has cellulose content of approximately 40.56–66.49% as shown in Table 2. The amount of various chemical compositions in SPF which were extracted from different parts of the sugar palm tree (sugar palm frond, bunch, ijuk and trunk) differs. Table 2 illustrated that SPF from sugar palm frond has the highest cellulose content followed by sugar palm bunch, ijuk and sugar palm trunk. Similarly, the mechanical strength of SPF from these different parts of the sugar palm tree followed the same pattern as the cellulose content; sugar palm frond 4sugar palm bunch 4ijuk 4sugar palm trunk [29]. The findings manifested the strong influence of cellulose content of natural fibers on their mechanical strength. Therefore, high cellulose content of SPF from sugar palm frond which in turn leads to better mechanical strength makes them potential reinforcement for polymer composite applications. The chemical composition of SPF might differ not only depending on plant components, plant age, growing environment, soil condition, weather effect and testing methods employed, but also on plant height. Hence, Ishak et al. [30] characterized the chemical composition of SPF obtained from different heights (1, 3, 5, 7, 9, 11, 13 and 15 m) of a single sugar palm tree. Their findings showed that SPF from the bottom (1–3 m) of the sugar palm tree possessed inferior fibers with the lowest percentage of cellulose, hemicellulose and lignin. This observation was attributed to the aging of sugar palm frond, and fibers found towards the bottom of the tree.

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Fig. 2. Naturally woven sugar palm fiber from sugar palm trunk.

Sugar palm like all other members of the palmae family are monocotyledons and their outward growth occurs through the expansion of the trunk by overlapping their leaf bases. Subsequently, the older sugar palm fronds are located at the bottom followed by new fronds at the upper region of the tree. With time, the former fronds eventually degrade due to microbial attacks that damage their structural components. The SPF extracted from these dead sugar palm frond becomes rotten, weakened and chemical components are broken down compared to the younger fronds found at higher heights. SPF from 5 to 15 m were observed to have higher and more stable chemical content where cellulose, hemicellulose and lignin range between 53.41–55.28%, 7.36–7.93%, and 20.45–24.92%, respectively [31]. 4.2. Physico-mechanical properties of SPF Sugar palm fibers are originally found wrapped around the sugar palm trunk from top to bottom of the tree. The extraction and preparation of SPF does not require any secondary processes such as mechanical retting, chemical retting, steam retting and water/microbial retting [32]. Most of these retting processes pollute water bodies and, thus, not environmental friendly. Fig. 2 shows the natural woven form of SPF from the tree trunk. Generally, SPF are brown to black in color with different diameters ranging between 50 and 800 mm [33]. Coconut fiber (coir), oil palm fiber and sisal possess similar diameter range with SPF. The recorded diameter range of SPF is 3–50 times that of the glass fiber (15 mm). Though, SPF proved to have a larger diameter compared to the glass fiber, the weight of the former is twice lower. According to Razak and Ferdiansyah [34], the density of SPF is 1.29 g/cm3 whereas Bachtiar et al. [35] reported 1.05 g/cm3. The SEM image of SPF closely resembles the surface morphology of oil palm and coir fiber [29,30,34]. Parallel lines are observed along the length of the fiber and visible pore-like spots are almost evenly distributed on the fiber surface. The parallel lines may be referred to as microfibrils while the pore spots are considered to be tyloses as in the case of coir [50]. These porous structures on the SPF surface significantly help in obtaining a better mechanical interlocking with matrix resin in composite fabrication [35,36]. On the other hand, the pores also entertain easy penetration of water into the fiber by capillary action, especially when exposed to an aquatic environment [37]. Table 3 shows the mechanical properties of synthetic fibers and the most commonly found natural fibers. The tensile strength of Eglass and S-glass are three or more times superior to most natural fibers. In the case of tensile modulus, pineapple, hemp and flax

Table 3 Mechanical properties of synthetic and natural fibers [38–46]. Fiber

Tensile strength (MPa)

Tensile modulus (GPa)

Elongation at break (%)

Abaca Bagasse Banana Coir Cotton Flax Hemp Henequen Jute Kenaf (bast) Oil palm (empty fruit bunch) Pineapple Ramie Sisal Sugar palm (frond) E-glass S-glass

980 20–290 355 220 400 800–1500 550–900 430–580 400–800 295 248

– 19.7–27.1 33.8 6 12 60–80 70 – 10–30 – 3.2

– 1.1 5.3 15–25 3–10 1.2–1.6 1.6 3–4.7 1.8 2.7–6.9 2.5

170–1627 500 600–700 421.4 2000–3500 4570

82 44 38 10.4 70 86

1–3 2 2–3 9.8 2.5 2.8

Table 4 Mechanical properties of fibers from different parts of sugar palm tree [29]. Fibers

Sugar palm frond

Sugar palm bunch

Sugar palm trunk

Ijuk

Tensile strength (MPa) Tensile modulus (GPa) Elongation at break (%)

421.4

365.1

198.3

276.6

10.4

8.6

3.1

5.9

9.8

12.5

29.7

22.3

fibers are comparable to the synthetic fibers. Sugar palm fiber manifested better mechanical properties compared to some other natural fibers as presented in Table 4. Sahari et al. [29] investigated the tensile properties of sugar palm (ijuk) fiber together with fibers from various parts of the tree, namely the trunk, frond and bunch. Fibers obtained from the frond of the tree exhibited the highest tensile properties followed by bunch fiber, ijuk fiber and lastly trunk fiber (see Table 5) [31]. The trend of the tensile properties of these fibers is in-line with their cellulose content (frond4 bunch 4ijuk 4trunk fiber) [31]. Aji et al. [47] reported that mostly the tensile properties of plant fibers increase as the cellulose content of the fibers increase. Bledzki and Gassan [48] also reported that the mechanical properties of plant fibers in

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Table 5 Mechanical properties of sugar palm fibers from different heights of the tree [31]. Height (m)

1

3

5

7

9

11

13

15

Tensile strength (MPa) Tensile modulus (GPa) Elongation at break (%) Toughness (Mj/m3)

15.5 0.49 5.75 0.58

81 1.15 12.54 7.36

149 1.97 27.75 33.58

201 2.76 28.32 46.09

266 3.22 24.68 50.64

292 3.34 23.08 52.46

279 3.37 21 45.21

270 2.68 18.80 35.71

Table 6 Investigations on sugar palm fiber reinforced polymer composites. Fiber

Matrix

Authors

Sugar palm fiber

Epoxy

Sastra et al. [25] Leman et al. [50] Suraini et al. [51] Bachtiar et al. [52] Ishak et al. [53] Sahari et al. [54] Ali et al. [55] Ticoalu et al. [56] Ishak et al. [57] Bachtiar et al. [58] Sapuan and Bachtiar et al. [28] Sahari et al. [59]

Unsaturated polyester

Polyester resin Phenol formaldehyde High impact polystyrene Sugar palm starch

general depend on their own cellulose content. Most notably, the cellulose content of fibers from a single plant type may differ from different parts of the plant [49]. The tensile properties of fibers extracted from different altitudes of a sugar palm tree were studied by Ishak et al. [31]. The findings in Table 5 showed that fibers attained from the area of live palm frond manifested superior tensile properties compared to the ones acquired from the bottom part of the tree. It was observed that the tensile strength, tensile modulus, elongation at break and toughness of the fibers incessantly increased with height (1–11 m). However, slight drops in fiber tensile properties were realized between 13 and 15 m. These variations in tensile properties of these fibers from different heights of the same tree were ascribed to the differences in their chemical composition. Dissimilarity in properties of fibers of the same type or even from a single plant source is not rare due to factors such as environmental conditions, temperature, humidity, climate, harvesting, separation process, fiber’s chemical compositions and moisture content play a part in their variation [33].

5. Sugar palm fibers as reinforcement for polymer composites In the past decade, a number of articles were published on sugar palm fiber reinforced petroleum derived polymers. Table 6 shows various investigations on sugar palm fiber reinforced petroleum derived polymers. Ishak et al. [31] recently provided a detail review on sugar palm fiber reinforced with epoxy [25,50– 52], unsaturated polyester [53–55], polyester resin [56] phenol formaldehyde [57] and high impact polystyrene [28,58]. Ticoalu et al. [33] reviewed sugar palm fiber composites with thermoset resins. Sahari et al. [59] also studied sugar palm fiber reinforced sugar palm starch composite.

6. Increase usage of sugar palm fibers as reinforcement in polymer composites Utilization of natural fibers with polymer matrices is essential for the mitigation of ecosystem devastation and provides low cost polymeric reinforced composites [60]. The introduction of

Fig. 3. Life-cycle of sugar palm fiber-based products.

sugar palm fibers into polymer matrices further helps to address environmental problems associated with land filling of nonbiodegradable conventional composites. Landfill areas are drastically decreasing due to heavy ongoing solid waste disposal. These environmental impacts triggered considerable concern in the development of sugar palm fiber reinforced polymer composites. Interestingly, fibers from sugar palm tree which could be discarded as agro-waste are now utilized for the manufacturing of biocomposite materials. This has opened a new avenue for sugar palm farmers to convert waste to wealth. It also entertains the use of agro-waste materials into commercially viable products; else it would alternatively be disposed. Moreover, sugar palm fiber like other natural fibers are excellent substitute for the widely used non-renewable fibers. Renewability and availability of natural fibers are the prime factors behind their low cost. Considering the fast depletion of global petroleum resources, the use of synthetic fibers is non-sustainable. Thus, the shift to more sustainable fibers is an initiative towards cost efficiency and environmental protection. The employment of renewable fibers replaces the “cradle to grave” concept of consumer products with the “cradle to cradle” concept. Fig. 3 illustrates the life-cycle of sugar palm fiber composite materials `which represent the ‘cradle to cradle’ concept. Such natural fiber reinforced composites undergo natural decomposition into carbon dioxide (CO2) and water at the end of product lifespan. Their synthetic fiber counterparts are non-renewable and nonbiodegradable, inevitably causing insidious solid waste disposal problems. Globally, there is an alarming concern that anthropogenic CO2 emissions are contributing to global climate change. The drastic emission of CO2 has contributed about 70% of the enhanced greenhouse effect which has resulted in global warming and caused disastrous environmental consequences such as increased frequency of storms, floods and droughts. Therefore, it is necessary to adapt greener technologies and use environmental friendly

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materials to cope with the global demand of CO2 reduction. Hence, sugar palm fibers are considered as renewable resources and their use can help to mitigate CO2 emission into the atmosphere. In addition, glass fibers cause irritation to the skin, eyes and upper respiratory tract. This inherent health hazard of glass fiber has fuel the extensive search for safer and cheaper fibers [50,61]. Thus, natural fibers including sugar palm fibers are highly potential alternatives for glass fibers. They are less abrasive to tooling causing zero respiratory problems for workers or consumers. Moreover, they are low cost and have loading bearing potential.

7. Downsides of sugar palm fibers as reinforcement for polymer composites 7.1. Inconsistent fiber properties Besides the numerous advantages of sugar palm fibers, they also possess drawbacks which still limit their application in the composite industry. SPFs are unable to provide uniform and consistent pattern of physical properties. Their properties mostly vary from one harvesting season to another or even from one plant to another [62]. The variation in the properties of SPFs depends on (1) growing environment (i.e. rain and soil conditions) of the plant, (2) maturity of the plant, (3) part of the plant where the fibers are extracted from, and (4) harvest and processing method of the fiber. These variations in physical properties reflect the non-uniformity of their mechanical properties as compared to synthetic fibers. The answer to this problem is to mix batches of fibers from various harvest or parts of a single plant [62]. 7.2. Hydrophilicity of natural fibers The high moisture sensitivity of natural fibers has placed a huge restriction to their successful exploitation in manufacturing durable composite for outdoor applications (i.e. exterior automotive parts), and SPF is not an exception. The hydrophilic nature of SPFs leads to their low macrobial resistance and susceptibility to rotting [62,63]. This particular drawback worth contemplating especially during shipment and long-term storage, as well as during composite processing. The hygroscopic character of cellulose in SPFs enable it to absorb water from the surrounding environment and swell. Their swelling does not only change the mechanical and physical properties but also reduces the dimensional stability of the composite [64]. However, surface modification approach can be helpful in reducing water sensitivity of SPFs as discussed in Section 8 of this paper. 7.3. Poor fiber–matrix adhesion One of the most challenging problems facing the application of natural fibers is their poor fiber–matrix adhesion [60,65–70]. Most polymeric matrices (i.e. thermoplastics/thermosets) are hydrophobic (“non-polar”) in nature whereas natural fibers are hydrophilic. Hence, there is poor compatibility between the two. The interface between SPFs and matrix requires strong bonding for the matrix to smoothly transfer load to the stiff fibers through shear stresses. Therefore, poor fiber–matrix adhesion significantly reduces the mechanical properties of the SPF reinforced polymer composites. The full potential of the composite cannot be exploited under such condition and may entertain environmental attacks that can lead to severe reduction of mechanical properties and delamination [1,62]. The affinity and adhesion between natural fibers and thermoplastic matrices during fabrication can be enhanced by using chemical “coupling” or “compatabilising” agents [62,70]. Thus, various surface modifications are conducted

on SPFs to improve their adhesion with different matrices as discussed later (Section 8) in the current review. 7.4. Low thermal stability Another hindrance for the wide usage of natural fibers in composites is their low thermal stability [62,63]. Natural fibers can withstand processing temperatures below 200 °C, above which they start to degrade and shrink. Exposing fibers to high temperatures change their physical and/or chemical structures due to depolymerization, hydrolysis, oxidation, dehydration, decarboxylation and recrystallization [6]. The prevention of such processing defects necessitate limiting the range of processing temperature, pressure and time [10]. In addition, recent studies devoted to address the low thermal resistance of SPF and natural fibers in general were reported in the next Section (8)

8. Mitigating the downsides of sugar palm fibers for better reinforcement performance It is necessary to overcome the drawbacks associated with SPFs to optimize their full potential as an alternative to synthetic fibers. This will improve the properties of SPF reinforced polymer composites and expand their field of application. Therefore, many investigations are recently being undertaken to mitigate the drawbacks of SPFs. Poor fiber–matrix adhesion and consequently low mechanical properties are issues mostly related with natural fiber reinforced polymer composites. Hence, surface modification of natural fibers is vital to enhance the poor compatibility between fibers and matrix as well as improve their high moisture sensitivity [5,71]. Leman et al. [26], Ishak [72], Bachtiar et al. [25,33,54] carried out surface modifications of SPF to determine their effects on mechanical properties of SPF composites. Leman et al. [26] treated SPF with seawater and freshwater for the period of 6, 12, 18, 24 and 30 days. The modified SPFs were used to reinforce epoxy matrix. Numerous tensile tests were conducted to determine the effect of SPFs modification on the mechanical properties of the fabricated SPF/epoxy composites. Test results manifested that the composite with freshwater treated SPFs for 6 days showed the lowest tensile stress of 17,306.91 kPa. This average stress was still 25.63% higher in strength compared to the untreated SPF reinforced epoxy composite. Steady increase in tensile stress was obtained from freshwater treatment period of 6 to 30 days with a slight drop for the treatment period of 24 days. Thus, the tensile strength of the treatment period of 18 days was slightly higher than those for 24 days. The reduction in tensile stress for treatment period of 24 days was attributed to the presence of air bubbles in the composite, which serve as a potential fracture triggering point. This decrease in tensile stress eventually weakened the strength of the composite and caused fracture to occur at an undesirable position. The recommended fracture position according to ASTM 638-99 was in the middle of the narrow section. On the contrary, the results presented by Leman et al. [26] for seawater treated SPF/epoxy composites showed continuous steady increase in tensile stress from treatment period of 6 days (16,715.14 kPa) to 30 days (23,042.48 kPa). SPF treated with seawater for 30 days had the highest stress value of 23,042.48 kPa, followed by 21,266.5 kPa for freshwater treatment period of 30 days. Generally, the SPF/epoxy composite strength improved by 67.26% and 54.37% for seawater and freshwater treated SPF for 30 days, respectively, as compared to the untreated SPF. Based on the findings, the authors [26] concluded that SPF can be effectively utilized in the marine sector as a potential substitute for the conventional glass fiber for manufacturing fishing boats.

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Ishak et al. [53] also used seawater for SPF surface modification and investigated its effect on the impact and flexural strength of SPF reinforced epoxy composite. The aim of the study was to find a suitable replacement for chemical treatment of natural fibers. Thus, they used biological base treatment agent in the form of sea water to enhance fiber–matrix interfacial adhesion in sugar palm fiber reinforced epoxy composites. Sugar palm fibers were soaked in the sea water for the duration of 30 days. Impact and flexural tests were carried out in order to examine the effectiveness of this treatment in accordance to the ASTM D256 and ASTM D790 respectively. The experimental results revealed that the sea water treated composites of 20% and 30% fiber content had higher impact value at 18.46 MPa and 14.16 MPa. These impact values for treated composites with 20% and 30% fiber content corresponded to 5.06% and 4.27% of improvements respectively, when compared to untreated composites. The flexural strength result for sea water treated SPF composite of 30% fiber content had higher flexural value (53.87 MPa) with 7.35% of improvements. For the composite of 20% fiber content, the flexural strength decreased (54.22 MPa) by 8.12% compared to untreated composites. The overall results proved that sea water treatment significantly improved surface characteristics of SPF by removal of the outer layer of hemicellulose and pectin and consequently improved the fiber–matrix interface. Bachtiar et al. [27] used alkaline treatment technique to modify SPF surface and then studied its effect on tensile and impact properties of SPF/epoxy composites. The treatment was conducted using two different sodium hydroxide solution concentrations (0.25 and 0.5 M) and three different soaking times (1, 4 and 8 h). The alkali treatment in all conditions (different alkali concentration and soaking time) significantly enhanced the tensile properties of SPF/epoxy composite particularly for tensile modulus. SPF treatment with alkali removed the hemicellulose and lignin content, making the fiber relatively ductile and provided rougher fiber surface than the untreated SPF. This created better interlocking mechanism between the fiber and matrix surface. However, the treatment had a negative effect on the tensile strength of SPF/ epoxy at higher alkali concentration. Very high alkali solution for fiber treatment certainly causes damage to the fiber and consequently decreases the tensile strength of fiber and also their composites. On the contrary, higher alkali concentration provided better impact performance for the SPF/epoxy composite. At strong alkali concentration treatment, the lignin and hemicellulose were washed out enabling better exposure of the fiber to epoxy matrix, leading to better bonding between their surfaces [25,72]. Furthermore, the tensile and impact properties of alkaline treated SPF reinforced epoxy composite were investigated by Bachtiar et al. [25,53]. The prime objective of treating SPF with alkali was to improve the interfacial bonding between matrix and fiber surfaces. The maximum flexural strength reported was 96.71 MPa, which was obtained after 1 h of soaking time with 0.25 M NaOH solution. The flexural strength of the untreated SPF composite improved by 24.41% as compared to the maximum flexural strength of the alkaline treated samples. But, the maximum flexural modulus of treated SPF composite (6.95 GPa) occurred at 0.5 M NaOH solution with 4 h soaking time and thus, improving the untreated SPF composite by 148%. Bachtiar et al. [73] also studied the effect of polystyrene-blockpoly (ethylene-ran-butylene)-block-poly (strene-graft-maleicanhydride) as compatibilizing agent (2% and 4%) and alkali treatment (4% and 6%) of short SPF on the flexural strength and flexural modulus of SPF/HIPS composites with 40 wt% of fiber content. The flexural strength, flexural modulus and impact strength of SPF/ HIPS composite treated with 6% NaOH improved respectively by 12%, 19% and 34% compared to the untreated composites. On the other hand, the SPF/HIPS composites treated with compatibilizing

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agent indicated no improvement in flexural strength and flexural modulus. However, significant improvements were reported for impact strength of the alkali and compatibilizing agent treated composites. The impact strength of the 4% alkali and 3% compatibilizing agent treated composites were about 16% higher than the untreated SPF/HIPS composites. The enhancement of the impact strength of alkali treated SPF/HIPS composites were due to the development of rough surface fibers which offered good fiber– matrix adhesion. Secondly, the removal of hemicellulose and lignin parts of the treated SPF fibers also helped in enhancing the impact strength of the composites. SPF treatment with the compatibilizing agent also upgraded the impact strength of the composites due to chemical reaction of hydroxyl groups of SPF fibers with the anhydride groups of the copolymers which resulted into good interface adhesion between SPF fiber and HIPS matrix [74]. Ishak et al. [75] modified the surface of sugar palm fibers by impregnating the fibers with unsaturated polyester (UP) via vacuum resin impregnation process at a pressure of 600 mm Hg for 5 min. The group later investigated the effect of resin impregnation on the interfacial shear strength (IFSS) of sugar palm fibers. Furthermore, the effect of resin impregnation on the mechanical properties of sugar palm fiber reinforced UP composites was evaluated as well. It was observed that the impregnation process caused the fibers to be enclosed by UP resin and this gave a strong influence to the increase of its interfacial bonding by the increase of its IFSS from single fiber pull-out test. The treated composite samples exhibited considerable higher tensile strength, tensile modulus, elongation at break, flexural strength, flexural modulus and toughness than the untreated (control) samples, due to the high interfacial bonding of the impregnated fiber and matrix. The embedded matrix on the fiber surface acted as an interphase layer and improved the stress transfer between the fiber and the matrix, which resulted in improving the interfacial bonding of the impregnated composites. In addition, it was also reported that the impregnated sugar palm fiber was less moisture sensitive than the control. This indicates that surface modification of sugar palm fiber through vacuum resin impregnation process helps in enhancing the fiber–matrix adhesion and moisture resistance of sugar palm fiber and composites.

9. Sugar palm starch Nowadays, many investigations are conducted regarding the development and characterization of biopolymers since conventional synthetic plastic materials are resistant to microbial attack and biodegradation [45,46]. Among all biopolymers, starch has been considered as one of the most promising due to its easy availability, biodegradability, lower cost and renewability. Starches are commonly used biopolymers. They are the major form of stored carbohydrate in plants such as corn, wheat, rice, and potatoes. They are also hydrophilic polymers that natively exist in the form of discrete and partially crystalline microscopic granules which are held together by an extended micellar network of associated molecules [5]. Starches are composed of both linear and branched polysaccharides well known as amylose and amylopectin, respectively. Native starches contain about 70–85% amylopectin and 15–30% amylose. The ratio of amylose and amylopectin in starches varies with the botanical origin [76]. The Amylopectin is mainly responsible for the crystallinity of the starch granules. Starch granules exhibit hydrophilic properties and strong intermolecular connection through hydrogen bonding formed by hydroxyl groups on the granule surface [77]. Commercial industrial starches are mostly from tubers (potatoes, sweet potatoes, etc.), cereals (rice, wheat, etc.) roots (cassava, yam, etc.) and legumes (bean, green pea, etc.). These are food

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Fig. 4. Extraction process of sugar palm starch from sugar palm trunk.

sources for several poor nations. Therefore, the utilization of such carbohydrates as matrix in polymer composites has ignited serious condemnation and criticism. In recent years, several researches are been conducted to develop biopolymers (starches, PLA) from nonfood sources in order to dissipate the debate and criticism regarding the use of food sources as polymeric matrix. Thus, sugar palm starch is a potential novel alternative. Like the commercial sago, sugar palm starch (SPS) also accumulates in the core of the stem of the sugar palm [78]. Not all sugar palm trees yield sugarrich sap from the flower bunches. The non-productive palms can sometimes sum up to half the trees in a plantation [15]. Starch is normally harvested from these unproductive trees following similar procedures as in the production of sago starch. The starch is extracted from the trunk of the sugar palm tree. It was reported that one sugar palm tree can yield 50–100 kg of starch [20,27]. 9.1. Extraction of sugar palm starch (SPS) Fig. 4 illustrates SPS extraction process from sugar palm trunk. In the SPS extraction process, the sugar palm tree is brought down just before the first bloom and the trunk is split lengthwise to remove the woody fiber mixed with the starch powder from the inner soft core of the sugar palm trunk [78]. This is followed by the washing process, where water was gradually introduced into the fiber and starch mixture and thoroughly kneaded by hand. The mixture is filtered to allow the water to flow through the sieve with starch granules in suspension. The starch is granted enough time to settle at the bottom of the container and the water is later decanted. Thereafter, the white powdered starch is kept in an open air for a moment and later dried in an air circulating oven at 120 °C for 24 h [78]. 9.2. Properties of SPS Sahari et al. [78] investigated the properties of SPS to explore their potential as a novel alternative polymer. SPS registered superior Amylose (37.60%) when compared to other starches such as tapioca (17%), sago (24–27%), potato (20–25%), wheat (26–27%) and maize (26–28%) [77,79]. As for amylopectin, it is a highly branched polysaccharide component of starch that consists of hundreds of short chains formed of α-D-glucopyranosyl residues

Table 7 The chemical composition of SPS and other commercial starches. Starch

Density

Water content (%)

Amylose (%) Ash (%) Reference

Tapioca Sago Potato Wheat Maize Sugar palm starch

1.446–1.461 – 1.54–1.55 1.44 1.5 1.54

13 10–20 18–19 13 12–13 15

17 24–27 20–25 26–27 26–28 37.60

0.2 0.2 0.4 0.2 0.1 0.2

[81,82] [83,84] [80,82] [79,80,82] [79,80,82] [78]

with (1-4) linkages. These are interlinked by (1-6)-α-linkages and 5–6% of which occur at the branch points. As a result, the amylopectin shows high molecular weight (107–109 Da) and its intrinsic viscosity is very low (120–190 ml/g) because of its extensively branched molecular structure [80,81]. SPS have a low protein and fat contents of 0.10% and 0.27% (w/w), respectively [16]. The density of SPS (1.54 g/cm3) is closely comparable to other biopolymers as shown in Table 7. SPS has similar ash content with tapioca, sago and wheat (0.2%) whereas potato has higher ash content (0.4%). SPS like all other starches have moisture content within the range of 10% and 20 % under normal atmospheric condition [78]. Thus, SPS is also moisture sensitive due to the presence of hydroxyl functional groups as indicated by the strong peak at 3200–3500 cm 1. Adawiyah et al. [16] conducted a study on the characterization of sugar palm (Arenga pinnata) starch in comparison with sago starch. By the way, both starches have similar properties and are usually sold commercially under the same name. Table 8 presents detail comparison of SPS and sago starch. 9.3. Modification of SPS A wide variety of modification techniques are employed to improve the properties of biopolymers to meet market expectation and lower their cost, for they are still expensive compared to commodity polymers [85]. Fig. 5 shows three main approaches that tailor the properties of biopolymers. Plasticization, blending

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and incorporation of reinforcements or fillers are modification approaches that develop the potentials of biopolymers to penetrate new markets. Modification of SPS by plasticization, composite and blending will be introduced in the subsequent subsections. 9.3.1. Plasticization of SPS In general, biopolymers mostly demonstrate inferior properties compared to petrochemical derived polymers. Modification techniques such as plasticization, blending, incorporation of fillers and reinforcements are common effective methods to improve the properties of biopolymers [85]. Starch is not meltable in its Table 8 Properties of sugar palm starch in comparison with sago starch [16]. Characterization

Parameters

Chemical composition

Amylose (%w/w) Fat (%w/w) Protein (%w/w) Moisture (%w/w) Ash (%w/w) Onset temp. (TO) (°C) Peak temp. (TP) (°C) Conclusion temp. (TC) (°C) Range (TC–TO) (°C) ΔH (J/g) Stress at 10% strain (kPa) Stress at shoulder point (kPa) Strain at shoulder point (%) Working until shoulder point (N mm) Breaking stress (kPa) Breaking strain (%) Work until breaking point (N mm) Compressive force after breaking at 70% strain (N) Compressive force at 90% strain (N) Working until 90% strain (N mm) Adhesive force (N)

Gelatinization properties

Mechanical properties

Sugar palm starch

Sago starch

37.0 7 1.46 0.277 0.00 0.107 0.00 9.03 7 0.00 0.20 7 0.00 63.0 7 0.12 67.7 7 0.07 74.6 7 0.42

36.6 7 1.55 0.247 0.00 0.08 7 0.00 9.177 0.00 0.167 0.00 58.17 0.28 67.3 7 o.21 79.4 7 0.88

11.6 7 0.49 15.4 7 0.25 0.617 0.10

21.3 7 0.79 16.4 70.24 0.417 0.04

23.0 7 3.65

15.5 70.96

54.4 7 3.54

59.17 2.28

20.2 7 1.80

14.17 0.82

29.8 7 2.64 60.17 2.61 29.6 7 2.45

– – –

8.777 0.59

9.97 71.11

43.8 7 2.34

44.0 7 3.89

1087 6.11

90.3 7 8.37

3.647 0.96

8.99 7 1.57

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pure form and thus cannot be processed as a thermoplastic [85]. The comparative large modulus and strength of neat starch also come with its poor deformability and impact resistance owing to the restricted conformational mobility of its inflexible chains [86]. Therefore, plasticization is repeatedly employed for the modification of starches to further upgrade their processability and other properties. Plasticization of starch is the process in which low molecular weight polar compounds such as water, glycerol, urea and formamide [85,87] swap the intermolecular bonds among polymerchains to bonds between the macromolecules and the plasticizer. In the process, the starch granules are interrupted and the crystalline structure order is disoriented due to the influence of plasticizers, heat and shear [86,87]. Upon plasticization, both the glass transition and the processing temperature of the starch decrease. This phenomenon allows its melt-processability and thus increases the flexibility, workability, distensibility or deformability of the material [87–89]. Plasticizing starch enhances polymer-chain flexibility and increases resistance to fracture. Over and above, it reduces the tension of deformation, hardness, density, viscosity and facilitates faster filler or reinforcement incorporation, and unproblematic dispersion. Plasticization also affects the degree of crystallinity, optical clarity and resistance to biological degradation, amongst many other properties [90]. The plasticized starch is typically termed as thermoplastic starch (TPS). The effect of plasticization on the properties of SPS was investigated by Sahari et al. [91]. The plasticized SPS were prepared using 15%, 20%, 30% and 40% w/w glycerol. Their findings show that the densities (g/cm3), moisture content (%) and water absorption (%) of the SPS decreases as more glycerol was introduced. The low molecular weight of glycerol permits it to replace intermolecular bonds existing between the polymer-chains of SPS, lessening secondary forces among them. The decrease in water absorption capacity of plasticized SPS as the glycerol concentration increased can be attributed to the fact that the glycerol formed stronger hydrogen-bond with SPS. This holds back the water molecule from combining with the plasticizer or with the SPS [92]. Therefore, it becomes more strenuous for water molecules to penetrate into the plasticized SPS. Glycerol proves to be an efficient plasticizer as a result of its elevated boiling point (290 °C) causing the plasticized SPS become less water sensitive [87,91]. The neat SPS has a high glass transition temperature (242.14 °C) which endowed it with high brittleness. However, the brittle nature of SPS decreases with the increase of glycerol from 15% to 40% [29] by lowering their glass

Fig. 5. Biopolymer modification techniques.

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transition temperature and thus improving their flexibility and processability. Sahari et al. [91] also studied the thermal behavior of glycerol plasticized SPS compared the neat SPS. The TGA results demonstrated similar mass loss curves for all plasticized SPS. Considerable thermal degradation of the neat SPS was realized even at temperatures less than 100 °C. The neat SPS has high moisture content and its rapid mass loss below 100 °C was attributed to loss of water. Plasticizing SPS with glycerol drops the boiling point of glycerol to temperature less than 290 °C [92,93]. Therefore, the mass loss below 290 °C was ascribed to the vaporization of glycerol. The sharp degradation observed at 310 °C appears to involve the elimination of polyhyroxyl groups, accompanied by depolymerization and decomposition [93,94]. The tensile strength and elongation at break of SPS consistently increased with the addition of 15%, 20% and 30% w/w glycerol. It was reported that the tensile strength and the elongation at break of SPS/G30 showed the highest value (2.42 MPa and 8.03%). Further increase of glycerol to 40 wt% significantly decreased the tensile strength and elongation at break of SPS/G30 by 79.34% and 31.26%, respectively. The inferior tensile strength demonstrated by SPS/G40 was due to the large quantity of glycerol causing poor adhesion with SPS. On the other hand, the tensile modulus of SPS decreases as the plasticizer increase from 15 to 40 wt%. These findings indicate that the plasticized SPS is more flexible when subjected to tension or mechanical stress. The smoothness of SPS surface increased as more glycerol was added to the starch, rendering it softer and non-brittle as compared to the neat SPS. The plasticizer effectively reduced internal hydrogen bonding while increasing intermolecular spacing, thereby decreasing brittleness [90,93]. The intense peaks at 3200– 3500 cm 1 observed in all FTIR spectra of plasticized SPS with different glycerol concentrations were attributed to the presence of O–H groups. This manifested that the hydroxyl groups of the plasticized SPS decreased with the increase of glycerol [91]. 9.3.2. Sugar palm starch/Chitosan blend The modification of polymers by blending is a mature technology developed in the 1970s or even earlier. It is an effective method to develop new materials with the desired combination of properties. Blending can be carried out by using conventional machinery with less investment, which is an important aspect for industry. Numerous vital properties can be obtained through this technique to satisfy the requirements of the targeted application in relatively short time and for low cost compared to the development of new monomers and polymerization techniques [85]. The general aim for blending might be to improve mechanical properties and water sensitivity for some polymers (i.e. starch) whereas for others (i.e. PLA, PHA, etc.), to lower cost of material. In the case of sugar palm starch, Poeloengasih et al. [95] developed and characterized edible films from chitosan and sugar palm starch with glycerol and sorbitol as plasticizers. This study was aimed at producing films with better physical and mechanical properties using biopolymer blending technique. Chitosan was blend with sugar palm starch at different ratio of (chitosan:sugar palm starch) 0:100, 25:75, 50:50, 75:25, and 100:0 with 30 (w/w) concentration of plasticizers. The plasticizers were added to produce strong and flexible films. The prepared films were characterized for thickness, solubility in water, water vapor transmission rate, tensile strength and elongation of films. The thickness of films with glycerol and sorbitol as plasticizer were reported to be within the range of 0.091–0.113 mm and 0.084–0.113 mm, respectively. Among the films plasticized with glycerol, chitosan: SPS blend ratio of 75:25 was reported to demonstrate the most suitable mechanical properties as edible film material. However, chitosan: SPS blend ratio of 0:100 obtained the best barrier

property with water vapor transmission rate of 12.87 g/h m2. For film with sorbitol as plasticizer, the highest solubility in water was 49.41% obtained from film with a chitosan:SPS blend ratio of 75:25, whereas the lowest water vapor transmission rate was 7.39 g/h m2 from film with 0:100 blend ratio. The lowest tensile strength (5.38 MPa) and the highest elongation (22.59%) were reported from a film with chitosan:SPS ratio of 50:50. 9.3.3. Sugar palm fiber reinforced sugar palm starch composite (green biocomposites) Starch has gain increasing attention as a biobased polymer owing to its complete biodegradability, low cost and renewability [77]. In view of this, starch is a highly potential candidate for developing sustainable materials, for it is simply generated from carbon dioxide and water by photosynthesis in plants [96,97]. However, starch itself is poor in processability as well as in the dimensional stability and mechanical properties for its end products [77]. To improve the properties of starch, fibers are normally incorporated as reinforcement. For better environmental consideration and sustainability, Sahari et al. [59] fabricated and characterized a 100% renewable and biodegradable biopolymer and natural fiber from sugar palm tree. Sugar palm starch reinforced by sugar palm fiber is a typical example of ‘green composites’. Overall, the reinforcement of plasticized SPS (containing 30% glycerol) with SPF has enhanced the mechanical properties of the resultant composite material. Although the increase in SPF loading (10–30 wt%) lessen the elongation at break of SPF/SPS composite, it significantly increased the tensile strength, tensile modulus, flexural strength and flexural modulus. The SPS matrix simply transfer stress to the fiber during tensile testing, making the fiber as a load carrier in the composite. Therefore, increasing the SPF content in the SPS matrix boosted the load carrying capacity (tensile strength) and stiffness (tensile modulus) of SPF/SPS composite. The flexural strength and modulus also escalated when the weight percentage of fibers increased from (10–30 wt%). Sahari et al. [59] also reported that water absorption of SPF/SPS biocomposite shrinked with increasing fiber loading due to the better matrix–fiber interfacial bonding as well as the impediment to absorption instigated by the fibers. In addition, the fiber loading improved the thermal stability of the biocomposite.

10. Potential applications 10.1. Automotive The primary driving reason why plastics are increasingly been utilized in the automotive industry to replace heavier materials like steels is due to their lightweight. Besides reducing the weight of vehicles, automakers are looking into selecting the most resource efficient plastics (i.e. biobased plastics) for better sustainability. This further contributes to the deduction of CO2 emissions and energy usage [98]. Moreover, several million vehicles reach the end of their useful lives each year. The plastic, fiber and composite components which total to about 25–40% of the vehicle weight remains as waste. Since most of these components are made from non-biodegradable materials, they cease to disappear from the environment. Therefore, the integration of biobased materials in automotive components can help in minimizing the negative environmental impact of car production [73,74]. Polymer materials occupy about 100–150 kg of the total body parts of modern cars. The main reasons behind the growing demand of biobased polymers and composites in automotive applications are (1) to reduce weight of cars for economical fuel consumption, (2) to minimize carbon foot print generated by cars

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in the form of carbon dioxide emission, (3) to reduce the dependence on non-renewable materials and (4) to increase design flexibility for easier assembling/dismantling and integration of car parts and systems. In addition, government environmentally friendly policies and consumer preference also contribute to the escalation of biobased material usage by automakers. The European commission issued guideline 2000/53/EG which states that 85% of the weight of vehicles had to be recyclable by 2005. Later by 2015, this recyclable percentage is expected to increase up to 95% [62]. The constant improvement in the properties of biobased polymers and composites increasingly provides the automotive industry with green alternative materials which are more suiting to their specific requirements [99]. Each part of the vehicle is subject to specific constraints based on its function and location in the vehicle. Most recent vehicles constitute of 15,000 parts and 40% are plastics, in other words 600 plastic parts [99]. The positions of such plastic parts in automobiles can be categorized into four main locations, namely, interior trims, external parts, structural parts and fuel systems and under-the-hood applications. Furthermore, plastic materials are also present on “hidden” car parts, such as electronics and electrical components, sealers, adhesives, paintings, vanishes and coatings [99]. Bio-based materials were introduced in several vehicles to manufacture components such as door panels, package trays, seat backs, trunk liners, dashboards and other interior trim units, first in Europe and later in North America [100,101]. Faurecia and Mitsubishi Chemical recently came up with a joint program for developing a bioplastic based on biobased PBS that can be employed in mass production for automotive interior parts, such as door panels, trim and strip, structural instrument panels, etc. The generated bioplastic will be a natural fiber composite called BioMat. This makes Faurecia to be the first automotive equipment supplier to mass produce a 100% biobased plastic [98]. On the other hand, incorporation of biobased materials in exterior or under-the-hood applications is still limited. Exterior vehicle components are required to withstand extreme environmental conditions like wetness. Nevertheless, Toyota has used natural fibers in its exterior tire covers and under-the-hood radiator end tanks. Rieter automotive utilized abaca fibers in place of glass reinforcement to manufacture underbody panels for Mercedes. Flax fibers were also used in car disk brakes to replace asbestos fibers [102]. In 2000, Mercedes-Benz Travego travel coach model were made with polyester/flax reinforced engine and it became the first sample of natural fibers used for exterior components in a production vehicle [62,99]. Daimler innovate an air filter system using 60% polyamide which was installed in its Mercedes Benz line [103]. Later in 2004, the spare tire well covers of the MercedesBenz two door coupe vehicle were produced by Daimler chrysler AG using abaca fibers. This was considered the first large scale application of natural fibers in an exterior parts [62,101]. Daimler also produced under-floor body panels made of abaca fibers and these panels are used on the spare-wheel compartment cover in the three-door version of the Mercedes Benz A-Class model. The abaca plant fibers used have very high tensile strength [103]. The door cladding, seatback linings, and package shelves of the Mercedes Benz contain process flax, hemp, and sisal. Moreover, seat bottoms, back cushions, and head restraints contain coconut fiber and caoutchouc (a source of natural latex) [103]. Of late, there have been trials in the use of natural fiber composites in structural applications—an area which was earlier been reserved for synthetic fibers like glass and aramid [100]. Natural fibers like hemp, flax, abaca, kenaf and so on, display higher strength to weight ratio than steel as well as comparatively cheaper to produce. Natural fiber based composites are receiving considerable acceptance among automakers. Therefore, they are emerging as a strong promising alternative to glass reinforced

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composites. Natural fiber reinforced composites can provide the same performance for lower weight and can also be 25–30% stronger for the same weight as compared to their synthetic counters. Apart from that, they fulfill a vital requirement in the passenger compartment by demonstrating a non-brittle fracture property on impact [100]. In 2007, Mazda illustrated its commitment to continue developing environmentally friendly vehicles by producing a new fabric made entirely from plant fibers. These biobased fabrics were used for seat covers and door trim in the Premacy Hydrogen RE Hybrid car [103]. General Motors utilized kenaf and flax mixture for package trays and door panel inserts to replace synthetic fiber in its Saturn L300 and European-market Opel Vectra. Similarly, Honda also worked out a plant-based fabric that is used for its vehicle interiors including seat covers, door coverings, headliners, floor mats, and other fabric-covered surfaces. The developed biobased material has the potential to reduce energy consumption during production by 10–15%. The fabric is also used in Honda’s fuel cell vehicles. Doors, fenders, engine hood, bumpers, spoilers, and trunk lids of a new generation BioConcept-Car, the Renault Mégane Trophy, was made completely from biocomposites [103]. There are numerous means to use biobased materials for automotive parts. Biobased materials are either used as polymers, reinforcements or fillers. Biobased polymers can be reinforced or filled using natural fibers to produce biocomposites [102]. Biobased materials were deployed in the production of automotive parts and components since the 1930s. Henry Ford always had the belief that agriculture and industry are natural partners. On this basis, he initiated the use of agricultural products as automobile materials. Many products nowadays move from farm to ford motor company to contribute to the splendor of ford-built cars and trucks. The company adopted the culture of employing recyclable and renewable biomaterials whenever technically and economically viable. Ford was the first car manufacturer to incorporate biobased plastics in paints, enamels and molded plastics parts. Ford also integrated natural fibers like hemp, wood pulp, cotton, flax, and ramie in different components of the vehicle [100,104]. In 1937, Ford produced 300,000 gallons of soy oil for use in car enamels. Afterwards, straw, flax and soy bean meal were used in the manufacture of their car’s body whereas its tires were made from golden rod latex [105]. Fig. 6 shows Ford’s eminent “soybean car” which had soy-based plastic body panels. The interior storage bins of the 2010 Ford Flex’s third-row contained 20% wheat straw biofillers as presented in Fig. 7 [102,107]. Ford also used wheat straw in making vehicle steering wheels. Nowadays, the use of biobased materials in Ford manufactured vehicles is on the increase year by year and model by model [106]. Ford’s latest vehicles such as Ford Mustang, Expedition, F-150, Focus, Escape, Escape Hybrid, Mercury Mariner, Lincoln Navigator, Lincoln MKS, and Taurus are built with soy based polyurethane foam seat cushions, seat backs and seat headrests [105]. The 2010 Ford Escape and Mercury Mariner were also designed with soy based polyurethane foam headliner as shown in Fig. 8. The company further developed gaskets from soy foam together with 25% recycled tires in 14 vehicle platforms. The amalgamation of soy materials in Ford vehicles can help to reduce the consumption of petroleum by more than 5 million Ib annually and this, in turn, reduces CO2 emission by more than 20 million Ib annually [106]. Lately, Ford and Heinz (United State food processing company) have matched to investigate the use of tomato skins for automotive applications. Scientists at Heinz have been searching for innovative ways to recycle and reuse peels, stems and seeds from the more than two million tomatoes the company uses every year to produce Heinz tomato ketchup [98]. In the 1960s, coconut fibers were exploited for the first time in car seats [108]. Decades later, coconut fibers were used in seat

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Fig. 6. Soy-based composite car [106].

Fig. 7. Interior storage bin made from 20% wheat straw biofillers.

bottoms, back cushions, and head restraints. Notably, sugar palm fiber has a competitive property to coconut fiber and the usage of the latter has gradually accelerated over the years. As observed in Table 3, sugar palm fibers demonstrated similar or even better mechanical (i.e. tensile strength and tensile modulus) and physical (i.e. density, moisture content) properties compared to many other natural fibers (i.e. kenaf, cooconut, oil palm fibers, etc.) used as reinforcement in polymer composites for automotive components. The low density of sugar palm fibers provides them with relatively good specific mechanical and physical properties which are sometimes higher than those of glass fibers. Nevertheless, to the best of our knowledge, no work has reported the use of sugar palm fiber as any automotive components. Hence, their usage in hybridizing glass/sugar palm fiber reinforced polyurethane composites for automotive components is currently being studied by the authors. The fabricated hybrid composites are to be utilized on the front anti roll bar (ARB) design for typical Malaysian sedan vehicles (Proton). It is a step in the right direction, and is the easiest way for Malaysian automotive manufacturers (Inokom, Naza Automotive Manufacturing, Perodua, Proton, etc.) to go green and be more sustainable. Sugar palm fibers can serve as alternative resource for the near future and have the potential to be commercially manufactured into various biocomposites for automotive components. In addition, the development of sugar palm fiber reinforced sugar palm starch composites (mentioned in Section 7.3) could provide 100% biodegradable and renewable composites options to the next generation automotive designers. Therefore, the utilization of sugar palm fiber, biopolymer and their composites in the automotive industry would pose a positive impact on local sugar palm farmers, reduce dependency on fossil fuel, enhance environmental quality by developing a sustainable resource supply chain, and considerably decrease greenhouse gas emissions through a better CO2 balance over the vehicle’s lifetime.

Fig. 8. Ford’s soy based polyurethane foam components.

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10.2. Packaging Since olden times, paper, plastic, glass and metal are the basic packaging materials used for various types of packaging. Among these materials, petroleum based plastics have been extensively employed since the mid twentieth century. Their widespread usage is due to their superior processing property, good esthetic quality and acceptable physico-chemical properties [109]. Yearly, about 30 million tons of plastics are used for packaging related applications such as agricultural mulch films, waste bags, shopping bags or food packaging. This value is almost equivalent to 25% of plastics produced worldwide and their utilization is still on the increase [110]. In fact, the global plastic production is anticipated to exceed 300 million tons by 2015 [109,111]. Despite the numerous merits attached with the use of petroleum based plastics, they bring about severe environmental effects. High resistance to biodegradation is the root cause of their undesirable environmental impacts. Therefore, several researches have been conducted to develop environmentally friendly plastics from renewable sources. Over the years, there is mounting interest in the development and use of biobased packaging materials. Besides minimizing the accumulation of plastics in the environment, they also shrink the reliance on fossil fuel for better sustainability [102]. The biobased plastic market is gradually exiting its infancy and taking over the petroleum-based plastic market at a growth rate of 30% annually [110,111]. The term “biobased” and “biodegradable” are used interchangeably in many literatures but they are not one and the same. Biodegradable materials are not necessarily biobased whereas biodegradability is a typical property of biobased materials [112]. Therefore, biobased packaging materials are packaging derived from renewable sources. The most commonly available biobased plastics are from marine and agricultural sources. However, the scope of discussion will be limited to starch which is an example of polysaccharide. Of late, starch-based packaging materials have emerged in the biobased plastic market and are becoming more commercialized. Their usage is expected to surpass 30,000 tons (annually) within the subsequent years ahead [112]. The consumption of such environmentally friendly packaging materials is on the growth, especially in countries where landfill is the primary waste management option [113]. Municipal solid waste generation increased 37% from 1988 to 2005, and packaging materials contributed 31.2% of the total solid waste [114]. Furthermore, food packaging alone covers almost two-thirds of the total packaging waste by volume [112,113]. Thus, exploring biopolymer based materials for food packaging is a potential mitigation tool to address environmental pollution from non-biodegradable food packaging materials. Numerous research works are being directed to the development of environmentally friendly biopackaging materials from renewable resources. Food packaging protects food from environmental effects to preserve food quality and extend their self-life. It also provides ingredient and nutritional information to consumers [114]. Hence, suitable food packaging materials ensure proper safety and quality of food products from processing and manufacturing through handling and storage and finally consumption [112]. The use of sugar palm starch based films as potential packaging alternative choice to petroleum derived plastics is imperative for environmental waste management. Most recently, the authors [115,116] studied sugar palm starch (SPS) based films for food packaging, developed by using solution casting technique. The effect of different plasticizer type (glycerol (G), sorbitol (S) and glycerol/sorbitol (GS)) and concentration (15, 30 and 45, w/w%) on the mechanical and thermal properties of SPS films were evaluated. Regardless of plasticizer type, the tensile strength of

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plasticized SPS films decreased while their elongation percent (E%) increased as the plasticizer concentrations increase. However, the E% of G and GS-plasticized films significantly reduced at 45% (w/w) due to antiplasticization effect of plasticizers. High thermal stability was evident in S-plasticized films compared to G and GSplasticized films. Plasticizer concentration showed insignificant effect on the thermal properties of S-plasticized films. The obtained results indicated that 30% (w/w) G, S or GS plasticized SPS films manifested better thermal and mechanical properties and may be useful for food packaging. Many efforts are currently being undetaken to enhance the functional properties of sugar palm based films as an effective food packaging material. 10.3. Renewable energy (bioethanol) The world economy heavily depends on fossil energy resources. Fossil fuel combustion contributes about 98% of carbon emissions. Carbon dioxide emission into the atmosphere can be reduced significantly by minimizing the use of fossil fuels. Thus, switching to renewable energy sources is expected to gain considerable attention (30–80% in 2100) [117]. According to the European Renewable Energy Council in 2006, renewable energy will cover approximately half of the global energy supply by 2040. Bioethanol and biodiesel are the two global biomass-based liquid transportation fuels that are potential to substitute gasoline and diesel fuel in the near future. The backbone of the increasing interest in biofuels includes sustainability, reduction of greenhouse gas emissions and security of supply [114,118]. Looking at the use of bioethanol as a transportation fuel, it became well-known around the 1980s in many countries like Brazil, United States or Sweden. The production of bioethanol has multiplied many folds in the last few decades from 17.3 billion litres in 2000 to more than 46 billion litres in 2007. Its production is further expected to exceed 125 billion litres in 2020 [117,119]. Feedstocks used for bioethanol production ranges from starchcontaining (e.g. corn, wheat), sugar-containing (e.g. beet and cane) to cellulose-containing (e.g. wood) plants [120]. Sugar palm tree is categorized as both starch-containing and sugar-containing plant; and, thus, a potential source for bioethanol production. After the sugar palm tree matures and its inflorescence developed, the sugar-rich juice gush-out from the stem by cutting off the inflorescence. A vessel is attached under the stem to collect sugar juice. After few days, the collected sugar juice in the vessel ferments, whereas the vessel is emptied daily, in the case of sugar production. Fig. 9 shows the fementation of sugar palm juice for bioethanol production. The fermented juice is inoculated with

Fig. 9. Fermentation of sugar palm.

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yeast for the production of bioethanol. The amount of fresh sugar juice yield under favorable conditions is approximately 8.7– 25 tons/ha/year throughout the lifecycle of the palm. This quantity is equivalent to about 4610–13,000 liters of ethanol/ha per year [15]. Tapergie’s Arenga palm sugar factory in Tomohon (Indonesia) reported the production of about 24,000 liters of ethanol per hectare per year. This output-to-land area ratio, outnumbered the ethanol yield from corn (4200 liters/ha/year), sugarcane (5700 liters/ ha/year), cassava (4500 liters/ha/year), sago (4133 liters/ha/year), and sweet sorghum (6000 liters/ha/year) [24]. The ethanol yield from sugar palm far exceeds that of other feedstocks that are most commonly in use. Yet still, this production can possibly be increased by shortening the non-productive vegetation phase of sugar palm (9 years) using plant breeding techniques [24]. The produced sugar palm based ethanol is used to substitute gasoline in small generators, vehicles, motorcycles and as cooking fuel in specially designed burners. The Eco-Integration project for ethanol production as fuel was publicized in 2008. The project looks forward to export bioethanol to Europe through the port of Rotterdam. Therefore, the project covers 1 million hectares of sugar palm forest in Indonesia. Existing semi-natural palm plantations and additional established plantations are utilized for the project. Innovative ways of harvesting and fermenting sugar palm juice for conversion into bioethanol were developed. The technology and economic viability of bioethanol production from sugar palm is high. Thus, there are plans to extend the project for ethanol production from sugar palm, to countries like Columbia and Tanzania [15]. 10.4. Other applications Sugar palm fibers are extremely durable, even in contact with seawater. They possess good resistance to seawater and thus, use

for making shipping ropes [15,24]. Fig. 10 shows a 12 ft (length) hybrid composite boat that was fabricated from the combination of sugar palm and glass fiber with unstaurated polyester as the matrix [25,120,121]. Compress molding and hand-lay-up technique are used for the fabrication of the boat. The weight of the boat was reduced 50%, due to the utilization of sugar palm fiber in place of the glass fiber. The density of sugar palm fiber (1.22–1.26 kg/m3) is half of the commercial E-glass fiber (2.55 kg/m3) normally use in fishing boats [122–124]. In addition, a safety helmet was also developed from epoxy reinforced with sugar palm fiber. It is water resistant and could absorb and withstand high impact. The helmet was referred to as Helmet-Ijuk Reinforced Composite (HIReC) [122,125].

11. Conclusions Renewable and biodegradable materials are the hope of the near future. The devastating environmental issues generated by petroleum-based materials can be eliminated or at least minimized with the corporation of natural fibers and biopolymers in composite materials. The development of such green composites can yield significant environmental improvements, addressing plastic waste disposal and the reduction of carbon footprint of petroleum-based materials. For better sustainable future, bioresources are increasing being utilized as potential alternative for non-biodegradable synthetic materials. Abundant availability and low cost of these green materials grant them much attention for the past few decades. However, more research works are required to overcome the inherent drawbacks attributed to the usage of natural fibers and biopolymers in composites. Sugar palm (Arenga pinnata) is a multipurpose tree with several traditional uses. Different components of the tree have been

Fig. 10. Fabrication of sugar palm/glass fiber hybrid boat.

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extensively used for making numerous local products. Due to their outstanding mechanical properties, sugar palm fibers can compete with most natural fibers in the market such as coir, oil palm fiber, kenaf, cotton, jute and many more fibers. Most interestingly, ‘one-source’ green composite can be fabricated by ‘marrying’ natural fiber with biopolymer from a single sugar palm tree. In general, use of sugar palm fiber and starch in green composites can help in: (1) reducing the negative environmental impact of synthetic polymers and fibers; (2) decreasing the pressure for the dependence on petroleum products; and (3) developing sugar palm as new industrial crop in the future, most especially in tropical countries. Consequently, this can lead to better socio-economic empowerment of the rural people by increasing revenues and creating more job opportunities. However, the gigantic opportunity of utilizing sugar palm fiber and biopolymer in the composite industry for various potential industrial applications has not been widely exploited. Nevertheless, more advance characterization of sugar palm fibers, biopolymer and their biocomposites should be performed in terms of analysis and testing. Besides the basic mechanical (tensile and flexural), thermal (thermal gravimetric analysis), chemical (FTIR) and physical (density, moisture content, SEM imaging) characterizations, there is need for more characterizations using advance techniques and equipment such as attenuated total reflection Fourier transform infrared spectroscopy (ATRFTIR), atomic forced microscopy (AFM), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), and thermal analysis instruments (i.e. dynamic mechanical thermal analyzer (DMTA)). For effective packaging applications, it is essential to determine the barrier properties, sealibility, moisture absorption of sugar palm based films and biocomposites. So far, substantial works were done on sugar palm based composite but there is no reported investigation on sugar palm based nanocomposites. Venturing into sugar palm nanocomposites can enhance the reputation of sugar palm biocomposite industry and open new markets such as pharmaceutical and electronic packaging. This is a virgin research and innovation area to address some concerns hindering potential industrial applications of sugar palm fibers, biopolymer and their composites.

Acknowledgments We gratefully acknowledge the Ministry of Higher Education, Malaysia for the Commonwealth Scholarship and Fellowship Plan awarded to Muhammed Lamin Sanyang and for funding this project through Exploratory Research Grant Scheme (ERGS), ERGS/12013/5527190.

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