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Ibrahim, M. I. J., Sapuan, S. M., Zainudin, E. S., and Zuhri, M. Y. M. (2019). "Extraction, chemical composition, and characterization of potential lignocellulosic biomasses and polymers from corn plant parts," BioRes. 14(3), 6485-6500.


Corn is a plant that can be used as a potential source of biomass for various biomaterial applications. Thermoplastic corn starch and corn hull, husk, and stalk fibers were extracted from different corn plant parts. The chemical composition, physical properties, thermal stability, crystallinity index, and surface morphology of the extracted samples were characterized on a powder basis. The corn husk and corn starch revealed an excellent combination of properties. Corn husk provided the highest cellulose content as well as the most favorable surface morphology. Corn starch revealed acceptable amylose content and tolerable thermal stability. The cellulose and starch demonstrated an excellent correlation between the function and structure of biomolecules. Hence, both corn starch and husk have potential for use in many applications of the biomaterial.

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Extraction, Chemical Composition, and Characterization of Potential Lignocellulosic Biomasses and Polymers from Corn Plant Parts

M.I.J. Ibrahim,a,b S.M. Sapuan,a,c,* E.S. Zainudin,a and M.Y.M. Zuhria

Corn is a plant that can be used as a potential source of biomass for various biomaterial applications. Thermoplastic corn starch and corn hull, husk, and stalk fibers were extracted from different corn plant parts. The chemical composition, physical properties, thermal stability, crystallinity index, and surface morphology of the extracted samples were characterized on a powder basis. The corn husk and corn starch revealed an excellent combination of properties. Corn husk provided the highest cellulose content as well as the most favorable surface morphology. Corn starch revealed acceptable amylose content and tolerable thermal stability. The cellulose and starch demonstrated an excellent correlation between the function and structure of biomolecules. Hence, both corn starch and husk have potential for use in many applications of the biomaterial.

Keywords: Corn biomasses; Chemical composition; Physical; Thermal; Morphological properties

Contact information: a: Advanced Engineering Materials And Composites Research Centre, Department of Mechanical and Manufacturing Engineering, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia; b: Department of Mechanical and Manufacturing Engineering, Sabha University, Libya; c: Laboratory of Biocomposite Technology, Institute of Tropical Forestry and Forest Products (INTROP), Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia; *Corresponding author:


Contemporary environmental concerns, such as non-biodegradable disposal materials, plant wastes, and rising mountains of garbage are increasingly documented as environmental barriers (Ibrahim et al. 2019). The area for landfills is limited, and further incineration capacities require high capital investment and cause additional environmental threats. These issues have prompted the design and manufacture of eco-friendly materials from renewable sources to replace conventional non-biodegradable materials. Reducing the dependence on synthetic plastic and petroleum products is one reason for investigating biomasses in reinforcing polymer composites (Mori et al. 2018). Furthermore, the use of biomasses as reinforcement in composites would lead to partial degradation of wastes, which in turn contributes to the solution of environmental complications.

Corn (maize) is one of the most abundant sources of plant residues, which as biomass provides multiple advantages such as high concentration of starch, excellent consistency, cost-effectiveness, availability, and biodegradability (Mendes et al. 2016). According to Sandhu et al. (2004), corn is among the most abundant agriculture cereals planted on earth. There are typically six common sorts of maize, namely dent, flint, pop, pod, flour, and sweet corn. These sorts vary remarkably in their physiochemical characteristics due to environmental influences. The production of corn in 2014 was estimated at 1.04 billion tons, which corresponded to 31% of the global cereal production; therefore, corn became the third most important food grain (Singh et al. 2016). The corn plant consists of one stem or more associated with a combination of short roots. The stem branches at each node and ends with inflorescences. After harvest, the corn parts are turned into residues that are disposed (Weatherwax 1950).

Corn is a vital source of commercial starch, which is a type alpha-linked glucose that is used extensively in food factories as a gelling, water retention, and bulking agent (Zobel 1988). More than 70% of corn kernel composition is starch, and the rest is sugar, protein, oil, and ash. However, many natural fibers can be extracted from corn plant parts including the stalk, straw, leave, and husk. Compared with other agricultural bioproducts, corn fiber offers distinct features such as saving 90% of the cost and being more accessible than other natural fibers (McAloon et al. 2000).

The use of natural fibers as reinforcing materials in polymers and composites is a major area of research interest. The chemical composition, morphological structure, and thermal stability of biomass are essential criteria to select the best lignocellulosic material (Brinchi et al. 2013). To date, there is insufficient research on the applications of corn polymers, fibers, and composites, with no study conducted on the physical, morphological, and thermal properties of corn biomass. This study considers the physiochemical composition, thermal characteristics, and crystallinity index and morphological properties of corn biopolymers and biofibers with the aim of exploring their potential in the development of biocomposites.



Corn was collected from a local farm in Malaysia. Corn starch and corn hull fiber were extracted from the granules of a fresh sweet corn ear. Corn stalk and husk were obtained from the stems and leaves of corn plants, respectively. All samples were characterized in a powder basis.

Starch and Fiber Extraction Processes

The isolation of corn starch was carried out in accordance with Ali et al. (2016). Corn grains (1 kg) were steeped in distilled water (4 L) for 12 h at 4 °C. The purpose of the steeping is to increase grain moisture to facilitate grinding process. After the water was evacuated, the grains were crushed in a lab electric blender (wet milling) until the minimum likely fraction was achieved. The crushed fractions were sifted through a 75 µm mesh sieve and then left to sediment for 8 h. The supernatant liquid was discarded, and the sedimented particles were suspended in distilled water to remove any residual protein from the starch. The slurry of starch and water was separated by centrifugation at 3000 rpm for 20 min. The obtained corn starch was dehydrated at 50 °C for 12 h in an air circulation oven (type Venticell 22, Planegg, Germany); the dried corn starch was blended and sieved to achieve uniform particle size distribution.

Corn hull fiber was obtained via the wet milling process during starch isolation. The industrial production of corn starch involves the elimination of proteins and separation of fibers resulting in purified starch and solid residues called de-starched corn hull fiber which exists in corn grain pericarp. Subsequently, the remaining fiber was washed many times with hot distilled water to remove starch molecules and then was separated by centrifugation. Either by drying in an oven or direct sunray, the hull fiber was dehydrated and converted to powder form via grinding and sieving processes.

Corn husk fiber was obtained according to Sari et al. (2016). Husks surrounding the ear of corn were soaked in condensed water for 3 days to remove the residuals and dust. The husks were thoroughly washed by fresh water and brushed with a soft plastic comb. The husks were air-dried, ground, and screened through a sieve to be in powder form. The extraction of corn stalk fiber was performed as described by Baranitharan and Mahesh (2014). Raw corn stalks were cleaned thoroughly and chopped into specific sizes; they were completely dehydrated in an oven for 12 h at 60 °C. The outer skins of the dried corn stems were separated manually. The corn stalk fiber appeared light white in color and was directly converted into powder.

Fig. 1. Extraction and preparation of corn biomass

Chemical Composition

The chemical composition of the corn samples was measured according to published methods (Razali et al. 2015; Alzorqi et al. 2017). These methods were employed to examine on dry matter the percentages of cellulose, hemicellulose, lignin, and ash of corn fibers. The amylose and amylopectin contents of starch were obtained (James 2013).

Physical Properties

Density (ρ)

A gas pycnometer AccuPyc II 1340 (Micromeritics Instrument Corp., Norcross, USA) was used to obtain the density and volume of known weight powder samples. Helium gas was used as a replacing fluid to measure volume because it has the ability to penetrate and expand through the pores into a chamber containing the sample. Density (ρ) is defined as the ratio of mass m (g) to volume v (m3) of material, as expressed by Eq. 1.

ρ (g/m3) = / v (1)

Moisture content (MC)

The moisture content of the material is defined as the amount of the water that could be removed from the material without changing the chemical composition for the main weight of the material (Jindal and Siebenmorgen 1987). The powder samples were weighed individually and then kept on an oven for 24 h at 110 °C. The weight differences before (w1) and after (w2) drying were used to obtain the MC for each sample indicated by percentage or gram/100 g as shown in Eq. 2.

MC (%) = ((w w2/ w1) × 100 (2)

Water-holding capacity (WHC)

Water-holding capacity of a substance is expressed by the ability of the material to hold over water and is indicated by the quantity of water seized by 1 g of the dehydrated material. The water-holding capacity of the maize samples was measured by a similar method explained by Kirwan et al. (1974) with insignificant modifications. A powder sample (3 g) in a pre-weighed centrifugal tube (Minitial) was submerged in 25 mL of distilled water. After centrifuging at 3000 rpm for 25 min the supernatant was disposed, and the residue was dehydrated in an air circulation oven at 50 °C for 30 min and weighed again (Mfinal). The test was repeated several times until the tested specimen reached a constant mass. Hence, the WHC percentage was obtained from the average of several measurements according to Eq. 3.

WHC (%) = ((Mfinal  Minitial) / Minitial) × 100 (3)

Particle size distribution (PSD)

A Mastersizer 2000 E Ver. 5.52 (Malvern Instruments Ltd., Worcestershire, UK) was used to find out the PSD for the samples via a built in Q-space powder feeder. The particle size for tested samples was examined through a 1000 μm sieve prior to distribution analysis.

Thermal Gravity Analyzer (TGA)

A thermogravimeter analyzer (Q500 V20.13 Build 39, Bellingham, USA) was used to record the specimens’ thermal properties. Samples with mass ranging 5 to 10 mg were placed in platinum crucibles and exposed to a temperature varied from room temperature to 450 °C at a rate of 10 °C/min-1 and under a nitrogen atmosphere. TGA measures the mass loss over time as a function of temperature.

Morphological and Structural Properties

Scanning electron microscopy (SEM)

A scanning electron microscope (Hitachi S-3400N, Nara, Japan) was employed to study the surface morphology of the samples. Before the test, the sample was soaked in nitrogen liquid and covered by a golden layer. A 20 kV voltage was applied through a high vacuum to generate a beam of electrons. The applied electrons interacted with the sample atoms creating signals containing information about surface topography and producing images with high resolution.

Fourier transform infrared spectroscopy (FT-IR)

An infrared spectrometer (Bruker vector 22, Lancashire, UK) was used to obtain the FT-IR spectrum of samples at a frequency over a broad spectral range of 4000 to 400 cm-1 with a spectral resolution of 4 cm-1. The tested samples preparation was conducted via KBr pressed-disc technique. Using 16 scans per specimen.

X-ray diffraction (XRD)

The XRD analysis was performed using a 2500 X-ray diffractometer (Rigaku, Tokyo, Japan) with a scattering speed of 0.02 (θ) s-1 within an angular range from 5° to 60° (2θ). The operating voltage and current were set to 40 kV and 35 mA, respectively.


Chemical Composition

Table 1 reveals the chemical composition of corn starch. The comparative analysis of composition indicated that corn starch is characterized by a relatively high concentration ofpolysaccharides, (amylopectin and amylose), while the amounts of extractives, such as crude fats, protein, and ash, were quite low. This formulation is consistent with the standard chemical structure of the native starch as mentioned in the previous report (Lu et al. 2009). The amylose content, the main compound of native starches, was 24.6 g/100 g. This amount is roughly equivalent to 25 g/100 g obtained in an earlier study by Chinnaswamy and Hanna (1988). Also, this amount was found within the normal range (14% to 29%) of the amylose content of all native plant starch (Bertoft 2017).

Table 1. Chemical Composition and Physical Properties of Corn Starch

Table 2. Comparison of Chemical Composition and Physical Properties of Corn Fibers with Selected Natural Fibers

Table 2 displays the chemical composition of maize fibers with a comparison to selected natural fibers. The natural fibers are composed primarily of carbohydrate polymers (cellulose and hemicellulose), aromatic polymers (lignin), and ash. Typically, cellulose acts as a primary constituent for fiber structure and plant strength (Chen 2014). Of the three fibers, corn husk contained the highest concentration of cellulose at 45.7%. This amount was slightly higher than the 43% previously discovered by Youssef et al. (2015). Corn hull cellulose content from the current study was to some extent lower than the 16% cellulose content detected by Sugawara et al. (1994). The lignin, which is responsible for flexibility and stiffness of the fiber wall (Varanasi et al. 2013), was found to be present in the corn husk at a more remarkable percentage than in the corn hull and stalk counterparts. A minor concentration of ash was observed in the composition of corn hull and husk fibers, while the ash concentration reached a noticeable amount of about 10.7 g/100g on a corn stalk.

Density (ρ) and Moisture Content (MC)

The density of each specimen was measured among the average of five replicates. As shown in Tables 1 and 2, the density values of corn starch, husk, and stalk were roughly the same at around 1.4 g/cm3, while the corn hull recorded a lower value at about 1.3 g/cm3. However, the density values obtained in this study were within the range of various natural fiber densities between 0.81 and 1.450 g/m3, as indicated in the literature (Rao and Rao 2007). The low-density of biomaterials made it more attractive for manufacturing of bio-composites in comparison with artificial composite materials, such as fiberglass (2.5 g/m3) (Mendes et al. 2015).

The moisture content of the samples was measured and included in Tables 1 and 2. Cornstalk contained the highest moisture content and reached 11.1 g/100g. Ashori et al. (2014) attributed that to the presence of the hydroxyl group in cellulose and lignin of corn stalk, whereas corn husk achieved the lowest quantity at 7.81 g/100g. However, a similar result of corn hull moisture content (8.59 g/100g) from this study was detected by Yadav et al. (2007) when the corn hull fiber was extracted through the wet milling process it was found that the moisture content reached 8.41 g/100g.

Water-Holding Capacity (WHC)

The ability of the material to absorb water is an important criterion when manufacturing composite materials because it has a great influence on dimensional stability, porosity, tensile strength, and swelling behavior of natural composite materials (Jawaid and Khalil 2011). Based on the data, corn starch, which has a hygroscopic nature, retained the lowest amount of water (22%) as compared to the fiber samples, which are characterized by a high hydrophilic nature (Munthoub and Rahman 2011). Cornstalk offered the highest amount of water retention with a value of 93.7%, while corn husk and hull counterparts recorded 78.8% and 37.4%, respectively; this observation refers to the low amount of cellulose content in the composition of the corn stalk (Ashori et al. 2014). Cellulose decreases the free volume in the fiber intermolecular chain and leads to a reduction of water penetration (Razali et al. 2015). This conclusion is compatible with its chemical composition shown in Table 2.

Particle Size Distribution (PSD)

The strength of composite materials depends on the efficiency of transferred stress between matrix and fillers. Parameters, such as particle size distribution, particle loading, and particle/matrix interfacial strength, are strongly affected on the composite strength (Fu et al. 2008). Thus, the PSD of corn starch is presented in Fig. 2a. The histogram displays that the highest percentage (43%) of starch particles had sizes of less than 10 µm, followed by 24% for the sizes within 10 to 20 µm. Nonetheless, the vast majority (89%) of the corn starch particles had sizes less than 40 µm; such results are identical to the findings of Han et al. (2009). On the other hand, corn husk and stalk exhibited a similar distribution of particle sizes. As revealed in Fig. 2c and d, both fibers showed a large particle size of 200 to 300 µm making up 42% and 39% of the total particles, respectively. Meanwhile, corn hull had larger particles with 35% having a particle size of 300 to 400. This observation is due to the presence of non-removed starch particles attached to hull fiber during the extraction process. Nevertheless, the diminishing size of fiber particles enhances the biodegradability and tensile characteristics of the composite material (Radford 1971; Zhao et al. 2013).

Fig. 2. PSD of a) corn starch, b) corn hull, c) corn husk, and d) corn stalk

Thermal Gravity Analyzer (TGA)

Thermogravimetric analysis (TGA) and differential thermogravimetry (DTG) are accurate techniques used extensively to investigate the thermal stability and evaluate the weight loss of composite materials (Guinesi et al. 2006). The TGA and DTG curves in Fig. 3a and b reveal three distinct phases of weight loss represented in the prominent peaks on the DTG curve. The first phase exhibits the loss of weight due to dehydration of water content, the second phase presents the weight loss resulting from the decomposition of the material side chains, and the third phase displays the weight loss due to the decomposition of the main chains of the material (Othman et al. 2011). For the corn starch, the first loss of weight occurred immediately after the dehydration began at a temperature slightly below 100 °C. The weight loss in this phase relies on the moisture content of the starch as a higher moisture content results in higher weight loss. The second phase began with decaying of the water-soluble amylopectin at an onset temperature (To) corresponding to 161.2 °C and continued until 281.1 °C, resulting in 66.3% weight loss. The highest rate of thermal degradation of corn starch occurred at about 450 °C leaving 16.2% residue of ash. These findings were closer to what was previously obtained by other authors (Liu et al. 2009). Regarding corn (hull, husk, and stalk) fibers, the first weight loss occurred approximately at the same temperature for the three samples at slightly above 100 ºC, as shown in Fig. 3. In the second stage, the fiber material degradation took place due to the decomposition of hemicellulose and cellulose. For all different plant fibers, cellulose content begins to deteriorate at a temperature exceeding 300 °C and dissolves into its components at about 400 °C (Yang et al. 2007). The corresponding data are shown in Table 3.

Fig. 3. a) TGA and b) DTG of corn starch, hull, husk, and stalk

Table 3. Thermal Degradation of Corn Starch, Hull, Husk and Stalk, Comparison with Cassava Biomass

The onset decomposition temperatures achieved in this study suggest that the use of corn fibers as fillers for polymer composites production is possible because the majority of polymer composites are processed at above of 180 °C (Mendes et al. 2015). In the final stage, the highest rate of thermal degradation occurred above 400 °C as a result of lignin decomposition. However, the results are well in agreement with the thermal decomposition of natural fibers, which begins with the decaying of hemicellulose (200 °C to 260 °C), cellulose (240 °C to 350 °C), and lignin (280 °C to 500 °C) (Lomelí-Ramírez et al. 2014).