3.1 FTIR Analysis
Functional groups and any potential chemical alterations upon addition of cellulose was observed using the FTIR analysis. It allows for the quick, accurate, and effective identification of functional groups (Shafqat et al.,2021). The FTIR spectra of bioplastics starch film with various cellulose loadings is illustrated in Fig. 1. Tables 2 and 3 recovered the summarized the absorption peak of the FTIR analysis for all film.
Table 2
Wavelength range of FTIR analysis of banana peel and tapioca powder
Functional Group with Wavenumber
|
Sample
|
O-H (3400-
3200 cm-1)
|
C-H (3000-
2841 cm-1)
|
C = C (1680-
1600 cm-1)
|
C-O (1300-
1000 cm-1)
|
1. Control Tapioca
|
3269
|
2888
|
1625
|
1244, 1068
|
2. Control Banana
|
3264
|
2918
|
1620
|
1264, 1059
|
Table 3
Wavelength range of FTIR analysis of different of cellulose loadings
Wavenumber
of 3g Cellulose
|
Wavenumber
of 6g Cellulose
|
Wavenumber
of 9g Cellulose
|
Wavelength range (cm-1)
|
Functional group
|
(cm-1)
|
(cm-1)
|
(cm-1)
|
|
|
3332
|
3340
|
3340
|
3700 − 2800
|
OH
|
2914
|
2890
|
2892
|
2920 − 2800
|
CH
|
1503
|
1512
|
1493
|
1520 − 1400
|
CH₂, C-H,
|
1244
|
1249
|
1220
|
1300 − 1200
|
C-O C-O-C
|
746
|
766
|
732
|
790 − 690
|
C-C and C- H from aromatic hydrogen
compounds
|
From Tables 2 and 3 shown the characteristics of peak of the starch from all bioplastics film. The presence of the OHgroup was indicated by a broad peak at around 3400 − 3200 cm-1 and a distinguished peak at 3000 − 2841 cm-1attributed to CH2 stretching vibrations (Suciyati et al.,2021). Peak observed at 1680 − 1600 cm-1 correspond to the C = O stretching of amide group in the starch. The bands shown between 1300 − 1000 cm-1 were the results of C-O stretching in the glycosidic backbone of the starches (Suciyati et al.,2021). In comparison to tapioca starch, banana peel has the highest intensity at wavenumber 2918 cm-1, indicating the stretching's of C-H bond because bananas have higher starch content at those peaks. Tapioca powder has high C = C spectra which was 1625 cm-1, that can beattributed to the stretching vibration of alkene (Olagundoye and Moray, 2022).
Furthermore, the broad band range between 3700 − 2800 cm-1, which was due to the OH stretching vibration, gives considerable information concerning the hydrogen bands, which can be correlated with the scissionof the intra- and inter-molecular hydrogen bond (Md Salim et al., 2021). Peaks that were shifted and enlarged suggest that the OH group in cellulose has a weak hydroxyl bond, which makes it possible to transform 9g of cellulose into a biocomposite material. The changes of peak at 3340 cm-1 was due to the increase of the group value by the hydrogen interaction when starch and cellulose were combined in bioplastics. The range peaks of 2920−2800 cm-1 was attributed to the CH stretching vibration. According to Md Salim et al., (2021), found that the presence of amorphous cellulose samples can be further confirmed by the shift of the band from 2920 cm-1, which corresponded to the CH stretching vibration.
Besides that, range of wavenumber 1400–1520 cm-1 shows the widening of the peak in cellulose due to the functional groups bending CH2, C-H and C-O which attributed to the aromatic skeletal ring (Suciyati et al.,2021). The spectrum associated with functional group impurity has also detected in the range of intensity of wavenumber 1050–1110 cm-1 with lipid, protein, and nucleid content (Suciyati et al.,2021). The intensity of IR absorption at the peak of 790 − 690 cm-1 indicated the stretching of C-C and stretching C- H from aromatic hydrogen compounds. The peak of 746 cm-1, 766 cm-1, 732 cm-1, was an amorphic structure in 3g cellulose, 6g cellulose and 9g cellulose.
3.2 Tensile Properties
The tensile strength, Young's Modulus, and elongation at break for bioplastics presented Figs. 2, 3 and 4 respectively. Based on Fig. 2, the tensile strength of the tapioca films showed an increment compared to tapioca/ banana from 4.49 MPa to 14.35 MPa. This is because film that contain banana peel have high fiber and high amylose content compared to tapioca itself. The addition of cellulose into the tapioca/ banana film had significantly decreased the tensile strength. Interesting to note that, the highest tensile strength for the modified film was with the addition of 6g of cellulose loading which was 5.6 MPa. This could be attributed to a good dispersion and strong interaction formed between the hydrogen bond of the starch matrix and the cellulose loadings. This condition can be attributed to the distribution of the developed stress within the filler under tensile load by the matrix and the filler reinforcement carried the tensile load which was more effective to withstand the matrix breakage (Nagaraj et al., 2020, Olagundoye & Morayo, 2022). Cellulose (9g) produced the lowest tensile strength with 1.46 MPa which was responsible for weak intermolecular interaction leading to a heterogeneous film structure and forming agglomeration. This can be attributed to weak tensile strength that indicate the insufficient bonding between the filler and banana peel at a higher filler percentage. It resulted voids and weaker strength during tensile testing (Nagaraj et al., 2020).
In the case of Young’s modulus between types of tapioca, tapioca/ banana showed the highest Young’s modulus value at 1465.74 MPa.This is because both of these sources are high in amylose content which suggests that both of these sources are used to make a bioplastic. Those made from banana peel are much stronger than those made from tapioca starch alone. Moreover, when the tapioca/ banana modified with cellulose,Young’s modulus had significantly reduced to the lowest value of 205.41 MPa. It could be attributed to the degree of dispersion and percentage of cellulose loadings in the starch matrix (Olagundoye & Morayo, 2022). The higher value of young modulus indicated vulnerability to brittleness. Similarly, interfacial adhesion between the filler and matrix might ease the transmission of loads between the filler and matrix. In addition, the increase in filler content had increased the number of interfacial regions between the filler and matrix, resulting in a greater load-bearing capability. In the case of random filler reinforcement, the increase in strength and modulus is proportional to the weight gram of filler loadings (T et al., 2019). Low young modulus in a sample containing 9g of cellulose could be attributed to poor cellulose dispersion within the starch matrix. This may be ascribed to some agglomeration of the cellulose particles when the weight was further increased. Also, the increased in the Young’s modulus may also be due to the presence of microfibrils compounds in the cellulose loadings (T et al., 2019). However, as the weight of the filler increased, it can be seen that there are some irregular distributions with some filler aggregates within the banana peel and tapioca powder matrix.
Figure 4 depicts the percentage of elongation at break for all samples. As the mixture of banana peel and tapioca starch increased in tensile strength and modulus, the elongation at break had gradually decreased. This data suggests that the decreased in elongation at break was caused by the increase in fibre content. The percentage of elongation of the control tapioca was only 0.02%, which was less than the tapioca/ banana. The elongation at break of control tapioca powder was less than that of the mixture of tapioca starch and banana peel because the control tapioca lacked the components that act as a thickening agent in the banana peel. The ratio of amylose to amylopectin in a starch also affects thickening, viscosity, solubility, and shear resistance. 6g cellulose has the highest percent of elongation at break with 0.0254% while the lowest elongation at break was at 9g of cellulose loadings with the value of 0.0103%. The percent of elongation at break reduced with the increased in the filler content. This indicates that the filler acted as a rigid component in the composites (T et al., 2019). According to Olagundoye & Morayo, (2022), a decrease in the value is possible due to molecular interaction between the O-H group of the starch and the hydroxyl and carboxylic (COOH) groups of the cellulose, which led to high tensile strength and low elongation at break for the films.
3.3 Thermogravimetric analysis (TGA)
The TGA and derivative thermogravimetric (DTG) profiles of banana peel and tapioca powder with different addition of cellulose contents starch based bioplastics films are shown in Fig. 5a,b, respectively. Both thermal studies were conducted concurrently within a temperature range of 30 to 800℃. Both films depict five instances of weight loss. The initial decrease in weight seen within the temperature range of approximately 30°C to 100°C was found to be linked to the process of free water evaporation (Azevedo et al., 2020). The second weight loss observed within the temperature range of approximately 100°C to 200°C was shown to be associated with the process of moisture evaporation from the bioplastic films (Syafri et al., 2018). Where the moisture evaporation encompasses the broader concept of any liquid transitioning into a vapor state, including substances beyond water. The weight loss range between about 200°C and 300°C observed in the study can be attributed to the thermal disintegration of starch in the bioplastic films and the degradation of glycerol, which has a boiling point of 290°C (Azevedo et al., 2020). Starch is composed of amylose particles that have the ability to undergo volatilization, resulting in the release of carbon, hydrogen, and oxygen (Wahyuningtyas et al., 2017). Between about 300°C and 500°C, the thermal decomposition process resulted in the release of substances of lower molecular weight, including plasticizer (glycerol) and additive (cellulose), with the destruction of starch. At temperatures over 500°C, the process of pyrolysis occurred, leading to the formation of inorganic substances within the residual samples (Krishnamurthy & Pavithra, 2019).
The TGA results for all of the bioplastics starch films are presented in Fig. 5a. It shown that as cellulose's composition changes, weight loss will also change from high to low. The thermal stability of the film made from a combination of banana peel and tapioca powder is also declining. This is so that after the cellulose is mix, it will be simpler to decay and lose weight because the lignin and hemicellulose structure were removed (Othman et al., 2011).
From the DTG curves shown in Fig. 5b, the results suggested that the control film and the modified film with cellulose starch based bioplastics might be subjected to the applications below 316 ℃ and 290℃, respectively, without any degradation loss in their characteristics. Most of the applications associated with this kind of bioplastics such as packaging and containers, are usally operated from the room temperature to slightly higher than 100 ℃. These operating temperature are well below the thermal stability of the bioplastics film (Tan et al., 2022). From the Table 4 below, cellulose 9g have the most stable in high thermal condition compared to other films.
Table 4
Thermal Properties of Bioplastics film
Sample
|
Degradation Temperature (℃)
|
Residual weight (%) at 700 ℃
|
T20
|
T50
|
Control
|
99.4554
|
100.504
|
16.7671
|
Control B + T
|
99.4203
|
100.474
|
17.1386
|
Cellulose 3g
|
99.3229
|
100.666
|
11.7369
|
Cellulose 6g
|
96.7743
|
97.5788
|
14.335
|
Cellulose 9g
|
99.0394
|
100.16
|
18.5547
|
3.4 Water Absorption
The purpose of the water absorption test was to identify the sample's capacity for water absorption in a given circumstance. One of the weak points of starch-based bioplastics is its poor resistance to water and moisture. Therefore, filler addition does not only aim to enhance mechanical properties but also to improve the water resistance of starch- based materials. The effects of cellulose loadings on the properties of banana peel starch bioplastics was illustrated in Fig. 6. To maintain structural integrity, composite materials must have less water absorption when used in humid environments. All samples show an increment of weight reading in the first 3 days until 9 days but when it comes to 12 daysand 15 days the sample appears to decline in the weight reading.
Bioplastic film of control tapioca has the highest value of water absorption compared to the film of tapioca/ banana. This is because different content of tapioca and banana starch were used, which this it indicates changes of percent of amylose and amylopectin content from both material. Tapioca/ banana film had the lowest value of water absorption which was due to the competition occurring in the two components of high starch and fiber content. This reduces the water absorption when fiber content increases due to the comparatively poor absorption of fibers.
An increased in cellulose fibers content resulted in a decreased in water absorption. The highest percent of water absorption shown by 3g of cellulose while 9g of cellulose has the lowest weight loss. The decrease can be attributed to the formation of hydrogen bonding between the cellulose and the hydroxyl functional group of the starch matrix. The resulting hydrogen-bonded network of cellulose with the starch in the composite could have prevented the formation of voids where water molecules can pass through.
3.5 Swelling Behaviour
Figure 7 shows the result of the swelling test ofstarch bioplastics with different cellulose loadings. There is not much change in the integrity of bioplastic film when it was soaked in chloroform and methanol solvents. However, there was a slight increase in the weight of bioplastic film when it was soaked in water has made it a reliable material than other materials (Jayachandra et al.,2016).
It was observed that, distilled water has the highest potential of swelling. All samples from control tapioca powder to 9g of cellulose loading displayed excellent swelling behavior in distilled water. However, the samples immersed in methanol and chloroform only shows slightdifferences. The major qualities used to determine if a bioplastic material is
sustainable are engorgement and solubility. If the bioplastic material has a low or zero engorgement property, it can be called an excellent material with stability which is a distinguishing quality. However, if the bioplastic material swells or engorges excessively, it will be regarded as a low-quality material. Less swell formation in the prepared bioplastic material when soaked in chloroform and methanol containing medium, but swells slightly higher in water since most additives are prepared using organic solvents, and it will easily aid in the stabilization of product synthesis and development.
Cellulose 3g has highest swelling properties in distilled water while 9g cellulose was the least swell towards water. Cellulose is hydrophilic and readily absorbs water in the amorphous regions. It is believed that water could be absorbed by cellulose materials. However, because of the significantly higher crystallinity of individual cellulosemicrofibrils and higher fiber or resin hydrogen bonding, water absorption of cellulose-reinforced starch composite could be lower compared to pure starch resin (Fu & Netravali, 2020).
3.6 Solubility Behaviour
Solubility test helps to determine how much solute is or can be dissolved in a solvent at equilibrium. Solubility is also another important characteristic feature, where it is essential to have bioplastic material which is less soluble in water than any other organic solvents. Insoluble property of the bioplastic material in water medium is promising for the synthesis of economically viable product development and because of the unbroken nature of these biopolymers has made it a sustainable product.
Table 5
Solubility result after 72 hours
Sample No.
|
Solvents used
|
|
|
Solubility test
|
|
|
|
|
Insoluble
|
Partially
|
|
Fully soluble
|
|
|
|
|
soluble
|
|
|
1.
|
Acetic acid
|
+
|
|
-
|
-
|
|
2.
|
Ammonia
|
-
|
|
+
|
-
|
|
3.
|
Sulphuric acid
|
-
|
|
-
|
+
|
|