Extraction and fabrication of starch-based reinforced bioplastics from potato : Circular and sustainability aspects

Abstract

Biodegradable bioplastic films have emerged as promising alternatives to conventional plastics due to their environmental benefits. However, starch-based bioplastics often exhibit poor mechanical properties, which limit their practical applications. The incorporation of reinforcing agents can enhance these properties while promoting sustainability. This study aims to investigate the mechanical properties and biodegradability of starch-based bioplastic films reinforced with organic waste fillers, including eggshell, sawdust, and biochar. The films were fabricated from isolated potato starch, glycerol, vinegar, and water using a starch:glycerol:vinegar:water weight ratio of 1:0.23:0.23:10, with 10% weight by weight (w/w) filler reinforcement. Mechanical properties were evaluated using a universal testing machine (UTM). Functional groups were analyzed by Fourier Transform Infrared (FTIR) spectroscopy, and biodegradability was assessed through soil burial tests. Sawdust reinforced films (SD) exhibited a significantly higher tensile strength of 5.7 ± 0.510 MPa and a Young’s modulus of 130 ± 2.050 MPa compared with the control pure starch film (PS), which showed 1.9 ± 0.352 MPa tensile strength and 13.7 ± 0.456 MPa Young’s modulus. FTIR spectra confirmed the presence of functional groups conducive to biodegradation. Soil burial tests revealed up to 36% mass loss within 15 days, indicating substantial biodegradability. The integration of organic waste fillers, particularly sawdust, significantly enhances the mechanical and biodegradation properties of starch-based bioplastics. These findings support the potential of organic waste reinforcements for developing sustainable and biodegradable plastic alternatives.

Graphical Abstract

Keywords

bioplastic film mechanical properties reinforced bioplastics biodegradability circular economy

Highlights

• Potato starch successfully extracted in its grounded form for bioplastic preparation.

• Bioplastic films formulated using starch, glycerol, vinegar, water, and organic waste reinforcements.

• Fabricated reinforced films characterized for their mechanical and structural properties.

• Biodegradability of developed films assessed through soil burial under natural conditions.

Introduction

The growing environmental impact of petroleum-based plastics has intensified the global demand for sustainable alternatives.^1,2 Conventional petrochemical plastics derived from fossil fuels, are non-biodegradable and persist in the natural environment for decades, contributing to plastic pollution, ecological degradation, and adverse health effects.^3–5 The accumulation of plastic waste in sanitary landfills and watercourse ecosystems, along with the rising presence of microplastics, underscores the urgent need for eco-friendly materials.^6–8 In response, bioplastics made from renewable resources have emerged as promising alternatives, offering reduced carbon footprints, enhanced biodegradability, and support for a circular economy.^9–11 A polymeric material is considered bioplastic if it is derived from renewable resources or has the potential for biodegradability.^10,12,13 Among bioplastics, starch-based materials are particularly appealing due to their abundant availability, eco-friendliness, and biodegradability.^14–16 These bioplastics are produced using renewable resources such as potatoes, corn, sweet potato, rice, soy, yam, sugarcane, wheat, and vegetable oil.^17–19 Notably, potato is a promising source of starch primarily composed of polysaccharides containing amylose (17%–24%) and amylopectin (76%–83%). Its high biodegradability is attributed to its susceptibility to enzymatic attack.^10,20,21

However, they face several limitations, including poor mechanical strength, high water absorption, and limited durability, which hinder their widespread application.^15,22,23 To overcome these challenges, various reinforcement strategies have been explored, including natural fibers such as jute, flax and nanoparticles as titanium dioxide, silica, to enhance mechanical properties, thermal stability, and moisture resistance.^24–27 Despite their effectiveness, these reinforcements pose challenges such as poor compatibility with the starch matrix, moisture sensitivity, and environmental concerns related to nanoparticle disposal.^28–30

Recent studies have focused on integrating renewable fillers, particularly from industrial and agricultural waste, to enhance the mechanical properties and sustainability of starch-based bioplastics.^31–33 Organic waste materials, such as sawdust, eggshells, and biochar, have gained attention due to their rich cellulose, lignin, hemicellulose, and calcium carbonate content, which offer potential for mechanical reinforcement and improved biodegradability.^33–37 Additionally, utilizing these organic waste fillers promotes waste valorization, supports circular economy practices, and reduces environmental pollution.^29,38

Although several studies have investigated the use of natural fibers and nanoparticles as reinforcing agents, limited research has focused on the effects of waste fillers such as sawdust, eggshells, and biochar on starch-based bioplastics.^39–41 Individually, sawdust enhances tensile strength and thermal stability, eggshell improves mechanical strength, and biochar contributes to moisture resistance and structural integrity.^42–44 A study on potato starch-based bioplastics reinforced with organic and inorganic fillers such as charcoal, metal powder, and calcium sulfate by Thakkar et al.⁴⁵ reported various properties of the developed films, including moisture absorption, moisture content, tensile strength, elongation at break, biodegradability, and FTIR characteristics. However, to the best of our knowledge, the influence of these organic waste fillers on the mechanical properties and model of biodegradable kinetics of the synthesized films has not been extensively investigated in the literature.

The objectives of this study are to extract potato starch, fabricate reinforced bioplastic films, characterize them using Fourier Transform Infrared (FTIR) spectroscopy, evaluate their key mechanical properties including tensile strength, Young’s modulus, and elongation at break and assess their biodegradability under natural soil conditions. The novelty of this study lies in the utilization of organic waste fillers (both individually and combined), specifically sawdust and eggshells containing cellulose and calcium carbonate, to enhance the film properties while simultaneously investigating their effects on the mechanical and structural properties of starch-based bioplastic films, as well as determining the biodegradation rate constant (k) through fitting of the experimental data. The integration of these filler materials advances sustainable material design and provides a kinetic understanding of biodegradation behavior under real-world conditions. Overall, this study supports the development of eco-friendly starch-based bioplastics for packaging, mulching, and nursery bags, offering a viable pathway to reduce plastic pollution and promote environmental sustainability.

Materials and methods

Materials

The experimental work intends to investigate the utilization of widely available and abundant resource potatoes served as the primary material for fabricating bioplastic films. The required materials included glycerol, natural vinegar, and distilled water. Additionally, eggshells were washed, dried, ground into a fine powder, and sieved through a 100-mesh screen to ensure consistency. Similarly, sawdust collected from a local sawmill was sieved and thermally processed for 1 hour to produce biochar, which was also sieved through a 100-mesh screen to achieve uniformity.

Five types of bioplastic films were developed: sawdust reinforced bioplastic film (SD), biochar reinforced bioplastic film (BC), eggshell reinforced bioplastic film (ES), eggshell and sawdust combined reinforced bioplastic film (ES + SD), and pure potato starch bioplastic film (PS) as the control.

Extraction of starch from potato

This study followed the method outlined by Kovac et al.⁴⁶ for the isolation of potato starch. The procedure for extraction of starch from potatoes commenced with an initial thorough washing of the raw potato using tap water, followed by an additional wash with distilled water to ensure cleanliness. Subsequently, the potatoes were sliced into small pieces and ground using a blender, with a ratio of 0.5 kg of potatoes to 500 mL of distilled water. The grinding process was carried out for approximately 60 s. The resulting mixture was then filtered through a sieve to segregate the liquid from the solid matter. The filtered liquid was left to settle undisturbed at room temperature for 2 h. Once the sedimentation was complete, the supernatant (clear liquid) was carefully decanted, leaving behind the solid residue, which constituted the wet starch. This residue was left to dry at room temperature (20°C ± 5) for 2 days. After drying, the starch was gently pulverized into a fine powder using a grinder. A schematic representation of the various stages involved in the starch isolation process presented in Figure 1. The pulverized starch powder was stored in an airtight plastic container to prevent moisture absorption and contamination, ensuring its quality for subsequent analyses.

Figure 1.

The schematic illustrates involved in the isolation of potato starch: (a) cleaned potato ready for grinding to make the slurry; (b) sedimented semi-solid starch; (c) dried starch; (d) dried starch ready to ground; and (e) pulverized starch powder.

Formulation and fabrication of film

A bioplastic film was fabricated using potato starch powder, glycerol, vinegar or citric acid, and distilled water.⁴⁷ The blending process was conducted on a weight basis, incorporating starch powder, glycerin (Pure Glycerin, Malaysia), vinegar (Cuka Bhutan artificial vinegar, diluted acetic acid), and distilled water. The formulation was modified from the work of Kasmuri et al.⁴⁸ proportions, at 10g starch, mass of vinegar equals to 2.3 g, mass of glycerol equals to 2.3 g, and 100g or 100 ml of distilled water has required for the fabrication.⁴⁸ The amount of distilled water considered in the formulation was 10 times the weight of the starch. Based on the amount of starch utilizing, the corresponding masses of the other components are determined respective to the empirical ratio:

{(C_{6} H_{10} O_{5})}_{n} : {CH}_{3} COOH : C_{3} H_{8} O_{3} : H_{2} O = 1 : 0.23 : 0.23 : 10

(1)

This ratio provides a scalable framework, allowing the formulation to be proportionally adjusted according to the desired starch input while maintaining consistent composition and performance characteristics.

Sawdust was incorporated as a reinforcing agent at 10% of the starch mass, while eggshell and biochar were added in equivalent proportions, as detailed in Table 1. In the ES + SD formulation, the total reinforcement content (1.0 g) was evenly distributed between eggshell and sawdust (0.5 g each). The proportion of reinforcing materials was adjusted based on previous works.^48,49

Table 1.

Formulation ingredients in fabrication of bioplastics.

Formulation code	Starch (g)	Glycerol (g)	Vinegar (g)	Distilled water (g) (10 × starch)	Reinforcement content (g)	Reinforcement type
SD	10	2.3	2.3	100	1	Sawdust
BC	10	2.3	2.3	100	1	Biochar
ES	10	2.3	2.3	100	1	Eggshell
ES + SD	10	2.3	2.3	100	0.5/0.5	Eggshell + sawdust
PS	10	2.3	2.3	100	0	None

The mixture was uniformly heated to approximately 80°C together with continuously stirred until gelatinization occurred. Afterwards gelatinized, the sticky jelly or obtained starch paste was evenly poured and spread across the surface of a steel plate. The paste-coated plate was then placed in front of a heater and allowed to dry for 6 hours, facilitating the formation of the bioplastic film. After the drying process was complete, the bioplastic film was carefully detached from the steel plate by hand. To preserve its structural and chemical integrity, the film was stored in an airtight plastic container at room temperature. Figure 2 illustrates the drying processes and synthesized bioplastic films. A potential chemical equation at blending:

{(C_{6} H_{10} O_{5})}_{n} + H_{2} O + {CH}_{3} COOH + C_{3} H_{8} O_{3} \overset{heat + stirring}{\to} Plasticized starch hydrogel

(2)

Figure 2.

Bioplastic fabrication: (a) drying process; (b) SD reinforced bioplastic film; (c) fabricated plain potato starch (PS) bioplastic film control.

This reaction (2) represents the plasticization of starch to form a starch-based hydrogel. (C₆H₁₀O₅)_n starch (a polysaccharide composed of glucose units), H₂O (water) helps in gelatinization by swelling starch granules, CH₃COOH (acetic acid/vinegar) acts as a mild acid catalyst, aiding starch chain mobility and partial hydrolysis, C₃H₈O₃ (glycerol) serves as a plasticizer, reducing intermolecular hydrogen bonding and increasing flexibility.

By systematically following this standardized procedure, the study ensures the resynthesized of bioplastic film, thereby enhancing the reliability and validity of the experimental results. This methodical approach is consistent with established formulation of prior work, promoting uniformity and enabling meaningful comparisons in subsequent research endeavors. However, by adjusting the concentration of the ingredients, the material properties can be tuned to meet specific requirements.

Thickness and density measurement of bioplastics

The thickness of the bioplastic films was measured using a micrometer and validated with a digital vernier caliper with a least count of 0.01 mm (Brand-Jiavarry, model 20-F). Figure 3 shows a typical measurement of the film’s thickness. For each sample, three measurements were taken, and the average thickness was calculated. Density was calculated by first weighing each sample and then determining its volume using measured dimensions length, breadth, and thickness.⁵⁰ The density was subsequently determined using an equation (3):

Density of the film (ρ) = \frac{M}{V} (g / {cm}^{3})

(3)

Where, M stands for mass of the sample (weight in g) and V stands for volume of the bioplastic sample cm³.

Figure 3.

Measurement of film thickness: (a) thickness measurement using a micrometer of bioplastics film; (b) thickness measurement using a vernier caliper; (c) thickness measurement of plain potato starch control.

Mechanical properties of the bioplastic film

After the fabrication of the bioplastic film, a tensile test was conducted in the laboratory to evaluate its mechanical properties, specifically tensile strength (TS), elongation, and Young’s modulus (E). The test was performed following ASTM D-638, the standard for determining the mechanical properties of bioplastics.

Initially, three samples from each of the five types of bioplastics were prepared, with dimensions ranging from 120 mm × 40 mm to 200 mm × 42 mm. Each sample was securely clamped in the grips of a computer-controlled Universal Testing Machine (Cheng Yu Model WDW-100D, China) and tested at a crosshead speed of 10 mm/min until failure, as illustrated in Figure 4. During testing, applied loads, gauge length, width, and elongation were recorded both manually and digitally using UTM software. Each specimen underwent uniaxial extension at a constant strain rate until failure. The maximum recorded tensile force was used to determine the ultimate tensile strength, while the rupture point was analyzed to assess elongation at break. The key mechanical properties ultimate tensile strength obtained using the equation (4), elongation at break computed using the equation (5), and Young’s modulus were calculated using the equation (6).

Ultimate Tensile Strength (TS) = \frac{F}{A} (MPa)

(4)

Elongation at Break (%) = \frac{(L_{1} - L_{°})}{L_{°}} \times 100

(5)

Young ’ s Modulus (E) = \frac{Stress}{Strain} = \frac{\frac{F}{A}}{\frac{(L_{1} - L_{°})}{L_{°}}} (MPa)

(6)

Where, E stands for Young’s Modulus (MPa), F stands for the maximum force applied (N), A stands for the initial cross-sectional area of the bioplastic (mm²), L₁ is the final length at the rupture point of the bioplastic after fracture (mm), and L₀ is the initial length of the bioplastic (mm). This procedure was repeated for the remaining bioplastic samples. All recorded data were subsequently analyzed, averaged, and used to plot graphs comparing the results across the different types of bioplastics.

Figure 4.

Tensile testing: (a) specimens prepared for testing; (b) BC reinforced specimen; (c) specimen secured in the jaw, ready for tensile testing using a UTM; (d) testing conducted with a universal testing machine.

Fourier Transform Infrared (FTIR) test of bioplastics

Fourier Transform Infrared (FTIR) Spectroscopy is a critical analytical technique used to identify the molecular structure, functional groups, and chemical composition of various materials, including organic, polymeric, and, in some cases, inorganic substances.^51,52 FTIR (Nicolet Summit Lite, Thermo Fisher Scientific, USA) test was conducted according to the ASTM E168. A 20 mm × 20 mm sample was precisely cut into a square shape and carefully placed on the sample plate. The FTIR generates peaks and spectra that serve as a unique fingerprint for identifying specific molecular structures and chemical bonds.⁵³ A reference database is necessary for interpreting FTIR results, and several research papers on FTIR analysis were referred for the same.^54–56

Biodegradation behavior test

The biodegradation test was performed using the soil burial method, a simple and effective technique for evaluating bioplastic degradation. One of the most straightforward ways to assess biodegradability is by measuring mass loss, which indicates how much of the material has broken down over time. This process involves weighing the bioplastic samples before and after a specified degradation period to determine the extent of mass reduction.⁵⁷ The test was conducted in vitro, using soil as the environmental medium, and followed standard procedures recommended by the American Society for Testing and Materials (ASTM). Biodegradable plastics, are materials that degrade through the activity of natural microorganisms, including algae, bacteria, and fungi, making them an environmentally friendly alternative to conventional plastics.^10,58 Each sample was cut into 4 cm × 4 cm pieces, and its initial weight was recorded before burial. The samples were then buried in an open, sunlit place at a depth of approximately 3 cm for 15 days under natural, open environmental conditions to observe their biodegradation process.⁵⁷ After 15 days, the samples were dig up from the soil, and their final weight was measured. Biodegradability indication was assessed with visual examination and based on the bioplastics weight reduction as using an equation (7):

Weight Loss (%) = \frac{(W_{1} - W_{2})}{W_{1}} \times 100

(7)

Where: W₁ represents the initial weight of the sample before burial, and W₂ represents the final weight of the sample after burial.

Biodegradation kinetics curve fitting

The degradation rate is assumed to be directly proportional to the amount of material (bioplastic film) yet to degrade:

\frac{dW}{dt} = k [W_{\infty} - W (t)]

(8)

This is the standard first-order kinetic form, where k is the first-order rate constant:

W (t) = W_{\infty} . (1 - e^{- k . t})

(9)

When n = 1, describes ideal first-order kinetics. For n ≠ 1, the equation becomes a generalized first-order model, where n accounts for deviations from ideal first-order behavior due to environmental or material heterogeneity. In this study, the mass loss data of the buried films were fitted to the generalized model:

W (t) = W_{\infty} . (1 - e^{{- (k . t)}^{n}})

(10)

Here, in the equation (10) W(t) is the mass loss (%) at time t (days), W∞ is the maximum mass loss (%), k is the rate constant (per day), and n is the empirical reaction order.⁵⁹ The fitting was performed using nonlinear regression in python. The fitted k values were obtained for each film type (PS, BC, ES, SD, and SD + ES), and the quality of fit was evaluated using the coefficient of determination (R²) and residual analysis.

Results

Thickness and density of bioplastic film

Thickness and density of the bioplastic films has depicted in Table 2. The thickness of the bioplastic films increased with higher solid content and was also influenced by the solution’s volume and surface area in the mold.⁵⁷ The thickness of the film increased with the addition of reinforcing materials, likely due to the particle size of the reinforcements. A similar observation was reported by Oluwasina et al.,⁶⁰ who noted that film thickness tended to rise as more materials were incorporated into starch-based film formulations. The results reveal differing relationship between density and thickness, where higher density of PS control appears more compact and thinner, while lower density films ES are thicker and less compact. This correlation arises because an increase in thickness results in a larger volume, leading to a reduction in density, this is in agreement with those reported by Razavi et al.⁶¹ and Tarique et al.⁶² A study by Nigam et al.⁵⁰ reported thickness of 0.181 to 0.259 mm and density 1.33-1.54 g/cm³ of bioplastic films produced from parthenium hysterophorus by incorporating a plasticizer (PEG600). Furthermore, this study confirms that the results obtained aligned with expectations and support a differing relationship between thickness and density. However, density is influenced by the degree of crystallinity in the material. Bioplastics with amorphous molecular structures exhibit lower density than their crystalline counterparts, as increased crystallinity leads to tighter molecular packing and consequently higher density.⁶³ Moderate physical properties were observed in SD and BC reinforced, while ES + SD combined reinforcement demonstrate a balance between density and thickness, indicating variations in material packing and porosity.

Table 2.

Density and thickness of films.

Description	Density (g/cm³)	Thickness (mm)	Correlation
SD	1.356 ± 0.097	0.21 ± 0.001	Slightly higher density than ES but lower thickness, indicating better material packing
BC	1.689 ± 0.048	0.17 ± 0.001	Similar thickness to PS control but lower density, suggesting some porosity
ES	1.246 ± 0.061	0.23 ± 0.001	Lowest density, highest thickness, suggesting a less compact structure
ES + SD	1.587 ± 0.128	0.21 ± 0.001	Intermediate density and thickness, indicating a balance between material compactness and flexibility
PS control	2.763 ± 0.106	0.17 ± 0.001	Highest density, lowest thickness, implying a very compact structure

Fourier Transform Infrared (FTIR) spectroscopy of bioplastic film

The FTIR analysis of the plain starch (PS) control and reinforced films (BC, SD, ES, and SD + ES) reveals almost similar key peaks, as shown in Figure 5. Key absorption peaks corresponding to hydroxyl (O-H), carbonyl (C=O), and triple-bonded groups (C≡C or C≡N), suggest hydrogen bonding, structural stability, and intermolecular interactions. These characteristics enhance the films’ strength while maintaining their molecular structure.⁶⁴ The broad and intense absorption around 3680 cm^-1 is typically associated with O-H stretching vibrations, frequently from hydroxyl groups present in starch, cellulose, or moisture content in the films. Such a sharp band indicates hydrogen bonded or free -OH groups, common in biopolymers.⁶⁵ Similar absorption peaks have previously been reported in starch-based bioplastic samples.⁴⁹ The absorption near 2141 cm^-1, this region corresponds to C≡N (nitrile) stretching or sometimes C≡C (alkyne) stretching in bioplastic formulations, possibly arising from additives or degradation products introduced during reinforcement or processing.⁶⁶ These groups can influence chemical reactivity, but their presence alone does not indicate biodegradability, which is primarily governed by hydroxyl and carbonyl functionalities.⁶⁷ The absorption near 1700 cm^-1 corresponds to C=O stretching vibrations, typically associated with carbonyl containing groups such as aldehydes, ketones, esters, carboxylic acids, or amides. In reinforced films, the increased intensity of this band suggests the introduction of additional carbonyl functionalities, which may enhance biodegradability by facilitating hydrolytic and microbial degradation, particularly through ester bond cleavage.¹⁷ Additionally, PS and BC indicate the peak at 488 cm⁻¹ and suggest metal oxygen bonds and are attributed to Si-O bending vibration.⁶⁸

Figure 5.

FTIR Spectroscopy of bioplastic films: PS (pure potato starch film) control (Black line); BC reinforced film (Red line); SD reinforced film (Green line); ES reinforced film (Blue line); ES + SD reinforced film (Purple line).

A study by Tan et al.⁴⁹ developed chitosan-reinforced starch-based bioplastic film and peak observed 3276.45 cm⁻¹ suggests strong intermolecular hydrogen bonding, 3925.32 cm⁻¹ strong free (O-H) stretching, 1643.04 cm⁻¹ (C=O) stretching, confirming the presence of amide or carboxyl groups. Jangong et al.⁶⁶ investigated starch/chitosan reinforced polypropylene as biodegradable film performed FTIR test to identify functional groups, and the analysis results indicate that the primary bonds present are (O-H) hydrogen bonds (carboxylic acid), (C-H) alkanes, (C=C) alkenes, and (C-O) alcohols. Additionally, study on synthesis and characterization of biodegradable starch-based bioplastics by Ismail et al.¹⁷ found major absorption peaks which are (O-H) stretch, (C-H) stretch, (C=O) stretch and (C-O) stretch. Based on observed peak analysis and prior studies report, as a result the materials synthesized in this study validate biodegradable bioplastics, as evidenced by the presence of characteristic functional groups.⁶⁹ Furthermore, the presence of -OH and C-H stretching vibrations indicates strong compatibility between the starch and the filler materials.⁷⁰

Mechanical properties of bioplastic film

Tensile strength

The tensile strength of the film represents the maximum stress it can withstand during a tensile test.⁷¹ The incorporation of SD, which exhibits porosity in the range of 0.79 to 0.84, this porous architecture not only provided numerous active sites for monosaccharides adsorption and promote intramolecular force supporting glycosidic bonds alongside facilitated the integration of holocellulose (comprising cellulose and hemicellulose, both polysaccharides) within the sawdust structure, leading to an increase in tensile strength.⁷² The hydroxyl groups in starch, along with the aldehyde and hydroxyl functional groups in the dialdehyde starch reinforcement material, likely facilitate the formation of both intermolecular and intramolecular hydrogen bonds, strengthening crosslinking interactions between the filler material and the polymer matrix.⁷³ Additionally, strong interactions between starch polysaccharides (amylose and amylopectin) and lignin and cellulose induce a crosslinking effect, which reduces free volume and restricts the molecular mobility of the polymer chains.⁷⁴ These behaviors contribute to the enhancement of tensile strength, as demonstrated by the results, which show that SD reinforced bioplastics exhibit the highest tensile strength of 5.7 ± 0.51 MPa. The combination of ES and SD demonstrates moderate tensile strength, performing better than the PS control but lower than SD reinforcement alone. BC reinforced bioplastics rank the weakest. According to tensile strength test results on bioplastics made from different starch types, most bioplastics meet the minimum biodegradable plastic tensile strength standard of 13.7 MPa (SNI 7818:2014).⁷⁵ However, none of the treatments met this tensile strength standard, as shown in Figure 6.

Figure 6.

Tensile strength of starch-based bioplastic films prepared with different reinforcement: SD reinforced, BC reinforced, ES reinforced, combined ES + SD reinforced, and pure potato starch (PS) control film.

The tensile strength recorded in previous studies has depicted in Table 3, validating that the combined effect of organic waste SD and ES posing nature as blocking water penetration due to their hydrophobic nature plays a significant role in improving tensile strength in bioplastic fabrication.²²

Table 3.

Some of the similar prior studies recorded tensile strength.

Materials used	Tensile strength (MPa)	Reference
Polyester with eggshell (35 wt.%) & sawdust (35 wt.%)	Improved by 13% (sawdust), 10% (eggshell)	⁴¹
Potato starch-based bioplastic with eggshells & chitosan	Improved by 4.94% (eggshell), 1.28% (chitosan)	⁴⁸
Starch-based bioplastic with dialdehyde starch & silica	1.63-3.06 MPa (dialdehyde starch)	²⁵
Potato and yam starch-based bioplastic	0.6 MPa (potato), 1.9 MPa (Yam)	¹⁷
Dent corn starch-based bioplastic with glycerol	2.58 MPa	⁷⁶
Synthesized using titanium dioxide nanoparticles with corn starch	3.95 MPa	⁷⁷
Potato starch film with glycerol	4.2 MPa (optimized with 7.1 g starch, 0.5 ml glycerol)	⁷⁸
Sweet potato starch	3.29 MPa	⁷⁹
Chitosan reinforced starch-based bioplastic	5.19 MPa	⁴⁹
Starch-based bioplastics (reinforced with lemongrass essential oil)	2.08 MPa	⁸⁰
Potato starch with sawdust	5.7 MPa	This work

Elongation at break

Elongation refers to the increase in length from its original state to the maximum stretchable limit of the bioplastic.⁸¹ The elongation result for all formulation has presented in Figure 7.

Figure 7.

Elongation at break of the bioplastic films: SD reinforced, BC reinforced, ES reinforced, ES + SD reinforced, and pure/plain potato starch (PS) bioplastic.

BC reinforced bioplastic emerges as the most flexible, achieving an optimal balance between reinforcement and elasticity of 25.48 ± 9.45%. The surface of the biochar particles appeared rough or irregular, showcasing features such as cracks, crevices, and fissures along with a porous structure. This porous architecture provides numerous active sites for monosaccharide adsorption and also facilitates the integration of monosaccharides within the biochar structure, supporting the promotion of glycosidic bonds. Additionally, the amylopectin in starch acted as a plasticizer, enhancing the molecular mobility of the polymer chains and contributing to greater elongation.^43,49 The ES and SD combination exhibits moderate flexibility, permitting a reasonable amount of stretching before breaking. In contrast, both PS control and ES reinforced bioplastics demonstrate lower flexibility, resulting in average stretchability. SD stands out as the least flexible option, failing under minimal elongation.

Dami et al.⁸¹ reported an elongation of 4.47% in the bioplastic synthesized from sorghum Eucheuma spinosum, modified with sorghum stalk powder filler. Similar study by Ismail et al.¹⁷ reported that potato starch-based bioplastics poses 1.66% elongation at break. According to the elongation at break test results for bioplastics made from different types of starch, most bioplastics fall within the biodegradable plastic elongation standard range of 400%–1120% (SNI 7818:2014).⁷⁵

Young’s modulus

Young’s Modulus, illustrated in Figure 8, measures a material’s stiffness and its resistance to deformation, with higher values indicating greater stiffness and lower values signifying enhanced flexibility. Among the treatments, SD reinforced bioplastic exhibits the highest stiffness (130 ± 2.050 MPa), making it the most rigid option. This rigidity is somehow attributed due to the presence of holocellulose (60.1% to 70.4%) and lignin (20.5% to 25.8%), which resemble the base material and promote intramolecular force in glycosidic bonds.⁸²

Figure 8.

Young’s modulus of the bioplastic films: SD reinforced, BC reinforced, ES reinforced, ES + SD reinforced, and pure/plain potato starch (PS) bioplastic.

The combination of ES and SD reinforced bioplastics, along with PS control, presents moderate stiffness, striking a balance between flexibility and rigidity. SD (cellulose) and ES (CaCO₃) reinforce starch-based bioplastics by increasing crystallinity, aligning polymer chains, reducing free volume, and enhancing stiffness, rigidity, and resistance to deformation.⁸³ ES reinforced bioplastic shows moderate both stiffness and flexibility relative to other treatments. Notably, BC reinforced bioplastic demonstrates the least stiffness, signifying the greatest level of flexibility, as it deforms readily under applied stress. The SD reinforced film shows significantly high Young’s Modulus to previous study by Kwaasniewska et al.³³ reported 52.36 MPa. A comparison of the properties of sorghum filler-based bioplastics, bioplastic films produced from Parthenium hysterophorus by incorporating a plasticizer (PEG600), and organic waste filler-based bioplastics is shown in Table 4. Even with organic waste reinforcement, bioplastics exhibit properties suitable for specific applications. While organic waste-based bioplastics offer higher flexibility (elongation 5%–25%), making them ideal for packaging, sorghum-filled bioplastics provide superior strength (22.27 MPa) for structural applications. Plasticized bioplastics (PEG600) balance strength and flexibility, making them versatile for moderate load uses like biodegradable containers.

Table 4.

Comparison of the mechanical properties of bioplastics incorporating filler-sorghum, plasticizer (PEG600), and filler-organic waste.

Mechanical properties	Bioplastics (filler-Sorghum)⁸¹	Bioplastics plasticizer (PEG600)⁵⁰	Bioplastics (filler-organic waste) This work
Tensile strength, MPa	22.27	8.7-11.5	0.98-5.7
Elongation, %	4.47	2.86-9.13	5-25
Young’s modulus, MPa	498.64	131-170	4-130
Density, g.cm⁻³	0.95	1.33-1.54	1.35-2.76

Biodegradation behavior of bioplastic film

Biodegradability is an end-of-life property and strongly depends on environmental conditions such as temperature, the presence of microorganisms, and the availability of oxygen and water.^9,10 The biodegradation test revealed that incorporating SD (cellulose) most likely catalyzed the films’ biodegradability, whereas the addition of ES (CaCO₃) slightly slowed degradation due to the increased hydrophobicity of the bioplastic films’ surface matrix.⁸³ Figure 9 shows the biodegradation stages of bioplastic films in natural earth soil. The initial phase of the biodegradation has shown in Figure 9(a) placed in natural soil without any noticeable structural change. The material remained intact, indicating the beginning of the biodegradation process. Early degradation of the bioplastic films was observed in the day 10 and shown in Figure 9(b). Minor microbial activity had started, but no significant weight loss was recorded yet. Some noticeable surface changes or morphological alterations were noticed. Active Biodegradation observed in the Day 15 and has shown in the Figure 9(c). Fragmentation, structural changes and microbial activity became more prominent in the films. The surface of the film appeared fragmented or showed holes due to enzymatic action. This phase suggested that the material was undergoing active biodegradation. The Figure 9(d) shows the close-up reveals alterations in the film’s morphological structure, indicating that the enzymatic action is in an active stage.

Figure 9.

Biodegradation of bioplastic films: (a) Specimen remained intact after 5 days burial in soil; (b) early degradation stage showing minor morphological changes; (c) active disintegration phase; (d) close-up of fragmented film.

The mass loss at this stage ranged between 25% and 36% as presented in Figure 10, indicating effective breakdown of the material. A study by Tan et al.⁴⁹ investigated that chitosan reinforced starch-based bioplastic film exhibited 52.1% degradation in 28 days. Furthermore, similar study by Ismail et al.¹⁷ reported that bioplastics fabricated from potato starch undergoes 26% degradation over the 5 days period, while this study took 15 days to achieve similar degree of degradation.

Figure 10.

Biodegradation of all formulations: SD reinforced, PS pure starch, ES eggshell reinforced, hybrid (SD + ES), BC reinforced bioplastic films (5-Day; 10-Day; and 15-Day).

Mass loss analysis and biodegradation kinetics

After 15-days burial period, all specimens (PS, BC, ES, SD, and SD + ES) were unearthed, and their weights were measured. The percentage of mass loss was calculated based on the initial and final weights, as described in equation (7). The kinetics of biodegradation of the fabricated films are fitted to the model in the equation (11) presented in Figure 11.

W (t) = W_{\infty} . (1 - e^{{- (k . t)}^{3}})

(11)

Where, W(t) is the percentage of the mass loss at a time t (days), W∞ = 100 is the total mass loss percentage, and k as the rate constant. The fitted rate constants are PS (k = 0.04393), BC (k = 0.04848), ES (k = 0.04367), SD (k = 0.04682) and SD + ES (k = 0.04489).

Figure 11.

The biodegradation kinetics of all formulations are presented as mass loss versus time (in days), with fitted curves based on the $W (t) = W_{\infty} . (1 - e^{{- (k . t)}^{3}})$ model. The reaction constants are PS (k = 0.04393), BC (k = 0.04848), ES (k = 0.04367), SD (k = 0.04682) and SD + ES (k = 0.04489).

Discussion

The enhancement in tensile strength likely attributed with the incorporation of sawdust (SD), whose chemical constituent’s cellulose, hemicellulose, and lignin co-agglomerate with the polysaccharides (present in potato starch, namely amylose and amylopectin) develop the synergistic interaction promotes stronger intermolecular bonding, thereby improving the material’s mechanical strength.^20,44,84 In contrast, BC reinforcement promoted flexibility due to its porous structure, which facilitates better stress distribution and enhances the films’ ability to deform under stress.³⁷ ES reinforcement increased tensile strength but reduced elongation at break, likely due to its calcium carbonate content, which contributes to increased stiffness.⁸⁵ BC reinforced films degraded more rapidly, likely due to enhanced microbial colonization facilitated by their porous structure.⁸⁶ In contrast, ES reinforced films showed slower degradation, likely due to their higher density, which resists microbial attack. The combination of SD and ES provided a balanced profile of mechanical durability and biodegradability, offering a versatile solution for various applications that require both strength and environmental sustainability.⁴¹

The incorporation of organic waste materials, SD and ES, into bioplastic fabrication from renewable potato starch presents a promising approach to addressing global challenges, including sustainability, pollution, and resource utilization.²² While concerns persist about using edible materials amidst a global food crisis, this renewable alternative reduces dependence on fossil fuels, supports circular economy, and minimizes plastic pollution through natural degradation.⁸⁷ From a resource utilization perspective, integrating edible materials into bioplastic production is a crucial step toward reducing plastic dependency on fossil fuels as their reserves decline. The increasing demand and consumption of potatoes not only fulfill the growing need for bioplastics but also contribute to the expansion of agricultural economy. Higher demand for potatoes in secondary markets can create economic opportunities for farmers, bridging the gap between food production and plastic needs.⁸⁸

Furthermore, incorporating starch rich waste materials such as sugarcane bagasse, spent grain from alcohol fermentation, and organic food waste into bioplastics offers a sustainable solution to both plastic pollution and waste management.⁸⁹ These materials not only reduce reliance on fossil fuels but also repurpose agricultural and food industry residues, giving them a valuable second life.⁹⁰ By utilizing these waste products, bioplastics can be produced more sustainably, supporting circular economy, reducing landfill waste, and providing a viable alternative to conventional plastics.⁹¹

Despite global food scarcity, the integration of edible starch sources into bioplastic production presents a proactive solution to mitigating environmental pollution, decreasing fossil fuel reliance, and promoting sustainable material development.^1,88 Starch-based materials have demonstrated significant potential, particularly as more countries, such as Spain and Brazil, implement regulations banning disposable conventional plastics.¹⁴ One of their key advantages is superior biodegradability, as they break down more quickly in the natural environment and help reduce landfill waste, whereas non-biodegradable plastics remain for a longer period and accumulate in landfills.^10,12 Additionally, the production of bio-based polymers is expected to generate positive socio-economic impacts, particularly in the agricultural sector, as commercially available starch sources such as potatoes, corn, and cassava are widely used for plastic production.⁹²

The potential applications of starch-based films include packaging/wrapping materials, mulching, and nursery bags for plant transplantation.⁹³ Notably, their ability to degrade within a reasonable period eliminates the need for plastic removal, making them a sustainable alternative.⁹⁴ Furthermore, this innovation strengthens ecological and economic resilience while promoting environmental sustainability by incorporating renewable agricultural resources and organic waste reinforcements.^29,95

Conclusion

In this study, it can be ascertained that the extraction and fabrication of potato starch-based bioplastics films and reinforced bioplastic films incorporating organic waste have been successfully characterized by various analyses. The reinforced bioplastic exhibited significantly improved mechanical properties compared to native starch bioplastic, with tensile strength increasing from 1.9 ± 0.352 MPa to 5.7 ± 0.510 MPa and Young’s modulus rising from 13.7 ± 0.456 MPa to 130 ± 2.050 MPa upon the incorporation of SD, indicating enhanced stiffness and structural integrity. FTIR analysis revealed that all reinforced bioplastic films (SD, BC, ES, and SD + ES) exhibited almost similar characteristic absorption peaks to the pure potato starch (PS) control film, indicating the retention of key functional groups such as hydroxyl (O-H), carbonyl (C=O), nitrile (C≡N), and alkyne (C≡C). However, slight variations in peak intensities and sharpness were observed in the reinforced films, suggesting enhanced intermolecular interactions and hydrogen bonding due to the incorporation of organic reinforcements. Soil burial biodegradation assessments showed that all formulations native starch bioplastics and reinforced bioplastic films followed a similar biodegradation trend, although ES bioplastics demonstrated a slightly slower degradation rate. Notably, BC reinforced bioplastics exhibited up to 36% biodegradation within 15 days, highlighting their environmental sustainability. The successful development of potato starch reinforced bioplastic films with enhanced mechanical properties marks a significant advancement, presenting a viable alternative to conventional plastics due to their high biodegradability and suitable mechanical strength. Starch, being a renewable, inexpensive, and easily modifiable resource, adds further value. The incorporation of organic wastes sawdust and eggshell not only promotes waste valorization but also supports circular economy principles and sustainability efforts. This approach contributes to reducing dependence on fossil resources and helps mitigate current environmental issues. While this study focused on using a combination of eggshell (ES) and sawdust (SD), future research could explore hybrid formulations incorporating additional reinforcements to further optimize composite properties. Additionally, evaluating the impact of these films on soil by assessing nutrient levels and other characteristics before and after biodegradation could provide valuable insights into their environmental compatibility. Overall, this study opens new avenues for designing hybrid starch-based bioplastic films with tailored properties for sustainable applications.

Footnotes

Acknowledgements

The authors gratefully acknowledge the Nepal Technology Innovation Center (NTIC), Kathmandu University, for providing laboratory access for FTIR analysis. We also thank the Strength of Materials (SOM) Laboratory, Department of Mechanical Engineering, for facilitating tensile testing using the Universal Testing Machine (UTM). Our sincere appreciation goes to the Department of Physics for laboratory support and access to the digital vernier caliper. Additionally, we acknowledge the Department of Environmental Science and Engineering for their valuable support and laboratory access, which were instrumental in conducting the experimental work.

ORCID iD

Shreekrishna Neupane

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

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