Characteristic of a Biodegradable Foam With Bagasse as a Filler

TL;DR

This study develops a biodegradable foam using sugarcane bagasse and PVA to create sustainable packaging with better mechanical and thermal properties than traditional options.

Contribution

The paper introduces a new biodegradable foam formulation using bagasse and PVA that improves mechanical strength and water resistance.

Findings

Biofoam density ranged from 0.2282 to 0.2952 g/cm³ with thickness between 2.82 and 2.92 mm.

Higher PVA concentrations reduced crystallinity and affected pore morphology in the foam.

Formula 1 (35 g PVA) showed the best mechanical strength, density, and water resistance.

Abstract

The main issue driving this research is the need to develop sustainable packaging materials that can replace conventional nonbiodegradable plastics. Traditional biodegradable foams often exhibit inadequate mechanical and thermal properties, which limit their practical use in food packaging. The study explores sustainable packaging alternatives using agricultural waste like sugarcane bagasse and polyvinyl alcohol (PVA) as a binder, aiming to improve structural integrity, reduce water absorption, and optimize performance, while also addressing the growing environmental demand for renewable and eco‐friendly packaging solutions. Various physical properties were assessed, including moisture content, density, thickness, water absorption, X‐ray diffraction (XRD), and scanning electron microscopy (SEM) morphology. The results indicated that the biofoam density ranged from 0.2282 to 0.2952 g/cm3, and thickness values were between 2.82 and 2.92 mm. Water absorption increased significantly after 2 min of immersion, while XRD analysis indicated a reduction in crystallinity with higher PVA concentrations. The morphology of the biofoam, including the shape, size, and distribution of pores, was influenced by the addition of PVA. A lower concentration of PVA led to an increase in the size of the pore holes. Among the formulations tested, the treatment with 35 g PVA (Formula 1) is recommended due to its superior mechanical strength, optimal density, and improved water resistance.

Figures

Representative biofoam bowls produced by thermopressing, showing the bowl‐shaped design (10 cm diameter) used for physical‐property testing.

Water absorption versus immersion time (0.5–5 min) for biofoam formulations with different PVA contents (Formulas 1–4: 35, 30, 25, and 20 g PVA). Error bars indicate standard deviation (n = 3).

X‐ray diffraction (XRD) patterns of biofoam formulations (Formulas 1–4) with varying PVA content, highlighting differences in peak intensity and amorphous background associated with crystallinity.

Peak compressive force (force strength) of biofoam formulations (Formulas 1–4). Bars show mean ± standard deviation (n = 3).

SEM micrographs of biofoam cross sections for Formulas 1–4, illustrating pore structure differences (pore size, coalescence, and cell‐wall thickness) as a function of PVA content.

Tables

TABLE 1. Composition of biofoam formulations.

Formula	Starch (g)	PVA (g)
1	200	35
2	200	30
3	200	25
4	200	20

TABLE 2. Density and thickness of the product.

Formula	PVA (g)	Density (g/cm3)	Thickness (mm)
1	35	0.2952 ± 0.005a	2.92
2	30	0.2509 ± 0.010b	2.82
3	25	0.2356 ± 0.020b	2.82
4	20	0.2282 ± 0.010b	2.82

TABLE 3. The color of biodegradable foam.

Formula	PVA (g)	L	a	b
1	35	74.43 ± 1.12a	3.45 ± 1.29a	19.21 ± 0.95a
2	30	73.51 ± 2.10a	3.90 ± 1.09a	20.68 ± 1.51a
3	25	74.17 ± 0.78a	3.68 ± 0.95a	19.08 ± 2.01a
4	20	74.67 ± 1.39a	3.72 ± 1.98a	19.24 ± 3.21a

TABLE 4. Amorphous, crystallinity, and degree of crystallinity of formula.

Formula	PVA (g)	Amorphous (%)	Crystallinity (%)	Degree crystallinity (%)
1	35	79.10	20.90	26.42
2	30	77.20	22.80	29.53
3	25	63.90	36.10	56.49
4	20	64.80	35.20	54.32

Full text

1. Introduction

The rising environmental issues about plastic waste have driven demand for sustainable packaging substitutes higher. Foam materials used for packaging can be made from plant fiber [1], metals [2], ceramics [3], or organic components. Organic foam materials are materials that have the best performance and cost‐effectiveness by combining organic base materials (sodium alginate, cellulose, or starch), emulsifiers, foaming agents, curing agents, and synthetic adjuvants such as expanded polystyrene (EPS) or expanded polyethylene (EPE) foams. These formulations create durable, lightweight structures with excellent support properties, making them popular in packaging, insulation, and cushioning applications [4]. Conventional petroleum‐based foams such as EPS and polyurethane provide excellent cushioning and thermal insulation but are not readily biodegradable and create serious end‐of‐life waste management problems [4, 5].

In contrast, plant fiber foams are made by combining natural plant fibers with starch to form a microcellular structure that can distribute external pressure evenly while significantly increasing shock absorption and buffering capacity. Unlike the cellulose‐ or starch‐only foams described earlier, which consist of a single continuous biopolymer phase, plant fiber foams contain a distinct fibrous reinforcement phase dispersed within the starch (or cellulose) matrix. From a materials‐science perspective, these systems are more accurately described as fiber‐reinforced biocomposite foams, in which a continuous starch (or cellulose) matrix is reinforced by dispersed lignocellulosic fibers. The fiber phase contributes stiffness and toughness, whereas the plasticized starch matrix governs processability, cellular morphology, and interfacial bonding. They feature unique attributes like expansion during baking and adaptability, making them a promising solution in the quest for sustainable packaging materials [6, 7]. Metal foam and ceramic foam materials are not often used in packaging today.

Biodegradable packaging materials like corrugated cardboard, honeycomb cardboard, and pulp molding are used in the market, but these materials have less optimal mechanical performance and are more susceptible to damage due to excessive pressure or impact [8]. They lack the cellular architecture needed for efficient energy dispersion. In contrast, plant fiber foams are made by combining natural plant fibers with starch, which results in a microcellular structure that can distribute external pressure evenly while significantly increasing shock absorption and buffering capacity.

Agricultural by‐products such as sugarcane bagasse and maize cob serve as eco‐friendly fillers for biodegradable foams [9, 10], enhancing their mechanical and thermal properties [11]. Various agricultural wastes like sawdust, rice husks, and coconut fiber are also viable fillers for biofoam formulation [11, 12]. Notably, sugarcane bagasse’s compact structure and smooth surface contribute cellulose, hemicellulose, and lignin [13, 14], with cellulose recognized for its thermoplastic properties [11], making it suitable as a bioplastic and filler in biodegradable foam. Bagasse exhibits advantageous properties, including impact strength, flexural strength, and tensile strength [15]. When processed into foamed composites, sugarcane bagasse can provide cushioning performance and compressive strength suitable for protective packaging and has been reported to approach the functional performance of conventional polystyrene‐based foams used as cushion materials [4, 11]. Although their absolute strength is generally lower than that of high‐density synthetic foams, bagasse‐based foams can still satisfy the mechanical requirements for many packaging and insulation applications while offering superior biodegradability. Additionally, reviews of bio‐based foams suggest that soybean, corn, and starch‐based variations can match the density and performance of conventional synthetic foams, despite certain processing challenges, and hold potential for insulation and packaging applications [5].

Despite the increasing development of biodegradable foam packaging materials derived from natural polymers and agricultural by‐products, there remains a critical need for direct food contact coatings to ensure safety and performance. Coatings based on polyvinyl alcohol (PVA), polylactic acid (PLA), and starch are favored over traditional options like paraffin due to their superior tensile strength, flexibility, and resistance to fat and grease. In particular, the incorporation of PVA not only reinforces the composite’s structural integrity when combined with eco‐friendly fillers such as sugarcane bagasse but also significantly influences the biofoam’s physical properties, including density, porosity, and water absorption. However, while these coatings show considerable promise, a systematic investigation into the precise mechanisms by which varying PVA concentrations alter the microstructure and functional characteristics of biofoam is still lacking. Addressing this research gap is essential for optimizing formulations that fully leverage the benefits of natural fillers and advanced coatings in sustainable packaging applications. This study is designed to bridge that gap by quantitatively analyzing the impact of different PVA concentrations on density, thickness, color, and water absorption. Ultimately, the objective is to determine the optimal formulation that offers the best balance between mechanical strength, durability, and esthetic quality, thereby paving the way for more reliable biodegradable packaging applications.

2. Materials and Methods

2.1. Material

The research utilized starch, sugarcane bagasse, PVA, PLA, magnesium stearate, chitosan, and distilled water. Cassava starch (food grade, Rose Brand—ASM group, Indonesia), PVA (analytical grade, Ananya, India), PLA (China plastic resin pellet form, PT. Chori), magnesium stearate (Merck), and chitosan (Himedia, India) were obtained from commercial suppliers, and their specifications (purity, moisture content, and, for PVA, degree of hydrolysis) followed the manufacturers’ certificates of analysis. Sugarcane bagasse was collected from a local sugarcane‐processing plant in PTPN III, Subang, air‐dried, milled, and sieved prior to use. Distilled water was produced in‐house using a laboratory purification system.

2.2. Experimental Design and Variables

The study employed a controlled experimental design. The independent variable was the PVA concentration, which was varied according to the four formulations detailed in Table 1. In contrast, the control variables were maintained constantly across all samples: PLA (5 g), magnesium stearate (15 g), bagasse (40 g), chitosan (5 mL), distilled water (5 mL), and starch (200 g). This approach allows for a focused investigation of the effect of PVA on the physical properties of the biofoam.

2.3. Replication and Statistical Analysis

Each formulation was prepared in triplicate. At least three separate samples were used for each test, which included density, water absorption, color, force strength. X‐ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were conducted using a single representative sample from each formulation. Data are presented as mean ± standard deviation. A one‐way analysis of variance (ANOVA) was used to evaluate the effect of formulation on the measured parameters, with p < 0.05 considered statistically significant. When a significant effect was detected, Tukey’s honestly significant difference (HSD) test was applied as a post hoc comparison to identify differences between formulations.

2.4. Processing Conditions and Preparation of Biofoam

The biofoam was prepared using a thermopressing method, chosen for its efficiency in gelatinizing starch and promoting foam expansion under controlled heat and pressure. The processing temperature was set at 180°C and maintained for 4 min. These conditions were selected based on preliminary experiments and literature reports [16] to achieve optimal starch gelatinization foam formation while preserving the structural integrity of the filler and binder. The biofoam was prepared following a detailed protocol available at protocols.io [17].

• a.Mixing: The solid ingredients (cassava starch, PLA, magnesium stearate, and bagasse) were initially blended using a mixer until a homogeneous mixture was achieved. Next, the liquid ingredients (chitosan, PVA according to the respective formula, and distilled water) were added gradually and stirred until the mixture became smooth and consistent.
• b.Thermopressing: A 35 g portion of the prepared dough was placed into a molding machine preheated to 180°C. The dough was thermopressed for 4 min to facilitate starch gelatinization and foam expansion. During thermopressing, a constant pressure of 3.45 MPa (500 psi) was applied using the molding machine, and this pressure was kept the same for all four formulations to ensure comparable starch gelatinization and foam expansion conditions.
• c.Postprocessing: After removal from the mold, the biofoam samples were allowed to cool at room temperature. Subsequently, the edges were trimmed, and the surfaces were smoothed using a mechanical smoothing device to ensure uniformity.

2.5. Physical Properties Measurements: Density

Density was determined by measuring the dry mass of each sample (in grams) and its dimensions (length, width, height) to calculate volume (in cm^3^). Density was then calculated as mass/volume [16].

2.6. Water Absorption

Water absorption was measured by cutting the biofoam into 5 × 5 cm samples. The initial weight (W 0) of each sample was recorded, followed by immersion in water for predetermined time intervals. After each interval, samples were weighed again (W). Samples were immersed for 0.5, 1, 2, and 5 min, representing a short‐term exposure regime commonly used to characterize the initial water uptake of starch‐based biodegradable foams [18, 19]. The 2 min value was selected as a representative time point for comparing formulations because it marks the onset of the rapid‐absorption regime observed in this study (Section 3.4) and falls within the early‐contact period relevant to typical food‐packaging scenarios. Longer immersion times (up to several hours or 24 h) are also reported in the literature for equilibrium sorption measurements [11], but were beyond the scope of the present work, which focused on the early‐stage absorption behavior. The percentage of water absorption was calculated using the following equation:

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2.7. Color

Color was measured using a calibrated colorimeter (or spectrophotometer) in the Commission Internationale de l’Éclairage Lab (CIELAB)^∗^ color space. The device provided CIE Lab^∗^ values for each sample, with measurements taken at three different locations on each sample to ensure homogeneity. For each specimen, the three measurements were first averaged to obtain a single L, a, and b^∗^ value. Differences among formulations were then evaluated by one‐way ANOVA followed by Tukey’s HSD test, as described in Section 2.3, with p < 0.05 considered statistically significant.

2.8. Force Strength (g/N)

Force strength was determined using a texture analyzer (TA.XT plus) equipped with a 75 mm cylinder probe (P/75) and a 30 kg load cell. The test was conducted at a constant crosshead speed, and the maximum force required to compress the biofoam was recorded.

2.9. XRD

The crystallinity of the biofoam samples was analyzed using a Shimadzu XRD 600 diffractometer, operated at 30 kV and 30 mA with CuKα radiation (λ = 1.540 Å). The patterns were recorded, and the degree of crystallinity was calculated using standard methods.

2.10. SEM

The surface morphology of the biofoam was examined using a JEOL JSM 6510 microscope at an operating voltage of 10 kV. Samples were sputter‐coated with a thin layer of gold prior to imaging to enhance conductivity.

3. Result and Discussion

3.1. Physical Properties of Biofoam

The biodegradable foam product was observed to be bowl‐shaped with a circular diameter of 10 cm and a thickness ranging from 2.82 to 2.92 mm. The surface of the product is smooth and exhibits a bright color, making it particularly suitable as a food container for dry foods. The consistent geometry (diameter and thickness) and smooth surface finish obtained across batches reflect good precision in the molding process, which helps ensure structural integrity while maintaining a lightweight profile, making it easy to handle and transport.

The product’s smooth surface enhances its usability, as it minimizes friction and prevents residue accumulation, a critical feature for food safety. Additionally, the vibrant foam color enhances esthetic value and branding opportunities, appealing to consumers seeking practicality and style in eco‐friendly products (Figure 1).

Representative biofoam bowls produced by thermopressing, showing the bowl‐shaped design (10 cm diameter) used for physical‐property testing.

3.2. Density and Thickness

The density of the biofoam increased with PVA concentration, ranging from 0.2282 g/cm^3^ (Formula 4, 20 g PVA) to 0.2952 g/cm^3^ (Formula 1, 35 g PVA), as shown in Table 2. Thus, higher PVA contents produced denser foams, whereas reducing PVA allowed more expansion and higher overall porosity. The different superscript letters in Table 2 indicate that the density of Formula 1 is significantly higher (p < 0.05) than those of the other formulations, while thickness remained statistically unchanged (2.82–2.92 mm), implying that PVA content mainly affects internal cellular structure rather than macroscopic dimensions.

These densities are considerably higher than those of conventional EPS packaging foams (typically 0.005–0.015 g/cm^3^) [20], but they are comparable to plant‐fiber composite foams reported in the literature [1, 21]. In agreement with previous work on starch–PVA systems, increased PVA contents tend to reduce the number and size of internal voids and produce a more compact matrix, thereby increasing density [18, 19]. PVA acts as an effective binder that fills interstitial gaps between starch granules and bagasse fibers, stabilizing the cellular structure during expansion and limiting the formation of large, coalesced pores.

In polymeric foams, mechanical properties such as compressive strength generally scale positively with density, because thicker cell walls and fewer large defects increase the effective load‐bearing cross section and reduce local stress concentrations [1]. In the present formulations, the higher density of Formula 1 therefore indicates a more robust microstructure, consistent with its slightly higher mean force strength (Section 3.6) and lower water absorption (Section 3.4). At the same time, all four densities remain within the range required for lightweight packaging materials, so the choice of PVA content can be used to balance structural integrity (pressure resistance, resistance to local crushing) against minimal material usage and weight, depending on the targeted application.

3.3. Color

The color of the biofoam, measured using the CIELAB system (L, a, b), shows subtle variations across formulations with differing PVA content. As shown in Table 3, no significant differences (p > 0.05) were detected among formulations for L, a, or b values, consistent with the shared superscript letters. The L (lightness) values range from 73.51 ± 2.10 (Formula 2) to 74.67 ± 1.39 (Formula 4), indicating that all formulations produce foams that are quite bright. Notably, Formula 4 exhibits the highest lightness, followed by Formula 1, Formula 3, and Formula 2. This suggests that reducing PVA content does not linearly correlate with lightness; instead, the relationship appears non‐uniform, possibly due to interactions between PVA and other components (e.g., starch, bagasse) during processing (Table 3).

The a values (green‐red axis) remain relatively stable across all formulas, leaning slightly toward red, while b values (blue‐yellow axis) range from 19.08 ± 2.01 (Formula 3) to 20.68 ± 1.51 (Formula 2), indicating a mild yellowish hue. These fluctuations in a and b values could stem from minor variations in raw material homogeneity, thermal degradation during processing, or interactions between PVA and natural polymers like starch or bagasse, which may release pigments under heat.

3.4. Water Absorption

Water absorption in starch‐based biofoams increases over time, with a sharp rise after the 2‐min mark. The rate of absorption remains low from 0.5 to 1 min but accelerates significantly between 2 and 5 min, as shown in Figure 2. By the 5‐min mark, most samples exhibit substantial absorption, highlighting the hydrophilic nature of starch‐based biofoams. The product exhibits a notable hydrophilic nature, as indicated by the tendency for water absorption to increase with prolonged immersion.

Water absorption versus immersion time (0.5–5 min) for biofoam formulations with different PVA contents (Formulas 1–4: 35, 30, 25, and 20 g PVA). Error bars indicate standard deviation (n = 3).

The presence and concentration of PVA play a critical role in modulating water absorption. Rusdianto et al. [18] showed that varying PVA concentrations directly influenced the water absorption behavior of cassava starch‐based biodegradable foams, with their best‐performing formulation still absorbing 25.93% water [19]. Although PVA is intrinsically water soluble, in a thermopressed starch–bagasse matrix it participates in extensive hydrogen bonding with starch and cellulose, forming a semi‐continuous network that partially seals intergranular voids and increases packing density [22, 23].

This network reduces the size and connectivity of capillary pathways so that water transport is governed more by diffusion through a dense polymer phase than by rapid capillary flow in large open pores. Consequently, higher PVA contents tend to yield more compact and less porous structures, which explains the lower water absorption observed in formulations with increased PVA [6, 18]. Whereas formulations with less PVA retain larger, interconnected pores that facilitate faster water uptake. Formula 1 (35 g PVA) consistently displayed the lowest water absorption after 5 min of immersion, highlighting the protective effect of a denser PVA‐rich matrix on water uptake.

The concentration of PVA and filler, as well as the type of filler, affects the characteristics of water absorption. Experimental evaluations demonstrate how incorporating natural fillers can mitigate water absorption issues associated with high PVA concentrations. The study of PVA blended with pomegranate peel powder noted that while the PVA matrix showed a higher tendency for moisture absorption, the addition of natural fillers could potentially decrease the rate of water solubility within the PVA matrix, thus offering improved structural integrity [24]. Conversely, in other research, it was found that the integration of starch alongside PVA has been shown to increase water absorption capacity but also provides a pathway for improved biodegradation, as evidenced by findings from the study on starch and PVA blends [25]. The biofoam cup with a 1.5 weight ratio of soybean flour to bagasse exhibited superior thermal stability and compressive strength compared to those without soybean flour and less starch filler [26].

Formula 1 is specifically well‐suited for applications where moisture exposure is likely, such as food packaging for products with increased humidity, because it exhibits the best balance between decreased water absorption and structural integrity. This formulation provides increased resistance to water absorption without sacrificing mechanical strength by preventing the creation of large voids and taking advantage of PVA’s partial hydrophobicity.

3.5. XRD Pattern

The crystallinity of the biofoam decreased with increasing PVA content; Formulas 1 and 2 exhibited significantly lower crystallinity percentages than Formulas 3 and 4 as shown in Table 4.

Formula 1 has the highest PVA concentration (35 g) and displays the lowest crystallinity and highest amorphous fraction. This trend indicates that as the PVA content increases, the degree of crystallinity decreases, leading to a more amorphous structure. Studies have shown that increasing the concentration of PVA in biodegradable foams results in a change in the crystallinity and packing of the polymer matrix. Liu et al. demonstrated that as the PVA content increases in the blend, there is a noticeable shift in peak intensity and position in the XRD patterns, indicating changes in crystallinity and intermolecular interactions among polymer chains [27]. PVA disrupts the orderly packing of starch molecules by interacting with starch chains and inhibiting their ability to form well‐defined crystalline regions.

In semicrystalline starch–PVA systems, crystallinity is governed by how efficiently PVA chains pack together with starch helices to form ordered domains. At moderate PVA contents, segments of PVA can participate in hydrogen‐bonded microdomains with starch, contributing to a semicrystalline network that increases stiffness. As PVA content becomes higher, a larger fraction of amorphous PVA interrupts the regular packing of starch and breaks up existing crystalline lamellae, leading to the predominantly amorphous patterns observed for Formulas 1 and 2 [27–29]. This evolution explains why the foams become more flexible and slightly less rigid at higher PVA contents yet do not lose compressive strength: The reduction in crystalline stiffness is offset by improved packing of the amorphous phase, more uniform stress distribution, and stronger interfacial bonding with bagasse fibers (Section 3.6).

In our system, this reduction in crystallinity does not lead to a marked loss of compressive strength, because the mechanical response is governed not only by crystalline order but also by PVA–starch–bagasse interfacial bonding and foam morphology. As discussed in Section 3.6, the compressive force values of the four formulations are not statistically different (p > 0.05), indicating that higher PVA contents can decrease crystalline order while maintaining comparable strength. This behavior is consistent with PVA acting as a compatibilizer that improves stress transfer across the matrix–fiber interface and reduces large structural defects, thereby compensating for the lower crystallinity and preserving overall mechanical performance.

From a structural standpoint, these observations suggest that PVA has an optimal concentration window. At lower PVA levels, crystallinity remains higher, but interfacial adhesion and defect healing in the matrix are limited. At very high PVA levels, however, the matrix becomes increasingly plasticized and amorphous, which can reduce stiffness and dimensional stability, as also indicated by Marlina et al., who observed diminishing mechanical performance beyond an optimum PVA content in sorghum‐fiber foams [30]. The relatively constant force strength measured for 20–35 g PVA in this study likely corresponds to a plateau region within this window. We therefore anticipate that further increasing PVA beyond the range tested here would eventually lead to a decline in structural integrity due to excessive softening and loss of crystalline reinforcement, although this hypothesis still warrants experimental verification in future work.

The results obtained from the research show that the higher the PVA content can improve compressive strength and overall structural stability, as observed in Formula 1. Biodegradable foam Formula 1 exhibits both a lower degree of crystallinity and favorable mechanical performance. This is likely due to the occurrence of interfacial bonding between starch and bagasse fibers. The XRD pattern graph (Figure 3) for four biofoam formulations reveals that the materials are predominantly amorphous, with some variation in crystallinity among the different formulations.

X‐ray diffraction (XRD) patterns of biofoam formulations (Formulas 1–4) with varying PVA content, highlighting differences in peak intensity and amorphous background associated with crystallinity.

The amorphous background is typical of starch‐ and polymer‐based materials that lack extensive long‐range crystalline order. Small peaks or shoulders can be observed at certain 2θ angles (around 17°–23°). These may correspond to residual crystalline regions of starch or cellulose from bagasse. The intensity of these peaks varies among formulations, suggesting differences in the degree of crystallinity. Formulas with less PVA may exhibit slightly higher peak intensities, indicating more ordered regions. When PVA content increases, it tends to disrupt the formation of crystalline starch regions, causing peaks to diminish in intensity and the pattern to appear more diffuse. This disruption leads to increased amorphousness, which is reflected by a broader, less defined hump in the XRD pattern. Formulations with higher PVA concentrations typically show lower crystallinity values. A higher amorphous fraction often implies greater chain mobility and flexibility but may also reduce stiffness. Nonetheless, PVA can enhance interfacial bonding between starch and filler (bagasse), which may compensate for the lower crystallinity and still yield good mechanical performance [31].

3.6. Force Strength

PVA enhances interfacial bonding between starch and filler particles in biofoam, acting as a critical adhesive material. Higher PVA concentrations tend to produce a denser, more cohesive structure by partially filling voids and strengthening the matrix–fiber interface. Previous work has shown that the incorporation of PVA can markedly enhance tensile or compressive strength in starch–fiber foams [22, 30]. Consistently, starch foams reinforced with water hyacinth fiber showed that an addition of around 10% WHF, especially when combined with 10% PVA, improved compressibility, density, and water absorption behavior, whereas higher fiber loadings (15%–20%) weakened the foam and increased water uptake [31]. However, in the present study, one‐way ANOVA followed by Tukey’s test did not reveal statistically significant differences (p > 0.05) in force strength among the four formulations, even though Formula 1 (35 g PVA) often exhibited slightly higher mean force values. This suggests that, within the tested range of PVA contents (20–35 g), the positive effect of PVA on interfacial adhesion and defect reduction balances the decrease in crystallinity observed by XRD, resulting in similar macroscopic compressive performance across formulations.

The mechanical performance (force strength) of the biofoam therefore reflects a balance between two competing factors: interfacial bonding (strengthened by PVA) and structural rigidity (linked to crystallinity). PVA acts as a compatibilizer, improving adhesion between the hydrophilic starch and lignocellulosic bagasse fibers. This improved interfacial bonding reduces internal voids and increases load transfer efficiency across the matrix–fiber interface [29]. However, excessive PVA content can disrupt the native crystalline structure of starch, particularly the A‐type and B‐type crystallinity, due to the plasticizing and morphing effect of PVA [28]. Despite these trade‐offs, no statistically significant differences in force strength were observed across formulations. This convergence likely arises from the following:

• 1.Overlapping error ranges: Variability in starch gelatinization or bagasse fiber distribution during processing introduces measurement noise, masking subtle trends.
• 2.Synergistic compensation: While PVA reduces starch crystallinity, bagasse fibers counteract this by distributing stress and inhibiting crack propagation, balancing net strength.
• 3.Optimal PVA range: The tested PVA concentrations (20–35 g) may represent a “sweet spot” where bonding efficiency and crystallinity retention offset each other.
• 4.Measurement limitations: Force strength tests (e.g., texture analyzer) prioritize peak force measurement but may overlook nuanced differences in energy absorption or elastic recovery.

These factors collectively explain the equilibrium in mechanical performance, visualized in Figure 4. The interplay of PVA‐induced bonding, fiber reinforcement, and crystallinity modulation underscores the complexity of optimizing biofoam formulations for sustainable packaging.

Peak compressive force (force strength) of biofoam formulations (Formulas 1–4). Bars show mean ± standard deviation (n = 3).

3.7. SEM Result

During thermopressing, starch undergoes gelatinization and expansion, creating a network of interconnected cavities or pores [32]. PVA functions as a binder and stabilizer in this network, filling void spaces between starch granules and bagasse fibers and helping maintain the structural integrity of the foam as it expands. Numerous cavities are observable in Figure 5, consistent with the formation of a cellular structure typical of starch‐based foams [7]. At the magnification used, the overall pore morphology of Formulas 1 and 3 appears broadly similar, with both exhibiting approximately circular cells in the submillimeter range. Rather than performing a full stereological analysis, we therefore adopted a semiquantitative approach based on the frequency of obviously coalesced pores, apparent cell‐wall thickness, and the presence of large defects, and we interpreted these microstructural observations together with the bulk density and water‐absorption data for each formulation.

SEM micrographs of biofoam cross sections for Formulas 1–4, illustrating pore structure differences (pore size, coalescence, and cell‐wall thickness) as a function of PVA content.

When the two extreme formulations in terms of PVA content are compared, Formula 1 (35 g PVA) exhibits smaller, more uniformly distributed pores with thicker cell walls, indicating a denser and more cohesive matrix, whereas Formula 4 (20 g PVA) displays larger, irregularly shaped, and sometimes coalesced cavities, suggesting higher open porosity and weaker local cell walls. These qualitative differences are in good agreement with the bulk properties: Formula 1 shows the highest density and lowest water absorption, while Formula 4 has the lowest density and higher water uptake (Table 2 and Figure 2). The combination of higher density and reduced water absorption therefore supports the interpretation that increasing PVA content leads to a more compact pore structure with fewer large, interconnected voids. A composition of 5% PVA yielded optimal mechanical properties (tensile strength of 5 MPa) and water resistance, while higher concentrations had minimal benefits.

From a mechanical perspective, such a pore refinement is expected to improve stress distribution and reduce stress concentrations at defects, thereby helping to preserve compressive performance even when crystallinity decreases (Section 3.5). Although porosity was not quantified directly in this work, the consistent trends among SEM images, density values, and water absorption behavior strongly indicate that PVA acts as a microstructural modifier controlling pore size and connectivity. Future work should complement SEM observations with image‐analysis‐based pore size distributions or open‐porosity measurements to provide quantitative validation of these microstructural trends. Similar behavior has been reported for starch‐based foams filled with rice husk ash, which exhibited smaller internal pores and higher strength than unfilled foams [33].

4. Conclusion

Biofoam, characterized by its high biodegradability, low cost, and nontoxic environmental profile, suffers from inadequate mechanical and thermal properties, necessitating the incorporation of fillers to enhance its performance. This study demonstrates that incorporating sugarcane bagasse and PVA into starch‐based biofoam significantly enhances its mechanical and thermal properties, addressing the limitations of conventional biodegradable foams. Bagasse improves tensile strength, impact resistance, and overall durability, while PVA increases density by reducing water absorption and stabilizing the foam’s porous structure. XRD analysis reveals that higher PVA content disrupts starch crystallinity, leading to a more amorphous structure. Despite this reduction in crystallinity, compressive strength is maintained, most likely because improved interfacial bonding among PVA, starch, and bagasse and a denser foam structure compensate for the loss of crystalline rigidity. Furthermore, the foam’s degradation into CO_2_, H_2_O, and humus helps conserve fossil fuels and reduce carbon emissions. Among the tested formulations, Formula 1, containing the highest PVA concentration, emerges as the optimal choice. Its elevated PVA content yields a denser matrix with fewer voids, which not only reduces water uptake but also improves the foam’s mechanical integrity. These findings underscore the critical role of PVA in governing pore structure, crystallinity, and overall performance, and highlight sugarcane bagasse and PVA as promising components for sustainable, cost‐effective, and environmentally friendly packaging applications.

NomenclatureEPEExpanded polyethyleneEPSExpanded polystyreneCIELABInternational Commission on Illumination (CIE) LabPLAPolylactic acidPVAPolyvinyl alcoholSEMScanning electron microscopy

Funding

No funding was received for this manuscript.

Conflicts of Interest

The authors declare no conflicts of interest.