Battle of the Bioplastics

Approximately 400 million tons of plastic are produced annually, yet only 9% is recycled (OECD, 2022. Figure 1). The resulting waste accumulates in ecosystems (Geyer et al., 2017) and fragments into microplastics that infiltrate the human body (Marfella et al., 2024. Figure 2).

Despite growing awareness, plastic production continues to accelerate (UNEP, 2023).

Bioplastics—particularly starch-based materials—are proposed as a sustainable alternative, yet their widespread adoption remains limited (Guranathan et al., 2018).

Starch composition varies between sources — corn, tapioca, potato, and rice differ in amylose-to-amylopectin ratios and phosphate groups (Wang, 2015) — yet research rarely compares starches under identical conditions, making it difficult to determine which is best suited for specific real-world applications (Šárka et al., 2023).

Understanding starch performance is essential for designing physically practical, targeted alternatives to conventional plastic (Kohsari et al., 2016).

It was hypothesized that bioplastic performance is determined by the molecular architecture of the starch source: (Figure 3, 4)

Potato starch: high tensile strength due to high amylose content and phosphate-aided inter-chain bonding, but low water resistance due to hygroscopic phosphate groups.

Corn starch: superior water resistance due to a crystalline, densely packed polymer network.

Tapioca starch: middle-ground performance, offering greater flexibility than corn but lower strength than potato due to intermediate amylose levels.

Rice flour: fastest biodegradation due to its heterogeneous matrix disrupting the polymer network.

By varying starch sources while controlling synthesis conditions, functional properties can be attributed to differences in molecular architecture, providing a framework for designing targeted bioplastics.

Research identified amylose and amylopectin — the two key polymers in starch — as the primary drivers of differences in tensile strength, water resistance, and biodegradability (Zhang et al., 2019).

Four starch-based bioplastics were synthesized under carefully controlled conditions to isolate starch source as the sole independent variable. Each formulation used an identical recipe of 20g starch, 5mL vegetable glycerin, and 90mL water, heated to 80°C while stirring until thick and semitranslucent (Figure 5).

The films were cast onto parchment paper, allowed to solidify for 48–72 hours, then cut into uniform 8.0 cm × 2.0 cm × 0.2 cm strips to ensure consistent testing conditions across all samples.

Three performance properties were then evaluated systematically. Water resistance was measured by timing how long a water droplet 30 µL took to absorb or leak through each sample, repeated across three trials per starch (Figure 6a).

Tensile strength was assessed by suspending weighted coins onto strips until visible deformation occurred, with stress calculated as Force/Area (Figure 6b).

Biodegradability was investigated through two parallel methods — surface degradation by wrapping samples in moist paper towels observed over 6–8 days, and soil degradation by burying strips 2cm deep in moist soil and monitoring every 3–4 days over 12 days — to simulate both humid and natural environmental conditions (Figure 7).

Across all three tests, starch source proved to be a decisive factor in bioplastic performance, revealing clear trade-offs between strength, water resistance, and biodegradability.

Tensile strength testing revealed that potato starch produced the highest tensile strength at 0.249 MPa, followed by corn at 0.243 MPa, tapioca at 0.228 MPa, and rice flour at 0.219 MPa. I developed a custom tensile test using weighted coins to compare relative strength. While not a lab-grade tensiometer, the data suggests potato starch outperforming rice by 13.7% (Figure 8).

Higher amylose content in corn and potato (Gularte et al., 2019) generally correlated with greater tensile strength, while rice flour’s added proteins and fibers (Lu et al., 2024) created structural inconsistencies that weakened the film and exhibited the highest degree of variance.

Water resistance produced the most surprising findings. Corn starch demonstrated the highest resistance, with water remaining on the surface for an average of 64.1 seconds, while rice flour absorbed water almost immediately upon contact, absorbing the whole drop within 25.1 seconds on average (Figure 9).

However, corn’s result may be partially attributed to its low surface roughness, which increases the contact angle of water droplets. This suggests that corn’s specific crystalline packing contributes to water shedding independently of the material's internal hydrophobicity.

Tapioca averaged 43.3 seconds and performed the most consistently across trials, while potato showed unexpectedly low resistance at 30.3 seconds despite its high amylose content — suggesting that surface morphology plays a role beyond molecular composition alone (Figure 9)

Biodegradation results aligned most closely with the hypothesis. Rice flour degraded fastest, becoming visibly compromised within the first 48 to 96 hours of both moisture-controlled and soil-immersion trials (Figure 10, 11)

Corn starch degraded the slowest, reflecting its dense crystalline amylose structure which resists microbial penetration. Rice flour degraded the fastest, likely due to its heterogeneous matrix containing proteins and fibers that disrupt the polymer network and increase susceptibility to breakdown. Tapioca and potato fell in between, with potato softening rapidly after sustained moisture exposure (Figures 10, 11), consistent with its hygroscopic phosphate groups attracting water and accelerating degradation (Pérez et al., 2010).

Taken together, these results suggest that no single starch is universally superior. Instead, each has a distinct performance profile that could be strategically matched to specific applications — corn for durability and water resistance, tapioca for a balanced everyday alternative, and rice for applications where rapid biodegradation is prioritized over strength.

This research demonstrates that starch-based bioplastics are not a single solution, but a versatile family of materials with distinct performance profiles.

By identifying the trade-offs between starch sources, we can move toward strategic material substitution rather than a one-size-fits-all approach. Corn starch, with its superior water resistance and slow degradation, is the ideal candidate for durable, moisture-exposed packaging.

Potato starch provides the highest tensile strength (0.249 MPa) for load-bearing needs, while tapioca offers a middle-ground balance of durability and flexibility for everyday alternatives. Conversely, rice flour's rapid biodegradation makes it uniquely suited for short-cycle agricultural uses where structural strength is secondary to environmental breakdown.

Ultimately, these results prove that starch molecular architecture

—specifically the amylose-to-amylopectin ratio, is a tunable lever that allows us to engineer bioplastics to meet the specific functional demands of conventional plastic.

This project provides a low-cost methodology and evidence base for designing the next generation of application-specific bioplastics.

This project establishes a foundation for starch-based bioplastics, highlighting molecular architecture as a key determinant of performance.

Future work will focus on optimizing formulations through starch blending, combining complementary properties such as the strength of potato starch with the flexibility of tapioca or water resistance of corn.

Hybrid systems, including starch–cellulose nanocrystal composites, could outperform single-source materials across multiple properties (Cozzolino et al., 2013). In parallel, alternative plasticizers such as sorbitol or citric acid will be investigated to enhance mechanical strength and water resistance independent of starch source (Majdzadeh-Ardakani et al., 2010), expanding this framework into a multi-variable design.

There are several people I would like to acknowledge for their support throughout this project.

First, I would like to thank my mom for purchasing all of the materials required to carry out my experiments. Without her support, this project would not have been possible.

I would also like to acknowledge the WWSEF volunteers for providing feedback and revision assistance during the preparation of my project for WWSEF. Their thoughtful suggestions helped strengthen both the science and the presentation.

Finally, I would like to thank the CWSF Delegates for their guidance in preparing this project board to CWSF standards, and for organizing group chats and meetings to support participants throughout the process. Thank you for facilitating this opportunity and for supporting young scientists in sharing their work on a larger stage.

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