Microplastic Fragmentation Simulation

ISEF Category: Materials Science

Subcategory: Polymers  ·  Difficulty: Advanced  ·  Setup: University Lab  ·  Time: Full Year

The Hook

Microplastics do not appear all at once. Big plastic pieces break, rub, and crack into smaller ones over time. You can model that process with simulation, then compare it with a simple bottle-tumbler test using PET shards. That gives you a project that connects clean code, real materials, and a real pollution problem.

What Is It?

This project studies how plastic breaks into smaller pieces when it gets stirred, bumped, and dragged through fluid. PET is the plastic used in many drink bottles. When PET shards move through turbulent flow, they can lose mass, chip at the edges, and form more fragments. Your goal is to model that behavior with a coarse-grained molecular dynamics approach, then compare the model with an experiment that tumbles bottle shards in water or another safe fluid.

Coarse-grained MD means you do not track every atom. You group atoms into larger particles, then watch how those particles move and interact. DPD, or dissipative particle dynamics, is a style of simulation that adds fluid-like motion and energy loss. Think of it like building a simplified Lego version of a city, where you keep the roads, traffic, and crowding, but skip tiny details. That makes the problem easier to compute while still capturing the main breakup patterns you want to study.

Why This Is a Good Topic

This is a strong science fair topic because you can test clear variables, compare model predictions with physical data, and study a real environmental problem. You can ask how flow strength, shard size, or fragment shape changes breakup rate. You also get to learn simulation setup, parameter fitting, data analysis, and validation, which are all useful research skills. A careful student can build a project that goes past a simple demo and becomes a real model comparison study.

Research Questions

• How does flow intensity change the fragmentation rate of PET shards in a tumbling setup?
• What is the effect of starting shard size on the number of fragments produced over time?
• Does shard shape, such as sharp-edged versus rounded pieces, change the breakup pattern?
• To what extent does the DPD model match the size distribution seen in bottle-tumbler experiments?
• Which simulation parameters best predict the observed fragmentation trend in PET?
• How does adding more fluid turbulence change the predicted collision frequency in the model?

Basic Materials

• PET bottle shards of similar thickness and mass.
• Clear sealed bottles or jars for tumbling tests.
• Digital kitchen scale with 0.1 g accuracy.
• Ruler or digital calipers.
• Sieve set or mesh screens for sorting fragment sizes.
• Smartphone camera for before and after photos.
• Lab notebook or spreadsheet for tracking fragment counts and sizes.
• Safety gloves and eye protection.

Advanced Materials

• Access to a workstation or lab computer that can run LAMMPS.
• DPD input scripts for coarse-grained polymer and fluid models.
• PET material property data from published studies.
• Optical microscope or stereo microscope for fragment sizing.
• Image analysis setup for particle counting and shape measurement.
• Controlled tumbling or mixing apparatus for calibration experiments.
• High-speed video, if available, for observing fragment motion.
• Statistical software for model fitting and uncertainty analysis.

Software & Tools

• LAMMPS: Runs coarse-grained molecular dynamics and DPD simulations for the fragmentation model.
• OVITO: Visualizes particle motion and helps you inspect breakup behavior in simulation outputs.
• ImageJ: Measures fragment size, area, and shape from photos or microscope images.
• Python: Cleans data, fits trends, and compares simulation results with experiment.
• RStudio: Runs statistical tests and makes publication-style plots for size distributions and breakup rates.

Experiment Steps

1. Define the breakup signal you will measure, such as fragment count, size distribution, or mass loss.
2. Choose one control variable to change first, such as flow intensity, shard size, or shard shape.
3. Build a simple physical test plan that gives you repeatable tumbling data for calibration.
4. Set up a coarse-grained DPD model that matches the same starting conditions as the experiment.
5. Plan how you will convert photos or simulation output into numerical fragment measurements.
6. Decide how you will compare model and experiment with error bars, trend lines, or distribution tests.

Common Pitfalls

• Using mixed shard sizes at the start, which makes it impossible to tell whether breakup changed because of flow or because of the samples.
• Comparing raw simulation particles to photo counts without matching the same size bins, which creates a false mismatch.
• Ignoring wall effects in the tumbler, which can make the bottle boundary look like a flow effect.
• Letting image lighting change between runs, which shifts the apparent edges of fragments.
• Tuning the model until it matches one data point, then skipping a check against the full size distribution.

What Makes This Competitive

A stronger project does more than show that plastic breaks. It tests whether the model predicts the whole fragment size distribution, not just the average. You can raise the level by comparing several PET shapes, fitting parameters with a clear method, and checking whether one set of DPD settings works across multiple flow conditions. Careful uncertainty analysis and honest model limits make the work look like real research.

Project Variations

• Study how polyethylene or polypropylene shards fragment, then compare whether polymer type changes the breakup trend.
• Replace the tumbler with a stirred beaker or mixer to test whether a different flow pattern changes calibration quality.
• Analyze fragment shape, not just fragment count, by measuring aspect ratio, edge roughness, or circularity after tumbling.

Learn More

• LAMMPS documentation: Search the official LAMMPS site for DPD and coarse-grained molecular dynamics guides.
• OVITO documentation: Use the official OVITO help pages to learn particle visualization and trajectory analysis.
• Molecular Simulation journal: Search the journal for review articles on coarse-grained polymer simulation and DPD methods.
• PubMed: Search for review articles on microplastic fragmentation, polymer degradation, and environmental transport.
• NOAA Marine Debris Program: Read background material on microplastic sources, transport, and environmental impact.