Polymer Pyrolysis in ReaxFF

ISEF Category: Chemistry

Subcategory: Computational Chemistry  ·  Difficulty: Advanced  ·  Setup: University Lab  ·  Time: Full Year

The Hook

Plastics do not just melt, they break apart molecule by molecule. In a computer, you can watch those bonds snap and new products form. That lets you compare how PET and bio-based PEF behave when heat climbs fast. Your project can ask which polymer makes more useful or more harmful products.

What Is It?

Pyrolysis means breaking a material down with heat in very little oxygen. For polymers, that means long chains split into smaller molecules, gases, and char-like leftovers. ReaxFF is a reactive force field, which is a physics-based model that can let bonds break and form during a simulation. In LAMMPS, a popular simulation program, you can track those reactions step by step.

Think of each polymer chain like a long zipper. Heating pulls at the zipper, then the teeth snap apart in different places. PET, which is common in bottles and packaging, and PEF, a bio-based cousin, may not snap the same way. Their different shapes and atom arrangements can lead to different product mixes, and your job is to measure those differences in a controlled simulation study.

Why This Is a Good Topic

This is a strong science fair topic because you can ask a real chemistry question with clear inputs and outputs. You can change heating rate, compare two related polymers, and measure product distributions, bond-breaking patterns, or reaction counts. The topic connects to plastic recycling, waste reduction, and material design. You will also learn molecular simulation, reaction analysis, and data visualization, which are useful skills for computational chemistry.

Research Questions

• How does heating rate change the distribution of pyrolysis products in PET?
• How does heating rate change the distribution of pyrolysis products in PEF?
• What is the effect of polymer type on the number of bond-breaking events during pyrolysis?
• To what extent do PET and PEF differ in the timing of chain scission under the same heating schedule?
• Which heating rate produces the largest fraction of small-molecule products for PET versus PEF?
• Does the ratio of oxygen-containing fragments differ between PET and PEF as temperature rises?

Basic Materials

• A computer with enough memory and storage to run molecular simulations.
• LAMMPS with ReaxFF support and the needed input scripts.
• A ReaxFF parameter file published for polyester-like systems.
• A molecular editor or builder such as Avogadro for checking structures.
• Python with NumPy, pandas, and Matplotlib for data analysis.
• A spreadsheet program for organizing runs and summary tables.
• A text editor for editing simulation inputs and logs.
• Access to published PET and PEF structure files or a way to build them from monomers.

Advanced Materials

• University or shared high-performance computing access for repeated simulation runs.
• LAMMPS compiled with MPI support for parallel execution.
• A validated ReaxFF parameter set for oxygen-rich polymer chemistry.
• A trajectory analysis toolkit such as OVITO for visual checks of reaction events.
• Python packages for reaction counting, clustering, and statistical testing.
• A molecular modeling package for building amorphous polymer cells.
• Reference data from literature pyrolysis studies for comparison.
• Version control software such as Git for tracking script changes.

Software & Tools

• LAMMPS: Runs the reactive molecular dynamics simulations for PET and PEF pyrolysis.
• Avogadro: Builds and checks polymer structures before you export them for simulation.
• Python: Processes trajectories, counts products, and makes plots of heating-rate trends.
• OVITO: Lets you inspect trajectories and confirm that bond changes match the output data.
• Excel or Google Sheets: Organizes run metadata, summary tables, and quick comparisons.

Experiment Steps

1. Define the exact question you want to test, then choose one primary output such as product counts, bond scission timing, or fragment size.
2. Select or validate a ReaxFF parameter set that covers the atom types in PET and PEF, then check that it matches published chemistry for related polymers.
3. Build comparable simulation cells for both polymers so differences come from chemistry, not from starting structure quality.
4. Plan a heating schedule matrix with one variable changed at a time, then decide which runs will serve as controls and repeats.
5. Design a product analysis method that turns raw trajectories into counts, fractions, or rates you can compare across conditions.
6. Set up a statistics plan that tests whether PET and PEF differ in a real way, not just by visual inspection.

Common Pitfalls

• Using a ReaxFF file that does not cover all atom types in PET and PEF, which can make the chemistry unreliable.
• Comparing polymers with different starting densities or chain lengths, which mixes setup differences into the result.
• Treating one simulation run as enough evidence, which makes random trajectory noise look like a real trend.
• Counting every tiny fragment the same way, which blurs the difference between gas-like products and larger intermediates.
• Changing analysis rules between PET and PEF, which creates a false comparison.

What Makes This Competitive

A stronger project goes past a simple side-by-side movie of two polymers breaking apart. You need careful controls, repeat simulations, and a clear way to turn trajectories into measurable product distributions. A competitive entry often compares more than one heating rate, uses statistics to test differences, and explains why the chemistry changes. If you can connect your simulation patterns to recycling or low-waste material design, your story gets much stronger.

Project Variations

• Compare PET and PEF pyrolysis under a single heating rate, then focus on the first bond types that break.
• Swap product counts for reaction pathway graphs, and map which intermediate fragments appear before the final small molecules.
• Extend the same method to another bio-based polyester, then compare whether oxygen-rich backbones follow similar breakdown patterns.

Learn More

• LAMMPS Documentation: Search the official LAMMPS manual for ReaxFF, reactive dynamics, and trajectory output options.
• ReaxFF Review Articles on PubMed: Search PubMed for review papers on reactive force fields and polymer degradation.
• NIH PubChem: Look up PET-related and PEF-related monomers or fragments to confirm molecular formulas and structures.
• NIST Chemistry WebBook: Search for thermochemical data on small pyrolysis products that may appear in your simulations.
• MIT OpenCourseWare: Find free materials on molecular simulation, statistical mechanics, and computational chemistry.
• OVITO User Guide: Read the free documentation for visualizing atomistic trajectories and reaction events.