Bio-Based Thermoset Crosslinking and Glass Transition

ISEF Category: Chemistry

Subcategory: Organic Chemistry  ·  Difficulty: Intermediate  ·  Setup: School Lab  ·  Time: 1 to 2 Months

The Hook

A bottle of syrup and a food acid can become a solid plastic. That sounds simple, but the mix can act soft, rubbery, or stiff depending on how many crosslinks form. You can measure that shift yourself. This project turns kitchen-safe ingredients into a real materials study.

What Is It?

This project studies a bio-thermoset, which is a plastic that hardens into a fixed network when its molecules link together. Glycerol has three alcohol groups, and citric acid has several reactive groups, so they can connect like a tiny 3D web. Change the citric acid to glycerol ratio, and you change how tight that web becomes.

Think of it like building a net. A loose net bends easily. A tight net resists motion. In polymer terms, tighter crosslink density usually raises stiffness and can change the glass-transition temperature, the point where a material shifts from hard and glassy to softer and more rubbery. You can estimate that change with a DIY dynamic mechanical analysis setup, where a speaker or other vibration source drives a cantilever and you track how the material responds.

Why This Is a Good Topic

This is a strong science fair topic because you can control one clear variable, the reactant ratio, and measure more than one property, like stiffness, damping, and glass-transition behavior. It connects to sustainable plastics, packaging, coatings, and bio-based materials, so the real-world link is easy to explain. You do not need a professional lab to start, but you do need careful planning, good controls, and real data analysis.

Research Questions

• How does the citric acid to glycerol ratio affect the stiffness of the cured bio-thermoset?
• What is the effect of crosslink density on the glass-transition estimate from a DIY cantilever test?
• Does the curing time change the damping behavior of the polymer network?
• To what extent does moisture exposure change the mechanical response of samples with different reactant ratios?
• Which citric acid to glycerol ratio gives the best balance of stiffness and flexibility?
• How does sample thickness affect the measured resonance response in the DIY DMA setup?

Basic Materials

• Citric acid powder, food or reagent grade.
• Glycerol, USP or reagent grade.
• Digital kitchen scale with 0.1 g accuracy.
• Heat-safe glass beakers or borosilicate jars.
• Hot plate with temperature control.
• Silicone baking mat or PTFE sheet for casting.
• Disposable spatulas or glass stirring rods.
• Thermometer or temperature probe.
• Mold or flat casting tray.
• Ruler or calipers.
• Smartphone with slow-motion video.
• Computer with spreadsheet software.

Advanced Materials

• Analytical balance.
• Hot plate with magnetic stirrer.
• Vacuum desiccator or drying oven.
• Dynamic mechanical analyzer, if available for comparison.
• Piezo sensor or accelerometer for vibration pickup.
• Function generator or audio amplifier.
• Speaker or shaker for cantilever excitation.
• Vernier calipers or micrometer.
• Differential scanning calorimetry access, if available.
• FTIR access for tracking ester formation.
• Universal testing machine for flexural comparison.
• ImageJ for displacement tracking from video.

Software & Tools

• Python: Fits resonance curves, compares sample groups, and handles repeated-measures data.
• ImageJ: Tracks cantilever motion from video frames and estimates displacement.
• Google Sheets: Organizes sample ratios, trial labels, and summary statistics.
• Audacity: Generates repeatable test tones for a speaker-driven vibration setup.
• R or JASP: Runs t-tests, ANOVA, or regression on mechanical response data.

Experiment Steps

1. Define the one variable you will change first, then keep the curing method, sample shape, and test setup fixed.
2. Plan a ratio series that spans soft, medium, and highly crosslinked samples so you can see a trend, not just two points.
3. Design controls that separate chemistry effects from thickness, moisture, and incomplete curing.
4. Build a mechanical test that gives a numerical response, such as resonance frequency, damping, or displacement.
5. Decide how you will turn raw video or sensor output into comparable values across samples.
6. Choose one statistical test before you collect data, so your analysis matches your question.

Common Pitfalls

• Using samples with different thicknesses, which makes stiffness look like a chemistry effect when it is really a geometry effect.
• Testing before the polymer finishes curing, which blurs true crosslink differences.
• Letting samples absorb different amounts of moisture, which changes flexibility and damping.
• Driving the cantilever at inconsistent volume or frequency, which shifts the resonance peak between trials.
• Comparing only one sample per ratio, which hides normal variation and weakens your conclusions.

What Makes This Competitive

A stronger project goes past a simple stiffness comparison. You can map a full ratio-response curve, connect it to crosslink density, and test whether mechanical trends match thermal behavior. Good entries also control moisture, thickness, and curing history, then use statistics to separate real effects from noise. If you add a second measurement, like FTIR or DSC access, your story gets much stronger.

Project Variations

• Test how adding a second bio-based polyol, such as sorbitol, changes stiffness and glass-transition behavior.
• Compare air curing versus heated curing to see how reaction conditions change the final network.
• Measure how humidity exposure changes the resonance response of the same thermoset formulations over time.

Learn More

• PubMed: Search for review articles on glycerol-citric acid polyesters, bio-based thermosets, and crosslink density.
• NIH PubChem: Look up the structures and properties of citric acid and glycerol.
• NASA NTRS: Search for materials testing methods and vibration analysis references.
• MIT OpenCourseWare: Find free materials science and polymer chemistry lecture notes for background on networks and glass transition.
• Journal of Polymer Science: Search recent papers on bio-based thermosets and thermal or mechanical characterization.
• ACS Sustainable Chemistry & Engineering: Search for peer-reviewed studies on renewable polymers and solvent-free synthesis.