# Bio-based phase-change materials

The physics of latent-heat storage, how fatty-acid blends and eutectics tune the transition temperature, and why encapsulation is the enabling discipline.

Latent heat is stored in the change of state itself, and fatty acids deliver it well — until supercooling and segregation erode the stock cycle after cycle.

Source: https://en.bioecon.ru/docs/bioenergy-climate/biofuels-bioenergy/bio-based-phase-change-materials/
Updated: 2026-09-07



A phase-change material stores heat in the change of state itself: melting absorbs energy at a nearly constant temperature, freezing returns it. Latent heats of organic PCMs run roughly 150–250 J per gram, against 2–4 J per gram-kelvin for ordinary sensible storage — so a small mass buffers a room or a garment isothermally, which is exactly what building comfort and textiles want. The isothermality is the point: heat only moves while a temperature difference exists, so a buffer holding at its melting point keeps absorbing after a sensible store of the same mass has already warmed through.

## The fatty-acid ladder

Saturated even-carbon fatty acids melt in convenient steps — capric near 31 °C, lauric 44, myristic 55, palmitic 63, stearic 69 — a ladder spanning human comfort and most thermal-storage targets. Latent heats of roughly 150–200 J/g put them level with paraffins, and as food-chain molecules they biodegrade. Blending tunes the transition: in an ideal mixture the melting point drops below either pure component, so eutectic formulations are how a single application temperature is dialled in. Temperature becomes a formulation variable, not a property you inherit.

## What cycling destroys

Three mechanisms erode the stored heat. Supercooling: the melt passes below its own melting point without solidifying, because nucleation needs an ordered cluster to clear an energy barrier — fatty acids and their esters are notoriously prone; the heat comes back late or in an uncontrolled jump, and nucleating additives are the standard patch. Segregation: blends can un-mix as successive freezes sort crystals by composition, so the transition temperature drifts cycle after cycle — the failure mode that made salt hydrates notorious, milder here but present, along with slow oxidative drift of esters and the acidity of free acids attacking metal contacts. And organics conduct heat poorly, around 0.2 W per metre-kelvin, so charge and discharge are slow unless fins or graphite spread the flux. Add a volume change on melting of roughly a tenth, and the container becomes part of the chemistry.

## Encapsulation as the discipline

Encapsulation is what turns a fatty acid into a product. Macroscopic panels hold the melt and absorb the volume change; microcapsules multiply surface area and stop leakage, but the shell adds thermal resistance, dilutes the latent heat per gram of product, and its polymer raises the microplastic question that bio-PCM was partly recruited to answer. The honest performance metric is therefore not the latent heat on the datasheet but the latent heat still delivered after hundreds of cycles — chemistry only counts if it survives cycling.