raw · notes · ingested 2026-07-02
Sugar-alcohol PCM crystallization & optical state — erythritol/xylitol/dulcitol (research note)
confidence: high
Source: https://pmc.ncbi.nlm.nih.gov/articles/PMC5506912/
Purpose: close gap #3 — how translucent are sugar-alcohol PCMs, really? Bottom line: Their optical state is phase-history dependent (clear when molten or vitrified, opaque when polycrystalline), and they vitrify readily due to strong supercooling — but their 90–167 °C melt points rule them out for comfort glazing regardless of clarity.
Mechanism (well-supported)
- Polycrystalline solid → grain-boundary scattering → opaque/cloudy.
- Vitrified/amorphous (glass) solid → no grain boundaries → transparent.
- Melt → clear liquid.
- These polyols supercool deeply and often vitrify instead of crystallizing; a cooled sample can stay glassy-transparent then cloud on cold-crystallization when reheated or seeded — thermoreversibly opposite to paraffin.
Thermal data (primary sources)
- Rodríguez-García et al., PMC5506912 — Erythritol: two crystal forms, melt onsets 105.1 & 118.1 °C, enthalpies 316 & 352.9 J/g, crystallizes ~71 °C (supercooling ~47 K). Xylitol: melt 90 °C, 237.6 J/g, supercools so strongly that “crystallisation never starts after it is molten once” even at 100 g. https://pmc.ncbi.nlm.nih.gov/articles/PMC5506912/
- Lopes Jesus et al. (2009), erythritol crystal growth from the melt — the melt supercools and can vitrify as an amorphous glass; devitrification (crystallizing the glass) destroys transparency via crystal-boundary scattering. The citable mechanism paper. https://pubmed.ncbi.nlm.nih.gov/20045045/
- Dulcitol/starch shape-stabilized bio-PCM, PMC11598460 — sugar alcohol (dulcitol/galactitol) + starch matrix (30–50% starch stops leakage); melt up to 190 °C, 126 J/g; stays supercooled on cooling, releases heat via cold crystallization on reheating (the glassy-then-clouds regime). https://pmc.ncbi.nlm.nih.gov/articles/PMC11598460/
Leads (not fetched)
- NaOH-stabilized supercooled erythritol stays glassy at room temp for months (~200 J/g retained) — a way to hold the clear/glassy state.
- Carboxymethyl-cellulose form-stable PCM with reversible transparency (ACS Sustainable Chem. Eng.) — PEG-based, not a sugar alcohol, but the closest transparent-composite prior art.