Which of glycerol, sorbitol, polyethylene glycol (PEG), polyvinyl alcohol (PVA), polylactic acid (PLA), chitosan and gelatin are more tolerant to thermal decomposition?

When considering the thermal stability of the substances you listed, it's important to note that different materials have varying thermal degradation temperatures. Here's a brief overview of each to provide context regarding thermal tolerance:

**Glycerol**: Typically has a melting point around 17.8 °C and can decompose at higher temperatures if heated for prolonged periods. It is less thermally stable compared to the others.

**Sorbitol**: Melting occurs around 95-106 °C, and it may start to decompose if subjected to high temperatures for an extended duration. Its thermal stability is moderate.

**Polyethylene Glycol (PEG)**: The thermal stability of PEG depends on its molecular weight, but it generally starts to decompose around 220 °C. Larger molecular weights tend to exhibit greater thermal stability.

**Polyvinyl Alcohol (PVA)**: PVA has a thermal degradation temperature around 200-220 °C. It exhibits good thermal stability, particularly for applications where moderate heat exposure occurs.

**Polylactic Acid (PLA)**: It has a glass transition temperature around 60 °C and begins to decompose at higher temperatures (around 200-250 °C). PLA is relatively stable under heat but can weaken under prolonged exposure.

**Chitosan**: The thermal degradation of chitosan typically starts around 200-300 °C, demonstrating good thermal stability compared to some others listed.

**Gelatin**: This protein can start to degrade at temperatures around 40-50 °C, making it less thermally stable under high temperatures.

Based on these considerations, the materials that show more tolerance to thermal decomposition, particularly at higher temperatures, would be **Chitosan, Polyethylene Glycol (PEG), and Polyvinyl Alcohol (PVA)**, with Chitosan typically having the highest thermal stability among the listed substances.