Autoxidation of medium chain length polyhydroxyalkanoate.

Area of Science:

• Polymer Science
• Materials Science
• Biotechnology

Background:

• Polyhydroxyalkanoates (PHAs) are versatile biopolymers with diverse applications.
• Autoxidation (aging) is a known phenomenon in synthetic polymers, but less understood in biopolymers.
• Medium chain length PHAs (mcl-PHA) are under investigation for their material properties.

Purpose of the Study:

• To investigate the autoxidation behavior of mcl-PHA with varying levels of olefinic side chains.
• To understand how double bond content affects the chemical and physical properties of mcl-PHA during aging.
• To predict the shelf-life and stability of mcl-PHA based on oxidation kinetics.

Main Methods:

• mcl-PHA copolymers with 0-75 mol% olefinic side chains were aged at 60°C in air for 3 months.
• Samples were analyzed weekly using sol-gel analysis, size exclusion chromatography (SEC), IR, and GC/FID.
• Isothermal DSC experiments were performed to study oxidation kinetics.

Main Results:

• The degree of unsaturation significantly influenced mcl-PHA autoxidation.
• Low double bond content (0-10 mol%) resulted in polymer chain scission.
• High double bond content (50-75 mol%) led to cross-linking and insolubility within weeks.

Conclusions:

• mcl-PHA's sensitivity to autoxidation is strongly dependent on its double bond content.
• Storage at low temperatures (≤ -5°C) and under inert gas or with antioxidants is recommended for mcl-PHA.
• Understanding these aging mechanisms is crucial for optimizing PHA applications and predicting material lifespan.