Incorporation of plasticizers in sugarcane-based poly(3-hydroxybutyrate)(PHB): Changes in microstructure and properties through ageing and annealing

• The incorporation of a plasticizer does not always improve poly(3-hydroxybutyrate)’s mechanical performance.
• Annealing, which normally improves PHB mechanical properties, has a negative effect on the properties of PHB/plasticizer.
• This negative effect is due to a plasticizer migration by interlamellar amorphous layer reduction.

Poly(3-hydroxybutyrate)(PHB), a natural polymer produced by bacteria via crop-based manufacturing, presents interesting characteristics like thermoplastic behaviour and biodegradability. However, its peculiar fine lamellar structure is highly susceptible to an intrinsic ageing phenomenon that contributes to a remarkable brittleness and low toughness. It has been shown that an annealing treatment can be used to increase toughness and avoid ageing for some PHB-based materials. The incorporation of plasticizers can be another alternative to increase toughness in brittle polymers. In this work, three industrial plasticizers, tri(ethylene glycol) bis(2-ethylhexanoate)(TEG-EH), triethyl citrate (TEC) and tributyl citrate (TBC), were incorporated in PHB via melt-mixing and the effect of these additives through ageing and after annealing was investigated. TEC and TBC were also added to a reactive blend of PHB/PEMGMA. All the compositions studied had 10 wt% of plasticizer. Samples were characterized by differential scanning calorimetry, small angle X-ray scattering, scanning electron microscopy, tensile and impact testing and dynamic mechanical analysis. The compositions with plasticizers presented poor mechanical performance even though they were less affected by ageing. Annealing the samples deteriorated even further their mechanical properties due to plasticizer migration out of the interlamellar amorphous regions.