Sulfur Vulcanization and Material Properties of Polyhydroxyalkanoates with Unsaturated Side Chain

Area of Science:

• Polymer Science
• Materials Science
• Biotechnology

Background:

• Polyhydroxyalkanoates (PHAs) are biodegradable polymers with potential for various applications.
• Modifying PHA properties is crucial for expanding their use, particularly towards elastomeric materials.
• Unsaturated side chains in PHAs offer sites for crosslinking and property enhancement.

Purpose of the Study:

• To investigate the effects of sulfur vulcanization on the physical properties and biodegradability of poly(3-hydroxybutyrate-co-3-hydroxy-5-hexenoate) [P(3HB-co-3H5HE)].
• To assess the potential of vulcanized P(3HB-co-3H5HE) as an elastomeric material.
• To evaluate the biodegradability of the sulfur-vulcanized PHA copolymers.

Main Methods:

• Biosynthesis of P(3HB-co-3H5HE) with varying 3-hydroxy-5-hexenoate (3H5HE) fractions using recombinant Escherichia coli.
• Sulfur vulcanization of P(3HB-co-3H5HE) using varying sulfur contents and standard curing agents.
• Characterization of physical properties (tensile strength, elongation at break, tensile set) using mechanical testing.
• Analysis of crosslinking via chloroform insolubility and Raman spectroscopy to confirm double bond functional loss.

Main Results:

• Vulcanized P(3HB-co-3H5HE) became insoluble in chloroform, indicating successful crosslinking.
• Tensile strength and elongation at break significantly increased after vulcanization, with a sample containing 47 mol% 3H5HE showing a tensile strength of 6.3 MPa and elongation at break of 813%.
• The vulcanized material exhibited rubber-like properties with a low tensile set (8%) after 200% elongation.
• Biodegradability decreased with increased crosslink density but remained higher than vulcanized rubber.

Conclusions:

• Sulfur vulcanization effectively enhances the resilience and elastomeric properties of unsaturated PHAs.
• Vulcanized P(3HB-co-3H5HE) shows promise for applications requiring rubber-like characteristics.
• The balance between enhanced physical properties and retained biodegradability makes these materials attractive for sustainable elastomeric and environmental applications.