The Mechanical Properties of a Thermoplastic Elastomer Produced by the Bacterium Pseudomonas oleovorans

Abstract

PHO, a poly(β-hydroxyalkanoate) copolymer containing mostly β-hydroxyoctanoate repeating units, was produced in a fed batch fermentation process by Pseudomonas oleovorans when grown on sodium octanoate as the sole carbon source. The polymer from different batches—evaluated with regards to composition, molecular weight distribution, thermal transition temperatures, and decomposition temperature—was found to be highly consistent batch-to-batch. Polymer composition as a function of growth time did not change significantly once the culture reached the stationary growth phase. PHO when crystallized at room temperature from the melt, forms a physically crosslinked network with the crystalline regions acting as the physical crosslinks. The molecular weight between physical crosslinks was determined to be approximately 4000. The stress-strain properties, hardness, and tensile set of PHO were found to be within the range of values defined by a variety of commercially available thermoplastic elastomers with differing chemical structures. The tensile set of PHO was high, 35% after 100% elongation. Experimental evidence supports three possible sources of the high tensile set: permanent strain-induced orientation or displacement of the physical crosslinks, irreversible strain-induced crystallization, and deformation-induced changes of the size and purity/perfection of crystalline regions.

Epoxidation of bacterial polyesters with unsaturated side chains. II. Rate of epoxidation and polymer properties

“…10 As previously reported, the glass transition temperature (T g ), melting temperature (T m ), and heat of fusion (⌬H m ) all decreased as the unsaturated unit content of the PHOU copolymer increased. 5 …”

Structural, topographical, and mechanical characteristics of purified polyhydroxyoctanoate polymer

“…The elastic modulus was 11.4 MPa, measured for PHO strips (10 × 4 × 0.63–0.70 mm) obtained by extraction in a hypochlorite/chloroform dispersion followed by a purification procedure using acetone for dissolving and a methanol/ethanol mixture for polymer precipitation. On the other hand, PHO strips prepared by melting in 90 °C polymer extracted earlier in chloroform and precipitated in methanol showed a Young's modulus of 9.3 MPa . These slight differences in elastic moduli values may result from the material preparation procedure and the technological differences of the research techniques involved (i.e., lack of an additional purification step over activated carbon, as done in our procedure).…”

The homopolymer poly(3‐hydroxyoctanoate) as a matrix material for soft tissue engineering

“…Marchessault et al21 found the E ′ value for P(3HO) to be 17 MPa and the percentage elongation values to range between 250 and 350% 21. For mcl‐PHA containing 86% of 3‐hydroxyoctanoate (3HO) and minor quantities of 3‐hydroxydecanoate and 3‐hydroxyhexanoate (3HHx), the E ′ value of the polymer film (1.6 mm thickness) was 7.6 ± 0.5 MPa, and the percentage elongation at break was 380% 22. Similarly, Asrar et al23 observed E ′ values ranging from 155 to 600 MPa and elongation at break values ranging between 6.5 and 43% for P(3HO) thermally processed films (micrometer thick, values not given) containing 2.5–9.5 mol % 3HHx.…”