Effect of calcium stearate as a lubricant and catalyst on the thermal degradation of poly(3-hydroxybutyrate)

Poly(3-hydroxybutyrate) nanocomposites modified with even and odd chain length polyhydroxyalkanoates

Poly(3-hydroxybutyrate) (PHB) was blended with medium-chain-length PHAs (mcl-PHAs) for improving its flexibility while nanocellulose (NC) was added as a reinforcing agent. Even and odd-chain-length PHAs, having as main component poly(3-hydroxyoctanoate) (PHO) or poly(3-hydroxynonanoate) (PHN) were synthesized and served as PHB modifiers. The effects of PHO and PHN on the morphology, thermal, mechanical and biodegradation behaviors of PHB were different, especially in the presence of NC. The addition of mcl-PHAs decreased the storage modulus (E') of PHB blends by about 40 %. The further addition of NC mitigated this decrease bringing the E' of PHB/PHO/NC close to that of PHB and having a minor effect on the E' of PHB/PHN/NC. The biodegradability of PHB/PHN/NC was higher than that of PHB/PHO/NC, the latter's being close to that of neat PHB after soil burial for four months. The results showed a complex effect of NC, which enhanced the interaction between PHB and mcl-PHAs and decreased the size of PHO/PHN inclusions (1.9 ± 0.8/2.6 ± 0.9 μm) while increasing the accessibility of water and microorganisms during soil burial. The blown film extrusion test showed the ability of mcl-PHA and NC modified PHB to stretch forming uniform tube and supports the application of these biomaterials in the packaging sector.

Poly(3-hydroxybutyrate) Nanocomposites with Cellulose Nanocrystals

Poly(3-hydroxybutyrate) (PHB) is one of the most promising substitutes for the petroleum-based polymers used in the packaging and biomedical fields due to its biodegradability, biocompatibility, good stiffness, and strength, along with its good gas-barrier properties. One route to overcome some of the PHB’s weaknesses, such as its slow crystallization, brittleness, modest thermal stability, and low melt strength is the addition of cellulose nanocrystals (CNCs) and the production of PHB/CNCs nanocomposites. Choosing the adequate processing technology for the fabrication of the PHB/CNCs nanocomposites and a suitable surface treatment for the CNCs are key factors in obtaining a good interfacial adhesion, superior thermal stability, and mechanical performances for the resulting nanocomposites. The information provided in this review related to the preparation routes, thermal, mechanical, and barrier properties of the PHB/CNCs nanocomposites may represent a starting point in finding new strategies to reduce the manufacturing costs or to design better technological solutions for the production of these materials at industrial scale. It is outlined in this review that the use of low-value biomass resources in the obtaining of both PHB and CNCs might be a safe track for a circular and bio-based economy. Undoubtedly, the PHB/CNCs nanocomposites will be an important part of a greener future in terms of successful replacement of the conventional plastic materials in many engineering and biomedical applications.

The Modification of Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) by Melt Blending

Crystalline and noncrystalline poly(3-hyroxybutylate-co-4-hyroxybutylate) (P(3HB-co-4HB)) were melt blended to obtain mixtures of P(3HB-co-4HB) copolymers. The mixtures and P(3HB-co-4HB) copolymers of different 4HB contents were compared to study the effect of 4HB content on the properties of the copolymers and mixtures. P(3HB-co-4HB) copolymer mixtures, having various 4HB content, have been successfully made by melt blending instead of bacterial biosynthesis. In the case of copolymers, they were noncrystalline when the 4HB content was over 16%, while the P(3HB-co-4HB) mixtures at the same 4HB content were crystalline. The mixtures had a higher glass transition temperature, suggesting that their chain mobility is relatively low compared with the copolymer having the same 4HB content. Due to this effect, the mixture is expected to have a higher melt viscosity and a lower loss tangent to exhibit better melt processing properties. The mechanical properties of the mixtures show a similar behavior to the copolymers in that the tensile strength and the modulus decreases and elongation at the break increases with an increase in the 4HB content.