Abstract
Polyhydroxyalkanoates (PHAs) represent a promising group of bacterial polyesters for new applications. Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) is a very promising bacterial polyester with potential uses in the packaging industry; nevertheless, as with many (almost all) bacterial polyesters, PHBH undergoes secondary crystallization (aging) which leads to an embrittlement. To overcome or minimize this, in the present work a flexible petroleum-derived polyester, namely poly(ε-caprolactone), was used to obtain PHBH/PCL blends with different compositions (from 0 to 40 PCL wt %) using extrusion followed by injection moulding. The thermal analysis of the binary blends was studied by means of differential scanning calorimetry (DSC) and thermogravimetry (TGA). Both TGA and DSC revealed immiscibility between PHBH and PCL. Mechanical dynamic thermal analysis (DMTA) allowed a precise determination of the glass transition temperatures (Tg) as a function of the blend composition. By means of field emission scanning electron microscopy (FESEM), an internal structure formed by two phases was observed, with a PHBH-rich matrix phase and a finely dispersed PCL-rich phase. These results confirmed the immiscibility between these two biopolymers. However, the mechanical properties obtained through tensile and Charpy tests, indicated that the addition of PCL to PHBH considerably improved toughness. PHBH/PCL blends containing 40 PCL wt % offered an impact resistance double that of neat PHBH. PCL addition also contributed to a decrease in brittleness and an improvement in toughness and some other ductile properties. As expected, an increase in ductile properties resulted in a decrease in some mechanical resistant properties, e.g., the modulus and the strength (in tensile and flexural conditions) decreased with increasing wt % PCL in PHBH/PCL blends.
Highlights
Nowadays, awareness of environmental protection, sustainable development, and the use of renewable energies has become a priority for our society
An increase in ductile properties resulted in a decrease in some mechanical resistant properties, e.g., the modulus and the strength decreased with increasing wt % PCL in PHBH/PCL blends
The aim of this work is to overcome the intrinsic fragility of a bacterial copolyester, namely poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)—PHBH, by blending with a flexible polyester, namely poly(ε-caprolactone)—PCL
Summary
Awareness of environmental protection, sustainable development, and the use of renewable energies has become a priority for our society. The waste generated in a consumer society, such as the present one, comes mainly from the packaging sector. This need has favoured the development of new environmentally friendly. Polymers 2020, 12, 1118 materials [1] For this reason, the use of the so-called biopolymers is increasing in the packaging sector. The use of the so-called biopolymers is increasing in the packaging sector Most of these materials are obtained from renewable resources and they are, in many cases, biodegradable (or compostable in controlled compost soil). They positively contribute to minimizing plastic wastes, reducing the carbon footprint and contributing to circular economies by upgrading industrial wastes [2] and/or by-products [3]
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