Abstract
Two major obstacles to utilizing polyhydroxybutyrate (PHB)—a biodegradable and biocompatible polymer—in commercial applications are its low tensile yield strength (<10 MPa) and elongation at break (~5%). In this work, we investigated the modification of the mechanical properties of PHB through the use of a variety of bio-derived additives. Poly(lactic acid) (PLA) and sugarcane-sourced cellulose nanocrystals (CNCs) were proposed as mechanical reinforcing elements, and epoxidized canola oil (eCO) was utilized as a green plasticizer. Zinc acetate was added to PHB and PLA blends in order to improve blending. Composites were mixed in a micro-extruder, and the resulting filaments were molded into 2-mm sheets utilizing a hot-press prior to characterization. The inclusion of the various additives was found to influence the crystallization process of PHB without affecting thermal stability. In general, the addition of PLA and, to a lesser degree, CNCs, resulted in an increase in the Young’s modulus of the material, while the addition of eCO improved the strain at break. Overall, samples containing eCO and PLA (at concentrations of 10 wt %, and 25 wt %, respectively) demonstrated the best mechanical properties in terms of Young’s modulus, tensile strength and strain at break.
Highlights
While petroleum-based polymers exhibit excellent properties and are low in cost, the negative environmental effects resulting from their use continues to grow
This work aimed to improve the mechanical properties of PHB by blending it with epoxidized canola oil (eCO), cellulose nanocrystals (CNCs) and poly(lactic acid) (PLA), and to establish whether these additives affect the thermal stability of this biopolymer
The results in this study demonstrated that the combination of more than one or all components (e.g., PHB/PLA/10eCO) led to synergistic effects on mechanical and thermal performance
Summary
While petroleum-based polymers exhibit excellent properties and are low in cost, the negative environmental effects resulting from their use continues to grow. Some biopolymers are degradable, which can reduce the accumulation of plastics in the environment after disposal [1,2]. Polyhydroxybutyrate (PHB)—part of the polyhydroxyalkanoate (PHA) aliphatic polyester class—is a semi-crystalline polymer produced through numerous mechanisms, including the bacterial fermentation of sugars. PHB can be enzymatically-degraded by microorganism found in a variety of environments [3]. These microorganisms produce enzymes (PHA depolymerases) that catalyze the hydrolysis of the polymer, yielding monomers and oligomers that can be consumed by the microorganisms. PHB—as well as its degradation products—are both food safe and biocompatible, Polymers 2019, 11, 933; doi:10.3390/polym11060933 www.mdpi.com/journal/polymers
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