Abstract
Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB-V) has not been used for demanding technical applications yet due to its limited mechanical properties, particularly its high brittleness. An appropriate route to overcome these limitations is the implementation of plasticizers in the PHB-V matrix via compounding. In this paper the use of different types of fatty acids esters as PHB-V plasticizers were investigated. The study describes how the difference in the fatty acid esters structure (mainly fatty acid hydrocarbon chain length) affects their plasticizing effect and thus the PHB-V ductility performance. The best impact properties of PHB-V compounds were obtained for oleic acid methyl ester, palmitic acid methyl ester or lauric acid ethylene glycol monoester. The increase of notched impact strength from 1.4 (for neat polymer) to 4.0–4.1 kJ/m2 was observed. At the same time stiffness and strength of the polymer decreased but remain on a level sufficient for technical applications. Additional drawback of PHB-V materials is increasing the brittleness over time. Moreover this study shows that the use of oleic acid ethylene glycol monoester or stearic acid ethylene glycol monoester as plasticizers significantly reduces the increase of the brittleness of PHB-V over time. It is relevant that this drawback of PHB-V materials can be significantly improved by plasticizer addition.
Highlights
In recent years various reports have shown processing routes for the lab-scale biosynthesis of polyhydroxyalkanoates (PHAs) using different carbon sources and strains of bacteria [1, 2]
For the synthesis of fatty acid esters used as PHB-V plasticizers, fatty raw materials differing in the fatty acid profile were used
The fatty raw materials used in this paper are characterized by very high contents of distinctive fatty acids of more than 90 wt% (Table 2), e.g. the product named as oleic acid contained 90.9 wt% oleic acid and product named as palmitic acid include 98.6 wt% of palmitic acid
Summary
In recent years various reports have shown processing routes for the lab-scale biosynthesis of polyhydroxyalkanoates (PHAs) using different carbon sources and strains of bacteria [1, 2]. PHB poly(3-hydroxybutyrate) and its copolymers, e.g. poly(3hydroxybutyrate-co-3-hydroxyvalerate) PHB-V, are the most popular members of the PHAs. PHB poly(3-hydroxybutyrate) and its copolymers, e.g. poly(3hydroxybutyrate-co-3-hydroxyvalerate) PHB-V, are the most popular members of the PHAs Both -PHB and PHB-V as a thermoplastic polymer- can be processed using conventional equipment [3, 4]. These polymers could be used for the production of films, fibres, packaging materials or thermoformed rigid products. PHB is a stiff and brittle polymer and it is characterised by a poor thermal stability and a narrow range of processing temperature. This results in weak mechanical properties with low elongation at break properties
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