Bio‐based blends from poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) and natural rubber for packaging applications

Abstract

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is a promising bioplastic but has limited packaging applications due to its brittleness and poor processability. Incorporation of highly viscous high-molecular-weight natural rubber (HMW-NR, gel extracted from NR) into PHBV can improve these properties. HMW-NR is not commercially available, impeding commercialization of the PHBV/rubber blends. Therefore, an organic peroxide was used to selectively crosslink NR to increase its viscosity during its melt blending with PHBV. The PHBV/NR blends were fabricated through a two-step extrusion process using a twin-screw extruder. The blends contained two phases with crosslinked rubber being dispersed in PHBV, and had clear rubber loading-dependent differences in performance. The thermal stability and melt strength of the blends were enhanced over pristine PHBV, indicating improved processability. The flexibility and toughness of the blends were improved by 59 and 20%, respectively, compared with pristine PHBV, and were comparable to commercial petroleum-based plastics.

Synergistic Mechanisms Underlie the Peroxide and Coagent Improvement of Natural-Rubber-Toughened Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Mechanical Performance

“…The new PHBV/NR blend had significantly improved toughness (by ~75%) and ductility (by ~100%) with minimal strength loss (~30%). This enhanced mechanical performance was much improved from that of other conventional dynamically vulcanized PHBV/NR blends, where rubber addition significantly decreased PHBV strength (by 40–80%) with only slight to moderate toughness improvement (by 10–50%) [35,38,104,105]. The new PHBV/NR material has mechanical properties (strength of 28 MPa and toughness of 28 J m −1 ) and processing windows comparable to those of some commercial plastics, such as PP and HDPE, and can replace some petroleum-based conventional thermoplastics in cast sheets and thermoforms, including those used in food packaging.…”

“…In our previous study, peroxide alone was used during reactive blending of PHBV and NR to improve blend compatibility and morphology [34]. Blends containing 10–15% NR provided an optimal combination of processing and mechanical properties [35]. However, further improvements in blend strength and toughness are desired to obtain materials with balanced mechanical properties for broadened industrial applications.…”

“…The effect of the coagent on the thermal, crystallization, morphological, and mechanical properties of PHBV/NR blends was investigated. In our previous work [34,35], we investigated the effect of peroxide (0.15–0.45 wt %), coagent (0–0.63 wt %), and rubber (10–20 wt %) concentrations on the mechanical properties of PHBV/NR blends. The optimal formulation of the blends was 0.45 wt % peroxide, 0.63 wt % coagent, and 15 wt % NR, and this was used to fabricate blends of PHBV and NR in this work.…”

Value-Added Use of Invasive Plant-Derived Fibers as PHBV Fillers for Biocomposite Development

“…The addition of the fibers restricted the mobility of the PHBV molecular chains; restrained the chain diffusion to the surface of the nuclei [ 65 , 66 ]; and disordered the growth of the crystals, especially at the fiber–matrix interface, causing the discontinuous introduction in the crystal structure of the matrix [ 63 ] and the formation of imperfect (e.g., thinner) crystals, resulting in decreased melting temperature and degree of crystallinity [ 67 ]. This is also reflected in the slightly decreased nonisothermal crystallization temperatures of the composites ( Figure 8 C,F), which suggests that the presence of the fibers delayed the crystallization process [ 56 ], i.e., fiber addition made it more difficult for the PHBV to crystallize, and as a result, the composites needed more potential energy to crystallize during the cooling scan, i.e., crystallizing at lower temperature [ 68 ].…”

Compatibilization of Poly(Lactic Acid) (PLA) and Bio-Based Ethylene-Propylene-Diene-Rubber (EPDM) via Reactive Extrusion with Different Coagents

“…Most of them use PLA as matrix phase with different commercially available soft segments like natural rubber (NR) [17,18], epoxidized natural rubber (ENR) [19,20], poly(ethylene-co-vinyl acetate) (EVA) [21,22] and different synthesized bio-based unsaturated elastomers [23,24]. Nevertheless, there are also publications with other matrices, for example polyhydroxyalkanoates (PHAs) [25,26]. Most of the mentioned publications use a batch process to produce the bio-based TPVs, e.g., by using an internal mixer and long reaction times.…”