Effect of ultrafine talc on crystallization and end‐use properties of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate)

Abstract

Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) is a highly versatile polyhydroxyalkanoate. To enhance its slow crystallization, the performance of ultra-fine talc (median diameter of 1 mm) as a nucleating agent is studied. This study focuses on crystallization, but also on the effect on fundamental properties (i.e., thermal stability) and selected end-use properties (i.e., color, opacity, tensile properties, and gas permeability), to assess its applicability for food packaging purposes. Samples containing 0.5, 1, and 2 wt % were prepared through melt blending and compression molding. First, it was proven that ultra-fine talc is a highly performant nucleating agent for PHBHHx. The isothermal crystallization half time at 70 8C was reduced to 97% by adding 2 wt % of talc, which could greatly improve the processability of PHBHHx. Thermal stability increased with 3-4 8C, due to increased barrier effect. Permeability for O 2 , CO 2 , and water vapor increased slightly upon addition of 0.5 wt % and 1 wt % talc, but decreased at 2 wt % talc. Nevertheless, the results remained within the same applicability range. An acceptable total color change of 0.9 was observed. Furthermore, the PHBHHx matrix was rendered stiffer (Young's modulus increased with 100 MPa), while showing hardly any change in elongation at break or tensile strength. Overall, it can be concluded that ultrafine talc is a very efficient nucleating agent for PHBHHx. Besides the beneficial effect on crystallization, the ultrafine talc hardly influenced any other property, which could prove to be of high added value for the application of these composites as food packaging material.

In vivo and Post-synthesis Strategies to Enhance the Properties of PHB-Based Materials: A Review

“…Actually, although the crystallization mechanism and the crystal cell structure do not change, the overall isothermal crystallization rate of PHBHHx copolymers reduces with HHx content and occurs at lower crystallization temperature from the melt (Cai and Qiu, 2009 ). Indeed, due to their steric hindrance, the 3HHx does not co-crystallize with 3HB units; thus, PHBHHx displays slower crystallization rate than PHB homopolymers, which can be a challenge for its efficient processing (Vandewijngaarden et al, 2016 ). The fact is that due to reduced crystallinity, when PHBHHx copolymers with different mol% HHx are subjected to anaerobic biodegradation, the higher is the HHx, the faster is the rate of weight loss (Morse et al, 2011 ).…”

“…In fact, the addition of different additives acting as nucleating agents has been proposed. Ultrafine talc was reported to drastically improve PHBHHx crystallization, causing also an increase in the YM (Vandewijngaarden et al, 2016 ) without modification of the material barrier properties, thus opening the way to its use as a protection layer for moisture-sensitive O 2 barrier layers. The use of zinc oxide as filler, on the other hand, also improved PHBHHx crystallization but strongly affected its opacity, although resulting in a successful UV-blocking property.…”

Extrusion and Injection Molding of Poly(3-Hydroxybutyrate-co-3-Hydroxyhexanoate) (PHBHHx): Influence of Processing Conditions on Mechanical Properties and Microstructure

“…PHBV and PHBHHx display slower crystallization rates than the homopolymer PHB because the co-monomer units are excluded from the PHB lattice during crystallization from the melt, which can be a challenge for efficient processing of PHBHHx, especially in methods with high cooling rates like injection molding [15,16]. Despite the rise in attempts to further improve both thermal and mechanical properties of PHAs with or without processing aids [17][18][19][20], current research regarding PHA processing and compound fabrication mostly relates to batch processing methodologies without the involvement of high temperatures and/or high shear rates, like solution casting [21][22][23], compression molding [24,25], or spinning techniques [26][27][28]. While these techniques are practical for use in a lab-scale context, they often have limited applicability on larger scales.…”

Cationic Cyclopentadienyliron Complex as a Novel and Successful Nucleating Agent on the Crystallization Behavior of the Biodegradable PHB Polymer

“…These results could be attributed to the presence of the strong interaction between the organoiron centers (CpFe + ) and the PHB matrix. As can be seen in Figure 5 , the appearance of the crystallization peaks of the PHB nanocomposites became sharper and narrower compared with those of the pure PHB, which demonstrated that the CpFe + acts as an efficient nucleating agent and suggested that the PHB crystallization occurs through a heterogeneous nucleating mechanism [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ]. Therefore, the values of the ∆H c for all the PHB nanocomposites were higher than those of the pure PHB.…”

“…Various reports have revealed that the addition of nucleating agents to PHB has resulted in a significant improvement in thermal, mechanical, and other physical properties. Examples of these nucleating agents have included the following: NH 4 Cl [ 18 ], melamine [ 19 ], boron nitride [ 20 , 21 ], talc [ 22 , 23 ], cyanuric acid [ 24 ], cyclodextrin [ 25 ], lignin [ 26 ], and thermally reduced graphene (TRG) [ 27 ]. Recent examples have incorporated nanofillers, such as multi-walled carbon nanotubes [ 28 , 29 ], TiO 2 , and ZnO nanoparticles [ 30 ], graphite nanosheets [ 31 ], and WS 2 inorganic nanotubes [ 32 ].…”