Influence of Chitin Nanocrystals on the Crystallinity and Mechanical Properties of Poly(hydroxybutyrate) Biopolymer

Abstract

This study focuses on the use of pilot-scale produced polyhydroxy butyrate (PHB) biopolymer and chitin nanocrystals (ChNCs) in two different concentrated (1 and 5 wt.%) nanocomposites. The nanocomposites were compounded using a twin-screw extruder and calendered into sheets. The crystallization was studied using polarized optical microscopy and differential scanning calorimetry, the thermal properties were studied using thermogravimetric analysis, the viscosity was studied using a shear rheometer, the mechanical properties were studied using conventional tensile testing, and the morphology of the prepared material was studied using optical microscopy and scanning electron microscopy. The results showed that the addition of ChNCs significantly affected the crystallization of PHB, resulting in slower crystallization, lower overall crystallinity, and smaller crystal size. Furthermore, the addition of ChNCs resulted in increased viscosity in the final formulations. The calendering process resulted in slightly aligned sheets and the nanocomposites with 5 wt.% ChNCs evaluated along the machine direction showed the highest mechanical properties, the strength increased from 24 to 33 MPa, while the transversal direction with lower initial strength at 14 MPa was improved to 21 MPa.

Biopolymer Blends of Poly(lactic acid) and Poly(hydroxybutyrate) and Their Functionalization with Glycerol Triacetate and Chitin Nanocrystals for Food Packaging Applications

“…Moreover, the addition of ChNCs leads to a reduction in the vaporization peaks of the GTA in the isothermal temperature region due to its plasticizer antimigration capability, making it difficult to remove GTA at the isothermal temperature. 29 These findings indicate that the ChNCs have a favorable impact on the nanocomposite performance, with the maximum improvement obtained in the 75:25:20:1 blend. The first DSC heating scans of the nanocomposites and their reference materials are shown in Figure S6b in the Supporting Information.…”

“…Additionally, the presence of ChNCs lead to a shift of the T max of the 75:25 blends toward higher temperatures, and this behavior was particularly pronounced in the 75:25:20:1 blend, where the increase in T max was approximately 57 °C (from 288 to 345 °C) for the PHB degradation peak and 61 °C (from 365 to 426 °C) for the PLA degradation peak. Moreover, the addition of ChNCs leads to a reduction in the vaporization peaks of the GTA in the isothermal temperature region due to its plasticizer antimigration capability, making it difficult to remove GTA at the isothermal temperature . These findings indicate that the ChNCs have a favorable impact on the nanocomposite performance, with the maximum improvement obtained in the 75:25:20:1 blend.…”

“…Both PHB and ChNCs were produced on a pilot scale at the Bio Base Europe Pilot Plant (BBEPP, Belgium) as described in the previously reported study. 29 Briefly, PHB was produced by the fed-batch fermentation of glucose syrup using Parabulkholderia sacchari at 29 °C, followed by downstream processing that involves cell lysis and enzymatic hydrolysis of the bacterial intracellularly stored granules and then concentration and grinding to form PHB powder. The purity of the produced PHB was higher than 95%.…”

“…Extrusion grade PLA (Ingeo 4043 D, NatureWorks) with an average molecular weight (MW) of 200000 g mol –1 was purchased from Resinex Switzerland AG (Freienbach, Switzerland). Both PHB and ChNCs were produced on a pilot scale at the Bio Base Europe Pilot Plant (BBEPP, Belgium) as described in the previously reported study . Briefly, PHB was produced by the fed-batch fermentation of glucose syrup using Parabulkholderia sacchari at 29 °C, followed by downstream processing that involves cell lysis and enzymatic hydrolysis of the bacterial intracellularly stored granules and then concentration and grinding to form PHB powder.…”

“…Several studies have been published on the laboratory-scale preparation of ChNCs from various raw materials using HCl acid hydrolysis. , However, if the hydrolysis is done on a large scale, H 2 SO 4 is a more suitable acid to hydrolyze the chitin because HCl is a strong reducing acid, which makes it highly corrosive when in contact with industrial equipment. It was shown in EU Horizon 2020 project Newpack that chitin nanocrystals can be produced with H 2 SO 4 ; however, their colloidal stability is not as good due to the low negative surface charge.…”