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

Marta Zaccone,Laurens De Brauwer,Marco Monti,Mitul Kumar Patel,Kristiina Oksman,Maria Luana Montalbano,Rakesh Nair

doi:10.3390/polym14030562

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.

Highlights

In recent years, bio-based and biodegradable polymers, such as polylactic acid (PLA), polycaprolactone (PCL), and thermoplastic starch-based polymers (TPS), have emerged as promising alternatives to fossil-based materials because of their many advantages, such as biodegradability, environmental compatibility, and their renewable origin [1,2]
These results show that the drying step makes it more difficult for ChNCs to be redispersed in water by forming irreversible strong hydrogen bonds, resulting in agglomeration and loss of birefringence
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Summary

Introduction

Bio-based and biodegradable polymers, such as polylactic acid (PLA), polycaprolactone (PCL), and thermoplastic starch-based polymers (TPS), have emerged as promising alternatives to fossil-based materials because of their many advantages, such as biodegradability, environmental compatibility, and their renewable origin [1,2]. In addition to these biopolymers, polyhydroxyalkanoates (PHAs) possess these properties [3–6]. PHB exhibits good mechanical and oxygen barrier properties. It is stable under normal usage conditions but undergoes rapid biodegradation under composting conditions [14]. PHB is susceptible to thermal degradation, has a narrow processing window, and shows severe post-process embrittlement, which reduces the applicability of this biopolymer [3,10,15–17]

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Results

Conclusion