Impact of the Surface Properties of Cellulose Nanocrystals on the Crystallization Kinetics of Poly(Butylene Succinate)

Hatem Abushammala,Jia Mao

doi:10.3390/cryst10030196

Abstract

The hydrophilicity of cellulose nanocrystals (CNCs) is a major challenge for their processing with hydrophobic polymers and matrices. As a result, many surface modifications have been proposed to hydrophobize CNCs. The authors showed in an earlier study that grafting alcohols of different chain lengths onto the surface of CNCs using toluene diisocyanate (TDI) as a linker can systematically hydrophobize CNCs to a water contact angle of up to 120° depending on the alcohol chain length. Then, the hydrophobized CNCs were used to mechanically reinforce poly(butylene succinate) (PBS), which is a hydrophobic polymer. As a result of hydrophobization, PBS/CNCs interfacial adhesion and the composite mechanical properties significantly improved with the increasing CNC contact angle. Continuing on these results, this paper investigates the impact of CNC surface properties on the crystallization behavior of PBS using differential scanning calorimetry (DSC). The results showed that the crystallization temperature of PBS increased from 74.7 °C to up to 86.6 °C as a result of CNC nucleation activity, and its value was proportionally dependent on the contact angle of the CNCs. In agreement, the nucleation activity factor (φ) estimated using Dobreva and Gutzow’s method decreased with the increasing CNC contact angle. Despite the nucleation action of CNCs, the rate constant of PBS crystallization as estimated using the Avrami model decreased in general as a result of a prevailing impeding effect. This decrease was minimized with increasing the contact angle of the CNCs. The impeding effect also increased the average activation energy of crystallization, which was estimated using the Kissinger method. Moreover, the Avrami exponent (n) decreased because of CNC addition, implying a heterogeneous crystallization, which was also apparent in the crystallization thermograms. Overall, the CNC addition facilitated PBS nucleation but retarded its crystallization, and both processes were significantly affected by the surface properties of the CNCs.

Highlights

Cellulose nanocrystals (CNCs) are rod-shaped nanoparticles with a thickness of 3–10 nm and a length of few hundreds of nanometers [1]
A previous work by the authors has shown that grafting alcohols of different chain lengths onto the surface of CNCs using toluene diisocyanate (TDI) as a linker is a relatively simple process for tailoring CNC surface properties [19]
Thermomechanical studies showed that the surface modification had a direct positive impact on the reinforcement capabilities of the CNCs, as it improved their interfacial adhesion with poly(butylene succinate) (PBS)

Summary

Introduction

Cellulose nanocrystals (CNCs) are rod-shaped nanoparticles with a thickness of 3–10 nm and a length of few hundreds of nanometers [1]. They can be extracted from pulp fibers, microcrystalline cellulose, and wood using a variety of reagents including strong acids, bases, oxidizing agents, and ionic liquids [2,3,4]. The possibility to modify their surfaces has led to CNCs with a wide range of surface properties and functionalities [7,8] Due to their mechanical strength, CNCs have often been used to reinforce synthetic and bio-based polymers [9,10,11].

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Results

Conclusion