Water-assisted extrusion and injection moulding of composites with surface-grafted cellulose nanocrystals – An upscaling study

Lilian Forsgren,Abhijit Venkatesh,Florian Rigoulet,Karin Sahlin-Sjövold,Gunnar Westman,Mikael Rigdahl,Antal Boldizar

doi:10.1016/j.compositesb.2020.108590

Abstract

The large-scale surface modification of cellulose nanocrystals (CNC) was carried out to produce CNC-containing composites, in a scale of 3 kg, using industrial-scale melt processing techniques such as twin-screw extrusion and injection moulding. Two different polymer matrices, ethylene-acrylic acid copolymer (EAA) and low-density polyethylene (LDPE), were reinforced with 10 wt% unmodified cellulose nanocrystals (CNC) or surface-treated CNC, where a 2-hydroxyproyl-N-diallyl group had been grafted onto the sulphate half-ester groups on the CNC surfaces. This was achieved by mixing an aqueous CNC dispersion and the polymer pellets directly in the twin-screw extruder followed by a second dry compounding step prior to shaping by injection moulding. The injection-moulded materials were characterized with respect to their mechanical properties and thermal stability. The addition of 10 wt % CNC resulted in all cases in an increase in the yield strength and stiffness by 50–100%, most significantly for the EAA based composites. There were indications of the presence of a stable interphase and a percolating network in the EAA-based materials, according to dynamic-mechanical measurements. A reduction in thermal stability was observed for the melt-processed samples containing diallyl-modified CNC and discoloration in the EAA based samples.

Highlights

There is a drive towards a more sustainable society with a reduction in the use of fossil-based materials
FTIR showed the typical peaks for nanocellulose; a broad band at 3600-3100 cm− 1 attributed to O–H stretching, a band at ca. 2899 cm− 1 attributed to aliphatic C–H stretching, a band at 1429 cm− 1 attributed to CH2 scis soring in cellulose I, bands at 1162 cm− 1 and 898 cm− 1 typical of the glycosidic bond, bands at ca. 1030 cm− 1 attributed to C–O stretching, as well as the characteristic band at 809 cm− 1 attributed to the C–O–S stretching associated with sulphate ester groups
This study has successfully achieved the continuous and relatively large-scale manufacture of Cellulose nano crystals (CNC)-containing composites based on aqueous mixing in a twin-screw extruder fol lowed by injection moulding

Summary

Introduction

There is a drive towards a more sustainable society with a reduction in the use of fossil-based materials. A possible way to address both these concerns could be to use lignocellulosic materials as fillers/reinforcements This has been recognized for many years, but there is a renewed interest due to the commercial availability of nanocellulose [1]. Herrera et al have shown that water-assisted extrusion using cellulose nano fibers and chitin nanocrystals in a polylactic acid matrix improved the dispersion and mechanical properties [17,18]. Another advantage may be that the discoloration can be reduced by the presence of water in the system [19,20,21]. When such surface-modified CNC was added to an ethylene acrylic-acid copolymer matrix both me chanical properties and thermal stability were improved [11]

Methods

Results

Conclusion