Abstract
Sustainable and cost-effective solutions are crucial for the widespread adoption of 4D printing technology. This paper focuses on the development of a cellulose-hydrogel composite ink for additive manufacture, presenting the development and physical characterisation (stability, swelling potential and rheology) of the cellulose-hydrogel composite to establish its suitability for 4D printing of responsive structures. The use of a carboxymethyl cellulose (CMC) hydrocolloid with incorporated cellulose pulp fibres resulted in an ink with a high total cellulose content (fibre volume fraction ≈50% for the dehydrated composite) and good dispersion of fibres within the hydrogel matrix. The composite ink formulation developed in this study permitted smooth extrusion using an open source 3D printer to achieve controlled material placement in 3D space while retaining the functionality of the cellulose. The addition of montmorillonite clay not only resulted in enhanced storage stability of the composite ink formulations but also had a beneficial effect on the extrusion characteristics. The ability to precisely apply the ink via 3D printing was demonstrated through fabrication of a complex structure capable of morphing according to pre-determined design rules in response to hydration/dehydration.
Highlights
With an increased focus on multifunctionality, the research community has been actively looking for new approaches for the developmentM.C
The pulp linters were saturated in water for ≈24 h (Fig. 2 c), to disrupt the hydrogen bonding between individual fibres followed by manual agitation of the linters using a spatula, before drying at room temperature (Fig. 2 d)
Addition of carboxymethyl cellulose (CMC) polymer served the function of bypassing the undesirable shear thickening by changing the nature of the material system and enabled effective transfer of shear forces to separate pulp fibres
Summary
M.C. Mulakkal et al / Materials and Design 160 (2018) 108–118 the hygroscopic unfolding response of pinecones (Fig. 1), the heliotropic sun tracking behaviour of various plants such as sunflowers and Cornish Mallow (Lavatera cretica) and the tactile response of ‘touch-me-not’ plants (Mimosa pudica) and various carnivorous plants are notable examples of structures that respond to an array of stimuli. Mulakkal et al / Materials and Design 160 (2018) 108–118 the hygroscopic unfolding response of pinecones (Fig. 1), the heliotropic sun tracking behaviour of various plants such as sunflowers and Cornish Mallow (Lavatera cretica) and the tactile response of ‘touch-me-not’ plants (Mimosa pudica) and various carnivorous plants are notable examples of structures that respond to an array of stimuli These naturally responsive structures, relying on controlled arrangement of materials and simple responsive processes such as swelling, require no additional energy input to achieve the actuation [2]. These intercalating water molecules result in swelling throughout the material, which can be used to drive the reversible actuation of specific architectures created by these materials [12,15]
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