Reprogrammable, Sustainable, and 3D-Printable Cellulose Hydroplastic

Abstract

Modern human societies are highly dependent on plastic materials, however, the bulk of them are non-renewable commodity plastics that cause pollution problems and consume large amounts of energy for their thermal processing activities. In this article, a sustainable cellulose hydroplastic material and its composites, that can be shaped repeatedly into various 2D/3D geometries using just water are introduced. In the wet state, their high flexibility and ductility make it conducive for the shaping to take place. In the ambient environment, the wet hydroplastic transits spontaneously into rigid materials with its intended shape in a short time of <30 min despite a thickness of hundreds of microns. They also possess humidity resistance and are structurally stable in highly humid environments. Given their excellent mechanical properties, geometry reprogrammability, bio-based, and biodegradable nature, cellulose hydroplastic poses as a sustainable alternative to traditional plastic materials and even "green" thermoplastics. This article also demonstrates the possibility of 3D-printing these hydroplastics and the potential of employing them in electronics applications. The demonstrated hydroshapable structural electronic components show capability in performing electronic functions, load-bearing ability and geometry versatility, which are attractive features for lightweight, customizable and geometry-unique electronic devices.

Keywords: 3D‐printing; cellulose; electronics; hydroplastic; sustainability.

Figure 1

Overview of cellulose hydroplastic. The schematic diagram at the top illustrates the switchable distinctive mechanical behavior of the sustainable cellulose hydroplastic, which is also bio‐based, reprogrammable, and biodegradable. Schematic illustrations in the middle detail the molecular origins of the switchable mechanical behavior of cellulose hydroplastic in its wet and dry state. The radar plot and images at the bottom illustrate the distinctive mechanical properties of cellulose hydroplastic in its wet and dry state.

Figure 2

Cellulose hydroplastic as a sustainable alternative. A) Representative stress‐strain curve of cellulose in its wet and ambient (60%RH) dry state. B,C) Ashby plot showing tensile strength and Young's modulus of cellulose hydroplastic in comparison with (B) commodity plastics and with (C) “green” thermoplastics. The star symbol represents the average values and the oval encompasses the standard deviations. D) Snapshots of the rehydration process, taken from Movie S2 (Supporting Information). E) Dry state mechanical properties of cellulose hydroplastic as a function of hydroshaping cycles. F) Total sugar content as a function of time in the enzymolysis solution of cellulose hydroplastic undergoing enzymatic biodegradation. G) Image showing prototypes of hydroshaped commercial products, including a stationery holder, photo frame, and a purse, made from cellulose hydroplastic.

Figure 3

Origins of cellulose hydroplastic state transition. A) Dynamic vapor sorption measurement of cellulose hydroplastic at various relative humidity levels conducted at 25 °C. B) The equilibrated absorbed water content of cellulose hydroplastic at various humidity levels. C) Dynamic mechanical analysis measurement of cellulose hydroplastic showing storage modulus (G’) and loss modulus (G”) of cellulose hydroplastic with increasing relative humidity (RH) from 5 to 95% RH. D) Molecular dynamics simulation box modeling cellulose hydroplastic in the ambient dry state (60%RH), humid dry state (90%RH), and wet state, with 10, 25, and 45 wt.% of absorbed water content respectively. (blue: water molecules, grey: cellulose's carbon atoms, red: cellulose's oxygen atoms). E) Simulated number of hydrogen bonds (H‐bond) for cellulose‐water per anhydroglucose unit (AGU), cellulose–cellulose per AGU, and water‐water per water molecule, as a function of different absorbed water content. F–H) Connected water cluster histogram of simulated amorphous cellulose with (F) 10 wt.%, (G) 25 wt.%, and (H) 45 wt.% absorbed water content.

Figure 4

Cellulose‐carbon hydroplastic composites. A) Young's modulus of cellulose‐carbon hydroplastic composites with various carbon nanoparticles (CBNPs) loading. B) Representative stress‐strain curves of cellulose‐carbon hydroplastic composites in both wet and dry state. C) Absorption spectra of cellulose‐carbon hydroplastic composites at different wavelengths. D) Surface temperature of cellulose–carbon hydroplastic composites under 1‐sun illumination as a function of time. E) Thermal images of CB00 and CB20 at different time periods under 1‐sun illumination. F) Drying time of cellulose‐carbon hydroplastic composites in a room ambient environment and under 1‐sun illumination. G) Electrical conductivity of cellulose‐carbon hydroplastic composites as a function of CBNPs loading. H) Demonstration of the “corkboard method” to hydroshape a CB20 strip for a capacitive sensor. I) Schematic illustration of dome‐shaped CB20 capacitive sensor with four quadrants controlling in‐game turtle movement. J) In‐game image of CB20 capacitive sensor.

Figure 5

3D‐printed hydroshapable electronics. A) The viscosity of conductive (CB30) and non‐conductive (CB00) inks as a function of three shear rate steps (low, high, low). B,C) Storage modulus (G′) and loss modulus (G″) as a function of three oscillation stress steps (flow stress,