Carbon-sequestration gradient insulation composites

Abstract

The massive use of carbon-sequestration building materials promises a potential global carbon sink in decarbonizing the building industry. Renewable biogenic materials from abundant agriculture waste for building practice have been around over thousands of years. However, in addition to their flammability and moisture problems, addressing their low thermal and structural performance is also becoming indispensable and urgent when it comes to environmentally sustainable and energy-efficient buildings. Here, we report a nature-inspired biogenic gradient insulation composite with an optimized silica concentration of 30 wt %, a density of 0.246 g/cm³, and a porosity of 86%. The gradient hybrid composite exhibits a thermal conductivity of 28.2 mW m^-1 K^-1, which is the lowest achieved under optimal preparation conditions. It also shows a flexural modulus of 590 MPa for the aerogel-rich layer without surface modification, and it demonstrates superior fire retardancy and superhydrophobicity after surface treatment.

Figure 1.. Schematic diagram and building application

(A) Chemical recycling pretreatment of wheat straw and schematic manufacturing diagram of G-composites. (B) TEM image of the cross-linked composite consisting of nanoporous silica-impregnated cellulose fiber. Scale bar, 2 μm. (C) Ashby plot of different thermal insulation materials. (D) Carbon footprint of the G-composites with a 30 wt % silica concentration.

Figure 2.. Chemical pretreatment of wheat straw

(A) FTIR spectra of hot-water-, acidified-glycerol H₂SO₄, and sodium hydroxide-treated straw fibers. (B) XRD patterns of water, acidified-glycerol-, H₂SO₄-, and sodium hydroxide-treated wheat straw. (C) Thermal conductivity and CI vs. different pretreatment plot of wheat straw. (D–F) SEM images of water-treated, acidified-glycerol-treated, and sodium hydroxide-treated straw fibers. The concentration of NaOH used is 0.5 M. Scale bars, 200 μm.

Figure 3.. Thermal insulation and mechanical strength of G-composites

(A) Schematic diagram of the G-composites. (B–D) SEM images of cellulose-rich layer, intermediate layer, and aerogel-rich layer of G-composites, respectively. Scale bars, 100 μm. (E) FTIR spectra of different layers of the G-composites. (F) Porosity and density variation with respect to aerogel wt %. (G) Thermal conductivity changes between different layers of G-composites. (H) Flexural modulus changes between different layers of G-composites. Error bars are standard deviations from five repeats.

Figure 4.. AM of G-composites

(A) Shear-thinning rheological property of the printable cellulose-aerogel ink. (B) Storage modulus (G′) and loss modulus (G″) as a function of shear stress for the cellulose-aerogel ink. (C) 3D-printed cellulose-aerogel specimens. (D) 3D printability for rapid-prototyping biogenic G-composites. (E) 3D-printed house model with wall thicknesses of 5, 8, and 10 mm, and corresponding infrared (IR) images showing the thermal insulation performance of the 3D-printed house models. Scale bars, 10 mm.

Figure 5.. Building applications of G-composites

(A) Roll-to-roll system built for automatic continuous manufacturing of composite panels. (B) Picture of the prepared composite panel with the length of 25 cm. Scale bar, 2 cm. (C) Car-driving test of the G-composites. (D) Thermal insulation performance of commercial polystyrene and G-composites. Scale bars, 10 cm. (E) Thermal conductivity vs. humidity (%) plot of G composites and wax-coated G-composites. Inset: change in water absorption capacity of G-composites and wax-coated G composites, and water contact angle for the wax-coated G-composites. Error bars indicate standard deviations from five repeats. (F) Mass loss vs. burning time plot of 30 wt % G-composites. Inset: flame retardancy test of boric acid-treated (no wax coating) and untreated G-composites. (G) Mass loss vs. boric acid concentration plot of 10, 20, and 30 wt % G-composites.

Figure 6.. Carbon footprint and reusability of G-composites

(A) Carbon footprint vs. aerogel wt % plot of G-composites. Error bars indicate standard deviations from five repeats. (B) Reusability test of G-composites.