News & Events

TREEtments In My HEAT List: Thermal Behaviour of Cellulose Materials

Date: 
Wednesday, March 24, 2021 - 17:00 to 18:00
Speaker: 
Francesco D'Acierno
Affiliation: 
University of British Colombia
Event Category: 
IDG - Inorganic Discussion Group
Host: 
Mark MacLachlan
Location: 
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Abstract:

With the compelling necessity of a rapid shift towards sustainable practices to counteract climate change, testing the thermal properties of biodegradable materials is a crucial step in this process. Among biodegradable materials, those extracted from plants play a predominant role due to the abundance, low cost, and renewability of the sources. Among the components isolated from plants, cellulose represents the greater and most interesting fraction.

Cellulose is a natural polysaccharide, consisting of long parallel chains of bonded glucose units. Several properties can be improved when cellulose is treated to extract cellulose materials (CMs) at the microscale or the nanoscale. For example, acid hydrolysis of pulps is used to dissolve the weak amorphous domains so that highly crystalline nanoparticles, called cellulose nanocrystals (CNCs), can be obtained. CNCs are 3-50 nm wide and 50-1000 nm long, depending on the hydrolysis conditions. Their crystalline nature makes them mechanically strong and an ideal candidate as reinforcing fillers in biodegradable bioplastics. In addition, when aqueous suspensions are dried CNCs self-assemble in chiral nematic phases, showing the potential of the resulting thin films as photonic devices. Another notable example of cellulose treatment is the mechanical shearing of slurries to achieve microscopic materials, known as cellulose filaments (CFs). Although their mechanical and optical properties are not comparable to CNCs, CFs show great potential as additives to cement pastes due to their ability to absorb the surrounding moisture.

From the discussion of their properties, CMs appear to be ready to replace obsolete materials with a large carbon footprint in order to steer toward an ecological transition. However, the most challenging aspect that prevents their large-scale commercialization is their low thermal stability. An emblematic example is represented by CNCs, which, in addition to a large surface area, carry acidic groups on the surface as by-products of the hydrolysis, strongly decreasing their resistance to heat, despite their high crystallinity index. Understanding their thermal behaviour is a key factor in the large-scale development of CMs because several industrial processing techniques involve high temperatures and unstable partially degraded materials display decreased performances.

Here, the thermal behaviour of CMs is uncovered. Based on the current state-of-art, a multi-analytical investigation of the thermal degradation of different types of CNCs, and CFs is carried out. From the effects of dynamic heating cycles, the consequences of static heating cycles on CNCs (both in birefringent aerogel and iridescent thin film forms) and CFs are investigated, with an emphasis on the possible applications of thermally modified CMs.