Influence of Thermocompression Conditions on the Properties and Chemical Composition of Bio-Based Materials Derived from Lignocellulosic Biomass

Abstract

The aim of this study was to assess the influence of thermocompression conditions on lignocellulosic biomasses such as sugarcane bagasse (SCB) in the production of 100% binderless bio-based materials. Five parameters were investigated: pressure applied (7–102 MPa), molding temperature (60–240 °C), molding time (5–30 min), fiber/fine-particle ratio (0/100–100/0) and moisture content (0–20%). These parameters affected the properties and chemical composition of the materials. The density ranged from 1198 to 1507 kg/m3, the flexural modulus from 0.9 to 6.9 GPa and the flexural strength at breaking point from 6.1 to 43.6 MPa. Water absorption (WA) and thickness swelling (TS) values ranged from 21% to 240% and from 9% to 208%, respectively. Higher mechanical properties were obtained using SCB with fine particles, low moisture content (4–10%) and high temperature (≥200 °C) and pressure (≥68 MPa), while water resistance was improved using more severe thermocompression conditions with the highest temperature (240 °C) and time (30 min) or a higher moisture content (≥12.5%). Correlations were noted between the mechanical properties and density, and the material obtained with only fine particles had the highest mechanical properties and density. Material obtained with a 30 min molding time had the lowest WA and TS due to internal chemical reorganization followed by hemicellulose hydrolysis into water-soluble extractables.

Aqueous Pretreatment of Lignocellulosic Biomass for Binderless Material Production: Influence of Twin-Screw Extrusion Configuration and Liquid-to-Solid Ratio

“…As previously described, the use of high pressure improved the cohesion and mechanical strength of the material through densification. For SCB thermocompression at a comparable pressure, the mechanical properties reported in our previous work reached a maximum of 43.6 MPa for the flexural strength and 6.9 GPa for the flexural modulus [6]. These values are comparable for the flexural modulus, but pretreatment by twin-screw extrusion provided a clear improvement, with a significant increase in flexural strength due to fiber deconstruction and better internal reorganization of the components during thermocompression.…”

“…The main reasons for the density results obtained are the high pressure and temperature applied during thermocompression (102 MPa at 200 °C) compared to the pressures reported in other studies, which were <30 MPa [7,45]. This could also be explained by the high proportion of fine particles in the raw SCB and extrudates (15-35%) that could fill the voids within the materials, thereby increasing the material density [6]. The material obtained with raw SCB had a lower density (1432 kg/m 3 ) than those obtained with extrudates (1475-1503 kg/m 3 ).…”

“…The material had a lower density, which facilitated the penetration of water into the material. For SCB thermocompression at a comparable pressure, the TS value reported in our previous work reached a minimum value of 9% [6] due to a higher thermocompression time (30 min) and the particle size of the SCB used, which had been finely ground using a 2 mm sieve. For a thermocompression time of 10 min, the TS value was 47%, which was comparable to the values obtained with the twin-screw extrusion pretreatment.…”

“…A correlation even indicated that a reduction in hemicellulose content was linked with a reduction in water absorption in the final material [9]. In a previous study, hemicellulose degradation during binderless SCB thermocompression improved the water resistance of the final material by allowing internal chemical reorganization [6]. Nevertheless, the lignocellulosic materials obtained with the best tradeoff between mechanical properties and water resistance had shortcomings in terms of their behavior in the presence of water, with much higher thickness swelling values (41%) than those reported for materials bound with synthetic resin, i.e., <13% [10].…”

“…This type of application has been tested recently with delipidated cake obtained after sunflower oil extraction from whole sunflower plants [1], Broussonetia papyrifera [2], sugarcane leaves [3], and bamboo [4]. In addition, SCB-based materials have been produced using thermocompression without any other treatments [5,6]. SCB has high lignin (~20%) and sugar (~60%) contents, which could contribute to self-bonding, thereby offering an opportunity to produce cohesive materials without adding any synthetic resin [7].…”