Conductivity measurements on bio-based, cellulosic materials

The use of bio-based materials in construction can greatly reduce carbon dioxide emissions through: their sustainable production, their contribution to air quality in housings, the reduction of energy consumption for heating or cooling in building which they induce, their partial or full recyclability, and their role of carbon sink. The original hygrothermal properties of these materials are in part due to one remarkable property: their ability to absorb vapor in the form of nanoscale water inclusions between the microfibrils of cellulosic fibers. The ERC Advanced Grant PHYSBIOMAT project aims at developing a physical approach to the hygrothermal behavior of such materials. Within this framework, one particular challenge is to measure the thermal conductivity of these poorly conductive materials. By using a standard Heat Flow Meter we encountered anomalies attributed to edge effects, i.e., radial heat flux deviations, prompting a reevaluation of measurement strategies. Our investigations revealed that conventional thickness limitations are insufficient for accurate thermal conductivity assessments, leading to the innovative analysis of heat flux at both sample interfaces. This approach uncovered that for larger sample thicknesses, an unconventional in-flow of heat from both the top and bottom plates occurs, significantly affecting measurement accuracy. By integrating these findings with simulation comparisons and measuring temperature distribution by thermocouples, we offer novel insights into minimizing errors and refining the thermal conductivity measurement process for insulating materials. On this basis we can now look at the thermal conductivity of cellulose samples of different porosities and bound water saturations and analyze these variations taking into account the fiber orientation.

Work In Progress