A new experimental methodology for swelling and shrinkage assessment of biobased materials
Résumé
The high sensitivity of bio-composites to hygrothermal conditions affects their performance in real-life conditions resulting in dimensional variations. The measurement of the displacement resulting from swelling and shrinkage is a subject of great complexity due to their heterogeneity. The objective of this work is to develop an efficient methodology to measure and quantify these dimensional variations. The paper presents a new experimental investigation based on laser displacement sensors. The main feature of these sensors is that they provide nondestructive and non-contact measurements of the sample. The measurements are made after a cure of the samples of 3 months and an exposure to different humidity conditions. The exposure of the samples to variable humidity consists of a cycle of humidification and drying by several levels. This leads to the identification of specific hygroexpansion and shrinkage coefficients β for each formulation. The results show a highlighting of the phenomena of swelling and shrinkage depending on the type of aggregates with non-reversible behavior with significant hysteresis and inverse behaviour according to different directions. This behaviour is due to water sorption and plant type aggregates. Two treatments are then applied to control the swelling and shrinkage behavior of the aggregates in the biocomposite by using NaCl and NaHCO 3 solutions. The treatment of the aggregates decreases the rate of swelling and shrinkage of biocomposites, highlighting a key role of NaHCO 3 treatment.