The usage of non-renewable resources like fossil fuels is one of the main reasons why society has to reduce the consumption of electrical energy. A high amount of electrically powered devices can be found in technical applications, so there is great potential for increasing energy efficiency through technological upgrades, for example by transferring evolutionary evolved adaptive mechanisms of plants for alternative and sustainable approaches in terms of eco-sufficiency.
Autonomous actuators are stimuli adaptive materials with an integrated sensor and actuator system able to make a direct use of primary energy, like temperature or humidity, to produce motion. In this context, Cottonid is a functional material based on chemically modified cellulose, which shows a pronounced and directed humidity-driven swelling and shrinking behaviour.
For characterization of process-structure-property-relationships of Cottonid, the material’s sorption behaviour was investigated over instrumented actuation experiments in an alternating climate chamber based on varying manufacturing parameters. Further, mechanical load increase tests were performed using a servohydraulic testing system with an integrable climate chamber to determine the fatigue behaviour under varying environmental conditions. The experimental study was accompanied by microstructural investigations via scanning electron microscopy (SEM) as well as computed tomography (CT).
Hygroscopic loading cycles during actuation experiments and resulting swelling/shrinkage strains of Cottonid revealed a fully reversible mechanism. By plotting material’s moisture content as a function of relative humidity, a sorption hysteresis could be detected, which is a known phenomenon from wood and leads to a profound understanding of the interaction of Cottonid with its environment. During mechanical tests, Cottonid shows a pronounced influence of the superimposed environmental loading, leading to varying stresses at failure correlating with different values of relative humidity. The aim of the research project is the structural optimization of Cottonid to produce smart functional materials for bio-inspired solutions in civil engineering.