Chitosan, which is a derivative of chitin, is particularly popular due to its biodegradable and renewable nature. However, the properties of chitosan can be inconsistent due to the extraction process and its natural origin, which poses a challenge to its use in composite materials as a matrix. The properties of chitosan can be tuned by controlling the degree of deacetylation (the extent to which acetyl groups are removed from chitin to form chitosan) and molecular weight. This paper presents a detailed study on the extraction and characterization of chitosan from shrimp shells. The structural thermal and mechanical characterization were studied using several techniques: Fourier-transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis and differential scanning calorimetry. The intrinsic viscosity and deacetylation degree were determined using various methods. The results showed an average degree of deacetylation of 77%. The chitosan films exhibited a high tensile strength of 43.9 MPa and an elongation at break of 3.14%. The thermal analysis revealed that the films had a glass transition temperature of 88 °C and a maximum thermal degradation temperature of 320 °C. The findings of this research could contribute to the development of chitosan-based materials with improved properties, leading to its wider adoption in the future for composite matrix application. The simple and efficient method used for the extraction and purification of chitosan from shrimp shells makes it a cost-effective and eco-friendly alternative to synthetic polymers.

The performance of the thermoelectric module highly depends on the geometry of the legs, the module area, and implicitly on the number of the pairs, besides the properties of the materials. The geometry of the legs consists of the shape, the dimensions on three axes, and whether the legs are filled or are hollow. The legs can have one hollow or more, the hole can be from the top to bottom or not. This paper studies and compares the performance of different thermoelectric modules in function of the shape: square, triangular, trapezoid, reverse trapezoid, hourglass, inverse hourglass (filled and with the hollow from the top to the bottom or not), and with different dimensions of the length and width. The simulations are performed using the COMSOL Multiphysics software, where 3D numerical models are developed and solved using the finite element method. The results are compared with others from the specialized literature for a one pair square shape. The current-voltage and power-voltage characteristics have a good matching, which proves the simulations are good and the model can be used for other shapes. A steady-state heating condition is applied to the hot side of the thermoelectric generators, while the cold side is subjected to steady state, natural convection, and forced convection heating conditions. The square shape with an internal hollow is studied first. The best performance when the length and width are 1 mm × 1 mm, 1.5 mm × 1.5 mm, and 2 mm × 2 mm is obtained for the thermoelectric generator with filled square legs. The highest maximum power is obtained for thermoelectric generator with the sizes 2 mm × 2 mm. The gain in power for the square shape in comparison with the worst value of the TEG (Inverse Hourglass for filled and Triangular for hollow) for the three dimensions considered is for those filled 199%, 202%, and 204%, respectively, and for those that are hollow 198%, 232%, and 243%, respectively. The reduction in maximum power is 5%, for the thermoelectric generator with square legs (2 mm × 2 mm) and with hollow legs, in comparison with one filled. The maximum power increases for the thermoelectric generator with square legs which have a hollow interior, in this case 2 mm × 2 mm, with 0.2% and 1% for the thermoelectric generator with sizes of 1 mm × 1 mm. Additionally, the results obtained for the square filled shape are compared with the real ones obtained for a thermoelectric generator with sizes 40 mm × 40 mm × 4 mm. The matching is very good, which confirms that the model can be used for different geometry of the thermoelectric generators in order to help the manufacturers improve their performance.

This paper investigates energy harvesting performances of porous piezoelectric polymer films to collect electrical energy from vibrations and power various sensors. The influence of void content on the elastic matrix, dielectric, electrical, and mechanical properties of porous piezoelectric polymer films produced from available commercial poly(ethylene-co-vinyl acetate) using an industrially applicable melt-state extrusion method (EVA) were examined and discussed. Electrical and mechanical characterization showed an increase in the harvested current and a decrease in Young’s modulus with the increasing ratio of voids. Thermal analysis revealed a decrease in piezoelectric constant of the porous materials. The authors present a mathematical model that is able to predict harvested current as a function of matrix characteristics, mechanical excitation and porosity percentage. The output current is directly proportional to the porosity percentage. The harvested power significantly increases with increasing strain or porosity, achieving a power value up to 0.23, 1.55, and 3.87 mW/m³ for three EVA compositions: EVA 0%, EVA 37% and EVA 65%, respectively. In conclusion, porous piezoelectric EVA films has great potential from an energy density viewpoint and could represent interesting candidates for energy harvesting applications. Our work contributes to the development of smart materials, with potential uses as innovative harvester systems of energy generated by different vibration sources such as roads, machines and oceans.

Collecting the vibration energy existing in the surrounding environment and its transformation to a useful electrical energy in order to supply ultra-low power systems remains an emerging and promising technology. During the last decades, most of research efforts dealt with energy-harvesting technology using piezoelectric ceramics. However, those materials are stiff and limited in mechanical strain abilities. In addition, they lose their stiffness and piezoelectricity at high levels of mechanical strain. Thus, they are unsuitable for many applications in which low frequency and high strain level are required. However, electrostrictive polymers are lightweight, very flexible, have low manufacturing costs and are easy to mould into any desired shapes. These special properties led to them being considered as potential actuators. However, it is not well known that these materials also can be used for mechanical-to-electrical energy harvesting. In this research paper, electromechanical characterization of polymer/lead zirconate titanate composites was extended. The first part develops the analytical model predicting the energy harvested by polyurethane/PZT composites from electrical and mechanical properties of their constituent materials. Indeed, this model was based on the approach of representing the experimental setup with an equivalent electrical scheme. The second part focuses on the assessment of model performance by comparison between predicted and observed values. As a result, good agreements were observed between the two sets of data; in addition, the model could be used to optimize the choice of constituent materials. The last part concerns the contribution of both the electrostrictive effect and piezoelectric effect in electrical powers harvested by PU/PZT composites.