A Review on the Thermal Characterisation of Natural and Hybrid Fiber Composites

The thermal stability of natural fiber composites is a relevant aspect to be considered since the processing temperature plays a critical role in the manufacturing process of composites. At higher temperatures, the natural fiber components (cellulose, hemicellulose, and lignin) start to degrade and their major properties (mechanical and thermal) change. Different methods are used in the literature to determine the thermal properties of natural fiber composites as well as to help to understand and determine their suitability for a certain applications (e.g., Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and differential mechanical thermal analysis (DMA)). Weight loss percentage, the degradation temperature, glass transition temperature (Tg), and viscoelastic properties (storage modulus, loss modulus, and the damping factor) are the most common thermal properties determined by these methods. This paper provides an overview of the recent advances made regarding the thermal properties of natural and hybrid fiber composites in thermoset and thermoplastic polymeric matrices. First, the main factors that affect the thermal properties of natural and hybrid fiber composites (fiber and matrix type, the presence of fillers, fiber content and orientation, the treatment of the fibers, and manufacturing process) are briefly presented. Further, the methods used to determine the thermal properties of natural and hybrid composites are discussed. It is concluded that thermal analysis can provide useful information for the development of new materials and the optimization of the selection process of these materials for new applications. It is crucial to ensure that the natural fibers used in the composites can withstand the heat required during the fabrication process and retain their characteristics in service.

Three-Dimensional Non-Destructive Inspection Using Novel Infrared-Terahertz Fusion Approaches

The imaging of structures with a complex material composition and geometry is still a challenge in the field of non-destructive testing (NDT). In this study, a non-invasive imaging technique is proposed for the non-destructive inspection of both cultural heritage and natural fiber composites. The proposed technique combines the surface information provided by infrared thermography (IRT) and the internal structure retrieved with terahertz (THz) time-domain spectroscopy using an unsupervised deep residual fusion network. Experiments show that the fusion results contain more material information than a single modality. In addition, 3D imaging has been achieved using the fusion results on natural fiber composites.

Predictions of the Mechanical Performance of Leaf Fiber Thermoplastic Composites by FEA

The available potential plant waste could be worthy material to strengthen polymers to make sustainable products and structural components. Therefore, modeling the natural fiber polymeric-based composites is currently required to reveal the mechanical performance of such polymeric green composites for various green products. This work numerically investigates the effect of various fiber types, fiber loading, and reinforcement conditions with different polymer matrices towards predicting the mechanical performance of such natural fiber composites. Cantilever beam and compression schemes were considered as two different mechanical loading conditions for structural applications of such composite materials. Finite element analysis was conducted to modeling the natural fiber composite materials. The interaction between the fibers and the matrices was considered as an interfacial friction force and was determined from experimental work by the pull out technique for each polymer and fiber type. Both polypropylene and polyethylene were considered as composite matrices. Olive and lemon leaf fibers were considered as reinforcements. Results have revealed that the deflection resistance of the natural fiber composites in cantilever beam was enhanced for several reinforcement conditions. The fiber reinforcement was capable of enhancing the mechanical performance of the polymers and was the best in case of 20 wt.% polypropylene/lemon composites due to better stress transfer within the composite. However, the 40 wt.% case was the worst in enhancing the mechanical performance in both cantilever beam and compression cases. The 30 wt.% of polyethylene/olive fiber was the best in reducing the deflection of the cantilever beam case. The prediction of mechanical performance of natural fiber composites via proper numerical analysis would enhance the process of selecting the appropriate polymer and fiber types. It can contribute finding the proper reinforcement conditions to enhance the mechanical performance of the natural fiber composites to expand their reliable implementations in more industrial applications.