Hitoshi Takagi

Natural fibers exhibit noticeable variations in their cross-sections, and measurements assuming a circular cross-section can lead to errors in the values of their properties. Providing more accurate geometric information of fiber cross-sections is a key challenge. Based on microscopic images of natural fiber structures, this paper proposes a natural fiber microstructure detection method based on the CA-DeepLabv3+ network model. The study investigates a natural fiber microstructure image segmentation algorithm that uses MobileNetV2 as the feature extraction backbone network, optimizes the Atrous Spatial Pyramid Pooling (ASPP) module through cascading, and embeds an Efficient Multi-scale Attention (EMA) mechanism. The results show that the algorithm proposed in this paper can accurately segment the microstructures of multiple types of natural fibers, achieving an average pixel accuracy (mPA) of 95.2% and a mean Intersection over Union (mIoU) of 90.7%.

We studied the morphology of yarns obtained from Manila hemp (also known as Abacá) fiber bundles to find a possible correlation with the enhancement in mechanical properties of yarns relative to the original natural fiber bundle. Long Manila hemp fiber bundles had lignin and hemicelluloses removed, twisted and dried to form yarns. Scanning electron micrography revealed that the collapse of lumens inside the fibers leads to densification and consequent increase of tensile properties of the yarns. The densification occurs after the chemical removal of noncellulosic substances from the interstices of cellulose fibrils. These cellulosic elements are then bridged by hydrogen bonds during the drying step of yarn fabrication.

In this study, agricultural waste-derived cellulose nanofiber (CNF) was extracted from parenchyma cells of citrus fruit residue by chemical pulping and fibrillation by a kitchen blender. By changing the pulp blending conditions such as carrying under negative pressure and alkaline aqueous medium, it was possible to obtain CNF morphology at an affordable cost and in a relatively short time.

Natural fiber-reinforced polymer composites are attracting researchers’ attention as environmentally friendly and sustainable materials because of their low environmental load imposed by manufacture and disposal. Natural fiber-reinforced composites have comparable or somewhat inferior mechanical performance when compared to glass fiber-reinforced plastics (GFRP), but have some unique characteristics, which include low thermal conductivity, biodegradation in natural environments and effective suppression of vibration. This paper presents a review of the typical functionalities of natural fiber-reinforced composites including thermal insulation property, biodegradable property and vibration damping property. As described herein, the author will introduce each functionality and discuss the effects of many factors affecting the performance of each function. Consequently, this paper reports that composite materials that fully use their functionality rather than mechanical performance are important for the future development of natural fiber-reinforced composites.

Cellulose is found in the cell wall of plant fibers in the form of nanofibers. The Young’s modulus of the crystalline portion is close to 140 GPa whereas the tensile strength of nanofibers is estimated to be above 2 GPa. Cellulose nanofiber has the potential to become an environmentally benign substitute for conventional reinforcements, but the overall cost of production is prohibitive due to the high energy demand and low yields of the mainstream processes, along with the need for expensive devices for proper extraction. This study proposes the use of an affordable kitchen blender adapted to extract cellulose nanofiber from agricultural crop byproducts to reduce production cost. Preliminary results showed that blending of pulp fibers from grass straw produces nanofibers similar to commercially available morphologies. So far, the raw material for nanofiber extraction has been mainly pulp fibers from wood, but the availability of cellulose in plant cells other than fibers would make nanofibers accessible to a wider research community and accelerate the development of cellulose-based nanocomposites.

The development of all-bio-based composites is one of the relevant aspects of pursuing a carbon-neutral economy. This study aims to explore the possibility to reinforce polylactic acid by the combination of cellulose and chitin nanofibers instead of a single reinforcement phase. Polylactic acid colloidal suspension, cellulose and chitin nanofiber suspensions were mixed using only water as mixing medium and subsequently dewatered to form paper-like sheets. Sheets were hot pressed to melt the polylactic acid and form nanocomposites. The combination of cellulose and chitin nanofiber composites delivered higher tensile properties than its counterparts reinforced with cellulose or chitin nanofibers alone. Cellulose and chitin appear to complement each other from the aspect of the formation of a rigid cellulose nanofiber percolated network, and chitin acting as a compatibilizer between hydrophobic polylactic acid and hydrophilic cellulose.

The presence of nanoscale cellulosic fiber; namely cellulose nanofiber, increases year by year because the mechanical and physical properties are believed to be comparable to those of common glass fibers. On the other hand, most of the reported strength data for the cellulose nanofiber-reinforced polymeric composite materials was not as high as expected. In order to obtain high-strength cellulose nanofiber-reinforced polymer composites, we tried to optimize the fiber orientation of cellulose nanofibers in poly (vinyl alcohol)-based polymer matrix by using a repeated mechanical stretching treatment. The fiber orientation of cellulose nanofibers in the poly (vinyl alcohol) matrix can be modified by changing the total amount of stretching strain applied during the multiple stretching treatments. The degree of fiber alignment was directly evaluated by observing the cellulose nanofibers on the sample surface with a digital microscope. The efficacy of proposed nanofiber alignment control has been explored experimentally and theoretically. The tensile strength and modulus of the cellulosic nanocomposites after applying the multiple stretching treatments increased by approximately 80% and 40% respectively, as compared with those of the untreated nanocomposites.