Ajith Kuriakose Mani

The use of renewable reinforcements in natural rubber (NR) composites is gaining attention as a sustainable alternative to petroleum-derived fillers. This study evaluates the reinforcing efficiency of untreated bristle coir fibers in NR composites fabricated through two-roll milling and hot-press vulcanization. The effects of fiber length (5, 10, and 15 mm) and fiber loading (10–30 wt.%) on mechanical performance and fracture morphology were systematically investigated. While tensile strength decreased moderately with increasing fiber content due to limited interfacial adhesion, significant improvements were observed in tear strength (up to 63%), Shore A hardness (up to 76%), and abrasion resistance (5.2% reduction in wear loss). Scanning electron microscopy revealed fiber bridging, pull-out, and mechanical interlocking as the dominant reinforcement mechanisms. Among the studied configurations, composites containing 10 mm fibers at 20 wt.% exhibited the most balanced performance. The results demonstrate that untreated bristle coir fibers can effectively enhance durability-related properties of NR without chemical modification, making them suitable for eco-friendly, medium-load, and wear-resistant rubber applications.

The pressing issue of global warming has prompted industries to seek sustainable and renewable materials that can reduce the use of petroleum-based products. Natural fibers, as bio-based and environmentally friendly materials, offer a promising solution. In this study, ramie fiber, which is one of the strongest natural fibers, is used as reinforcement, and the mechanical properties of natural rubber composites are evaluated. The composites were fabricated using a vulcanizing technique at 150 °C, and the fibers were cut into different lengths (5 mm, 10 m, and 15 mm) and weights (15 g, 30 g, and 60 g). Mechanical performance tests, including tensile and tear strength and hardness, were conducted. The results showed that as fiber concentration increased, so did the curing time. Moreover, the composites with higher fiber concentration had higher strength. The composite with a 10 mm fiber length and 60 g weight showed the highest tensile strength (10.35 MPa). Maximum tear strength (52.51 kN/m) was achieved with 5 mm fiber length and 60 g weight. Hardness values reached up to 88 Shore A (10 mm fiber length and 60 g weight), indicating excellent wear resistance. The specimen with the highest tensile strength was subjected to scanning electron microscope analysis. The SEM analysis revealed that the composite had a ductile type of fracture with appreciable plastic deformation, confirming good fiber–matrix interaction. These findings underscore the potential of ramie fiber–reinforced natural rubber composites as sustainable, high-performance alternatives to petroleum-based materials in structural and vibration-damping applications.

A number of natural fibers are being proposed for use in composite materials, especially those extracted from local plants, especially those able to grow spontaneously as they are cost‐efficient and have unexplored potential. Sansevieria cylindrica, within the Asparagaceae (previously Agavacae) family, has recently been considered for application in polymer and rubber matrix composites. However, its characterization and even the sorting out of technical fiber from the stem remains scarce, with little available data, as is often the case when the fabrication of textiles is not involved. In this study, Sansevieria cylindrica fibers were separated down to the dimensions of a filament at an 8–15 micron diameter from the stem of the plant, then characterized physically and chemically, using Fourier transform infrared spectroscopy (FTIR), morphologically by scanning electron microscopy (SEM), as well as their thermal degradation, by thermogravimetric analysis (TGA). Their crystallinity surface roughness was measured by X‐ray diffraction (XRD) and atomic force microscopy (AFM), respectively. The results indicate over 70% cellulose fibers content with a very high crystallinity (92%) and small crystallite size (1.45 nm), which suggests a low water absorption, with thermal degradation peaking at 294°C. Despite this, due to the significant porosity of the cellular structure, the density of 1.06 g cm⁻³ is quite low for a mainly cellulose fiber. Roughness measurements indicate that the porosities and foamy structure result in a highly negative skewness (−3.953), in the presence of deep valleys, which may contribute to an effective relation with a covering resin.

Apart from the widely discussed pineapple leaf fibers, normally referred to as PALF, fibers from other parts of the plant also exist, particularly those in the fruit crown, which are known as pineapple crown leaf fibers (PCLF). In this work, PCLF were characterized using thermogravimetric analysis (TGA), Fourier transform IR spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The results indicated that the properties of PCLF do not greatly differ from those observed for PALF. In particular, a cellulose content of over 67% was observed, with approximately 76% crystallinity. The main degradation phenomena of the fibers took place between 230 and 380 °C, peaking at 324 °C, which is in line with observations in other fibers which have similar cellulose and crystalline contents. There was 13.4% residue at 680 °C. Bare mechanical retting of PCLF, although not allowing a full and thorough degumming, which would only be achieved through more aggressive chemical treatment, enabled aspect ratios of over 10³ to be obtained. This indicates some potential for their application as short fibers in composites. In this respect, the considerable roughness of PCLF when compared to other leaf-extracted fibers, and in particular when compared to PALF, could suggest an ability to obtain a sufficiently sound fiber–matrix interface.