STUDIES ON FLAME RETARDANT HEMP FIBER REINFORCED EPOXY COMPOSITES

Abstract

The growing environmental concerns and the need for sustainable materials have fueled the exploration of eco-friendly alternatives, including composite materials, in various industries. Natural fibers, such as jute, flax, hemp, and bamboo, are renewable resources that can be cultivated with lower environmental impact than synthetic fibers. Cultivating natural fibers generally requires less energy and results in fewer greenhouse gas emissions compared to producing synthetic fibers. Natural fibers are often biodegradable, meaning they can decompose naturally over time, reducing the environmental impact at the end of their life cycle. This is in contrast to many synthetic fibers, which can persist in the environment for extended periods. Using natural fibers as reinforcement has many issues, such as hydrophilic nature, moisture absorption, variability in properties, and poor flammability. Different surface modification techniques are used to overcome some of the drawbacks associated with natural fibers. It aims to improve their compatibility with matrix materials, enhance performance, and address issues such as moisture absorption and variability in properties. The primary surface modification methods for natural fibers include chemical treatments, coating and sizing, plasma treatment, silane treatment, UV radiation treatment, and the incorporation of nanomaterials. The flammability of natural fibers is an essential consideration in various industries, mainly when these fibers are used in products such as textiles, composites, and other materials. The flammability of natural fibers can vary depending on the type of fiber, its processing, and the specific conditions of exposure to fire. The flammability of natural fibers is influenced by various factors, and measures can be taken to mitigate their inherent flammability. Researchers and industry professionals continue to explore ways to enhance the fire resistance of natural fibers to broaden their applications in a safe and sustainable manner. Epoxy resin is a widely used polymer matrix in the field of composites, offering several advantages that make it suitable for various applications, such as high strength, strong adhesion, low shrinkage during curing, and good thermal stability. The present study is focused on the exploration of different modification techniques for fibers, their extensive characterization, and the assessment of their suitability as reinforcement in an Epoxy matrix. The fiber was treated with 5w/v % alkali solution for different time intervals and with 5 w/v % silane solution. The fiber properties were analyzed using FTIR (Fourier transform spectroscopy), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive X-ray analysis (EDX). Two different methods, i.e., Flynn-Wall-Ozawa (F-W-O) and Kissinger-Akahira-Sunose (K-A-S) methods were utilized to calculate the degradation activation energy and analyze the thermal kinetics of untreated and treated fibers. The alkali-treated fibers for 30 min show the maximum increment in average activation energy from 141 kJmol−1 to 175 kJmol−1. At 30 min, the alkali treatment of fibers shows the best thermal properties, and afterward, the fiber starts to degrade. Raw and treated fiber composites developed using hand layup with different fiber loadings of 5, 10, 15, and 20 wt%. The developed composites were characterized for thermal (thermogravimetric analysis), chemical (Fourier transform spectroscopy), morphological (scanning electron microscopy and X-ray diffraction), and mechanical behavior. Further, the flammability behavior of the developed composites was investigated using vertical cum horizontal flammability test apparatus and limiting oxygen index (LOI) tester. The results of mechanical characterization reveal that alkali treated fiber composites (20% loading) have the highest tensile strength (24.4 MPa) and flexural strength (46.1 MPa). Composite reinforced with silane-treated fibers have shown excellent flame retardancy with the lowest horizontal burning rate (16.11 mm/min) and higher LOI (23.5%). Scanning electron microscopy confirms the better fiber-matrix compatibility of silane-treated fiber with epoxy. ( Soni and Sinha 2022) The flame-retardant additives (magnesium hydroxide Mg(OH)2 [A] and aluminum hydroxide Al(OH)3 [B]) were used in hemp fiber-based epoxy composites with a different fire retardant (FR) loading, that is, 0%, 8%, 12%, and 24%. An evaluation of flame-retardant effectiveness on composites was carried out using thermogravimetric analysis, limited oxygen index (LOI), UL-94 horizontal burning, morphological analysis scanning electron microscopy (SEM), and char residue analysis. The results show that introducing the flame retardants in the hemp–epoxy composites improved the thermal stability and flame retardancy of hemp–epoxy composites When composites were incorporated with flame retardants, the Horizontal burning rate was decreased, and LOI was increased. The lowest Horizontal burning rate of prepared composites was recorded as 11.6 mm/min, and the highest LOI was 25.3%. (Soni and Sinha 2023) SEM shows a uniform distribution of FR particles in the prepared composite. It is concluded that adding flame-retardant additives efficiently improves the flame retardancy properties of the prepared composites