Comprehensive Review of Banyan Tree Fibre-Reinforced Epoxy Composites: Structure–Property Relationships and Performance Evaluation

Technical Summary: Comprehensive Review of Banyan Tree Fibre-Reinforced Epoxy Composites

Problem Statement
The paper addresses the growing demand for environmentally friendly, biodegradable, and cost-effective materials to replace synthetic fibre composites (such as carbon, glass, and aramid) in various engineering applications. While synthetic fibres offer high performance, they present health hazards, are expensive, and lack biodegradability. The study focuses on evaluating the viability of Banyan tree fibres (specifically from the roots) as a natural reinforcement agent within an epoxy matrix. The core problem involves understanding the structure–property relationships of these bio-composites, specifically how fibre treatment, extraction methods, and matrix interactions influence mechanical, thermal, and tribological characteristics.

Methodology
This work is presented as a systematic review and performance evaluation of existing research and experimental data regarding Banyan tree fibre-reinforced epoxy composites. The methodology encompasses:

• Material Extraction and Treatment: The study examines fibres extracted from Banyan tree roots using various treatments, including NaOH (alkali) treatment, steam explosion processes, and enzymatic treatments. The goal of these treatments is to remove lignin and hemicellulose, thereby improving fibre-matrix adhesion.
• Matrix Selection: The primary matrix used is Epoxy Resin (LY556), a thermosetting polymer. The paper distinguishes between thermosetting polymers (which cure and remain solid) and thermoplastic polymers (which melt upon heating), noting that epoxies are preferred for high-performance structural applications despite their inherent brittleness.
• Characterization Techniques: The review synthesizes data obtained through several analytical methods:
  • Scanning Electron Microscopy (SEM): Used to analyze surface morphology, fibre-matrix interfacial bonding, and the presence of contaminants.
  • Thermogravimetric Analysis (TGA): Conducted to assess thermal stability by measuring weight loss as temperature increases (up to 600°C).
  • X-Ray Diffraction (XRD): Utilized to determine crystalline structure, including crystallite size and inter-layer spacing, comparing alkali-treated vs. untreated fibres.
  • Fourier Transform Infrared Spectroscopy (FTIR): Employed to identify functional groups and chemical bond characteristics within the composite.
  • Mechanical Testing: Standardized tests (ASTM D3039 for tensile, ASTM D790 for flexural, and impact/sway tests) were used to evaluate tensile strength, flexural modulus, impact strength, and hardness.

Key Contributions and Results
The paper provides a comparative analysis of the mechanical and physical properties of Banyan tree fibre composites against other natural fibres (sisal, jute, bamboo, banana) and synthetic alternatives.

• Mechanical Properties:

  • Tensile Strength: Results indicate that NaOH-treated fibres yield superior tensile strength compared to untreated fibres. The treatment removes binding agents (lignin/hemicellulose) and enhances crystallinity, leading to better stress transfer. However, tensile strength increases only up to an optimal fibre loading level before declining.
  • Flexural Strength: Composites reinforced with bamboo and treated Banyan fibres demonstrate improved flexural characteristics over pure epoxy. A 5% NaOH concentration is noted to yield better results than 10%.
  • Impact Strength: Unlike tensile properties, impact strength tends to increase proportionally with fibre content. The composites show enhanced energy absorption capabilities.
  • Comparative Data: The paper presents tabular data showing specific values for various composites. For instance, epoxy with sisal fibre (6% NaOH) showed a tensile strength of 11.06 MPa and flexural strength of 38.02 MPa, while banana fibre composites showed significantly higher tensile values (388 MPa in specific configurations), highlighting the variability based on fibre type and orientation.

• Structural and Thermal Analysis:

  • SEM Analysis: Revealed that treated fibres exhibit better adhesion to the epoxy matrix, reducing voids and improving interfacial bonding.
  • XRD Analysis: Confirmed that alkali treatment increases the crystallinity of the fibres by removing amorphous cellulose parts, which correlates with improved mechanical performance.
  • Thermal Stability: TGA results indicate that natural fibres are eco-friendly, releasing fewer harmful gases compared to synthetics, though their thermal stability is generally lower than that of synthetic fibres.

• Material Characteristics:

  • The Banyan tree fibres possess antimicrobial properties, making them suitable for hygiene-related applications.
  • The composites exhibit low density, high porosity, and biodegradability.
  • The study notes that while natural fibres generally have lower strength than synthetics, they offer advantages in specific stiffness, corrosion resistance, and fatigue strength.

Significance and Claims
The paper concludes that Banyan tree natural fibres and epoxy matrices are highly compatible, forming strong bonds that result in composites with mechanical and physical qualities comparable to or superior to other organic fibres in specific contexts.

• Application Scope: The authors claim these composites are appropriate for small-area applications rather than heavy-load structural components. Specific suggested applications include:
  • Decorative pieces and lampshades.
  • Cushion pads and hollow rods.
  • Interior aeroplane parts and paneling.
  • Food trays.
• Environmental Impact: The study emphasizes the potential of these bio-composites to replace synthetic fibres, thereby reducing pollution, lowering toxicity, and aiding in waste management through biodegradability.
• Modesty of Claims: The paper maintains a modest tone regarding the limitations of natural fibres, acknowledging that while they offer significant environmental and economic benefits, their mechanical performance is highly dependent on fibre treatment, orientation, and loading. It does not claim these composites can universally replace synthetic fibres in all high-performance sectors but highlights their viability in specific, less demanding applications.

The authors declare no competing interests and note that no external funding was received for this research.