# Use of Citrus Peel Waste as Bio-Fillers in Polyester Resin Composites: Analysis of Mechanical Properties

## TL;DR

This study explores using citrus peel waste as eco-friendly fillers in polyester resin composites, showing improved hardness but reduced tensile strength.

## Contribution

The novelty lies in evaluating citrus peel waste as a sustainable bio-filler in polymer composites for non-structural applications.

## Key findings

- Citrus peel bio-fillers increased Shore D hardness, with lemon peel achieving the highest at 83.8 ShD.
- Tensile strength decreased with most fillers, but 10% key lime achieved similar peak load to the neat resin.
- 5% grapefruit filler increased stiffness by 10%, indicating effective reinforcement at this concentration.

## Abstract

In the context of global trends in sustainability and the circular economy (CE), this article aims to investigate the potential of microparticles derived from citrus peel waste (grapefruit, key lime, lemon, and orange), constituting approximately 50% of the fruit weight, as eco-friendly bio-fillers in polymer composites, thereby reducing the consumption of petrochemical resins. The composites were fabricated by gravity casting using polyester resin (PR) as the matrix at filler concentrations of 2.5%, 5%, and 10% by weight. Functional properties were assessed using static tensile testing (measuring Peak Load, Peak Stress, and Young’s modulus) and Shore D hardness testing. The incorporation of unprocessed fillers generally decreased tensile strength (Peak Stress REF: 31.48 MPa), attributed to poor interfacial adhesion. The lowest Peak Stress value was recorded for the 2.5O composite (16.04 MPa). The exception was the 10K composite (10 wt.%key limee), which achieved a Peak Load (1.28 kN) nearly identical to the neat resin (1.29 kN), although the Peak Stress remained lower due to the reduced effective cross-sectional area. Stiffness (Young’s modulus REF: 3.26 GPa) increased by more than 10 wt.% for 5G (3.63 GPa), indicating effective reinforcement at this concentration. A key positive finding was a universal increase in Shore D hardness across all biocomposites (REF: 78.4 ShD), with a maximum of 83.8 ShD for 10L (lemon), a typical response to rigid fillers that suggests enhanced surface resistance. The results suggest that citrus peel waste could be considered for non-structural applications where surface durability and efficient waste management are priorities.