Chemical Composition Analysis of Fine Fraction (<100µm) from Telfairia pedata Hard Shell for Biocomposite Applications

Abstract

Telfairia pedata, commonly known as Oyster Nut, produces a hard outer fruit shell that is typically discarded or incinerated as agricultural waste. This study investigates the fine fraction (<100 μm) derived predominantly from the softer, yellowish component of the shell, evaluating its chemical composition and potential as a natural filler in biocomposite formulations. Due to the heterogeneous structure of the shell comprising a dense black inner zone and a softer yellowish outer layer, conventional separation was challenging. To overcome this, mechanical grinding using a MELTEST grinder followed by manual sieving was performed. The first-pass grinding selectively fragmented the outer yellowish region, enabling its initial separation. Subsequent grinding cycles and particle-size sieving revealed three distinct fractions: a fine soft zone (<100 μm), an intermediate mixed zone (100–250 μm), and a coarse black-dominant zone (>250 μm). This study focuses on the fine yellowish fraction, which accounted for approximately 25% of the total shell mass. Standardized analytical protocols were applied to determine the chemical composition, yielding values of 12% moisture, 2.9% ash, 9.88% extractives, 27.48% lignin, 34.92% hemicellulose, and 24.82% cellulose (Figure 2). The relatively high holocellulose (hemicellulose + cellulose) content and balanced cellulose-to-lignin ratio suggest favorable characteristics for reinforcement in biodegradable polymer matrices. The moderate lignin concentration further supports its potential to impart thermal stability and dimensional integrity in composite systems. These findings underscore the value of underutilized agro-waste and highlight the fine fraction of Telfairia pedata shell as a promising, sustainable filler for lightweight bio-based materials.