Tea Stem Waste Powders for Epoxy-Based Composites: Processing, Mechanical Properties, and Fracture Behavior

Abstract

This study investigates the potential of mechanically processed tea stem waste powders as an environmentally friendly reinforcement for epoxy-based composites. Tea stem waste, a lignocellulosic byproduct of tea processing, was reduced in size by high-speed mixing and planetary ball milling without any chemical pretreatment, and incorporated into an epoxy system at varying weight fractions (1–10 wt.%). The composites were fabricated under controlled conditions and subjected to tensile, fracture toughness, hardness, thermal, and morphological evaluations. Mechanical testing revealed that tensile strength increased with filler loading up to an optimum of 7.5 wt.% (72.16 MPa), corresponding to a 14.8% improvement over neat epoxy, while higher content(10 wt.%) showed minor reduction due to potential filler agglomeration. The elastic modulus displayed a non-linear trend, decreasing slightly at low filler levels but reaching 1.30 GPa at 10 wt.%. Fracture toughness (Kıc) exhibited a continuous increase, with a maximum of 2,41 MPa√m at 10 wt.%—a 26.4% improvement compared to neat epoxy. Shore D hardness also improved progressively, with up to a 23% increase at the highest filler content. Thermal analysis confirmed that the addition of tea stem powder did not significantly affect the glass transition or initial degradation temperatures, while an increased char yield indicated enhanced thermal stability. FE-SEM fractography showed that fiber orientation strongly influenced crack propagation: longitudinal fibers remained intact, while transverse fibers fragmented and dissipated energy, thereby enhancing fracture resistance. These results confirm that tea stem waste powders, processed solely by mechanical means, can effectively reinforce epoxy matrices. Although samples made with 7.5% filler yield the best results in tensile testing, it has been observed that 10% content yields higher results in fracture toughness and hardness tests. The results of the study showed that the mechanical strength of the composite material made from this tea stem waste was higher than that of pure epoxy in all content variations tested here.

Keywords

• epoxy composites
• fracture toughness
• hardness
• natural fibers
• tea stem waste

Epoksi Bazlı Kompozitler için Çay Sapı Atık Tozları: İşleme, Mekanik Özellikler ve Kırılma Davranışı

Abstract

Bu çalışma, çay işleme sürecinin lignoselülozik bir yan ürünü olan çay sapı atığı tozlarının epoksi esaslı kompozitlerde çevre dostu takviye malzemesi olarak kullanım potansiyelini araştırmaktadır. Atık çay sapları herhangi bir kimyasal ön işlem uygulanmadan yüksek hızlı karıştırma ve planet değirmenle inceltilmiş ve %1–10 (ağ.%) oranlarında epoksi matrisine eklenmiştir. Üretilen kompozitler çekme, kırılma tokluğu, sertlik, termal ve morfolojik testlere tabi tutulmuştur. Deneysel sonuçlar, çekme dayanımının %7,5 dolgu oranında (72,16 MPa) saf epoksiye kıyasla %14,8 artış gösterdiğini, kırılma tokluğunun ise %10 dolgu oranında 2,41 MPa√m ile %26,4 iyileştiğini ortaya koymuştur. Shore D sertliği en yüksek dolgu oranında %23 artış göstermiştir. Termal analizler, camsı geçiş ve bozunma sıcaklıklarının büyük ölçüde korunmasına rağmen artan kömürleşme miktarının termal kararlılığı güçlendirdiğini göstermiştir. FE-SEM kırılma yüzey analizleri, lif yöneliminin çatlak ilerlemesi üzerinde belirleyici olduğunu; boyuna liflerin bütünlüğünü koruduğunu, enine liflerin ise parçalanarak enerji dağılımını artırdığını ortaya koymuştur. Elde edilen bulgular, yalnızca mekanik yollarla işlenen çay sapı atığı tozlarının epoksi matrislerini etkili biçimde güçlendirebildiğini göstermektedir. Özellikle %7,5 dolgu oranı çekme testlerinde en iyi sonuçları verirken, %10 içerikte kırılma tokluğu ve sertlik özellikleri daha yüksek bulunmuştur.

Keywords

• epoksi kompozitler
• kırılma tokluğu
• sertlik
• doğal lifler
• çay sapı atığı

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