Characterization of a novel natural cellulosic fiber from Calotropis gigantea fruit bunch for ecofriendly polymer composites

Highlights

• Calotropis gigantea fruit bunch (CGFB) fibers are characterized for first time.

• Reuse of renewable resources from discarded residues by simple extraction method.

• Results shows that CGFB fibers being used as a bio-degradable reinforcement for producing light weight polymer composites.

Abstract

In this current research, the change in properties of alkali treatment on the physicochemical, structural, thermal and surface morphological properties of Calotropis gigantea fruit bunch (CGFB) fibers are investigated. The alkali-treatment was discovered to reduce the amorphous contents and removed the non-cellulosic components which were inveterate by the FTIR analysis. The X-ray diffraction pattern showed that the crystallinity index of the alkali-treated CGFB fibers was fairly higher than raw fibers. Thermal degradability and stability of alkali-treated Calotropis gigantea fruit bunch fibers were more than that of the untreated fiber. Scanning electron microscopy and Atomic force microscopy images showed the partially roughened surface of the fiber due to the removal of non-cellulosic elements and surface impurities during alkali treatment.

Introduction

Now a day's renewable resource utilization is an important consideration due to environmental awareness and economic concerns. Natural lingo-cellulosic fibers are available in large quantities, are cheap, biodegradable, environmentally friendly and also more suitable for reinforcements in polymer composites instead of synthetic fiber. The cellulosic fibers were extracted from different plants and its parts such as leaf [1], stem [2], bark [3], root [4], pod [5], blossom pedal [6], fruit [7], fruit bunch [8], straw [9] and nutshell [10]. They can be used as a natural reinforcement or filler materials in polymer composites to produce components used for automotive, packaging and also building material sectors [11].

In general, lignocellulose fibers having a hydrophilic nature, exhibited high moisture absorption property, poor reactivity and compatibility with polymeric matrices. That can be overwhelmed by chemical treatment such as seawater, silane, alkalization, acetylation, treatment, etc., [12]. Treatments may activate the hydroxyl groups in the natural cellulosic fiber and remove the non-cellulosic elements and impurities from the fiber surface [4]. Among all treatments, alkali treatment is the cost-effective and effectual method to reduce amorphous substances such as hemicelluloses and lignin which results in the enhancement in chemical composition, surface topography, crystallinity index, mechanical properties and thermal stability of the fibers [3,13].

The alkaline treatment has improved the interfacial bonding among the fiber reinforcements and polymer matrices also enhanced the physical, mechanical, and thermal properties of the polymer composites [9,14]. From the previous literature, it is concluded that the treatment of cellulosic fibers with 5% NaOH having optimistic changes in the fiber properties [1,15].

Calotropis gigantea (crown flower) is a species of Calotropis native to Asia and Tropical Africa. It is a fast-growing and well-known flowering plant that grows in a harsh environment and be able to pinpoint by its thick oblong leaves and odorless purplish flowers [16]. Calotropis gigantea plant was identified as a valued medicinal plant and used as a folk medicine in India for many years [17]. Calotropis gigantea plants are harvested to obtain the fibers from their stems for a wide range of applications. Also, fibers from CG plant crops are durable which can be useful for ropes, carpets, fishing nets, and sewing thread. The fibers extracted from the Calotropis gigantea (CG) plant stems were characterized and reported [18,19]. Cellulosic fibers from CG plant bark were successfully extracted by the usual water retting method followed by alkali treatment [20]. Calotropis gigantea plant fiber reveals good adequate buoyancy, hydrophobic–oleophilic properties, high oil absorption capacity, and oil-water separation efficacy, and used as an oil-absorbing material in the oil separation process, to remove oil from water [21].

At present, the fibers were obtained from the Calotropis plant stem bast and bark and characterized [[18], [19], [20]] and they were used for various applications [21,22]. To date, no research work has reported on the physicochemical properties of alkali-treated and untreated Calotropis gigantea fruit bunch (CGFB) fiber. In this current research work, the effect of alkali treatment on the physicochemical properties of Calotropis gigantea fruit bunch fibers was studied.