Effect of Potassium Permanganate treatment on physico-Chemical and mechanical properties of extracted Pine Needle Fiber

. This study investigates the potential of extracted pine needle fiber (PNF) to substitute synthetic fibers in biopolymer composites as a reinforcing material. The study is focused on the surface modification and characterizing of the extracted PNF. Water retting method was used to extract the PNF before being subjected to potassium permanganate treatment. The surface treatment with potassium permanganate resulted in higher density (1058 kg/m 3 ) compared to the untreated fibers (1017 kg/m 3 ). X-ray Diffraction (XRD) analysis shows the surface treatments positively impacted the natural fiber’s crystallinity index (CI). Additionally, the tensile strength of PNF were found to be enhanced on potassium permanganate treatment from 49.67 ± 9.6 MPa (untreated PNF) to 56.75 ± 16.54 MPa (treated PNF). Based on the findings, it can be concluded that the potassium permanganate treated PNF will be suitable to be used as reinforcement in fabricating the ecologically friendly composites. (cid:3)


Introduction
The utilization of natural fibers (NFs) in composites has gained significant attention in recent years, as it provides a sustainable and eco-friendly alternative to synthetic fibers. NFs are materials derived from plants, animals, or minerals used for various applications for thousands of years [1]. Cellulosic fiber can be sourced from different plant parts, like its bark, root, seed, or leaf. Incorporating these fibers has become a significant consideration in the design and manufacturing of sustainable products [2]. Lignocellulosic NFs like coir, sisal, jute and kenaf have been recognized as potential alternatives to glass reinforcement materials in polymeric composites [3]. Natural cellulosic fibers are becoming popular composite reinforcing phases due to their renewable, biodegradable, inexpensive, excellent physical qualities, and low density, these fibers have been effectively employed in composite reinforcement in recent years [4]. The properties of NFs are significantly affected by the growth environment, temperature, and soil conditions, which impact fiber strength and density. *Corresponding author : rajeshkumaruit1@gmail.com NFs reinforced polymer composites have been extensively demonstrated to have the potential for use in numerous industries, including aerospace, construction, sports equipment and automotive [1][2][3][4][5]. Proper use and management of potassium permanganate are crucial to minimize its environmental impact. Avoid overuse and inappropriate disposal to protect the environment. Use wisely and dispose properly for environmental protection. [6]. The method used for extracting fibers, whether water retting, chemical retting or mechanical technique, can also result in distinct properties [7]. The moisture absorption capacity of a material can varies from 5% to 20% by its dry weight, depending on the environmental conditions. Therefore, one of the major concerns for composites that use cellulosic fibers as reinforcement is the fiber-matrix interaction, which can be negatively impacted by the dimensional changes that the fibers undergo due to the absorption of water [8]. Research suggests that the use of KMnO4 treatment can effectively lower the water absorption of natural fiber [9]. Pine needles, which are abundantly available and widely considered waste materials, have the potential to be utilized as a source of NFs. Pine trees grow in Uttarakhand's forests, with elevations from 500 to 2,000 meters above sea level, and they are abundant in the area. When the pine needles fall, they form a dense layer on the forest floor, which can stop other plants from growing and make forest fires more likely, especially when it's dry. To address this issue, the local people of Uttarakhand burn pine needles to clean the forest floor [10]. Burning pine needles emits air pollutants, harming the environment and health. Hence, by utilizing the pine needles in composite fabrication, instead of burning them, the demand for wood and synthetic fibers can be reduced, which would effectively prevent the unnecessary burning of pine needles and minimize its adverse effects. The current study involved the extraction of PNFs from pine needles and subsequent treatment of the fibers with potassium permanganate solution. The physical, chemical, and mechanical properties of the treated fibers were investigated.

Materials
Pine needle tree also known as chir tree is commonly found in the Himalayan region of India up to a height of 50 meters. The needle-shaped leaves of the pine tree are commonly referred to as "pine needles". This is because the leaves have a needle-like structure. Potassium permanganate (KMnO4) for extracted fiber treatment was procured from the local market of Pauri Garhwal, Uttarakhand.

Water retting
Various methods have been utilized for fiber extraction from plant stems, with retting being the predominant technique. Retting involves controlled degradation of the stem to separate the fibers from the woody core [3]. Retting is a biological process that depends on moisture and warm temperatures to enable microbial action. The collected leaves were soaked in water at ambient temperature for a period of 14 days. The microorganisms in the water broke down the non-fiber material, which caused the fibers to loosen and separate during the process [11]. After 14 days, a fine long metal wire brush was used to assist in the traditional combing process for separating the fibers.

Surface Modification of PNF
The extracted PNF was submerged in 0.05% KMnO4 solution at 25 °C for fifteen minutes [9]. After that PNF was washed repeatedly with deionized water to remove any trace of potassium permanganate. Subsequently, the solution was poured off and the fibers were rinsed with acetone to eliminate any remaining solution on the fibers. Finally, the treated PNF was dried in a oven at 80°C for six hours.

Diameter measurement
The diameter of the PNF was estimated by analyzing 25 fiber samples using an optical microscope. The analysis was conducted by examining longitudinal microscope images of the fibers [11]. The diameter of both untreated and treated PNF was measured at four randomly locations.

Density measurement
Measuring the density of NFs is typically done through the standard procedure of utilizing the pycnometer setup. This involves analyzing the fibers with a liquid of known density, such as toluene (toluene = 866 kg/m 3 at room temperature), for the density analysis [12]. PNF's density was calculated using Eq. 1.
Where, m1 weight of empty pycnometer, m2 weight of pycnometer filled with PNF, m3 weight of toluene in pycnometer, and m4 weight of pycnometer filled with both toluene and PNF.

Chemical composition analysis
Several distinct methods were utilized to determine the percentage of components present in PNF, specifically cellulose, hemicellulose, and lignin. To determine the cellulose content weight fraction, the Krushner and Hoffer method was utilized [13]. Hemicellulose was assessed using the neutral detergent fiber technique [12], while lignin was estimated using the APPITA P11s-78 method [14]. PNF moisture content was measured using the starting and oven-dry weights of the fibers. Eq. 2 was used for moisture calculation and the mean value was reported after five repetitions to assure data accuracy [15].
The fiber's weight before drying is W1, and after drying in a hot air oven is W2.

XRD analysis of PNF
XRD was utilized to predict the CI and CS of the PNF, which indicates the extent of structural arrangement. A Bruker D8 XRD equipment was used at room temperature [13]. The measurements were performed within a range of 10° to 35°, employing a scanning rate of 4° per minute. This measurement is crucial as it has a direct effect on the mechanical behaviour of the material. Using Eq. 3, the CI of PNF was calculated.
Where "Iamorphous" denotes the peak's amorphous intensity and "Icrystalline," the peak's crystalline intensity in the diffractogram. Scherrer's equation (Eq. 4) is a useful formula for estimating the size of cellulose crystals within a fibrous structure [11].

= (4)
Scherrer's constant, denoted as K = 0.89, is used in the formula, β represents the full width at half-maximum of the peak, and λ signifies the wavelength of radiation.

Single fiber tensile test
Tensile properties of a material, including its tensile strength and modulus are critical factors in assessing the suitability of a fiber for a specific application. The mechanical properties of plant-based fiber can vary and affected by several factors including retting duration, extraction method and plant age. To analyze the tensile properties of PNF, a tensile test was conducted using an INSTRON (5982) machine, with sample dimensions and testing parameters according to ASTM D3822-07 [16]. Untreated and treated groups were tested, with twenty-five specimens in each group, and the results were recorded. A setup consisting of a paper frame was used to carry out the tensile test (Fig. 1).

Fig. 1 (a) Paper frame designed for tensile tests on individual fibers. (b) Sample set into Instron machine
3 Results and discussion

Physical analysis of the fibers
The diameter of a NFs is a critical factor in determining its usability. Fig. 2 displays the optical microscope image of diameter measurements of the extracted fibers, indicating that the treated fiber had a smaller diameter of 131 ± 20 μm compared to the raw fibers 150 ± 17 μm. Table 1 compares the Physical, Mechanical and crystallinity properties of PNF with other NFs.

Fig. 2 Diameter Measurement of (a) Untreated and (b) Potassium Permanente treated PNF
There are various factors that can impact the density of fibers, which include soil, weather conditions, moisture levels, extraction methods. PNF has a lower density than manmade fibers like E-glass (2500 kg/m 3 ) and S-glass (2500 kg/m 3 ), making it a viable lightweight replacement [13].

Chemical composition analysis
The chemical composition of NFs depends on various factors, including extraction methods, climate, and soil conditions. This analysis shows that the cellulose content increased after the treatment which led to rise in tensile strength and Young's modulus. Table 2 confirms that the chemical treatment of PNF increased the cellulose wt.% compared to raw fibers. The chemical treatment decreases the hydrophilic characteristic of PNF by decreasing hemicellulose and lignin weight %. Furthermore, the lowered moisture and wax content in the chemically modified PNF suggests that the bonding between the fiber and matrix in composite applications may be improved [20]. Table 2 presents a comparison between the chemical composition of PNF and a few other NFs.  Fig. 3 shows two prominent peaks are observed at approximately 2θ = 15° and 23°, corresponding to the lattice numbers (1 1 0) and (2 0 0), respectively. These peaks are indicative of cellulose I and IV, respectively. These two peaks are commonly found in NFs [17]. The untreated PNF has a crystallinity index (CI) of 43.62%, but the alkali treatment results in an improved CI of 47.26%. The fibers' improved CI was due to the removal of noncrystalline substances, which was supported by chemical analysis. The untreated PNF exhibit a calculated CS of 4.03 nm, whereas the treated PNF show an increased crystal size estimated at 5.61 nm. The enlargement in crystallite size promotes the fiber's resistance to moisture absorption and chemical reactivity [21].

Mechanical Properties of PNF
The Mechanical properties of NFs is influenced by the existence of cellulose, hemicellulose, and lignin, as well as the method of extraction and chemical treatment applied [1].

Conclusion
The investigation of the chemical composition showed that the treatment of PNF with potassium permanganate led to a substantial enhance in cellulose content, while simultaneously causing a reduction in components such as hemicellulose, lignin, and wax. The density of PNF increased slightly to 1058 kg/m 3 after chemical treatment, but it remains significantly lower than that of synthetic fibers. XRD analysis confirmed that the CS enhanced from 4.03 nm to 5.61 nm as a result of chemically treatment. The single fiber tensile test indicated that the treatment had a positive impact on the tensile strength of PNF, with the chemically treated PNF exhibiting a strength of 56.75 ± 16.54 MPa compared to 49.67 ± 9.6 MPa for the untreated PNF. The results indicated that treated PNF are highly suitable for reinforcement in composite fabrication.