Plasma modification of natural fiber: A review

Abstract

Fibers obtained from fruits, stem, and plant leaves are nature-based fibers and are known as natural fiber. Due to their versatile properties such as good mechanical behavior, low cost, eco-friendly, less dense, biodegradable, etc. natural fibers are getting focus amongst researchers. Since the density of bio-composites reinforced by natural fiber is significantly inferior to other traditional materials they satisfy the automotive need of high-performance vehicle parts/components of lightweight. To decrease the cost and weight of the vehicle automotive manufacturers are extensively utilizing the natural fibers (as interior insulation, seat bottom, door panels, dashboard, body panels, boot liner, etc.). Although, the composite of natural fiber has few shortcomings like poor chemical and fire resistance, poor interfacial bonding among matrix and fiber, moisture intake. Thus, natural fiber is required to be surface treated. Among the finest method for physical treatment is plasma treatment. Herein plasma which participates within surface modification directly is produced within the vacuum chamber by the ionization of the gas. The improved interfacial bonding in fiber composite is obtained as a result of surface treatment of plasma, which results in increase mechanical strength. Effect of surface treatment of plasma on several natural fiber is included in this paper and the aim of this review paper is to occupy the literature gap through this paper.

Introduction

The usage of synthetic materials that are not biodegradable has polluted the environment to an alarming level [1].This big of a problem can be solved easily with the usage of natural or natural-synthetic hybrid materials that are far more biodegradable than most synthetic materials [2]. Natural fibres are mostly comprised of cellulose, hemicellulose, and lignin and therefore also known as lignocellulosic fibres [3]. Natural fibre boasts an admirable set of properties all thanks to their chemical structure [4]. Natural fibres have Young’s modulus comparable to Kevlar and surpass steel. The major factor contributing to these great tensile properties is the lignocellulosic fibers containing a high amount of cellulose [5]. The properties like biodegradability, economic, tensile strength on a par with most synthetic materials, and naturally abundant makes natural fibres an interesting topic for researchers [6]. Natural fibres are both economical and eco-friendly at the same time because they are mostly a by-product of some cultivation or agricultural processing [7]. In older times, only textile and packaging industries used natural fibres. Advancements in natural fibres and hybrids have made them a worthy alternative for materials used in conventional industries [8]. Implementing natural-fibre based materials instead of synthetic composites in an automobile can result in a significant (up to 40%) reduction of weight [9]. Natural fibre based composites are a viable option for intermediate loading purposes like interior and some exterior parts of an automobile as they have great strength to weight ratio [10]. The construction industry is also interested in natural-fibre based material in the form of concrete with natural fibre reinforcements and has been working on it [11]. The aerospace industry also has eyes on natural-fibre based materials as they are lightweight and may have applications in the interior [12], [13].Fig. 1.Fig. 2.Fig. 3.Fig. 4.

With all the great properties and viable alternate in industrial application, natural-fibre based materials are not considered as supreme [14], [15]. The chemical composition of natural fibres not only provides great properties but also some drawbacks [16]. Some of the drawbacks of natural fibres are inadequate water intake and polarization properties due to which the compatibility with the matrix is reduced. This results in bad interfacial bonding and lowered mechanical properties in comparison to synthetic fibre composites [17]. Resin is hydrophobic in nature whereas natural fibres are hydrophilic. This affinity towards water makes natural fibres to poorly bond in the matrix [18]. Natural fibres’ affinity towards water can lead to degradation and swelling. This will significantly reduce the mechanical properties of the fibre [19]. These all drawbacks can easily be removed by pre-treating fibre with various techniques of surface modification [20]. Chemical or physical surface treatment of the fibre helps in reducing affinity towards the water and the reduction of wax layers. The treatment also roughens the surface of fibre. This overall reduces affinity towards the water and better bonding in the matrix [21]. One such treatment namely plasma treatment is a widely researched technique and has been proven to be effective in reducing the affinity towards water thus bettering its properties [22]. This paper summarises the various types of plasma treatment techniques and their effect on the mechanical characteristics of natural fibre composite.