Natural fibers chemical treatment methods

The influence of physical and chemical treatment methods of natural fibers on mechanical properties was analyzed also. Additionally, the mechanical and other physical properties of the composite are generally dependent on the length, content, and dispersion of fibrous filler and processing parameters. 

The strength of the fiber is very important for natural fiber-reinforced composites. Polar natural fibers are inherently incompatible with hydrophobic polymers. Therefore, the surface modification of natural fibers is required to improve its physical and chemical properties. Various chemical treatment methods have been used to modify the surface properties of the natural fibers. Few methods of surface modification are described below ... 

The mechanical properties of composites are mainly influenced by the adhesion between matrix and fibers of the composite. As it is known from glass fibers, the adhesion properties could be changed by pretreatments of fibers. So special process, chemical and physical modification methods were developed. Moisture repel-lency, resistance to environmental effects, and, not at least, the mechanical properties are improved by these treatments. Various applications for natural fibers as reinforcement in plastics are encouraged. 

Native cellulose are commonly modified by physical, chemical, enzymic, or genetic means in order to obtain specific functional properties, and to improve some of the inherent properties that limit their utility in certain application. Physical/surface modification of cellulose are performed in order to clean the fiber surface, chemically modify the surface, stop the moisture absorption process, and increase the surface roughness. " Among the various pretreatment techniques, silylation, mercerization, peroxide, benzoylation, graft copolymerization, and bacterial cellulose treatment are the best methods for surface modification of natural fibers. 

To improve the adhesion between natural fiber and polymer matrix, chemical modification of natural fibers was investigated by a number of researchers. The mechanism and utilization of selected chemical treatments is discussed in this section. There are many different methods to improve the interfacial adhesion between fiber and matrix by modifying fiber surface such as acetylation, benzoyla-tion, acrylation, permanganate, and isocyanate treatment. These treatments are described in detail by Kalia et al. [69]. 

Various treatment methods onto oil palm fibers are already discussed in detail [22, 23, 45-47] including a detailed discussion on various treatments on lignocellulosic fibers in general to improve their properties [48]. Reviews on the developments in chemical modification and characterization of natural fiber-reinforced composites... 

ITowever, it has some disadvantages, mainly the incompatibility between the hydrophilic fibers and hydrophobic thermoplastic matrices, which can negatively affect the mechanical properties. This requires appropriate treatments to enhance the adhesion between the fiber and matrix [13]. Fiber modification is necessary to increase the adhesion between the hydrophilic natural fibers and the hydrophobic polymer matrix at the interface. Many investigations have been carried out by a number of researchers. However, different methods and chemicals were used. Accordingly, this crucial factor will be discussed in detail later. 

Several studies have been made to optimize the properties of natural fiber-reinforced PLA composites from the point of view of fiber-matrix adhesion. Pretreatment of fibers, such as chemical modification, seems to be the most promising approach, in which covalent bonds are formed between the fiber and matrix. One of the most common and efficient methods is alkali treatment (for example, with 2% sodium hydroxide aqueous solution) of fibers, which has been used to... 

The source of nanofiber is varied either from animal or plant that contains different amount of chemical composition. Thus, in nanofiber production, different natural fibers need to imdergo several chemical and physical treatments. In addition, every extraction method gave different results in term of quality and yields, hence other techniques of cellulose nanofiber production need to be explored. Furthermore, as found in previous research, combination of chemical, enzymatic, and physical... 

Therefore, a large number of studies on chemical and physical surface treatments of various natural fibers have been devoted not only to increasing the interfacial adhesion between the natural fiber and the polymer matrix but also to enhancing mechanical, thermal, and other properties of biocomposites consisting of different types of natural fibers and polymers [13-20]. Meanwhile, a few excellent papers have reviewed the surface modification of natural fibers for biocomposites [4, 11, 21, 22]. Many research results dealing with surface treatment of natural fibers and characterizing various properties of biocomposites with different modification methods as well as with different natural fibers and polymers have been reported in recent years. 

Physical methods for treating natural fibers before biocomposite processing involve electrical discharges such as cold plasma and corona, electron beam irradiation, ultraviolet (UV) treatment, and ultrasonic treatment,. Such physical approaches are of great interest because, in general, the processes are dry, clean, labor-friendly, environment-friendly, and fast in comparison with most of the chemical methods, which are wet processes. Under appropriate treatment conditions, they can effectively modify structural and surface characteristics of natural fibers, thereby improving the mechanical and thermal properties of biocomposites as well as enhancing the interfacial adhesion between the natural fibers and the polymer matrix. 

The hydrophilic nature of cellulose fibers often results in poor compatibiHty with hydrophobic polymer matrices. Therefore, it becomes necessary to modify the surface of natural fiber for better binding between fiber and matrix. Chemicals are commonly used for the modification of cellulosic materials but large amount of solvents are also usually involved. Surface modification of biofibers using bacterial cellulose (BC) is one of the best methods for greener surface treatment of biofibers. 

CNWs were initially isolated from natural fibers by Mukherjee and Woods [12] in 1953. They can be prepared from a variety of sources such as wood pulp, plant fibers (e.g., hemp, sisal, flax, ramie, jute, algae, cotton) [13, 14], tree leaves [15], microbial (acetobacter xylinum) [16], sea creatures (tunicates) [17, 18], fiuit skins (banana and grape) [19], fruit husks (coconuts) [20], and even agricultoral products (e.g., wheat straws and soy huUs) [21], which makes them more attractive and applicable. Three methods are available for producing nanocellulose, namely, chemical acid hydrolysis, chemical treatment in combination with mechanical refining and the enzymatic methods. 

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