Modification of natural fibers

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. 

Pommet, M. Juntaro, J. Heng, J.Y.Y. Athanasios, M. AdamF.L. Karen, W. Gerhard, K. Milo, S.P.S. Bismarck, A. Surface modification of natural fibers using bacteria Depositing bacterial cellulose onto natural fibers to create hierarchical fiber reinforced nanocomposites. Biomacromolecules 2008, 9 (6), 1643-1651. 

A. K. Mohanty, M. Misra and L.T. Drzal, Surface modifications of natural fibers and performance of the resulting biocomposites An overview , Polym Interfaces, 2001, , 313-17. 

Mohanty A, Misraa M, Hinrichsen G (2000) Biofibres, biodegradable polymers and biocomposites an overview. Macromol Mater Eng 276/277(1) 1-24 Mohanty A, Misra M, Drzal L (2001) Surface modifications of natural fibers and praformance of the resulting biocomposites an overview. Compos Interf 8(5) 313-343 Mohanty M, Misra M, Drzal L (2002) Sustainable bio-composites from renewable resources opportunities and challenges in the green materials world. J Polym Environ 10(1/2) 19-26 Morrison W, Akin D (2001) Chemical composition of components comprising bast tissue in flax. J Agric Food Chem 49(5) 2333-2338... 

Reinforcing fibers can be modified by physical and chemical methods. Chemical and physical modifications of natural fibers are usually performed to correct the deficiencies (described above) of these materials, especially to impart bonding and adhesion, dimensional stability, and thermoplasticity. Surface modification of natural fibers can be used to optimize properties of the interface. 

Pommet M et al (2008) Surface modification of natural fibers using bacteria depositing bacterial cellulose onto natural fibers to create hierarchical fiber reinforced nanocomposites. Biomacromolecules 9(6) 1643-1651... 

Gulati D, Sain M (2006) Fungal-modification of natural fibers a novel method of treating natural fibers for composite reinforcement. J Polym Environ 14(4) 347-352... 

In thermoplastic/fiber systems, the fiber may act as a series of nucleating sites for the polymer, resulting in a transcrystaUine region around the fiber. In this chapter, a large number of factors have been demonstrated to contribute to the interactions across the interface. The effect of various conditions such as the chemical modification of natural fibers and nucleation ability of semicrystalUne matrix on the formation of transcrystallinity was investigated. 

Further studies investigated the effect of earlier chemical modification of natural fibers on arising of hexagonal form of polypropylene. For these studies, it was important to consider the content of induced hexagonal phase in crystalline phase of the polypropylene matrix. Figure 10.2 shows how the content of p form changes upon the temperature in which modified and unmodified hemp fiber is moved. It is worth to mention that the curves course of modified and unmodified flax fiber is very similar to that of hemp [8,9]. 

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]. 

Based on the literature discussed in this chapter, it seems that surface modification of natural fibers is absolutely necessary to improve their thermal stability, dispersion in the polymer matrix, and compatibility with the polymer matrix. Physical and chemical methods reported have significantly modified the surface properties of the fibers as well as polymer matrices to improve the dispersion of the fibers and hence various properties of the polymers. Use of silane coupling agents and acetylation... 

Modifications of Natural Fibers to Increase Durability of Cement Composites... 

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 ... 

Mohanty A.K., Misra M., and Drzal L.T. 2001. Surface modification of natural fibers and erfor-mance of the resulting biocomposites. Composite Interfaces 8 313-343. 

Pommet, M Jimtaro, J Heng, JYY Mantalaris, A Lee, AF Wilson, K Kalinka, G Shaffer, MSP Bismarck, A. Surface Modification of Natural Fibers Using Bacteria Depositing Bacterial Cellulose onto Natural Fibers To Create Hierarchical Fiber Reinforced Nanocomposites. Biomacromolecules, 2008, 9, 1643-1651. 

SURFACE MODIFICATION OF NATURAL FIBERS FOR REINFORCEMENT IN POLYMERIC COMPOSITES... 

Compared to physical and biological methods, more vigorous research is conducted in the realm of chemical modification of natural fibers. Among the various chanical surface modifications, alkalization, silanization, and grafting with anhydrides are the most commonly adopted methods. 

Mukhopadhyay S, Fangueiro R. Physical modification of natural fibers and thermoplastic films for composites—a review. J Thermoplast Compos Mater 2009 22 (2) 135-162. 

SURFACE MODIFICATION OF NATURAL FIBER COMPOSITES AND THEIR POTENTIAL APPLICATIONS... 

Graft copolymerization is the most effective method utilized in the chemical modification of natural fibers. According to Gassan et al. [99], the reaction is initiated by free radicals on the fiber surface. Ionization polymerization of fibers is carried out in an aqueous solution, followed by exposure to a high-energy radiation. Fiber molecule cracks and radicals are subsequently formed. Next, the radical sites of the fiber are treated with a suitable solution compatible with a polymer such as vinyl monomer, acrylonitrile, methyl methacrylate, or polystyrene. Finally, this leads to the formation of a graft copolymer, which possesses fiber and graft polymer characteristics. 

Kumar R, Obrai S, Sharma A. Chemical modifications of natural fiber for composite material. Der Chem Sin 2011 2 219-228. 

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