The usage of natural fibers and nanofibres in biocomposites are grown due to the flexibleness in procedure, in add-on to the high mechanical belongingss, and above all, low cost. All these advantages doing the natural fibers more recognized to utilize in complexs. The complexs are stuffs that consist of two or more substances that might be different in physical and chemical properties.1-7 Different sort of stuffs are combined together to develop merchandises with more strong construction and more functional non possible to accomplish by any of the substance entirely. Complexs, the inquire stuffs are going an of import portion of our day-to-day life stuffs due to the advantages such as, comparatively low weight, high tensile strength, and the flexibleness during processing.8-12 They are used as stuffs in doing aircraft constructions, in edifice as dielectrics, and besides in biomedical applications. 13-15
As president Obama said when he visited Argonne National Laboratory in Illinois, 08/03/2013: ” The lone manner to interrupt the gas monetary value spike rhythm is to switch our autos off oil ” 16. Traveling back to nature, happening alternate stuffs is needed. The oil crises made the biocomposites as a charming stuffs used in really broad scope in industry. As any stuff, the biocomposites is under research and it needs more clip to happen more applications.
Using natural fibers in complexs gain credence and even the figure of publications and books are increased this means, the new universe go toward the nature and why non. But still the usage of glass and C fiber in composite is more dominate than natural fibre.17 The application of natural fibers in composite is undistinguished compared to others mineral and polymers. Yet, natural fibers have many advantages, since they are cheap, available, environmentally friendly, and renewable. But the job with utilizing natural fibers in complexs is related to the hydrophilic nature of fibers, the high wet soaking up and besides the contact with matrix is rather hapless, stoping up with low tensile strength.18 Thus fibre-based complexs needs a alteration of the fibre surface, and it can be done by either chemical or physical procedures. The physical facets of surface alteration of natural fibers are discussed in this essay. Before that we need to cognize a spot more about natural fibers.
Most of natural fibers comes from works. They are sustainable and renewable, the workss produce natural fiber classify to primary and secondary. Jute, hemp and sisal are illustrations of primary workss, while Ananas comosus and oil thenar are illustration of secondary workss. Table 1 shows the most natural fibers used in commercial complexs.
Table 1. Major natural fibers used in commercial composites.19
universe production ( 103 ton )
Sugar cane bagasse
The chief job of utilizing natural fiber in complexs is the hapless contact due to the hydrophilic nature of natural fiber. However, it is non ever the surface alteration of natural fibers needed in complexs. Joseph et. Al. made a complexs with phenol-formaldehyde matrix and fibers from Ananas comosuss foliages and banana without surface modification.20 The consequences shown in table 2 compared with man-made fibers, the belongingss of these complexs depends chiefly on fibre length and burden. On the same survey they used phenol-formaldehyde matrix with oil thenar fiber and the surface of oil thenar fruit was modified and in general the tensile strength improved. The surface of fiber can be modified physically by stretching, refinement and calendaring. The physical interventions change the construction and surface belongingss of fiber and therefore better the mechanical engagement with the polymer.
Table 2 Mechanical belongingss of natural fibers compared with other sort of fibres.21
Type of Fibre
Tensile strength, MPa
Young ‘s faculties GPa
Soft wood kraft
If we look for case to the wood fiber and its application in paper industry. The fibers normally are polishing significance, the physical intervention are applied to modify the surface of fiber. It is one of the most of import phase in order to obtain high quality paper. The chief thought beyond refinement is to better the fibre-fibre bonding and increase the tensile strength or sometimes you need to cut the long fiber in order to accomplish good formation. The refinement method is modifying the surface of fiber within H2O by metal bars. Figure 1 illustrate the refinement mechanism.
Fig.1 Refining mechanism23
The refinement alteration the morphology of fiber. The consequence chiefly is cutting long fiber and bring forth mulcts, besides important alteration in the fiber wall and some of removed parts return and attached to the fibre surface.
New Physical methods of surface alteration
Corona and plasma interventions are used late for alteration of the surface of fibres.24-25 These methods are physical significance, you do non necessitate to bring forth any substances that might guess the environment like some toxic substance green goods by chemical intervention of fibers. Particularly the plasma is really friendly to the environment. Sustainability and terminal of life after usage are of import considerations to do when developing polymer complexs from renewable resources.26 The toxicity and environmental issues of utilizing different chemical interventions for heightening the belongingss of these stuffs. Some chemical stuffs may be toxic, and hence, the usage of such stuff may harm the environment.27
Plasma is ionized gas with negatrons, photons and ions, it have the ability to change the surface belongingss of natural fibers by creative activity a free ions and negatrons on the surfaces of natural fibres.28 In this intervention the surfaces of fibers are bombarded with a beam of high energy, the surface raggedness and surface chemical science are changed without utilizing any substance might harm the environments. The plasma non merely take the dross on the surface of fiber but besides doing the fibers more porous, intending the mechanical bonding between the fiber and the matrix is increased as shown in figure 2. different sort of surface alterations can be achieved by altering the gas bombarded to the surface. One other of import facet is the clip, with plasma you need merely few proceedingss, while on the traditional methods you might necessitate yearss and ca n’t accomplish the same mechanical belongingss.
The He cold plasma intervention bombarded to flax fibers with polyester matrix complexs done by Marais et.al.29 The probe done by H2O incursion measurings and proving mechanical belongingss. The consequences showed that the plasma intervention enhances the fibre-matrix adhesion and besides improves the tensile strength and stiffness of the complexs.
Fig.2 Cross subdivision of natural fibre a- before plasma intervention b- after plasma intervention, the fiber more porous.28
The morphology of untreated fiber and treated one with plasma is shown in fig 3. with untreated fibre the surface is smooth as shown in fig 3a, where the primary wall of fibre consists of fatty acid and fatty intoxicant and many others intending, the outer bed covers the inner-layers. In fig 3b, utilizing plasma intervention we have a really unsmooth surface and non merely that, if the clip is sufficient it will take the outer bed every bit good as shown in fig 3c. it is non recommended to increase the clip of interventions i.e if you go beyond 15 min we might lose the attached filaments and besides the migration of hydrophilic infusion increased.
Fig 3. Surface morphology of fibre a- before intervention B and degree Celsius after plasma treatment.28
Martin and his co-workers, they made composite with sisal fibers and High Density Polyethylene matrix.30 The consequences showed a important betterment in mechanical belongingss by modifying the surface of fiber utilizing plasma.
The interfacial adhesion of Jute fibers and High Density Polyethylene matrix was studied by Seki et. Al. as a map of plasma power, where the O plasma beam was used for fibre surface modification.31 The power used was 30 W and 60 W. The shear strength increased by 32 and 47 % severally compared with untreated complexs.
The consequence of plasma intervention on the morphology and wettability of jute fiber and polyester matrix was studied by Sinha et.al.32 On the other manus the effect on the adhesion interfacial besides was investigated. The SEM image revealed the unsmooth surface and a debasement of fiber when plasma used. Plasma enhanced the hydrophobicity in fiber. Nevertheless, the flexible strength of the complexs made by different sort of treated fibers, the lone fiber treated for 10 proceedingss gives an improved of tensile strength of 14 % compared with untreated one.
Siky et. Al. they used different sort of O plasma reactor, the wireless frequence and low frequence for Jute fibers intervention with polyester matrix.33 The shear strength increased from 11.6 MPa for untreated fibers to 19.8 and 26.3 MPa with low frequence and wireless frequence severally. In general the consequences show a important betterment on the mechanical belongingss of jute fibers treated by O plasma with wireless frequence than low frequence.
Corona is one of the most popular techniques used late for fibre alteration. By this intervention the surface energy of cellulose fiber is changed. Corona electron discharge intervention of fiber and hydrophobic matrix found be a really effectual.
The aureole negatron discharge intervention was used by Pothan et. Al. in order to better the mechanical belongingss of fibre-epoxy composites.34 Corona treated fibers shows higher polar constituents of free surface energy when increasing the intervention energy end product.
The mechanical belongings of hemp fiber in complex was studied by Ragoubi et. Al. the tensile index and besides the emphasis strain measurings was performed.35 The physical intervention by aureole gives a important addition in mechanical belongingss ( tensile strength ) . The alteration of fiber enhanced the complexs belongingss with 30 % of Young modulus.
The Flax and Hemp fibers were modified by corona discharge intervention and the optimal value of corona intervention length was found by Pizzi et. Al. in order to accomplish the utmost value of tensile strength.36 The composite tensile strength breakage after 5 min of aureole intervention. The fibre appears good mechanical belongingss with comparatively short periods of aureole intervention and it found besides that no demands for more clip of intervention, it will non better the mechanical belongingss.
Comparison between mechanical and chemical interventions
The wheat straw fibers was treated by mechanical and chemical agencies and used with polypropylene matrix, and the mechanical, thermic belongingss were studied by Joseph et. Al. The fibers modified by chemical agencies appears better mechanical and thermic belongingss than the physical ones.37 Figure 4 shows the SEM images of fibers surface treated by physical and chemical agencies. The surface of fibers treated by chemical agencies are smooth and unvarying while the 1s treated by mechanical agencies exhibits irregular surfaces.
Fig 4. The morphology of fibers treated by a- mechanical b- chemical means.37
The consequence of mechanical and chemical agencies on the thermohydrometric analysis of the straw fibers is shown in figure 5. The get downing debasement temperatures were 217 oC in mechanical interventions and 242 oC in chemical. More onset debasement temperature, more thermic stableness of fibers treated.
Fig 5. Thermohydrometric analysis curve of straw fibers treated by different means.37
The usage of natural fiber on biocomposites is turning, they are cheap, flexible in processing, looking high mechanical belongingss and above all environmentally friendly. The biocomposites will happen more application in close hereafter due to the crude oil and oil crises. But still the interfacial adhesion with matrix is hapless because of the hydrophilic nature of fibers. Therefor ; an extended research is traveling in this country to heighten the contacts between fiber and the matrix. The research tells us that bettering the surface of fibre leads to better the mechanical belongingss of the complexs. The physical interventions of the surface of fiber by aureole or plasma improve the mechanical belongingss but still it seems the chemical interventions are more powerful.