Mercerized fiber-reinforced composites

From the earlier discussion, it is clear that mechanical, thermal, and dielectric properties of UPE matrix increase considerably on reinforcement with raw and surface-modified natural ceUulosic fibers. The mercerized C. indica fibers-reinforced composite materials have been found to have highest mechanical properties followed by raw C. indica fibers-reinforced composites. It has also been observed from the aforementioned data that raw and mercerized fiber-reinforced polymer composites showed best mechanical properties at 20% fiber loading. Furthermore, mercerized fibers-reinforced composites were also found to have better dielectric properties, that is, dielectric constant, dielectric loss, and dissipation factor, than raw C. indica fibers-reinforced polymer composites. 

J.T. Kim, and A.N. Netravili, Mercerization of sisal fibers Effects of tension on mechcuiiccil properties of sisal fibers and fiber-reinforced composites. Compos. A 41,1245-1252 (2010). 

Where W. = initial weight and W. = weight after a certain interval It has been observed from Tables 13.2 13.3 that chemical resistance of neat UPE and its composites reinforced with raw, mercerized and benzoylated particle fibers towards acid and base decreases with increase in normality, as well as with increase in immersion time. This behavior could be due to the propagation of microcracks which cause more and more internal penetration of acids and bases into the composite samples and hence decreased chemical resistance behavior. Among raw, mercerized and benzoylated particle fibers-reinforced composites, the benzoylated one has been found to have better chemical resistance properties towards adds, which may be due to the better interfacial adhesion between treated fibers and matrix because of the enhanced hydrophobic character of benzoylated fibers. However, the lower chemical resistance behavior of benzoylated fibers-reinforced UPE composites towards NaOH could be... 

It has been observed from the above discussion that mechanical, physico-chemical and fire retardancy properties of UPE matrix increases considerably on reinforcement with surface-modified natural cellulosic fibers. The benzoylated fibers-reinforced composite materials have been found to have the best mechanical and physico-chemical properties, followed by mercerized and raw Grewia optiva fibers-reinforced composites. From the above data it is also clear that polymer composites reinforced with 30% fibers loading showed the best mechanical properties. Further, benzoylated fibers-reinforced composites were also found to have better fire retardancy properties than mercerized and raw fibers-reinforced polymer composites. Fire retardancy behavior of raw and surface-modified Grewia optiva/GPE composites have been found to increase when fire retardants were used in combination with fibers. This increase in fire retardancy behavior of resulted composites was attributed to the higher thermal stability of magnesium hydroxide/zinc borate. 

Interest in natural fibers obtained from different resources to reinforce polymer so as to get the novel composites is growing rapidly because they are renewable, cheap, recyclable, and biodegradable. Research in this field has prompted surface modification of natural fibers in order to improve the compatibility between hydrophilic fibers and hydrophobic matrix [1], Major challenges for polymer scientists in the development of structural natural fiber-reinforced composites are to increase the moisture resistance, dimensional stability with minimized matrix material, and to decrease the manufacture costs of the composite materials. Different researchers have used different surface modification methods, that is, mercerization [2], benzoylation [3], silanation [4], acetylation [5], graft... 

From Figures 15.13 and 15.14, it has been observed that fiber surface modification also affects the dielectric loss and dissipation factor of resulted UPE matrix-based biocomposites. Furthermore, the mercerized fibers-reinforced polymer composites have been found to have low dielectric loss and dissipation factor followed by raw fibers-reinforced UPE matrix-based composites. It may be due to the incorporation of—COC Hj onto lignocellulosic fibers and partial removal of cellulose chain and surface impurities from fibers surface after surface modification. However, the exact explanation for the above behavior is somewhat difficult as dielectric loss or dissipation factor also depends on fiber orientation [ 16]. Since fibers were inserted in the composite materials in statistical random orientation manner, there may be... 

Kim, J.T. and Netravali, A.N. (2010) Mercerization of sisal fibers effect of tension on mechanical properties of sisal fiber and fiber-reinforced composites. Composites Part A, 41 (9), 1245 1252. 

Figure 15.4 Initial Young s modulus of continuous carbon fiber reinforced cement. Source Reprinted from Aveston J, Mercer RA, Sillwood JM, Conference Proceedings Composites Standards Testing and Design, NPL 1974, IPC Science Technoiogy Press, 93-103, 1974.

When reinforced with mercerized and benzoylated particle fibers. The UPE matrixhas been found to exhibit flexural strength of 55.26, 62.26, 66.29 and 57.26 MPa 61.7, 67.1, 69.52 and 62.32 MPa at 10,20,30 and 40% fiber loading, respectively. The results obtained were found to be consistent with results obtained in the case of AN graft copolymerized Grewia optiva fibers-reinforced unsaturated polyester composites [26]. Rai et al. have also reported similar results during their studies [16]. 

Figure 13.7 FTIR spectra of (A) neat, (B) raw, (C) mercerized and (D) benzoylated particle fibers-reinforced UPE composites.

Water absorption results of neat UPE and its composites reinforced with raw, mercerized and benzoylated fibers have been shown in Table 13.1. It can be seen from the table that water absorption characteristics of polymer composites depend upon the content of fiber loadings, water immersion time and surface modification techniques. The water absorption of raw and surface-modified fiber-reinforced UPE composites has been found to increase with the increase in percent loading. Similar results were also reported by Rashdi et ah during their studies on the water absorption behavior of kenaf fibers-reinforced polyester composites [27]. This may be due to greater affinity of water for OH groups present on the fiber backbone, whose number increases with the increase in fiber contents. In comparison to raw filler, composites reinforced with surface-modified filler exhibited low water absorption, which may be due to the reduction in the hydrophilic character of cellulosic biofibers after surface modification. 

Between mercerized and benzoylated fibers-reinforced UPE composites, benzoyl chloride grafted fibers-reinforced UPE matrix has been found to have better water resistant behavior, which may be due to better compatibility of benzoylated fibers and hydrophobic matrix. 

It has been observed from the Table 13.4 that percent moisture absorbance of neat UPE and its composites increases with an increase in percent humidity level from 20-80%. Also, moisture absorbance has been found to increase with increase in percent fiber loading. This could be due to the presence of more -OH groups on the polymeric backbone at high loading, which causes more moisture absorption by UPE matrix-based composite materials. Further, among raw, mercerized and benzoylated fibers-reinforced UPE matrix-based composites, benzoylated fibers-reinforced ones have been found to have the highest moisture resistance, followed by mercerized and raw fiber. This trend matches with the trend obtained in the case of the water absorbance study and can be accounted for by the same explanation as given earlier in the water absorbance section. 

Williams T, Hosur M, Theodore M, Netravali A, Rangari V, Jeelani S. Time effects on morphology and bonding ability in mercerized natural fibers for composite reinforcement. J Polym Sci 2011 2011 1-9. 

FIGURE 15.3 Compressive strength of raw and mercerized Cannabis indica particle fibers-reinforced unsaturated polyester composites. 

FIGURE 15.7 SEM images of (a) neatUPE, (b) UPE+20% raw, and (c) UPE+0% mercerized Cannabis indica particle fibers-reinforced UPE composites. 

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