**5.5 Hybridization**

*Renewable and Sustainable Composites*

improve mechanical properties.

**5.4 Addition of nanoparticles**

between the two phases and increase miscibility [146]. The high interfacial tension caused by coalescence phase separated blends can be reduced by the compatibilizers, allowing a continuous flow of externally applied stress from the matrix to the fibers [130]. Compatibilization can be done by (i) introduction of specific interacting groups, (ii) in-situ polymerization grafting, (iii) addition of a ternary polymeric component, (iv) addition of block co-polymers of the blend polymers, (v) interpenetrating networks of crosslinked system and (vi) using reactive compatibilization methods [147–150]. For instance, polyhydoxyether of bisphenol A (Phenoxy: PHE) a non-reactive compatibilizer has been noted in some reports to have provided improved interfacial adhesion between immiscible and marginally compatible polymer blends [129]. Specifically, the addition of PHE to some polymers blends led to the blends yielding improved dispersion of the polymers within the blend, gave uniform injection molded surfaces and considerably increased the notched impact strength of the blends (polysulfone (PDF)/ABS; PSF/PA, PMMA/ PA6 and PHE/PBT) [129, 151, 152]. Also reactive compatibilizers can be design to react with the fiber when introduced during processing. This method will involve modifying the fiber surfaces prior to the composite preparation. If successful, this method has the capability to improve interfacial interaction and subsequently

The use of nanoparticles to enhance the properties of NFPCs have been widely reported [99, 153, 154]. Nanoparticles are inorganic materials which possess a very high surface to volume ratio in which one or its entire dimension is less than 100 nm [155]. The addition of these nanoparticles influences the crystallization process during the solidification of the polymer composites leading to improved mechanical and thermal properties. These particles can be modified to selectively interact with a particular phase of the composites in a controlled manner [23, 156–158]. They can also be modified to act as a compatibilizer and react with both the matrix and the fibers to bring about good interaction and a better composite with stress transfer

Vargas et al. [159] reported the influence of nanofilters on some properties of polypropylene including mechanical properties. Their findings revealed that the nanofilters, in the presence of PP grafted MA, improved the tensile strength and Young's modulus properties which are indicative of the synergistic effect between the nanoparticles and compatibilizers. According to Lee and Youn [160], the addition of layered silicates worsened tensile properties of PP nanocomposites prepared by them. Similar investigation was presented by Rault et al. revealing that the addition of a maximum 1 wt% led to improvement in tensile properties but above the maximum, the silicate nanoparticle caused difficulties for processing the composites due to the formation of aggregates [161]. However, Joshi et al. [162] has reported improvement in tensile properties of PP/nanoclay composites. Therefore, we can conclude with certainty that there are other factors interfering in the positive influence expected from the addition of nanoparticle such as clay. According the Vargas et al. [159], fibers geometry plays a vital role in determining the composites eventual properties. Nanoparticles of different shapes and sizes were used to prepare polyamide 6 (PA6) composites in some research work conducted by Vlasveld et al. [163]. Their findings revealed that the rheological properties of the composites samples were highly dependent on the aspect ratio of the nanoparticle used. Therefore utmost care must be taken when the option of nanoparticles are being considered. Other nanoparticles have been used and their influence on the mechanical properties have been positive and very encouraging [164, 165].

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behavior.

Hybrid composites involve the combination of two or more different types, shapes or sizes of reinforcement in one composite material [166]. The hybrid composite properties have been reported to depend on many factors such as; fibers individual property, fiber-matrix compatibility, roughness of fiber surfaces, orientation of fibers and the extent of their intermingling [167]. Recently, investigations on the hybrid composites properties were based on the natural/synthetic fibers, natural/natural fiber and natural/synthetic/additive modified reinforced polymer composites. The popularity of these types of composites are increasing rapidly owning to their capability to provide freedom to tailor the composites and realizing properties that cannot be obtained in fabricated composites containing singular type reinforcement [21, 79].

Fiber-based hybrid composites have been reported to have improved properties compared with the unhybridized composites having single reinforcement [168–170]. Many research reports have shown that the addition of synthetic fibers at various amount to form hybrid fibers have composites of better-quality, especially in respect to their mechanical properties [171–179]. According to Ashik and Sharma [180], in one of their reviews, they listed some factors that may impact the mechanical properties of natural fiber hybrid polymeric composites, with the processing parameters featuring as one of the factors. Also, Nunna et al. [181] listed fiber content, fiber treatment, and the environmental conditions as some of the conditions that affect the properties of hybrid composites. For hybrid natural/ synthetic fibers, it has been reported that as wt% of the synthetic fiber rises, the mechanical properties also rises. However, at a certain wt% of the synthetic fiber content added, the properties of the composites mechanical properties starts dropping and this may be ascribed to poor interfacial adhesion, high fiber-to-fiber contact, and poor wettability.

Mishra et al. [182] prepared hybrid glass fiber (GF) and pineapple leaf fiber (PLF) polyester composite with a total fiber content of 25 wt%. The tensile strength was observed to have increased as the GF was increased from 0 to 7.5 wt% to approximately 70 MPa, after which the strength started dropping. The flexural strength kept increasing as glass content increased from 4.3 to 12.9 wt%, in the hybrid biocomposite. The authors also prepared a similar hybrid biocomposite, but this time with 30 wt% total fibers (sisal and glass fibers). They reportedly observed a major improvement in tensile strength as the GF content was increased to 5.7 wt%. After this, the tensile strength was almost static even as the GF content was increased above this value. A similar trend was observed for the flexural strength. However, comparing the hybrid biocomposites with the biocomposites containing only pineapple or sisal fibers, the hybrid showed better improvement. Nevertheless, more evidence is available to show that the overall properties of hybrid composites depend greatly on (i) the percentage elongation at break and (ii) Young's modulus of the reinforcing fibers present.

Shahzad [183] presented the impact and fatigue properties of hybrid biocomposites of hemp and chopped strand mat glass fibers using unsaturated polyester resin as the matrix. Two different variations of hybrids composites were prepared. The first denoted with "A" containing 35.8 wt% hemp fiber and 11.1 wt% GF, while the second denoted with "B" had 36.6 wt% and 11.3 wt% hemp and glass fibers respectively. From the results, "A" had 70.1 ± 10.2 MPa, 8.3 ± 0.4 GPa and 1.31 ± 0.25% for tensile strength, Young's modulus and strain to failure respectively, while "B" showed 81.6 ± 3.7 MPa, 7.7 ± 0.3 GPa and 1.73 ± 0.08% for tensile strength, Young's modulus and strain to failure improvement respectively when compared with biocomposites reinforced only with hemp fibers, having

46.4 ± 4.6 MPa, 7.2 ± 0.9 and 1.03% respectively. The increase in the percentage of GF led to the observed increase in tensile strength and better strain to failure in "B" as compare to "A." The hemp fiber is a low strain to failure fiber while the glass fiber is a high strain to failure fiber. Their combination, leads to enhance strain to failure composites. This is referred to as "hybrid effect" and it has being well observed in hybrid composites. Therefore the increase in strain to failure of the hemp-glass fiber composites can be attributed to the hybrid effect. Also, there was an observed improvement in the fatigue strength of hybrid biocomposites while the fatigue sensitivity showed no improvements when compared to hemp only fiber composites.

Hybrid of glass/natural fibers have been reported to have improved impact, tensile and flexural strength [182]. Furthermore, Velmurugan and Manikandan [184] reported that good strength, especially mechanical strength is achieved when the synthetic fiber is placed at the ends of the composite for laminated composites.

In another research work, Ahmed and Vijayarangan [185] prepared composites with jute only and jute/glass fibers hybrid reinforced polyester composites, keeping the total weight fraction of fibers constant at 42 wt%. From their results, the composites consisting of 40:60 ratio of jute:glass fibers, the reinforced hybrid laminate gave an increase in the tensile strength, Young's modulus, flexural strength and flexural Young's modulus of 53, 30, 31 and 62% respectively over those of the jute only fiber composites. They further indicated that in the event properties, environmental impact and costs were to be considered, composites with 60:40 fiber fraction of jute:glass fibers ratio gave optimum material combination. This clearly highlights that the type of matrix and/or fiber, method of preparation, fiber content and fiber modification have a huge impact on the mechanical properties of hybrid biocomposites.

### **5.6 Other factors**

In the preparation of NFPCs, there are many other additives or processes that can also influence the final properties of the composites but are seldom considered, for example impurities in the polymer matrix are introduced via fibers addition. These elements can influence the process of crystallization, just like the nanoparticles, although, this depends greatly on their chemical nature. Also it is worthy to mention that the annealing of the composites allows the crystals to grow to their maximum size. Thus, the temperature at which the materials are annealed is also very influential to the final properties of the composite obtained. Therefore from the selection of materials to the final product, care must be taken to achieve the properties desired.

Liu et al. [186] assessed the influence of processing method on the physical properties, especially mechanical properties, of kenaf fiber reinforced biocomposites prepared using soy fiber. The compression molded specimens were observed to have similar Young's modulus to those from injection molding at room temperature. However, at elevated temperature, the heat deflection temperature (HDT) and notched Izod impact strength were higher compared to those obtained from injection molded specimen. The improvements observed with the compression molded samples were attributed to a surge in Young's modulus at high temperature and fiber bridging effects.

Generally, biomedical applications desire for fabrication of grafts which are biocompatible and enable cell differentiation and expression with apt mechanical properties, but the ability to achieve such mechanical capacity has been a challenge for decades. As over the years, the focus and efforts have been geared towards biocompatibility and not necessarily mechanical prowess. But the formation of stresses occurring in implant locations due to mechanically inept implant materials have

**125**

**Table 1.**

*Namvar et al. [188]).*

**Figure 2.**

*tissue under repair [187].*

device thereof

medicine

high-wet-modulus fiber

fibers and root fibers

and process for producing the same

between its liner and its structure

*Improving the Mechanical Properties of Natural Fiber Composites for Structural and Biomedical…*

*Illustration of potential application of collagen fibers embedded in a hydrogel bio-composite for medical applications with adjusted mechanical properties that provide support and allow motion and flexibility of the* 

3. Medical natural porous fiber filler and vacuum sealing drainage

4. Manufacturing process of antibacterial bamboo pulp used for

6. Far-infrared fiber fabric functional bellyband by utilizing

10. Manufacturing of nano-fibers, from natural fibers, agro based

12. Absorbable protective coatings for wound with the use of sponge

13. Medical prosthesis, especially for aneurysms, with a connection

nano-selenium, germanium and zinc elements traditional Chinese

**No. Patent title Patent no. Year** 1. Medical balloon with incorporated fibers W0/2013/148399 2013 2. Polyester cool-fiber antibacterial pillow CN102715804 2012

5. Flushable moist wipe or hygiene tissue CN102665510- 2012

7. Medical device for insertion into a joint US20090234459 2008 8. Medical device for insertion into a joint EU1896088 2008 9. Antiviral fiber and producing method and use thereof CN1609336 2006

11. Natural antibacterial material and its use CN461827 2003

*Summary of some patents published employing nature fibers for biomedical applications (adapted from* 

CN102715983 2012

CN102677504 2012

CN101703317 2010

CA2437616 2005

W0/20021054998 2006

EPOB18184 1998

*DOI: http://dx.doi.org/10.5772/intechopen.85252*

*Improving the Mechanical Properties of Natural Fiber Composites for Structural and Biomedical… DOI: http://dx.doi.org/10.5772/intechopen.85252*

### **Figure 2.**

*Renewable and Sustainable Composites*

46.4 ± 4.6 MPa, 7.2 ± 0.9 and 1.03% respectively. The increase in the percentage of GF led to the observed increase in tensile strength and better strain to failure in "B" as compare to "A." The hemp fiber is a low strain to failure fiber while the glass fiber is a high strain to failure fiber. Their combination, leads to enhance strain to failure composites. This is referred to as "hybrid effect" and it has being well observed in hybrid composites. Therefore the increase in strain to failure of the hemp-glass fiber composites can be attributed to the hybrid effect. Also, there was an observed improvement in the fatigue strength of hybrid biocomposites while the fatigue sensitivity showed no improvements when compared to hemp only fiber composites. Hybrid of glass/natural fibers have been reported to have improved impact, tensile and flexural strength [182]. Furthermore, Velmurugan and Manikandan [184] reported that good strength, especially mechanical strength is achieved when the synthetic fiber is placed at the ends of the composite for laminated composites. In another research work, Ahmed and Vijayarangan [185] prepared composites with jute only and jute/glass fibers hybrid reinforced polyester composites, keeping the total weight fraction of fibers constant at 42 wt%. From their results, the composites consisting of 40:60 ratio of jute:glass fibers, the reinforced hybrid laminate gave an increase in the tensile strength, Young's modulus, flexural strength and flexural Young's modulus of 53, 30, 31 and 62% respectively over those of the jute only fiber composites. They further indicated that in the event properties, environmental impact and costs were to be considered, composites with 60:40 fiber fraction of jute:glass fibers ratio gave optimum material combination. This clearly highlights that the type of matrix and/or fiber, method of preparation, fiber content and fiber modification have a huge impact on the mechanical properties of hybrid

In the preparation of NFPCs, there are many other additives or processes that can also influence the final properties of the composites but are seldom considered, for example impurities in the polymer matrix are introduced via fibers addition. These elements can influence the process of crystallization, just like the nanoparticles, although, this depends greatly on their chemical nature. Also it is worthy to mention that the annealing of the composites allows the crystals to grow to their maximum size. Thus, the temperature at which the materials are annealed is also very influential to the final properties of the composite obtained. Therefore from the selection of materials to the final product, care must be taken to achieve the

Liu et al. [186] assessed the influence of processing method on the physical properties, especially mechanical properties, of kenaf fiber reinforced biocomposites prepared using soy fiber. The compression molded specimens were observed to have similar Young's modulus to those from injection molding at room temperature. However, at elevated temperature, the heat deflection temperature (HDT) and notched Izod impact strength were higher compared to those obtained from injection molded specimen. The improvements observed with the compression molded samples were attributed to a surge in Young's modulus at high temperature and fiber

Generally, biomedical applications desire for fabrication of grafts which are biocompatible and enable cell differentiation and expression with apt mechanical properties, but the ability to achieve such mechanical capacity has been a challenge for decades. As over the years, the focus and efforts have been geared towards biocompatibility and not necessarily mechanical prowess. But the formation of stresses occurring in implant locations due to mechanically inept implant materials have

**124**

biocomposites.

**5.6 Other factors**

properties desired.

bridging effects.

*Illustration of potential application of collagen fibers embedded in a hydrogel bio-composite for medical applications with adjusted mechanical properties that provide support and allow motion and flexibility of the tissue under repair [187].*


### **Table 1.**

*Summary of some patents published employing nature fibers for biomedical applications (adapted from Namvar et al. [188]).*

led to numerous implant failures and lead to investigations to improve mechanical properties of biomedical devices for diverse applications (**Figure 2**).

There have been quite a number of patents registered over the years of researchers employing natural fiber for biomedical applications and **Table 1** presents a summary of some of these patents.
