**2.1. Mechanical properties**

severe environment issues during the landfills or burning. Most of these composites are made from petroleum-based nonrenewable resources [1]. In order to replace the petroleum-based nonrenewable resource-based composites, the eco-friendly biocomposites need to reduce environmental impact. Generally, biocomposites are formed with one or more phases of reinforcement of natural fibers with organic matrix or biopolymers. These reinforcements (cotton, hemp, flax, sisal, jute, and kenaf or recycled wood and paper) and biopolymers (natural biopolymers such as gelatin, corn zein and soy protein; synthetic biopolymers such as poly(lactic acid) (PLA), poly(vinyl alcohol) (PVA); and other microbial fermentation such as microbial polyesters) are renewable and degradable [2, 3]. Meanwhile, in another approach, these biocomposites are formed from the renewable, recyclable, and sustainable agricultural and forestry feedstocks but nor food or feed, this can make better change in an environment dayto-day. Systematically, the utilization of bio-based polymers as a reinforced matrix to form biocomposites increases more and more. The spectacular effect on developments of biopolymer-based composites, which lead the rapid growth of biocomposites in the market place, can be seen. In the duration of 2003–2007, globally the average annual growth rate was 38%. During the same period, the annual growth rate was as high as 48% in Europe. On the other hand, from 2007 to 2013, the capacity of utilization of these biocomposites was projected from 0.36 to 2.33 million metric ton by 2013 and 3.45 million metric ton in 2020. Indeed, PLA, PHA, and starch-based plastics were large volumes of production in biocomposites [4]. The U.S. Department of Energy (DOE) had sponsored to the Technology Road Map for Plant/Cropbased Renewable Resources 2020. The main intension of this program is to use plant-derived renewable resources for making 10% of basic chemical building blocks by 2020, and further this concept should be extended to achieve 50% by 2050. The U.S. agricultural, forestry, life sciences, and chemical communities have developed a strategic vision for using crops, trees, and agricultural residues to manufacture industrial products, and have identified major bar-

The reinforcement of many agricultural and forestry feedstocks with biopolymers comprises change in mechanical, thermal, and biodegradable properties of the composites. This chapter

The most important characteristic feature of selection materials for various applications is depending on its properties. The properties of materials are often dependent on the isotropic and anisotropic nature of the materials. The properties of materials that relate to different physical phenomena often behave linearly (or approximately so) in a given operating range. Modeling them as linear can significantly simplify the differential constitutive equations that the property describes. On the other hand, the relevant equations are also used to determine the material properties. If we know the original length of a material, then we can determine the gain or loss of its original length by calculating change of the length. Material properties are most reliably measured by standardized test methods. Many such test methods have been documented by their respective user communities and published through ASTM

elucidates the properties of renewable biocomposites and their applications.

riers to its implementation [5].

178 Composites from Renewable and Sustainable Materials

**2. Properties of biocomposites**

Most of the plastic materials are used because they have desirable mechanical properties at an economical cost. For this reason, several polymers were used in numerous applications. Indeed, several research studies have focused on such materials to gain knowledge on mechanical behavior of numerous structural factors depending on polymers. Moreover, these mechanical properties of the materials depend on the applied load. For this reason, most of the materials can be predictable their service life for future needs. In addition, mechanical properties were also useful in identification and classification of materials for different applications. The considerable properties of mechanical tests are tensile strength, modulus, impact resistance, compression, hardness, and toughness. These properties also depend on the orientation of the reinforcements and atmospheric conditions.

Generally, the properties of biocomposites depend on a matrix, natural filler, and interfacing between them. For this reason, the stress transfers between the two components. The presence of hydroxyl groups in natural fillers exhibits poor interfacial bonding with the matrix. This result concludes that biocomposites exhibit poor mechanical properties. This effect could be reduced by introducing a suitable compatibilizing agent. The effect of different compatibilizing agents on mechanical properties of natural flour filled [bamboo flour (BF) and wood flour (WF)] with biodegradable polymers [poly(lactic acid) (PLA) and poly(butylene succinate) (PBS)]. The maleic anhydride (MA) grafted biopolymers significantly improved the tensile strength of PBS-BF, PBS-WF, and PLA-BF and PLA-WF composites compared to the untreated biopolymers. This tensile strength can be improved by 25–35 MPa [7].

A novel biodegradable hybrid biocomposite system developed with the reinforcement of kenaf fiber (KF) and corn husk flour and investigated the role of the aspect ratio of natural fibers against their tensile properties. **Figure 1** shows the influence of the aspect ratio reinforcement on mechanical properties before and after passing through the extrusion process. The difference between theoretical and experimental values of the tensile modulus was not significant and the aspect ratio determined after extrusion did not influence the predicted values [8].

The use of petroleum-based polymers in composites creates serious environmental problems; it is necessary to replace it with green composites. Baek et al. [9] developed the green composites using coffee ground (CG) and bamboo flour (BF) as a reinforcement to poly(lactic acid) (PLA) and investigated mechanical, thermal, optical properties. Because of the tensile and flexural properties, BF/PLA and CG/PLA composites decrease with addition of CG and BF fillers, but pure PLA showed a tensile strength of 60.1 MPa and the tensile strength of BF/PLA and CG/PLA composites is decreased from 48 to 27 MPa. The addition of a coupling agent

**Figure 1.** Comparisons of the predicted tensile modulus before and after extrusion.

improved the interfacial adhesion between the filler and PLA, and the tensile strength of the composites increases with increasing 4, 40-methylene diphenyl diisocyanate (MDI), as shown in **Figure 2**.

The similar results obtained in flexural strength of these composites. Without the coupling agent in composites, the flexural strength varies from 98 to 28 MPa, and it is low when compared with pure PLA. With the addition of the coupling agent, the flexural strength might be increased with the increase of MDI, which is shown in **Figure 3** [9].

A similar result was obtained by Kim et al. [10] for cassava and pineapple flour-filled PLA biocomposites. The tensile and flexural strength of the PLA biocomposites decreased with the increasing amount of flour. However, a 3% loading of the compatibilizer in the PLA biocomposite increased the strength up to that observed with the 10% loading flour [10]. To generate the sustainable biocomposites, Sukyai et al. [11] developed the biocomposites with the reinforcement of kenaf fiber (KF) and bacterial cellulose (BC) using the PLA matrix. In particular, BC is nanocellulose, which was anticipated to increase the interfacial area and therefore low volume fractions of additives. That was consequently to attain mechanical property improvement. The elastic modulus of the composites increased concurrently with the increasing KF content. Remarkably, the incorporation of 1 wt% of BC to 60/39 wt% of PLA/KF significantly improved the tensile and flexural strength, which indicates that the BC makes good compatibility between PLA and KF [11]. The tropical crop residues such as particular starch containing bioflours were used for producing biocomposites and the feasibility and industrial potential of using biocomposites were investigated. Polypropylene (PP) and poly(butylene succinate) (PBS) were compounded with bioflours from pineapple skin (P) and from nondestarched (CS) and destarched (C) cassava root by twin-screw extrusion. The impact on mechanical properties observed when the proportion of bioflour was increased to 40% w/w, it reduced the tensile strength by 26–48% and impact strength by 14–40%. However, the different flexural

**Figure 2.** Tensile strength of the green composites with (a) natural fillers (bamboo flour and coffee grounds) and (b) MDI.

improved the interfacial adhesion between the filler and PLA, and the tensile strength of the composites increases with increasing 4, 40-methylene diphenyl diisocyanate (MDI), as shown

The similar results obtained in flexural strength of these composites. Without the coupling agent in composites, the flexural strength varies from 98 to 28 MPa, and it is low when compared with pure PLA. With the addition of the coupling agent, the flexural strength might be

A similar result was obtained by Kim et al. [10] for cassava and pineapple flour-filled PLA biocomposites. The tensile and flexural strength of the PLA biocomposites decreased with the increasing amount of flour. However, a 3% loading of the compatibilizer in the PLA biocomposite increased the strength up to that observed with the 10% loading flour [10]. To generate the sustainable biocomposites, Sukyai et al. [11] developed the biocomposites with the reinforcement of kenaf fiber (KF) and bacterial cellulose (BC) using the PLA matrix. In particular, BC is nanocellulose, which was anticipated to increase the interfacial area and therefore low volume fractions of additives. That was consequently to attain mechanical property improvement. The elastic modulus of the composites increased concurrently with the increasing KF content. Remarkably, the incorporation of 1 wt% of BC to 60/39 wt% of PLA/KF significantly improved the tensile and flexural strength, which indicates that the BC makes good compatibility between PLA and KF [11]. The tropical crop residues such as particular starch containing bioflours were used for producing biocomposites and the feasibility and industrial potential of using biocomposites were investigated. Polypropylene (PP) and poly(butylene succinate) (PBS) were compounded with bioflours from pineapple skin (P) and from nondestarched (CS) and destarched (C) cassava root by twin-screw extrusion. The impact on mechanical properties observed when the proportion of bioflour was increased to 40% w/w, it reduced the tensile strength by 26–48% and impact strength by 14–40%. However, the different flexural

increased with the increase of MDI, which is shown in **Figure 3** [9].

**Figure 1.** Comparisons of the predicted tensile modulus before and after extrusion.

180 Composites from Renewable and Sustainable Materials

in **Figure 2**.

strength appeared upon the addition of bioflours; it increased initially but then decreased at higher loads. This effect was also studied by using a compatibilizer of maleic anhydride polypropylene (MAPP), it enhances the flexural strength compared to pure PP, and this resultant material becomes stronger and less flexible [12]. A similar effect was observed while adding 3-glycidoxypropyltrimethoxysilane (GPS) as a coupling agent in the PLA/kenaf fiber biocomposites. The flexural strength and flexural modulus of the composites increased with increasing the content of GPS, while compared with pure PLA. This coupling agent significantly increases the interfacial strength between resin and fibers [13]. There are many value-added composite products obtained from the raw materials of biomass and it consist most promising beneficial resources, for example rice straw, rice husk, and paper sludge are the by-products and industrial waste and are beneficial resources as raw biomass. Kim et al. [14] investigated mechanical properties by adding rice straw, rice husk, and paper sludge to wood composites to replace wood particles for manufacturing green pallets using urea-formaldehyde (UF) resin. The obtained mechanical properties of the composites showed the decrement, upon increasing the contents of rice straw and rice husk flours. The presence of wax and silicate creates less interfacial bonding with UF resin. Moreover, the mechanical properties of woodpaper sludge composites are similar to wood particles so it was replaced with paper sludge [14]. Yang et al. [15] studied the effect of compatibilizing agents on rice-husk flour-reinforced polypropylene (PP) composites. The mechanical properties of these composites were studied

**Figure 3.** Flexural strength of the green composites with (a) natural fillers (bamboo flour and coffee grounds) and (b) MDI.

at different filler loadings, temperatures, and crosshead speeds. The obtained results indicated that tensile strength of the composites decreased with increasing filler contents in the absence of compatibilizing agent, whereas in the presence of compatibilizing agents, these mechanical properties were significantly increased [15]. Another report showed that the bioflour-filled [rice husk flour (RHF), wood flour (WF)] maleic anhydride grafted polypropylene (MAPP) composites have good mechanical properties compared with pure polypropylene (PP) composites. The enhancement of mechanical properties was strongly dependent on the amount of MA graft (%) and the MAPP molecular weight, which is shown in **Figure 4** [16].

The most interesting study proved the manufacturing effect on mechanical properties of lignocellulosic material-filled polypropylene biocomposites. The obtained results of tensile strength and modulus of the biocomposites significantly improved with a fabricated twinscrew extruding system compared with a single-screw extruding system [17]. The mechanical properties of the biodegradable polymers and PBS-WF, PBS-BF biocomposites were analyzed with increasing hydrolysis time at 50°C and 90% relative humidity (RH). The resultant properties of these polymers and biocomposites show decrement with the increasing hydrolysis time, due to the easy hydrolytic degradation of the ester linkage of the biodegradable polymers. However, when the antihydrolysis agent trimethylolpropane triacrylate (TMPTA) was treated with PBS, tensile strength was significantly increased with the increasing hydrolysis time as compared to the nontreated PBS. The same results were observed for the PBS-based biocomposites [18]. The addition of paper sludge to thermoplastic polymer composites significantly improved the tensile properties with increasing mixing ratios, and tensile strength

**Figure 4.** Tensile strength of RHF- and WF-filled PP composites as a function of different MAPP types. A, Polybond 3150; B, Polybond 3200; C, G-3003; D, E-43; E, Bondyram 1004.

vary from 230 to 280 MPa. Moreover, tensile modulus improved with the increasing paper sludge content. On the other hand, flexural properties showed a similar trend as tensile properties [19]. A similar effect was observed in the tensile strength properties of lignocellulosic filler-reinforced polyethylene biocomposites [20].
