**4. Biocomposites**

Biocomposites are formed by a polymer matrix and natural fibers, which act as reinforcements. There are six types of natural fibers commonly used in biocomposite elaboration: grass and reed fibers (wheat, corn, and rice), core fibers (kenaf, jute, and hemp), bast fibers (jute, flax, hemp, ramie, kenaf, bamboo, and banana), seed fibers (coir, cotton and kapok), leaf fibers (abaca, sisal, and pineapple), and other types (wood and roots) [52].

The composition of natural fibers consists mainly of cellulose, hemicellulose, and lignin. Cellulose in plants is the main component that provides stability and strength to the cell walls, and this component directly influences the biocomposite production for a defined application, whether in the textile, automotive, and others. Lignin is a highly cross-linked structure, and the amount of this directly influences the structure, properties, morphology, hydrolysis rate, as well as the flexibility of the fibers. Besides, fibers with greater amount of lignin have less amount of cellulose, and this will also depend on the application of the fiber.

**89**

*Agro-Industrial Waste Revalorization: The Growing Biorefinery*

The fibers can be used in both thermoplastics and thermosets. Thermoplastic matrices include polypropylene (PP), high-density polyethylene (HDPE), polystyrene (PS), and polyvinyl chloride (PVC). Thermosets include epoxy, polyester, and phenolic resins. In recent years, the number of studies focused on these materials has increased, because they are environmentally friendly and have low production costs, easy workability, good properties of lightness, mechanical strength, and thermal insulation [53]. However, due to the hydrophilic nature of natural fibers and hydrophobic nature of polymer matrix, there is no good interfacial interaction between the two materials, and therefore, the mechanical properties are deteriorated. Based on the above, chemical and physical treatments have been developed to modify the surface of natural fibers and promote interfacial adhesion with the

Among the chemical treatments stands out alkali, benzoylation, cyclohexane, silicon, peroxide, acetylation, sulfuric acid, stearic acid treatment, and the modification with maleic anhydride. The chemical modification provides more dimensional stability and reduces water absorption capacity [55]. Alkaline treatment is the most used and consists in eliminating the lignin, wax, and oil of the fibers, since these components act as a barrier between the polymeric matrix and the fibers; and in turn, it is possible to increase the roughness in the surface of the fibers [56]. Another alternative to improve the compatibility between these materials is using compatibilizing agents, such as maleic anhydride grafted with polyolefins, either polypropylene or high-density polyethylene. The main factors that affect the processing and performance of biocomposites are the presence of moisture, type, shape (short or long), concentration, and orientation of the fibers. The processing method for obtaining biocomposites will depend on the type of fiber, for example: twin-screw extruder and hydraulic press, injection molding, melt mixing, and single-screw extruder for short-fiber-reinforced composites [57]. New technologies

The main applications of the biocomposites are automotive parts, packaging, military industry, aerospace, medical articles, etc. The interest of the automotive sector in developing biocomposites lies mainly in reducing the consumption of fiber glass because it is more expensive than the natural one and, in turn, making the vehicles lighter, and it also contributes to the consumption of less combustible and to the fact of being eco-friendly. In recent years, Toyota, Mercedes-Benz, Ford, Mitsubishi, and Daimler Chrysler AG have incorporated biodegradable materials in the exterior parts of some of their vehicles [58]. Pracella et al. [58] studied the functionalization, compatibilization, and properties of polypropylene (PP) composites with hemp fibers. The fibers were functionalized with glycidyl methacrylate (GMA). PP/hemp composites at various compositions were prepared in a Brabender internal mixer. All modified composites showed improved fiber dispersion in the polyolefin matrix and higher interfacial adhesion with respect to the unmodified PP/hemp. Composites showed an increase in Young modulus as compared to PP due to the addition of PP-g-GMA. Vilaseca et al. [59] studied the effect of alkali treatment on interfacial bonding in abaca fibers. They used an epoxy resin, and the results showed that alkali treatments modify the structure and chemical composition of abaca fibers. Abaca fibers treated in 5 wt. % NaOH showed excellent interfacial adhesion with epoxy resin. Bledzki et al. [60] carried out polypropylene-based biocomposites with different types of natural fibers (jute, kenaf, abaca, and softwood) to compare their performance under the same processing conditions, and they found that the properties of biocomposites depend on geometry of the fibers. Kenaf provides strength to biocomposites, abaca obtains the best results in impact resistance, jute fibers are the most stable thermally, and the wood microfibers have good resistant strength. Currently, several studies have been carried out with other

can improve the processing of these materials to make it easier.

*DOI: http://dx.doi.org/10.5772/intechopen.83569*

polymer matrix [54].

#### *Agro-Industrial Waste Revalorization: The Growing Biorefinery DOI: http://dx.doi.org/10.5772/intechopen.83569*

*Biomass for Bioenergy - Recent Trends and Future Challenges*

antidiabetic, and antihypertensive activities [46].

lose, and this will also depend on the application of the fiber.

Biocomposites are formed by a polymer matrix and natural fibers, which act as reinforcements. There are six types of natural fibers commonly used in biocomposite elaboration: grass and reed fibers (wheat, corn, and rice), core fibers (kenaf, jute, and hemp), bast fibers (jute, flax, hemp, ramie, kenaf, bamboo, and banana), seed fibers (coir, cotton and kapok), leaf fibers (abaca, sisal, and pineapple), and

The composition of natural fibers consists mainly of cellulose, hemicellulose, and lignin. Cellulose in plants is the main component that provides stability and strength to the cell walls, and this component directly influences the biocomposite production for a defined application, whether in the textile, automotive, and others. Lignin is a highly cross-linked structure, and the amount of this directly influences the structure, properties, morphology, hydrolysis rate, as well as the flexibility of the fibers. Besides, fibers with greater amount of lignin have less amount of cellu-

**4. Biocomposites**

other types (wood and roots) [52].

Bioactive peptides are encrypted within the protein sequences with different bioactivity functions and relevant in some important disorders in human health such as cancer, hypertension, antioxidant functions, diabetes mellitus, and other important diseases. These peptides may have different sizes, around 2–20 amino acid residues per molecule with molecular masses between 1 and 6 kDa and based on their physical properties and amino acid composition [47] which make them very attractive for different applications in pharmaceutical and food industries. Waste can contain many valuable substances, and through a suitable process or technology, this material can be converted into value-added products or raw materials that can be used in secondary processes. Residual wastes generated by agro-industries are a protein-rich source and have become an alternative for obtaining compounds with bioactivity, mainly from protein hydrolysates; their extraction processes do not involve negative environmental impacts [48]. The principal residual wastes generated by the agro-industrial activities are soybean meal, residues of oiled plants, and rapeseed meal [48]. Those peptides can generate in the market peptides and protein drugs more than \$40 billion/year, with an accelerated pace in the drug market [48]. The press cake, after oil extraction from *J. curcas (*not toxic genotypes*)* in biodiesel production, represents a potential of new source of protein for food and feed uses. The seed cake of *Jatropha* contains a high concentration of storage proteins mainly glutelins and globulin fractions [49] that encrypted peptides with antioxidant, chelating, and antihypertensive activities [50]. Some peptides have activities against bacteria that can reduce the human infections. In that sense, a trypsin inhibitor was purified from castor bean waste of seed cakes; the 75-kDa peptide displayed antibacterial activity against *Bacillus subtilis*, *Klebsiella pneumoniae*, and *Pseudomonas aeruginosa*, which are important human pathogenic bacteria. In addition, microscopy studies indicated that this peptide disrupts the bacterial membrane with loss of the cytoplasm content and ultimately bacterial death. The author concludes that this peptide is a powerful candidate for the development of an alternative drug that may help reduce hospital-acquired infections [51]. Other important seed cakes from oiled plants can be used for the peptide characterization. For example, chia (*Salvia hispanica*) seed cake is novelty for the peptide extraction; the seed cake contains high amounts of proteins that encrypted different peptides with antioxidant,

**3.3 Peptides**

**88**

The fibers can be used in both thermoplastics and thermosets. Thermoplastic matrices include polypropylene (PP), high-density polyethylene (HDPE), polystyrene (PS), and polyvinyl chloride (PVC). Thermosets include epoxy, polyester, and phenolic resins. In recent years, the number of studies focused on these materials has increased, because they are environmentally friendly and have low production costs, easy workability, good properties of lightness, mechanical strength, and thermal insulation [53]. However, due to the hydrophilic nature of natural fibers and hydrophobic nature of polymer matrix, there is no good interfacial interaction between the two materials, and therefore, the mechanical properties are deteriorated. Based on the above, chemical and physical treatments have been developed to modify the surface of natural fibers and promote interfacial adhesion with the polymer matrix [54].

Among the chemical treatments stands out alkali, benzoylation, cyclohexane, silicon, peroxide, acetylation, sulfuric acid, stearic acid treatment, and the modification with maleic anhydride. The chemical modification provides more dimensional stability and reduces water absorption capacity [55]. Alkaline treatment is the most used and consists in eliminating the lignin, wax, and oil of the fibers, since these components act as a barrier between the polymeric matrix and the fibers; and in turn, it is possible to increase the roughness in the surface of the fibers [56]. Another alternative to improve the compatibility between these materials is using compatibilizing agents, such as maleic anhydride grafted with polyolefins, either polypropylene or high-density polyethylene. The main factors that affect the processing and performance of biocomposites are the presence of moisture, type, shape (short or long), concentration, and orientation of the fibers. The processing method for obtaining biocomposites will depend on the type of fiber, for example: twin-screw extruder and hydraulic press, injection molding, melt mixing, and single-screw extruder for short-fiber-reinforced composites [57]. New technologies can improve the processing of these materials to make it easier.

The main applications of the biocomposites are automotive parts, packaging, military industry, aerospace, medical articles, etc. The interest of the automotive sector in developing biocomposites lies mainly in reducing the consumption of fiber glass because it is more expensive than the natural one and, in turn, making the vehicles lighter, and it also contributes to the consumption of less combustible and to the fact of being eco-friendly. In recent years, Toyota, Mercedes-Benz, Ford, Mitsubishi, and Daimler Chrysler AG have incorporated biodegradable materials in the exterior parts of some of their vehicles [58]. Pracella et al. [58] studied the functionalization, compatibilization, and properties of polypropylene (PP) composites with hemp fibers. The fibers were functionalized with glycidyl methacrylate (GMA). PP/hemp composites at various compositions were prepared in a Brabender internal mixer. All modified composites showed improved fiber dispersion in the polyolefin matrix and higher interfacial adhesion with respect to the unmodified PP/hemp. Composites showed an increase in Young modulus as compared to PP due to the addition of PP-g-GMA. Vilaseca et al. [59] studied the effect of alkali treatment on interfacial bonding in abaca fibers. They used an epoxy resin, and the results showed that alkali treatments modify the structure and chemical composition of abaca fibers. Abaca fibers treated in 5 wt. % NaOH showed excellent interfacial adhesion with epoxy resin. Bledzki et al. [60] carried out polypropylene-based biocomposites with different types of natural fibers (jute, kenaf, abaca, and softwood) to compare their performance under the same processing conditions, and they found that the properties of biocomposites depend on geometry of the fibers. Kenaf provides strength to biocomposites, abaca obtains the best results in impact resistance, jute fibers are the most stable thermally, and the wood microfibers have good resistant strength. Currently, several studies have been carried out with other

types of fibers, in which we can mention agave, castor plant, and *J. curcas* fibers [61]. During the tequila production process, large amounts of waste are produced (mostly fiber), and in the case of castor plant and *J. curcas*, only the seeds are used for the extraction of oils, and the rest of plant is discarded. Therefore, an alternative to take advantage of this waste is to use it to develop biocomposites. Zuccarello et al. [62] demonstrated that the agave variety plays an important role on the mechanical performance of the fibers and they proposed an innovative and eco-friendly method for the fiber extraction based on the simple mechanical pressing of the leaves, alternated to proper water immersions avoiding alkaline treatment. They used an eco-friendly green epoxy and a polylactic acid (PLA) to obtain renewable biocomposites. In another work, Zuccarello et al. [62] studied the effect of agave fiber size on epoxy resin and PLA composites. This study showed that biocomposites with short fibers fail to act as a reinforcement, while the long fibers in the compounds with PLA achieve a high mechanical strength. Vinayaka et al. [63] elaborated composites with polypropylene and fibers extracted from the outer layer of *R. communis* (castor plant), which exhibited an elongation at 5% that was higher than the common bast fibers jute and flax, and the strength at 350 MPa was similar to that of jute but lower than that of cotton. Biocomposites have an enormous potential of applications and a growth market especially in automotive industry.
