Bionanocomposites are a novel class of nanosized materials in the modern day world. The terminology “bionanocomposites” is introduced several years ago to classify an emerging class of biohybrid materials. Bionanocomposites are the com­bination of biopolymers such as proteins, polysaccharides, nucleic acids, etc. with a reinforcing agent having at least one dimension in the nanometer range. The rein­forcing agent may include plant fibers and by products from lignocellulosic renew­able resources or synthetic inorganic fraction of finely divided solids, spanning from clays to phosphates or carbonates, whose origin can be either natural or synthetic. The most important challenge in bionanocomposites is to achieve materials with improved performance characteristics, by the elusive management of the individual properties of the incorporated components. There are some similarities of bionano­composites with nanocomposites prepared by using commodity polymers but also have fundamental differences in the methods of preparation, functionalities, proper­ties, biodegradability, and applications. Processes and structure of bionanocompos­ites are regulated by water that is added in an amount to only hydrate functional groups in the carbohydrate macromolecule. In particular, the biodegradability and biocompatibility nature of biopolymers, along with the thermal and mechanical properties of the reinforcing counterpart, bridge the gap between functional and structural materials.114117 Engineered biopolymer-layered silicate nanocomposites are reported to have markedly improved physical properties including higher gas barrier properties, tensile strength, and thermal stability.118120 Chemically treated nanoscale silicate plates incorporated with appropriate polymers can provide ef­fective barrier performance against water, gases, and grease.121 These hyper-platy, nanodimensional thickness crystals create a tortuous path structure that inherently resists penetration.

Vijay Kumar Thakur, PhD

Staff Scientist School of Mechanical and Materials Engineering, Washington State University, USA

Vijay Kumar Thakur, PhD, PDF, is a Staff Scientist in the School of Mechanical and Materials Engineering at Washington State University, Pullman, Washington, USA. He is an editorial board member of several international journals including Advanced Chemistry Letters, Lignocel — luloses, Drug Inventions Today International Journal of Energy Engineering and Journal of Textile Science and Engineering (USA), to name a few, and also member of scientific bodies around the world. His former appointments include Research Scientist in Temasek Laborato­ries at the Nanyang Technological University, Singapore; Visiting Research Fellow in the Department of Chemical and Materials Engineering at Languha University, Taiwan, and Post Doctorate in the Department of Materials Science and Engineering at Iowa State University, USA. In his academic career, he has published more than 100 research articles, patents and conference proceedings in the field of polymers and materials science. He has published 10 books and 25 books on the advanced state of the art of polymers/materials science with numerous publishers. He has extensive expertise in the synthesis of polymers (natural/synthetic), nano materials, nanocomposites, biocomposites, graft copolymers, high performance capacitors and electrochromic materials.

Professor and Berry Family Director School of Mechanical and Materials Engineering, Washington State University, Pullman, USA

Professor Kessler is an expert in the mechanics, process­ing, and characterization of polymer matrix composites and nanocomposites. His research thrusts include the develop­ment of multifunctional materials (including the develop­ment of self-healing structural composites), polymer matrix composites for extreme environments, bio-renewable poly­mers and composites, and the evaluation of these materials

using experimental mechanics and thermal analysis. These broad-based topics span the fields of organic chemistry, applied mechanics, and processing science. He has extensive experience in processing and characterizing thermosets including those created through ring-opening metathesis polymerization (ROMP), such as poly di — cyclopentadiene, and the cyclotrimerization of cyanate ester resins. In addition to his responsibilities as professor of Mechanical and Materials Engineering at Washington State University, he serves as the Director of the school. He has developed an active research group with external funding of over 10 million dollars—including funding from the National Science Foundation, ACS Petroleum Research Fund, Strategic En­vironmental Research and Development Program (SERDP), Department of Defense, Department of Agriculture, and NASA. His honors include the Army Research Of­fice Young Investigator Award, the Air Force Office of Scientific Research Young Investigator Award, the NSF CAREER Award, and the Elsevier Young Composites Researcher Award from the American Society for Composites. He has published more than 110 journal papers and 3700 citations, holds 6 patents, edited a book on the char­acterization of composite materials, presented more than 200 talks at national and international meetings, and serves as a frequent reviewer and referee in his field.

MTS array as applying for mazan (CellTiter 96® Aqueous One Solution Cell Prolif­eration Assay, Promega, Madison, WI) used the novel tetrazolium compound (MTS) and the electron coupling reagent, phenazine metho sulfate (PMS). MTS is chemi­cally reduced by cells into formazan, which is soluble in tissue culture medium. The measurement of the absorbance of the formazan can be carried out using 96 well microplates at 492 nm. The assay measures dehydrogenase enzyme activity found in metabolically active cells.

The metabolic activity of cells was monitored using the MTS that is chemically reduced by metabolically active cells into formazan. The amount of formazan pro­duced is an indicator of the cell viability. The measurement of formazan absorbance was performed in 96 well plates after several days of incubation. Standard curves were prepared by diluting a series of cell suspensions from 15.7 cells/mL to 157,000 cells/ mL. An aliquot (1.0 mL) of each dilution was transferred to wells of a 24-well tissue culture plate in triplicate. Subsequently, 150 nL of the MTS solution was added to each suspension.

The plate was incubated at 37 °C in a humidified atmosphere containing 5% CO2 in the dark for 4 h, after which 1.0 mL of the kit’s solubilization/stop solution was added to each well. Plates was sealed and incubated overnight. Absorbance was read at 570 nm wavelength and also at 650 nm as a reference wavelength using the plate fluorimeter.

The scaffolds were sterilized by incubating with 70% ethanol for 30 min, seeded with human osteoblast-like cells (SaOS-2) and cultured for up to 14 days. The vi­ability of the osteoblasts seeded to the electrospun scaffolds was determined first by using the MTS assay (Fig. 2.13). The amount of formazan produced is proportional to number of living cells in culture since the chemical reduction of formazin to a colored product is dependent on the number of viable cells. The MTS viability assay demon­strated that the cells exposed to these scaffolds maintain the ability to proliferate for up to 14 days that the experiment lasted for.

To evaluate cell morphology on the scaffolds, samples were prepared for elec­tron microscopy (EM) staining. Samples were washed 2 times with PBS and fixed with 2.5% gluteraldeyde [Sigma] for 2 h then washed with PBS. The cell-scaffold constructs were then attached to aluminum stubs, sputter-coated with gold, and then examined under a LEO-Gemini Schottky FEG scanning electron microscope.

The cells exposed to the nano scaffolds interacted with multiple fibers. Anchoring sites for cell attachment to the fibers were visualized by SEM. The nanoclusters of HAp mineral were consistently located at the edge of cells, which provides additional evidence that they act as anchoring sites for cell attachment to the fibrous hybrids. This improvement in cell adhesion and growth are deemed to the biological role of HAp. Figure 2.14 shows the morphology of the cells cultured on the scaffolds for 1, 7 and 14 days. The size and number of the cells are both increasing with time.

Our studies suggest that the morphology and structure of the CA-HAp composite scaffolds play important roles in facilitating cell spreading and differentiation and en­hance apatite mineralization. Based on our observations, the electrospun CA scaffolds with nanosized HAp are considered as a promising candidate for bone tissue engineer­ing application.

The first major step in noise control is to determine the source of the noise be­fore designing the sound absorber. To give an automotive-related example where biocomposites find applications; the engine, the tire-road interaction and the wind are the three major factors that affect the acoustics of the passenger department of a vehicle. Hence, the floor coverings, the headliner, and the hood insulation are the critical contributions to the acoustic performance of vehicles.2 The other most important characteristic to be sought in the design of absorption materials are the noise absorption capacities in the audible frequency range of interest. For example, medium range (1200-4000 Hz) is of interest for the interior of passenger vehicles.45 Also, cost effectiveness and other conditions should be considered including dura­bility in hostile environments such as high temperature, contamination, and high speed turbulent flow, etc.17 Recyclability, lightweight, thermal comfort and contri­bution to passive safety systems are also desirable characteristics of noise absorbers in vehicles.2

Different researchers give importance to different material parameters as influ — encers of sound absorption. Among the material parameters, which are applicable to porous absorbers, Bies and Hansen29 cite only the flow resistance/resistivity, Cox and D’antonio14 consider flow resistivity and porosity, whereas Fahy,13 and Atten­borough and Ver17 refer to porosity, and structure factor (tortuosity) in addition to flow resistance/resistivity as the primary parameters that affect the sound absorption properties.

Several authors give various parameters as factors affecting the sound absorp­tion of fibrous structures. Cox and D’antonio14 report that sound absorption effi­ciency of fibrous structures can be achieved by manipulating:

• Material density

• Fiber composition

• Fiber orientation

• Fiber dimensions.

Banks-Lee et al.36 reported that the mass per unit area, thickness and porosity of the material and fiber fineness to be of significant importance to the airflow resis­tance and sound absorption of needled fibrous materials.

The factors affecting sound absorption behavior of fibrous materials, biocom­posites in particular, are classified as fiber parameters, macroscopic physical pa­rameters, process parameters of the porous material production and treatments as shown in Table 5.1 and explained below. It is important to note, beforehand, that the parameters to be described are not independent from each other.3

TABLE 5.1 (Continued)

Source: Yilmaz (2009).3

Normal specific sound absorption coefficient of the materials has been determined by using an impedance tube, two microphones, dual channel frequency analyzer and the Indian Institute of Technology Kharagpur developed MATPRO software36. Test has been done as per ASTM E-1050 standard19. The impedance tube fabricated at the Indian Institute of Technology Khaargpur is used to measure the normal specific sound absorption coefficient of the biocomposite materials is shown in Fig. 6.6. Noise reduction coefficient (NRC), a simple quantification of absorption of sound by an acoustical material was calculated by averaging the four values of acoustical normal specific absorption coefficient at specified octave band levels. The NRC val­ue lies anywhere between 0 and 1. Higher the NRC value better is its sound absorb­ing property. Figure 1.7 gives a comparison of the normal specific sound absorption coefficient of some of the sound absorbing materials used for noise control. Each of the material in Fig. 6.7 is of 25 mm thickness with a rigid backing. The normal specific sound absorption coefficient of all the materials increases with frequency. Fiberglass and wool have high sound absorption coefficients. Gypsum board has a low sound absorption coefficients since it is denser with less porosity. The natural materials like jute, cotton and coir also have relatively high sound absorption coef­ficient. The polyurethane open cell has a sound absorption coefficient higher than that of gypsum though less than the porous natural materials and fiberglass.

Table 6.9 gives the values of the normal specific impedance with both the real and imaginary part of a 50 mm jute felt with a density of 117.2 kg/m3 as a function of frequency from 100 Hz to 1000 Hz. The jute felt was provided with a rigid backing. The data in the Table 6.9 can be used in numerical simulations20.

Injection molding process is the most extensively used molding method in the in­dustry used for the production of polymer composites due to its simplicity and fast processing cycle. Injection molding machine mixes and injects a measured amount of matrix and fiber mixture into the mold resulting in the desired product. It consists of three major sections: the injection unit, mold, and ejection and clamping unit (see Fig. 8.4).

The injection unit consists of a heated screw barrel having a compression screw, which can rotate as well as reciprocate. The function of the heated barrel is to pro­vide heat to the polymer matrix to melt before injection. The function of the recip­rocating screw is to carry and compress the pellets from the hopper into the heated barrel, mix the polymer matrix and fiber, provide heat to the matrix by viscous shearing and inject the mixture into the closed mold by acting as a piston. In other words injection unit consists of an extruder with an added function of reciprocating screw that injects the mixture into the mold. The cavities in the mold are the replica of the desired geometry of the product. The molds consist of cooling and/or heat­ing coils to regulate the mold temperature. The mold temperature determines the cooling rate of the product. The clamping unit clamps the mold tightly against the injection pressure to prevent burr formation and the ejector unit actuates the ejectors in the mold to eject the part when the cycle completes.

A typical injection molding process cycle is shown in Fig. 8.5. Generally the injection molding cycle is assumed to start from mold close position. After the mold closes it is tightly clamped against the injection pressure by the clamping unit. In the mean time the screw is retracted to its back position and then it injects the molten mixture with the desired injection pressure and speed into the mold cavity. The in­jected mixture undergoes shrinkage during solidification and to compensate that the screw is kept forward by the desired holding pressure for some time. After this point the screw starts to retract and plasticize the mixture while the part is being cooled in the mold. The part is allowed to cool sufficiently to be able to bear the ejector force and meet the desired dimensions. In the mean time the screw is being pushed backward as it is rotating and accumulating the mixture in the front. The part is then ejected and the cycle repeats itself.

FIGURE 8.5 Injection molding cycle.

Among all the natural fiber reinforced biocomposites, the flax based composite shows the best properties when compared to other natural composites, including glass-reinforced traditional composites. Flax fibers offer higher reinforcing prop­erties than hemp and kenaf natural fibers. Namely, comparison of the mechanical properties of the natural fiber reinforced composites has shown that composites based on flax fibers exhibited higher tensile strength relative to those based on hemp or kenaf fibers. Flax fibers exhibit a higher fineness and more unique distribution compared to hemp or kenaf. According to current theories, a higher fiber fineness should results in better fiber embedment during compression molding and conse­quently higher mechanical properties. Generally, mechanical properties of natural fibers are determined by the cellulose content and microfibrillar angle. The cells of the flax fibers consist mostly of pure cellulose cemented by means of noncellulosic incrusting such as lignin, hemicellulose, pectin or mineral substances, resins, tan­nins and small amount of waxes and fats. Flax cell wall consists of about 70-75% cellulose, 15% hemicellulose and pectin materials. The Young’s modulus of the nat­ural fibers decreases with the increase of diameter. The mechanical properties of the natural fibers are also closely related to the degree of polymerization of the cellulose in the fiber21. Basic physicochemical properties and cellulose content for flax fibers versus other natural reinforcing fibers are shown in Table 10.3.

Oksman et al.22 have studied the mechanical properties of PLA/Flax composites versus PP/Flax. The addition of flax fibers increase the modulus, but the higher fiber content has not improved the modulus in PLA composites as it has been ob­served for PP composites due to the fiber orientation in the polymer matrix. The test composites were compression molded and the fibers could be orientated differently from one sample to another. Because of the brittle nature of PLA, triacetin was used to plasticize the pure PLA and for the PLA/Flax composites. The addition of triac­etin has shown a positive effect on the elongation to break for pure PLA and PLA/ Flax composites, which was expected because of the softening effect. The highest triacetin addition (15%) clearly shows a negative effect for PLA/Flax composites, both the stress and stiffness were strongly decreased. As expected, it was shown that the addition of triacetin did not affect the impact properties of the PLA/Flax com­posites. The addition of 5% triacetin in PLA has shown the best results on impact strength. The authors also reported that thermal properties of PLA were increased with the incorporation of flax fibers. The softening temperature was increased from about 50°C for pure PLA to 60°C with flax fibers, and it is further increased if the composite is crystallized.

Tensile tests on fibers were conducted on a tow (strand) disassembled from the fab­ric. The tows in the longitudinal direction in the fabric were separated from the ones in the orthogonal direction. Tests were carried out for both series separately. The tensile properties of the fiber tow were determined at room temperature and 50% relative humidity on an Instron 5548 microtester machine, with crosshead distance of 50 mm and speeds of 120 mm/min. The maximum load at break was recorded for each specimen. A minimum 10 specimens were tested for each type of sample.

The tensile properties of the composites were evaluated at room temperature and 50% relative humidity on an Instron 5500R machine, with crosshead speeds of 5 mm/min according to ASTM 3039-00. A minimum 5 specimens were tested for each type of sample.

As indicated already, the fiber-matrix interface quality is very important to promote successful reinforcement of composite materials. There are a number of physical and chemical methods to optimize the interface for varying degrees of efficiency for the adhesion.43

14.4.4 PHYSICAL METHODS

Physical methods for improving the adhesion of surfaces attempt to enhance or im­prove existing surface chemistry or functionalities. For example, surface fibrillation is one method that has been previously used; this is a type of refining or homogeni­zation (NFC, vide supra) that takes a top-down approach in increase the surface area of the materials under study. What this means is that the macrofibers are “opened” up to reveal more of the micro and nano-fibrils that compose the fibers. Such an approach allows for the native high surface energy and area to be increased and promote adhesion. Another method is electric discharge that includes corona or cold plasma. Cold plasma has been used to increase bondability without significantly im­pacting the bulk properties of the substrate treated. Carlsson44 was able to show via a hydrogen plasma treatment of a pure cellulose substrate that the hydroxyl content on the surface was diminished to provide lower molecular weight fragments that were more hydrophobic.

The highly transparent and flexible films prepared using NFCs exhibited a dras­tic improvement mechanical properties, with a maximum enhancement in Young’s modulus of 78% and 150% for high molecular weight chitosan and water-soluble high molecular weight chitosan (WSHCH), respectively with 20 wt.% of NFC load­ing; and of 200% and 320% for low molecular weight chitosan and water-soluble low molecular weight chitosan, respectively with 60 wt.% of NFC loading. The tensile strength values were in closer agreement with the trend of modulus values. As it can be assumed from a classical reinforcement effect, the values for elongation at break were reduced.39 Similar trends was also observed using bacterial cellulose.44