After obtaining a free energy of Gibbs or optimization geometry using AMBER/ AM1 methods, we can plot two-dimensional contour diagrams of the electrostatic potential surrounding a molecule, the total electronic density, the spin density, one or more molecular orbitals, and the electron densities of individual orbitals.

HyperChem software displays the electrostatic potential as a contour plot when you select the appropriate option in the Contour Plot dialog box. Choose the val­ues for the starting contour and the contour increment so that you can observe the
minimum (typically about -0.5 for polar organic molecules) and so that the zero potential line appears.

A menu plot molecular graph, the electrostatic potential property is selected and then the 3D representation mapped isosurface for both methods of analysis. Atomic charges indicate where large negative values (sites for electrophilic attack) are likely to occur.

Unlike many biopolymer products being developed and marketed, very few biode­gradable composites have been developed, with most of their technologies still in the research and development stages. This is despite the fact that the environmen­tally friendly composites, where biodegradability is important, provide designers new alternatives to meet challenging requirements. These include aquatic and ter­restrial environments, municipal solid waste management and compostable packag­ing, while those for automobiles include parcel shelves, door panels, instrument panels, armrests, headrests and seat shells. Accordingly, a wide range of biodegrad­able products have been produced using LC fibers and biopolymers for different applications, ranging from automotive vehicles including trucks, construction (hur­ricane resistant housing and structures, especially in the USA) and insulation pan­els, to special textiles (geotextiles and nonwoven textiles).122 The hurricane resistant housing, structures and a variety of products developed using soy oil with LC fi­bers could be the predecessor for diverse range of applications for the biodegrad­able composites. Other identified uses for these materials include bathtubs, archery bows, golf clubs and boat hulls. This is further underlined with the estimated global market of about 900,000 metric tons of wood plastics and natural fiber composites as per Steven Van Kourteren, Consultant, Principia Partners.123 Hence the market for biodegradable composites can be expected to grow in the future. This is based on continued technical innovations, identification of new applications, persistent political and environmental pressures, and investments mostly by governments in new methods for fiber harvesting and processing of natural fibers.124125

17.2 CONCLUDING REMARKS

Renewable resources based products finding privilege particularly because of envi­ronmental friendliness and dwindling petroleum resources. Biopolymers reinforced

with natural fibers have developed significantly over the past two decades because of their significant processing advantages, biodegradability, low cost, low relative density, high specific strength and renewable nature. These composites are preor­dained to find more and more application in the near future. Interfacial adhesion between natural fibers and matrix will remain the key issue in terms of overall per­formance, since it dictates the final properties of the biocomposites. Research on biodegradable polymer and its composites has been very impressive due to their environmental friendliness, carbon dioxide sequestration, sustainability, nontoxicity and varieties of other reasons. The potential areas of applications for these compos­ites are packaging, structural, transportation and automotive, agriculture and various consumer products. The market scenario has been changing continuously due to the development of newer biodegradable polymers, processing techniques and imposi­tion of stringent environmental laws. Raw materials, processing techniques and ap­plication of biocomposites have been studied and well documented in recent years. Still there are lot of issues need to be addressed for further improvement pertaining to those above areas.

One of such issue is the nonavailability of quality fiber used as reinforcing agent in the composites. The production of quality fiber may be obtained through better cultivation, which includes the use of generic engineering. Exploration of nontra­ditional fiber as a source of reinforcing agent is another important area. In order to achieve proper reinforcement, the introduction of hybrid nanocomposite may be at­tempted. The processibility and development of new biodegradable polymers with much improved properties in terms of moisture resistance, mechanical strength, thermal stability and biodegradability are some of the areas which require much attention. The variation of properties along with the high cost of the bio-composites prevents their uses in various application sectors. The possibility of using high per­centage of reinforcing fiber may be tried in order to achieve a reduction in cost. Therefore, the requirement of improving interfacial interaction between reinforcing agent, filler and matrix is another critical area to be looked upon. The develop­ment of newer processing tools at lower temperature is another important aspect that needs to address.

The introduction of nanomaterials in the biocomposites is one of the effective ways to enhance the properties. Research effort should be directed towards develop­ment of nanowhiskers and nanofibers from different lignocellulosic materials and their inclusion in biocomposites for improving various properties. Efforts may also be required to derive resin, reinforcing agent and coupling agent from renewable resources. Efforts may be directed towards searching for new and improved bio­resin, fiber with better properties or new composite manufacturing technology to meet with the future environmental goals. The concept of biodegradability should be directed to ‘triggered’ biodegradability.

The price of biodegradable polymers for making composites is expected to re­duce further in the coming years due to development of raw material, manufacturing techniques and hence it may be considered as a valid alternative to conventional composites. It is also envisaged that further research and development on biode­gradable composite may lead to open up new avenues to meet the local as well as global challenges and thus may expand the horizon of applications.

[1]1 Coefficient of thermal expansion (CTE) between (Tg — 35)°C and (Tg -10)°C. *2 Coefficient of thermal expansion (CTE) between (Tg + 10)°C and (Tg + 35)°C.

The flagelliform gland appears to have different biological functions in orb-weavers relative to cob-weavers. Orb-weavers spin flagelliform silk (Flag silk) into two­dimensional webs and these fibers are known as spiral capture silk. The main pro­tein constituent of Flag silk has been shown to have several distinctive features, including iterations of GPGGX motifs, GGX, highly conserved spacer regions with charged and hydrophilic residues, and a nonrepetitive C-terminal domain that is di­vergent from the other spidroin family members.46 Flag silk represents the most ex­tensible silk type produced by orb weaver spiders, being able to stretch 200% of its own length before fiber failure. The GPGGX module, which is also present within the protein sequence of MaSp2, is responsible for the elasticity and extensibility of flagelliform silk; iterations of these motifs have been hypothesized to form type II beta-turns that assemble into beta-turn nano-spring structures.47 Recently, ana­lyzes of flagelliform silk using Raman spectroscopy from three different orb-weaver species have revealed correlations between increased tensile strength and higher amounts of beta-sheet structure, which can be attributed to greater number of spacer regions.48 This is consistent with the observation that recombinant fibers spun with only spacer regions are stronger relative to synthetic silks spun from recombinant proteins that contain spacer regions, GGX and GPGGX modules.49 In cob-weavers, which spin three-dimensional webs that lack spiral capture, the flagelliform gland has not been reported to extrude fibroins or fibroin-like proteins (Fig. 1.1); however, two small peptides dubbed Spider Coating Peptide 1 (SCP-1) and Spider Coating Peptide 2 (SCP-2) have been detected.50 MS/MS studies have demonstrated that the SCPs are present on egg cases, scaffolding threads, gumfooted lines and attachment discs. Recombinant expressed SCP-1 has been shown to bind to a nickel resin, sug­gesting it has intrinsic metal binding activity and potential antimicrobial effects. Growth studies with the gram-negative bacterium E. coli support this assertion, as addition of either SCP-1 or SCP-2 to rapidly dividing bacterial cells is able to slow cellular division (unpublished data).

Most of epoxy hardeners such as polyamines, polyphenols, and carboxylic acid an­hydrides are derived from petroleum resources. The past studies on bio-based ep­oxy hardeners are less than that on the bio-based epoxy resins. Basically, bio-based polyamines, polyphenols, and carboxylic acid anhydrides can be used as epoxy­hardener. We investigated a possibility of bio-based polyamines and polyphenols as hardeners of bio-based epoxy resins for biocomposites with lignocellulosic fibers considering an interfacial adhesion between matrix resin and fibers. Although the reaction of polyamine or polyphenol with epoxy resin generates hydroxy groups which can form hydrogen-bonding with lignocellulosic fibers, carboxylic acid an­hydrides do not produce hydroxy groups but ester groups.

As a bio-based polyamine hardener, e — poly(L-lysine) (PL) was investigated.37 The PL is produced by aerobic bacterial fermentation using Streptomyces albulus in a culture medium containing glucose, citric acid, and ammonium sulfate.3839 The PL has been used as food preservatives,40 while has not yet been applied to the industrial polymeric materials. PL differs from usual proteins in that the amide linkage is not between the a — amino and carboxylic groups in typical of peptide bonds, but is be­tween the e — amino and carboxy group. The pendant a -amino groups are expected to react with epoxy groups. When GPE or PGPE was cured with PL, a soft cured resin (GPE/PL or PGPE/PL) with a tensile modulus lower than 10 MPa and glass transition temperatures (Tg’s) measured by DSC lower than 50 °C was obtained. Although PL is interesting as a hardener for bio-based epoxy/clay nanocomposites,37 we did not use PL as a hardener for bio-based epoxy/natural fiber biocomposites because of the inferior mechanical and thermal properties.

As bio-based polyphenol hardeners, we investigated tannic acid (TA) and quer­cetin (QC) as are shown in Fig. 4.2.2124 Commercial TA is comprised of mixtures of gallotannins from sumac galls, Aleppo oak galls, or sumac leaves.41 The chemical formula for commercial TA is often given as C76H52O46 as shown in the figure. But, in fact it contains a mixture of related compounds. Its structure is based mainly on glucose ester of gallic acid. QC (3,3,’4,’5,7-pentahydroxyflavone) is one of the most abundant flavonoid found in glycosylated forms in plants such as onion, capers and tea. TA is industrially available from various Makers (for example, Fuji Chemical Industry, Co., Ltd. (Wakayama, Japan)), we used the reagent grade TA of Kanto Chemical Co., Inc. (Tokyo, Japan). QC can be obtained from plants via extraction of the quercetin glycosides followed by hydrolysis to release the aglycone and sub­sequent purification.42 Although QC is used as an ingredient in supplements, bever­ages and foods, it has not been used as an ingredient of polymer materials to the best of our knowledge. When QC is used as an epoxy hardener, it is expected that the cured resin has a high Tg and superior adhesiveness to plant fibers because of the rigid and polar polyphenol moiety. We used the QC purchased from Sigma-Aldrich Japan Co. Ltd. (Tokyo, Japan).

Also, bio-based phenols such as pyrogallol (PG) and cardanol (CD) are promis­ing raw materials for the preparation of bio-based phenolic epoxy hardeners (Fig. 4.3). PG is obtained by decarboxylation of gallic acid, which is a basic component of hydrolysable tannin. Utilization of PG as a raw material of the preparation of epoxy hardeners was described in the following section in detail. CD is a phenol meta-substituted with a flexible unsaturated hydrocarbon chain, which is derived from cashew nutshell liquid.43 There have been many studies on the utilization of CD to phenol resins44,46 and epoxy resins4649, and some of them have been already commercialized by Cardolite Corp. (Newark, NJ, USA) and Shanghai Meidong Biomaterials Co. Ltd (Shanghai, China), etc.

Various forms of cover screens are used both to protect the porous absorbers from damage77 such as loss of fibers,14 to fine-tune their absorptive performance to meet practical demands,13 and to give a more esthetical appearance.10 Cover screens may be in the form of mineral wool felt sprayed on plastic, steel wool, mineral wool or glass fiber cloth; wire mesh cloth; or thin perforated metal. They are characterized by their specific flow resistance, r, and their mass per unit area.17 The addition of a cover screen increases the sound absorption at low frequencies substantially, if it is not in contact with the porous material and able to vibrate freely. However, this may be at the cost of attenuation at high frequencies if flow resistance, r, of the screen is higher than 1 pc.35 If the cover screen has very low porosity77 or is in contact with the porous absorber, the result will be decreased high frequency absorption with unaltered low frequency absorption14. The thinness and the lightness of the film in­crease the absorption.75 Rebillard et al.78 reported that a heavy film behaves like it is in contact with the porous absorber whether or not it is so. Jayaraman et al.47 found the presence of PVC film on the side facing the sound source had a positive impact on NAC values in the frequency range below 4500 Hz. In this case, the curve has a completely different shape, similar to a bell shape rather than a typical “S” curve in 500-6400 Hz frequency range due to the decrease in higher frequencies. The maxi­mum absorption was recorded to take place at 2200 Hz. When the PVC film was placed at the backside, it caused a slight increase in NAC values.

Similarly, Seddeq et al.56 reported a shift to the lower frequency value of maxi­mum sound absorption from 6300 Hz to 2250 Hz ofjute mats with the incorporation of a perforated sawdust board as a cover plate. In terms of the absorption coefficient for frequency values higher than 3500 Hz a drastic decrease was observed, as “S” curve became a “bell” curve similar to that reported by Jayaraman et al.47 When a cover plate and a back air space were incorporated to the porous absorber at the same time, multipeaked graphs of sound absorption was observed as seen in Fig. 5.11.

Using the sound intensity method the noise radiated by a 3-door domestic frost free refrigerator was measured. The overall sound intensity contours of the five surfaces of the refrigerator in the frequency band from 20 Hz to 2000 Hz are shown in Fig. 6.22. This method helps to rank the noise source of the refrigerator. It is seen that the compressor located at the rear bottom of the refrigerator is the most noise pro­ducing part followed by the evaporator fan in the freezer compartment. A detailed measurement is done to determine the air-borne and structure borne noise path in the refregirator63. The radiated noise spectrum is rich in the harmonics of 50 Hz of the compressor operating speed, and the harmonics of the vane pass frequency of the evaporator fan. In order to reduce the noise radiated from the compressor apart from applying dampening materials on to the compressor shell, the sheet metal of the refrigerator body around the compressor are lined ure6.23 shows a view of the compressor compartment with the jute lining. Usually the compressor generates heat which is to be radiated while in operation, thus to ensure that the heat trans­fer from the compressor is not significantly affected, a temperature measurement on the compressor was done by monitoring round the clock using thermocouples. The temperature rise of the compressor with the jute treatment was 4°C with the maximum temperature reaching to 74°C. Further the jute-based temperature can withstand such increase in temperature with no adverse effects on the performance of the refrigerator.

The swift growth of new materials based on natural fibers and biopolymers is pri­marily accelerated by factors such as greater environmental awareness and the de­pletion of petrochemical resources.11

9.2.1.1 ENVIRONMENTAL CONCERN

The disposal of composite derived from glass fibers and petroleum based polymer matrices, after their intended life span is becoming a problem and very expensive. Their recycling and reuse is critical because they are made from two different ma­terials. The two most implemented disposal alternatives are land filling and incin­eration. Landfill space is drastically decreasing due to the heavy ongoing waste disposal.2 The increasing environmental pollution due to the use of abundant plas­tics and emissions during incineration is greatly affecting the food we eat, water we drink, and even the air we breathe.2 Composite consisting of biofibers which are biodegradable and conventional thermoplastics or thermosets which are nonbiode­gradable would partially resolve these mentioned problems. However, if the matrix resin/ polymer is biodegradable such biofiber reinforced biopolymer composites would become completely biodegradable. Biopolymer or synthetic polymers rein­forced with natural fibers (known as biocomposites) are a feasible alternative to glass fiber composites. Figure 9.3 shows the life cycle of natural fiber reinforced composites.

11.4.1 FIBER TREATMENT

11.4.1.1 FIBERS TREATED WITH SINGLE COMPONENT SOLUTIONS

Flax fiber C1 and C2 as described in Table 11.2 was treated with different single component solutions as indicated in Table 11.3 for 120 s using the process P1. Burn­ing tests were conducted in accordance with the general procedure described above and the results from the burning tests are also shown in Table 11.3. It is evident from Table 11.3 that all of the C1 fibers treated with various single component systems are not self-extinguishing, although these treatments slowed down flame propaga­tion. Fibers treated with NaOH or KOH did not continue to burn but did continue to glow. Fibers treated with NaOH and then washed with water did continue to burn, demonstrating that any fire resistant effect afforded by an alkali metal hydroxide alone is easily removed if the fibers get wet. Collectively, Table 11.3 demonstrates that single component systems of metal hydroxides, metal salts or clays do not im­part self-extinguishing properties on fibers treated with the systems.

The difference in surface structure between the untreated and treated flax fibers are illustrated in Fig. 11.3. In general the single component systems do not provide a good coating on the flax fiber surface. Among them LDH and MMT provide better coverage but the can be peeled off easily during handling the fibers. These can be the reason for their poor fire retardant performance.

FIGURE 11.3 SEM image of the flax fibers: treated with a) NaOH, b) BaCl2, c) Ba(OH)2, d) LDH, e) MMT and f) untreated.

11.4.1.2 FIBERS TREATED WITH BI-COMPONENT SOLUTIONS

Flax fiber C1 and C2 were treated with different bi-component systems as indicated in Table 11.4. It is evident that all of the C1 fibers treated with bi-component systems involving the mixture of barium chloride and sodium hydroxide are self-extinguish­ing. Fibers treated with barium chloride alone then with clay or barium hydroxide alone then with clay are not self-extinguishing. Thus, single component systems are not self-extinguishing, even with the subsequent addition of clay. A mixture of both the alkaline metal salt and the alkali metal hydroxide is needed to make the fibers self-extinguishing. It is further clear that washing the fibers after treatment with a bi-component system does not remove the self-extinguishing properties imparted by the treatment. Further, the order in which clay is introduced into the bi-component does not affect the self-extinguishing properties of the fibers after treatment.

For the C2 series fibers treated with (MgCl2+NaOH) and with (CaCl2+NaOH) are self-extinguishing. Fibers treated with (Mg(NO3)2+NaOH) and with (Ca(NO3)2+NaOH) did not burn but continued to glow. Fibers treated with (MgSO4+NaOH) continued to burn, but at a slower rate than untreated fibers. The efficiency of the (MgCl2+NaOH) system is greater than the (Mg(NO3)2+NaOH) sys­tem, which is greater than the (MgSO4+NaOH) system. This is also similar for the calcium-containing systems where the efficiency of the (CaCl2+NaOH) system is
greater than the (Ca(NO3)2+NaOH) system. Thus, chloride is the most preferred counter anion for the alkaline earth metal cation.

Figure 11.4 illustrates the fibers treated with the bi-component systems provid­ing better coating and adhesion of the chemical on the fiber surface thus preventing the treated fiber from burning.

FIGURE 11.4 SEM image of the flax fibers treated with a) NaOH+MgCl2, b) NaOH+BaCl2 and c) NaOH+BaCl2+MMT.

with BaCl2 formed the black char and the fibers treated with (NaOH+BaCl2) or (NaOH+BaCl2+MMT) become self extinguishing. This indicates this treatment method is very effective depending on the selective chemical combination and event the treatment can be performed directly in the fabric and not necessary at individual filament level.

There are numerous chemical methods that have been used to modify the surface energy characteristics of natural fibers, but only a few prominent methods will be briefly mentioned here, including alkaline, liquid ammonia, and esterification.

In the alkaline or basic treatment, natural fibers are dissolved or mercerized so that they can be incorporated into thermoplastics or thermosets as reinforcement agents. It is one of the very best ways known to increase the amount of amorphous cellulose at the expense of the crystalline cellulose; this latter event occurs by com­promising the tight spacing between the cellulose chains by disruption of the hydro­gen bonding interface and loss of the crystallinity. The following reaction is a good summation of the chemistry that occurs:

Fiber-OH + NaOH a Fiber-O- Na+ + H2O (1)

The mercerization process consumes the crystalline cellulose I form as shown in the reaction above by the penetration of the alkali into the cellulose H-bonding network which forms alkali cellulose. The alkali cellulose is then washed by a water treatment to remove the unreacted alkali upon which a regenerated cellulose, cel­lulose II, is then formed. It has been reported that flax fibers have tremendously enhanced strength and stiffness as a result of the treatment.45 These results are like­ly due to two important effects resulting from the treatment: 1-increase in surface roughness which increases the friction and resultant interlocking among the fibers, and 2-increase in the number of exposed cellulose groups on the surface thus having more hydroxyl groups available for H-bonding or reaction.

The second chemical treatment, liquid ammonia, arose as an alternative to mer- cerization for cotton in the 1960s. Due to its low viscosity and surface tension, it penetrates the cotton H-bonded network very effectively to form a complex com­pound after the rupture of the H-bonded network. The ammonia is small enough to penetrate crystalline regions very well and cause cellulose I to cellulose III which can reform I after treatment with hot water.

Esterification and the associated etherification are two of the dominant meth­odologies used to derivatize cellulosics. The reaction generally proceeds via the hydroxyl groups via the introduction of organic acids or anhydrides. Many esters are possible depending on the nature of the alkylating/acylating group used. Pos­sibilities for esterification include the formation of the formate, acetate, propionate, and butyrate (1-4 carbon atoms) in addition to the longer laurate (12 carbons) and stearate (18 atoms) final products. However, the most popular esterification method is acetylation, which occurs by the use of acetic anhydride to form the natural fiber acetate and acetic acid.

With respect to nanocrystals, two routes are available to obtain nonflocculated dispersions in an appropriated organic medium:

1. Surface coating with long-chained surfactants (polar heads and long hydro­phobic tails);

2. Hydrophobic chain grafting at their surface.

The main poor attributes of natural polymers like chitosan that limits them in pack­aging applications are water / moisture absorption and gas barrier (high permeabil­ity of gas) properties. As the mechanical properties are highly influenced by water absorption (through plasticization), it is very important to improve the gas barrier properties and moisture absorption or water uptake for chitosan based materials.