Female spiders use the tubuliform gland to spin fibers that are constituents of egg sacs. The tubuliform gland has a cylindrical shape and extrudes fibers referred to as tubuliform silks (Fig. 1.1). The main component found in tubuliform silks repre­sents the spidroin family member Tubuliform Spidroin 1 (TuSpl). Northern blot and quantitative real-time PCR analyzes have demonstrated that TuSpl transcripts are highly expressed in the tubuliform gland.34 MS/MS analyzes of tryptic peptides gen­erated from enzymatic digestion of dissolved egg sacs have demonstrated the pres­ence of TuSpl, along with two other fibroins, Egg Case Protein 1 (ECP-1) and Egg Case Protein 2 (ECP-2) in the cob-weaver L. Hesperus.35 Immunoblot analysis has also confirmed that TuSp1 is specifically expressed in the tubuliform gland.36 Full — length cDNA sequences for CySp1 and CySp1 (equivalents of TuSp1 and TuSp2, respectively) from the orb-weaver, Argiope bruennichi, have been described.37 The basic architecture of TuSps resemble other spidroin family members, consisting of nonrepetitive N — and C-terminal domains and internal block repeats that are larger in size relative to repeats within MaSp1 and MaSp2. Repetitive regions from TuSp1 consist of approximately 180-200 amino acid residues. Relative to other spidroin family members, the TuSp1 C-terminal domain shows little similarity to other spi — droin family members, and it has been proposed to represent a silk protein that is spun into an evolutionary ancient silk.38 Inspection of the internal block repeats of TuSpl reveals little, if any, representation of the spider silk motifs commonly dis­cussed earlier, such as the GPGXX, GGX, poly A and/or GA couplets, and the spac­ers regions. Instead, different amino acid motifs are used, which include Sn, (SA) n, (SQ)n, and GX (X represents A, V, I, N, Q, Y, P or D).34b Interestingly, the ECP-1 and eCp-2 protein sequences lack recognizable internal block repeats as well as the nonrepetitive conserved N- and C-termini. These proteins also have predicted molecular masses that are approximately 80-kDa, which is considerably smaller relative to the spidroin family members. Protein alignments between ECP-1 and ECP-2 reveal a 52% identity at the amino acid level. Despite having well defined internal block repeats, the ECPs contain poly A/(GA) modules that are similar to sequences reported from dragline silk fibroins.35a Analysis of protein sequences of ECPs show cysteine-rich N-terminal domains, suggesting these molecules function as intermolecular cross linkers that interact with the TuSps to provide structural roles in tubuliform silks.

Mechanical studies performed using tubuliform silk collected from L. hesperus reveal that these fibers contain lower breaking stress than dragline silk, but higher breaking strain11b. When considering both properties, tubuliform silks are shown to be tougher relative to dragline silks. Synthetic fibers have been wet spun from truncated, purified TuSpl and ECP-2 recombinant proteins.39 Artificial fibers spun from TuSpl molecules that contain the C-terminal domain showed slightly lower breaking stress relative to truncated ECP-2-spun fibers, having values of 95.1 and 121.9 MPa, respectively (Table 1.2). Interestingly, reconstituted egg case silk fibers, which contain full-length fibroins, display lower tensile strength relative to natural tubuliform silks.11b40 This implies that the lower mechanical properties for the syn­thetic silks, is impart, due to imperfections in the artificial spinning process.

TABLE 1.2 (Continued)

MITSUHIRO SHIBATA

ABSTRACT

In recent years, renewable resources-derived polymers (bio-based polymers) and composites (biocomposites) are attracting a great deal of attention because of the advantages of these polymers such as conservation of limited petroleum resources, possible biodegradability, the control of carbon dioxide emissions that lead to global warming. This chapter deals with the preparation, thermal and mechanical proper­ties of the bio-based network polymers prepared by bio-based epoxy resins and bio-based polyphenols, and their biocomposites with lignocellulosic fibers. As bio­based epoxy resins, glycerol polyglycidyl ether (GPE), polyglycerol polyglycidyl ether (PGPE), sorbitol polyglycidyl ether (SPE) and epoxidized soybean oil (ESO) were used. As bio-based polyphenols, tannic acid (TA) which is a hydrolysable tan­nin and quercetin (QC) which is a flavonoid were used. Also, the polyphenols (TPG) prepared by the reaction of tung oil (TO) and pyrogallol (PG) and guaiacyl pyrogal — lol[4]arene (PGVNC) prepared by the reaction of PG and vanillin (VN) were also used. As lignocellulosic fibers, wood flour (WF) made from Sanbu cedar crushed into powders through 3 mm screen mesh and microfibrillated cellulose fiber (MFC) were used. The thermal and mechanical properties of the bio-based polymer net­works and their biocomposites were investigated in detail by means of dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA) and tensile test. The morphology of the fractured surface of the biocomposites was observed by field emission-scanning electron microscopy (FE-SEM). Consequently, the SPE cured with PGVNC showed the highest tan 5 peak temperature (148 °C). The PGPE/TA/ WF and GPE/TA/WF biocomposites with WF content 50-60 wt.% showed the high­est Young’s modulus (4-5 GPa). The SPE/TA/MFC biocomposites with MFC con­tent 10 wt.% showed the highest tensile strength (80 MPa).

4.1 INTRODUCTION

Biocomposites which are composed of matrix resins and natural fibers such as wood and plant fibers have recently gained much attention due to their low cost, environ­mental friendliness, and their potential to compete with man-made fiber-reinforced composites.13 Furthermore, the concept of using bio-based polymers as matrix res­ins for biocomposites is becoming increasingly important due to dwindling petro­leum resources.45 Such biocomposites composed of bio-based polymers and natural fibers are especially termed as green composites. For example, the green compos­ites of bio-based polymers such as poly(lactic acid),614 poly(hydroxyalkanoate),1518 and cellulose acetate1920 with lignocellulosic natural fibers such as flax, jute, hemp, kenaf, abaca, bamboo, and wood flour have been reported by several groups. How­ever, the main problem encountered in using their bio-based polymers is its rather poor interfacial adhesion between the polar lignocellulose and the more hydropho­bic characteristics of those polymeric matrices. The poor adhesiveness results in a poor strength, a relatively low stiffness and high moisture uptake. Another major shortcoming of this type of matrix is the relatively low fiber content, typically of less than 50-60 wt.%. One way to improve the poor adhesion is a modification of the interface of matrix and fiber.689121516 However, the surface treatment normally increases both processing steps and its cost. Bio-based epoxy resin cured with poly­phenol-based hardener should be a good candidate for a matrix resin of the green composite, because high loading of natural fiber is possible due to a low viscosity of the resin before curing, and superior interfacial adhesion is expected due to the hydrogen bonding interaction between lignocellulosic fiber and hydroxypropyl (or hydroxyethyl) moiety formed by the curing reaction of glycidyl (or epoxy) group with phenol. In this chapter, after the promising bio-based aliphatic epoxy resins and bio-based polyphenol hardeners are introduced, the thermal and mechanical properties of the biocomposites using their bio-based epoxy resins/hardeners and lignocellulosic fibers are reviewed based on our previous studies.2126

The use of multilayer absorbers has become increasingly important in noise reduc — tion.74 It is possible to tailor the materials for maximum absorption for the broadest frequency range by layering them.2

NAC values for various frequency ranges can be enhanced by changing the den­sity and composition of the fibrous structure. This area needs more investigation on the inner structure of multilayer absorbers.74 Multi-layer absorbers achieve higher sound absorption than the mono-layer absorbers with the same thickness.17 Ingard35
reported a significant drop in the critical frequency above which maximum absorp­tion was achieved when the fibrous absorber consisted of layers with different flow resistivities. The critical frequency was significantly higher for a single-layer mate­rial with the same total thickness and flow resistance.

Ingard35 reported that the sound absorption is greater when the flow resistivity, r0, increases from the surface toward the rigid backing except for low frequencies below 150 Hz. This is in agreement with the statement that the sound waves should be able to penetrate the porous absorber in order for sound attenuation to occur. Ackermann et al.75 reported that the smoothness and evenness of the surface of the absorbers facing the flow keeps frictional losses low and this allows higher sound absorption.

Yilmaz et al.4 investigated the effect of sequence of two layers of poly (lactic acid) (PLA) and one layer of hemp fibrous webs on NAC values. They found that the biocomposite with the hemp layer facing the sound source higher sound absorp­tion than the fabric with the hemp layer facing back plate or the hemp layer between the other two PLA layers. In fact, the composites including hemp layers facing the sound source or the back plate were actually the same materials, but just reversed. Hemp layer had greater pore sizes due to the coarser hemp fibers compared to man­made PLA fiber layer, so they allowed more sound waves to penetrate into the mate­rial. Consequently, it is possible to achieve better sound absorption only by chang­ing the direction of the same composite absorber.

Using a different approach, Atalla et al.76 produced nonhomogeneous absorbers from rock wool and glass fiber which include patches with different flow resistiv­ity values in the same single layers. They found that surrounding patches interact together and better performances are obtained compared to homogeneous materials. This approach may also be applied to biocomposites.

Vacuum cleaner is a very noisy and an irritating appliance in any house hold. Design improvements have been done to improve the sound quality of the radiated noise from such vacuum cleaner. A wet and dry domestic vacuum cleaner was used for
noise control studies using jute derivatives. The physical dimensions and the weight of this dryer are 41.5 x 41.5 * 44.0 cm and 6 kg. The suction of the vacuum cleaner motor was 30 L/sec. From the sound intensity mapping using a two-microphone sound intensity probe the most noise producing component of the vacuum cleaner was found to be the exhaust pipe. A 2.5 cm lined dissipative muffler of 30 cm length consisting of jute fibers wrapped in jute textile was placed as shown in Fig. 6.18. An overall noise reduction of 8 dB was obtained by such a treatment with an improve­ment in its sound quality as well. The measured radiated sound power octave band spectrum of the vacuum cleaner with and without treatment is shown in Fig. 6.19. The overall radiated sound power of the vacuum cleaner was reduced to 57.1 dBA from 67.6 dBA with jute-based treatments59. The sound power measurements of the vacuum cleaner was done as per ISO 9614 standard60. It may be noted that the sound power of a sound radiating body is estimated by at first performing a normal sound intensity measurement over a surface area, and then summing up the product of the sound intensity times the surface area as given in Eq. (17). The sound intensity of the entire radiating area needs to be measured as a function of frequency. For a rectangular body, usually the intensity from the five radiating surfaces are measured, leaving aside the bottom surface, which may be placed against a sound radiating hard floor or an absorbing floor.

Sound Power, W = S IA (17)

where Ii is the measured sound intensity and A is the corresponding normal surface area. Usually these areas are predefined and marked before the sound intensity mea­surements are done61. The sound power thus calculated is a function of frequency, and is usually represented in octave frequency bands. The sound intensity being a vector quantity is very much dependent on the direction of measurement. Thus enough care needs to be taken while traversing the two-microphone probe over a product during sound intensity measurements so that no directional error is made.

FIGURE 6.18

S. M. SAPUAN, L. SANYANG, and J. SAHARI

ABSTRACT

Natural fibers have recently become attractive as an alternative reinforcement for fiber reinforced polymer composites. They are gaining more attention due to their low cost, easy availability, less health hazards, fairly good mechanical properties, high specific strength, nonabrasive, ecofriendly and bio-degradability characteris­tics. Polymers from renewable resources have attracted tremendous amount of at­tention to researchers and engineers over two decades. The increasing appreciation for biopolymers is mainly due to environmental concerns, and the rapid petroleum resources depletion. Sugar palm fiber (SPF) reinforcement of a novel biodegradable sugar palm starch (SPS) has been studied in this chapter. The result shows that the mechanical properties of plasticized SPS improved with the incorporation of fibers. Fiber loading also increased the thermal stability of the biocomposite. Water uptake and moisture content of SPF/SPS biocomposites decreased with the incorporation of fibers, which is due to better interfacial bonding between the matrix and fibers as well as the hindrance to absorption caused by the fibers. It can be seen that ten­sile strength and impact strength of biocomposites increase with increasing fiber content. This enhancement indicates the effectiveness of the SPF act as reinforce­ment. SPF reinforcement of epoxy and high impact polystyrene (HIPS) have also been looked into. Overall, SPF treatments enhanced the mechanical properties of both polymers (epoxy and high impact polystyrene). Thus, indicating that SPF has a promising potential to be used as reinforcement in polymer composites.

A minimum of five specimens of each fiber sample having width x length (W x L) of 0.5 x 6.0 inch (12.7 x 152.4 mm) were cut from bulk fiber. Specimens were held at one end in a horizontal position and tilted at 45° with marks at 1, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0 inch from the free end. A flame was applied to the free end of the specimen for 30 seconds or until the flame front reached the 1 inch mark. If combus­tion continued, the duration was timed between each 0.5-inch mark. A thin metallic wire was inserted to support the specimen.

For the composite samples, five specimens having WxL of 0.5×6.0 inch (12.7×152.4 mm) were cut from the 3 mm thick composite plaque. Specimens were held at one end in a horizontal position and tilted at 45° with marks at 1, 2.0, 3.0, 4.0, 5.0 inch from the free end. A flame was applied to the free end of the specimen for 30 seconds or until the flame front reached the 1 inch mark. If combustion con­tinued, the duration was timed between each 1.0-inch mark.

11.3.4 VERTICAL BURNING TEST (VC-2)

A Govmark VC-2 chamber was used to conduct burning tests for some composites. This chamber is widely cited through out the USA and internationally to measure the ignition resistant properties of aircraft and transportation materials, tents and protective clothing.

For phenol formaldehyde composite samples, three specimens having width x length (WxL) of 3×12 inch (76.2×304.8 mm) were cut from the 3 mm thick compos­ite plaque. Specimens were held at one end in the vertical position. The flame was applied for 60 seconds and then removed until flaming stopped. The combustion time and burning length was recorded. If the specimen has burning length and burn­ing time less than 8 inch and 15 seconds, respectively, it is considered to be passed the standard (self-extinguished) Each separate set of specimens prepared for testing will consist of at least three specimens (multiple places).

The major problem in designing cellulose based-biocomposites is the lack of misci­bility between components, that is, hydrophilic biopolymers from wood fibers and hydrophobic substances (matrix), leading to poor adhesion between matrix and fiber in the final composite. To overcome this problem, chemical coupling agents have been employed to improve the adhesion between fibers and matrix through a variety of approaches that include chemical linking, secondary forces, self-assembly, en­tanglement, and mechanical interblocking.41 Chemical treatments, therefore, should be considered for improving any type of chemistry for the bonding/adhesion. For example, a number of compounds can promote adhesion such as sodium hydroxide, silane, acetic acid, acrylic acid, isocyanates, potassium permanganate, peroxide, etc. Later, chemical coupling agents such as amphiphilic polymers could be used in small quantities to allow the substrates of interest to bond.15

Cellulose based-nanocomposites (whiskers and nanofibrillated cellulose) will be explored in this section because they have been extensively investigated as re­inforcing materials in recent years. Whiskers, nanocrystalline cellulose, cellulose nanoparticles, etc., all refer to the isolated crystalline regions of cellulose that pos­sess on of the highest material mechanical strengths known. They are highly ordered and contribute greatly to reinforcing materials because of their high surface area and excellent mechanical properties.42

Yet, a critical parameter to good final material properties for the whiskers is that they should be well separated and homogeneously distributed in the matrix. Unfortunately, cellulose whiskers possess a very high surface energy and thus can­not be dispersed well in nonpolar media such as organic solvents or related media; their incorporation as a reinforcement filler for nanocomposites or in complex fluids has up until now be limited to aqueous or polar environments. Their flocculation or aggregation in nonpolar solvents (alkanes, olefins, etc.) can only be avoided by two routes, viz., application of surfactants onto the whiskers (formation of pseudomi­celles) or graft-onto or -from the whisker surface using the appropriate polymeriza­tion technique.42

Surface modified cellulose nanocrystals are also gaining a significant attention to improve the compatibility between the filler and matrix.45 In a recent study, nano­composites of chitosan were prepared using methyl adipoyl chloride functionalized cellulose nanocrystals in which the primary amine groups of chitosan were shown to conjugate with functionalized cellulose, as shown in Fig. 16.3.

This phenomenon of conjugation allowed to prepare nanocomposites with high amount of nanofillers, that is, up to 60% (MA-CNC 0.8). These nanocomposites

exhibited a linear improvement in the tensile strength and modulus from 45 MPa to 108 MPa and 1.2 GPa to 3.7 GPa, respectively.37