It is very difficult to test the tensile properties of individual fibers thus the test was performed on the fiber tow removed from the fabric tested instead in accordance with the procedure described above. Table 11.6 lists the fiber tows come from dif­ferent treated and untreated fibers that were tested as well as their tensile properties. The tows in the longitudinal direction in the fabric are denoted as parallel, whereas the ones in the orthogonal direction are denoted as perpendicular.

It is evident from Table 11.6 that the tensile properties of the fiber tow did not change much for most of the systems indicating that the treatment did not generally have a detrimental effect on tensile properties except for fibers treated with alkali metal hydroxide alone (e. g., KOH and NaOH). It is clear, therefore, that cellulose materials treated with both alkaline earth metal salt and alkali metal hydroxide are advantageously fire retardant, often self-extinguishing, while retaining good tensile

properties,

in contrast to fibers treated only with alkali metal hydroxide or treated

with another metal salt.

TABLE 11.6

Tensile Force of Tows of Treated C2 Fibers

Max load pounds force (N)

Fiber

Description

Parallel Perpendicular

C2

Untreated C2

4.6 (20.4) 5.4 (23.8)

C2-1/P1

Ba(OH)2

4.9 (21.7) 5.4 (24.1)

C2-2/P1

BaCl2

4.7 (21.1) 5.6 (25.1)

C2-4/P1

Mg(NO3)2

5.4 (23.8) 5.7 (25.5)

C2-7/P1

Mg((OH)2

4.3 (19.2) 5.3 (23.6)

C2-10/P1

KOH

3.6 (15.8) 4.5 (20.2)

Few studies on mannan-based composites are emphasized on the use of glucoman — nan as a film-forming component. Films produced from pure glucomannan have excellent mechanical properties and the improvement of those properties has been sought by blending glucomannans with other polysaccharides, proteins (chitosan, soy protein, sodium alginate, carboxymethyl cellulose, cellulose, gelatin, starch, etc.) or synthetic polymers.33

14.5.6 FACTORS INFLUENCING THE CHEMICAL, THERMAL, AND PHYSICAL PROPERTIES OF BIOCOMPOSITES

In recent decades, the interest in wood-based materials has increased especially for their biodegradability and abundance in nature. The main bio-based materials as al­ready have been targeted within this chapter are natural fibers (NF), microfibrillated cellulose (MFC), nanofibrillated cellulose (NFC), nanocrystalline cellulose (NCC), Xylan and lignin. The majority of these materials can be used alone or especially in combination with other polymeric materials. Except lignin, which has a hydro­phobic nature, the combination of those materials with other polymers usually faces the issue of the hydrophilic-hydrophobic incompatibility, an issue that has generally been evident with most synthetic polymers from base oil. Therefore, the surface modification of those materials is an excellent strategy to achieve the desired prop­erties of the final composite.

In the following sections, the effect of the hydrophilic nature of wood base ma­terials, the type of material and its concentration, the degree of dispersibility of such materials in nonpolar solvents and their characteristics according to obtaining the targeted mechanical, thermal, and surface energy properties of the composites will be considered.

The incorporation of cellulose nanocrystals in the chitosan matrix was observed to decrease water vapor permeability values, for example, from 3.31 to 2.23 gm/m2 day kPa, with 10 wt.% loading of CNC.36 The protection against oxidation of food or meat products can be reduced by packaging films with reduced oxygen perme­ability. The significant reduction in oxygen permeability was demonstrated with nanocomposite films prepared via layer by layer assembly by alternatively dipping in chitosan solution and CNC dispersion.43 The reduction in oxygen permeability of 180 mm thick A-PET substrate was about 94%, after 30 numbers of bilayers coating of chitosan and CNC via LBL assembly (Fig. 16.5).

Pyriform glands secrete fibers that are important constituents of attachment discs. Attachment discs function to fasten dragline silk fibers to solid supports, including wood, concrete, glass, and other surfaces. This attachment is central to locomotion and web construction. The exact mechanism of the adhesion to the support has yet to be fully elucidated. Biochemical studies have revealed that the attachment discs fibers are embedded in a liquid matrix that rapidly dries. The major constituent of attachment disc silks from L. hesperus represents Pyriform Spidroin 1 (PySp1).53 Real-time quantitative PCR analysis support high levels of PySp1 transcripts in the pyriform gland relative to other silk-producing glands. From a protein architecture standpoint, PySp1 contains the conserved C-terminal domain characteristic of spi­droin family members, as well as internal block repeats ranging from 238-300 resi­dues that are rich in A, Q and E, along with a 78 amino acid spacer region that is ex­tremely hydrophilic in nature. Traditional GGX, GPGGX, and poly A stretches are absent. Block modules contain submotifs with the sequence AAARAQAQAEARA — KAE and AAARAQAQAE, which have been shown to form beta-sheet structures

when synthetic peptides containing iterations of these sequences were investigated by circular dichroism (unpublished data). Analysis of the amino acid composition profile reveals the protein sequence of PySp1 contains the most hydrophilic residues relative to other spidroin family members, a likely feature that is linked the observa­tion that it is spun into a liquid matrix that readily dries.53 Because these fibers are difficult to collect from spiders, mechanical data have been difficult to obtain from traditional stress-strain analyzes. In orb-weavers, the equivalent spidroin has been reported and dubbed PySp2 or PiSp1.54 MS/MS analysis ofboth the attachment discs and luminal contents from the pyriform gland of orb-weavers, similar to PySp1, has confirmed the presence of PySp2 as one of the major constituents.54^ Comparable to PySp1, PySp2 contains the highest degree of polarity among the spidroin fam­ily members, conservation within its C-terminal domain, but differences in protein sequence within its internal block repeats relative to the cob-weaver PySp1. PySp2 contains block repeats that are approximately 200 amino acids, flanked by spacer regions that are 44 residues; these spacer regions are Pro-rich and have iterations of the submotif PAPRPXPAPX, with X representing a subset of amino acids that mostly contains hydrophobic R groups. The block motifs have repetitive motifs that are Gln-Gln-Ser-Ser-Val-Ala (QQSSVA). Synthetic fibers spun by wet-spinning methodology with purified proteins containing the C-terminal domain, block repeat, and spacer region have been reported.54a The high degree of polarity within the pro­tein sequences of the PySp fibroins, along with their ability to form fibers, suggests strategies to allow for fabrication of fibers in liquid environments.(Fig. 1.4.)

4.4.1 BIO-BASED EPOXY RESINS CURED WITH TA

The GPE, PGPE, SPE, and ESO were cured with TA in order to compare the proper­ties of the cured bio-based epoxy resins.2123 Because TA is soluble in liquid GPE and SPE, the mixing of GPE/TA and SPE/TA is very easy. In case of PGPE/TA and ESO/ TA, it is necessary to add ethanol to get homogenous solutions. The chemical for­mula for the commercial TA is often given as C76H52O46 (Fig. 4.2). However, in fact it contains a mixture of related compounds. Also, it is supposed that all of the three hydroxy groups of PG moiety of TA are hard to react with epoxy groups. Therefore, the curing temperature, curing time and epoxy/hydroxy ratio were optimized for GPE/TA, SPE/TA and ESO/TA. First, curing temperature and time were changed at the fixed epoxy/hydroxy ratio of 1/1. As ESO with alicyclic epoxy groups has a lower reactivity than GPE and SPE with glycidyl groups, ESO/TA was cured at a higher curing temperature range (150-230 °C) than that of GPE/TA and SPE/TA (120-200 °C). The GPE/TA and SPE/TA had the maximal tan 5 peak temperatures (73 and 95 °C), when cured at 160 °C for 3 h and 2 h, respectively. Also, ESO showed the highest tan 5 peak temperature (57 °C), when cured at 210 °C for 2 h (Table 2). These results indicate that the control of curing temperature and time is very important for the bio-based epoxy curing system containing aliphatic and sug­ar-based moieties with relatively low heat resistance. When PGPE/TA with epoxy/ hydroxy 1/1 was cured at the same curing temperature and time (160 °C and 3 h) as GPE/TA, the tan 5 peak temperature was 77 °C. When the tan 5 peak temperatures of the materials cured at epoxy/hydroxy 1/1 are compared, the higher order was SPE/ TA (95 °C) > PGPE/TA (77 °C) > GPE/TA (73 °C) > ESO/TA (57 °C), as is sup­posed from the relationship between epoxy functionality and the shortest distance between the two cross-linked points.

Next, epoxy/hydroxy ratio was changed at the curing temperature/time, which showed the highest tan 5 peak temperature at epoxy/hydroxy 1/1. The tan 5 peak temperatures of GPE/TA and SPE/TA increased with decreasing epoxy/hydroxy ra­tio (Table 4.3). The increase of Tg with TA content should be attributed to an increase of the content of highly hindered aromatic framework rather than an increase of crosslinking density. However, the cured resins at epoxy/hydroxy 1/1 showed the highest tensile strength and modulus. Judging from the trend of tensile properties, it is thought that the incorporation of TA component in the crosslinked structure is in­sufficient for the TA-rich compositions (GPE/TA 1/1.2—1/1.4, SPE/TA 1/1.2—1/1.4). Consequently, the epoxy/hydroxy ratio 1/1 was selected for both GPE/TA and SPE/ TA, considering the balance of T and tensile properties. The epoxy/hydroxy ratio of PGPE/TA was fixed to 1/1, considering the result of GPE/TA, In case of ESO/ TA, both the tan 5 peak temperature and tensile properties increased with decreasing epoxy/hydroxy ratio. When the epoxy/hydroxy ratio was lower than 1/1.4, the ESO/ TA mixture became so viscous that we could not prepare a void-free cured sample. Consequently, the condition of curing temperature 210 °C, curing time 2 h, and epoxy/hydroxy ratio 1/1.4 was selected for the curing of ESO/TA. When petroleum — based PN is used as a hardener of SPE, the tan 5 peak temperatures for SPE/PN resins cured at epoxy/hydroxy ratios 1/0.8-1/1 were 78-81 °C, which were lower than those of SPE/TA resins cured at epoxy hydroxy ratios 1/1-1/1.4 (95-111 °C).

Different treatments may be applied to biocomposite according to the effect required. Examples of some chemical treatments include alkalization, enzymatic treatments, flame-retardant and antimicrobial agent applications. Physical treatments include compression and thermal treatments.

Among physical treatments, compression and thermal treatment play a very im­portant role as they form the basis of molding process, which is a must for most of the noise control composites. Compression of a fibrous mat deteriorates its sound absorption properties according to Castagnede et al.81 For a given homogeneous po­rous layer, compression is followed by a decrease in terms of porosity and thickness, and at the same time by an increase of tortuosity and resistivity. Jayaraman et al.,47 Yilmaz et al.,4 and Yilmaz et al.58 also found a decrease in sound absorption with compression. The finding of Yilmaz et al.20 is presented in Fig. 5.12.

Yilmaz et al.4,8 investigated the effects of thermal treatment on noise control ca­pability. Yilmaz et al.8 treated three-layered sandwich structures of PLA/Hemp/PLA at temperature points of 125, 145, 165 and 185°C. An increase in air flow resistivity and a decrease in NAC were found. The decrease in NAC reached a substantial ex­tent when the melting point of the constituent thermoplastic fiber, PLA, is reached as seen in Fig. 5.13. Yilmaz et al.4 investigated the effects of thermal treatment on noise reduction performance of three-layered PP/Hemp/PP sandwich structures at 150 and 185°C (see Fig. 5.14). They reported a slight increase in NAC for the lower frequency range for 150°C treated composite and a drastic decrease in NAC for the biocomposite treated at 185°C as shown in Fig. 5.12. Similar to the find­ing of Yilmaz et al.8, temperature exceeding the melting point of the thermoplastic component was reported to be very deteriorating for sound absorption performance. The slight increase in the lower region which is experienced for the 150°C treated sample might be due to increase airflow resistance. Accordingly, by fine-tuning the parameters of thermal treatment, the noise reduction capability of the biocomposite may be preserved or it can even be enhanced.

Among chemical treatments, Jayaraman et al.47 studied the effect of fire retar — dancy treatment on sound absorption. They found that the treatment had a positive impact on the sound absorption of kenaf fibers. Yilmaz et al.9 applied alkalization treatment on PP/hemp/PP to detect the effect of the treatment on sound absorption. As known, the alkalization process partially removes lignin, pectin and hemicel — luloses present in the fibers and leads to a separation between the fibrils of the natural technical fibers. This results in finer fibers and a rougher surface, which might enhance sound attenuation. However, alkalization did not increase the sound absorption coefficient as expected. In contrary, the NAC values decreased with the decrease in the mass of the material due to loss of hemp fiber constituents and pos­sibly the distortion of the pores during the wet treatment as given in Fig. 5.15.

Among wet treatments, Huda and Yang55 extracted fibers from cornhusks by al­kalization and further treated a part of them with cellulose and xylanase enzymes to produce finer fibers with the elimination of extracellulosic materials. They blended cornhusk fibers with PP fibers then formed a web by carding and thermally bonded the web to produce a composite structure. They obtained better sound absorption from composites consisting enzyme treated cornhusk fibers compared to those that were untreated as shown in Fig. 5.16.

5.4 CONCLUDING REMARKS

Fibrous materials act as noise control elements in a wide range of applications as they present a cost-effective, light-weight, and environmentally friendly alterna­tive to conventional materials. Fibrous materials should be designed as composite structures to address the demands in terms of esthetics and performance character­istics such as moldability, durability and enhanced noise reduction capacity. De­signing of an effective composite sound absorbing noise control element requires a good understanding of sound propagation in fibrous materials. This chapter has presented an overview of natural fiber based biocomposites as rigid porous sound absorbers. Sound absorption mechanisms that take place during sound wave propa­gation through fibrous media have been given. An overview of empirical models which may be applicable to explain sound propagation in biocomposites has been explained. Based on the models, factors that affect sound absorption behavior of biocomposites have been investigated referring to previous studies.

Most of the research and modeling effort for understanding the sound absorption characteristics of fibrous materials have been devoted to conventional petro-based materials. More study is needed with sound absorbers of biocomposites, which of­fer a safer production and service life with effective utilization of scarce resources.

Natural fibers, engineered environmentally friendly polymers, and recycled ma­terials can be given as examples of “green” materials to be used during production of noise absorber biocomposites based on previous studies. There is especially very limited knowledge pertaining to the acoustical properties of biocomposites consisting of engineered biopolymers or agricultural byproduct materials. Future research ef­forts devoted to the understanding of these materials may enhance our understand­ing of sustainable materials as noise reduction elements.

KEYWORDS

Biocomposites

Fiber reinforced Composites

Noise Control

Noise Pollution

Sound Absorption Materials

Sound Absorption Mechanism

HVAC (Heating, ventilation and air-conditioning duct) are usually wrapped in fiber glass for thermal insulation. Fiber glass also have good sound absorbing properties and help in the breakout noise from the sheet metal duct. Jute-based composites have yet another application for noise control in ducts. The jute felt faced with a jute textile is applied to the inner walls of the duct. Since jute felt have good sound absorbing properties they help in the noise reduction. Since they are faced with jute textiles, the fibers do not separated due to the flow of air in the HVAC duct. It is recommended by ASHRAE (American Society of Heating, Refrigeration and Air-conditioning En­gineers) that the maximum flow velocity of air at the exit of a duct from an AHU (Air Handling Unit) should be less than 7.5 m/s64. At these speeds in the duct the fibers do not separate from the felt. Figure 6.24 shows a sheet metal duct lined with 25 mm jute felt faced with jute textile of 400 gsm (grams per square meter). Fiber glass is not rec­ommended to be used inside a duct, since if the fibers get carried by the air flowing inside the duct, they can be harmful to persons breathing the conditioned air, which is not so in the case of jute. Jute being hygroscopic can also withstand and moisture or condensate getting deposited in it in the inner of the duct walls. Jute felt can also be wrapped outside the duct to reduce the breakout noise.

The inside linings of AHU (Air Handling Units) of HVAC systems can also be lined with jute felt with a perforated facing backed with a 5 mm thick composite jute panel, for substantial noise reduction. Particularly in hospitals and classrooms where low noise levels are required, such a treatment can be done.

Biodegradable polymers can originate from biomass or petroleum-based and can be classified as green polymeric matrices.14 It is essential to differentiate biodegradable polymers from biopolymers because the origin of the raw material can vary. For instance, poly(caprolactone) (PCL) is a petroleum-based polymer but is completely biodegradable and thus can be referred to as green matrix. These polymers can be degraded by anaerobic and aerobic biological processes, which mainly produce carbon dioxide, water, and biomass.13 Biopolymers (bio-based polymers) are con­sidered biodegradable but not all biodegradable polymers are biopolymers. Rein­forcement of the biodegradable materials with natural fibers give improved material properties, desired in various applications without compromising biodegradability. Figure 9.5 shows the life cycle of biodegradable polymers, which includes conser­vation of fossil resources, water and CO2 production. The rate of biodegradation depends on humidity, temperature (50-70°C), amount and type of microbes.

Polymers from renewable resources have attracted tremendous amount of atten­tion over two decades. The increasing appreciation for biopolymers is predominant­ly due to: environmental concerns, and the rapid petroleum resources depletion.14 Figure 9.6 presents the classification of polymers in four different groups.1115 All the three groups of polymer are derived from renewable resources except the last group, which is from petroleum products.11 Generally, biopolymers can be classified into three groups: (1) natural polymers, like starch, protein and cellulose; (2) synthetic polymers from natural monomers, such as polylactic acid (PLA); and (3) polymers from microbial fermentation, such as polyhydroxybutyrate (PHB).14

Numerous new polymer materials were developed from renewable resources, such as starch, which is a natural polymer. Other biopolymers are poly lactic acid from fermentable sugar and polyhydroxyalkanoate (PHAs) from vegetable oils next to other bio-based feedstocks.16

Table 13.1 summarizes the various treatments conducted in this research project. DDGS were modified by direct treatment with acetic anhydride and maleic anhy­dride solutions. Acetic anhydride and maleic anhydride were obtained from Sigma — Aldrich Chemical Company, St. Louis, MO and used as supplied without further purification. STDDGS and STPW particles were vacuum-oven dried for 24 hr at 80°C. Four hundred grams of filler were boiled in a stirred jacketed reaction ves­sel fitted with a distillation trap at 90°C containing 6 M acetic anhydride/acetone mixture for 24 hrs. In addition, a 5 M acetic anhydride /1 M maleic anhydride/ acetone reaction mixture was also employed. Following incubation, filler materials were filtered, washed three times with acetone, and vacuum-oven dried for 48 hr at 80°C. Hereafter, STDDGS and STPW treated with acetic anhydride (A) or acetic anhydride/maleic anhydride (AM) mixtures will be designated as STDDGS/A and STDDGS/AM, respectively. Weight percentage gains were calculated for the A and AM mixtures to be ~11 and ~12%, respectively.

TABLE 13.1 Weight Percentages in Test Formulations

Composition HDPE MAPE DDGS STDDGS PINEW PW STPW Modifiers

HDPE 100 — — — — — — —

HDPE-MAPE 95 5 — — — — —

To investigate the influence of mixing different fillers to produce an improved composite, STDDGS was mixed with PINEW at various concentrations with and without presence of a 5% maleic anhydride coupling agent (MAPE) (Table 13.1).

The influence of the presence or absence maleic anhydride coupling agent on the physical properties of HDPE-fiUer blends was also investigated (Table 13.1).

Composite blends were extruded with a 27 mm corotating intermeshing twin — screw extruder, with a length/diameter ratio of 40 (Model ZSE-27 American Leis — tritz Extruder Corporation, Branchburg, NJ). The barrel had ten different zones, each 90 mm long, which were controlled at the following temperatures (oC): 100, 160, 170, 190, 200, 200, 210, 210, 205, and 205, respectively. The cord die temperature was set at 200°C. Premixed fillers and HDPE were dry blended in 1 gallon-resalable plastic bags. Materials were then transferred into a single drive feeder (Flex-Tuff Model 306, Schenck/AccuRate, Whitewater, WI) and fed into the extrusion feeder at the rate of 100 g/min. Extruder screw speed was set at 100 rpm. Extruded strands were cooled by immersion in a water bath and then pelletized with a strand pellet­izer (Model 60E, Automatick Plastics Machinery GMbH, Grossotheim, Germany).

Molding was conducted with a 30-ton molding machine (Engel ES 30, Engel Machinery Inc., York, PA) with set point temperatures (°C) for the four zone injec­tion molding barrel set at: feed = 160; compression = 166; metering = 177, and nozzle = 191. The mold temperature was 37 °C. An ASTM test specimen mold was used that included cavities for a ASTM D790 flexural tensile bar (12.7 mm W x 127 mm L x 3.2 mm thickness) and an ASTM D638 Type I tensile bar (19 mm W grip area x 12.7 mm neck x 165 mm L x 3.2 mm thickness X 50 mm gage L). Impact specimen bars were obtained by cutting the flexural specimens in half to 12.7 mm W x 64 mm L x 3.2 mm thickness and notched. The Type I bars were used for the tensile strength property tests. The flexural bars were used to evaluate flexural prop­erties and also used to make impact strength measurements. The Type I bars were used to evaluate changes due to prolonged exposure to water: weight change, color change, and changes in tensile mechanical properties of the composites.

Wheat gluten (WG) is a protein composite found in foods processed from wheat and related grain species, including barley and rye. WG husk is the composite of a gliadin and a glutenin (Fig. 15.4), which is conjoined with starch in the endosperm of various grass-related grains.

The prolamin and glutelin from wheat (gliadin, which is alcohol-soluble, and glutenin, which is only soluble in dilute acids or alkalis) constitute about 80% of the protein contained in wheat fruit.

The gliadin and glutenin components contribute to dough quality either in an independent manner (additive genetic effects) or in interactive manner (epistatic effects). Commercial WG has a mean composition of 72.5% protein (77.5% on dry basis), 5.7% total fat, 6.4% moisture and 0.7% ash; carbohydrates, mainly starches, are the other major

Gliadins are monomeric proteins that can be separated into four groups, alpha-, beta-, gamma — and omega-gliadins. Glutenins occur as multimeric aggregates of high molecular weight (HMW) and low-molecular-weight (LMW) subunits held together by disulfide bonds. In wheat, omega — and gamma-gliadins are encoded by genes at the Gli-1 loci located on the short arms of group 1 chromosomes, while al­pha and beta-gliadin-encoding genes are located on the short arms of group 6 chro­mosomes. LMW glutenins are encoded by genes at the Glu-3 loci that are closely linked to the Gli-1 loci. HMW glutenins are encoded by genes at the Glu-1 loci found on the long arms of group 1 chromosomes. Each Glu-1 locus consists of two tightly linked genes encoding one ‘x’-type and one ‘y’-type HMW glutenin, with polymorphism giving rise to a number of different alleles at each locus.

The gliadin and glutenin components contribute to dough quality either in an independent manner (additive genetic effects) or in interactive manner (epistatic ef­fects). It was suggested that the apparent effects of gliadins on dough quality should be attributed to the LMW glutenins due to the close linkage of the Gli-1 and Glu-3 loci.

The film forming property of hydrated wheat gluten is a direct outcome of its viscoelasticity. Whenever carbon dioxide or water vapor forms internally in a gluten mass with sufficient pressure to partially overcome the elasticity, the gluten expands to a spongy cellular structure. In such structures, pockets or voids are created which
are surrounded by a continuous protein phase to entrap and contain the gas or vapor. This new shape and structure can then be rendered dimensionally stable by applying sufficient heat to cause the protein to denature or devitalize and set up irreversibly into a fixed moist gel structure or to a crisp fragile state, depending on final moisture content.