Polyethylene is a thermoplastic polymer consisting of long hydrocarbon chains. De­pending on the crystallinity and molecular weight, a melting point and glass transi­tion may or may not be observable. The temperature at which these occur varies strongly with the type of PE. For common commercial grades of medium — and high — density polyethylene (MDPE, HDPE) the melting point is typically in the range 120 to 130 °C (248 to 266 °F).

Most LDPE, MDPE and HDPE grades have excellent chemical resistance, meaning that it is not attacked by strong acids or strong bases. It is also resistant to gentle oxidants and reducing agents. PE burns slowly with a blue flame having a yellow tip and gives off Adour of paraffin. The material continues burning on re­moval of the flame source and produces a drip. Crystalline samples do not dissolve at room temperature. PE (other than cross-linked polyethylene) usually can be dis­solved at elevated temperatures in aromatic hydrocarbons such as toluene or xylene, or in chlorinated solvents such as trichloroethane or trichlorobenzene.

“Bio” is a Greek word that means “life.” Bio-based materials, therefore, refer to products that consist mainly of a substance, or substances, derived from living mat­ter (biomass) and either occurs naturally or is synthesized. The term “bio-based materials” should not be confused with “biomaterials,” which has another meaning and relates to biocompatible materials used in and adapted to medical applications, which include implantable medical devices, tissue engineering, and drug delivery systems.34

The range of bio-based materials, from natural fibers to biopolymers, is mak­ing significant advances in petroleum-based materials industries.35 Renewable resource-based chemicals and bio-based polymers, such as 1,3-propanediol, soy, polyol, polylactic acids, and so on, are gaining momentum in commercialization as supplements and possible replacements for petroleum based products. For decades, cellulosic polymers have played a key role in a wide range of applications, such as apparel, food, and varnishes. Since the 1980s, an increasing number of starch polymers have been introduced, which have made them one of the most important groups of commercially available bio-based materials.

Bio-based materials, are commonly thought to be greener alternatives than their petroleum-based counterparts, which are nonbiodegradable, have potentially devastating effects on animal and ocean life, and for the most part, have an inher­ently toxic life cycle from their production through their final disposal. Bio-based materials frequently are labeled as produced from “renewable” resources, although this term is used loosely because biomass production requires nonrenewable inputs, which include fossil fuels, and ties up other finite resources such as land and wa­ter. The claim that bio-based materials are friendlier to the environment than their petroleum-based counterparts is being scrutinized closely.3639

Structural investigations showed that the diameter of the fibers is nearly uniform, about 500-1000 nm, but too many beads were formed and spheres developed with a few hundred microns in diameter (Fig. 2.12a). The EDS confirmed that the fibers contain the HAp, but the element mapping shows that the distribution of it is not homogenous. The EDS measurement showed C (found in CA), O (CA and HAp), P (HAp), Mg, S (HAp-eggshell trace element) Si (sample holder) and Al (sample cover) compounds. According to the Ca (Fig. 2.12b)) and P element maps (Fig. 2.12c)) the HAP presence in 1-2 micrometer sized clusters. The presence of Ca and P can be in 1-2 micron clusters. The distribution of O (Fig. 2.12d)) is homogenous, because the CA contains it too.

In our study, the mixing parameters were between 15 and 25 w/w% solid mate­rial (HAp+CA), increasing the concentration varied of Hap+CA resulted larger fiber diameter and fewer beads 47. Using more than 30 w/w% and less than 5 w/w% it was impossible to produce fibers. Applying 20 w/w% acetic-acid electrospinning process generated uniform fiber diameter. Using any other w/w% acetic-acid caused larger fibers diameter and more beads. It could be concluded that the composition of the solution has the most striking influence on the morphology of the final mats.

Most of the useful models for predicting acoustical properties of porous materials can be categorized in two groups: microstructural theoretical models and phenom­enological empirical models.14

Theoretical models generally deal with the behavior of sound waves in micro­structural elements of porous material. However, it is confoundedly complicated to explain the acoustical behavior of many sound absorbers based on theoretical mod­els due to structural and geometrical complexities of porous materials.13 As a conse­quence, in order to predict sound absorption behavior of fibrous materials, empirical models with a macroscopic point of view have been developed. Nevertheless, these empirical models, which do not deal with the microstructure, may only contribute with a limited guidance during the design phase of an absorber.14

Among these empirical models, one has encountered general acceptance for the last several decades: the empirical model, which was presented by Delany and Ba — zley.28 They investigated the sound absorption behavior of many fibrous materials with porosity close to unity for a large range of frequency. Based on their measure­ments, they found sound absorption indicators, the quantities of the wave number, k, and the characteristic impedance, Zc, to mainly depend on the frequency, f (or an­gular frequency, о), and the flow resistivity, r0, of the material, as explained below.

The flow of a fluid in a circular cylinder of diameter a flowing at a steady Poi — seuille flow can be given by

dp _ 128mu

Эх na4

where p represents pressure in Pa, p stands for dynamic viscosity of air in kg-m-1-s-1, u denominates the volume flow rate in m3-s-1, and a symbolizes the diameter of the channel in m.

Assuming that the number of parallel tubes is n per unit cross-sectional area in the porous material, the relation becomes,

dp _ _ 32mu (11)

Эх ha2

where u’ stands for the average volume flow rate over cross-sectional area, and h=(n/4)na2, where a represents the pore diameter, gives porosity. The ratio of the pore radius to the boundary layer, n, (rnp 0a2/4 ^.)m defines the acoustic character­istic of the sound absorber as explained by Fahy13. Here, can be replaced for 8 ц/rft in this ratio, n, using Eq. (11) to give

where rn, is the angular frequency, p0 is the density of air. The porosity, h, can be ig­nored, as h1/2~1 for most sound absorbers. This gives the nondimensional parameter (mp/r0) or:13

x _rf

r

f0

where X is the dimensionless sound absorber variable, which is denoted by E by some other researchers.1318

Delany and Bazley28 obtained sound absorption indicators, the values of the wave number, k, and the characteristic impedance, Zc, through the following expres­sions:

Zc _Poc0[l + 0.0571X4X754 _ І0.087X4X732 J, (14)

k _— [1 + 0.0978X-0700 _І0.189X“0595J, (l5)

c 0

where c0 is the sound propagation velocity in air. X became a universal descriptor of fibrous sound absorbers as it collapsed all the sound absorption data for the 70 different fibrous materials that Delany and Bazley28 measured.18 The boundary sug­gested for the validity of the model is

0.01<X<1.0. (16)

At low frequencies, Delany and Bazley’s28 formulas produce unfeasible results such as negative values for the real part of surface impedance of a hard-backed porous layer.17 Several researchers modify these formulas to give more accurate predictions, such as Mechel18. Mechel’s18 modified formulas are as follows:

Z= p °C0(1+0.08X-0-6")-i0.19X-0-556, (17)

^=(1+0.136X-0-641)-/0.322X-0-502 (18)

for X<0.025.

Zc= p °C0(1+0.0563X-0J25)-i0.127X-0-655, (19)

a

k=—(1+0.103X-0■76)-i0.322X-0■663 (20)

c 0

for X>0.025.

Yilmaz3 developed a model with the frequency, f, thickness, l, and air flow resis­tivity, ro, variables, presented in Eq. (21). The investigated materials included nu­merous fibrous composite materials from polypropylene, poly (lactic acid), hemp fi­bers and glassfibers in single, or multifiber, untreated, compressed, alkalized, heated and different layer-sequenced forms. The model estimates gave a goodness-of-fit, R2, value of 0.97 and the boundary suggested for the validity of the model is a basis weight of 1.13 to 2.36 kgm-2, fiber diameter of 16.3M0-6 to 33.3M0-6 m, a material thickness of 3.9M0-3 to 1.31×10-2 m, porosity of 0.62 to 0.92, and a frequency range of 500 Hz — 5 kHz.

an = sin(-5.27 x 10-1 + 2.54 x 10-4 f+1.72 x 10-6 r0 + 3.54 x 1041) (21)

The theoretical and empirical models provide guidance during the design of optimum sound absorbers in deciding which characteristics should be manipulated and how. Based on theoretical and empirical models, the factors, which directly or indirectly affect sound propagation through fibrous materials can be given as fiber properties (fiber size, fiber shape, etc.), material properties (flow resistance, density, thickness, and so on), process parameters and sound frequency. The following sec­tion investigates the factors that affect sound absorption.

Tortuosity ensures that the sound waves in a porous material do not travel in a straight path but interact with the pores in a tortuous path thus having maximum energy transfer at the pores. The tortuosity (aj is determined by using the empirical formula in terms of porosity (H) as given by Eq. (10)35.

6.5.3.2 CHARACTERISTIC LENGTHS

There are two measures of characteristic length which are of use. The viscous char­acteristic length is related to the size of the interconnection between two pores of the porous sound absorbing material. The thermal characteristic length is related to the diameter of the pore of the interconnecting channels. The thermal characteristic length is given as the ratio of the total inner surface area to the volume of the pore.

Here, the viscous and thermal characteristic lengths were estimated based on Allard’s model and its extensions to Biot theory35. Assumption was made that jute fibers are cylindrical. Viscous characteristic length (л) depending on the frame ge­ometry and is given by Eq. (11)

1

л =———-

2nrl

where 2nrl is total perimeter of fiber per unit volume of material, is diameter of fiber and total length of fiber per unit volume of material defined by Eq. 12

l =-£- (12)

nr p

p and p’ are density of the sample and density of fiber, respectively.

Allard showed that for the material with porosity close to unity, л’ = 2 л. For

material having pores of triangular cross section, л’= 1.14 л where л’ is thermal characteristic length35.

The above properties of these jute felt and jute fibers are shown in Table 6.8. The range of diameter of jute fibers which was measured by scanning electron mi­croscope is 50-90 pm. By the statistical averaging of diameter at different locations, the effective diameter of single jute fiber is 68 pm. Density is about 1084.4 kg/m3.

NFCs can be processed by various processing techniques like compression molding, hot pressing, resin transfer molding and injection molding. The ideal manufacturing process should be able to transform the raw materials to the desired shape without any defects. The selection of the manufacturing process for the fabrication of NFCs is based on:

1. Desired properties of NFCs.

2. Geometry of resultant composites.

3. Processing limitations of matrix and fibers.

4. Production output desired.

5. Manufacturing cost.

NFCs can be tailor made according to the desired properties of the composite by varying the percent fraction of reinforcement and additives into the polymer matrix. The manufacturing processes might limit the amount and size of fibers to be used as in case of injection molding process. The manufacturing process should be careful­ly chosen while designing the composite. The geometry of the desired composites plays an important role in determining the appropriate fabrication process. Large components are usually manufactured by open mold process where as for small to medium size products compression and injection molding process is preferred. The complexity of geometry of a component also plays an important role in determining the manufacturing process. Usually, complex components which require precision are made by injection molding process. The shape of the component to be made is the replica of the mold cavity. During the molding process the polymer matrix and natural fibers are subjected to heat and both the matrix and natural fibers have a ten­dency to degrade at higher temperatures. Hence, suitable raw materials and appro­priate processing technology should be selected based on the desired performance of the composite. The selection of the manufacturing process for NFCs involves various considerations to be taken into account. The aspect (length/diameter) ratio, interfacial bonding, orientation, and amount of percentage of natural fibers highly influence the properties of the end product.

Extensive research has been underway to study the potential of different natural fibers as reinforcement for biodegradable (a synthetic or renewable) polymer ma­trices in order to develop the components for different body parts of automobiles.56 Natural fibers are incorporated into door panel trims, package trays, trunk trims and other interior parts.5

The interest in using biocomposites based on natural fibers and biocompatible polymer matrices has grown because they are lightweight, biodegradable, nontoxic, nonabrasive during processing, have low cost and are easy to recycle. Natural fiber reinforced materials offer environmental advantages such as reduced dependence on nonrenewable energy/material sources, lower pollutant and greenhouse emis­sions. Lacarin et al. have compared the environmental impacts of the biocomposites and the glass/PP composite for the different steps of the life cycle.7 The energy consumption to produce a flax-fiber mat (9.55 MJ/kg/1), including cultivation, har­vesting and fiber separation, amounts to approximately 17% of the energy needed to produce a glass-fiber mat (54.7 MJ/kg/1).2 Environmental aspects reveal that natural fibers display an increase of about 15% of the performance of the composites, while focusing on economical aspects they cost about seven times less than glass fibers (Table 10.1).

Depending on their performance when they are included in the polymer matrix, lignocellulosic fibers can be classified into three categories: 1) Wood flour particu­late which increase the tensile and flexural modulus of the composites, 2) Fibers of higher aspect ratio that contribute to improve the composites modulus and strength when suitable additives are used to regulate the stress transfer between the matrix and the fibers, 3) Long natural fibers with the highest efficiency among the lignocel — lulosic reinforcements.

Natural fibers may be classified by their origin as either cellulosic (from plants), protein (from animals) or mineral. Plant fibers may be further categorized as: seed hairs (e. g., cotton), bast or stem fibers (e. g., linen from the flax plant), hard (leaf) fibers (e. g., sisal), or husk fibers (e. g., coconut).

Cellulose is one of the most abundant renewable and biodegradable biopoly­mer resource with high mechanical performance. It is a hydrophilic glucan polymer consisting of a linear chain of p-1,4-bonded anhydroglucose units that contains alcoholic hydroxyl groups. Cellulose represents the main structural component of plant cell walls. These hydroxyl groups form intra and intermolecular hydrogen bonds inside the macromolecule and among other cellulose macromolecules, re­spectively, as well as with hydroxyl groups from the surrounding air and polymer matrices. In terms of primary walls, cellulose fibrils have been found to be preferen­tially deposited perpendicular to the axis of cells during their initial state of growing. Due to the great stiffness and strength of cellulose fibrils, it is much easier to expand the cell wall perpendicular to the orientation of cellulose. The secondary cell walls consist of different layers that are deposited on the primary cell wall in a charac­teristic manner (strictly parallel). The interaction between the stiff cellulose fibrils and the plant matrix polymers in the cell wall is one of the key issues to elucidating the mechanical performance of plants.8 The most efficient natural fibers considered include threads with a high cellulose content coupled with a low microfibril angle, resulting in high filament mechanical properties. Due to their hollow and cellular nature, natural fiber preforms have up to 40% lower density. They act as acoustic and thermal insulators, and exhibit reduced bulk density.

The absolute mechanical data of natural fibers are inferior relative to E-glass and Carbon fibers. But when they are used in composites, their mechanical properties are even higher than E-glass reinforced composites (Table 10.2).9

So, natural fibers have lower densities and they can be found to be cheaper than glass fibers, although their strength is usually significantly less. Because of their good specific modulus values, natural fibers can be preferable to glass fibers in ap­plications where stiffness and weight are primary concerns. Theoretically, tensile and flexural moduli of composites are strongly dependent on the modulus of the components and display slight sensitivity to interfacial adhesions. In natural fiber reinforced biocomposites, the inclusion of a rigid phase such as cellulose fibers, contribute to increase the polymer matrix stiffness.

In fact, not only the modulus, but also the tensile and flexural strengths are sen­sitive of the fiber/matrix interfacial adhesion, and interface is a determent factor in transferring the stress from the matrix to the fibrous phase. So, in order to create a good and strong fiber/matrix interfacial adhesion between fibers (highly polar) and common polymer matrices (nonpolar), a proper strategy to improve fiber/matrix compatibility is required. Today, for optimization of a strong fiber/matrix interfacial adhesion, generally two approaches are considered as effective: the fiber surface modification and the use of an appropriate compatibilizing agent. Generally, the me­chanical properties of natural fiber reinforced biocomposites have been improved by using surface modification treatment of the fibers such as dewaxing, merceriza — tion, bleaching, cyanoethylation, silane treatment, benzoylation, peroxide treatment, acylation, acetylation, latex coating, and steam-explosion.910

Poly(lactic acid) (PLA) is currently the most popular polymer derived from re­newable resources, which is fermented to lactic acid. The lactic acid is then, via a cyclic dilactone, lactide, ring opening polymerized to the desired polylactic acid. This polymer is modified by certain means, which enhance the temperature stability of the polymer and reduce the residual monomer content. The resulting polylactic acid can be processed similarly as polyolefins and other thermoplastics although the thermal stability could be enhanced. The polylactide is fully biodegradable. Accord­ing to our current understanding, the degradation occurs by hydrolysis to lactic acid, which is metabolized by microbes to water and carbon monoxide. By composting together with other biomasses, the biodegradation occurs within two weeks, and the material fully disappears within 3-4 weeks. PLA is a thermoplastic, aliphatic polyester, which is useful in the packaging-, electrical — and automotive industry, for example, applications where biodegradable materials started competing with cheaper synthetic plastics.

It was widely reported that tensile and flexural modulus of PLA could be im­proved by increasing the cellulose content or cellulose based reinforcements in PLA based composites [1112]. Regarding the impact properties, it was shown that tough­ness results were impaired for PLA composites reinforced with cellulose fibers12- while small improvement were obtained with the addition of cotton or kenaf fibers6. Different natural fibers have been employed in order to modify the properties of PLA. Up to now, the most studied natural fiber reinforcements for PLA have been kenaf61112, flax1314, hemp15, bamboo16, jute17, wood fibers 18. Besides conventional natural fibers, recently reed fibers have been tested in appropriate PLA composites in order to improve the tensile modulus and strengths19. Other innovative methods over the last few years to improve the mechanical properties of PLA based compos­ites have been utilization of continuous hybrid fiber reinforced composite yarn ob­tained by the microbraiding technique20. Naturally derived microbraided-yarn was fabricated by using thermoplastic biodegradable PLA resin fiber as the resin fiber and jute spun yarn as the reinforcement. Using jute spun yarn/PLA microbraided — yarn, continuous natural fibers reinforced biodegradable resin composite plates was molded by hot press molding with various molding conditions.

Since DDGS sells for around $0.03 to $0.05/lb. and PINEW flour sells for $0.08 to $0.22/lb. there appears to be a case for combining the two ingredients to obtain a “mixed” DDGS composite and accessing the mechanical properties of the resulting PINEW/DDGS composites. Therefore, it is the contention of this study to mix these two chemically dissimilar fillers (DDGS and PINEW) together in order to deter­mine if an enhancement of the lower-grade filler (i. e., DDGS) can be achieve by the partial mixing with higher-grade filler (PINEW). Pine wood flour was selected to be employed as the wood of choice in the DDGS mixture filler study due to its common usage in WPC.81163 PINEW formulations (HDPE-25PINEW and HDPE-25PINEW — MAPE) exhibits mechanical properties comparable or better to neat HDPE values except for %El values (Table 13.2 and 13.3; Fig. 13.4). For example, the HDPE — 25PINEW formulation exhibited oU, E, and %El values that were -9, +141 and -74%, respectively, that of neat HDPE. Similarly, the HDPE-25PINEW-MAPE for­mulation exhibited oU, E, and %El values that were +8, +98 and -65%, respectively, that of neat HDPE (Table 13.2). Similarly, the flexural and impact strength proper­ties of PINEW formulations were comparable or superior to neat HDPE except for impact strength values. For example, the HDPE-25PINEW formulation exhibited ofm Eb and impact strength values that were +9, +68 and -88%, respectively, that of neat HDPE. The HDPE-25PINEW-MAPE formulation exhibited o„ E and im-

fm, b

pact strength values that were +18, +52 and -89%, respectively, that of neat HDPE (Table 13.3). The mechanical properties of DDGS formulations have been discussed previously. The PINEW formulations were superior to the DDGS formulations in several mechanical properties.

Mixing PINEW and STDDGS fillers in equal proportions resulted in a “combi­nation” composite that manifested somewhat different tensile, flexural and impact strength properties than that of composites composed of the individual ingredi­ent fillers. Refer to Tables 13.2 and 13.3 and Fig. 13.4. For example, the HDPE — 12.5STDDGS/12.5PINEW formulation exhibits oU values that were significantly less than in HDPE-25PINEW but slightly higher than in HDPE-25STDDGS. The E values of HDPE-12.5STDDGS/12.5PINEW were significantly higher than HDPE-25STDDGS but less than HDPE-25PINEW. Percent elongation values of the HDPE-12.5STDDGS/12.5PINEW formulation were significantly lower than either of the single filler composite formulations. The flexural values, ofm and E of HDPE-12.5 STDDGS/12.5PINEW were lower than HDPE-25PINEW

b,

but higher than the HDPE-STDDGS composites. The impact strength of HDPE —

12.5STDDGS/12.5PINEW composite was significantly higher than the HDPE — 25PINEW but likewise was significantly lower than the HDPE-25STDDGS composites. These trends were mimicked when the “mixed” composites con­tained MAPE. See Tables 13.2 and 13.3, and Fig. 13.4. Interestingly, the HDPE — 12.5STDDGS/12.5PINEW-MAPE composite exhibited higher impact strength values than in the HDPE-25STDDGS-MAPE composites. Inclusion of MAPE in the “mixed” composite formulation caused a decrease in impact strength com­pared to composite formulations without MAPE. Obviously, some benefits and drawbacks in terms of the mechanical properties of the “mixture” composite was obtained by mixing STDDGS with PINEW over that of composites containing a single filler ingredient. To summarize, comparing the HDPE-25STDDG to HDPE — 12.5STDDGS/12.5PINEW for oU E, %El, o^ Eb, and impact strength values the following changes occurred: +5, +65, -49, +7, +15, and -40%, respectively. When comparing the HDPE-STDDG-MAPE to the HDPE-12.5STDDGS/12.5PINEW- MAPE for oU, E, %El, ofm, Eb, and impact strength values the following changes occurred: +16, +15, -28, +6, +13, and -43%, respectively.

When comparing the two 40% filler composites, HDPE-40PINEW and HDPE- 10STDDGS/30PINEW, dissimilar mechanical and flexural properties also occurred between them. Refer to Tables 13.2 and 13.3, and Fig. 13.4. The difference between the HDPE-10STDDGS/30PINEW to the HDPE-40PINEW for n E, %El, E, and impact strength values were +24, -11, +60, +6, -18, and +16%, respectively. Obviously, some benefits and drawbacks were obtained comparing these “mixed” formulations. These results suggest that further work needs to be conducted to iden­tify and maximize the merits of mixing fillers from dissimilar sources in order to obtain novel composites. This report is a preliminary evaluation employing this line of research but suggests that a useful inexpensive LPC composed of mixing DDGS and WF is feasible.

15.2.1 GEOMETRY OPTIMIZATION

In this study the semiempirical method was used for describing the potential en­ergy function of the system. Next a minimization algorithm is chosen to find the potential energy minimum corresponding to the lower-energy structure. Iterations number and convergence level lead optimal structure. The optimizing process of structures used in this work was started using the AM1 method, because it gener­ates a lower-energy structure even when the initial structure is far away from the minimum structure.

The Polak-Ribiere algorithm was used for mapping the energy barriers of the conformational transitions. For each structure, 1350 iterations, a level convergence of 0.001 kcal/mol/A and a line search of 0.1 were carried out.

Nanomaterials are such a stuff, which has at least one dimension in nanometer scale, that is, 1 to 100 nm. Nanomaterials can be classified into two categories viz. nano­structured material and nanophase/nanoparticle materials. Nanostructured materials usually refer to condensed bulk materials that are made of grains (agglomerates), with nanometric size range. The latter are generally the dispersive nanoparticles. Nanotechnology is the study and control of nanomaterial which also deals with the design, fabrication and application of nanostructures. Nanomaterials, a new branch of materials research, are attracting a great deal of attraction because of their poten­tial applications in areas such as optics, electronics, magnetic data storage, catalysis and polymer nanocomposites (PNs).

Incorporation of inorganic/organic nanoparticles as additives into polymer sys­tems has resulted in PNs displaying multifunctional, high performance polymer characteristics beyond what conventional filled polymeric materials acquire. Mul­tifunctional features attributable to PNs consist of improved mechanical proper­ties, thermal properties and/or flame retardency, moisture resistance, chemical re­sistance, decreased permeability, and charge dissipation. Through control/alteration of the nanoscale additives, one can maximize the property enhancements of selected polymers to meet or exceed the needs. Uniform dispersion of these nanoscale ma­terials produces super interfacial area per volume between the nanoparticle and the polymer. There are different types of commercially available nanoparticles such as montmorillonite organoclays, carbon nanofibers, carbon nanotubes, nanosilica, nanotitanium dioxide, nano ZnO and others that can be incorporated into the poly­mer matrix to form PNs.113