The water absorption of jute-based biocomposite samples were measured according to ASTM D 5708. This test is carried out to determine the amount of water absorbed and performance of the materials in water environments. This is very similar to the moisture absorption test. Three square shaped samples of 3.0 cm x 3.0 cm of 5% natural rubber based jute composite were kept in an oven at a temperature of 100°C. Then weight of the three samples were measured. After that these samples were kept in a Petri dish full of distilled water. Then after 24 h and 48 h, the weight of the samples were taken and the water absorption was calculated using the Eq. (3).

W — W

Water absorption, Wa = —1——- 1 x100 (3)

W

where W1 is original weight of the sample and W2 is final weight of the sample after 24, 48 and 120 h.

The results of water absorption test are shown in Table 6.2. The percentage of the water absorption gradually increases with time and then it reaches a saturation point and an average of 114% of water is absorbed at the end of 120 h.

The first tests are carried out for reinforcement 1 with an orientation 0°. The blank holders’ pressure is set to 1bar. The preform in its final state is presented on Figs. 7.6a and 7.6d. The final shape is in good agreement with the expected tetrahedron punch without large wrinkle or un-weaving on the useful zone. Only very small wrinkles can be observed on corners of the edges for both reinforcements 1 and 2. At the local scale, on faces and edges, the tow buckling defects (Figs. 7.6.b and 7.6.d) and misalignment of tows (Fig. 7.6.b) are identified. Tow buckling only takes place on the Face C and on the opposed edge (between Faces A and B) whereas misalign­ment of tows is observed on all faces.

Depending on the initial orientation of the fabric, tow buckling (Fig. 7.6.b) ap­pears on faces and on one edge of the formed tetrahedron shape. These buckles zones converge from the bottom of the useful shape up to the triple point (top of the tetrahedron) (Fig. 7.6.d) Due to this defect the thickness of the preform is not ho­mogeneous. The height of some of the buckles can reach 3 mm near the triple point. Due to this thickness in-homogeneity generated by these buckles, the preform could not be accepted for composite part manufacturing.

At the fabric scale, the buckles are the consequence of out of plane bending of the tows perpendicular to those passing by the triple point. The tows passing by the triple point (vertical ones, or weft tows for orientation 0°) are relatively tight. They seem to be much more stressed than the warp tows, perpendicular to the one pass­ing by the triple point. It can be expected that the size of the buckles depends on those tows tension. In this zone, there is no homogeneity of the tensile deformation. This is illustrated by the orientation of the tows perpendicular to the one passing by the triple point on both sides of the buckle zone (drawn Fig. 7.2.d). These tows are

curved instead of being straight, and this phenomenon is probably at the origin of the buckles. The tow misalignment is also observed for reinforcement 2 (Figs. 7.7.a and 7.7.b) globally at the same location as for reinforcement 1. However, tow buck­les do not appear on the faces of the shape. Only very small buckles can be observed on the edge opposed to Face C in the case of a 0° orientation with a low blank holder pressure of 1 bar, as observed in Fig. 7.8.

However, tow buckles do not appear on the faces of the shape. Only very small buckles can be observed on the edge opposed to Face C in the case of a 0° orienta­tion with a low blank holder pressure of 1 bar, as observed in Fig. 7.8.

If tow buckles and small wrinkles can be observed on the shapes formed using the tetrahedron punch, the causes of the defects have not yet been discussed. It is therefore proposed to discuss the issues concerning the appearance of the defects that can be encountered during sheet forming of natural fiber based woven fabrics.

Sugar palm tree is one of multipurpose trees grown in Malaysia. The inner part of sugar palm stem contains starch. It was used as raw material for starch and glue sub­stances.79 For the production of one ton of starch, ten to 20 trees are needed which suggests that one tree can produce 50 to 100 kg of starch.76 This accumulated starch is harvested from the trunk of matured palms (after 25 years) and can be applied as ‘green’ material. Starch will act as biopolymer in the presence of a plasticizer such as water, glycerol and sorbitol at high temperature. Previously, the characteriza­tion of sugar palm starch as a biopolymer have been done by using the glycerol as a plasticizers.76 From the research, it was found that the tensile strength of SPS/ G30 showed the highest value 2.42 MPa compared to the other concentration of the plasticizer. The higher the concentration of the plasticizers, the higher the tensile strength of plasticized SPS and optimum concentration was 30 wt.%. The tensile strength decrease to 0.5 MPa when concentrations of plasticizer was 40 wt.%. As the plasticizer content increased to 40%, not enough SPS to be well bonded with glycerol and thus poor adhesion occurred which reduce the mechanical properties of SPS/G40. This result well agreed with the finding of Laohakunjit and Noomhorm80 who claimed that the films outside this range are either too brittle (< 20 wt.%) or too tacky (> 45 wt.%).

Generally, as the plasticizer increase, the tensile strength and elongation of plas­ticized SPS increase, while the tensile modulus decreased. This phenomena indi­cates that the plasticized SPS is more flexible when subjected to tension or me­chanical stress. The results from this study prove the finding done by Beerler and Finney81 whereby they reported that the plasticizers such as glycerol will interfere the arrangement of the polymer chains and the hydrogen bonding. It is also most likely affect the crystallinity of starch by decreasing the polymer interaction and cohesiveness. Thus, this make the plasticized SPS become more flexible with the increasing of glycerol.

For the thermal properties, the Tg of dry SPS reaches 242.14 °C and decreased with addition of glycerol. This value was higher than Indica rice starch where Tg values was237°C.82 Meanwhile, Myllarinen et al.83 claimed that for dry starch the Tg reaches 227 °C. The sample with high glycerol concentrations showed lower Tg values and Tg of starch without plasticizer were higher than those of samples with glycerol (Table 9.3). This behavior was also observed by Mali et al.84 for yam starch and by Forssell et al.33, for films based on barley starch, in both cases with glycerol as plasticizer. According to Guilbert and Gontard85, plasticization decreases the in­termolecular forces between polymer chains, consequently change the overall cohe­sion, leading to the reduction of Tg. Mitrus86 has been claimed that the plasticizer decreased Tg because it facilitates chain mobility. Brittleness is one of the major problems connected with starchy material due to its high Tg.87 In the absence of plasticizers, starch are brittle. The addition of plasticizers overcomes starch brittle­ness and improves its flexibility and extensibility of the polymers.

Each composite has its own unique chemical properties which is attributable to the filler type and method of preparation which in turn affects the composite’s thermal properties.26,49,80,81 For example, DDGS contains a higher concentration of protein («26%) than found in most wood and lignocellulosic fiber particles («1.5-7%). The DSC thermal properties of the DDGS, PW and PINEW composites are shown in Table 13.7. Only single endothermic (melting) temperature and exothermic (crystal­lization) peaks were observed in the DSC curves for all formulations conducted. Little difference was found between the melting points (Tm) of neat HDPE (i. e., 130.4°C) and the original DDGS formulations (HDPE-25DDGS and HDPE — 25DDGS-MAPE). Chemical modification (A or AM) treatments caused DDGS for­mulations to exhibit slightly higher Tms than HDPE or the nonchemically treated — DDGS composite controls. This trend was duplicated with the PW formulations given the same chemical modification treatments. Generally, biocomposites will exhibit a slightly higher Tm compared to that the neat thermoplastic resin.49,80 The increase in Tm in the composite is probably due to the disruption of the HDPE crystal lattice network by the presence of the filler particles. This is demonstrated by the HDPE-40PINEW formulation, which contains 40% Pine wood filler and subsequently exhibits the highest Tm value (133.5°C) recorded in this study (Table 13.7). Interest­ingly, the HDPE-10STDDGS/30PINEW, which also contains 40% filler had a lower Tm value (131.8°C). Although both of these formulations contained 40% filler, de­cidedly different mechanical and physical properties were exhibited by them (Tables 13.2-13.5). Considerably more research needs to be conducted to determine how the mixing fillers of different chemical composites interact and affect their resulting thermal properties.

The addition of fillers to the HDPE results in composites with lower crystalliza­tion enthalpy (DHc) and melting enthalpy (DHm) values compared to neat HDPE (Table 13.7). It has been suggested that that wood fillers absorb more heat energy in the melting of composites which results in their lower DHm values when compared to neat thermoplastic resins.43

The degree of crystallinity (xc) varied considerably depending on the filler type employed in the composite. Other investigators have also observed a variation in the degree of crystallinity values associated with various LPC.3049 The degree of crystal­linity values for DDGS, PW and PINEW biocomposites were higher when MAPE was included in the formulation (Table 13.7). This situation may also be related to the HDPE resin employed. For example, PW blended with a different HDPE source showed distinctly lower x values than neat HDPE employed in this study.30 When the concentration of PINEW is increased to 40%, x values decreased markedly be­low that of neat HDPE. One explanation for this phenomenon for the reduction in X values is due to the amount of free volume occurring between the polymer chains capable of allowing filler to be intermixed.81 As the volume of the filler increases less resin polymer intermolecular free volume is available for dissipating the filler material.81

The thermal properties of biocomposites need to be determined because the pro­cessing temperatures (extrusion and injection molding) may often exceed 200°C. Commercial HDPE products are often made with high melt temperature resins. The thermogravimetric curves for the various composites are plotted in Fig. 13.7 and these results are summarized in Table 13.8. The degradation of neat HDPE em­ployed in this study, occurs in a single stage, beginning at 461.7°C, with a maximum decomposition peak occurring at 478.3°C. HDPE degradation was 99.7% complete at end of this stage. Similarly, the HDPE-MAPE blend mimicked these parameters, although exhibiting somewhat lower degradation and peak maximum temperatures. In contrast, there are several earlier degradation peaks for the DDGS composites. Examining the HDPE-25DDGS formulation reveals a major degradation tempera­ture (Td) for the DDGS flour occurring at ~ 242.2°C which subsequently results in maximum peak temperature at 322°C. Minor degradation peaks also occur and are the decomposition of low molecular weight components such as hemicellulose which degrades between 225 to 325°C.782 Next a larger second higher degradation peak occurs with a maximum at 321°C, which is corresponds to the decomposi­tion of cellulose which degrades in the 300 to 400°C.82 Further, a third degradation peak corresponds to lignin decomposition which is reported occurring near 420°C; however it is not readily seen in this study.82 This peak was obscured by the de­composition of the HDPE. The DDGS composite has a residual weight of 5.9% ash residue from the heterogeneous ingredients associated with the filler. Differences among the DDGS composite Td’s are due to the association of the filler material and the plastic resin. Higher Td’s and maximum peak temperatures occurred for STD — DGS composites compared to the DDGS composites; this can be attributed to the occurrence of higher levels of low-molecular-weight organic compounds in DDGS composites compared to that found in the STDDGS composites. Similarly, other investigators report that addition of extractables (clay) caused a decrease in Td val­ues to occur.12 The results presented here confirm a previous study using DDGS formulations blended with a different HDPE resin.30 The addition of the coupling agent MAPE had a somewhat complex influence on the decomposing behavior the DDGS composites. In some cases, inclusion of MAPE in the DDGS and STDDGS formulations (HDPE-25DDGS-MAPE and HDPE-25STDDGS-MAPE) resulted in occurrence of lower degradation temperatures (1st Td) compared to formulations without MAPE (HDPE-25DDGS and HDPE-25STDDGS) (Table 13.8). Chemi­cally modified DDGS formulations (HDPE-25 STDDG/A) showed considerably higher 1st peak degradation initiation temperatures (Td) and 1st degradation maxi­mum peaks compared to the untreated DDGS formulations (HDPE-25DDGS). The chemical modification treatments (A and AM) improves the thermal stability of for­mulations. This phenomenon has been reported by other investigators where the 1st decomposition temperatures of HDPE-acetylated-WF were reported to higher when compared to HDPE-WF formulations.51 Likewise, chemically treated PW formula­tions (HDPE-25STPW/A and HDPE-25STPW/AM) exhibited higher 1st peak deg­radation initiation temperatures (Td) and 1st degradation maximum peaks compared to the untreated PW formulations (HDPE-25PW).

“Mixed” filler formulations (HDPE-12.5 STDDGS/12.5PINEW) and HDPE- 12.5DDGS/12.5PINEW-MAPE) exhibited much higher 1st degradation initiation temperatures (Td) and 1st degradation maximum peaks than the nonmixed DDGS filler formulations (HDPE-25STDDGS and HDPE-25STDDGS-MAPE). This is at­tributed to the presence of PINEW in the mixture, which probably masks the pres­ence of DDGS particles in these formulations. Perhaps, mixed filler composites containing PINEW flour and DDGS could be considered more “thermally stable” than the DDGS formulations tested (Table 13.8). More study is necessary to prove this contention. However, these “mixed” fillers composites were not as stable as em­ployment of formulations containing PINEW alone. Based on the TGA analysis and since the processing temperatures did not exceed 210°C the DDGS, PW and DDGS — PINEW composites were thermally stable for the temperatures in which they were subjected to in this study.

13.4 CONCLUSIONS

The mechanical properties of two potential lignocellulosic material reinforcements, DDGS and PW, for use in commercial LPC was conducted in this study. Further, the benefit of “mixing” chemically dissimilar fillers, DDGS with PINEW, was assessed. The tensile, flexural, impact strength, environmental durability (soaking responses), and thermal properties of injection molded test specimens were measured. Compari­son of the composites to neat HDPE that was processed with the same conditions was conducted to determine the relative merits of using a filler against a control. Using DDGS subjected to solvent extraction (STDDGS) produces a composite with superior mechanical properties (HDPE-25 STDDGS) compared to the composite made with the original DDGS material (HDPE-25DDGS). Further, formulations of STDDGS with MAPE (HDPE-25STDDGS-MAPE) exhibited slightly lower tensile and flexural moduli but slightly higher ultimate stresses than similar formulations made without MAPE. The flexural properties and the tensile modulus of a solvent extracted DDGS with MAPE exceeded those of neat HDPE. The PW composites in general exhibited greater tensile and flexural properties than the DDGS com­posites made with similar formulations. Chemical modification by acetylation and malation of DDGS and PW fillers prior to compounding had mixed effects on im­proving the mechanical properties of the composites studied when compared to the untreated controls. In fact, the tensile and flexural moduli of composites containing chemically modified fillers were slightly lower than the baseline solvent treated filler with MAPE. The mixing of PINEW and STDDGS resulted in formulations (HDPE-12.5DDGS/12.5PINEW and HDPE-12.5DDGS/12.5PINEW-MAPE) with
improved mechanical properties compared to the STDDGS formulations (HDPE- 25STDDG or HDPE-25STDDGS-MAPE). All DDGS and PW composites soaked in water for 872 h exhibited weight gain, color changes, and some alteration in their mechanical properties, especially El%. The thermal stability of LPC formulations can be improved by mixing with wood filler and employing chemical modification.

13.5 ACKNOWLEDGEMENTS

The authors acknowledge Kimberly Pelphrey for technical assistance and Dr. N. Joshee for Paulownia wood material. Mention of a trade names or commercial prod­ucts in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the US Department of Ag­riculture. USDA is an equal opportunity provider and employer.

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.

During the last few decades, the environmental problems primarily caused by the excessive use of conventional petrochemical based materials such as plastics have become one of the major public concerns all around the globe. Many countries are making enormous efforts to overcome these problems by making and adopting vari­ous policies as well as management programs. With the growing concerns towards the environment, industries and researchers are also looking forward to the use of environmentally friendly materials for product development in a number of appli­cations. Among various environmentally friendly materials, renewable resources — derived polymers (e. g., bio-based polymers) and composites (e. g., natural fibers reinforced composites) are attracting a great deal of attention because of the inherent advantages of these polymers such as conservation of limited petroleum resources, biodegradability, low toxicity, easy availability, economy and the control of carbon dioxide emissions that lead to global warming.

From the view of sustainable development, the new materials associated with biorenewable sources are enormously being explored. Indeed the concerns over new materials from renewable resources, especially in the automotive and biomedical industries, have recently increased because of the economic consequences of de­pleting petroleum resources, the demands from industrialists and customers for high performance low-cost materials and environmental regulations. From biorenewable natural resources, ecofriendly materials can be obtained as native biopolymers, raw materials for monomers and bio-engineered biopolymers to name a few. Biopoly­mer based materials such as cellulose, starch, chitosan/chitin, poly (lactic acid), and poly (hydroxyalkanoate), etc. are among the most abundantly available biopolymers on the planet Earth. They are replacing the materials for many industrial applica­tions where synthetic polymers have been materials of choice, traditionally. One of the important aspects of biobased materials is that they can be designed and tailored to meet different desires. As the native biopolymers are not conventionally process — able, research efforts have been focused on the processing and meeting the require­ments of particular applications. The biobased materials are most frequently being used in the form of biocomposites. These biocomposites materials contain at least one component form the biorenewable resources that may either be the polymer matrix/ reinforcement or may contain both.

Using the recently developed techniques and technologies, biocomposites with better mechanical properties and thermal stability can be efficiently developed de­pending upon the applications. In fact the use of biocomposites may provide us a healthier environment owing to their multifaceted advantages over conventional polymers.

Keeping in mind the advantages of bio-based materials, this book focuses on the potential efficacy of different biocomposites procured from diverse natural re­sources and preparation and processing of the biocomposites to be used for a variety of applications. The book consists of 17 chapters, and each chapter gives an over­view of a particular biocomposite material, its processing, and successful utilization for selected applications. The chapters summarize recently developed research con­cerning spider silk biocomposites; biogenic hydroxyapatite based implant biocom­posites; liquid crystals and cellulose derivatives biocomposites; bio-based epoxy resins, bio-based polyphenols and lignocellulosic fibers; wood based biocompos­ites; flame retardant biocomposites; biocomposites for industrial noise control, cel­lulose based bionanocomposites, etc. Each individual chapter also focuses on the knowledge and understanding of the interfaces manifested in these biocomposites systems and optimization of different parameters for novel properties. In addition to this, the book also summarizes the recent developments made in the area of injection molding of biocomposites; chemical functionalization of natural fibers, processing of biocomposites and their applications in automotive and biomedical. A number of critical issues and suggestions for future work are discussed in a number of chapters, underscoring the roles of researchers for the efficient development of biocomposite materials through value addition to enhance their use.

As the editors of Green Biorenewable Biocomposites: From Knowledge to In­dustrial Applications, we have attempted to compile, unify, and present the emerg­ing research trends in biopolymers based biocomposites. We hope that this book will contribute to the advancement of both science and technology in this exciting area.

—Vijay Kumar Thakur, PhD

Washington State University — U. S.A.

—Michael R. Kessler, PhD, P. E.

Washington State University — U. S.A.

Titanium (Ti) is most commonly used as orthopedic implant materials or bone substi­tute materials. Ti possesses the good biocompatibility and the sufficient mechanical properties for medical applications (Table 2.6) 48. One negative property of Ti is a low abrasion resistance and minute Ti abrasion powders may cause inflammatory reac­tions 49. Scaling treatment is only method for removal of plaque and dental calculus adheres, and it is a necessary treatment process to obtain good prognosis throughout the long-term maintenance of implant 50. Therefore, for abutment division of implant, it is important to possess high abrasion resistance to keep the smoothness of the im­plant surface after scaling treatment 51. Biomaterials must be nontoxic, noncarcinogen­ic, chemically inert, stable and mechanically strong enough to withstand the repeated forces of a lifetime. From this point of view, TiC is a very stable phase in comparison to pure Ti or Ti alloys. Titanium carbide (TiC) is an useful material for biomedical instruments because it possesses a range of desirable properties. The combination of very high hardness, high melting temperature, and excellent thermal and chemical stabilities makes TiC suited to a number of commercial applications. TiC is often used in abrasives, cutting tools, grinding wheels, and coated cutting tips 52.

Ti based implants are classified as bioinert. Bioinert refers to a material that retains its structure in the body after implantation and does not include any immunologic host reaction. Bioactive materials should be used for modification of the surface that occurs upon implantation. Bioactive refers to materials that direct chemical bonds with bone or even with soft tissue of a living organism. One of most used bioactive materials is a hydroxyapatite. The major inorganic constituent of bones and teeth is calcium phosphate, whose composition is similar to that of synthetic hydroxyapatite (HAp; Ca10(PO4)6OH)2. This similarity provides HAp based materials excellent bioactivities like bone bonding capability, osteoconductivity, and biocompatibility. The major dis­advantage of HAp is its poor adhesion, poor mechanical integrity, high brittleness, degradation in acidic/basic conditions and incomplete bone growth, which restricts its application only in non load-bearing areas of the human body. The creation of nanocomposites of ceramic materials with particle size few ten nanometers can sig­nificantly improve the bioactivity of the implant and enhance the osteoblast adhesion.

5.3.1.1 FIBER TYPE

A wide variety of fibers are used in biocomposite sound absorbers, including con­ventional synthetic fibers, conventional plant fibers, exotic plant fibers, animal fi­bers, reclaimed fibers of chemical and natural origin and engineered compostable fibers like poly (lactic acid), as given in Table 5.2. The characteristics of the con­stituent fibers also have an important effect on sound absorption.

The effect of fiber type on sound absorption is hard to detect as it is often ac­companied by differences in fiber size and shape as seen in Figs. 5.5 and 5.6. Fiber type determines the relationship between the fiber size and flow resistivity.14 The following relationships have been reported:

where r0,g, r0,p, and r0,w represent flow resistivity values of glassfiber, polyester14 and wool46 webs in mks rayl/m, respectively; ц stands for viscosity of air which is 1.84×10-5 kg m1 s1, h denominates porosity, a is fiber radius in m, and p represents density of the fiber mat in kgm-3.

Fiber/material Production method Investigated parameters Measured parameters Frequency range (Hz) Thickness (mm) Fiber diam­ eter (ціп) Max. NAC Publication PP, PLA, glass — fiber, hemp Air laying, needle- punching, thermal treatment Heat treatment NAC, air flow permeability 500-5000 3.90-13.1 9-42 0.99 Yilmaz et al.8 PES, PP, cotton, wool, jute, rice straw, sawdust, jute, Needle-punching Thickness, cover plate, air gap, composition NAC 100-6300 2.53-22.6 N. S. 0.99 Seddeq et al.56 PP, PLA, glass — fiber, hemp Air laying, needle — punching Compression NAC, air flow permeability 500-5000 7.91-13.1 9-42 0.99 Yilmaz et al.9 PP, hemp Air laying, needle- punching, alkaliza­tion Alkalization NAC, air flow permeability 500-6400 10.61-12.53 32M2 0.99 Yilmaz et al.20 PP, Bamboo strips Laying stacking com­pression molding Blend ratio, thick­ness, fiber type, fiber orientation NAC, Noise Reduction Coefficient (NR) 0-3000 1.16-10.12 75 0.80 Huda et al.48 Coir fiber, wood particle debris, phenolic resin Needle-punching, resin bonding Blend ratio, needle-punching, fiber placement NAC, Noise Reduction Coefficient (NR) 125M000 N. S N. S 0.99 Yao et al.57 PU binder, pine sawdust, recycled rubber Resin bonding Blending ratio, thickness, mate­rial type, NAC 50-10,000 20-40 1-4* mm 0.92 Borlea et al.26 PP, PLA, glass — fiber, hemp Air laying, needle — punching Porosity, fiber type and size, layer sequence NAC, air flow permeability 500-6400 11.45-12.68 9-42 0.99 Yilmaz et al.58

Fiber/material Production method Investigated parameters Measured parameters Frequency range (Hz) Thickness (mm) Fiber diam­ eter (Mm) Max. NAC Publication PES, formalde­hyde, recycled PS, woodchip, furnace slag, municipal waste, power plant ash Granulation Resin bonding Material type 10-3,150 2.5-10* mm 1-2* mm 0.91 Bratu et al.51 Flax tow Grinding, washing, microwave, molding Grinding, micro — wave treating, molding, thick­ness NAC 100^1000 2-10 N. S 0.82 El Hajj et al.54 Recycled pulp, luffa fibers, yam waste Wet laying, cold pressing Blend ratio, mate­rial type NAC 500^1800 N. S N. S 0.13 Karademir et al.52 PP, Jute, PES Carding, needle — punching Material density, number of layers Sound insula­tion N/S 2.6-51 8.7 N/A Sengupta59 Jute, bamboo, banana, jute Carding, needle — punching Fiber type NAC 100-1600 49-6.4 N. S 0.20 Thilagivath21 PP, hemp, rapeseed straw, beech and flax Extrusion granulat­ing, compression molding Fiber type NAC 1000 -6500 N/S N. S 0.32 Markiewicz et al.49 PP, mechani­cally split corn husks, jute Spunbonding, mold­ing Fiber type, blend ratio, NAC 300-3000 3.2 1.3 0.42 Huda and Yang60

N/A: Not applicable, N. S: Not stated, *: granule diameter, PES: polyester, PP: polypropylene, PU: polyurethane, PS: polystyrene, PLA: poly lactic acid.

Studies related to sound absorption properties of biocomposites include struc­tures made up of different fibers. Surface properties of fibers and their cross-sections also play an important role. Accordingly, Nick et al.45 found greater absorption for cotton-polypropylene (PP) blend fibrous material for automotive applications com­pared to the flax-polypropylene and hemp-polypropylene blends. This was probably due to the inherent superior fineness of cotton fibers as compared to flax and hemp.

Jayaraman et al.47 examined the effect of kenaf fiber inclusion, which is a natural bast fiber, on the absorption of sound in fibrous absorbers. The addition of kenaf had a negative effect on the noise reduction performance compared to polyester and re­claimed polyester fibers, however, this effect is less pronounced in high frequencies. This negative effect may also be due to natural coarseness of kenaf fiber compared to synthetic fibers.

Parikh et al.22 developed composites in various weight ratios of natural and syn­thetic fibers including kenaf, jute, waste cotton, and flax with recycled polyester and off-quality polypropylene and compared to absorbers of conventional fibers, that is, 70% polyester and 30% polypropylene. They reported that each of the natural fibers contributed to noise reduction because of their absorptive properties in comparison with the conventional material. Furthermore, adding a soft cotton underpad was found to greatly enhance the sound absorption properties of the nonwoven floor coverings.

Huda et al.48 produced unconsolidated light-weight (0.312 g/cm3) composites by laying fine bamboo strips on a PP web and by a subsequent compression molding process. They reported better mechanical and noise reduction capabilities for the mentioned composites compared to jute-based composites.

Markiewicz et al.49 produced composites including PP and lignocellulosic fillers and measured their sound absorption performance in the 1000-6500 Hz frequency range. They reported the hemp filler addition allowed for significant increase in noise reduction over 3000 Hz, whereas rapeseed straw, beech and flax filler added to PP suppressed sound in the 3000-4000 Hz range.

Brencis et al.50 presented a research study with an aim to develop a sound ab­sorber from gypsum foam reinforced by fibrous hemp. They claimed that the gyp­sum, Gypsies rock, a local resource in Latvia, can have performance characteristics comparable to other state-of-the-art thermal and sound insulation materials. Addi­tionally, gypsum poses an important fire-resistance characteristic. Fragility, which is the disadvantage of the gypsum material, claimed to be avoided with the use of plant fibers, such as hemp, as a reinforcement element.

Bratu et al.51 studied composite materials including pellets from plastic bottles, sawdust, and ash from plant and sterile municipal wastes in a polymer type organic matrix in different blend ratios. The effects of the blend ratio and the type of the waste material on the sound absorption performance were investigated. They re­ported that use of sawdust and woodchips were advantageous in terms of noise reduction compared to the other recycled materials.

Karademir et al.52 prepared biocomposites through a wet laying process from recycled corrugated boards with addition of 30% yarn waste and 15% luffa fibers. They found that the addition of luffa fibers and yarn waste led to an increase in sound absorption together with an increase in air permeability at the expense of tensile strength.

Among the very few examples of biocomposites containing materials of ani­mal origin, Huda and Yang examined the sound absorption performance of ground chicken quill based PP composite and compared it with jute-based PP composites.53 They reported that the chicken quill based composites resulted in better sound ab­sorption performance in 500-2200 Hz frequency range as shown in Fig. 5.7.

ё 0.30 —

tL 0.20

0.10

0. 00

0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2

Frequency (kHz)

FIGURE 5.7 Sound absorption of PP-chicken quill composites compared to PP — jute mats at different thicknesses and blend ratios (From Huda, S.; Yang, Y Composites Science and Technology, 2008.53 With Permission from Elsevier.).

The sound absorption coefficient improves with frequency since at high frequencies the wavelengths reduce and for a given sample the velocity is a maximum at the in­terface. Better sound absorption occurs when the incident velocity is at a maximum at the interface. Thus to improve the low frequency sound absorption either the thickness of the sound absorbing material can be increased or an air gap between the material and the rigid backing can be provided. Usually in many applications where low frequency absorption is to be improved an air gap is usually provided as shown in Fig. 6.8. Figure 6.9 shows the effect of air gap on the sound absorption coefficient of a 50.8 mm jute fiber with a density of 348.2 kg/m3.