The ultrastructure for dragline silk has been intensely investigated and different numbers of layers have been reported in the literature, ranging from two to five.2,6 For the purpose of this discussion, we will assume that dragline silk consists of a core, skin, thin glycoprotein layer, and a lipid outer coating. Chemical analysis of MA silk has revealed this material contains at least two distinct proteins. To date, two different structural polypeptides referred to as fibroins or spidroins (spidroin is a contraction of the words spider and fibroin) have been identified as major con­stituents (Table 1.1).7 Full-length DNA sequences have been reported for both con­stituents, which have been named Major Ampullate Spidroin 1 (MaSp1) and Major Ampullate Spidroin 2 (MaSp2).8 This nomenclature reflects their restricted pattern of mRNA and protein expression and the order of discovery of the proteins.9 Manual inspection of the full-length translated sequence for both MaSp1 and MaSp2 pre­dicts large molecular weight proteins that are >250-kDa.8 Analysis of these protein architectures reveals nonrepetitive N — and C-termini along with internal repetitive block modules. These internal modules are approximately 40-50 amino acids in length and can be further broken into submodules. Amino acid composition studies of the MA luminal contents and the natural fibers using acid hydrolysis or NMR have generated experimental data that are similar to the predicted amino acid com­position profiles from full-length MaSpl and MaSp2 sequences, both showing compositions that are A, G and Glx-rich.10 However, although the experimental and theoretical amino acid composition profiles are similar, they are not identical and the differences support the assertion that other proteins are spun into MA fibers. MS/ MS analyzes of peptides generated from solubilized MA silk digested with trypsin are consistent with this hypothesis; these peptide sequences do not match regions from the full-length translated MaSp1 or MaSp2 sequences (unpublished data).

ADINA MARIA DOBOS, MIHAELA-DORINA ONOFREI, and SILVIA IOAN

ABSTRACT

This chapter summarizes recently developed researches concerning cellulose de­rivatives composites obtained by blending of cellulose derivatives or of cellulose derivatives with different polymers, as well as by processes involving nano-particles in the cellulose derivative matrix. Knowledge and understanding of the interactions manifested in these cellulose systems constitute essential elements for the concep­tion and optimization of novel structures. Different characterization techniques al­low a more complete evaluation of the mechanisms of multicomponent systems, of their fundamental interactions, such as hydrogen bonding, and the manner in which these interactions affect the final properties. This research reveals the rela­tion between the molecular interactions and physical properties, which represents an important challenge from both scientific and industrial perspectives. On the other hand, the chapter shows that, like many other cellulose derivatives, hydroxypropyl- cellulose (HPC), is the most common ether of native cellulose, whose concentrated solutions possess optical properties characteristic to cholesteric liquid crystals. In crystalline state, on one hand, these types of cellulose present specific arrangements, while, on the other, these arrangements depend on the concentration of their solu­tions. In cellulose derivative composites, the absence or presence of liquid crystals properties is dependent on mixture composition, solution concentration and used solvent, according to the application in biomedical or electronic domain.

3.1 INTRODUCTION

Cellulose is a natural polymer used in a variety of applications. Like most poly­mers, cellulose is not completely crystalline, also containing disordered regions. Out of the variety of models that explain its dual nature, the fringed micelle pattern considers that chains pass through both crystalline and amorphous (disordered) re­gions, whereas other models attribute the disorder to imperfections, chain ends, and

surface regions of the microfibril. Cellulose derivatives use is limited by their poor solubility in various solvents, which is primarily due to the hydrogen bonds formed between the hydroxyl groups from the anhydroglucose chain. In dissolved state, all hydroxyl groups are accessible to the reactant molecules, so that the cellulose struc­ture can be chemically modified to improve their processability and performance for particular uses. To this end, various cellulose derivatives have been synthesized for the diversification of their characteristics. Thus, cellulose acetates are cellulose es­ters partially substituted at the C-2, 3 and 6-positions of the anhydro glucopyranose residue. They can be easily molded into different forms, such as membranes, fibers, and spheres. To conjugate the mechanical properties of the polymer with the intrin­sic properties of cellulose acetates, hybrid organic/inorganic materials have been prepared.1 The obtained composite materials present many intrinsic advantages,2 such as low cost, availability, biodegradability and easy handling. At the same time, the modern technology makes possible to manufacture, from the existing suitable polymeric materials, different optical cellulosic components for a wide variety of applications, such as spectacle lenses, contact lenses, intraocular lenses, consumer products, instrumentations, etc. Generally, cellulose acetates are not used for cor­rective lenses, but are occasionally employed for plane lenses. High optical trans­parency, high moisture absorption and low dimensional stability characterize these derivatives of cellulose.13 Recent researches describe different processes for obtain­ing membranes with optical and dielectric properties for biomedical applications. Cellulose acetates have been widely used for dialysis membranes, for example, in artificial kidneys, as membranes in plasmapheresis, and as drug delivery matrices for controlled release.46 Mention should be here made of the researches on the in­tegration of cellulose acetates onto silicon wafers by the standard microfabrication process, to add filtration capability on the chip. The membranes are biocompatible, showing good structural integrity and good adhesion to the substrate.78 Moreover, cellulose acetate membranes are recommended for applications that require superior clarity, for example, for optical sensors.9 Also, a pH-sensitive membrane, consist­ing of a polyester support covered with a thin layer of cellulose onto which a pH — indicator was covalently immobilized, has been developed.10

Cellulose acetate phthalate (CAP), a mixed ester of cellulose obtained through phthaloylation of cellulose acetate, is used in different domains as a pharmaceutical excipient, due to its pH dependent solubility in aqueous media. CAP enteric coat­ings are resistant to gastric acid and easily soluble in the slightly alkaline environ­ment of the intestine. The pH-dependent solubility is mainly determined (among other properties of the mixed ester) by the substitution degree (DS), namely the average number of substituent groups linked by one unit of anhydro glucopyranose and by the molar fraction (acetyl and phtaloyl groups). These two structural charac­teristics are dependent on the synthesis conditions. The potential of this polymer to inhibit infections caused by several types of herpes virus, such as Herpes Simplex type 1, and by other sexually transmitted diseases, has been analyzed in-vitro.1113

Also, CAP is a well-established safety record for human application, being used for enteric film coating of tablets and capsules.14

Cellulose ethers, such as methylcellulose, ethylcellulose, hydroxypropylcel — lulose, hydroxypropyl-methylcellulose, methylhydroxyethylcellulose possess a remarkable combination of important properties for biomedical and pharmaceuti­cal applications, for example, as carriers for drug targeting,15 vaccine bullets,16 sus­tained release of drugs,1718 as materials for the disintegration of matrix tablets,19 as electro-optical devices,2021 as transparent media for liquid crystalline display tech­nology,22 and for stabilization of dispersion polymerization.23 On the other hand, the most common ether of native cellulose, whose concentrated solutions display optical properties typical for cholesteric liquid crystals, is hydroxypropylcellulose (HPC). In crystalline state, the HPC molecules are present in a helical arrange­ment. The structure is not dependent on the solvent alone, but also on concentration. Thus, the rheological behavior of HPC,24,25 either pure or in mixtures with other polymers, involves the absence or presence of liquid crystals properties, as a func­tion of composition, solution concentration and solvent,2628 on also considering to the applications areas, for example, food industry,29 medicine,30, etc. HPC is cheap and biocompatible, which makes it a valuable tool for applications in biological and medical fields, especially for the fabrication of macromolecular prodrugs.3133 Recently, cross-linked HPC derivatives have been shown to form elastomeric thin films.34 At the same time, researchers have found chiral nematic order in natural materials, such as animal and plant tissues.3537 In this context, literature shows dif­ferent stages in which these natural materials, similarly with cellulose crystallites and nanocrystallites, may be replicated in-vitro.3840

In the present study, CAP and HPC have been preferred especially for the large range of their pharmaceutical and biomedical applications. Their miscibility is gen­erally considered as a result of the specific interactions between polymer segments in casting solutions of organic solvents. Thus, literature shows that CAP/HPC com­posite films obtained in different organic solvents, such as ethanol, rapidly reduce the infectivity of several sexually transmitted disease pathogens, HIV-1 included.41 The infections reduction mechanism involves conversion of these composite films into gel in the presence of water. These films were used in different biomedical ap­plications, such as controlled release of drugs.4243

Knowledge of the solution properties is important for handling/formulation, and also for a better understanding and control of polymer blending processes.

Extensive studies have been conducted on the effect of the used solvents, on the morphology and performance of derivative cellulose or derivative cellulose blends with various polymers in different applications, such as ultrafiltration membranes, reverse-osmosis membranes, gas-separation membranes, and pervaporation mem­branes. Addition of a second solvent to the casting solution increases the permeation flux of a membrane or improves the performance of nano-fibers.44 Literature data reveal that the polymer structures, boiling point, content of solvent mixture, and
intrinsic viscosity may affect performance in some applications.4546 Moreover, the electrospinning process of polymers in solvent mixtures employs an electrostatic potential to form fibers with different diameters. These fibrous mats with high spe­cific surface area and nano-degree of porosity lend themselves to a wide range of applications.

As explained above in Measuring Sound Absorption section, flow resistance is the most critical factor that determines the sound absorptive properties of porous mate­rials. Ingard35 introduces the normalized specific flow resistance as follows:

where rn is the normalized specific flow resistance, p is density of the fluid, and c is the speed of sound, and pc is the impedance of the fluid. The S. I. unit of specific flow resistance, r, is kg-m-2-s-1, of the density, p, is kg-m-3, and of the speed of the sound, c, is m-s-1; thus, the normalized specific steady flow resistance, rn, of the porous material, is nondimensional.35

There is a close relationship between the flow resistivity and the density of the porous web. Flow resistivity increases in high densities, as air permeability, which is the reciprocal of air flow resistance, reduces when fiber packing density increases
with an increase in the pressure drop.68 Ballagh46 found the following relationship for woolen fibrous webs:

r — 16 a,1-61 (24)

where r0 is the flow resistivity in mks rayls/m and p w is the density of web in kg-m~3.

Yilmaz3 generated an empirical model to explain how the fiber diameter and web density effect ro, based on samples including layered webs of untreated, com­pressed and alkalized biocomposites of hemp, poly (lactic acid) (PLA), polypropyl­ene (PP) and glass fibers in single or multifiber versions with a goodness-of-fit, R2 value of 0.90:

5.39 x 10-4 і 6

r0 -15,651 + , 6 p, , (25)

a pf

where is the weighted root mean square fiber diameter of the composite in meters, pf is the weighted average fiber density and, pw is the density of the composite struc­ture. As seen from the expression, air flow resistivity is inversely proportional to the square of the fiber size and is proportional to the quotient between the density of the biocomposite to its constituent fibers. The boundary suggested for the validity of the model is a basis weight of 1.13 to 1.57 kg-m-2, fiber diameter of 16.3ХІ0-6 to 33.3×10-6 m, a material thickness of 7.91×10-3 to 1.31×10-2 m, and porosity of 0.84 to 0.92. The agreement of the theoretical predictions with the experimental data is given in Fig. 5.8.

90000 80000 г 7000

The flow resistivity is proportional to the coefficient of shear viscosity, p, of the fluid (i. e., air) involved and is reported to be inversely proportional to the square of the pore size of the material when the microstructure is considered. As the material is fibrous, the flow resistivity increases with the decreasing fiber size in accordance with Eq. (25).35 However, the relationship between the fiber size and the flow re­sistivity depends on the fiber type.14 Other than density and fiber diameter, flow resistivity is determined also by porosity, tortuosity, pore size distribution19 and fiber orientation.18

Sound absorption increases with increasing flow resistivity up to a point then starts to decrease for higher resistivity values. If the resistivity is too low, there is a small amount of fibers to interfere with the sound wave to cause energy loss,69 whereas when the flow resistance is too high, the material acts as a reflector rather than an absorber. High-frequency sound absorption requires relatively lower flow resistance.68 Consequently, the absorption coefficient curve shifts to a lower fre­quency range as the flow resistance increases.

There is an optimum flow resistance for each frequency range. However, in practice, the specific flow resistance, r, of an absorber is typically in the range of 2 pc, as reported by Ingard.35 Fahy13 recommends a specific flow resistance of 3 pc, whereas Attenborough and Ver17 report the range of 1-2 pc to be an optimal choice. Ballagh46 finds a specific flow resistance of 1000 mks rayls, which is approximately 2.5 pc, gives optimum absorption of wool absorber. Fahy13 reports that most of the sound absorbers have flow resistivity values between 2*103 to 2*105 Pa-s-m-2 or mks rayl/m.

In engineering applications of jute-based composite panels the knowledge of their tensile and flexural strength is required. Several researchers have measured and re­ported the mechanical properties of biocomposites including jute and its deriva — tives47,49. The Tensile test was measured as per the ASTM D638 standard and the flexural strength was measured as per the ASTM D790 standard50,51. It has been ob­served that by a pretreatment of raw jute fibers with ultra violet light a better strength is obtained5. Figure 6.11 shows the SEM view of a untreated and UV treated failed jute fiber. A facture mode can be seen in Fig. 6.11(a) due to poor bonding between the fiber matrix and the natural rubber latex resin. The bonding is better between the fiber and the matrix in the case of pretreatment. However the improvement in mechanical strength has no significant change in the acoustical transmission loss of the jute composite panels as long as there is no change in the density of the panel.

Mold temperature is also an important process parameter in case of injection mold­ing process. Mold temperature can be regulated by the use of heaters and the cooling channels provided in the mold. Low temperatures of the mold can be attained using chilled water channels, which continuously take the heat from the mold, but low temperature of the mold leads to rapid cooling of the part resulting in the develop­ment of residual stresses in the part. High mold temperature is desired to obtain glossy parts. To avoid warpage the molded parts should be cooled below the heat deflection temperature.

8.3.1.3 BACK PRESSURE

Back pressure is the pressure exerted on the screw by the melt while screw is re­covering to back position after the injection stroke. While returning the screw feeds the pellets into the heated screw barrel for plasticizing, this material after melting accumulates in front of the screw pushing the screw backwards. It is used for the uniform mixing of the fibers in the polymer melt. It also removes the entrapped air and ensures consistent shot density. However, high back pressure might also de­crease the plasticization ability.

In this method cellulosic material is treated with an aqueous mixture of alkali metal or ammonium hydroxide and alkaline-earth or aluminum metal salt simultaneously with or within a short period of time of preparing the mixture. The treated cellulosic material becomes self-extinguishing and may also have improved thermal stability, improved interfacial thermal resistance, improved resistance to damage by oxidants and other chemical agents, improved resistance to damage by ultra-violet light and/ or reduced negative impact on fiber strength and/or modulus. The fire-resistant cel — lulosic material may also be treated with a layered nanoparticulate material either simultaneously with, subsequent to or prior to treatment with the aqueous mixture of alkali metal or ammonium hydroxide and alkaline-earth or aluminum metal salt to impart further fire resistance to the cellulosic material.

In principle, the mentioned chemicals attached on the cellulose surface to form a nonflammable layer that can protect cellulose effectively from fire. Single or double or multiple layer can deposit on the cellulose surface as desired. These layers can be based on the same or different chemical compositions as desired. Figure 11.1 describes the principle of the cellulosic fiber after the treatment.

The treatment is very simple and easy to scale-up and it consists of the soaking of the cellulose in the aqueous chemical solution bath and drying as illustrated in Fig. 11.2.

Polymer composites produced from cellulosic material treated according to this method have significantly improved fire resistance with minimum negative impact on the mechanical performance, and may have the added benefit of one or more of improved thermal stability and improved interfacial thermal resistance.

Individual cellulose microfibrils have diameters ranging from 2 to 20 nm and are made up of 30-100 cellulose molecules that are the major structure elements for providing mechanical strength to the fiber.21 The cellulose macromolecules are ar­ranged parallel to one another with very close spacing. As indicated earlier, cellu­lose is a linear homo-polysaccharide composed of р-D-glucopyranose units linked together by P-1-4 glycosidic linkages.22 Each glucose unit has three hydroxyl groups with the ability to stabilize the entire cellulosic crystalline lattice structure via later hydrogen bonds that a priori are responsible for the crystalline packing and control­ling the overall properties of the cellulosic.

The overall properties of the cellulosic fibers are controlled by the MFA, nano­crystalline cellular dimensions, defects (number and degree), and molecular con­stituents. As a rule, the tensile and Young’s modulus of the fibers increase with increasing cellulosic content whereas the stiffness of the fibers are controlled by the MFA. The spiral angle of the fibrils and the content of cellulose in general therefore determine the mechanical properties of the cellulose-based natural fibers. Essen­tially, a very high tensile strength, inflexibility, and rigidity are obtainable if the microfibrils are oriented parallel to the fibril axis.

Clearly, the overall magnitude of the final properties of the cellulosic fibers are a function of chemical composition, internal fiber structure, MFA, cell dimensions, and defects in the raw material. The mechanical properties of natural fibers also de­pend on the DP, crystallinity, and its degree, chain orientation, void structure (void content, size, and specific interface), and fiber diameter.

Very long cellulosic macromolecules (as observed for viscose and acetate-type fibers) give rise to very high tensile strength fibers. It has also been found that even very high DPs can give a negative correlation to strength by changing the orienta­tion of the cellulosic chains (melting the cellulose and reforming it), by varying the crystallite dimension and crystallinity degree, by doping with contaminants or pores and by a native nonuniform fiber cross-section.23

Fibers that are too long would also excessively increase the viscosity and more­over would introduce rheopect behavior, which is unwanted in processing. An im­portant parameter in fiber-reinforced materials is the strength of bonding between the fibers and the matrix material.

To repeat, the reinforcing efficiency of lignocellulosic fibers is related to the nature of cellulose and its crystallinity. Indeed, because the crystallite is composed of an aggregate of tightly bound (almost fused) parallel-aligned chains, the material exhibits very little flexibility. The overall physical and chemical properties (e. g., tensile, density, stiffness, swellability, and heat response) of the cellulosics are es­sentially governed by the size, shape, and organization of the crystals. A higher degree of amorphous regions will increase extensibility (less flexibility) and reduce mechanical properties.24

Cellulose fibril aggregate isolation from wood pulp was described previously and has been modified over the years to successfully isolate high quality NFC by using high-shear homogenization or refining.25 Individual crystallites can be also obtained from wood pulp26 using hydrochloric (one of several mineral acids that can be used) or sulfuric acids. The action of the acid hydrolysis is predicated on a facile deconstruction/removal of the amorphous cellulosic regions in addition to facile dis­solution of the remaining polysaccharides, including the hemicelluloses and pectins. The acid acts by hydrolysis of the cellulosic macromolecules that are accessible by virtue of the noncrysallinity; what actually happens near the end of the hydrolysis is a leveling off of the DP (degree of polymerization) which corresponds to the resid­ual (basic) highly crystalline regions of the cellulose. At this point, a rapid dilution of the acid will cause the termination of the hydrolysis. Afterwards, the nanocrystals can be isolated by the combination of centrifugation and extensive dialysis (remov­ing acid and small molecular fragments) followed by a brief sonication to disperse the nanoparticles and provide an aqueous suspension.14

As discussed above, Chitosan (CH) is a unique polysaccharide derived from partial de-acetylation of chitin, which is, after cellulose, the most abundant nitrogen-rich polysaccharide. Chitosan is nontoxic, biodegradable, biocompatible and antibacte­rial and biologically renewable. CH has reactive amino (-NH2) and hydroxyl (-OH) groups that provide many possibilities for covalent and ionic modifications (Fig. 16.1). The advantages of CH are as follows: (a) CH intrinsically possesses strong biological activity, (b) it is biocompatible, biodegradable, bioresorbable and has a hydrophilic surface, which facilitates cell adhesion, proliferation and differentiation (c) due to its cationic nature in physiological pH, CH mediates nonspecific binding interactions with various proteins.19

Since then, CH material has been widely investigated in a number of biomedi­cal applications from wound dressings, drug or gene delivery systems, and nerve regeneration to space filling implant.1517

1.2.1 STRATEGIES FOR SPIDER SILK PROTEIN PRODUCTION

Several challenges remain to be resolved before spider silks can be truly manufac­tured on an industrial scale with mechanical properties that rival or exceed natural fibers. Firstly, scientists will need to develop cost-efficient, rapid methods to pro­duce large amounts of recombinantly expressed spider silk protein that can be easily purified. Secondly, and equally as important, chemical methodologies to spin silks from aqueous solvents needs to undergo substantial advancements. Although the tools of molecular biology and biochemistry have allowed many foreign proteins to be expressed and purified at high levels in bacteria and yeast, the high molecular masses of the silk proteins, combined with their biasness toward specific amino acids within their protein sequence, has presented technical challenges for the pro­duction of vast amounts of full-length, and even truncated recombinant dragline silk proteins for synthetic fiber production.

When GPE was used as a bio-based epoxy resin, direct mixing method of GPE with MFC (water content 90 wt.%) is possible, because GPE has much lower viscosity (150 cps, 25 °C) than SPE (5000 cps, 25 °C). For GPE/TA/MFC, the direct mix­ing method was compared with a water suspension method where 50% aqueous solution of GPE and TA in epoxy/hydroxy ratio 1/1 is mechanically mixed with MFC.21 The obtained mixtures were subsequently freeze-dried, and finally pressure — molded at 160 °C for 3 h. Figure 4.12 shows the comparison of tensile properties of the GPE/TA(1/1)/MFC biocomposites with fiber content 10 wt.% (GPE/TA(1/1)/ MFC10) prepared by both the methods. The GPE/TA(1/1)/MFC prepared by water suspension method had higher tensile strength and modulus than the GPE/TA(1/1)/ MFC by direct mixing method. Figure 4.13 shows the FE-SEM images of fracture surfaces of both the composites. It is obvious that the composite by water suspen­sion method has a better dispersion of MFC, and some aggregation of MFC is ap­peared for the composite by direct mixing method. In the following experiments, water suspension method was used for both the GPE/TA/MFC and SPE/TA/MFC because all the reagents except for MFC are water soluble.

20 rim

GPE/TAO/1)

GPE/TAO/1 )/MFC10 Water suspension

GPE/TA(1/1 )/MFC10 Direct mixing

FIGURE 4.13 FE-SEM images of the fracture surfaces of GPE/TA(1/1) and the GPE/ TA(1/1)/MFC10 biocomposites prepared by water suspension method and no solvent method.21

Figure 4.14 shows the relationship between tensile properties and fiber content for GPE/TA(1/1)/MFC and SPE/TA(1/1)/MFC. Tensile modulus increased with in­creasing fiber content for SPE/TA(1/1)/MFC, while the modulus did not improved for GPE/TA(1/1)/MFC. What GPE/TA(1/1) itself has much higher tensile modulus than SPE/TA(1/1) may be related to the difference of influence of fiber content on the modulus. The SPE/TA(1/1)/MFC10 (2660 MPa) had a 55% higher tensile strength than SPE/TA(1/1) (1710 MPa). Although SPE/TA(1/1)/MFC3 had a lower tensile strength than SPE/TA(1/1), the tensile strength of SPE/TA(1/1)/MFC increased with

fiber content over the range of 3-10 wt.%, and leveled off at around 15 wt.%. It is supposed that critical fiber content where the fracture mode is changed from matrix control to fiber control is around 3 wt.%. When the fiber content is not more than 3 wt.%, the MFC in the composite had been pull out or broken at the maximal stress point. The SPE/TA(1/1)/MFC10 (78.6 MPa) had a 30% higher tensile strength than SPE/TA(1/1) (60.6 MPa). In case of GPE/TA(1/1)/MFC, tensile strength increased with the fiber content over the range of 0-10 wt.%, and then dropped at 15 wt.%.

Figure 4.15 shows FE-SEM images of the fractured surfaces of GPE/TA(1/1)/ MFC composites. The fractured surface of GPE/TA(1/1) is very smooth, indicating brittle crack propagation, as is shown in Fig. 4.13. On the other hand, uneven cor­rugation with the size of several tens micrometers was observed on the fractured surface of GPE/TA(1/1)/MFC3, indicating heterogeneous distribution of MFC. The uneven texture became more homogeneous and finer with increasing amount of MFC, and GPE/TA(1/1)/MFC10 had a rough surface, suggesting a complex fracture process involving both localized deformation of the matrix polymer as well as local interaction of finely dispersed MFC with cracks formed in the matrix. However, GPE/TA(1/1)/MFC15 showed bigger and more heterogeneous uneven texture than GPE/TA(1/1)/MFC10 did. This result suggests that some aggregation of MFC oc­curs for GPE/TA(1/1)/MFC15. Figure 4.16 shows FE-SEM images of the fractured surfaces of SPE/TA(1/1)/MFC composites. The heterogeneous texture observed for GPE/TA(1/1)/MFC3 and GPE/TA(1/1)/MFC5 was not appeared for SPE/TA(1/1)/ MFC composites. The relatively homogenous surface gradually became rougher with an increase of MFC content over the range from 3 to 15 wt.%. These results suggest that SPE/TA(1/1)/MFC composites have better dispersion of MFC than GPE/TA(1/1)/MFC composites do, and that the aggregation of MFC does not occur even at MFC content 15 wt.%.

GPE/TA(1/1)/MFC3

GPE/TA(1/1)/MFC5

GPE/TA(1 /1 )/MFC10

GPE/TA(1/1)/MFC15

Figures 4.17 and 4.18 show the temperature dependency of E and tan d for GPE/TA(1/1)/MFC and SPE/TA(1/1)/MFC measured by DMA, respectively. The E’ at the rubbery plateau region over 100 °C increased with MFC content for both the composites, suggesting a good dispersion of MFC in the matrix is attained. The tan S peak temperature related to Eg increased a little with MFC content for both the composites, indicating that there is some interaction between MFC and crosslinked epoxy resins. The composites composed of MFC and the bisphenol F-type epoxy resin (BPE) cured with polyether amine (PEA) is known to have a little lower tan S peak temperature than the control cured epoxy resin (BPE/PEA), and that the peak temperature rises up to the value as high as the control by using the MFC surface — modified with 3-aminopropyltriethoxysilane (AMFC).66 Table 4.5 summarizes the DMA data of various epoxy resins and their MFC composites. The E’ at 30 and 130 °C and tan S peak temperature of bio-based epoxy resin systems, GPE/TA(1/1) and SPE/TA(1/1), are comparable to those of petroleum-based epoxy resin system, BPE/PEA. Also, the biocomposites, GPE/TA(1/1)/MFC5 and SPE/TA(1/1)/MFC5 had higher E at 130 °C than did BPE/PEA/MFC5 and BPE/PEA/AMFC5. In agree­ment with the results of DMA, the Eg measured by TMA rose with MFC content. The coefficient of thermal expansion’s (CTE’s) below Eg and above Eg somewhat increased with MFC content (Tables 4.5 and 4.6). The density of both the compos­ites (1.3-1.2) a little decreased with MFC content. Considering that the density of cellulose fiber such as cotton is ca. 1.5, micro bubbles or voids are contaminated into the composites. Although we focused on the properties of the biocomposites prepared by a general procedure, a better result should be obtained by the addition of homogenizing operations such as sonication and subsequent vacuum degassing.

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