Home About us Contact
|
Home About us Contact | ||
|
|
||
Thermomechanical Properties (thermomechanical + property)
Selected AbstractsEffect of Green Density on the Thermomechanical Properties of a Ceramic During SinteringJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2006Sam E. Schoenberg The thermomechanical properties of a commercial barium titanate were experimentally or theoretically determined for samples with green densities ranging from 45% to 55%. For stresses less than 300 kPa, sample deformation was determined to be linear viscous for all three stages of sintering. The shrinkage rates at a given temperature can differ by up to ,25% as the green density changes from 45% to 55%, and the maximum shrinkage rate increased with decreasing green density. The increase in shrinkage rate with lower green density samples persisted through the final sintering stage. The viscosity was determined by cyclic loading dilatometry to range from 5 to 6 GPa·s in the initial stage of sintering, to 2 GPa·s in the intermediate stage, and to increase to 10,20 GPa·s for all specimens in the final stage of sintering. Differences in the final-stage viscosity were attributed to grain size differences. Relaxation times for the sintering body were estimated to be less than 1 s, indicating that viscous behavior is dominant throughout the sintering process. [source] The Effect of Nanofiller on the Thermomechanical Properties of Polyimide/Clay NanocompositesMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 6 2008Khine Yi Mya Abstract The interaction between PI and partially exfoliated clay nanofillers is investigated by studying the thermomechanical properties of the resulting nanocomposites by NMR, XPS, XRD, TEM, TGA, TMA, and DMA. XRD and TEM showed more exfoliated structure at ,2.5 wt.-% clay and a macrophase separation above 2.5 wt.-% clay. Td and the storage modulus increased with increasing clay content. A decrease in CTE was observed for clay content ,2.5 wt.-% because of the good dispersion of the clay in the polymer and the reduced segmental motion of polymer matrix. NMR confirmed the quality of clay dispersion, and XPS exhibited that the interaction in PI/2.5 wt.-% clay is much stronger than that in PI/5 wt.-% clay. [source] Exploiting Chemical Switching in a Diels,Alder Polymer for Nanoscale Probe Lithography and Data Storage,ADVANCED FUNCTIONAL MATERIALS, Issue 11 2006B. Gotsmann Abstract Reversibly crosslinked polymer films have properties that are beneficial to scanned-probe data storage and lithographic applications that use thermomechanical nanoindentation as a write or expose mechanism. The novel polymer under study contains linkages based on thermally reversible Diels,Alder crosslinking. Thermomechanical properties on the nanometer scale are analyzed by indentation experiments on polymer thin films using heated tips. The underlying indentation mechanism is studied at varying tip temperatures and indentation times, revealing Arrhenius kinetics. This is in contrast to the Williams,Landau,Ferry kinetics usually observed for polymer systems. The discrepancy is explained by the reversible crosslinking incorporated into the structure of the polymer that allows switching between two different states: a rigid, highly crosslinked, low-temperature state, and a deformable, fragmented, high-temperature state. An individual indentation volume of less than 10,20,L (10,000,molecule pairs) is estimated. These kinetics experiments demonstrate that a chemical reaction of only a few thousand molecules can be transduced into a mechanically measurable action. The ability to cycle between two sets of properties in these materials opens up new perspectives in lithography and data storage. Examples of data storage with densities up to 1,Tb,in.,2 and maskless lithography with resolution below 20,nm are demonstrated at writing times of 10,,s per bit/pixel. [source] Colorless polyimide nanocomposite films: Thermomechanical properties, morphology, and optical transparencyJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Hyo-Seong Jin Abstract Polyimide (PI)/organoclay hybrid films were prepared by the solution intercalation method, using dodecyltriphenylphosphonium-mica (C12PPh-Mica) as the organoclay. The variations with organoclay content of the thermomechanical properties, morphology, and optical transparency of the hybrids were examined for concentrations from 0 to 1.0 wt %. For low clay contents (, 0.5 wt %), the clay particles are better dispersed in the matrix polymer, without the formation of large agglomerates of particles, than they are for high clay contents. However, agglomerated structures form and become denser in the PI matrix for clay contents , 0.75 wt %. This is in agreement with the observed trends in the thermomechanical properties and the optical transparency, which worsen drastically when the clay content of the C12PPh-Mica/PI hybrids reaches 0.75 wt %. However, when the amount of organoclay in the hybrid is 0.75 wt %, the initial modulus of the hybrid film is at its maximum value. The PI hybrid films were found to exhibit excellent optical transparencies and to be almost colorless. It was found, however, that the transparency decreases slightly with increases in the organoclay content because of agglomeration of the clay particles. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Thermomechanical properties of virgin and recycled polypropylene impact copolymer/CaCO3 nanocompositesPOLYMER ENGINEERING & SCIENCE, Issue 10 2010A. Elloumi The effect of successive injection moldings on the thermal, rheological, and mechanical properties of a polypropylene impact copolymer (PP) was investigated. The crystal content decreased as the molecular weight decreased due to chain scission with repeated injection molding. The Young modulus and the yield stress remained constant, despite a drop in the strain to break. Virgin and recycled PP matrix were filled with nanosized calcium carbonate (CaCO3) particles. The effect of morphology on the thermal and mechanical properties of nanocomposites of virgin and recycled PP filled with nanosized CaCO3 particles was also studied. The mechanical properties of the nanocomposites were strongly influenced by the intrinsic toughness of the matrix and the concentration and dispersion of the filler. The yield strength and strain of virgin PP decreased gradually, while its Young's modulus increased slightly with increasing CaCO3 loading. These phenomena were less pronounced for the recycled matrix. Incorporation of nanoparticles to virgin matrix produced an increase in tensile stiffness and ductility, when good dispersion of the filler was achieved. However, the impact strength dropped dramatically for high filler contents. A significant increase in impact strength was observed for the recycled PP. POLYM. ENG. SCI., 50:1904,1913, 2010. © 2010 Society of Plastics Engineers [source] Some important aspects in designing high molecular weight poly(L -lactic acid),clay nanocomposites with desired propertiesPOLYMER INTERNATIONAL, Issue 12 2008Subhendu Ray Chowdhury Abstract BACKGROUND: The main aim of the work reported here was to investigate the effect of clay aspect ratio and functional edge group on the dispersion, degree of order of clays and interfacial strength of high molecular weight poly(L -lactic acid) (PLLA),clay amorphous nanocomposites and consequently their properties. Three kinds of clays (two montmorillonites (SMMTC18 and NMMTC18) and one fluoro-mica (MC18) with the same surfactant) were used to synthesize three amorphous nanocomposites. Thermomechanical properties, permeability, etc., were compared among composites and with pure PLLA. RESULTS: From X-ray diffraction and transmission electron microscopy, both MMTs with lower aspect ratio showed better dispersion and greater degree of disorder, which led to stronger interfacial strength and consequently higher storage modulus than MC18-based composites. All composites showed better properties than pure PLLA. The oxygen barrier efficiencies of SMMTC18- and NMMTC18-based composites were higher than that of the MC18-based composites. Due to the highest exposed area and probably stronger interactions, SMMTC18 had the highest nucleating efficiency. CONCLUSIONS: Along with aspect ratio, dispersion and degree of intercalation, the interfacial strength of composites and degree of order of clays are also important issues for property development. Compared to reported results in the literature, our amorphous composites showed less of an improvement of thermomechanical properties as real reinforcement was solely from clays. Copyright © 2008 Society of Chemical Industry [source] Structure and properties of cross-linked polyurethane copolymersADVANCES IN POLYMER TECHNOLOGY, Issue 3 2009S. Oprea Abstract Polyurethane elastomers based on polyester diols and aromatic or aliphatic diisocyanates can be used as vibration dampers and isolation materials. Two series of cross-linked polyurethanes with various hard segment structures and different amounts were prepared and thermomechanical properties of these materials were studied. Cross-linked polyurethane copolymers composed of poly(ethylene adipate)diol as soft segment and 4,4,-methylenebis(phenylisocyanate), 1,6-hexamethylene diisocyanate, and diols glycerin, 1,4-butanediol, and 1,6-hexanediol as hard segments were synthesized by a two-step process. The networks have been prepared by end-linking a mixture of the bifunctional precursor chains with trifunctional cross-linkers at off-stoichiometric ratios. The results show that the cross-link and the polyurethane hard segment interaction play a special role in the interconnected chain density and its magnitude is revealed by the mechanical properties. Of most importance, maximum stress, tensile modulus, and elongation at break increased significantly at the 22 wt % composition of hard segment content. Interchain cross-linking improves thermal stability, which was measured by thermogravimetric analysis and differential scanning calorimetry. Cross-linked polyurethane behaves as an elastomer and is useful for shock, noise, and vibration control. © 2009 Wiley Periodicals, Inc. Adv Polym Techn 28:165,172, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20155 [source] Microstrain and grain-size analysis from diffraction peak width and graphical derivation of high-pressure thermomechanicsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2008Yusheng Zhao An analytical method is presented for deriving the thermomechanical properties of polycrystalline materials under high-pressure (P) and high-temperature (T) conditions. This method deals with non-uniform stress among heterogeneous crystal grains and surface strain in nanocrystalline materials by examining peak-width variation under different P,T conditions. Because the method deals directly with lattice d spacing and local deformation caused by stress, it can be applied to process any diffraction profile, independent of detection mode. In addition, a correction routine is developed using diffraction elastic ratios to deal with severe surface strain and/or strain anisotropy effects related to nano-scale grain sizes, so that significant data scatter can be reduced in a physically meaningful way. Graphical illustration of the resultant microstrain analysis can identify micro/local yields at the grain-to-grain interactions resulting from high stress concentration, and macro/bulk yield of the plastic deformation over the entire sample. This simple and straightforward approach is capable of revealing the corresponding micro and/or macro yield stresses, grain crushing or growth, work hardening or softening, and thermal relaxation under high- P,T conditions, as well as the intrinsic residual strain and/or surface strain in the polycrystalline bulk. In addition, this approach allows the instrumental contribution to be illustrated and subtracted in a straightforward manner, thus avoiding the potential complexities and errors resulting from instrument correction. Applications of the method are demonstrated by studies of ,-SiC (6H, moissanite) and of micro- and nanocrystalline nickel by synchrotron X-ray and time-of-flight neutron diffraction. [source] Effect of glucose crosslinking on thermomechanical properties and shape memory effect of PET-PEG copolymersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Yong-Chan Chung Abstract Poly(ethylene terephthalate) (PET) and poly (ethylene glycol) (PEG) copolymers crosslinked with glucose as a crosslinker are prepared to improve their mechanical and shape memory properties compared to the one without crosslinking. Composition of PEG and glucose is varied to search for the one with the best mechanical and shape memory properties. The highest shape recovery rate is found in the copolymer composed of 25 mol % PEG-200 and 2.0 mol % glucose. The result that crosslinking by glucose improves the shape recovery rate and supports the high shape recovery rate under the repetitive cyclic test conditions, compared to the one without crosslinking, will be discussed in the points of the structure and shape memory mechanism. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Colorless polyimide nanocomposite films: Thermomechanical properties, morphology, and optical transparencyJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Hyo-Seong Jin Abstract Polyimide (PI)/organoclay hybrid films were prepared by the solution intercalation method, using dodecyltriphenylphosphonium-mica (C12PPh-Mica) as the organoclay. The variations with organoclay content of the thermomechanical properties, morphology, and optical transparency of the hybrids were examined for concentrations from 0 to 1.0 wt %. For low clay contents (, 0.5 wt %), the clay particles are better dispersed in the matrix polymer, without the formation of large agglomerates of particles, than they are for high clay contents. However, agglomerated structures form and become denser in the PI matrix for clay contents , 0.75 wt %. This is in agreement with the observed trends in the thermomechanical properties and the optical transparency, which worsen drastically when the clay content of the C12PPh-Mica/PI hybrids reaches 0.75 wt %. However, when the amount of organoclay in the hybrid is 0.75 wt %, the initial modulus of the hybrid film is at its maximum value. The PI hybrid films were found to exhibit excellent optical transparencies and to be almost colorless. It was found, however, that the transparency decreases slightly with increases in the organoclay content because of agglomeration of the clay particles. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Preparation and thermomechanical properties of epoxy resins modified by octafunctional cubic silsesquioxane epoxidesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2004Khine Yi Mya Abstract The thermomechanical properties of octafunctional cubic silsesquioxane-modified epoxy resins associated with dicycloaliphatic hardener (4,4,-dimethyldiaminodicyclo hexyl methane) were studied using thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis. The structures of epoxy resin containing cubic silsesquioxane epoxides were characterized by Fourier transform infrared spectroscopy and wide-angle X-ray scattering techniques. In this work, octa(dimethylsiloxybutylepoxide) octasilsesquioxane (OB), and octa(glycidyldimethyl-siloxyepoxide) octasilsesquioxane (OG), were synthesized and used as additives to improve the properties of a commercial epoxy resin by exploring the effects of varying the ratio of OB or OG. The commercial Ciba epoxy resin (Araldite LY5210/HY2954) was used as a standard. It was found, by thermogravimetric analysis and dynamic mechanical analysis, that the highest thermal stability was observed at N = 0.5 (N = number of amine groups/number of epoxy rings). No glass transition temperature was observed by adding 20 mol % OB to the Ciba epoxy resin, indicating the reduction of chain motion in the presence of octafunctional cubic silsesquioxane epoxide. The storage modulus of the OB-modified epoxy resin also increased, especially at higher temperatures, compared with the Ciba epoxy resin under identical curing conditions. Fourier transform infrared data elucidated the preservation of cubic silsesquioxane structure after curing at high temperature. In contrast, the OG/Araldite LY5210/HY2954 systems gave poorer thermomechanical properties. The low viscosity of OB at room temperature (, 350 cPs) makes it suitable for composite processing and, when used in conjunction with the Ciba epoxy, lowers the viscosity of this system as well. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3490,3503, 2004 [source] Mechanical Properties and Dimensional Effects of ZnO- and SnO2 -Based VaristorsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2008Miguel Angel Ramírez A comparison between traditional ZnO-(modified Matsuoka system, [ZnO]) and SnO2 -based varistors (98.9%SnO2+1%CoO+0.05%Nb2O5+0.05%Cr2O3, [SCNCr]) regarding their mechanical properties, finite element (FE) modeling, and macroscopic response with current pulse is presented in this work. The experimental values of the elastic (static and dynamic) modulus and bending strength are given. Both the static and the dynamic modulus were two times higher for SnO2 (,200 GPa) with respect to ZnO (,100 GPa). A similar behavior was found for the bending strength, confirming the superior mechanical properties of SCNCr associated with a homogeneous microstructure. The finite element analyses yielded the most appropriate thickness/diameter aspect ratio (H/D), while thermomechanical stress is minimized. The values of (H/D) were lower for the SCNCr in comparison with the ZnO-based varistors, allowing the production of smaller pieces that can resist the same thermomechanical stress. Finally, preliminary analyses of the macroscopic failures for samples treated with degradation pulses of 8/20-,s type allowed to confirm the absence of failures due to cracking and/or puncture in the SCNCr. The absence of these failures originates from the good thermomechanical properties. [source] The Effect of Nanofiller on the Thermomechanical Properties of Polyimide/Clay NanocompositesMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 6 2008Khine Yi Mya Abstract The interaction between PI and partially exfoliated clay nanofillers is investigated by studying the thermomechanical properties of the resulting nanocomposites by NMR, XPS, XRD, TEM, TGA, TMA, and DMA. XRD and TEM showed more exfoliated structure at ,2.5 wt.-% clay and a macrophase separation above 2.5 wt.-% clay. Td and the storage modulus increased with increasing clay content. A decrease in CTE was observed for clay content ,2.5 wt.-% because of the good dispersion of the clay in the polymer and the reduced segmental motion of polymer matrix. NMR confirmed the quality of clay dispersion, and XPS exhibited that the interaction in PI/2.5 wt.-% clay is much stronger than that in PI/5 wt.-% clay. [source] Thermomechanical studies of aluminum nitride filled shape memory polymer compositesPOLYMER COMPOSITES, Issue 3 2007Muhammad Yasar Razzaq High thermal conductivity polyurethane shape memory polymer (SMP) composites filled with aluminum nitride (AlN) were fabricated, and their thermal and thermomechanical properties were studied. The purpose of this microstructure is to improve the thermal properties of the SMPs at low filler content. Morphology of AlN filler in polyurethane SMP matrix and the resulting thermal conductivity was also investigated. Thermal studies have shown that AlN is an effective filler for reinforcement of the polyurethane SMP and that it does not deteriorate the stable physical crosslink structure of the polyurethane, which is necessary to store the elastic energy in the service process of the shape memory material. The thermal conductivities of these SMP composites in relation to filler concentration and temperature were investigated, and it was found that the thermal conductivity can increase up to 50 times in comparison with that of the pure SMP. Furthermore, differential scanning calorimetry tests have shown a significant decrease in the glass transition temperature of the switching segment. Dynamic mechanical studies have shown that the storage modulus of the composites increase with higher AlN content in both glassy and rubbery state. Damping peak decreases and also the curve of damping becomes broader with increasing filler content. Strain fixity rate which expresses the ability of the specimens to fix their strain has been improved slightly in the presence of AlN filler but the final recovery rate of the shape memory measurement has decreased evidently. POLYM. COMPOS., 28:287,293, 2007. © 2007 Society of Plastics Engineers [source] The effects of alumina and silica nanoparticles on the cure kinetics of bisphenol E cyanate esterPOLYMER ENGINEERING & SCIENCE, Issue 6 2010Xia Sheng Nanoparticles can be used as fillers to reinforce polymers, forming nanocomposites with better thermomechanical properties than composites with macrosized fillers. Furthermore, the addition of nanoparticles may influence the curing behavior of the polymer matrix during processing. In this study, the effect of various loadings of alumina or silica nanoparticles on the cure kinetics of bisphenol E cyanate ester (BECy) is investigated by differential scanning calorimetry (DSC). Alumina nanoparticles are shown to have a catalytic effect on the cure of BECy. The greater catalytic effect of alumina nanoparticles, compared with silica, is attributed to the increased number of hydroxyl groups on the surface and the Lewis acidity of ,-phase alumina. Kinetic parameters were obtained from dynamic DSC experiments. For an autocatalytic model of the cure process, the kinetic parameters obtained from the model suggest that the addition of alumina nanoparticles changed the cure reaction mechanism of BECy. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers [source] Film extrusion of sunflower protein isolatePOLYMER ENGINEERING & SCIENCE, Issue 11 2006Antoine Rouilly Film extrusion of sunflower protein isolate (SFPI) was studied. The influence of die temperature (85,160°C), water and glycerol contents were investigated through appearance, mechanical and thermomechanical properties, and swelling behavior in water of films. It was demonstrated that highest temperature, well above SFPI denaturation temperature in the compound, highest glycerol content (70 parts for 100 parts of SFPI), and medium water content (20 parts for 100 parts of SFPI) gave the most regular and smoothest film (as seen on SEM micrographs). Its ultimate tensile strength, Young's modulus, and strain at break were, respectively, 3.2 MPa, 17.7 MPa, and 73%. Soaked in water, its swelling was about 186% w/w but the film was quiet insoluble. Effect of temperature and plasticizer content were discussed in relation to the kinetic of SFPI denaturation. These first results are very promising for the development of biodegradable protein-based films. POLYM. ENG. SCI. 46:1635,1640, 2006. © 2006 Society of Plastics Engineers. [source] Influence of the rubbery phase on the crystallinity and thermomechanical properties of poly(3-hydroxybutyrate)/elastomer blendsPOLYMER INTERNATIONAL, Issue 6 2010Patrícia S Calvão Abstract Poly(3-hydroxybutyrate) (PHB) is a very promising biopolymer. In order to improve its processability and decrease its brittleness, PHB/elastomer blends can be prepared. In the work reported, the effect of the addition of a rubbery phase, i.e. ethylene,propylene,diene terpolymer (EPDM) or poly(vinyl butyral) (PVB), on the properties of PHB was studied. The effects of rubber type and of changing the PHB/elastomer blend processing method on the crystallinity and physical properties of the blends were also investigated. For blends based on PHB, the main role of EPDM is its nucleating effect evidenced by a decrease of crystallization temperature and an increase of crystallinity with increasing EPDM content regardless of the processing route. While EPDM has a weak effect on PHB glass transition temperature, PVB induces a marked decrease of this temperature thank to its plasticizer that swells the PHB amorphous phase. A promising solution to improve the mechanical properties of PHB seems to be the melt-processing of PHB with both plasticizer and EPDM. In fact, the plasticizer is more efficient than the elastomer in decreasing the PHB glass transition temperature and, because of the nucleating effect of EPDM, the decrease of the PHB modulus due to the plasticizer can be counterbalanced. Copyright © 2010 Society of Chemical Industry [source] An investigation of the effect of silane water-crosslinking on the properties of poly(L-lactide)POLYMER INTERNATIONAL, Issue 5 2010Changyu Han Abstract A silane-grafting water-crosslinking approach was developed to crosslink poly(L -lactide) (PLLA) by grafting vinylalkoxysilane onto PLLA using dicumyl peroxide, followed by silane hydrolysis to form siloxane linkages between PLLA chains. The degree of silane grafting onto PLLA was qualitatively characterized using Fourier transform infrared spectroscopy and quantitatively determined using inductively coupled plasma mass spectrometry. Crosslinked PLLA films were obtained by curing of silane-grafted PLLA in hot water. Gel fractions were evaluated in order to calculate the crosslinking reaction kinetics and crosslinking density. Various techniques were used to investigate the effect of silane water-crosslinking on the thermomechanical properties, hydrolysis resistance and biodegradation of PLLA. In addition to an improvement in thermal stability and mechanical properties, hydrolysis resistance was significantly enhanced as a result of silane water-crosslinking of PLLA. Moreover, the biodegradation of silane water-crosslinked PLLA was retarded compared with neat PLLA. Copyright © 2010 Society of Chemical Industry [source] Some important aspects in designing high molecular weight poly(L -lactic acid),clay nanocomposites with desired propertiesPOLYMER INTERNATIONAL, Issue 12 2008Subhendu Ray Chowdhury Abstract BACKGROUND: The main aim of the work reported here was to investigate the effect of clay aspect ratio and functional edge group on the dispersion, degree of order of clays and interfacial strength of high molecular weight poly(L -lactic acid) (PLLA),clay amorphous nanocomposites and consequently their properties. Three kinds of clays (two montmorillonites (SMMTC18 and NMMTC18) and one fluoro-mica (MC18) with the same surfactant) were used to synthesize three amorphous nanocomposites. Thermomechanical properties, permeability, etc., were compared among composites and with pure PLLA. RESULTS: From X-ray diffraction and transmission electron microscopy, both MMTs with lower aspect ratio showed better dispersion and greater degree of disorder, which led to stronger interfacial strength and consequently higher storage modulus than MC18-based composites. All composites showed better properties than pure PLLA. The oxygen barrier efficiencies of SMMTC18- and NMMTC18-based composites were higher than that of the MC18-based composites. Due to the highest exposed area and probably stronger interactions, SMMTC18 had the highest nucleating efficiency. CONCLUSIONS: Along with aspect ratio, dispersion and degree of intercalation, the interfacial strength of composites and degree of order of clays are also important issues for property development. Compared to reported results in the literature, our amorphous composites showed less of an improvement of thermomechanical properties as real reinforcement was solely from clays. Copyright © 2008 Society of Chemical Industry [source] Biocomposites based on plasticized starchBIOFUELS, BIOPRODUCTS AND BIOREFINING, Issue 3 2009Luc Avérous Abstract The potential of biodegradable polymers, and more particularly that of polymers obtained from agro resources, such as polysaccharides like starch, has long been recognized. This paper examines the effects of sustainable materials based on starch on the macro or nanostructure and subsequent processing, thermomechanical properties and performance properties of plasticized starch polymers. This examination includes a detailed review of the complexity of starch polymers, recent advances in novel starch modifications and compounds, and a detailed examination of the effects of plasticized starch macro-biocomposites and nano-biocomposites. Specific structures and subsequent properties are controlled by many specific factors, such as filler shape, size and surface chemistry, processing conditions and environmental aging. In the case of nano-biocomposites, it is evident that nanomaterials polymer matrix interfacial interactions are extremely important to the final nanostructures and performance of these materials. © 2009 Society of Chemical Industry and John Wiley & Sons, Ltd [source] Metabolic Carbon Fluxes and Biosynthesis of Polyhydroxyalkanoates in Ralstonia eutropha on Short Chain Fatty AcidsBIOTECHNOLOGY PROGRESS, Issue 4 2004Jian Yu Short chain fatty acids such as acetic, propionic, and butyric acids can be synthesized into polyhydroxyalkanoates (PHAs) by Ralstonia eutropha. Metabolic carbon fluxes of the acids in living cells have significant effect on the yield, composition, and thermomechanical properties of PHA bioplastics. Based on the general knowledge of central metabolism pathways and the unusual metabolic pathways in R. eutropha,a metabolic network of 41 bioreactions is constructed to analyze the carbon fluxes on utilization of the short chain fatty acids. In fed-batch cultures with constant feeding of acid media, carbon metabolism and distribution in R. eutropha were measured involving CO2, PHA biopolymers, and residual cell mass. As the cells underwent unsteady state metabolism and PHA biosynthesis under nitrogen-limited conditions, accumulative carbon balance was applied for pseudo-steady-state analysis of the metabolic carbon fluxes. Cofactor NADP/NADPH balanced between PHA synthesis and the C3/C4 pathway provided an independent constraint for solution of the underdetermined metabolic network. A major portion of propionyl-CoA was directed to pyruvate via the 2-methylcitrate cycle and further decarboxylated to acetyl-CoA. Only a small amount of propionate carbon (<15% carbon) was directly condensed with acetyl-CoA for 3-hydroxyvalerate. The ratio of glyoxylate shunt to TCA cycle varies from 0 to 0.25, depending on the intracellular acetyl-CoA level and acetic acid in the medium. Malate is the node of the C3/C4 pathway and TCA cycle and its decarboxylation to dehydrogenation ranges from 0.33 to 1.28 in response to the demands on NADPH and oxaloacetate for short chain fatty acids utilization. [source] | |||||||||||||