bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preparation and Properties of Metallocene-catalyzed PE/Starch Nanocomposites: Role of Nanocompatibilizer
Authors: Lai S.-M. , Ti K.-T. 
Published: November 2007

Abstract
The properties of metallocene catalyzed polyethylene (mPE)/starch blends and nanocomposites containing mPE-g-maleic anhydride (mPE-g-MA) compatibilizer, reinforced with 1 phr commercial organoclay (20A) at various amounts of pristine starch are discussed. The results from X-ray diffraction (XRD) and transmission electron microscope (TEM) experiments revealed that nanocomposites were achieved in all cases. No observable diffraction peaks in the low angle region were detected. Clay was preferentially located within the mPE and starch interface and the mPE matrix. The crystallization temperatures of nanocomposites increased with the addition of clay acting as a nucleating agent. However, the melting temperatures and the glass transition temperatures remained largely unchanged. Clay incorporation provided a heat barrier that profoundly increased the blend thermal stability. A maximum increase in tensile strength and Young's modulus was obtained, up to 60% and 105%, respectively, using nanoclay reinforced compatibilizer (termed nanocompatibilizer) in comparison with neat compatibilizer for pristine starch filled cases. Slightly lower water absorption capability was observed for nanocompatibilizer reinforced cases through the sheet-like structure of clay compared with neat compatibilizer cases.
Effects of Starch Types on Mechanical Properties of Poly(lactic acid)/Starch Composites
Authors: Sun X. S. , Acioli-Moura R. , Li W. 
Published: November 2007

Abstract
Poly(lactic acid) (PLA) and its blends with starch and methylenediphenyl diisocyanate (MDI) were extruded in a twin-screw extruder and compress-molded in a dog-bone shaped tensile bars to form test specimens. The effects of starch types (rice, corn, wheat, and potato) on mechanical properties of the PLA/starch/MDI composites were evaluated. Starch type and granule size had no significant effects on mechanical properties of the composite. But crystallinity of the composite decreased as the starch granule size increased. Potato starch was used to study effects of granule size (19 to 63 μm) on mechanical properties of the PLA/starch composites. Both tensile strength and elongation of the PLA/starch/MDI (55/45/0.5) composites reduced slightly as starch granule size increased from 19 to 63 μm. While crystallinity of the composites was significantly decreased as granule size increased. Modulus of the composites remained the same regardless starch types and granule size.
Rheological Evaluation and Observations of Extrusion Instabilities of Biodegradable Polyesters
Authors: Kanev D. , Takacs E. , Vlachopoulos J. 
Published: November 2007

Abstract
The rheological properties of two commercially available biodegradable polyesters – poly(lactic acid) (PLA) and aliphatic-aromatic co-polyester Ecoflex™ – have been investigated. The rheological study was focused on measuring the viscosity and examining sharkskin, melt fracture, and extrudate swell phenomena, which are crucial in industrial applications. The experiments show that the two biodegradable polyesters exhibit shear-thinning behavior similar to other polymers and the Cox-Merz rule is obeyed. It was observed that with increasing shear rate PLA exhibits sharkskin and gross melt fracture while Ecoflex™ exhibits only gross melt fracture. Experimental results indicate that both biodegradable polyesters exhibit small extrudate swell, up to 28% for PLA and up to 34% for Ecoflex™.
Tapioca Starch-poly (lactic acid)-based Nanocomposite Foams as Affected by Type of Nanoclay
Authors: Lee S.-Y. , Xu Y. X. , Hanna M. A. 
Published: November 2007

Abstract
Tapioca starch (TS), poly (lactic acid) (PLA), and clay nanocomposite foams, with three clays (Cloisite 30B, Na+, and 20A), were prepared by melt-intercalation method. The structural, thermal, physical and mechanical properties were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and Instron universal testing machine, respectively. XRD results indicated that the intercalation of TS/PLA into the nanoclay layers occurred for all three clays. The extents of intercalation depended on the types of clay and were exhibited in the sequence of Cloisite 30B>Na+ > 20A. At the same time, a mixture of intercalation and tactoid phenomena was observed for the TS/PLA/Cloisite Na+ nanocomposite. SEM results indicated a decrease in cell size of the TS/PLA foam matrix with the addition of nanoclay and cells had hexagonal and pentagonal shapes. Melting temperature (Tm) decreased with the addition of clays into TS/PLA matrix. Expansion ratios of the nanocomposites were significantly different (p<0.05) from each other. TS/PLA/Cloisite Na+ nanocomposite had the highest expansion ratio of 20.9 compared to its TS/PLA/Cloisite 20A (9.65) and TS/PLA/Cloisite 30B counterparts (8.23). Addition of Cloisite Na+ resulted in the lowest unit density of 0.046 kg/m3, while no significant differences in unit density were observed for the foams with addition of Cloisite 30B and Cloisite 20A. Bulk spring index (BSI) was influenced significantly (p<0.05) with the addition of nanoclays into the TS/PLA matrix. TS/PLA/Cloisite Na+ nanocomposite had the lowest BSI of 0.936. The bulk compressibility was decreased from 14.1MPa for pure tapioca starch foam to 4.45MPa with the addition of PLA. The nanocomposite with Cloisite 30B showed the highest value of 17.4MPa, followed by those with Cloisite 20A (10.4MPa), and Cloisite Na+ (6.47MPa).
Viscous Properties of Thermoplastic Starches from Different Botanical Origin
Authors: Valle G. Della , Vergnes B. , Lourdin D. 
Published: November 2007

Abstract
Starches from various botanical origins were plasticized in a twin screw extruder with different glycerol contents (from 23 to 32%, total wet basis) in order to prepare pellets of amorphous thermoplastic starches (TPS) that can further be processed for manufacturing purposes. The viscous behaviour of these starches was studied with a capillary pre-shearing rheometer, which achieved an homogeneous molten phase under controlled thermomechanical conditions. After performing Bagley corrections and Rabinowitsch analysis, it was found that all samples exhibited a non-Newtonian shear-thinning behaviour, which could be modeled in the range 1 to 103 s−1 either by a simple power law or by a Herschel-Bulkley relationship. For the consistency index, the influence of temperature and plasticizer content was accounted for by Arrhenius-like laws, applying time-temperature and time-plasticizer superposition. For the same plasticizer content and temperature, comparison of starches from different botanical origins showed that shear viscosity values usually increased with the starch amylose content. This trend was partly confirmed for the elongational behaviour, estimated by the Cogswell's analysis of entrance effects. These results can be interpreted by the greater ability of linear molecules of amylose to entangle, compared to the more compact amylopectin molecules.
Biocomposites Based on Bacterial Cellulose and Apple and Radish Pulp
Authors: Gea S. , Torres F. G. , Troncoso O. P. , Reynolds C. T. , Vilasecca F. , Iguchi M. , Peijs T. 
Published: November 2007

Abstract
Bacterial cellulose (BC) pellicles obtained from an Acetobacter xylinum culture were disintegrated using mechanical methods to be used as reinforcement to produce biocomposite sheets with Apple and Radish Pulp. The nanosize disintegrated BC pellicles were blended with microsize apple and radish pulp in the wet state and then hot pressed to produce paper-like sheets.
Thermal analysis was carried out by Thermogravimetry Analysis (TGA). Mechanical properties were assessed by Quasistatic Tensile Tests and Dynamic Mechanical Analysis (DMA). High tensile moduli were obtained (up to 8 GPa) and a nearly linear dependence of Young's modulus on the BC volume fraction was observed. Morphological characterisation of biocomposite sheets and fracture surfaces performed by Scanning Electron Microscopy (SEM) revealed the structure of the disintegrated cellulose network and the failure mechanisms of the biocomposites.
Evaluation of Properties and Biodeterioration Potential of Polyethylene and Aliphatic Polyester Blends
Authors: Machado A. V. , Moura I. , Duarte F. M. , Botelho G. , Nogueira R. , Brito A. G. 
Published: November 2007

Abstract
Blends of high density polyethylene (HDPE) and biodegradable polymers – polylactic acid, PLA, poly(∊-caprolactone), PCL and Mater-Bi® (thermoplastic starch (TPS) with PLA or PCL) – were prepared in a co-rotating twin-screw extruder, together with polyethylene modified with maleic anhydride (PE-g-MA) used as compatibiliser. The mechanical and rheological properties, morphology and potential for biodeterioration of polymeric materials were evaluated. Blends with PLA showed a reduced elongation at break but an increased Young's modulus while the addition of PCL led to materials with a greater elongation at break and a lower Young modulus. The rheological results evidenced that HPDE and the blend with the highest TPS level exhibited the highest viscosity. The microbial growth test carried out to evaluate the potential for biodeterioration of the blends, using a pure culture of Pseudomonas fluorescens, indicated that HDPE/PCL had a lower resistance to bacterial attack than the blend of HDPE/PLA. This was verified by a higher cell number on its surface after 10 weeks of incubation. The addition of 30% starch to the HDPE/PLA blend enhanced its biodeterioration potential, the same was not observed in the case of the HDPE/PCL blend containing just 18% starch.
The Linear Viscoelastic Behavior of a Series of 3-Hydroxybutyrate-based Copolymers
Authors: Melik D. H. , Harrison G. M. 
Published: November 2007

Abstract
The thermal and linear viscoelastic behavior of a series of synthetically produced 3-hydroxybutyrate-based copolymers is reported. The comonomers employed include 4-hydroxybutyrate (4HB), 5-hydroxyvalerate (5HV), and 6-hydroxyhexanoate (6HH). The polymers investigated differed in the concentration of comonomer randomly distributed within the material and in the length of the carbon backbone of the comonomer. The glass transition temperature follows the Fox equation and decreases with increasing comonomer concentration. The molecular weight between entanglements Me was determined from the linear viscoelastic data for each copolymer, and a mixing rule was used to determine Me for homopolymers made from the comonomers studied. Depending on comonomer type and concentration, Me can be varied systematically, resulting in a wide range of potential applications depending on the chemistry employed. Using the complex viscosity data, master curves were constructed for both the zero-shear viscosity and the shear-thinning behavior depending upon the temperature and the molecular weight between entanglements. The analysis of rheological results and polymer properties based upon copolymer content provides an opportunity to process bio-based materials for a wide range of applications.
Thermoplastic Foams from Zein and Gelatin
Authors: Salerno A. , Oliviero M. , Di Maio E. , Iannace S. 
Published: November 2007

Abstract
The aim of this study was to characterize the foaming of natural proteins as thermoplastic polymers. In particular, two proteins, one of vegetal origin, zein, and one of animal origin, gelatin, were processed to achieve thermoplastic polymers, and subsequently foamed by a gas foaming batch process. The effects of suitable plasticizing additives and melt-mixing process on the thermal and mechanical properties of the thermoplasticized proteins were evaluated to assess the thermoplastic characteristics of these materials. Furthermore, selected protein/plasticizers systems were foamed with mixtures of CO2 and N2 as blowing agents, in a batch foaming apparatus, at different temperatures, pressures and pressure drop rates, to evaluate the processing window and the final properties of the foams. Foams with densities of 0.1 g/cm3 and morphologies characterized by uniform distributions of cells with 10 μm diameters were obtained. Results indicated the suitability of zein and gelatin for being processed with classical thermoplastic processing technologies including melt mixing and foaming and their potentials as biodegradable polymers.
Crystallization and Mechanical Propertiesof Poly (D, L) Lactide-based Blown Films
Authors: Stoclet G. , Elkoun S. , Miri V. , Séguéla R. , Lefebvre J.-M. 
Published: November 2007

Abstract
The crystallization, uniaxial and biaxial mechanical behavior of poly(D-, L-lactide)-based-blown films was investigated. It was shown that the selected grade of polylactic acid exhibits low isothermal and non-isothermal crystallization kinetics. In addition, the uniaxial stretching evidenced a ductile/fragile transition temperature located between 35 and 45°C. Eventually stress-induced crystallization was revealed upon uniaxial and simultaneous and sequential biaxial drawing.
Rheological Behavior and Modeling of Thermal Degradation of Poly(∊-Caprolactone) and Poly(L-Lactide)
Authors: Arraiza A. López , Sarasua J. R. , Verdu J. , Colin X. 
Published: November 2007

Abstract
Growing environmental concerns have led to the development of alternative biodegradable polymers with properties comparable to the conventional poly(ethylene), poly(propylene) or poly(ethylene terephthalate). In this paper the thermal degradation of poly(∊-caprolactone) (PCL) and poly(L-lactide) (PLLA) melts was investigated by rheometry and thermogravimetry under different temperatures and inert atmosphere. The chain scission process was modeled to explain the phenomenon. The analysis suggests that PLLA is degraded by an unzipping depolymerization process from the hydroxyl end of the polymer chains. In contrast, the thermal degradation behavior of PCL was very complex because various reactions occurred concurrently: post-polymerization, loss of structural regularities and random chain scissions.
Biaxial Orientation of Polylactide/Thermoplastic Starch Blends
Authors: Chapleau N. , Huneault M. A. , Li H. 
Published: November 2007

Abstract
The biaxial stretchability and film properties of polylactide/thermoplastic starch blends were investigated. Polylactide (PLA) and thermoplastic starch (TPS) were blended in various proportions. Blends containing 27, 42 and 60 wt.% TPS were prepared via a twin-screw extrusion process. Interfacial modification was performed by grafting the PLA with maleic anhydride. These blends were subsequently cast into sheets and biaxially drawn using a laboratory biaxial stretcher. The morphology of extruded strands and cast sheets was investigated using scanning electron microscopy. The compatibilized blends exhibited a much finer morphology as well as preferential minor phase size orientation along the machine direction. The addition of starch did not affect significantly the biaxial stretchability of the pure PLA. Even at high starch content (60 wt.%), the biaxial draw ratio at which the sample breaks is very similar to that of the pure PLA. At higher temperatures, all blends could be stretched at significantly much higher biaxial draw ratio and very thin films could be obtained. The starch content and processing variables affected the tensile properties.
Fabrication of Porous 3-D Structure from Poly(L-lactide)-based Nanocomposite Foam via Enzymatic Degradation
Authors: Bitou M. , Okamoto M. 
Published: November 2007

Abstract
In order to prepare a porous three-dimensional (3-D) structure in biodegradable polyester materials we have conducted the enzymatic degradation of a poly(L-lactide) (PLLA)-based nano-composite foam, having a nanocellular structure, using proteinase-K as a degrading agent at 37°C. The surface and cross sectional morphologies of the foam recovered after enzymatic hydrolysis for different intervals were investigated by using a scanning electron microscope. The nanocellular material took up a large amount of water, which led to the swelling of the foam due to the large surface area inside the nanocelluar structure, and facilitated the enzymatic degradation of the PLLA matrix as compared with the bulk (pre-foamed) sample. Consequently, we have successfully prepared a porous 3-D structure as a remaining scaffold in the core part of the nano-composite foam, reflecting the spherulites of the crystallized PLLA.
Improvement of the Mechanical Properties of Soy Protein Isolate Based Plastics through Formulation and Processing
Authors: Baboi M. , Srinivasan G. , Jane J.-L. , Grewell D. 
Published: November 2007

Abstract
This paper reviews the characterization of the base strength and impact of water absorption on biodegradable, namely, soy protein-based plastics prepared by different methods. The initial approach included using different quantities of soy hydrolysate plasticized with glycerol, which is widely known for its plasticizing effect. With the second approach, the raw polymer was which plasticized with glycerol compounded with different additives such as polycaprolactone or zinc sterate, and was also heat-treated at various temperatures after injection molding. The results indicated the polycaprolactone and, respectively, a medium to high heat treatment significantly enhanced tensile strength and greatly decreased water absorption. The soy hydrolysate formulations that were studied enhanced tensile strength but didn not significantly improve elongation or water absorption.
New Developments in Biodegradable Starch-based Nanocomposites
Authors: Raquez J.-M. , Nabar Y. , Narayan R. , Dubois P. 
Published: November 2007

Abstract
This contribution outlines the new developments in thermoplastic starch-based (nano)composites useful for more specific applications compatible with our environment, partially based on our ongoing research over the past few years. Accordingly, melt-intercalating starch macromomolecules into layered silicates (e.g., natural clays) has proved to be an efficient way for preparation of thermoplastic starch-layered silicate nanocomposites with interesting thermo-mechanical properties, as well as improved solvent-resistance. Cellulosic (nano)whiskers were also added as another environmentally benign (nano)filler in starch-based compositions. The design of such thermoplastic starch-based (nano)composites with enhanced properties relies upon the control over the phase behavior and morphology of the nanofiller within the matrix by more defined interfacial compatibility as well as by fine tuning of processing parameters. A special emphasis was also given to the introduction of layered silicates (nano)filler in biodegradable melt-blends made of hydrophilic thermoplastic starch and hydrophobic biodegradable polyesters as a valuable way to increase the compatibility between the two polymeric partners.
Semantic inheritance in unifying theories of programming
Authors: Chen Yifeng 
Published: November 2007

Abstract
This paper introduces a number of new techniques that support systematic manipulation of predicates, operators, healthiness conditions, laws and fixpoints of recursive programs. Necessary restrictions are imposed on the definition of each model so that the inheritance relation can be established by checking a few conditions on the healthiness conditions and the commands. In particular, we intend to identify the conditions that simplify the closure proof of the program operators and enable laws and fixpoints of a model to be inherited by its submodel without re-proof. A recursive program may correspond to different recursive functions in a model and its submodels, because the primitives such as abort and assignment statements are normally represented as different predicates in different models (although the original definition of each operator is unchanged). This paper studies meta-theory in this more general setting. A fixpoint theorem is discovered and applied to clarify the relationship between the partially correct relational model and the totally correct sequential model in UTP. It is shown that, although assignment statements are modified by the new healthiness conditions in the latter model, most laws (including many that are re-proved in UTP) and fixpoints can be inherited directly without re-proof, if the first argument of every sequential composition in each command tree corresponds to a terminating computation. This result also singles out a small number of laws and fixpoints that may no longer hold in the totally correct model.
Voting for an ethnic identity: procedural and institutional responses to ethnic conflict in Ethiopia
Authors: Smith Lahra 
Published: November 2007

ABSTRACTThe literature on democratisation in diverse and divided societies suggests that procedural and institutional innovations can help create the conditions for democracy by adjudicating among groups with competing claims for recognition and inclusion. Some of the most critical assumptions about the relationship between ethnic identity and formal political institutions have been tested in Ethiopia since the early 1990s. Ethnic federalism is a unique and controversial attempt to account for the contested nature of ethnic identities in contemporary Ethiopian politics through a variety of mechanisms, including the use of a referendum to determine ethnic identity. In 2001 the Siltie people voted to separate from the Gurage ethnic group. With this political manoeuvre, the Siltie accessed greater levels of political power and greater resources, but also recognition under the constitutional arrangement as a distinct ethnic group. The Siltie case suggests that formal political institutions have a limited, though important, role in resolving contested citizenship claims. At the same time, it raises vital questions about the challenges of procedural solutions in the context of contested citizenship and democratic transition in sub-Saharan Africa.
What can X-rays tell us about accretion, mass loss and magnetic fields in young stars?
Authors: Montmerle Thierry 
Published: November 2007

AbstractUntil recently, X-rays from low-mass young stars (105–106 yr) were thought to be a universal proxy for magnetic activity, enhanced by 3-4 orders of magnitude with respect to the Sun, but otherwise similar in nature to all low-mass, late-type convective stars (including the Sun itself). However, there is now evidence that other X-ray emission mechanisms are at work in young stars. The most frequently invoked mechanism is accretion shocks along magnetic field lines (“magnetic accretion”). In the case of the more massive A- and B-type stars, and their progenitors the Herbig AeBe stars, other, possibly more exotic mechanisms can operate: star-disk magnetic reconnection, magnetically channeled shocked winds, etc. In any case, magnetic fields, both on small scale (surface activity) and on large scale (dipolar magnetospheres), play a distinctive role in the emission of X-rays by young stars, probably throughout the IMF.