1,720,992 research outputs found
A proposal to modify the Kelly-Tyson equation to calculate the interfacial shear strength (IFSS) of composites with low aspect ratio fibers
No full textThe mechanical behavior of short-fiber composites generally differs from long-fiber composites. The mechanical response is influenced by the particular distribution of tensions and by the mechanism of load transfer from the matrix to the fibers. The transfer load from the matrix to the fibers occurs through shear stresses at the surfaces of the fibers (edges or ends effects). The end effects in long fiber composites, involving a small portion of fiber, are negligible; nevertheless, for short and very short fibers composites these end effects cannot be neglected. Interfacial adhesion between the reinforcement and the matrix plays an important role, in fact it influences both physical and mechanical properties of the composites, but the experimental determination is often laborious and analytical models are frequently used to evaluate the interfacial shear strength (IFSS). In this paper a modification of the Kelly-Tyson model for the calculation of the interfacial stress for short (aspect ratio < 20) and ultra-short fibers composites (aspect ratio < 10) has been proposed to take into account the end effects that in the original model were not considered. Successively, the Bader and Bowyer model (that derives from the Kelly-Tyson model) for the evaluation of the IFSS was also modified. A few examples of calculations of the IFSS, using this modified Bader and Bowyer model, have been provided using published literature data. Furthermore, a mechanical characterization of flax fibers has been carried out and their adhesion to poly(lactic) acid (PLA) matrix were evaluated for composites containing ultrashort fibers (aspect ratio < 10). The IFSS value obtained was compared with that obtained from the single fiber fragmentation test (SFFT). It was found that a very good estimation of IFSS can be done by using this analytical model that can be easily applied with a limited number of experimental tests
Study on the preferential distribution of acetyl tributyl citrate in poly(lactic) acid-poly(butylene adipate-co-terephthalate) blends
Full text linkIn this work, the preferential distribution of acetyl tributyl citrate plasticiser (ATBC) in poly(lactic acid) (PLA)-poly(butylene adipate-co-terephthalate) PBAT blends has been investigated. Pure plasticised PLA and PBAT blends and their binary blends (PLA/PBAT with 80 wt% of PLA and 20 wt% of PBAT and PBAT/PLA with 80 wt% of PBAT and 20 wt% of PLA) containing different ATBC amount (from 5 to 20 wt%) have been investigated. Dynamic mechanical thermal analysis (DMTA) has been performed in order to evaluate the shift of the glass transition temperature (Tg) in both the polymer systems. The results obtained showed a larger shift for PLA than the PBAT and the calculated plasticiser partition coefficient for both binary blends revealed a preferential distribution of ATBC in the PLA phase rather than PBAT (KA/B = 1.07 for PLA-based system and KA/B = 1.45 for PBAT-based system). The results obtained have also been confirmed by the Hansen Solubility Parameters (HSPs) methodology. The study is finally augmented by the differential scanning calorimetry (DSC) and morphology analysis in order to demonstrate the possible effects of crystallinity on the plasticiser distribution in the binary blends
Constrained amorphous interphase in poly(l-lactic acid): Estimation of the Tensile elastic modulus
No full textThe mechanical properties of semicrystalline PLLA containing exclusively α′- or α-crystals have been investigated. The connection between experimental elastic moduli and phase composition has been analyzed as a function of the polymorphic crystalline form. For a complete interpretation of the mechanical properties, the contribution of the crystalline regions and the constrained amorphous interphase or rigid amorphous fraction (RAF) has been quantified by a three-phase mechanical model. The mathematical approach allowed the simultaneous quantification of the elastic moduli of (i) the α′- and α-phases (11.2 and 14.8 GPa, respectively, in excellent agreement with experimental and theoretical data reported in the literature) and (ii) the rigid amorphous fractions linked to the α′- and α-forms (5.4 and 6.1 GPa, respectively). In parallel, the densities of the RAF connected with α′- and α-crystals have been measured (1.17 and 1.11 g/cm3, respectively). The slightly higher value of the elastic modulus of the RAF connected to the α-crystals and its lower density have been associated to a stronger chain coupling at the amorphous/crystal interface. Thus, the elastic moduli at Troom of the crystalline (EC), mobile amorphous (EMAF), and rigid amorphous (ERAF) fractions of PLLA turned out to be quantitatively in the order of EMAF < ERAF < EC, with the experimental EMAF value equal to 3.6 GPa. These findings can allow a better tailoring of the properties of PLLA materials in relation to specific applications
Volume change during creep and micromechanical deformation processes in pla–pbsa binary blends
Full text linkIn this paper, creep measurements were carried out on poly(lactic acid) (PLA) and its blends with poly(butylene succinate-adipate) (PBSA) to investigate the specific micromechanical behavior of these materials, which are promising for replacing fossil-based plastics in several appli-cations. Two different PBSA contents at 15 and 20 wt.% were investigated, and the binary blends were named 85-15 and 80-20, respectively. Measurements of the volume strain, using an optical extensometer, were carried out with a universal testing machine in creep configuration to deter-mine, accompanied by SEM images, the deformation processes occurring in a biopolymeric blend. With the aim of correlating the creep and the dilatation variation, analytical models were applied for the first time in biopolymeric binary blends. By using an Eyring plot, a significant change in the curves was found, and it coincided with the onset of the cavitation/debonding mechanism. Further-more, starting from the data of the pure PLA matrix, using the Eyring relationship, an apparent stress concentration factor was calculated for PLA-PBSA systems. From this study, it emerged that the introduction of PBSA particles causes an increment in the apparent stress intensity factor, and this can be ascribed to the lower adhesion between the two biopolymers. Furthermore, as also con-firmed by SEM analysis, it was found that debonding was the main micromechanical mechanism responsible for the volume variation under creep configuration; it was found that debonding starts earlier (at a lower stress level) for the 85-15 blend
Thermal, Mechanical and Micromechanical Analysis of PLA/PBAT/POE-g-GMA Extruded Ternary Blends
No full textIn order to toughen Poly(lactic) acid and binary blends with low PBAT content while maintaining a high biodegradability of the final material, poly(lactic) acid (PLA)/poly(butylene-adipate-co-terephthalate) (PBAT)/ polyolefin elastomer grafted with glycidyl methacrylate (POE-g-GMA) extruded ternary blends have been investigated in this work from a thermal, mechanical, and rheological point of view. The two elastomers have been added in different amounts as dispersed phases into the PLA matrix, paying attention to the final objective: the design of a 90% biodegradable formulation according to EN 13432. These ternary blends exhibited improved impact properties but still low elongation at break. Consequently, to the ternary composition with the best compromise of PLA quantity, biodegradability and thermo-mechanical properties (81 wt.% PLA, 9 wt.% PBAT, and 10 wt.% POE-g-GMA) a small quantity (10 wt.%) of a biobased plasticizer was added in order to further increase the impact properties in parallel with the tensile flexibility. Two types of plasticizers were investigated, one not reactive [Acetyl Tributyl Citrate (ATBC)], and one reactive [Glycidyl ether (EJ-400)]. A micromechanical study, in order to investigate the toughening mechanism of these systems, was carried out on the final formulations. They were also examined by dilatometric tests and elasto-plastic fracture mechanics correlating the data obtained to the morphology and to the rheological properties. In conclusion, the best compromise between impact, tensile properties and biodegradability content was achieved using the reactive plasticizer (EJ-400) whose interaction with the matrix is confirmed by the FT-IR analysis
Micromechanical analysis and fracture mechanics of Poly(lactic acid) (PLA)/Polycaprolactone (PCL) binary blends
Full text linkEven Poly(lactic acid)/polycaprolactone (PLA/PCL) blends have been studied in literature, the deformation mechanism that is related to the toughness increment with respect to pure PLA has not been investigated in detail. The novelty of this work is to understand in depth the correlation between the micromechanical deformation processes occurring in PLA/PCL blends to the macromechanical properties, their morphology and their fracture mechanism.PLA/PCL blends containing increasing amount of PCL (from 10 up to 40 wt%) were produced. A novel characterization approach, not yet investigated for these blends, was carried out by dilatometric uniaxial tests using a videoextensometer. The shape of the dilatometric curves coupled with SEM analysis revealed how changing the PCL amount different concurrent micromechanical deformation processes occurred. When 10 wt% of PCL was added only particles debonding occurred leading to lower enhancement of elongation at break; at 20 wt% both debonding and voids growth along the tensile direction occurred, while at 40 wt% of PCL shear yielding was predominant that lead to a great enhancement of the elongation at break. The PLA/PCL blends capability to absorb energy at slow rate, was evaluated by the elasto-plastic fracture approach based on the ESIS load separation criterion. The results obtained was then correlated with the final blend morphology
Blending recycled poly(lactic acid) (PLA) with elastane recovered from textile fibers: A sustainable valorization approach
No full textThe recycling of elastane from textile waste and its reintegration into polymeric matrices represents a possible pathway towards the achievement of a real circular economy in the textile industry. This study investigates the dissolution and recovery of elastane using environmentally friendly solvents and its subsequent blending with recycled poly(lactic acid) (PLA). Among tested solvents, dimethyl sulfoxide (DMSO) was the most effective, dissolving elastane at 120 °C with a solubility limit of 40.77 mg EL/g DMSO at 160 °C. Recovery via non-solvent induced phase separation (NIPS) allowed for 75–80 % solvent recovery, with residual DMSO reduced down to 5–6 % after drying. Blends of recycled PLA with recovered elastane (5–15 wt.%) were produced via melt extrusion and evaluated for mechanical and thermal properties. Tensile tests revealed that adding elastane reduced the elastic modulus (from 3.52 GPa for PLA to 3.14 GPa for PLA+15) while increasing elongation at break. However, tensile strength declined due to poor interfacial adhesion between PLA and elastane. Dynamic mechanical thermal analysis (DMTA) confirmed elastane's limited compatibility with PLA, showing separate glass transition temperatures at ∼60 °C (PLA) and ∼10 °C (elastane). Differential scanning calorimetry (DSC) indicated an increase in PLA crystallinity (from 19.5 % for PLA to 24.9 % for PLA+5), followed by stabilization around 20.7 % at higher elastane content. Scanning electron microscopy (SEM) revealed elastane dispersion within the PLA matrix, with droplet coalescence at higher elastane concentrations. Despite its limited compatibility, this study highlights the potential for elastane to have a second life and demonstrates the feasibility of incorporating it into recycled PLA. It lays the foundation for future research on compatibilization strategies to improve mechanical performance
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
- …
