1,721,308 research outputs found
Laser sealing of PLA-based compostable coffee capsules
No full textThe aim of the present work is to examine the possibility of using laser technology to make welded joints to hermetically seal bioplastic containers with aluminum or bioplastic foils. Specifically, the focus is on the laser sealing process of compostable coffee capsules with toplids in aluminum and in paper coated with compostable plastic (mainly based on polylactic acid, PLA). The aluminum toplid does not allow obtaining a compostable package, but represents the currently most used standard on the coffee capsule market. The welded joints made with laser technology were characterized by peel-off tests to evaluate the adhesion strength of the toplid to the capsule with the laser operational parameters, namely processing and pre-heating laser power, scanning speed of the laser beam. The results of the peel-off test allowed optimizing the choice of the operational parameters of the laser sealing process for the various scenarios examined. Based on the experimental findings, 3D process maps have therefore been built in which the adhesion strength between the toplid and the capsule has been plotted by varying the laser operational parameters process, making it possible to identify the optimal processing windows
Electrostatic fluidized bed (EFB) coating of heat sensitive and electrical insulating substrates with low-curing thermoset epoxy-polyester (EP) powders
No full textIn this study, the electrostatic fluidized bed (EFB) coating process of heat sensitive and electrical insulating substrates with low-curing thermoset epoxy-polyester (EP) powders is researched. A relatively novel prepaint treatment, based on a peening process of plastic substrates with copper powders and performed inside an abrasive fluidized bed (AFB), is developed and analyzed. The influence of EFB coating process parameters, that is, coating time, voltage and flow rate, on the resulting polymeric films has been investigated in terms of coating thickness and average roughness. Subsequently, the location of part to be coated in the bed is studied. In particular, the influence on coating thickness of part attitude, radial location, dip distance and time has been considered. Finally, the curing kinetic of EP powders has been worked out and, therefore, the analysis of baking temperature able to produce the best curing condition of the polymeric films has been led, with particular regard to the estimation of film properties, that is, coating thickness and surface finishing as well as scratch adhesion and gloss. © 2006
Application of instrumented micro-indentations to "in situ" mechanical characterization of wooden structures: Part I - Analysis of highly selected and decayed pinewood samples
No full textThe need for an experimental protocol, which allows determining overall mechanical properties of wooden structures by using a local, non-destructive and 'in situ' implemented testing procedure, has pushed towards the definition of several methodologies. In this work, an application of an instrumented micro-indentation, based upon a flat punch, is investigated, aimed at defining a technique less affected by typical discontinuities, defects and alterations of wooden materials, which, severely, jeopardize the reliability of all the other available testing procedures. First, a calibration of the experimental procedure is carried out, taking care of the influence on the collected data of the actual samples dimensions, their weight, number of growth rings, growth rings width, distance between indentation location and latewood layer and depth along indentation axis. Then, an application of testing procedure on pinewood is performed and strict criterion in executing experiments and choosing wooden specimens is defined to improve the reliability of results. At last, the capability of instrumented micro-indentations in detecting overall mechanical properties of new and decayed samples is checked out, stating the high sensitivity and effectiveness of the procedure. (c) 2005 Elsevier Ltd. All rights reserved
Progress in abrasive fluidized bed machining
No full textThe use of abrasive fluidized bed equipment in a broad range of manufacturing processes is reviewed. In particular, applications in deburring and finishing of complex-shaped metal components, in super-finishing of dies for injection molding, in cleaning and polishing of electronic devices, and in surface preparation of tungsten carbide milling tools are reviewed. Attention is focused on the effects of the most important process parameters, such as machining time, abrasive type and mesh size, and flow or jet speed. The extent of material removal and the change in surface roughness as a function of the process parameters are addressed. Selected numerical and analytical models that are useful for automation and control purposes are discussed. Finally, the industrial sustainability of the processes and equipment investigated is highlighted. © 2009 Elsevier B.V. All rights reserved
Optimizing crystallinity of engineered poly(lactic acid)/poly(butylene succinate) blends: The role of single and multiple nucleating agents
No full textThis work deals with the design and experimental development of formulations based on bioplastic materials optimized for the production processes of high-performance packaging products, suitable for food contact and characterized by high thermo-mechanical stability. For this purpose, mixtures of poly (L-lactic acid) (PLLA)/poly (butylene succinate) (PBS) (PLA/PBS) containing micro-lamellar talc as reinforcing agent and inorganic nucleating agent have been obtained on a pre-industrial scale. Through the addition in formulation of two organic nucleating agents, ethylene (bis)stereamide (EBS) and poly (D-lactic acid) (PDLA), evaluated separately and in combination with each other, four different PLA/PBS formulations were produced by means of a co-rotating twin screw extruder. The effects on the crystallinity of the materials obtained first in the form of pre-dried pellets, then in the form of films by casting extrusion and, finally, as thermoformed items were compared, according to the variation of the chosen nucleation system. The effect on the crystallinity of the materials was assessed by differential scanning calorimetry (DSC) and by Fourier transform infrared analysis in attenuated total reflection mode (ATR-FTIR). This approach aims to provide data for the further investigation on the processability and the thermo-mechanical properties of end-goods achievable by converting processes (melt processing) of the bioplastic compounds
Thermoforming of compostable PLA/PBS blends reinforced with highly hygroscopic calcium carbonate
No full textMineral fillers have always been used in engineered polymers to reduce the cost, promote the thermal and dimensional stability of the material, and contain its shrinkage and deformations generated by the conversion processes. Compounds based on compostable polymers are normally characterized by the presence of high levels of mineral fillers (up to 30 %), although mineral fillers with a limited ability to incorporate moisture are preferred. The bioplastic compounds are, in fact, based mainly on bio-derived polyesters, highly sensitive to hydrolytic degradation at high temperatures. Therefore, in the design of bioplastic compounds, the moisture content is kept strictly under control to avoid the onset of degradation mechanisms. Calcium carbonate is, however, the cheapest mineral filler and is broadly available on the market. It is the most widely used mineral filler in the design of engineered polymers based on polyolefins and polystyrenes. However, the use of calcium carbonate in the bioplastic compound segment is severely limited by the hygroscopicity of the carbonate. In this context, the use of calcium carbonate was studied, as a reinforcement element of binary blends between polylactic acid (PLA) and polybutylene succinate (PBS). In particular, the role of the percentage of the mineral filler on the absorption of moisture in the compound has been studied. The thermo-rheological properties of the compound were also evaluated. Finally, the processability of the compound was studied in the thermoforming process of containers suitable for food contact on a prototype system (machine - mold), specifically designed to transform polyolefins. Experimental results have shown that a correct design of the bioplastic compound, even in the presence of a highly hygroscopic filler, can allow the development of a material suitable for the thermoforming process, without the need to make changes to the conversion plant and to the mold
Thermo-Mechanical Properties of Injection Molded Components Manufactured by Engineered Biodegradable Blends
No full textEngineering of ductile, tough and thermal resistant PLA-based materials requires blending of PLA with other constituents by reactive twin-screw co-rotating extrusion to achieve compounds with adequate thermo-mechanical properties. Then, the compound of the polymeric blends must be melt processed to the final shape with an additional technology, namely the injection molding. The two-stage process the polymeric blends must undergo and the different rheological properties the blends must feature to be suitable to the different processing steps make extremely difficult to engineer the material. Extrusion compounding requires high viscous materials low melt flow index (MFI), while injection molding requires materials with low viscosity (high MFI). To overcome these shortcomings, this manuscript deals with the design of novel biodegradable PLA-based blends that rely on mixing PLA grades with different MFI (i.e. very low for extrusion and high for injection molding), each chosen to feature the rheological characteristics needed for each step of the two-stage transformation process. The ratio of the two PLA-grades inside the blends was the matter of the present investigation. The blends were subsequently tested for the manufacturing of single-use biodegradable and thermal resistant injection molded small cups, specifically designed for brewing of hot beverages. Lastly, the thermo-mechanical performance of the as-is and annealed cups were studied. Experimental evidences show blending of two-different grades of PLA is a promising route to formulate low impact polymeric materials suitable for demanding packaging solutions
Combined use of scratch tests and CLA profilometry to characterize polyester powder coatings
No full textThe use of scratch tests at different stages of the curing process is of crucial importance in powder coatings as it can provide helpful information on formulating the base material, on setting curing operational parameters and, above all, on progressively establishing coating properties during baking In particular this paper deals., with the use of sliding spherical contact geometry to characterize the scratch response of a clear polyester topcoat electrostatically sprayed onto metallic substrate and baked under different time-temperature programs in a convection oven. Friction force and penetration depth were on-line monitored during scratch tests. Following this, residual deformation patterns were analyzed by using a combination of non-contact CIA profilometry and FE-SEM. Analytical examination and simple mathematical simulation of the experimental results found good correlations between the size of the deformed area after scratch and curing operating parameters. This makes it possible to map the scratch response of the clear polyester topcoats to ranges of curing conditions. (C) 2009 Elsevier B.V. All rights reserved
Improvement of the fatigue behavior of stainless steel substrates by low pressure Fluidized Bed Peening (FBP)
No full textThis study investigates the effectiveness of fluidized bed peening (FBP) to improve the fatigue behavior of axial-symmetric stainless steel substrates. The substrates were rotated at moderate speed inside a fluidized bed of stainless steel media. Their fatigue failure was determined by rotating bending testing procedure. The number of cycles to fracture was plotted versus the maximum amplitude of alternating stress for fluidized bed peened and unpeened substrates. The effect of peening time was also looked into. FBP was found to definitely improve the number of cycles to fracture. Fatigue life was normally increased of four to five times, although improvements up to an order of magnitude were detected. Hardness measurements, profilometry, scanning electron microscopy, and X-ray diffractometry allowed interpreting the improvement of the fatigue behavior of the peened substrates. After FBP, the substrates surface was characterized by a higher hardness, a smoother and less defective morphology, as well as a beneficial compressive residual stress. Therefore, the improvement in surface and microstructural properties of the peened substrates induced a related increase in their fatigue life. Peening time was also found to influence the fatigue behavior of the substrates, although the sharpest variations in the number of cycles to fracture were observed at the beginning of the fluidized bed process. Based on the previous experimental findings, approximate analytical models, very useful for automation and process control, were proposed, thus providing to the practitioners first hints on how to best set FBP process parameters
Compatibilization strategies and analysis of morphological features of poly(butylene adipate-co-terephthalate) (PBAT)/poly(lactic acid) PLA blends: A state-of-art review
No full textPBAT is a compostable biopolyester, potentially obtainable from renewable resources, of great commercial interest. Thanks to its lower price, ease in processability and especially high ductility PBAT will very likely emerge in the next few years as the preeminent flexible bioplastic, ahead of contenders such as polybutylene succinate (PBS) or polycaprolactone (PCL) and it will likely become one of the most important biodegradable plastics, alongside PLA, which stays the major biopolymer for rigid applications. PBAT is often blended with PLA, a rigid bio-based polymer, that lends stiffness. PLA is a very rigid material with low impact resistance, it is, therefore, complementary to PBAT in the design of high performance and multi-functional biodegradable plastics. Despite the great and increasing interest of the market in PBAT, to date a general overview of the scientific literature which critically explores potentials of PBAT, with focus on design of engineered PBAT/PLA blends, is missing. The present works aims at filling this gap, laying the basis to create a link between fundamental research on PBAT and industrial applications. A general overview of the market and of the state of the art of PBAT based blends is herein provided, focusing on PBAT/PLA blends and possible compatibilization strategies. This work aims to achieve a double target: scientific and social. The scientific target is to summarize the main design criteria used in the conception of engineered plastics based on PBAT blends with PLA, revealing their implementation secrets and strategic aspects. The social target is to develop a useful guide for sector technicians, policy makers and stakeholders to promote the use of biodegradable materials instead of conventional plastics in an even wider range of applications, in order to significantly reduce the environmental impact of plastic products
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