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The aim of the present article is to study the different phenomena which are at the basis of the consolidation of commingled thermoplastic semi-pregs made of amorphous polyester fibers and E-glass reinforcement. The evolution of the void fraction during the consolidation of the composite was monitored by a dynamometer, equipped with parallel plates and a forced convection oven. Different physical changes were associated to the consolidation temperature. Scanning electron microscopy (SEM) and thermomecahnical analysis (TMA) showed that at low temperature, matrix fiber deformation and sintering are responsible of the initial void reduction. At a temperature higher than the onset of the flow region, reinforcement impregnation is responsible of the further void reduction. Dimensionless analysis confirmed that at lower temperatures, corresponding to higher viscosities, consolidation due to viscous flow of the polymer matrix is negligible compared to consolidation due to sintering of matrix fibers. The results indicate that the Darcy law can efficiently represent the consolidation during the microscale impregnation of the reinforcement, but cannot account for the initial stages of consolidation. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers

This study is aimed at the synthesis of antimicrobial hydroxyapatite (HAP)‐based composites for dental application by stereolithography (SLA). A micron‐sized commercial HAP was modified by methacrylate and quaternary ammonium salt, and, then, it was used in different amounts (namely 2.5, 5, and 10 wt%) as filler for a photocurable custom made resin for SLA. Thermal stability, microstructure, and particles size of the pristine (HAP) and modified HAP (mHAP) were evaluated by thermogravimetric analysis (TGA), X‐ray diffraction (XRD), and particle size analyser (CILAS). The suitability of each formulation for stereolithography process was assessed by measuring viscosity, degree of conversion (DC%) by Fourier transform infrared spectroscopy (FTIR), glass transition temperature, and thermal stability. Photo‐cured specimens for physical, mechanical, and antimicrobial testing were built by SLA. The flexural strength of the samples was measured using a 3‐point bending test method, and the fractured surface was analysed by scanning electron microscopy (SEM). The antimicrobial activity of samples was investigated against some standard microorganisms (Staphylococcus aureus, Escherichia coli, and Candida albicans), as representative Gram positive and Gram negative bacteria and fungus, respectively. The flexural strength increased with a filler content up to 5% and slightly decreased for higher content. SEM analysis confirmed the presence of uniformly distributed HAP. The incorporation of mHAP reduced the bacterial and fungal growth in dose‐dependent manner in comparison with the neat samples. Finally, a prototype of dental bite was built by SLA.

During autoclave processing of composites for high-performance applications, it is mandatory to limit the porosities, which mainly depend on the hydrostatic pressure in the resin. This pressure, which is not constant during heating being affected either by resin flow either by elastic stress in the fiber stack, can be significantly different from the autoclave pressure. Modeling of resin flow and stress in the fiber stack is a key issue for prediction of the resin hydrostatic pressure, which can be related to void development. Also, the viscosity of the thermosetting matrix is a relevant parameter since it is not constant but evolves during curing going through a minimum and then increasing to an infinite value at gel point. In this work, a viscoelastic model is adopted to calculate the evolution of resin pressure during an autoclave cycle up to gelation, accounting for viscosity and degree of reaction changes. Therefore, the model includes a kinetic and rheological model whose input parameters have been experimentally determined by Differential Scanning Calorimetry and rheological analysis. The predicted resin pressure for three case studies associated to different composite and bleeder thicknesses and reinforcement materials have been discussed. POLYM. ENG. SCI., 57:631–637, 2017. © 2017 Society of Plastics Engineers

The engineering aspects, which are associated with the development of nanocomposites, involve in either final properties or processability of nanocomposites. Both are affected by the distribution of nanofiller in the matrix and by the aspect ratio of the nanofiller. A nanofilled thermosetting resin can be exploited as a matrix for continuous fibers when the alignment of a high aspect ratio nanofiller is achieved, and in this case, a hierarchical composite is obtained. In this study, a new procedure for the alignment of nanofillers in a thermosetting matrix is proposed. The two-step approach is based on (i) the alignment of nanofillers (carbon nanotubes, graphene, etc.) in thermoplastic fibers by a fiber spinning process and (ii) the use of these nanocomposite fibers as a carrier to bring aligned nanofillers into a reactive thermosetting resin. These fibers, soluble in the thermosetting resin, release the nanofillers orientated according to the direction in which fibers are positioned, even after the curing of the matrix. The proof of concept is demonstrated by producing melt spun polyethylene terephtalate (PETg) fibers filled with graphene nanoplatelets (GNP) and multiwall carbon nanotubes (MWCNT) with a very high filler content (up to 10 wt%) in view of producing a hierarchical composite. POLYM. COMPOS., 36:1096–1103, 2015. © 2015 Society of Plastics Engineers

The current “gold standard” to treat bone lesions is allografts and autografts, both presenting important disadvantages such as risk of infection and morbidity. Synthetic grafts and scaffolds for bone regeneration represent a promising solution. Fused deposition modeling is a valid tool for developing synthetic bone grafts of complex shapes, which is a key issue. The possibility of building polylactic acid–nanohydroxyapatite (PLA/nanoHA) composites by 3D printing was systematically evaluated. PLA/nanoHA filaments for low-cost 3D printers were produced by a multistep solvent-free procedure and characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry, and rheometry. TGA analysis confirmed the presence of the nanoHA amounts used in the composites, equal to 5 and 15 wt %. The glass-transition temperature and degree of crystallinity of PLA are not influenced by presence of nanoHA, which remains substantially amorphous. The morphological analysis and compression testing on printed samples showed that nanoHA was uniformly dispersed within the PLA matrix and improved the PLA mechanical properties without changing the rheological performance. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 134, 44656.

An overview of the current state of art of the ultrasonic treatment technology applied to polymer melts is presented. The research and technological advancements of the ultrasonic treatment as applied to development of polymeric materials are discussed. An analysis of the technological progress shows that the mechanism of the effects of ultrasound on polymer melts is not fully understood at present. Such lack in fully understanding the mechanism could limit the use of this versatile technology in future applications. Based on the critical analysis of the research progress to date, some key issues for a deeper understanding of the chemical and physical effects of ultrasound on polymer melts are identified. © 2012 Wiley Periodicals, Inc. Adv Polym Techn 32: E582–E602, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.21303

Chloroform vapor sorption in semicrystalline syndiotactic polystyrene with a nanoporous crystalline form has been investigated by simultaneous gravimetric and calorimetric analysis to gather information on the sorption process and associated heat of sorption. At the investigated pressures of chloroform vapor, the sorption process is dominated by exothermic adsorption of penetrating molecules in the nanocavities of the crystalline phase. The mass uptake kinetics has been compared with the kinetics of evolution of heat of sorption measured simultaneously. The integral heat of sorption evaluated calorimetrically has been compared to the corresponding value calculated by elaborating gravimetric sorption isotherms at several temperatures evaluated independently through gravimetric sorption experiments. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1675–1681, 2005

This paper reports on the development and the optimization of a thermoforming process (compression molding) for thermoplastic sandwich panels. The skins of the panels are fabricated from polypropylene (PP)/continuous glass fibers dry prepregs in the form of a commingled fabric. The use of two different types of core material has been used, a PP foam and a PP honeycomb. Additionally, two alternative methods for the thermoforming process have been analyzed, using either a one-stage or a two-stage process. In the one-step process, skin molding and skin-core bonding are carried out simultaneously. In the two-stage process, the skins are first thermoformed and then bonded to the core as the second stage. The influence of the selected process parameters on the mechanical properties of the panels has been experimentally investigated, leading to the identification of the preferred processing conditions. Polym. Compos. 25:307–318, 2004. © 2004 Society of Plastics Engineers.

The quality of rotational molded products is strongly affected by the sintering behavior of the powders used in the process. In turn, for a given material, the sintering behavior of polymer powders is dependent on the size and the shape of particles obtained in the milling apparatus. The quality of powders for rotational molding is usually determined by means of size distribution, dry flow, and bulk density tests. However, these tests do not provide insight into the relationship between the shape of powders, the milling conditions, and the sintering behavior during the rotational molding cycle. Nevertheless, the application of mathematical tools to powder analysis can significantly improve the efficiency of the grinding process, looking not only at the size but also at the shape of the powder. This can in turn result in a higher reliability of rotational molding and in better performances of the products obtained in processes dominated by the sintering behavior of polymer powders. In this work the grinding process of recycled high-density polyethylene was analyzed using a quantitative approach to the shape and size of the powders. In particular, shape factors, capable of characterizing powders obtained in different milling conditions, were studied. Finally, the influence of the powders' shape and size on sintering behavior was studied by thermomechanical analysis. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 449–460, 2004

The possibility to modulate cellulose-based hydrogel sorption properties through the insertion of molecular spacers between the crosslinks was investigated. Starting polymers were the sodium salt of carboxymethyl cellulose, a polyelectrolyte cellulose derivative, and hydroxyethyl cellulose, a nonpolyelectrolyte derivative. Poly(ethylene glycol) with various molecular weights was linked by its free ends at two divinyl sulfone (DVS) crosslinker molecules, to increase the average distance between two crosslinking sites and thus to act as a spacer. Both the effect of the concentration and the molecular weight of the spacer on the hydrogel final sorption properties in water and water solutions were investigated. The presence of the spacer allowed us also to perform hydrogel synthesis with higher concentrations of cellulose in the reactive mixture, and the effect of the polymer concentration in the batch was analyzed. Hydrogels obtained in the presence of spacers displayed significantly higher equilibrium sorption properties than those of the ones obtained without spacers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 168–174, 2003

Ultrasonic inspection for nondestructive analysis is already widely applied to the control of structural integrity of concrete, presenting among other advantages the reliability, the simplicity and low costs. Although ultrasonic testing are mainly used for nondestructive evaluation of defects, it may be also applied to follow the changes of mechanical properties occurring in a material which evolves in time, such as during the crosslinking of thermosetting resins. These time dependent properties may be measured by longitudinal and shear ultrasonic velocity operating by pulse-echo and/or through-transmission methods. In this work, ultrasonic wave propagation has been applied to the monitoring of the progress of the curing reaction of an epoxy adhesive for civil applications. The data have been collected in isothermal conditions on the neat resin, as well as in a coupled system concrete-resin-concrete. The measurements of longitudinal and shear velocity have been used for the calculation of Young and shear moduli. The change of velocity during cure must be considered a powerful tool for the measurement of the progress of ambient temperature cure reactions like in the case of adhesives for civil applications.

A durable and flexible silicone-based backcoating (halogen free) is applied to the backside of an otherwise smoldering-prone and flammable fabric. When exposed to fire, cyclic siloxanes (produced by thermal decomposition of the backcoating) diffuse through the fabric in the gas phase. The following oxidation of the cyclic siloxanes forms a highly conformal and thermally stable coating that fully embeds all individual fibers and shields them from heat and oxidation. As a result, the combustion of the fabric is prevented. This is a novel fire retardant mechanism that discloses a powerful approach towards textiles and multifunctional flexible materials with combined smoldering/flaming ignition resistance and fire-barrier properties.

This review addresses thermoforming of thermoplastic matrix composites (TPCs) reinforced with long or continuous fibers and of sandwich panels obtained using TPCs as skins. Thermoforming is a very versatile class of processes, applied to the production of parts of different thickness, ranging from

The thermokinetic and rheological behavior of epoxy based composites during the pultrusion of carbon fiber composites is analyzed using a mathematical model accounting for the heat transfer and the heat generation characteristics of polymerizable systems. An energy balance and a kinetic expression for the chemical reaction are simultaneously solved to calculate the temperature and degree of reaction profiles. Afterwards the viscosity as a function of the degree of reaction is computed applying a theoretical model. The dimensionless mathematical model is applied to the description and optimization of the process variables. General optimization criteria are identified and applied to compute, through a tailored numerical simulation, the optimum set of processing conditions for different case studies corresponding to different die temperatures, pulling speeds, and composite thicknesses.