There is need for developing novel conductive polymers for Digital Light Processing (DLP) 3D printing. In this work, photorheology, in combination with Jacobs working curves, efficaciously predict the printability of polyaniline (PANI)/acrylate formulations with different contents of PANI and photoinitiator. The adjustment of the layer thickness according to cure depth values (Cd) allows printing of most formulations, except those with the highest gel point times determined by photorheology. In the working conditions, the maximum amount of PANI embedded within the resin was ≃3 wt% with a conductivity of 10−5 S cm−1, three orders of magnitude higher than the pure resin. Higher PANI loadings hinder printing quality without improving electrical conductivity. The optimal photoinitiator concentration was found between 6 and 7 wt%. The mechanical properties of the acrylic matrix are maintained in the composites, confirming the viability of these simple, low-cost, conductive composites for applications in flexible electronic devices.

No abstract

No abstract

The feasibility of novel controlled release systems for the delivery of active substances from films intended for food packaging was investigated. Because polyolefins are used highly for food-packaging applications, the reported high retention degree of antioxidants has limited their use for active packaging. Thus, in this study, PP films modified with different chain extenders have been developed to favor and control the release rates of the low molecular weight antioxidant tocopherol. The use of different chain extenders as polymer modifiers (PE-PEG M(w), 575; and PPG-PEG-PPG M(w), 2000) has caused significant changes in tocopherol-specific release properties. High-performance liquid chromatography coupled to PDA-FL and PDA-MS was used to test tocopherol and chain extender migration, respectively. The release of tocopherol from the prepared films with two chain extenders into two food simulants was studied. Different temperatures and storage times were also tested. Varying the structural features of the films with the incorporation of different levels of PPG-PEG-PPG, the release of tocopherol (food-packaging additive) into different ethanolic simulants could be clearly controlled. The effect of the temperature and storage time on the release of the antioxidant has been outstanding as their values increased. The migration of the chain extender, also tested, was well below the limits set by European legislation.

In the present study, different quantities of multiwalled carbon nanotubes and an immiscible blend of polyamides, 50 vol%/50 vol%. Polyamide 12/polyamide 6 (PA12/PA6), are melt blending by extrusion to obtain conducting polymer composites. The rheological and electrical properties of nanocomposites are evaluated as function of nanofiller content. Both rheological and electrical percolation thresholds are calculated by graphical methods and fitting the experimental data to the well‐known power‐law expression. The low percolation thresholds are probably due to the high aspect ratio of the nanotubes, kept after the composite processing and to the preferential localization of carbon nanotubes (CNTs) in the polyamides interface. This latter is predicted by the wetting parameter and finally confirmed by TEM micrographs. The mixing strategy followed, by using a PA12 masterbatch and an immiscible blend of polyamides, seems suitable to form a segregated conductive network in the matrix with low CNT quantities. POLYM. COMPOS., 38:2679–2686, 2017. © 2015 Society of Plastics Engineers

In this context, dielectric polymeric materials are being investigated due to their scientific and technological interest since they combine dielectric properties with appropriate mechanical flexibility and simple processability. [2,3] Such composite materials show huge opportunities to be integrated in devices such as electronics, [4][5][6] sensors and actuators. [7] Within this context, additive manufacturing emerges as a set of advanced fabrication techniques that enable the production of fully functional electronic devices in one step printing. [1,[8][9][10] However, for photopolymerization-based 3D printing techniques the number of UV curable materials suitable for the fabrication of sensors and actuators is still scarce. [1] Research in this field pursues 3D printing materials with new features but also environmentally more friendly and sustainable, as demanded by today's society. [11][12][13] Techniques as stereolithography (SLA) and digital light processing (DLP) are based on the layer-by-layer solidification of a liquid photosensitive resin via UV-light exposure. [14] This is a tailorable process where multicomponent resins provide the photo-rheological and mechanical properties necessary to ensure a successful print. [15] The design of suitable materials for the manufacture of pressure sensors with high sensitivity and flexibility in wearable electronics is still a challenge. In this study, a flexible and portable pressure sensor is developed based on a photopolymeric formulation of polyaniline (PANI)/Lignin/acrylate. The amount of photoinitiator and the presence of lignin within the filler are investigated to obtain the best printability and capacitive response. Low PANI contents drastically increase the dielectric constant and 4 wt% photoinitiator improves the signal and sensitivity. A sensitivity of 0.012 kPa -1 is achieved in a linear range (0-10 kPa) with only 3.5 wt% PANI. Lignin improves both the dispersion of the filler within the matrix and the printability of the resin, due to lower absorptivity at the UV wavelength of the 3D printer. Thus, the PANI-Lignin filler is selected for the fabrication of a piezocapacitive prototype transducer. The pressure transducer demonstrate its practical application by responding to a human footfall and transmitting its corresponding electrical signal. This study shows the enhanced properties of lignin modified PANI acrylate composites. Based on lignin, an abundant natural waste, a sustainable photocurable cost-effective polymer is proposed for the fabrication of printable, wearable electronics.

No abstract

In the last decade, Fused Deposition Modeling (FDM) has gained popularity for allowing the fabrication of pieces with complex shapes. The final quality of the pieces is strongly linked to the shape, size and surface finish of the strands deposited successively, which themselves depend on the printing parameters and extruded material properties. In this work, we present an experimental characterization of an extruded and deposited single strand of Poly-Lactic Acid (PLA), by means of high-speed visualization of the bead region between the substrate and the nozzle, where the molten polymer is still in liquid phase. A Computational Fluid Dynamics (CFD) model proposed in literature, and, based on isothermal and viscous flow assumptions, is validated with this data in terms of strand height and meniscus shape. The characteristics of the printed layer are also confronted to the measurements of the solidified strands by microscopy, with a good agreement. The focus on high printing speeds allows extending the conclusions of previous studies. Regarding the surface finish, the roughness patterns detected on the printed strands are correlated to the velocity fluctuations of the printing head. The CFD model does not capture those thickness variations, however, due to not accounting for solidification.