PP/MWCNT injection-moulded components: an analytical study of electrical properties and morphology

Since their early synthetization in the 30s, the interest in polymers potentialities has continuously expanded. Nowadays, the majority of everyday devices could not exist without plastics. The combination of their light-weight, versatility, easy processability and relatively low cost makes these materials essential in several industrial sectors. Their applications, in fact, range from consumer goods to specialist devices realization. Moreover, their powerful properties can be easily exploited, in combination with the numerous manufacturing techniques, with which they are transformed. Among all, melt mixing and injection moulding processes, which are the most known and used technologies to modify polymers, are effortlessly adopted to create new materials. Nonetheless, it is reported in literature that both these techniques and their working conditions strongly affect the final properties of the final components, in particular for what concerns the injection moulding process. It is known, in fact, that a tough orientation of molecular chains and fillers occurs inside the molten material during this process. This phenomenon creates a marked anisotropic behaviour of the final properties of the components, with a consequent non-uniform distribution of properties. Studying this mechanism is important to understand how to modify and to optimize the processing conditions, in order to tailor the final properties of the prepared materials. This thesis aims to investigate the electrical anisotropic behaviour of injection-moulded polymeric MWCNT-based nanocomposites, correlating the variations of process conditions and the morphological and electrical anisotropic properties of thermoplastic nanocomposites. With this purpose, multi-walled carbon nanotubes/polypropylene nanocomposites were prepared and manufactured using melt mixing and injection moulding processes. The processing parameters were changed and the variations in the electrical behaviour and in the morphological structure of the nanocomposites were observed. During the melt mixing phase, the temperature of the screw profile and the MWCNTs feeding zone along the screw were modified. During the injection moulding phase, three main parameters were modulated, namely injection rate, temperature of the mould and temperature of the melt. Moreover, an innovative injection moulding process, i.e. the Heat&Cool technique, was exploited in order to vary the temperature of the mould, quickly increasing and decreasing it. The prepared specimens were characterized electrically through DC, AC and surface resistance measurements. A multi-direction electrical testing was used to evaluate the electrical percolation threshold in the three main spatial directions, i.e. longitudinal and transversal to the flux of the molten material inside the mould and in the through-thickness direction. The morphological structure of the sample was observed through both Optical and Scanning Electron Microscopy. The influence of the change of processing parameters on these properties was deeply studied. As main results, different levels of inhomogeneity was observed. An inhomogeneous processing-induced morphological skin-core structure in the thickness was detected. The electrical behaviour appeared non-uniform and this aspect seems to be correlated directly to the internal morphological structure of the injection-moulded parts. Then, an alteration in the electrical behaviour is also observable in different positions of the same injection-moulded sample, namely nearer to or farther from the injection gate. Finally, the change of the processing conditions appears to play a fundamental role in the formation of both the inhomogeneous morphological structure and the anisotropic electrical behaviour of the MWCNT-based nanocomposites. In fact, the increase of the temperature of the mould and of the injection rate act as the main responsible for the decrease of the electrical resistivity of the prepared nanocomposites

Static and thermal FE analysis of a Flexible Electronic BOard (FEBO) prototype and the characterization of its innovative materials

An FE model of an experimental flexible electronic board was built to determine its performance in terms of mechanical and thermal distortions, heat and transient thermal flow, thereby detecting critical issues and identifying opportunities for improvement. Commercial sensors were connected to the flexible board (100x40x2mm), which was based on a commercial thermoplastic polyurethane (TPU), with a PEDOT-based conductive resin trapped in a PEGDA network, a biocompatible polymer. Three thermal loads (ΔT=175°C, ΔT=100°C, ΔT=50°C) were applied which revealed critical stresses for high ΔTs but at ΔT=50°C only the connectors had a critical σvm, while for ΔT=50°C + 1mm displacement a critical strain value occurred in one area of the substrate. Heat transient analysis and overheating simulations were performed to determine the heat flow behavior for the photodiode and accelerometer. FE analyses allow more studies to be undertaken to improve material properties and suggest redesign activities for similar concept demonstrators. The funds of the European Union and the Piedmont Region, and agreements with the most important players in SBE (Simulation Based Engineering) software sales and services, allowed the authors (ITACAe srl, Proplast, and Politecnico di Torino) to conduct industrial research and experimental development together with manufacturers and users of innovative technologies to identify, study and optimize the design parameters of the board while simultaneously contributing to its technological development

Active Coated PLA-PHB Film with Formulations Containing a Commercial Olive Leaf Extract to Improve Quality Preservation of Fresh Pork Burgers

Since fresh meat is often subject to several degradation reactions that decrease its safety and quality until it is considered unacceptable, the release of bioactive compounds into meat products may be a good option to slow down oxidation and extend its shelf-life by a few days. Therefore, this study aimed to test the application on fresh pork burgers of a PLA-PHB film coated with two different coating formulations (methylcellulose, MC and chitosan, CT), both containing a commercial olive leaf extract OL, to evaluate their effect on meat quality preservation. Samples were tested at 0, 2, 5, 7, 9, 12, and 14 days after packing for microbial, chemical, and sensory evaluations. Except for the chitosan-only formulation, all tested formulations (MC, MC+OL and CT+OL) adhered well to the PLA-PHB base without the use of specific treatments. Meat packed with the different coatings maintained a slightly brighter red colour than the control samples and, as a result, deteriorated more slowly. In the evaluation of lipid oxidation, the CT+OL coating showed lower mean values of mg MDA/kg meat, which were significantly different from the other samples, especially on the 7th and 9th day of storage. Moreover, the CT+OL coating showed a slight slowdown in Enterobacteriaceae growth, revealing promising results in maintaining the meat quality longer

Bioplastics and Carbon-Based Sustainable Materials, Components, and Devices: Toward Green Electronics

The continuously growing number of short-life electronics equipment inherently results in a massive amount of problematic waste, which poses risks of environmental pollution, endangers human health, and causes socioeconomic problems. Hence, to mitigate these negative impacts, it is our common interest to substitute conventional materials (polymers and metals) used in electronics devices with their environmentally benign renewable counterparts, wherever possible, while considering the aspects of functionality, manufacturability, and cost. To support such an effort, in this study, we explore the use of biodegradable bioplastics, such as polylactic acid (PLA), its blends with polyhydroxybutyrate (PHB) and composites with pyrolyzed lignin (PL), and multiwalled carbon nanotubes (MWCNTs), in conjunction with processes typical in the fabrication of electronics components, including plasma treatment, dip coating, inkjet and screen printing, as well as hot mixing, extrusion, and molding. We show that after a short argon plasma treatment of the surface of hot-blown PLA-PHB blend films, percolating networks of single-walled carbon nanotubes (SWCNTs) having sheet resistance well below 1 kω/□ can be deposited by dip coating to make electrode plates of capacitive touch sensors. We also demonstrate that the bioplastic films, as flexible dielectric substrates, are suitable for depositing conductive micropatterns of SWCNTs and Ag (1 kω/□ and 1 ω/□, respectively) by means of inkjet and screen printing, with potential in printed circuit board applications. In addition, we exemplify compounded and molded composites of PLA with PL and MWCNTs as excellent candidates for electromagnetic interference shielding materials in the K-band radio frequencies (18.0-26.5 GHz) with shielding effectiveness of up to 40 and 46 dB, respectively.Business Finland (project 1212/31/2020, All green structural electronics), EU Horizon 2020 BBI JU (project 792261, NewPack), and EU Interreg Nord Lapin liitto (project 20201468, Flexible transparent conductive f ilms as electrodes) and Academy of Finland (project 316825, Nigella)

Influence of Chitin Nanocrystals on the Crystallinity and Mechanical Properties of Poly(hydroxybutyrate) Biopolymer

This study focuses on the use of pilot-scale produced polyhydroxy butyrate (PHB) biopolymer and chitin nanocrystals (ChNCs) in two different concentrated (1 and 5 wt.%) nanocomposites. The nanocomposites were compounded using a twin-screw extruder and calendered into sheets. The crystallization was studied using polarized optical microscopy and differential scanning calorimetry, the thermal properties were studied using thermogravimetric analysis, the viscosity was studied using a shear rheometer, the mechanical properties were studied using conventional tensile testing, and the morphology of the prepared material was studied using optical microscopy and scanning electron microscopy. The results showed that the addition of ChNCs significantly affected the crystallization of PHB, resulting in slower crystallization, lower overall crystallinity, and smaller crystal size. Furthermore, the addition of ChNCs resulted in increased viscosity in the final formulations. The calendering process resulted in slightly aligned sheets and the nanocomposites with 5 wt.% ChNCs evaluated along the machine direction showed the highest mechanical properties, the strength increased from 24 to 33 MPa, while the transversal direction with lower initial strength at 14 MPa was improved to 21 MPa

Dielectric Spectroscopy of PP/MWCNT Nanocomposites: Relationship with Crystalline Structure and Injection Molding Condition

5nocarbon nanotubes; polymer nanocomposites; dielectric properties; crystallinit

Effect of Filler Morphology on the Electrical and Thermal Conductivity of PP/Carbon-Based Nanocomposites

In this paper, we studied the effect of different carbon-based nanostructures on the electrical and mechanical properties of polypropylene (PP) nanocomposites. Multi-walled carbon nanotubes (MWCNT), expanded graphite (EG), and two different carbon black nanoparticles (CB) have been dispersed at several weight contents in the polymer matrix through a melt extrusion process. The produced nanocomposites have been used to obtain samples for the characterization by injection molding. The dispersion of the nanoparticles in the matrix has been evaluated by scanning electron microscopy (SEM) analysis. The electrical characterization has been performed both in DC and in AC configuration. The mechanical properties have been evaluated with both tensile test and impact strength (Izod). The thermal conductivity has been also evaluated. As a result, MWCNTs are the nanoadditive with the lowest electrical percolation threshold. This allows MWCNT nanocomposite to drastically change the electrical behavior without a significant embrittlement observed with the other nanoadditives. However, CB with the lowest surface area allows the highest conductivity, even though at a high particle content. EG has a limited effect on electrical properties, but it is the only one with a significant effect on thermal conductivity

Fire behavior of polyamide 12 nanocomposites containing POSS and CNT

Nanocomposites of polyamide 12 with multiwall carbon nanotubes (CNT) and octaisobutyl polyhedral oligomeric silsesquioxanes (POSS) were studied to assess their flame retardancy properties. The fire behavior was investigated with a cone calorimeter using 50 kW/m2 heat fluxes, by means of the oxygen index and the UL 94 H classification. The fire residue was characterized using FT-IR and SEM. The best overall performance was observed for the composites containing 3.3 wt% of POSS and 4 wt% of CNT. This composite achieved HB in UL 94, an oxygen index of 27 and a 74% reduction in the peak heat release rate. A synergistic effect was evidenced using POSS and CNT together whereas FT-IR and SEM analysis of the residue from fire experiments confirms the formation of SiO2 shield on the surface of the burning sample