Felicia Stan

INFLUENCE OF INJECTION MOLDING PARAMETERS ON MECHANICAL PROPERTIES OF LOW DENSITY POLYETHYLENE FILLED WITH MULTIWALLED CARBON NANOTUBES

In this paper, we investigated the effect of injection molding parameters such as melt temperature, mold temperature, injection speed and holding pressure on the mechanical properties of low density polyethylene reinforced with 2.5 wt% multi-walled carbon nanotubes. The Taguchi methodology with four factors and two levels was used for the design of the injection molding experiments. The mechanical properties were evaluated by tensile tests in the flow direction at room temperature (23 °C) at crosshead speeds of 1 and 5 mm/min. It was found that the mechanical properties can be modified by manipulating the injection molding parameters. The Young’s modulus of the LDPE-MWNTs composite decreased as the melt temperature increased, while mold temperature, injection molding speed and holding pressure have a moderate influence on the Young’s modulus.

Experimental Investigation of the Adhesion Between Thermoplastic Polyurethane and Acrylonitrile-Butadiene-Styrene Substrate

In this paper we investigated the direct-adhesion of Thermoplastic Polyurethane (TPU) to Acrylonitrile-Butadiene-Styrene (ABS). Specimens with an initial pre-crack were obtained by overmolding the TPU onto ABS substrates, at different melt and mold temperatures. The interfacial adhesion between these two dissimilar polymers, represented by the peeling force, was measured directly by using the standard T-peel test at room temperature and at a crosshead speed of 254 mm/min. The peeled fracture surfaces were observed under optical microscope to identify the failure mechanism (adhesive or cohesive). A qualitative correlation was established between the adhesion strength and the injection molding parameters.Copyright

Effect of the Injection Moulding Parameters on the Creep Properties in Polypropylene/Carbon Nanotubes Composites

The goal of this paper is to study the time-dependent properties of multi-walls carbon nanotubes (MWCNTs)-filled polypropylene (PP) composites using the instrumented indentation technique. Two types of the indentation test, the 3-step and the 5-step indentation tests, were considered to investigate the creep response during sharp indentation. In order to characterize the state of distribution of MWCNTs, the Scanning Electron Microscopy (SEM) technique was used. It was found that the maximum indentation depth decreases with the increase in the MWCNTs concentration. At lower MWCNTs concentration, the effect of injection pressure on the creep displacement is not significant. Comparison of the creep displacements from 3-step and 5-step loading histories indicates a noticeable decrease in creep displacement when the 5-step loading history is used.

Tuning the Mechanical Properties of High-Density Polyethylene by ECAE Process

This paper investigates the ability of the equal channel angular extrusion (ECAE) process to induce morphological changes and hence tune the mechanical properties of high-density polyethylene (HDPE). In this study, differential scanning calorimetry (DSC), compression and cylindrical macro-indentation tests have been used to investigate the evolution of the mechanical properties of HDPE processed by ECAE up to four passes via route BC, i.e. counter clockwise 90° billet rotation about its longitudinal axis.It was found that the ECAE process induces significant plastic deformations with changes in the crystalline structure. The ECAE process increased the HDPE crystallinity by 10 to 15%. The number of ECAE passes has a significant effect on the magnitude of the mechanical properties especially on the elastic modulus and yield stress. Young’s modulus and yield strength decreased with increasing the number of ECAE passes and reached a stationary state after the third pass.Copyright

Investigation on the Effect of Carbon Nanotubes Concentration on the Electrical and Rheological Properties of PP/MWCNTs Composites

The objective of this paper was to investigate the electrical and rheological behaviors of polypropylene (PP) filled with 1.0, 3.0 and 5.0 wt.-% multi-wall carbon nanotubes (MWCNTs). The flow behavior was analyzed in terms of the melt flow index measured at temperatures relevant for the injection molding process and the flow activation energy was calculated using an Arrhenius type equation. The electrical behavior of PP/MWCNTs composites was examined by DC resistance measurements on injection molded samples.The experimental results have shown that the incorporation of MWCNTs effectively enhances the electrical conductivity of the injection molded PP/MWCNTs composites. The composites under analysis can be classified as semi-conductors with the conducting network arranged in 4 dimensions, i.e. the critical exponent of the power-law dependence of the conductivity on the wt.-% MWCNTs is 2.37. The increased conductivity is explained by the orientation of the MWCNTs along the melt flow and the increased nanotubes-to-nanotubes contact after the formation of the percolation network.Copyright

In-Mold Monitoring of Temperature and Cavity Pressure During the Injection Molding Process

This paper focuses on the in-mold monitoring of temperature and cavity pressure. The melt contact temperature and the cavity pressure along the flow path were directly measured using two pressure sensors and two temperature sensors fitted into the cavity of a spiral mold. Three melt temperatures and dies of different heights (1.0, 1.5 and 2 mm) were used to achieve a wide range of practically relevant shear rates. In order to analyze the extent to which the numerical simulation can predict the behavior of the molten polymer during the injection molding process, molding experiments were simulated using the Moldflow software and the simulation results were compared with the experimental data under the same injection molding conditions.© 2014 ASME

The effect of processing parameters on the bond strength and electrical conductivity of multi-wall carbon nanotube/low-density polyethylene composite

The objective of this paper is to study the influence of processing parameters, such as melt temperature and mold temperature, on the adhesion of low density polyethylene (LDPE) to 2.5 wt/% multi-wall carbon nanotube-filled polyethylene (LDPE/MWCNT). The adhesion was obtained using two-component injection-molding method and measured using tensile experiments. The electrical conductivity of the two-component injection-molded specimens was also measured through DC voltage and compared to the volume resistivity of the LDPE and LDPE/MWCNT composite. It was found that the bond strength increases with increasing melt and mold temperatures. However, increasing the melt and mold temperatures over a certain limit can decrease the bond strength. The range of the electrical conductivity of the LDPE-LDPE/MWCNT two-component injection-molded samples was in the range of dissipative materials.

Study of Flow Font Advancement during Filling Stage of a Spiral Mold

The objective of this paper consists in the determination of the flow front length using o circular spiral mold. The paper also studies the influence of the process parameters on the flow front length using the method of statistical analysis. For this purpose, a number of numerical simulations are carried out by utilizing the combination of four process parameters (i.e., the melt temperature, the spiral thickness, the injection pressure and the mold temperature) at three levels. In order to reduce the number of numerical simulations, a simplistic Taguchi L27 orthogonal array was chosen. The material chosen for this study was a low density polyethylene and a high density polyethylene. The flow front length was measured through a marked pattern of the circular spiral using the AutoCAD.

Statistical Cutting Force Model for Orthogonal Cutting of Polytetrafluoroethylene (PTFE) Composites

This paper presents an experimental investigation of the cutting forces response during the orthogonal cutting of polytetrafluoroethylene (PTFE) and PTFE-based composites using the Taguchi method. Cutting experiments were conducted using the L27 orthogonal array and the effects of the cutting parameters (feed rate, cutting speed and rake angle) on the cutting force were analyzed using the S/N ratio response and the analysis of variance (ANOVA). Statistical models that correlate the cutting force with process variables were developed using ANOVA and polynomial regression. The variation of the apparent friction coefficient was analyzed with respect to tool geometry and the cutting process. The results indicated that cutting and thrust forces increase with increasing feed rate, and decrease with increasing rake angles from negative to positive values and increasing cutting speed. A power law relationship between the apparent friction coefficient and the normal force exerted by the chip on the tool-rake face was identified, the former decreasing with an increasing normal force.© 2013 ASME

Correlation Between Mechanical Properties in Standard Test Specimens and Injection Molded Thin-Wall Parts

In this paper, we investigated the effect of injection molding parameters on the mechanical properties of thin-wall injection molded parts. A four-factor (melt temperature, mold temperature, injection speed and packing pressure) and three-level fractional experimental design was performed to investigate the influence of each factor on the mechanical properties and determine the optimal process conditions that maximize the mechanical properties of the part using the signal-to-noise (S/N) ratio response. The mechanical properties (e.g., elastic modulus, yield strength and strain at break) were measured by tensile tests at room temperature, at a crosshead speed of 5 mm/min, and compared with those of the injection-molded specimens.The experimental results showed that the tensile properties were highly dependent on the injection molding parameters, regardless of the type of the specimens. The values of Young modulus and yield strength of the injection-molded specimens were lower than those of the injection-molded parts, while the elongation at break was considerably lower for the injection-molded parts. The optimal process conditions were strongly dependent on the measured performance quantities (elastic modulus, yield strength and strain at break).Copyright