María Virginia Candal

Polypropylene/wood flour composites: treatments and properties

In this research, the variations produced on the mechanical, morphological and thermal properties and on the melt index (MI) of a composite of polypropylene and wood flour (WF) by the modification of the filler were studied. The filler was treated with sodium hydroxide at different immersion times and with vinil-tris-(2-metoxietoxi)-silane. Polypropylenes functionalized with maleic anhydride (maleated polypropylene, MAPP) were also used as compatibilizers. All the treatments showed the same tendency to slightly increase tensile modulus and tensile strength of the composites, but they did not affect their MFI. Morphological studies showed that the MAPP and silane improve the polymer–WF adhesion and the dispersion of the particles, while the alkaline treatment only improves the dispersion. The silane-modified samples and the use of MAPP produced samples with lower water absorption than those of untreated WF composites. The addition of the filler and the treatments carried out on it caused an increase in the crystallization temperature.

Dynamic thermal decomposition of blends of polyamide 6 with functionalized and non-functionalized PP

Abstract The processes of thermal degradation taking place in polyamide 6 (PA6) blends with functionalized (PP1-g-DEM) and non-functionalized polypropylene (PP2) have been studied by thermogravimetric analysis. Coats–Redfern, Van Krevelen and Horowitz–Metzger integral methods were used to determine kinetic parameters. It was observed that the starting temperature of the decomposition of the blends decreases from 380 to 340°C when increasing the concentration of functionalized polypropylene. When non-functionalized polypropylene is used, the decrease is from 360 to 300°C. On the other hand, although the activation energy of the functionalized polypropylene is smaller than that of the non-functionalized, it was demonstrated that the thermal stability is bigger for the mixtures of PA6 with PP1-g-DEM, the latter being at 30 wt% composition of PP. Also, the use of functionalized polypropylene in the blends with polyamide evidences a better dispersion and a smaller particle size; this behavior positively influences the thermal stability of these blends.

Effect of the Injection Molding Process Conditions Over the Determination of Kt Curves for Plastic Parts

Influence of process conditions (melt temperature, injection and holding/packing pressures and injection velocity) used for injected plastic part with a stress concentrator were studied. Specifically, the effect over the mechanical properties of polymer injected parts was studied. Crystal polystyrene (PS) plaques with a triangular stress concentrator were injected. Next, injected notches were compared with notch made in manual form, for determination the effect of the production method over the stress concentrator factor (Kt). It was verified that Kt varies with the injection molding process conditions and with the method for it elaboration.

Effect of the Finite Element Meshing for Designing Plastic Pieces

Abstract The objective of this work was to modify the simulation mesh model characteristics (critical areas evaluation, mesh density, and elements size) of a commercial compact disk (CD) case by using computer-aided design (CAD) and computer aided engineer (CAE) software. The designing process was carried out by studying the geometry and dimensions of the three pieces (cover, holder, and base) that form commercial and optimized CD cases.The mesh model was obtained using 3D (three dimensional) modeler software and the simulation results were obtained using a simulation program typically used for the injection-molding process. The exposed designs were evaluated and different mesh model characteristics were established. The filling time, cycle time, and residual stress concentration seemed to be influenced by the nodes number model. An analysis of the results of the simulations showed remarkable differences when a high number of nodes in the mesh model were used.

Influence of Geometrical Factors on Cavity Pressure During the Injection Molding Process

The influence of the geometrical factors of plastic parts (shape factor, thickness, length/thickness ratio, and section changes) on the behavior of the cavity pressure during the injection process was studied. The instrumentation of injection molds was proposed, placing pressure transducers in the more critical zones of the parts. The evaluation of the molds was made using solid modelator and simulator software of the injection process with different polymers. The geometric factors determine the processing conditions to be used, the behavior of the cavity pressure during filling and postfilling phases, the cooling, and the dimensional stability of the part.

Determination of Kt Curves for Plastic Parts with a Triangular Stress Concentrator

Influence of a triangular stress concentrator on the mechanical properties of polymer-injected parts was studied. Crystal polystyrene (PS) plaques with a different dimensions concentrator were injected. Specifically, the influence of the dimensions of a stress concentrator over the stress concentrator factor (Kt) was studied. It was verified that Kt depends on geometrical parameters, and it was obtained as a trend similar to that reported on metals.

Methodology for the Study of the Stress Concentrators in Plastic Parts

A methodology for the study of the stress concentrators on the mechanical properties of polymer-injected pieces was developed. PP inserts were designed and made with the shape of the selected multiple size concentrators. Inserts were put into one of the cavities of the mold and PS plaques with notches were obtained. Mechanical properties of all the injected plaques were evaluated through tensile tests. Based on these results of curves, Kt versus geometrical parameters of the plaques were made. It was tried to prove that such factor varies with the material used, with the process conditions and with the elaboration method of the notches.

Mold Design Optimization for Security Caps Used in the Pharmaceutical Industry

Abstract: The main purpose of this study was to design and evaluate an injection mold in order to make a security cap for pharmaceutical bottles using the tools found in the computer-aided design (CAD) and computer-aided engineer (CAE) software. The process design included studying the geometry and dimensions of the two pieces (internal and external) that constitute the security cap. Two mold designs were proposed: a four-cavity one with a type “x” distribution and removable core, and eight-cavity design with a type “x” family-mold distribution. They both were designed with the finality of modeling the internal and external pieces that form part of the security cap into one single mold. Two different cavity dispositions were evaluated for this design. Additionally, several cooling systems were evaluated using the injection process simulator program, C-MOLD. The most efficient cooling system was selected and it was used in simulations with a four-cavity mold to produce the internal and external pieces. Afterwards, another simulation was carried out using the same cooling system for the eight-cavity mold. The exposed designs were evaluated establishing different kinds of operative conditions until optimal process conditions were met. Finally, two injection molds were proposed: One with four cavities and a removable core, and another one with eight cavities that could allow the production of both pieces at the same time. Also, both molds were designed using the solid modeling Pro/ENGINEER software. The family molds showed more reliability, with an increase of 12% in the cycle time, compared to the molds with four cavities and a removable core.