Band 24, Heft 3

A hydrophobically modified ethoxylated urethane (HEUR) as a thickener was synthesized using poly (ethylene glycol), Dicyclohexylmethane diisocyanate (H 12 MDI) and cethyl alcohol via step growth polymerization technique. The molecular weight of the thickener was determined by GPC, and its behavior in aqueous solution was studied. The steady shear experiments were carried out by mixture of the synthesized thickener with two resins. These resins had different nature; one with hydrophilic and the other with both hydrophilic and hydrophobic segmental structure. The result showed the type of resin can be effective in the thickening efficiency of HEUR thickener.

The stretch-blow molding process of polyethylene terephthalate (PET) bottles generates some important modifications in the mechanical properties of the material. Considering, the process temperature (T > T g ) that is usually used, the material exhibits a very high viscosity and involves a strain hardening effect associated with the microstructure evolution. An anisotropic viscoplastic model coupled with induced properties, identified from experimental results of uniaxial and biaxial tensile tests previously published by Chevalier and Marco (2006), is presented in a first part of the paper. Secondly, we perform a numerical simulation to simulate the free inflation of a preform under an internal pressure with different parameters. Because the final strains are up to 300 to 400%, it generates important distortion of node distribution and we chose to use the mesh-free Constrained Natural Elements Method (C-NEM) for numerical simulation. The final goal is to use these simulations in order to fit the best parameter set leading to a quasi-homogeneous distribution of the thickness along the bottle. Homogeneous thickness implies homogeneous biaxial stretching and more uniform induced properties for the final bottle and this is an important industrial goal.

Water assisted injection molding technology has gradually become an important process for making hollow plastic parts, due to its light weight, relatively lower resin cost per part, faster cycle time, and its flexibility in the design and manufacture of plastic parts. Study of the temperature profiles in molded parts is of fundamental importance to a more complete understanding of many complicated phenomena. This report presents a novel experimental setup which allows the in-situ measurement of three-dimensional temperature field in the depth of molded parts throughout the molding cycles. A specific mold equipped with tubular needles for guiding embedded micro-thermocouples was designed and manufactured. Experiments were carried out on a lab developed water assisted injection-molding system, which included an injection molding machine, a water pump, a water injection pin, a water tank equipped with a temperature regulator, and a control circuit. The resin used was semi-crystalline polypropylene. The in-cavity temperature of the polymeric materials during the molding cycle was measured. In addition, an unsteady-state, nonlinear heat transfer model of water assisted injection molding has been proposed to numerically simulate the in-depth temperature profiles. It is shown that the numerical predictions are in good agreement with experimental data. Experimental investigation and numerical simulations of a water assisted injection molding cooling process will provide an improved understanding of the influence of water related parameters on the cooling process of water assisted injection molded parts.

Experimental and simulation studies of flow of a slipping polymer melt in a co-rotating twin screw extruder are presented. The experiments involve a wide range of polyolefins (polyethylene, isotactic polypropylene, isotactic polybutene-1, isotactic poly 4 methylpentene-1, and a cyclopolyolefin) with an octadecanoic acid additive. Mooney's capillary method is used to prove the occurrence and magnitude of slippage. In the twin screw extruder experiments, the die pressure is reduced for the compounds with octadecanoic acid compared to the neat polyolefins. Screw characteristic curves (Q vs.dpdx) were determined experimentally for both the polyolefin compounds and the neat polyolefins. These were found to be rather close. We modeled flow of a slipping non-Newtonian(power law) fluid in a screw channel and calculated screw characteristic curves. These were found to be close to our experimental observations.

In the filling phase of injection molding process, melt-front rate plays a particularly important role in determining the part quality. Prior researches recommend a constant melt-front rate for this phase. A measurement device based on a capacitor principle has been developed. It has been shown that this sensor is effective to measure online and continuously melt-front position in mold cavity. Based on this sensor, this work develops and tests closed-loop control system of direct in-mold melt-front rate control. Several advanced control algorithms, Generalized Predictive Control (GPC), Iterative Learning Control (ILC), and Generalized 2D Model Predictive Iterative Learning Control (2D-GPILC), are designed, implemented, and tested with different mold inserts. The results show that 2D-GPILC, a combination scheme of feedback and iterative learning scheme, gives the best control results.

Polyamide/organoclay nanocomposites have been prepared via direct melt intercalation in an internal mixer at 2.5% volume fraction, under various processing conditions. The influence of the melt mixing conditions on the structure and on the oscillatory and steady shear rheological properties of PA-12 layered silicate nanocomposites has been studied. Both structural properties and melt state material properties of nanocomposites were shown to exhibit similar trends when studied as a function of the specific mixing energy. Low frequency storage and loss moduli, but also yield stress and low-shear first normal stress difference were shown to increase up to a critical value of this specific mixing energy, and to level off above this value.

This paper investigates the kneading and molding of PP (polypropylene) with nano-TiO 2 (Titanium dioxide) powder having sizes in the range of 50 nm. It was found that quality feedstock with uniform nanopowder dispersion was achieved only when the kneading was performed for optimum time under optimum torque using a custom-made triple-screw kneader with a high shear stress. The torque and kneading time needed for PP composite with 40 wt.% nano-TiO 2 is double that required for the one with 10 wt.%. Rheological and impact properties of composites with 10 wt.% and 40 wt.% filler loading were also analyzed. In addition, a very important result revealed that a simple micro-grating can be successfully used as a mold insert to replicate micro-features made with PP/nano-TiO 2 feedstock using injection molding conducted under a high forming pressure and evacuation of the mold.

Rice flour was modified with water and glycerol in single-screw extruder to obtain bioplastic of low manufacturing cost. Sisal fibers were used as reinforcing fillers to enhance rice flour-based bioplastic properties. The effects of short sisal fiber content (5 to 20 wt.%), length (0.2 to 6 mm) and alkali treatment (5% w/v NaOH) on the moisture content, tensile properties, impact properties, dynamic mechanical properties and morphology of the biocomposites were studied. The results showed that incorporation of the sisal fibers with a fixed fiber length into the bioplastics improved moisture resistance, tensile strength, impact strength and storage modulus, and that the improvement level increased with increasing sisal fiber content. The optimum reinforcement was achieved at 20 wt.% of fiber loading and 4 mm long fibers. The tensile strength of the biocomposite was about 4 times more than that of the neat rice flour-based bioplastic. The use of 5% NaOH aqueous solution further improved the moisture resistance and mechanical properties of the biocomposites, mainly resulting from better interfacial adhesion between the sisal fiber and rice flour matrix. Furthermore, the performance of the rice flour-based bioplastics synergistically combined with the sisal fibers suggests that they have great potential in development of environmentally friendly/sustainable biomaterial products from renewable resources.

To investigate the orientation development behavior in high-speed in-line drawing process of poly(ethylene terephthalate) filament, simultaneous on-line measurements of diameter and optical retardation were conducted under various spinning and drawing conditions. In the measurement of optical retardation, the order of interference could be determined successfully from the successive assembly of phase shift versus filament diameter correlations collected at different measuring positions along the spinning and drawing lines. Analyzed birefringence increased steeply in the vicinity of neck-like deformation in the high-speed spinning line or in the vicinity of necking deformations in the in-line drawing line. It was verified that the thinning in the in-line drawing line is more effective for the development of molecular orientation in comparison with that in the high speed spinning line. Analysis on the time-course variations of diameter and birefringence in the vicinity of neck-like deformation caused by the fluctuation of its position along the spinning line was conducted to obtain detailed orientation development behavior. This analysis confirmed that the local birefringence is governed solely by the local diameter (or velocity) in the high-speed spinning line. On the other hand, it was relatively difficult to analyze the time-course variation of birefringence near the necking deformation in the in-line drawing line because of an overlapping of unique short-period diameter fluctuation of around 125 Hz, which corresponds to several tens of centimeters along the filament, occurring during the necking deformation. Such diameter fluctuation moves toward downstream at the speed of running filament, and therefore was speculated to be originated from the intrinsic characteristics of fiber materials.

The replication of polymeric microstructures on a flat surface is not easily achieved by conventional injection molding, because of the required micro-dimensional control and the stringent tolerances of most applications. Moreover, the flow behaviour of melts in micro cavities remains not well understood and challenging. On the other hand, injection-compression molding is an established process for the manufacturing of optical storage media, like compact discs (CD) or digital versatile discs (DVD), with grooves and pits at the micro-scale. The difficulties arise mainly from two sources: lack of adequate filling because of premature freezing of features with very small thicknesses and excessive deformation during ejection due to high friction at the polymer-metal interface. In this work, a study is carried out to investigate the effect of process parameters on the replication of various microstructures on a flat disk using microinjection-compression molding. A commercial microinjection molding machine has been used in the study. Two optical grade polymers poly(methyl methacrylate) (PMMA) and cyclic olefin polymer (COP) were used in conjunction with various mold inserts to reproduce the embedded microstructures. The dimensions of the microstructures on the inserts and molded parts were measured with a confocal profiler. A transcription ratio was defined to assess the quality of the replication. The design of experiment (DOE) method was used to obtain correlations between the process parameters and the development of the microstructure during injection-compression molding.

This paper investigates the viscosity behavior of melt polymer during the plastication stage in an injection molding machine (IMM). The objective of this paper is to develop theoretical viscosity-based models for evaluating and predicting the bulk viscosity of the melt polymer near the tip of the screw during the plastication stage. The uniqueness of these models is that they include the effects of material properties and machine processing parameters, such as screw rotational speed, hydraulic back pressure, barrel pressure drop, melt pressure and melt temperature. Several open loop tests were conducted on an industrial IMM in order to quantify process parameter effects on the plastication cycle. The derived model was used to predict bulk viscosity using the open loop tests data. The viscosity-based models in this work will be used for developing future optimal controllers for controlling the polymer viscosity during the plastication stage of the injection molding cycle.