The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
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The Effect of Resin Viscoelasticity on Extrudate Swell: Computational Modeling and Experimental Validation
Parison formation is the most critical stage in extrusion blow-molding process. This is due to the strong effect of extrudate swell on parison dimensions, which consequently affects the thickness profile of the blow-molded part. The swelling due to stress relaxation and sagging due to gravity are strongly influenced by the resin viscoelasticity, die geometry, and operating conditions. Computational modeling tools, once combined with experimental validations, can considerably reduce the development time and cost for the blow-molded parts. In this study, we have developed a dimensionless swell model to estimate the parison swell. The output of the swell model has been used to generate the 3D finite element mesh to predict the parison sag under gravity based on the generalized Maxwell model. The model predictions have been compared with the experimental data for three high-density polyethylene resins in order to validate the developed computational approach. We anticipate that the results of this study can also contribute to the development of similar approaches in fiber spinning and fused deposition modeling.
Failure of HDPE Butt Fusion Joint Due to Poor Manufacturing Practices
High density polyethylene (HDPE) pipes have been used successfully in applications ranging from potable water lines to chemical fluid transmission for nearly four decades because of its superior mechanical and chemical properties over other thermoplastic piping materials. The standard method of joining HDPE pipe in the field is the butt fusion process. The quality of the butt-fused joints depends largely on environmental and joining surface conditions. The failure modes commonly observed in butt fused joints are poorly fused and contaminated joints and initiation of cracking at stress concentration defects in the fusion weld. In this paper, a case study of fusion joint failure in a fabricated elbow fitting due to poor manufacturing practices is presented. The mechanism and type of failure have been deduced from a detailed morphological examination of the fracture surface. Various factors responsible for a brittle failure of the butt fused joints have been identified. Analytical and thermal testing was performed to identify a specific material characteristic responsible for the failure.
Modeling the Kinematics and Thermodynamic Interactions during the Dispersion of layered Silicates in Polymer melts
Polymer nanocomposites offer a unique solution to improve desired physical attributes while maintaining other incompatible properties, such as engineering plastics with increased stiffness and strength while maintaining or increasing toughness. Melt processing represents an attractive, economical and flexible route for producing thermoplastic nanocomposites. This paper extends the concepts presented in a previous publication by describing a kinematic and thermodynamic model of the dispersion of layered silicates in polymer melts in simple shear . A Monte Carlo-like method was adopted to simulate the time evolution of a particle size distribution in a shear field using a discrete event approach to drive particle breakup mechanisms. The model incorporates the effects of nanoclay organic modifiers, platelet and tactoid particle geometry, melt viscosity and process operating conditions. The model also provides insights into the factors governing lap shearing and peeling mechanisms of plate-let and tactoid breakup described in the literature.
Effect of Stereocomplex Crystallite as a Nucleating Agent on the Isothermal Crystallization Behavior of Poly (L-Lactic Acid)
Isothermal crystallization behaviors of poly (L-lactic acid) (PLLA) blended with different contents of Poly (D-lactic acid) (PDLA) were studied by wide-angle X-ray diffraction, differential scanning calorimetry and polarized optical microscopy. PDLA molecules added to PLLA formed stereocomplex crystallites in the PLLA matrix. The stereocomplex crystallites stayed unmelted at 190 °C and embedded in the PLLA molten matrix. Isothermal crystallization measurement at 100 °C revealed that the crystal radius growth rate decreased with an increase in the isothermal crystallization temperature. The spherulite growth rate has a peculiar PDLA concentration dependence. PLLA crystallization behavior might be affected by network structure and homogeneous dispersibility of stereocomplex crystal.
Injection Molding of Novel Polyactic Acid/Thermoplastic Polyurethane (PLA/TPU) Blends with Shape-Memory Behavior
This paper presents the development of shape-memory polymers (SMPs) based on amorphous polylactic acid (PLA) and thermoplastic polyurethane (TPU) blends. PLA was melt blended with TPU at weight ratios of 20, 30, and 40%, and then injection molded and hot compressed into permanent shapes. Unlike most of the existing SMPs, all three PLA/TPU blends could be formed (via bending, folding, compression, stretching, etc.) into temporary shapes at room temperature without an extra heating step. Upon heating to above the glass transition temperature of PLA (at 70 °C), the deformed parts regained their original shapes fairly quickly. Differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) tests showed that PLA and TPU were immiscible. The dynamic mechanical analyzer (DMA) data and the mechanical tests, including tensile, compression, and flexural tests, showed that the PLA/TPU with the 80/20 weight ratio had the best shape-memory properties, even if it was somewhat brittle. The 70/30 PLA/ TPU blend had the best combination of shape recovery and mechanical properties. The shape memory mechanisms for these types of SMPs are discussed here in detail.
The Influence of Compatibilizer Type and Concentration on the Properties of Immiscible Polymer Blends
The aim of this work was to investigate the effectiveness of industrially available additives (with different chemical nature) for compatibilization of HDPE – PA6 blends in terms of mechanical and rheological properties. Furthermore, the morphology of the samples should be assessed to get deeper insights into the interaction of the compatibilizer with the two immiscible polymers. We found, that it is possible to compatibilize immiscible blends via the addition of industrially available additives, as well as that the chemical nature of said compatibilizers and the concentration in the blend influence the various investigated properties, like impact strength and morphology.
Effect of Extensive Recycling on Flow Properties of LDPE
Low density polyethylene (LDPE) was exposed to one hundred (100) consecutive extrusion cycles to simulate the process of mechanical recycling. Collected samples were characterized by means of melt flow index measurements and small amplitude oscillatory measurements to investigate flow properties. The results suggest that thermal degradation and gelation of LDPE occur after extensive extrusion which leads to simultaneous chain scission and crosslinking of the polymer chains. However, after 40 extrusions crosslinking is more dominant than chain scission. Rheological observations were confirmed by solubility studies that showed a pronounced increase in insoluble fraction after 40 extrusion cycles. This indicates that the technological parameters should be modified when processing recycled LDPE, particularly after 40 extrusion cycles.
Initial Verification of an Induction Heating Set-Up for Injection Molding
Molding of thin and long parts by injection molding leads to special requirements for the mold in order to ensure proper filling and acceptable cycle time. This paper investigates the applicability of embedded induction heating for the improvement of the filling of thin long parts. The object selected for the investigation is a thin spiral. For the complete molding of the component, elevated mold temperatures are required. For this propose a new injection molding set-up was developed, which allows rapid heating of the cavity wall by an induction heating system. The temperature was measured by two thermocouples placed in the die insert. The system was used to heat up the cavity wall with heating rates of up to 10 °C/s. Experiments were carried out with ABS material. The lengths of the object were measured by a suitable measurement set up. The experimental result show that the use of the induction heating system process is an efficient way for improving the filling of the cavity.
A PID-Type Model Predictive Iterative Learning Control For Injection Molding Process
For batch processes like injection molding, iterative learning control is essentially a two-dimensional feedback control. By transforming the iterative learning control into a two-dimensional generalized predictive control, a new model predictive iterative leaning control scheme is proposed in this paper for the repetitive, cyclic or batch processes with both time-wise and cycle-wise dynamics. As the proportional, integral and derivative of the prediction errors are weighted in the cost function, the proposed ILC scheme can be referred to as a PID-type model predictive iterative learning control (PID- MPILC). Compared with the two-dimensional model predictive iterative learning control (2D-MPILC) proposed in the previous works, the proposed PID-MPILC can provide much better control performances not only along cycle but also along time, which is illustrated by the experimental results of the application to injection molding.
Influence of Melt-Mixing on the EM Shielding Effectiveness of Carbon Nanofiber-Based LLDPE Nanocomposites
The influence of different melt-mixing routes on the electromagnetic shielding effectiveness (EM SE) of carbon nanofiber/LLDPE nanocomposites was assessed. Two-minute, twin-screw continuously extruded nanocomposites containing 20 wt% PR-19 HT nanofibers displayed a DC in-plane electrical conductivity of 10.5±1.0 S/m, thermal conductivity of 0.68±0.02 W/m•K, and EM SE of ~15 dB (frequency range (30 MHz-1.5 GHz). At the same concentration, additional twenty minutes of batch-mixing in the twin-screw extruder produced nanocomposites with electrical and thermal conductivities of 2.0±0.2 S/m and 0.68±0.02 W/m•K, respectively, and shielding of ~6.5 dB. Two minutes batch-mixing in a Brabender geometry led to nanocomposites with electrical and thermal conductivities of 20.4±3.3 S/m, 0.89±0.03 W/m•K, respectively, and EM SE of ~22 dB.
Requirements and First Approach to use an Extruder for Future Use Enabling Additive Manufacturing Techniques
The plastics processing industry is witnessing the trend of miniaturization as well as the trend of individualization these days. Concurrently new manufacturing methods as additive manufacturing – widespread known as rapid prototyping techniques – gain more and more importance. But although plastic processing techniques usually are used in mass production they can still meet the challenge of miniaturization and individualization when adapting them. The aim of this work is to show how well- established extruder technology could be used for future additive manufacturing methods and thus contribute to further progress of such techniques.
Mechanical Properties of Foamed and Unfoamed Wood/Plastic Composites Produced by Extrusion-Calendaring
Foamed and unfoamed wood/plastic composites (WPC) were produced by extrusion-calendering. The effect of wood content on the material properties was studied by using different amounts of wood particles (0, 10, 20 and 30%wt). The samples were mechanically characterized in terms of tensile, flexural and impact properties. From the tensile stress-strain curves, three parameters are reported and discussed: modulus, strength and strain at break. For bending tests, only the flexural modulus was studied, while for the impact properties, Charpy impact strength was considered. The results show that foaming induces a global decrease of the mechanical properties, especially for impact and tensile tests, while the addition of wood particles results in higher Young’s modulus, but lower strain at break and strength. However, simultaneous wood addition and foaming seems to significantly limit the decrease of mechanical properties in the final material. Finally, as expected, the extrusion-calendering process leads to anisotropic properties; i.e. different results obtained in two perpendicular directions.
Effect of Metallic Loading on Through Transmission Infrared Weldability of High Heat ABS
Many studies were reported in the past regarding Through Transmission Infrared Welding (TTIR) of colored, transparent, and black ABS, however the effects of metallic loading within the absorbing material has not been reported. In this study, TTIR weldability of PC and PMMA to black and silver metallic high heat ABS was evaluated. It was found that the size of the melt pool was determined by the heating time and glass transition temperature of the absorbing substrate. The longer heating time resulted in a larger melt pool and higher breaking force. In addition, the surface reflectivity of the substrate affected the melt pool size. The results also indicated that the black high heat ABS substrate had significantly higher weld strength than that of the silver metallic high heat ABS.
Wood Plastics Composites Produced by Rotomolding
This study reports on the properties of wood plastic composites produced by rotomolding. As a special case, wood flour (maple) was dry-blended with linear low-density polyethylene (LLDPE) to produce composites up to 25%wt. From the samples produced, a complete characterization was performed including density, morphology, and mechanical properties (tensile and flexural). As expected, tensile and flexural moduli increased with wood content, while tensile strength and elongation at break decreased. The optimum wood content was found to be around 20%wt. for the range of conditions tested.
Effect of Cooling Rate and Mold Counter Pressure on the Crystallinity and Foaming Control in Microcellular Injection Molded Polypropylene Parts
The purpose of this study is to investigate Microcellular polymer injection molding, which is becoming increasingly popular in automotive, semiconductor, and industrial applications. While the technique has been widely successful using amorphous polymers, semi-crystalline polymers present new challenges not encountered during the processing of their amorphous counterparts. The polymer chains in a semi-crystalline material develop an organized crystal structure during the cooling stage. Crystal development generates two main issues for microcellular processing. First, the excess heat released during the crystal formation affects the expansion of the microcellular bubble causing unpredictable non-uniform growth. Second, the growth of the crystal structure within the polymer melt expels and displaces the supercritical fluid forcing the foaming to occur out at the edges of the part rather than uniformly through its core. This paper develops and explores strategies to control and overcome these problems.
The Effects of Gas Counter Pressure Combined with Dynamic Mold Temperature Control on the Skin Layer Thickness and Foaming Cell Size of Microcellular injection Molding
In this study, we developed a foaming control system using the Gas Counter Pressure (GCP) combined with Dynamic mold temperature control (DMTC) during the microcellular injection molding process and investigated its influence on part surface quality, skin layer thickness and foamed structure uniformity. The results show that under GCP control, part surface roughness for transparent polystyrene (PS) improved by 90%. When GCP increased, the skin thickness also increased and the weight reduction decreased. Applying mold temperature control alone with temperature at a high temperature near Tg, the surface roughness improved. Increasing mold temperature decreased the skin thickness; however, the cell size distribution became significantly non-uniform. It was found that rapid cooling speed is necessary for controlling the cell size and uniformity, with a 10°C/sec cooling rate alone, the average cell size decreased from 192.92 ?m to 84.97 ?m and uniformity was improved. We conclude that skin thickness, uniform cell size as well as good surface quality could be achieved efficiently by combining GCP and DMTC.
Preparation and Characterization of Poly(Lactic Acid)/Poly(Vinyl Alcohol) Blend
In this study, polymer blends based on poly(lactic acid) (PLA) and organic particles polyvinyl alcohol (PVOH) were prepared by melt mixing using a triple screw extruder. Phase morphology, thermal properties, dynamic mechanical properties and mechanical properties of the blends were investigated. Differential scanning calorimetry reveals that the addition of PVOH remarkably decrease the cold crystallization temperature and increase the degree of crystallinity of PLA/PVOH blends. Dynamic mechanical properties show that a general decrease of E? is observed with the addition of PVOH content, yet the loss tangent peaks broaden and slightly shift to higher temperature. From mechanical tests, it is found that tensile strength and the elongation at break decreased markedly with the addition of PVOH content, yet notched impact strength slightly increase.
True 3D Numerical Simulation in Compression Molding
The objective of this study is to develop a simulation tool of compression molding (CM) process to get a comprehensive understanding of the whole process. We primarily focused on numerical simulation of the flow during mold closure in compression molding process. The complex advancing flow front is simulated by means of novel moving mesh boundary technique to realize the effect of process conditions. The behavior of squish flow could be seen from the analysis. Furthermore, we also investigated the fiber orientation states in CM short-fiber-reinforced parts with rib geometry. By means of simulation tool, the distribution of fiber orientation can be tailored through the interpolation of fiber orientation tensor.
Synthesis and characterisation of PVA/SBMA crosslinked hydrogels with low fouling property
A novel zwitterionic poly(vinyl alcohol)/ sulfobetaine methacrylate (PVA/SBMA) cro-sslinked hydrogel was prepared by a two-step aqueous polymerization method, to improve the anti-protein fouling inadequacy of PVA hydrogels. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and scanning electron microscope (SEM) were used to study the composition and microstructure of the hydrogel samples. The deswelling behaviors and adsorption of bovine serum albumin (BSA) on the prepared PVA/SBMA hydrogel were measured as a function of ionic strength. The results showed PVA/SBMA hydrogel significantly reduced protein adsorption.
Performance Comparison of selected Rapid Heat Cycle Molding Systems and Models for predicting Heating and Cooling Behavior
Rapid heat cycle molding (RHCM) continuously gains importance in achieving high grade polymer surface finishes. To examine the performance of selected RHCM systems, a new test mold, using two RHCM technologies, was used. The mold’s nozzle side is equipped with the areal heating and cooling technology BFMOLD®, which tempers a chamber below the cavity by using hot and cold water sequentially. A local electrical ceramic heating element (Ultramic™) is installed into the ejection side, 3 mm below the cavity surface. To examine the performance of both RHCM systems a central-composite Design of Experiments (DoE) was developed. Low and high temperatures of the RHCM systems were systematically varied within the DoE. The mold surface temperature responses on both, the moving and the fixed mold half, were transiently recorded using Type K thermocouples. Polynomial models and response surfaces for characterizing the heating and cooling performance of the used RHCM systems were obtained. These models allow the prediction of the heating rate as well as the cooling speed at arbitrary temperature levels of cooling- and heating-temperatures.
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