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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Micro Injection Molding of Polymeric Substrates for Optimization of Stem Cell Development
A novel molding assembly was fabricated which offers an effective way to hold silicon tooling during injection molding. Processing parameters thought to be critical to the micro injection molding process were studied through the measurement of replication quality (RQ). To measure such effects, low density polyethylene (LDPE) plates containing microtopography were micro injection molded. RQ was most enhanced by higher mold temperatures and injection velocities, with mold temperature being the most influential parameter. Initial cell culture studies revealed that micro-patterned LDPE altered human mesenchymal stem cell (hMSC) morphology. Rapidly produced microfeatured synthetic polymer substrates have tremendous potential to revolutionize the cell culture industry.
Melt Compounding of Poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) / Nanofibrillated Cellulose (NFC) Nanocomposites: Properties and Solubility of Carbon Dioxide
Biodegradable nanocomposites were prepared using nanofibrillated cellulose (NFC) as the reinforcement and poly (3-hydroxybutyrate-co-3-hydroxyvalerate, PHBV) as the polymer matrix. PHBV powder was dispersed in water, mixed with an aqueous suspension of NFC fiber, and freeze dried. The resulting PHBV/15 wt% NFC was then used as a masterbatch in a subsequent melt compounding process to produce nanocomposites of various formulations. Its properties, such as mechanical properties, crystallization behavior and solubility of carbon dioxide (CO2), were evaluated. Scanning electron microscopy (SEM) images revealed that individual fibers with diameters less than 1 ?m were still clearly distinguishable even though some of the NFC agglomerated. Adding NFC increased the tensile modulus of the PHBV/NFC nanocomposites nearly twofold. Differential scanning calorimetry (DSC) analysis showed that the NFC served as a nucleating agent, promoting the early onset of crystallization. However, high NFC content also led to greater thermal degradation of the PHBV matrix. The solubility of CO2 in the PHBV/NFC nanocomposites decreased and the desorption diffusivity increased as more NFC was added.
Developoment of an Induction Heated Roll-To-Roll Lithography Process
Roll-to-roll (R2R) lithography is a continuous manufacturing process used to create patterns on a polymer substrate. Thermally curing of R2R embossed features is time consuming, and is commonly replaced with faster UV or chemical curing. A technique of induction heating the lithography stamp in a R2R process has been conceived for heating, forming and cooling along the perimeter of the roll. The patterned polymer surface needs no additional curing steps, which increases efficiency of the R2R lithography process. The results of initial investigation prove the feasibility of said conceptual process, and initial experiments confirm heating of the lithography roll by induction heating.
High Performance Processing Aid Designed for PVC Foam
A suitable processing aid (high molecular weight acrylic copolymer) was designed for PVC foam and its remarkable foam-ability was confirmed. The molecular chain entanglement of high molecular weight acrylic copolymer with PVC can enhance the melt elasticity of the PVC melt yielding excellent foamed cell structure and low density. The molecular weight of the processing aid and its dispersion into the PVC melt was optimized to maximize efficiency. A synergistic combination of optimized processing aid, blowing agents, and inorganic fillers creates much lower density while retaining excellent mechanical properties.
Preparation and Measurement of a Water-borne Thermal-insulating Glass Coating for Construction
A Water-borne transparent thermal insulation glass coating for construction was prepared with water- based polyurethane (PU) resin as matrix, functional filler and coating additives by the magnetic stirring. And then the coating obtained was painted on the surface of a piece of standard construction glass. Particle size distribution of the coating was tested and the results revealed that the particles in coating without agglomeration. The thermal insulation effects, optical performance and mechanical performance of coating film were also characterized and measured. In our case, the thermal-insulating effect was measured as better results with the content of nano-ATO as 10%, thermal difference as compared with blank in the same condition was more than 8.7°C. Furthermore, the transmittance of visible light through ATO/PU coating film in the visible light region (380-780nm) was kept more than 75% when the content of the nano-ATO was 10% and the thickness of film was under 50?m. The surface of coated glass is smooth, and the coating will have good prospect in market.
Material Properties and Their Influence on Molding Productivity and Effeciency of Medical Resins
The processability of three medical grade engineering resins were studied in terms of how their physical properties influenced their cycle times. We also compared the variability of molded parts and measured the energy necessary to process each resin. Our results suggest that the glass-transition temperature of the resins have very little effect on the cycle time, while the stiffness (i.e. modulus) of a material – particularly at the cooling temperature - exerts a dominant role. Higher energy consumption was observed for Tritan™ MX710 due to the longer cycle-times. For Makrolon® 2458, molding at three different barrel temperatures revealed that increasing the barrel temperatures actually reduced power consumption during molding.
An Investigation of the Incorporation of Expandable Microspheres into Stretch Wrap
Expandable polymeric microspheres as stretch film components were investigated for pallet wrap applications. Advantages of this novel technology may include reduced fossil-fuel based plastics, solid waste, film density, and weight. Multilayer stretch wrap samples containing microspheres were produced on a stretch film processing line. Optical microscopy showed that the microspheres were intact and expanded 3-5X. Overall, testing showed that tensile, modulus, water vapor barrier, and cling were decreased by the addition of microspheres.
Relationship Between Surface Haze and Crystalline Morphology of Polyethylene Blown Films
In previous work, light scattering was utilized to understand the relationship between internal haze and the crystalline morphology of films made by blending LDPE into LLDPE, including the spherulitic and fibrillar morphology. The Morphology Index was introduced to quantitatively describe the morphology change and its dependence on internal haze. In this work, the relationship between surface haze, Morphology Index, and surface roughness obtained from AFM are discussed along with the dependence of surface haze on crystalline morphology (spherulitc vs. fibrillar).
Effect of Aspect Ratio of Multi-Walled Carbon Nanotubes on Electrical, Thermal and Mechanical Properties of Composites with Polycarbonate
The purpose of this work is to explore the question of how the aspect ratio affects various properties in carbon nanotube/polycarbonate composites. Aspect ratios (prior to mixing) of multi-walled carbon nanotubes varied between 50-500. Tubes were mixed with polycarbonate in a conical twin-screw compounder and then compression molded into flat sheets. Differential scanning calorimetry, dynamic mechanical analysis and tensile properties were measured on the as molded sheets. It was found that the aspect ratio correlated to both the percolation threshold and the rubbery modulus in a simple linear fashion; however with a significant level of scatter. At high aspect ratios, the percolation threshold did not change with aspect ratio which was attributed to a higher relative amount of length reduction during processing. Reducing the amount of mixing, for example, led to a lower percolation threshold which was attributed to less nanotube breakage.
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.
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