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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Analysis of the Process-Induced Microstructure in Injection Molding of Long Glass Fiber-Reinforced Thermoplastics
Over all stages in the injection molding process of long fiber-reinforced thermoplastic (LFT) materials, the configuration of the fibers changes, which ultimately affects the mechanical performance of the finished part. This article presents a full microstructure analysis of an injection molded part made out of polypropylene reinforced with 40% by weight of glass fibers. The analysis takes into account local measurements of fiber orientation, fiber length, and fiber density distributions by applying sophisticated measurement techniques, such as micro-computed tomography.
The results of this work show that the assumption of a uniform fiber length and fiber density throughout the entire part is not valid. The number (weight) average fiber length increases from 0.64 mm (1.63 mm) close to the gate to 1.12 mm (2.81 mm) at the end of the flow path. Similarly, the fiber density varies along the flow path from 37.7 wt% in the gate region to 44.6 wt% at the end of flow. Moreover, the fiber density measurements across the part thickness show a significant fiber agglomeration in the core of the part that consistently suggests almost 30% more fibers in the core layer than in the shell regions.
Micropelletization and Their Application to Manufacture Porous Plastic Parts
A novel micropelletization technique yields micropellets with a controlled morphology and narrow particle size distribution which can be used for sintering applications and additive manufacturing processes such as laser sintering. A polymer melt is extruded through a capillary and the extruded thread is stretched with a hot air stream until flow instabilities cause it to breakup into small droplets. This work focuses on an improved experimental setup with additional temperature control for the production of micropellets. By performing a variety of test series, options for further optimization of the process have been worked out. This is another important step towards an economical, ready-to-use-process that can provide ideally shaped and size-distributed micropellets using a wide range of polymers. Furthermore, sintered parts were produced to demonstrate possible utilization of these micropellets for industrial and commercial applications.
Melt Devolatilization Extruson Process for Brominated Polymeric Flame Retardant
A brominated polymeric flame retardant has a significantly advantaged environmental, health and safety profile compared to small molecule halogenated flame retardants due to reduced molecular mobility and thus no bio-availability. The brominated polymeric flame retardant can be prepared using an innovative indirect bromination reaction, which requires the use of a halogenated solvent. A devolatilization extrusion process has been identified as an economically favorable and technically simplest isolation process among many other isolation technologies assessed. The development of a devolatilization extrusion process for the brominated polymeric flame retardant is presented.
Fiber Surface Treatment as an Approach to Increase Fiber Content in AGAVE-LMDPE Composites Produced by Rotomolding
In this study, Agave fibers (Agave tequilana Weber var. Azul) were surface treated with maleated polyethylene (MAPE) to increase the polymer-fiber compatibility with two main objectives: 1) to improve the mechanical properties of composites produced by rotational molding, and 2) to increase the fiber content in the composite. The rotomolded composites were produced at 0, 10, 20, 30 and 40% wt. of fiber contents (treated or untreated) and characterized in terms of morphology and mechanical properties (impact, tensile and flexural). The results show that the MAPE surface treatment was successful by causing a better fiber distribution and a more uniform composite morphology allowing the possibility to use higher fiber contents in rotational molding. At low fiber contents (10 and 20% wt.), the mechanical properties were improved (up to 52%) in treated fiber composites (TFC) compared to the neat polymer and untreated fiber composites (UFC). Although the mechanical properties of TFC decreased at high fiber contents (30 and 40% wt.), they were substantially higher than UFC (about 160%, 400% and 240% for impact, tensile and flexural properties, respectively).
Study on Extrudate Swell of High-Density Polyethylenes in Slit (Flat) Dies
Extrudate swell of a high molecular weight high density polyethylene (HDPE) in flat/slit dies is studied using both experiments and simulations. The experimental set-up consists of an optical micrometer to measure the extrudate dimensions (both thickness and width) and a pair of radiation heaters to control the extrudate temperature outside the die, attached to the capillary rheometer. The simulation of extrudate swell phenomenon is carried by using the well-known integral K-BKZ model. The effects of die geometrical characteristics, molecular characteristics of polymers and operating parameters on extrudate swell measurements are studied systematically. The experimental data are compared with corresponding two dimensional steady state numerical predictions. The thickness swell is predominant in comparison with width swell due to larger shear rates applied in that direction.
Dynamic Rheological Measurements of Aqueous Polyester Dispersion in Batch Reactor and Twin Screw Extruder
This paper reports on inline measurement techniques for the rheological behavior of aqueous polyester dispersion in batch reactor and twin screw extruder (TSE). Since the preparation of latex without hazardous solvent is a relatively new technique, very little has been reported to understand the kinetic aspects of the process for both batch reactor and TSE. A sudden viscosity drop is observed in a batch reactor whereas the viscosity tends to oscillate in TSE during the addition of water when surface tension is low enough. The viscosity changes during the addition of water are thought to be related to the morphological changes during the process since surfactant must be present else no change occurs. In this paper, different surfactant and NaOH concentrations have been studied for their influence on the viscosity so that emulsification may become a predictable process in a TSE.
Innovative Extrusion Process for Liquid Silicone Rubber: Calculation Versus Experiment
Silicone rubber with its good chemical and physical resistance properties is of major interest for elastic tubing. The breadth of silicone tubings is continuously manufactured by extrusion. The extruded silicone products are cured downstream of exiting the die. Thus the viscosity of the uncured silicones must be high enough for a dimensionally stable extrudate and even with high viscosities, achievable precision and tolerances are limited due to this fact. Therefore an innovative extrusion process, which uses a heated die in order to vulcanize the extrudate inside the die, has been developed.
In this work, a formula for the flow rate is derived for an in-die-curing silicone extrusion in order to mathematically describe this process and to be able to predict the capabilities of this technology. The results of the calculations are being compared to experimental results to determine their validity.
Standard Reference Materials for the Polymers Industry
The National Institute of Standards and Technology (NIST) provides science, industry, and government with a central source of well-characterized materials certified for chemical composition or for some chemical or physical property. These materials are designated Standard Reference Materials® (SRMs) and are used to calibrate measuring instruments, to evaluate methods and systems, or to produce scientific data that can be referred readily to a common base. In this paper, we discuss the history of polymer based SRMs, their current status, and challenges and opportunities to develop new standards to address industrial measurement challenges.
Rapid Spectral Measurement of the Mechanical Properties of Polypropylene Recovered from Shredded End-Of-Life Vehicles
Our industry leading separation technology enables us to recover polyolefin and styrenic plastics from complex mixed streams such as shredded end-of-life vehicles. Plastic flakes recovered using our process are compounded and sold as pellets suitable for use in injection molding and extrusion applications. This paper looks at some of the challenges of understanding and controlling the properties of the polypropylene product, including a discussion of how infrared spectroscopy and statistical analysis of the spectra may be used to rapidly measure the mechanical properties.
Injection Moulding of Solid Oral Dosage Forms
Oral solid dosage forms are the most patient-accepted and therefore industrially relevant pharmaceutical applications, representing 80% of the market share. In that context, polymer processing techniques, such as hot melt extrusion (HME) or injection molding (IM), are increasingly used to process primary material into the final dosage forms due to several benefits (e.g., enhanced solubility or solvent-free processes). In this study, tablets based on solid dispersion systems were processed via injection molding using either primary powder or pellets prepared by HME. Fenofibrate, a BCS Class 2 substance (low solubility, high permeability), was selected as model API, with loadings of 10%, 20% and 30%, while Soluplus® (PVCL-PVAc-PEG co-polymer) served as matrix. It could be shown that both the achieved mechanical properties (e.g., hardness) of the tablet, as well as the release kinetics, are suitable for oral dosage forms.
Morphology of HDPE/PS Blends along the Axial Position in a Novel Co-Rotating Non-Twin Screw Extruder
In this study, a novel co-rotating non-twin screw extruder with a clam-shell barrel was designed and invented. Then, the visualization of mixing an 80/20 (wt%) ratio HDPE/PS blend was carried out after the barrel was opened. The morphological development of HDPE/PS blends in this non-twin screw extruder was studied. Two groups of operating conditions were employed when the ratio of the screw speed to the feed rate was kept constant. The effects of the screw speed on the morphological development of the HDPE/PS blends along the axial direction during extrusion were discussed. The results revealed that coalescence happened during extrusion, and increasing the screw speed resulted in a smaller droplet size and a narrower size distribution of the product. The dispersive mixing was stronger in the nip zone than in the screw channel. In addition, it was found that the morphology pattern changed considerably and the particle size decreased sharply and became more uniform after the blend went through the holes of the die.
Numerical Simulation for the Viscoelastic Effects on the Birefringence Variation for an Injected Optical Lens
Recently, polymeric optical lens have been utilized in many fields and electronic devices, such as camera, mobile phone, tablet, and other optical devices. The quality is the key for the main suppliers to keep competition, however, how the material’s viscoelasticity influences the optical features is still not fully understood yet. In this study, we have investigated the viscoelastic effects on the optical property of a lens made of Zeonex COP 480R material by the traditional injection molding, simulated with n = 0.4 and ?* = 217,000 Pa in the Cross model for the melt viscosity. Results show that if the power-law index (n) was varied from 0.1 to 0.6, the total fringed order has no significant difference, but the fringed patterns were varying dominantly in the perpendicular direction, instead of the flow direction for the case at n = 0.4. This situation was matched with the distribution of the flow-induced residual stresses. Moreover, if the ?* in the Cross model was varied from 100,000 Pa to 300,000 Pa, the total fringed patterns were apparently changing from being dominated in the flow direction to being in the direction perpendicular to the flow. The influenced width of the fringed patterns was almost linearly increased with the increasing ?*. The results can be applied as some guideline for either the further material modifications or the new material developments.
3D-Simulation of Gas-Assisted Injection Molding
The gas-assisted injection molding (GAIM) process is so complicated that increasing reliance has been placed on CAE?Computer Aided Engineering?as a tool for both mold designers and process engineers. In this paper, a 3D theoretical model and numerical scheme is presented to simulate the GAIM process, in which an equal-order velocity-pressure formulation method is employed to eliminate the pressure oscillation. In addition, the whole flow field is calculated with the gas pressure as a boundary condition to obtain the gas penetration, and a 3D control volume scheme is employed to track the flow front of the melt and gas. Finally the validity of the model has been tested through case studies and experimental verification.
Thermal Analysis of the Rotational Molding Cycle Followed by Internal Air Temperature Profiles: An Application for Foamed Polyethylene
In this study, temperature profiles for the air inside the mold was measured to analyze the thermal behavior of a polymer for a complete rotational molding cycle. Foamed and unfoamed linear medium density polyethylene (LMDPE) parts were produced by biaxial rotational molding. A chemical blowing agent (azodicarbonamide, ACA) was used at different concentrations (0, 0.25, 0.50, and 1.0 % wt.). The temperature profiles inside the mold were measured for different oven temperatures (260-320 °C). The analysis proposed is based on the temperature profiles and their derivatives to better determine the different temperature transitions occurring in a complete molding cycle.
Effect of Residual Chlorine on Durability of Plastic Pipes Used for Hot Water Supply
Recently, polymer electrolyte fuel cell (PEFC) cogeneration systems using plastic pipes for hot water supply have been commercialized in Japan. However, it is expensive and difficult to replace these plastic pipes if they are damaged. Therefore, it is important to evaluate the durability and to predict the life expectancy of these pipe materials and systems. In this study, the immersion test was used for polybutylene (PB) and double-layer crosslinked polyethylene (PEX2) pipes to evaluate their long-term performance in the residual chlorine solutions at 80 °C for 30,000 consecutive hours. The mechanical and thermal properties of these pipes were investigated using tensile test and DSC. Based on the tensile test results, it was found that the elongation at break rather than the yield stress had a strong correlation with the melting enthalpy (?H) of the PB and PEX2 pipes. On the other hand, the DSC results revealed that the oxidation induction time (OIT) at the inner surface of the PB and PEX2 pipes decreased significantly with immersion time, in which the OIT of the PB pipe decreased more rapidly than that of the PEX2 pipe. The difference in the OIT behavior was discussed in terms of the influence of the residual antioxidants in these pipes.
The Mixing of Flame Retardant Polymer Materials in a Novel Co-Rotating Non-Twin Screw Extruder
The mixing process of a halogen-free intumescent flame retardant ABS composite was carried out to examine the priority of a novel co-rotating non-twin screw extruder (NTSE) over the traditional twin screw extruder (TSE). The homogeneity of the flame retardant additives of the composites processed by NTSE and TSE under the same operating condition was characterized qualitatively using mechanics performance, LOI and UL-94 tests, and quantitatively using FTIR and TG analysis. All the results suggested that NTSE could achieve better mixing of the flame retardant additives in the polymer matrix than in TSE, which was further clarified by the SEM analysis.
Blends Characterization by Thermal Techniques
Thermal analysis (TA) techniques are indispensable tools for polymer characterization and root cause analysis of various problem such as contamination and part failure. Thermal analysis were carried out using Thermo-Gravimetric (TGA), Differential Scanning Calorimeter (DSC) and Hot Stage Microscopy techniques were used to study compatibilization of blends. This study related Polyethylene terephthalate (PET) as major phase) with minor amounts of Polycarbonate (2%PC) and Polyethylene-liner-low-density (3-5% PE-LLD). PC is fully miscible with PET in a molten state or when it exists in infinitesimal domains. The binary (PET/PC) blend’s matrix yields a homogeneous phase in thermal analysis. Degradation kinetics (single degradation peak) suggests that PET/PC is a binary miscible blend. On the other hand, PE-LLD is immiscible with PET even in a minor concentration; a pronounced skin-core effect was observed in hot stage microscopy and a doublet degradation peak was observed in TGA. In a ternary blend (PET, PC and PE-LLD), surprisingly the PC acts as a compatibiliser for the PE-LLD in the blend matrix. The degradation doublet peak in ternary blend due to PE (TGA) was minimized and crystallinity of ternary blend (DSC) was increased than the binary blends. Therefore, ternary blend appears as a homogeneous matrix in all three TA techniques used.
Evaluating Rigid and Semi-Flexible Fiber Orientation Evolution Models in Simple Flows
As American vehicle fuel efficiency requirements have become more stringent due to the CAFE standards, the auto industry has turned to thermoplastic-fiber composites as replacements for metal parts to reduce weight while simultaneously maintaining established safety standards. Furthermore, these composites may be easily processed using established techniques such as injection molding and compression molding. The mechanical properties of these composites are dependent on, among other variables, the orientation of the fibers within the part. Several models have been proposed to correlate fiber orientation with the kinematics of the polymer matrix during processing, each using various strategies to account for fiber interactions and fiber flexing. However, these all require the use of empirical fitting parameters. Previous work has obtained these parameters by fitting to orientation data at a specific location in an injectionmolded part. This ties the parameters to the specific mold design used. Obtaining empirical parameters is not a trivial undertaking and adds significant time to the entire mold design process. Considering that new parameters must be obtained any time some aspect of the part or mold is changed, an alternative technique that obtains model parameters independent of the mold design could be advantageous. This paper continues work looking to obtain empirical parameters from rheological tests. During processing, the fiber-polymer suspension is subjected to a complex flow with both shear and extensional behavior. Rather than use a complex flow, this study seeks to evaluate and compare the effects of shear and extension on two orientation models independently. To this end, simple shear and planar extension are employed and the evolution of orientation from a planar random initial condition is tracked as a function of strain. Simple shear was imparted using a sliding plate rheometer designed and fabricated in-house, and a novel rheometer tool was developed
Effects of Blend Morphology and Operating Parameters on Foaming of Polylactic Acid/Thermoplastic Polyurethane
The effects of blend composition and foaming conditions on polylactic acid (PLA)/thermoplastic polyurethane (TPU) blend foams were studied. Thermal behavior of the blends showed that TPU weakened crystallization ability of PLA. It was found that foam morphology was impacted by the blend composition and foaming conditions used in the study. PLA and PLA/TPU (80/20) did not demonstrate any significant foaming behavior while PLA/TPU (50/50) foamed at high temperature and pressure conditions. TPU foam morphology demonstrated temperature and pressure dependence. Interestingly enough, PLA/TPU (20/80) showed pore formation at all the operating conditions with either open cell or closed cell structures.
On the Successful Fabrication of Auxetic Polyurethane Foams: Key Insights from Materials Science and Polymer Processing Perspectives
This paper aims to provide fundamental understandings in several issues critical to the fabrication of auxetic polyurethane (PU) foams: auxetic structure fixation mechanisms, materials characteristics essential for the successful auxetic conversion, and optimal conditions for auxetic conversion. The chemistry, microstructure and thermomechanical properties of starting PU foams for auxetic foam manufacturing were thoroughly analyzed. This is followed by the auxetic convertibility study of these three foams. Mechanisms for fixing the structure were elucidated and the windows for processing were interpreted in the context of polymer relaxation. Guided by these understandings, we finally report an ultrafast, room-temperature process for auxetic PU foams manufacturing that can be completed in as little as several seconds.
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