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.
This paper presents results of a preliminary proof-of-concept investigation into the effect of pressurized oxygen on UV photodegradation rates of a polystyrene standard reference material. Exposures under UVA and UVB revealed significant and important acceleration effects using pressurized oxygen compared with ambient air.
A simulation of an imprinting process using Smoothed Dissipative Particle Dynamics is shown. Cavity filling modes and their dependence on die parameters is demonstrated for single and multicavity die, showing results consistent with FEM simulations and experimental data. Particle-based simulation methods can allow for modeling of more complex fluid behaviors.
Novel nano-cellulose based nano-structures modified with hyper-branched polymers were prepared by using isocyanate linking chemistry. The chemistry was investigated using FTIR spectroscopy. The composites were homogenized utilizing solvent casting followed by injection molding of the samples. The thermal properties of the prepared samples were investigated using DSC and TGA.
A recent design of a new screw referred to as the No Solid Bed (NSB) screw was introduced and the initial operation was presented . This new screw has channels in the transition section that do not allow a compacted solid bed to form. The data presented here compliments the data that was previously published.
The paper describes the development of a variothermal process, which increases the mold surface temperature during the injection molding process without significantly extending the cycle time and minimizes unintentionally heated mold areas. To this end, the possibility of achieving the desired effects by direct introduction of heated gases into the mold cavity is being investigated. By addressing central issues such as gas distribution geometry, injection possibilities, required gas temperatures or the possibility of process implementation in a demonstrator mold, it was possible to develop a process with which it is possible to achieve temperature optimization for visually appealing parts within seconds. This means that weld lines, streaks or uneven mold impressions can be concealed even on flat parts.
Nanofibrillated cellulose (NFC) has properties ideal for applications in the packaging and medical industries. To understand if cellulose-based polymers could become a replacement for synthetic polymers in these fields, NFC suspensions were repeatedly exposed to elevated shear stresses to simulate industrial processing procedures and allow for observation of changes in material properties. A capillary rheometer was used to run aqueous NFC suspensions of 10 wt% at room temperature at shear rates beyond 30,000 s-1. Due to repeated shear rate exposure, a decrease in volume resulting from unavoidable water loss informed the observable increase in apparent viscosity and suggested that this increasing trend was not caused by a change in material morphology. Noisy data as a result of flocs was detrimental to the analysis of material behavior during rheological testing. Once preprocessing procedures are successfully designed to reduce noise in the data, material behavior at high shear rates will be further defined.
Co-injection molding has been introduced into industrial application for several decades. However, due to the formation of the interface between skin and core materials is very difficult to be observed, and controlled, a good quality of co-injection product can not be obtained effectively. The reason is that the formation of that interface in co-injection molding is very sensitive to various factors. In this study, the formation of the interfacial morphology and its physical mechanism in coinjection molding have been studied based on the ASTM D638 TYPE V system by using both numerical simulation and experimental observation. Results showed that the critical skin/core material ratio to generate the skin breakthrough is identified. The reason to cause the breakthrough is due to the flow front of core material catches up with the melt front of skin, and the skin is stop at a fixed distance. This mechanism is similar with that of literature. However, when the higher core material ratio is selected, the mechanism of the interfacial morphology is different. Specifically, after core melt front catches the skin melt front, the broken skin material can move forward with the inner core material to generate special core-skin-core structure. It could be due to different forces balance inside the skin and core melts, but needs to do more study in the future.
Precise predictive models are required for the use of machine learning methods for quality control in injection molding. Thermal images offer the advantage of containing information in the data that is not available in machine and process data. Currently, convolutional neural networks (CNN) have numerous applications in image recognition. Therefore, the objective of this work was to investigate the application of convolutional neural networks to thermal images of injection molded parts. For this purpose, 751 injection molding cycles from a central composite design were used. The goal was to predict the weight, height, and width of the injection molded part. The results were also compared with classical machine learning methods. Depending on the quality parameters, the networks were able to achieve an R² of up to 0.91 and were thus among the three best methods.
After nearly 80 years of research in constitutive modeling of polymeric fluids, simple yet capable models are still sought after today. In this work, we provide an explicit constitutive equation where the extra stress tensor is an explicit function of the objective velocity gradient while finite stretch of polymer chains are considered. With this model, the basic rheological functions in uniaxial extensional, planar extension and simple shear can all be obtained as closed-form analytical solutions with only elementary mathematical functions involved. The new model demonstrates excellent fitting to some sear and extensional data in the literature, and is able to simultaneously predict the major rheological functions in steady-state shear and extension.
A polyamide 11/carbon black (PA11/CB) SLS nanocomposite printing powder was characterized throughout a laser area energy density range (express by using Andrew’s numbers, AN) to elucidate significant changes to the PA11 microstructure and chemistry during the SLS printing process. We will show that there are specific microstructural changes that occur in PA11, some gradual and others more striking, between the as received PA11/CB powder and printed parts. The melting temperature (Tm), percent crystallinity (Xc), lamellae thickness (lc) and dhkl spacing of PA11 were all shown to change significantly upon printing, whereas the molecular weight was shown to have a rather gradual increase as a function of AN. These results imply that the printing conditions used result in an irreversible change in PA11 polymer microstructure and chemistry, and correlate well to the measured mechanical behavior of parts print with corresponding AN. The use of DSC, XRD, and molecular weight analysis provides a more complete picture of the changes due to the SLS printing process and can help optimize the printing parameters to create high-quality printed parts.
The melting of polymers in a twin-screw (T/S) extruder is an important operation in many industrial processes. Research by Shih, Gogos, Geng and others has identified the physical phenomena that take place during the melting phase transition. This paper describes a new approach for modeling the melting in a twin-screw extruder and the model predictions are compared with an experimental study of Low-Density Polyethylene (LDPE) melting in a co-rotating, intermeshing T/S extruder using on-line visualization and axial scanning of pressure and temperature techniques. This paper focuses on the physics and engineering concepts that are inherent in the melting mechanism in the extruder, and viscous energy dissipation in the melt with un-melted solids. The effects of throughput, Q, and at a constant rotation speed, N, is examined. Low and high Q/N ratios have significantly different axial pressure profiles.
Multi-wall carbon nanotubes (MWCNTs), graphene nanoplates (GNPs), and hybrid fillers (MWCNTs/GNPs) filled thermoplastic polyurethane (TPU) nanocomposites are prepared via melt mixing. The effects of filler (contents of 1, 2, and 3 wt%) and temperature are investigated on the rheological behavior of the TPU nanocomposites. The results demonstrate that the TPU/MWCNT nanocomposites exhibit stronger polymer-filler and filler-filler interactions than TPU/GNP and TPU/GNP/MWCNT nanocomposites. It is found that the nanocomposites with 2 and 3 wt% MWCNTs (2CNT and 3CNT) and 3 wt% MWCNTs/GNPs (3Hybrid) exhibit anomalous rheological behavior. As rising the temperature from 180 to 190 ℃, the complex viscosity values slightly increase in the low frequency region (< 0.4 rad/s) for the 2CNT and 3Hybrid samples, and more significantly increases over a wider frequency range (up to about 10 rad/s) for the 3CNT sample. The Fourier transform infrared spectroscopy spectra demonstrate that the anomalous rheological behavior is not caused by hydrogen bonding in the TPU nanocomposites. The results of scanning electron microscopy observation, time sweep tests, and volume electrical conductivity measurements reveal that the anomalous rheological behavior is attributed to physical contact of the MWCNTs under low shear.
Via two-step solid-state foaming using subcritical CO2 as blowing agent, the foamed acrylonitrile-butadiene-styrene/carbon fibers (ABS/CFs) composites are prepared. The results demonstrate that a bimodal cell structure (BMCS) is developed in the foamed ABS/CFs composites. Small and denser cells are developed in the ABS matrix, whereas large cells are formed around the CFs due to concentrated CO2 at the ABS-CFs interfaces. The mean cell diameters are 0.39–0.92 μm for the small cells and 12.5–25.6 μm for the large cells, being dependent on the CFs content. The CFs especially at 10 wt% or higher can refine the small cells via both increasing the strength and elasticity of the ABS matrix and restricting their growth under large cell growth. Interestingly, slow depressurization for the saturated composites followed by foaming is also favorable to refine the small cells, which is mainly attributed to no cells to be preformed in the saturated composite via the slow depressurization. Relatively higher saturation pressure or modest foaming temperature can further refine the BMCS in the foamed ABS/CFs composites.
Nonlinear warpage analysis which considers different kinds of nonlinearity effects has attracted more and more attention recently, especially in the automotive industry. This study is mainly aimed at using the new functions in Moldex3D, “Nonlinear warp analysis” and “Buckling analysis”, to predict the warpage of the products. These new solvers cooperate with the temperature distribution and the residual stress caused by the phase change from the manufacturing process and predict the deformation of the product considering the geometric characteristic and process conditions.
Multi-Layer extrusion (MLE) is an advanced co-extrusion processing technology, which enables two polymer systems to be melt extruded, combined in an alternating format to very small total thickness <100μm and arranged in higher number of layer typically ranging from 8 to 1024. The focus of this paper is to investigate polymeric materials which are high modulus (e.g. LNP™ EXL PC copolymer or polymethyl methacrylate PMMA) and relatively low modulus (e.g. TPU) in nature as an alternating material combination for MLE. By combining different modulus of polymeric materials in MLE films, it is possible to achieve desired balance of different properties like mechanical, thermal, optical, dielectric etc., by synergistically combining the properties of the individual resins. In this paper flexural test is shown as an example to discuss the mechanical performance of MLE films. One of the major challenges of the MLE process is the down-selection of materials that are thermoplastics and have “matching” viscoelasticity at the processing temperature, as assessed by viscosity measurement at lower shear rates. Additionally, in order to ensure inter-layer adhesion, solubility parameters and processing windows of the two resins must be considered. In this study differences in adhesion were noted between PC/PU and PMMA/TPU MLE system. In PMMA/TPU MLE modification of processing temperature resulted in an improved interfacial stability and interlayer adhesion.
The purpose of this study was to investigate the feasibility of in-situ foaming in fused filament fabrication (FFF) process. Development of unexpanded filaments loaded with thermally expandable microspheres, TEM is reported as a feedstock for in-situ foam printing. Four different material compositions, i.e., two grades of polylactic acid, PLA, and two plasticizers (polyethylene glycol, PEG, and triethyl citrate, TEC) were examined. PLA, TEM and plasticizer were dry blended and fed into the extruder. The filaments were then extruded at the lowest possible barrel temperatures, collected by a filament winder, and used for FFF printing process. The results showed that PLA Ingeo 4043D (MFR=6 g/10min) provides a more favorable temperature window for the suppression of TEM expansion during extrusion process, compared to PLA Ingeo 3052D (MFR=14 g/10min). TEC plasticizer was also found to effectively lower the process temperatures without adversely interacting with the TEM particles. Consequently, unexpanded filaments of PLA4043D/TEM5%/TEC2% was successfully fabricated with a density value of 1.16 g/cm3, which is only ~4.5% lower than the theoretical density value. The in-situ foaming in FFF process was then successfully demonstrated. The printed foams revealed a uniform cellular structure, reproducible dimensions, as well as less print marks on the surface, compared to the solid counterparts.
Due to the recent and ongoing pandemic – COVID-19 – there was an urgency to determine a method to delay the continuously rapid development of the new virus. As a result, Ultraviolet-C (UVC) light, also known as Ultraviolet Germicidal Irradiation (UVGI), has been in higher demand because of its known ability to disinfect quickly and effectively. However, because of its short wavelength/higher energy, either 222nm or 254nm, material degradation is usually much more accelerated than Ultraviolet-A (UVA) or Ultraviolet-B (UVB). At this moment, this study only observed color change when exposing polystyrene to UVC light, and it is believed that this is one of the first studies, if not the first, conducted with this material. Polystyrene was selected because of its availability, abundance of relevant research (ie. UVA/UVB exposure results), and its use in weathering standards. Additionally, since there are no standards specifically about UVC exposure, this preliminary research may provide some direction.
Thermoplastic polyolefins (TPOs) have been widely utilized in a variety of automotive applications. Most importantly, the TPOs used in interior and exterior parts in automotive applications require aesthetics and good mechanical properties simultaneously. Among many of the inorganic fillers, talc is an inexpensive and natural mineral, which has the platelet structure with individual layers holding together by week Vander Waals forces. This distinct layer structure can be delaminated at low shear forces to easily disperse in TPOs. Additionally, the talc particle size can be manipulated by the various micronizing processes. In this research, talc-reinforced polypropylene (PP) systems as a set of model systems have been chosen to investigate how the particle size and surface treatment of talc influence the TPO fundamental scratch and fracture behaviors.
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