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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Method for Determining Cooling Time in Injection Molding Using Infrared Thermography
Injection molders face confusion about the best way to determine cooling time. Many methods exist to estimate cooling time, but disagreement among results and fundamental flaws create error that leads to extra work, long cycle times, and a loss of profitability for molders. This paper proposes a new method for determining cooling time at the injection molding machine using infrared thermography and DMA data to relate part ejection temperature to dimensional stability. Experiments showed evidence that dimensional stability is linked to material modulus, which would allow molders to choose cooling times based on required dimensional stability by relating measured ejection temperatures to specific modulus values using DMA data.
Minimizing Interfacial Orientation During Processing of Immiscible Blends
An interface between two immiscible polymer phases represents a material weakness due to reduced cohesive adhesion. For a co-continuous polymer blend, this interface can be viewed as an elastic membrane. From continuum mechanics, we show that the deformation of this interface during normal melt processing is largely affine, involving a slow relaxation process as compared with the relaxation process of the polymer chain. Accordingly we propose a processing strategy to minimize the development of the unwanted interfacial orientation and yet promote the development of molecular orientation so that a strong blend material can be fabricated. Some experimental results are provided and discussed.
Modeling of Heat Generation in Spin Welding
Spin welding is a common joining process for plastic parts with circular joints such as insulated cups and bowls, filter housings, and valves. In this process, heat is developed from surface friction as one part is revolved about the axis of the joint, resulting in a high linear speed. Finite element analysis (FEA) of the process can provide insight into potential mechanical deformation or failure under load that may compromise the weld, as well as aid in determining proper process parameters to achieve sufficient heating for a good weld. In this work, an approach to predict the weld temperature has been investigated and compared to measured results.
Modeling the Non-Isothermal Conveying Characteristics In Single-Screw Extrusion By Application of Network Analysis
This paper deals with the modeling of the conveying behavior of polymer melts in single-screw extruders based on a network-analysis approach. The polymer-melt rheology is strongly temperature-dependent and hence the temperature profile affects the pumping capability. In this work, we propose an approach to predicting the non-isothermal, coupled axial pressure and temperature profiles. We present the fundamental background of the implemented pumping and dissipation models and the network theory for modeling the axial pressure and temperature profiles. The simulation procedure for calculating the non-isothermal conveying characteristics is shown and a few exemplary simulation results are presented. The novel algorithm provides fundamental insights into the non-isothermal extrusion characteristics and enables screw design and process optimization in single-screw extrusion.
Modern Rheological Techniques for Polymer Analysis: Capillary Rheometer, Screw Rheometer, and Melt Strength Tester
As a result of measuring the shear viscosity on a capillary rheometer and the screw rheometer, a viscosity function corresponding to 6 decades of shear rate of 0.1 to 10,000 [1 / s] was obtained. We have identified a new method for identifying crossover point with a single temperature measurement without performing complex ‘Time-Temperature-Superposition’. Also shear viscosity and melt strength functions were compared for eight LDPE grades. It was found that the melt strength showed a completely different behavior for similar melt index materials.
Morphology and Mechanical Performance of Pipe Grade HDPE Exposed to Chlorinated Water
Thin samples of a pipe-grade polyethylene with a bimodal molecular weight distribution were exposed to 5ppm 70C chlorinated water for up to 3000 hours. The samples were characterized by tensile tests, size-exclusion chromatography, infrared spectroscopy, and differential scanning calorimetry. Throughout exposure, the molecular weight data showed evidence of degradation: weight-average molecular weight was reduced, and a shift in the molecular weight distribution from a bimodal to a unimodal distribution (decreased dispersity). After 2250 hours of exposure, brittle behavior was observed, in which the average elongation at break was 12%. At this level of degradation, the weight-average molecular weight was 9 % of its undegraded value, and the crystallinity had increased from 70% to 85%. Average tensile strength was reduced from 31.8 to 16.6 MPa. The data imply that the presence of short-chain branching may inhibit chemicrystallization and subsequently delay the onset of brittle behavior.
Multi-layer Co-extruded Annular Structures Burst Pressure Performance
Recent developments in the area of multi-layer co-extrusion have led to the ability to produce annular structures with high numbers of very thin layers. The burst pressure of these pipe structures was investigated. It was observed that die head rotation can have significant impacts on the mechanical properties of these structures due to the elimination of weld lines as well as biaxially orientation effects in the annular structures. It was also observed that following the elimination of the weld lines, the burst strength increases, possibly due to the biaxial orientation effects at higher rotation speeds.
New Development in Adhesion Promotion Using Flame Plasma Surface Treatment - Tutorial
Adhesion promotion technologies have wide application in the numerous industries for a wide range of plastic parts, such as those made of PE, PP, PET, etc. One method used to modify the surface of these and other polymer products to promote adhesion of coatings and adhesives is flame plasma. This paper describes the theory behind natural gas, propane or LPG fired flame plasma surface treatment to promote adhesion of water based inks, coatings, adhesives, labels and other substrate laminates to polyolefin based substrates. Critical parameters in flame treatment are, flame chemistry, flame geometry, plasma output and distance of the burner to the part. The interrelationship between these variables, and how to control them for optimum surface treatment, will be discussed. The use of Schliren imaging technology, high speed photographs of the flame geometry, used to develop new burner designs, as well as advances in equipment technology will be presented. A completely new patented process design has been developed and successfully implemented providing significantly improved control of the flame chemistry, while at the same time simplifying the process control and mechanical hardware required. In addition, the new design improves the overall efficiency of the flame treating process Troubleshooting & maintenance of flame plasma surface treating systems will be discussed.
Novel Method of Compounding Cellulose Nanocrystal Suspensions into Polylactic Acid and Polyvinyl Acetate Blends
Cellulose nanocrystal (CNC) suspensions were compounded into blends of poly(lactic acid)(PLA) and poly(vinyl acetate)(PVAc) using a novel wet compounding approach in which drying and compounding werecarried out simultaneously. The resulting CNC/PLA composites were compared with those produced using a more traditional method of freeze-drying CNC suspensions followed bymelt-blending into PLA. CNCs in wet compounded composites appeared to be well-dispersed in the PLA/PVAc blends, and films extruded from these compounds exhibited high transparency compared with melt-blended composites. Gel permeation chromatography indicated that molecular weight degradation due to wet compounding was comparable to that from melt blending. The formulation, including surfactant modified CNCsand PVAc processing aids, played a significant role in the dispersion and properties of the nanocomposites. The elimination of a stand-alone drying stepfor cellulose nanomaterials can potentially overcome some of the challenges associatedwith producing thermoplastic cellulose nanocomposites and help advance commercialization of these materials.
Numerical Analysis of Polymer Micro-foaming Process in Extrusion Flow
In this paper, effects of microviscosity and wall slip were considered, and a mathematical model of isothermal extrusion micro-foaming process was adopted based on classical nucleation theory and cell model. A simulation scheme of the extrusion micro-foaming process was conducted combining with the cross-section/imaginary area method and the Runge-Kutta method. The simulation program of the extrusion micro-foaming process was realized on MATLAB. The effects of inlet pressure on evolution of cell morphology and cell size distribution during the extrusion micro-foaming process were analyzed by the numerical examples. The results indicate that the higher the inlet pressure, the higher the maximum nucleation rate, and the closer to the die outlet the nucleation spot, the shorter the growth distance of the bubble, which is more conducive to formatting smaller cell radius and higher cell density.
Optical 3D Metrology the Ultimate Biomechanics Tool
3D Digital Image Correlation (DIC) provides the ability to measure non-contact 3D coordinates, displacements and strains of materials and structures. Although widely accepted in mechanical engineering and materials engineering, this tool as yet to prove its capability within the biomechanics industry with soft tissues, bones and most medical-specific materials. Known for its unique capability to be used for rapid full-field measurements from material characterization to full component testing, providing the equivalent of the results of over 10,000 contiguous strain gauges or displacement sensors, this technique is now recognized and certified (NIST, Boeing...) as equivalent to standard mechanical testing tools in the aerospace and automotive industries. 3D DIC is used across industries for improving the quality and the accuracy of the data collected to best understand mechanical behaviors of components or validate FEA models. This work focuses on the integration of the DIC technology with load frame such as Instron, MTS and Zwick for simple coupon testing of soft tissues, implants and prostheses. It was shown that DIC could in fact provide a more flexible measurement platform with capabilities for any coupon size, very small to large strains with a single instrument as well as multi-axial data in every direction for each and every one of the biomechanics applications evaluated.
Optimization of Processing Properties of Co2 Rubber Compounds
In order to reduce the carbon footprint, carbon dioxide (CO2) can be used as a raw material for synthesizing innovative rubber materials. In the following, the process of testing and improving CO2-based rubber compounds is described. The substitution of parts of the polymer chain by CO2 contributes to a sustainable rubber industry. A wide range of different raw materials is provided by the manufacturer, compounded and then tested. In order to improve processability, compound recipes are modified and improved. The investigations focus on static and dynamical mechanical properties and caloric properties. After the ability to be processed in an internal mixer is proven and improved by the use of processing aids, the compounds are tested for extrusion and vulcanization. It is shown, that CO2-rubber compounds can be processed on a rubber extruder and can be vulcanized by using hot air and infrared radiation.
Overmolding of Thermoplastic Elastomers Onto Hard Substrate Materials
Historically, soft thermoplastic elastomer (TPE) materials have been applied onto the hard substrate materials via an overmolding process in order to enhance the performance of the molded articles. In this process, it is important that the soft TPE adheres well enough to the substrate materials to maintain the desired performance. Depending on the characteristics of the substrate material, a TPE must be formulated to facilitate the adhesion of a TPE onto the substrate during an overmolding process. KRAIBURG TPE has engineered and marketed TPEs that can bond to a variety of hard substrates including metals. The adhesion characteristics of these TPEs are presented in this paper.
Polyethylene/Graphene/Carbon Fiber Waste Hybrid Nanocomposites
With growing applications of polymer nanocomposites, the need to manufacture cost-effective nanocomposites is increasing. In this work, we report economical nanocomposites from polyethylene (PE) using graphene (GnP) and carbon fiber (CF) waste. The nanocomposites were prepared by simultaneously mixing PE, GnP and CF in a melt blender where CF appeared to be randomly dispersed along with GnP in PE matrix. A delayed crystallization was observed when nanocomposites were crystallized from the melts non-isothermally. The crystallization data was well explained using Avrami model. Moreover, the hybrid filler (CF and GnP together) showed better mechanical performance with increasing CF/GnP ratio.
Predicting Fiber Orientation For Injection Molded Thermoplastics
The goal of this research is to further the understanding of the relationship between flow properties, orientation, and related mechanical properties of injection molded parts. The properties and behavior of the flow of a fiber reinforced polymer composite during molding is directly related to the stiffness and the strength of the completed part. Flow affects the orientation of the fibers within the polymer matrix and at locations within the mold cavity. Mechanical properties of fiber reinforced polymer parts, such as stiffness and strength, are controlled by the average length of the fibers and how the fibers are oriented. The ability to predict, and ultimately control, flow properties allows for the ability to efficiently design safe parts for industrial uses, such as vehicle parts in the automotive industry. A lab developed simulation packaged has been designed to predict the orientation and modulus of long glass fiber reinforced polypropylene composites. With the improved simulation package, the flexible fiber model was proven to be more accurate for predicting fiber orientation than the traditional rigid fiber model. The goal of this work is to test the universality of the existing model using long carbon fiber reinforced nylon 6,6 composites by injection molding parts and then performing experiments to check their tensile strength and the modulus. The methodology for collecting the data and the ability of the simulation to converge has been proven for the new material. The universality of the simulation package will be determined by comparing the accuracy of the results for the two materials.
Predicting Fiber Orientation in Short Fiber Reinforced Injection Molding Process Using DEM
A new and efficient method using Discrete Element Method (DEM) to perform fiber orientation analysis for short fiber reinforced injection molding process is presented in this paper. This method uses a particle-based approach with one-dimensional two-node tracker particles that are convected by the flow field. Using this particle approach instead of solving a full tensorial equation yields higher accuracy and excellent computational efficiency. The underlying flow field for this analysis is computed using a FEM based simulation of the filling and packing phases of the injection molding process. Two case studies are presented to validate the implemented solution. The results show that the implemented solution is accurate and matches well with experimental data. Strengths and limitations of the model and the ongoing work to further improve this analysis are discussed.
Preparation of Cellulose Nanocrystal-Polypropylene Masterbatches by Water-Assisted Thermokinetic Mix
In an effort to avoid freeze-drying or solvent blending techniques and better leverage the fact that preparation of cellulose nanocrystals (CNCs) result in aqueous dispersions, we investigated a water-assisted melt compounding approach to disperse cellulose nanocrystals in polypropylene. A simple, water-based cetyltrimethylammonium bromide (CTAB) treatment of CNCs was used to reduce their hydrophilicity and inhibit hydrogen bonding. The aqueous suspension of treated CNCs was then blended with polypropylene in a thermokinetic mixer with various levels of a maleated polypropylene (MAPP) as a dispersing agent. CNC dispersion was evaluated by optical microscopy, scanning electron microscopy, and rheology. CTAB treatment alone was insufficient to provide good dispersion but dispersion improved greatly with increasing MAPP content. At the highest levels of MAPP, agglomerates were still present but nearly all were well below 1 µm in size. However, despite a CNC content of 8%, little rheological evidence of a network structure was found that would suggest well-dispersed nanocomposites.
Processing of Functionally Graded Integral-Skin Cellular Polymeric Composites Utilizing Rrfm
This paper presents the processing methods for producing functionally graded rapid rotational foam molded foam composites with supercritical CO2. The cell density of the foamed core is deliberately varied across the length of the part by gradually increasing the talc content from 1 wt% to 3 wt% or by increasing the chemical blowing agent content from 0.5 wt% to 2 wt%. The foamed core of the composite is produced with foaming grade LDPE. The cellular morphology is characterized by its foam density, average cell size, and cell density across the length of the part. A scanning electron microscope (SEM) was used in the characterization process at 37X magnification along with a digital microscope at 30X magnification. The analytical characterization of the foam revealed, LDPE foamed core processing is more suitable when the chemical blowing agent (CBA) is combined with the physical blowing agent (PBA) rather than just utilizing talc with PBA. The cell density within the water-cooled LDPE foam was 1.4e6 cells/cm3 with an average cell size of 137 um. These results demonstrate the capabilities of a new experiment setup designed to combine PBA foam extrusion and RRFM technology.
Pushing the Limits to the Next Level: A New Mold Steel for Demanding Plastics and Biocomposites Designed for the Best Polishability
The increasing use of advanced engineeringplastic compoundsand biocomposites causes problems in the mold thatcan bederivedfrom a combination of wear and corrosion. The degradation of the tool steel resultsin increased maintenance, downtime and in worst case premature breakage of the mold.Manufacturing of optical devices, such as lenses, demands an extremely goodsurface finishof the mold. In addition, it should be reached as fast as possible to reduce lead times.Uddeholm Tyrax® ESR isa newpremium martensitic tool steel from Uddeholm,developed to cope with these problems by combining corrosion resistance with high hardness,very goodwear resistanceand excellent polishabilitywithout compromising on ductility.The recommended hardness of Uddeholm Tyrax® ESR is in the range of 55-58 HRC.
Quantitative Determination of Interfacial Strength of Multilayer Films Using an Instrumented Machine
The ASTM D3359 and ISO 2409 standards are currently utilized to rank the adhesive strength between the coating layer and substrate by quantifying the damaged area across the crosshatched region after a tape pulling. However, these standards neither specify the forces needed to cut the film and rub the tape nor spell out the speed and angle of the tape required during peeling. These uncertainties lead to inconsistent results. Another issue is that the current standards only apply to rigid substrates. Consequently, the above methods cannot be applied to soft multi-layer films for adhesive strength determination. In this study, a new test methodology has been developed for quantitative determination of adhesion in soft thin multi-layer polymeric films. The depth of the surface cutting was controlled using an instrumented machine. The processes of attaching, rubbing, and peeling the tape were also automated by the instrumented machine to allow for repeatable and reliable test results. Lastly, instead of using visual assessment to rank adhesive strength of the multi-layer films as instructed in the standards, our proposed new method will quantify interfacial adhesion between the top-layer and in-layer of the multilayer films based on the principle of energy conservation. Fundamental structure-property relationships on multilayer films can now be established.
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