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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High Performance Polymers for Medical Device Applications
EVONIK is a technology leader for high-performance polyamides, EVONIK’s current portfolio of specialty polyamides include PA12, PEBA (flexible polyamide), bio-based polyamides, transparent polyamides, and polyphthalamide materials for the medical sector. From catheters and balloons to diagnostic equipment and surgical instrumentation, VESTAMID® Care and TROGAMID® Care are well established. EVONIK offers flexibility in the design and manufacturing through our new Bonding VESTAMID® Care and TROGAMID® Care grade polymers. EVONIK’s VESTAKEEP® Care PEEK materials are used in temporary contact and instrument applications, while VESTAKEEP® PEEK i-Grades are used for permanent implant applications. From spine and sports medicine, to drug delivery devices and heart valve applications, new compounds of VESTAKEEP® PEEK are designed to meet the specific application needs and performance demands of medical sector.
Effects of Material and Processing Conditions on the Shrinkage of an Injection Molded Liquid Silicone Rubber Part
An injection molded liquid silicone rubber (LSR) part was investigated for better understanding of how material properties, typical processing conditions, and packing affect shrinkage. This work showed no direct correlation between material durometer and shrinkage. In-flow shrinkage was greater than cross-flow shrinkage, but the diametric shrinkage was twice the in-flow shrinkage. Small (1%) increases in shot size significantly reduced shrinkage, whereas injection velocity and cure time had no direct effect on shrinkage. Packing of LSR parts is possible, with higher pack pressures and shorter pack times decreasing shrinkage. As expected, higher mold temperatures produced greater shrinkage, but this effect was offset by packing of the part near the gate.
Effect of Screw Speed on Polyethylene-Calcium Carbonate Composites Produced Using Twin and Quad Screw Extruders
The effect of ultra high screw speed on mixing was investigated using polyethylene microcomposites with 1 wt% calcium carbonate compounded on novel twin and quad screw extruders. The screws had similar designs and the screw speeds were 300 to 2000 rpm. Extruder type influenced the effects screw speed had on extruder residence time, melt temperature, drive torque, and head pressure. Parallel plate rheology indicated significant chain scission of the polymers and better filler dispersion at higher screw speeds of 900 and 1500 rpm, especially with the quad screw extruder. In the quad screw extruder, the lower melt temperatures and greater shear allowed better mixing at higher screw speeds than the twin screw extruder. The level of mixing in the quad screw extruder also depended on resin viscosity.
A Preliminary Study on the Performance of Additive Manufacturing Tooling for Injection Molding
Tooling for injection molding is expensive and the time it takes to manufacture a tool is also a concern, especially for companies who are on a tight production schedule. The introduction of Additive Manufacturing (AM) tooling for injection molding is an attractive option for cutting cost and time for not only prototype designs, but also for short production runs. The objective of this research is a preliminary study on two AM tooling questions: How long will the plastic tool survive, and will the parts look similar to the parts produced from a traditional steel tool? In this paper, we compare the mechanical integrity of ribs of different aspect ratio (length to thickness), both experimentally and via computer simulation. We show that there is good agreement between both. The rib with the larger aspect ratio (10 to 1) breaks as predicted by the simulation and the one with the smaller ratio (5 to 1) survives several moldings as expected. In the second case, if the cycle time is adjusted to allow the mold to cool down between cycles, the rib survived a large number of moldings. The effect of tool wall thickness under different packing pressures is also evaluated.
Characterization of Slow Crack Growth Resistance of Polyethylene Pipe Grades with Cyclic Cracked round Bar (CRB) Test in Correlation to Strain Hardening (SH) Test
Several test methods have been developed to determine slow crack growth (SCG) resistance of modern polyethylene (PE) pipe materials. Unfortunately, most of these test methods exceed practical time frames and take unfeasible time to reach brittle failure at standard test conditions. Therefore new acceleration methods for a reliable and quick material ranking are required. The Cyclic Cracked Round Bar (CRB) Test and the Strain Hardening (SH) Test are two of these recently developed standard test methods with a significant expediting of testing time. This study summarizes quite a few results of the Cyclic CRB test and compares them with results from Strain Hardening (SH) test to demonstrate the correlation between these two test methods and to highlight the advantages of the Cyclic CRB Test.
Crosslinking Polyethylene Resins via E-Beam Irradiation
In this work, the crosslinking of various thin polyethylene films via electron beam exposure in an inert environment was studied. Increasing Melt Flow Index and polymer density both decreased the insoluble gel fraction resulting from irradiation at a dosage of 800 kGy. The effect of adding low levels of two different polyfunctional monomers was also examined. Trimethylolpropane triacrylate (TMPTA) was found to decrease the dosage necessary to initiate gel formation, and gave higher gel fractions at lower dosages, but showed little effect at higher dosages. A low molecular weight polybutadiene (PBd) resin showed little effect on gel fraction as compared to the neat resin controls.
Next Generation LDPE Resins for Extrusion Coating Applications
The extrusion coating market is one of the last high pressure polyethylene markets that is still dominated by aged autoclave production technology. Recent proprietary developments in high pressure tubular process technology, however, have produced new resins with enhanced processability performance to meet the growing needs of the global market. This presentation will review the performance of these new resin technologies versus ones historically used in the extrusion coating industry. The data shown will suggest that these new LDPE resins will process and perform similarly to traditional autoclave resins, when utilized on existing extrusion coating lines. Thus they can provide for a new source of materials to be used in this expanding market.
Ultrasonic Method for Determining Ply Orientation in Unidirectional Carbon Fiber Composites
Carbon fiber composites are heavily used in a wide variety of industries from aerospace to automotive to marine to athletic equipment. In many industries, destructive testing is not a preferred option to obtain material properties as the desire to keep the part in service is quite high due to individual part costs. This research uses an ultrasound technique to scan unidirectional carbon fiber laminated composites. The data collected from the scan is analyzed in MATLAB and C-scans are created to visually determine the ply-orientation for each layer within the stack. In the presented instance, the technique for determining the ply orientation is based on detecting the stitching that is used to maintain the integrity of the unidirectional ply during fabrication that remains within the part after fabrication. The stitching runs perpendicular to the carbon fibers. Thus, once the stitching orientation is identified by post-processing the collected data the ply orientation is obtained. The results presented in this work demonstrate the ability to nondestructively identify the ply orientation for most of the lamina in the two laminate stacks presented. With the technique presented in this work it would not be possible to determine ply orientation – after the first layer – if there is no artifact in the fabric that may be correlated to the direction of unidirectional alignment, such as the stitching.
A Combination of FTIR, MS and NMR Techniques to Characterize an Aqueous Wax Emulsion
In this paper, a combination of FTIR, Thermal Desorption/Pyrolysis GC/MS, K+IDS MS, ESI MS, and 13C NMR techniques was utilized to characterize an aqueous wax emulsion. Analytical data suggests that this aqueous wax emulsion consists of 94.8 wt% paraffin, 3.2 wt% diethylene glycol butyl ether and 2.0 wt% oleic acid (water free basis). Since this is a water based emulsion system, no attempts were made to determine the amount of water. The detection of NH3 by GC/MS and determination of 547 ppm total nitrogen by TNA (Total Nitrogen Analysis) led to the estimation of about 1328 ppm NH4OH in the sample.
Orientation of Poly(Ethylene Terephthalate) in Incompatible Blends with an Elastomer: Influence of Functionalization
Drawing of PET and its blends with an elastomer with and without a compatibilizer was performed from their amorphous states at a constant strain rate and at a temperature just above PET glass transition temperature. Crystallinity values of drawn PET blends were determined by differential scanning calorimetry (DSC) whereas their crystalline orientations were measured by infrared linear FTIR dichroism. The stress-strain curves during stretching indicated stronger strain-hardening and higher yield stress in blends where the elastomer was compatibilized. They also have earlier strain-induced crystallization onsets as suggested by the thermal and orientation measurements. Lower PET crystalline orientation was observed in blends containing compatibilized elastomer dispersions in comparison with those of uncompatibilized blends and neat PET. Tilting of the crystals at 45 degrees to drawing direction was found by bimodal atomic force microscopy indicating interfacial shear alignment during uniaxial drawing which could be a direct consequence of the improved interfacial adhesion. This interfacial shear alignment may explain the observed crystalline orientation reduction in compatibilized blends.
Evaluation of the Cushions Effect on Process Consistency and Repeatibility
The importance of maintaining a consistent cushion in the injection molding process is universally agreed upon in the molding industry. However, the size at which the cushion should be set is not unanimously established. As such, several “rules of thumb” or “typical” cushion sizes are recommended and used by processors in the industry. These recommended cushion sizes have been deemed acceptable but without research being applied in order to determine their viability. This study will analyze and compare the variability and repeatability of the process and end product while applying various cushion sizes to a given process.
Assessment of the Influence of Moisture Percentage, Melt Temperature, and Residence Time on Material Degradation
The ASTM D1238 is a standard related to Melt Flow Rate Testing (MFR) of plastic materials. One of the purposes of the test is to help provide a determination of a polymer’s average molecular weight (MW). As such, injection molders may utilize the MFR test to help determine if a given plastic material used to mold a part was potentially degraded during the handling or processing of the material. If the material was degraded, it is expected that the MFR value obtained post molding will show an increase when compared to the pre-molded results. The increase in the MFR value comes as a result of the MW of the polymer being decreased. An allowable percent change in MFR for many unfilled plastics can be up to 40%, which is typically associated with a 10% loss in weight-average MW. When the MFR value exceeds the acceptable change limits, the material is likely considered degraded. The factors in injection molding that are most likely to increase the chance of degradation include melt temperature, residence time, and, if the material is capable of undergoing hydrolysis, moisture content. This study will investigate these variables in an attempt to determine the influence that these factors have on the MW of the material.
Accelerated Woehler Tests and Fatigue Simulation of Short Fiber Reinforced Thermoplastics
In order to use the high potential of Woehler curves as material and not component based data for life time estimation in part design, a time effective test strategy has been developed appropriate for short fiber reinforced thermoplastics. In addition to classical force-controlled Woehler tests for the basic material characterization, strain-controlled tests were used which allowed boundary conditions suitable for viscoelastic material behavior. E. g. the maximum strain rates in each test are constant and do not vary due to the creep behavior of the specimen. On the basis of the results of the investigated Polybuthyleneterephthalate, it is shown that the total number of Woehler curves to be determined for one type of matrix material can potentially be reduced due to the matrix-dominated material behavior of mainly transversely oriented test specimens. In addition, the test frequency can be increased in a defined way, as a certain self-heating due to dissipation of the material in Woehler tests is allowed. The acceptable temperature range is determined with the help of temperature dependent viscoelastic material data. The validated accelerated Woehler data are then used exemplarily in an integrative structural simulation method developed for thermoplastics to calculate the fatigue strength behavior of a model component. The results show good agreement with test data.
Accelerated Aging of Polyethylene Pipe Grades in Chlorine Dioxide and Hypochlorite Solution Applying a Newly Developed Exposure Device
Chlorine based disinfectants are frequently dosed into the drinking water network to maintain the high quality of potable water. Considering the strongly oxidative nature of these chemicals their long-term impact on the aging of polyolefin pipes is a matter of interest. In this study three polyethylene pipe grades were objected to an accelerated aging in 10 ppm of chlorine dioxide (ClO2) and 100 ppm of sodium hypochlorite (NaOCl) solution at 60 °C. After a few weeks of conditioning the surface analysis with scanning electron microscopy (SEM) revealed several micro cracks, confirming a highly degraded superficial layer. The cross section SEM images displayed the degraded surface layer with a thickness of about a 100 µm. Furthermore thermal analysis such as the Oxidation Onset Temperature (OOT) indicated a significant stabilizer consumption in various depths for each sample.
A Step-wise Approach for Color Matching Material that Contains Effect Pigments
A red color can be described as cherry red but that description can mean many different things. How can a color be matched with a description like “cherry red”? A method to describe the correlation between the physical color and the perceived color is necessary. Several models are used today to define the link between the common vocabulary used to describe color and a quantitative measurement of that color. This translation of color is very important to a colorist as these parameters allow for meaningful communication. The color space models and instrumentation to quantify the colors are tools used for many different applications, color matching being one of the most important for a colorist or color scientist. The development and standardization of instrumentation has allowed for further insight into the communication of color. In this paper, the method used to perform a color match is investigated through a stepwise approach to using different analytical tools. This approach is applied to some of the most difficult pigments to match; those that exhibit color shift.
Relaxation Behavior of Metal-Polymer Hybrid Structures Mechanically Joined by Clinching
Present and further part constructions will be increasingly designed as hybrid material combinations. Due to the optimized local material adaption, the final part properties can reach maximized performance and efficiency. The present article deals with metal-polymer hybrid structures joined by clinching. Clinching is a mechanical joining technology which enables the production of high-strength joints especially for thin-walled components. The realized investigations consider the resultant stability of the created form closure between the used mating parts. For the process evaluation the different material properties of steel (DC04) and short glass fiber-reinforced polymer (PA6-GF15) were analyzed regarding their mechanical and thermal behavior. The glass transition temperature of PA6-GF15 as a function of the conditioning level could be detected as a rate of the loss of tightness and preservation of form closure. However, suitable pre-treatment strategies ensure reliable joining with a high degree of automation as well as without additional elements.
Novel Liquid-Dispersion Technology for Making Industry Leading Highly Filled, Well-Dispersed Masterbatches
A novel method for making highly filled masterbatches (MBs) has been developed by Interfacial Consultants, LLC (IFC) and now employed commercially by REV Materials, LLC (REV). This patent-pending approach has set a new standard for the development and production of the market’s highest filled MB materials. The manufacturing method consists of three-steps: pre-coating of mineral or filler, removal of liquid carrier, and finally pelletization. To date, REV has designed, developed and manufactured using this technology MBs consisting of 93+ wt% talc, 93+ wt% calcium carbonate, 90+ wt% wood, 85+ wt% cellulose fiber, and 37+ wt% carbon nanotubes in polyolefin, polyamide, and polyester carriers. Furthermore, it has been shown that these MBs are compatible and disperse extremely well in the main plastic.
The Influence of Blend Composition on the Properties of LDPE-PA6-EVAL-Blends
The aim of this work was to investigate the effects of the composition on the properties of LDPE-PA6-EVAL blends with an emphasis on the influence of the EVAL grade on the system. Furthermore, also the effects of additional compatibilization by maleic anhydride grafted PE on the blend properties should be investigated. We found, that EVAL has some compatibility with PA6, as long as the vinyl alcohol content is high enough, in this case at least 62 mol%. This results, in combination with the high shear intensity applied, in a fine dispersed morphology and reasonable properties. In case of the non-compatible EVAL grade, the addition of MAPE improves the properties like impact strength and elastic modulus, which can also be seen from the morphology of the samples. The addition of a compatibilizer also shows an expectable stabilization effect, which can be seen by comparing the morphology of the extruded melt strands after compounding with the morphology of the injection molded specimen afterwards. In conclusion this shows that with compatibilisation, the blend properties are stable and sufficient for various applications, therefore such blends could be reused for another life cycle.
High Speed Twin Screw Extrusion for Biodegradable Polymer Blends: Analysis of Compatibility and Rheology Prediction
This work examines the effects of high shear on the degradation and compatibility of blends of poly(propylene carbonate) and poly(butylene succinate) (PPC/PBS) in twin screw extrusion. Also, since solid PPC has poor flowing capabilities, different feeding methods for the TSE trials were compared for their ability to produce consistent results. The blends were compounded at 200, 500, 1000 and 2000 rpm. Viscosity measurements were used to estimate degradation, and it was found that the Maron - Pierce model for viscosity of composites accurately predicted blend viscosity at low shear. The viscosity change was inversely proportional to the screw speed, indicating matrix degradation. Moreover, the blend was more sensitive to thermomechanical degradation than the neat PBS. However, the molecular weight loss did not exceed 22% even at the highest screw speed of 2000 rpm. Finally, morphology investigation showed that the TSE blends had smaller droplet size with a broader shape distribution than the batch mixed blends. All results supported the idea that the high levels of shear stress are the governing factor in the morphology and the degradation of blends in twin screw extrusion.
Investigation of the Effect of Filler Concentration on the Flow Characteristics of Filled Polyethylene Melts
All polymer slurries that have a high concentration of filler are shear thinning. Shear thinning is an important characteristic of polymers, filled and unfilled, because it leads to being able to increase the throughput, shear rate in a die or mold without having to use substantially more power to increase the flow rate. With a perfect pseudoplastic fluid, n = 0, there would be no increase in energy as the flow rate is increased. This is of course not allowed by the second law of thermodynamics. Newtonian fluid based slurries show an increase in shear thinning as the concentration of “filler” increases above the percolation threshold. As the maximum packing factor is approached they approach a perfect pseudoplastic fluid. At times the shear thinning characteristics of a filled polymer does not increase substantially as the filler is increased in the same manner as the Newtonian fluid based slurry. Therefore, it is important to investigate the physics that controls shear thinning so that flow in extrusion and injection flow models can be more predictive when dealing with filled polymer systems.
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