SPE Library
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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Conference Proceedings
Improving The Ductility Of Recycled Pet For Plastic Lumber Applications
Recycling of plastic waste at Forward Operating Bases. (FOBs) is continuing to be a topic of considerable interest to the Department of Defense. A previous paper [1] by the current authors described the need and opportunity to convert this waste stream to plastic lumber that could be used by the warfighter for various construction applications at forward operating bases (FOBs). The selected technique of flow intrusion molding of recycled PET (rPET) into 1 inch by 1 inch by 36 inch test specimens showed feasibility of this recycling technique and the resulting specimens were very stiff with high modulus but they failed during testing in a brittle fashion with fragmentation. This is not a desirable failure mode and work was conducted to improve the ductility of the plastic lumber specimens using both chain extenders and impact modifiers. This paper describes the investigation of using additives to improve ductility and therefore the utility of rPET to make plastic lumber using flow intrusion molding and the resulting performance characteristics.
Improving Part Properties During Injection Molding With 3D Printed Co2 Cooled Plastic Mold Inserts
This paper describes the development of innovative temperature control concepts for use in additively manufactured inserts based on CO2. These have been successfully investigated for their suitability in small batch production. The additive manufacturing processes have been evaluated in terms of their suitability for the production of mold inserts. It has been possible to reduce the time required to prepare the inserts. In the investigation of suitable plastics, POM has proven to be suitable. Of the generative manufacturing processes investigated, stereolithography was found to be suitable. Robust manufacturing in the injection molding process with the other additive manufacturing processes was not possible. The manufactured components were examined with regard to their properties and compared with conventionally injection-molded components. It was found that a clear dependence on the manufacturing process of the insert used for production can be observed, especially in the crystalline microstructure of the manufactured components. This makes it difficult to use additively manufactured tool inserts in small-batch production, since the resulting properties of the components in terms of crystallinity and thus distortion are not comparable with injection-molded components. In further investigations, the minimum necessary thermal properties of the printing materials must be determined in order to ensure robust small series production with component crystallinity comparable to the injection molding process.
Shape-Memory Polymers Based On Castor Oil And Lignin Sulphonate Synthesized From Waterborne Dispersion
Aqueous polyurethane dispersions based on castor oil and lignin sulphonate (LS) were successfully synthesized in homogenous solution with no organic volatile compounds and excellent dispersion stability. Transparent thin films of PU-LS with different LS contents were obtained via solution (dispersion) cast technique. The glass transition temperatures (Tgs) of the PU-LS films were evaluated from the dynamic mechanical analysis (DMA) at 1 Hz and 2 oC/min heating rate. The Tg was found to be strongly influenced by the incorporation of the small LS content. The Tg (temperature of tand peak maximum) for PU-LS film with LS content lower than or equal 3 wt.% increases considerable with increasing the concentration of LS. For higher concentrations, no significant additional increase in the Tg was observed. The crosslink density was also calculated from the elastic modulus at a temperature of 40 oC higher than the Tg based on the rubber elasticity theory. The crosslink density increases with increasing the LS content of the thin films. The thermal-induced shape-memory effect was investigated using DMA according to cyclic thermomechanical tensile tests. The PU-LS thin film was found to have an excellent shape-memory effect and the recovery was strongly dependent on the LS content. Fast recovery (17 sec) to the permeant shape was observed once the temporary shape sample was immersed in water bath at the programming temperature.
Anisotropic Structural Analysis For Injection Molded Fiber Reinforced Thermoplastics
A seamless modeling framework from injection molding simulation to anisotropic structural analysis is presented. Key features of the framework are anisotropic material modeling and fiber orientation data mapping, aspects that are facilitated by coupling Moldex3D, Digimat, and ANSYS software. The approach is exercised by modeling the mechanical response of injection molded tensile specimens with single and dual gates made of a thermoplastic resin with 20% glass fiber weight fraction. It is reassured that local fiber orientation is crucial for an accurate prediction of the mechanical strength of dual-gated tensile specimens with a weld line. Unlike the isotropic modeling approach, typical features of stress and strain concentrations along the weld line are clearly demonstrated. The capability of the approach is further highlighted by accurately predicting the break-off torque of a screw head used to adjust the seal compression in cable entry ports of optical closures.
Understanding The Effects Of Process Parameters On The Curing Of Hexcel As4/8552 Prepreg Composites
The effects of the processing parameters on the curing of continuous carbon fiber composite made from Hexcel AS4/8552 prepreg tape are studied. A commercial process simulation finite element method, that takes in account the residual stresses due to chemical, thermal, and mechanical shrinkages, is utilized. This method solves the curing process sequentially. In the first step, the distribution of temperature and degree of cure in the composite is computed. In the second step, the information from the previous step is used to calculate the stress evolution during cure. At the end of the second step, the composite deformation due to tool removal is also calculated. The impact of three different process parameters on the final degree of cure and the residual stresses are studied in detail.
Foaming Behavior And Property Of PMMA Nanofoam Fabricated By By Hot-Bath And Hot-Press Foaming
Nanocellular foam has attracted significant attention because of its superior physical and mechanical properties than microcellular foams. In this study, nanocellular foams were produced using the hot-bath and hot-press foaming methods. By lowering the saturation temperature (Tsat) to -30 ºC, the CO2 solubility was increased to 45.6%, and the cell size was reduced to less than 40 nm. Samples prepared by hot-bath exhibited smaller cell size, thinner solid skin, and transitional layer.
Complex Viscosity Of Star-Branched Macromolecules From Analytical General Rigid Bead-Rod Theory
The complex viscosity of planar star-branched polymers has been derived from general rigid bead-rod theory, but only for singly-beaded arms. Here, we explore the respective roles of branch functionality, arm length of non-planar arrangements, analytically from general rigid bead-rod theory. For non-planar, we include polyhedral, both regular and irregular. We fit the theory to complex viscosity measurements on polybutadiene solutions, one quadrafunctional star-branched, the other unbranched, of the same molecular weight. We learn that when general rigid bead-rod theory is applied to quadrafunctional polybutadiene, a slightly irregular center-beaded tetrahedron of interior angle 134º is required (with 1,360,000 g/gmol per bead) to describe its complex viscosity behaviour.
Biobased And Recyclable Polysulfones Using Imine Chemistry
An alternative to bisphenol A was used to synthesize polysulfones (PSs) that are chemically recyclable. Vanillin was reacted with 4-aminophenol to generate a diphenol with an imine. The synthesis of PSs is done by means of polycondensation of dibasic phenols with sulfur-containing aryl halides by the mechanism of nucleophilic substitution. The lignin based diphenol replaces traditionally used bisphenols (a xenoestrogen) and is the site for recycling the polymer. The polymerization is studied under various conditions (temperature, time, monomer ratio) for best properties and product purity. The polymer structure was confirmed via NMR and its thermal properties studied using DSC and TGA (Tg~122°C, Td5~270°C, Td10~400°C, Tprocess~180). The stability of the imine bond was studied under the reaction conditions for reactant stability.
Ultrasonic Joining Of Additively Manufactured Metalpolymer Lightweight Hybrid Structures
Ultrasonic joining is a novel friction-based joining technique to produce through-the-thickness reinforced hybrid joints between surface-structured metals and unreinforced or fiber-reinforced thermoplastics. The reinforcements’ presence is responsible for improving the out-of-plane strength of the parts, enhancing their damage tolerance. The process feasibility has been successfully demonstrated to join additively manufactured (AM) metal and polymer parts. However, further investigation of its main advantages and the joining process of subcomponents to support the technique’s further development is still missing. This paper aims to demonstrate the application of U-Joining to fabricate AM 316L and PEEK hybrid structures produced via laser powder bed fusion and fused filament fabrication, respectively. Firstly, the quasi-static single lap shear performance of coupon specimens produced with optimized joining parameters was assessed. The results indicate an improvement of 2.7 times in the ultimate lap shear force and 5.9 times in the displacement – when compared to non-reinforced flat samples. Fracture surface analyses of tested samples exhibited a mixture of cohesive and adhesive failure. Further microstructural analyses at the metal-polymer interface showed micromechanical interlocking between the parts. As observed, the PEEK was able to flow and penetrate the cavities at the metallic specimen’s rough surface due to the joining friction heat input. Finally, a selected skin-stringerbracket case study was analyzed, showing the potential of AM and U-Joining to drastically reduce the structure’s weight by about 64%. To validate this idea, a scaled-down skin-stringer-bracket technology demonstrator was successfully fabricated.
Turnkey Solution For 3D Metal Printed Conformally Cooled Injection Mold Inserts
In Spring of 2020, Instaversal was contracted to test our newly developed conformal cooling technology, CoolTool™, against existing production benchmarks for a plastic injection molded Pipe Bracket Adapter. The Product Innovator was going through a period of elevated demand where the current cycle time of the existing injection mold tool prohibited them from meeting their demand. When cooling cycles were sped up this led to higher scrap rates due to sink marks. This left the Product Innovator with two options: delay delivery of the product to their top customer with the risk of losing the sale and potentially losing the customer or to invest in additional injection mold tools to double production capacity. To meet the customer’s demand, 100,000 parts needed to be produced in a 60-day time period. This request created conflict with the contract manufacturer. They were being asked to absorb the cost of additional molds to meet the timing or run full 24-hour (Monday-Friday) shifts over the 60-day period which would create losses in revenue by eliminating other clients’ scheduled jobs.
Using In-Mold Switches For Control And Monitoring Of A Multicavity Hot Runner Mold
The use of in-mold melt-front detecting switches were used to control the velocity-to-pressure (v/p) transfer during injection and/or to monitor the injection in a 2-cavity, hot runner valve-gated mold. The switches were connected to a data acquisition/control system either independently, in series or in parallel. When the switches were not used for v/p transfer, screw position was used. It was found that using the in-mold switches for monitoring was more effective than either peak injection pressure or cushion monitoring to sort suspect parts and alert of changes in cavity balance. When the switches were either hooked up in parallel or independently, using the first switch closed for v/p transfer, overpacking of the mold was prevented when the heater in the drop/gate of one cavity was turned off.
Investigating The Processing Of Stimuli-Responsive Cellulose Nanocrystal Polymer Composites In Graded 3D Printing
Functionally gradient 3d printing is of great importance for polymer composites to be applied in soft robotics or smart electronic devices. Imparting mechanical gradients within the design of new materials would help to prevent premature failure of devices and could reduce strain mismatches. In this work, we first focus on investigating the mechanical gradients and water responsive behavior of cellulose nanocrystal (CNC) / thermoplastic polyurethane (TPU) films by changing the concentration of CNCs. After generating masterbatched feedstocks, CNC/TPU films were extruded with a single screw extruder to obtain 3D printable filaments. The thermal and rheological behavior of the nanocomposite system is characterized to evaluate the mechanical property gradient of CNC/TPU filaments as a function of CNC concentration within a 3D printed geometry.
Machine Learning Modeling to Predict Transient Cavity Pressure Profile in Injection Molding Process
A machine learning approach based on artificial neural network is presented and applied to injection molding process. Fill time, maximum fill pressure and transient cavity pressure profiles are predicted with the input process conditions of injection speed, melt temperature and mold temperature. The physics based model using Autodesk Moldflow is evaluated by comparing it with experimental fill pressure profiles for various process conditions, and it is used to generate enough data to train and validate the machine learning model. With the present machine learning model using 400 data samples, not only the fill time but also the transient pressure profiles are accurately predicted with less than 4.7% error. Further, a new machine learning model is trained with 200 data samples, instead of 400 samples, to check the dependence of the model accuracy on the sample size, and the error in prediction of transient pressure profiles increases only to 6.7%.
Compounding and Characterization of Polylactic Acid-Sawdust Deep Eutectic Solvent Extracted Lignin
There is an ever increasing need for sustainable and biobased materials. Plant-based feedstock such as cellulose and lignin can potentially become competitive resources as alternatives to fossil-based materials. Lignin as an inexpensive feedstock has been examined toward preparing polymer composites. It however faces some challenges including its detrimental impact on the mechanical and thermal properties of the resultant composites. This work reports the fabrication and characterization of polylactic acid/lignin composites with the incorporation of a new type of lignin, called deep eutectic solvent (DES) extracted lignin. White fir sawdust was used as feedstock to extract DES lignin. For comparison, commercial alkali lignin (CAL) was also used as a benchmark. PLA/lignin composites containing 0-15 wt.% lignin were fabricated using twin screw extrusion process followed by compression molding. Composites characterization were conducted using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and tensile testing. The results revealed that the mechanical and thermal behaviors of DES lignin composites significantly outperformed their CAL counterparts. For composites with 15 wt.% DES, the tensile strength, Young’s modulus, and elongation at break dropped by ~33, 7 and 45%, respectively, compared to those of neat PLA. However, the composites with 15 wt.% CAL showed 90, 45 and 86% drop in the strength, modulus, and elongation, respectively. The initial thermal degradation temperature of PLA dropped by ~ 8-27 °C with the incorporation of 5-15 wt.% DES lignin. On the other hand, the introduction of CAL to PLA lowered the degradation temperature by ~89-124 °C. DSC also showed a drop in the glass transition temperature (Tg) and melt temperature (Tm) for both the composites but the drop was less significant for DES lignin composites. The good performance of PLA/DES lignin composites may be associated with the DES lignin’s high purity, low heterogeneity, low molecular weight, fine particle size as well as its homogenous dispersion and compatibility with PLA matrix.
Integration of Polycarbonate Thermoplastic in LED Lighting
Thermally conductive (TC) polycarbonate was utilized as aluminum metal replacement in LED lighting luminaires, along with transparent, diffusion, and reflective polycarbonate thermoplastics in order to describe a light weight, design-friendly, cost efficient part. To assess suitability of the TC polycarbonate, the part was subjected to thermal testing. Results showed very similar thermal characteristics as aluminum.
Designing for Six Sigma (DFSS) - A Systematic Approach to Robust Plastic Part Design
Designing for Six Sigma (DFSS) - A Systematic Approach to Robust Plastic Part Design
To design and manufacture today's complex plastic components, product designers are under tremendous pressure to produce robust designs at a minimum cost and in the fastest possible time. Leading author David Wright wrote in his book titled “Failure of Plastics and Rubber Products” that design issues account for almost 20% of product failures. The fact is that many errors that manifest themselves as material, tooling or processing can also be attributed to design issues. Conventional plastic flow simulation does not necessarily help diagnose and avoid common design issues.
Decisions made at the design stage impacts manufacturing quality, product cost, and delivery lead times. Taking a proactive approach by including Six Sigma philosophy upfront into the early design stage can help develop high quality, profitable products eventually bringing sustained value to customers and markets.
The Paper will discuss the Design for Six Sigma (DFSS) philosophy and best practices and tools for its incorporation into new plastic product development. This will include:
• Understanding the DFSS concept and popular methodologies such as DMAIC and DMADV
• Learning how to use DFSS Methodology in early part of plastic product design lifecycle
• Applying DFSS techniques and available simulation and DFM tools for successful implementation
Analysis of the State of the Art of Technical Drawings of Plastic Molded Parts Regarding Tolerances
The plastic-specific material properties are often not taken into account in the specification of technical drawings of injection molded parts. As a result, tolerance requirements are specified, that are too tight and sometimes even impossible to manufacture, which result in high production expenses. To avoid this, it is necessary to coordinate the functionally required accuracies of plastic components with the technical possibilities available for injection molding production.
In this paper a systematic analysis of drawings from practice is used, to show the current state of the art regarding geometric product specification and tolerance assignment of plastic molded parts. In addition to the quantification of the number of specified features, the unambiguousness of the product specification is assessed. Beyond that, the degree of accuracy of the tolerance requirements is quantified and the manufacturing feasibility is checked in accordance with ISO 20457 in order to then determine the resulting production expense that is necessary to achieve the required tolerances. It is proven that for almost a fifth of the plastic parts tolerance requirements are specified that are not feasible to be produced in the injection molding process. Additionally, it is found that all drawings examined do contain ambiguously specified features, that do not allow for an unambiguous verification.
Three Trends in Healthcare Adhesives
With an aging global population growing, the demand for new healthcare products and telehealth systems will increase. The FDA aims to advance innovation and development in digital health while ensuring patient safety and effectiveness. Adhesives are critical in the new remote monitoring products, such as the small wearable devices that stick to skin. In addition, surgical adhesives are replacing stitches, and robotic surgical systems are rising. With healthcare adhesives, there are additional challenges in safety, performance, biocompatibility ISO 10993, and cost requirements.
This paper reviews three healthcare adhesive trends: (1) topical skin adhesive patches, (2) tissue adhesives, and (3) medical device assembly and equipment adhesives.
Adhesion of Overmolded TPE to FR-PC/ABS: Effect of TPE Properties and Substrate Color Recipe
Various grades of Thermoplastic Elastomer (TPE) were overmolded onto a FR-PC/ABS blend prepared with several different color recipes and tested for adhesion. All combinations prepared exhibited adhesive failure with a standardized peel test, yet showed relatively high average peak peel forces that ranged from 3.74-4.07 N/mm, which agreed well with literature values. Different color recipes for the substrate had no discernable effect on peel forces. Two-step overmolding of TPE using pre-molded (and therefore conditioned) substrates gave no significant difference to those prepared with direct 2-shot overmolding.
The Most Frequent Design Flaw That Leads to Part Failure
The topic presented in this paper is not new. There are numerous reasons why sharp transitions should not be present in a plastic part. However, the number of failures that are occurring at sharp transitions is still very common. In most cases, they can easily be avoided by simply removing metal from the mold to make a smooth transition. This paper will review where most of these transitions are being found, and why they are common in critical parts. A tensile testing study was performed to better understand the effect of geometric transitions. Two cases studies are given showing why the sharp corners can significantly reduce the lifetime of a plastic part.
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