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

Fibril-Flash Formation During Vibration Welding
P.J. Bates, C. Quijano-Solis, J. Vanderveen, B.K. Baylis, June 2022

Vibration welding flash occurs when molten polymer flows under pressure from the weld interface. This study examines the formation of small hair-like fibrils during vibration welding. Polypropylene and nylon 6 plates were butt-welded and the assemblies were assessed using a high-speed camera and digital microscopy. A mechanism has been proposed whereby initial asperities at the weld interface first melt to form a polymer pool. Thermal expansion of this pool allows polymer to be extruded laterally towards the edge of the weld interface. The extrudate is rolled up to form fibrils that can eventually grow to several millimeters in length.

Enhancing Emi Shielding Performance Of Thermoplastics With Long Steel Fibers And Carbon Fibers
Prabuddha Bansal, Suresh Subramonian, Young-Chul Yang, Soo Hee Choi, June 2022

Electromagnetic interference (EMI) is a common problem encountered by electronic devices, especially in electric vehicles. External electromagnetic (EM) waves affect the operation of an electronic device by interfering with the internal EM signals. To provide EMI shielding, various materials were studied, and the measured electromagnetic shielding effectiveness (SE) data are presented in this study. The main factors affecting EMI SE are quantified statistically – filler loading, shield thickness, and base polymer resin matrix. Long steel fiber thermoplastics provide the highest EMI SE, at over 60 dB at frequencies ranging from 30 MHz to 20 GHz, and at thickness as low as 1.6 mm. It is also demonstrated that carbon fiber filled thermoplastics can provide EMI shielding at levels greater than 50 dB.

Moisture Sensitivity Characterization In Pla/Pbs Parts During Ultrasonic Welding
Raihan Quader, David Grewell, Lokesh Narayanan, Leo Klinstein, Bill Reed, June 2022

Ultrasonic welding (USW) is a surface mating process where absorbed moisture in the surfaces of hydrophilic materials can negatively affect the weld joint quality and strength. USW is a secondary processing operation that is performed post-molding or extruding. Hence, during the storage time between primary processing and USW, the parts are susceptible to moisture absorption. Therefore, it is necessary to characterize the moisture sensitivity to meet the specified weld strength. Moisture sensitivity of Industrial standard test parts (ISTeP) made with PLA, PBS, and PLA/PBS 25/75 blend was characterized for USW in this study. ISTeP parts were moisture conditioned for one week at different relative humidity (RH) levels and then tested for weld strength. It was found that the weld strength decreased with increase in RH for 100% PLA ISTePs but it was not statistically significant. Above 65% RH, weld strength of 100% PBS was significantly decreased. Scanning electron microscopy of weld areas after the pull test revealed an increased amount of trapped porosity in the fractured surfaces of high relative humidity samples. It was also demonstrated that PBS and PLA/PBS composite can be ultrasonic welded.

Impact Modification Of Pla (Poly Lactic Acid) By Blending Small Amounts Of Amorphous Pha (Polyhydroxyalkanoate) Copolymers
John Licata, Raj Krishnaswamy, Michael Andrews, Allen Padwa, Zhiguan Yang, June 2022

This work demonstrates the efficacy of amorphous polyhydroxyalkanoate (a-PHA) copolymers in enhancing the impact strength of PLA without compromising the compostability and bio-based carbon content of the final product. The influence of PHA polymer composition on the performance of PLA will be highlighted for applications including thermoforming, film and injection molding. Finally, the morphology of the blend will be used to explain the impact modification mechanism. Blends of 100% bio-based and fully biodegradable a-PHA and PLA exhibit good toughness and clarity in injection molding, extruded sheet and blown film. It will be shown that the level of toughness increase and modulus reduction can be tuned by blend composition.

Long Term Aging Characteristics Of Post-Consumer Recycled (Pcr) Polycarbonates
Rashed Islam, Jacki Laiz, Dolaphine Kwok, Swanand Vaidya, Ayyana Chakravartula, June 2022

In this paper, the tensile properties of indoor and outdoor post-consumer recycled (PCR) polycarbonates (PC) have been compared with virgin PC at various aging conditions. 50% recycled PCs showed comparable tensile strength at breakage (~70 MPa) and maximum strain (~190 - 200%) before aging, when compared to virgin PC of same MFR of ~10 g/10 min. Three different high temperature and high humidity aging conditions were investigated: 40oC 90% RH, 60oC 90% RH, and 85oC 85% RH for up to 500 hours. Strength at breakage was found to decrease as the aging stress or aging time (with the same aging condition) was increased. Both the indoor resins were comparable in strength up to 60oC 90% RH. But in 85oC 85% RH both showed significant drop in strength. On the other hand, outdoor PCR resin showed much better performance (only ~12% degradation) in 85oC 85% RH compared to other two indoor resins (25 - 40% degradation). Outdoor UV aging characteristics were also compared between 0%, 50% and 75% PCR and degradation up to 600 hours were found to be within 5%.

Improving The Ductility Of Recycled Pet For Plastic Lumber Applications
Richard P. Heggs, Prabhat Krishnaswamy, June 2022

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
Ruben Schlutter, Stefan Hins, June 2022

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
Samy A. Madbouly, June 2022

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
Sean C. Kim, Esteban B. Marin, Christophe Desard, June 2022

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
Shardul Panwar, Royan J. D’Mello, and Umesh Gandhi, June 2022

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
Po-Chih Tseng, Kiday Fiseha Gebremedhin, Nigus Maregu Demewoz, Shu-Kai Yeh, June 2022

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.

Biobased And Recyclable Polysulfones Using Imine Chemistry
Vitasta Jain, James Sternberg, Mark Johnson, Srikanth Pilla, June 2022

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
W. S. de Carvalho, S. T. Amancio-Filho, June 2022

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
Zakary Smith, June 2022

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
Brad Johnson, June 2022

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
Yimin Yao, Michael J. Bortner, June 2022

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
June 2022

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%.

Deformation Analysis Of Mold Cavity With Sla Conformal Cooling Channel Insert
Olumide Aladesiun, Kyehwan Lee, Yooseob Song, Younggil Park, June 2022

Injection molding is the process of injection molten plastic into a mold to form desired shape of part and it’s widely used process for mass production of plastics over the world. This process is not complete without the mold as it is the most critical part of the process. The cost of producing mold is huge due to manufacturing process and technique, tool material and cost of labor. The more effective the mold, the more efficient the process and the more profitable to the business. A critical factor is the cooling time, and a well-designed mold can achieve even cooling in the shortest period, which leads to increased productivity and higher quality of molded parts. In this research, an alternative core design was employed, to achieve these goals during the molding process. The core has 2 parts: the core and core insert. The core insert was produced using SLA technology to achieve the conformal cooling while the core was machined, and the deflection was studied using finite element analysis.

A Semi-Genetic Process For Fitting Polymer Viscosities And Selecting Best Models
Paul Van Huffel, June 2022

This paper presents a process for fitting corrected viscosity data to constituent and temperature dependent data to a range of two-equation models. The process tests different models to determine the best fit model for each. Rheometer data for polymer melts, after corrections for shear rate and entrance pressure losses, may fit one model better than another, and as such the following constituent models are reviewed in the form as they are commonly applied in commercial software today: 1) Cross Model, 2) Modified Cross Model, and 3) Carreau-Yasuda. Once the constituent model is fit, the following temperature dependent models are compared: 1) WLF, Exponential, Arrhenius, and Masuko-Magill. The differences between the models are presented in order to highlight the need to compare different models to obtain a best fit. Lastly, a solution is presented to the problem of convergent viscosities with respect to shear rate as compared across a range of temperatures as no existing model in common use today can capture this specific behavior.

An Explicit Non-Newtonian Fluid Model For Polymeric Flow With Finite Stretch
Donggang Yao, June 2022

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.

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