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
A Study Of Melt Temperature Of A Lab-Scale Blown Film Line And Effect Of Melt Temperature On The Film Properties
Melt temperature is an important parameter in the blown film process, as it can impact melt strength, bubble stability, crystallization/orientation, and maximum throughput. The melt temperature at the extruder discharge, blown film die exit and film bubble of a lab-scale blown film research line were measured using a hand held thermocouple and a FLIR thermal camera. The die melt temperature was 10 to 18 °C higher than the die temperature set point, but the extruder discharge melt temperature had only a small influence on it. This could be caused by the balance of shear heating in the die and cooling from the metal.
Films were fabricated at high and low melt temperatures at the die and at the extruder discharge for two resins. All other process conditions such as rate, frost line height (FLH), film thickness, blow up ratio (BUR), die gap, and air ring, were kept the same to study the effect of melt temperature. Film properties, i.e., haze, dart, tear and tensile were characterized. Most properties did not show a clear trend with the melt temperatures in the range of the experiment (25 °C variation of die and 40 °C variation of extruder). The one exception was dart, which showed slightly reduced values at higher melt temperature. The results from this study provide important information for blown film process modeling.
Cavity Pressure Measurement During Injection Molding Via Ultrasonic Technology
Cavity pressure history during the injection molding process dramatically affects the properties of the product. This study proposes a non destructive method for measuring cavity pressure by evaluating stress on the tie bars of the injection molding machine using ultrasonic technology. Both theoretical discussion and experimental results are presented in this study, and the correlation between ultrasonic signals and stress es on the tie bars are further determined by a magnetic type clamping force detector. The method is then precisely calibrated with an R squared value up to 0.99 962 in average. Following this, it is a pplied to measure the cavity pressure and proves feasible, with r elative errors within 4.3 This method can be applied to online monitoring in the injection molding process to detect parameter variations and indicate product properties. This method has th e advantage of high stability, being non destructive, online and low cost, and can be widely promoted in injection molding industries.
Thermoforming Evaluation Of Coextruded Multilayer Evoh/Ldpe Film/Foam
A multi-layered film/foam system having 16, 32, and 64 alternating foam and film layers has been developed using multilayer coextrusion technology. The film layer was based on ethylene-vinyl alcohol (EVOH) copolymer and foam layer on low-density polyethylene (LDPE). The cellular structure was characterized by scanning electron microscopy investigating the effect of the number of layers and layer composition on the film/foam structure. The film/foam materials produced exhibited variable properties, such as density, cell size, cell density, and mechanical properties by changing the layer number and composition. The stress-strain behavior of these film/foam materials at several temperatures was examined. The stress‐strain curves obtained were referenced to understand the influence of temperature on the uniaxial deformation process. This information provides insight into the material properties and process conditions influencing thermoforming behavior and performance. The thermoformability of the film/foam materials were evaluated. Optimum forming capacity was achieved at 60ºC. These film/foam materials showed a lower reduction of thickness in the sidewalls, as well as a higher dimensional uniformity in the thermoformed product.
Investigating The Effects Of Dynamic Melt Manipulation On Pla Crystallization During The Injection Molding Process
The crystallization of poly(lactic acid) (PLA) under conventional injection molding and vibration assisted injection molding (VAIM) was studied by using differential scanning calorimetry, infrared spectroscopy, and polarized optical microscopy analyses. Application of VAIM appears to influence the crystal structure of the molded samples, where data suggests the technology may result in the formation of a more ordered crystal structure. The overall crystallinity of the molded samples is shown to be significantly affected by the mold temperature, and relatively less due to VAIM. However, polarized optical images reveal that crystallized PLA with VAIM appears to favor the formation of crystallized regions oriented in the direction of shear. The crystal structure and morphology of VAIM PLA parts may be a contributing factor affecting its crystallization behavior. In this regard, this study attempts at a further understanding of this element, such that injection molding of PLA can be performed within viable cycle times.
Evaluating Healing Behavior Of Reversible Adhesive Bonded Joints Subjected To Transverse Impact Loads
Impact loads transferred to the bond-line of adhesive joints can significantly decrease their load carrying capacity. If the damage in the adhesive layer can be healed, such losses in structural behavior can be recovered. One such healing technique is the use of thermoplastic ‘reversible’ adhesives which are reinforced with conductive nanoparticles. Such materials have been shown to heal through exposure to electromagnetic fields.
In this work, single lap joints were manufactured using ferromagnetic nanoparticle reinforced ABS thermoplastic polymer as the adhesive. The joints were tested under quasi-static tensile loading to determine their baseline performance. Similar joints were then subjected to impact load (10 J) to induce bond-line damage. Impacted joints were subjected to quasi-static lap-shear to obtain impact-induced performance. Next, the impacted joints were subjected to electromagnetic fields to heal the damaged adhesive and then subjected to quasi-static lap-shear tests to obtain the healed performance. The loss in joint strength due to impact, and its subsequent recovery due to healing was evaluated.
Molecular Dependence On Rheological And Mechanical Properties Of Sebs For Films And Fibers
A series of designed hydrogenated styrenic block copolymers have been synthesized for better understanding their molecular structural correlation with rheological and mechanical properties. The block copolymers are widely used in extrusion and injection molding; however, they are often compounded with other materials such as polyolefin and oil to avoid the processing issues caused by the nature of phase separation. Combining other materials would, in the meantime, reduce the elastic property and affect the application that require elastic recovery property. As the demand of elastic film and fiber is growing, this study offers an insight of the molecular design for processability and end-use applications. The structural parameters include molecular weight, styrene content, and vinyl content. The rheological property was performed within linear viscoelastic limit, and the mechanical property was measured under nonlinear deformation. These two sets of properties show different structural dependences demonstrated in this study.
Additive Blooming: Origins, Detection, And Control In Polymer Processing
Paint and adhesive adhesion issues to flame or corona treated injection molded thermoplastic olefin automotive components was not explainable by data generated through wetting tension tests using dyne solutions. Careful analysis of surfaces using FTIR identified additive blooming that was responsible for adhesion failures. Water contact angle measurements were equally sensitive to the presence of these blooming agents and furthermore provided a practical in-process measurement for detection and control of additive blooming that can occur in the manufacture of molded thermoplastics. This paper discusses the origins of blooming and common additives that are subject to blooming along with strategies for detecting, controlling, and avoiding issues associated with blooming.
Evaluating Residual Stresses In Bonded Lap Joints Through Experiments And Numerical Modeling
Structural adhesive joining is considered to be an excellent route to achieve both light weighting and dissimilar material joining for automotive structures. While adhesive joining eliminates the needs for drilling holes and distributes the load over larger areas; the processing/curing conditions, especially the thermal shock (rapid cooling) can create residual stresses that significantly reduce the strength of the resulting joints, in most cases prior to application of mechanical/service loads. These residual stresses can lead to dimensional instability, increased stress corrosion and reduced fatigue life. In this study, adhesively bonded single lap joints were manufactured using Acrylonitrile Butadiene Styrene (ABS) adhesive and glass fiber reinforced epoxy (Garolite, G-10) substrates. The joints were processed at a constant temperature of 240℃ maintained via oven-heating and subsequently allowed to cool under natural convection in ambient air. The residual strains generated in the adhesive layer were measured experimentally using an embedded high-resolution fiber-optic strain sensor. The results were compared against a coupled thermo-mechanical finite element (FE) model. Initial results show good agreement between the experiments and numerical models for the elastic behavior.
Introduction
Adhesive bonded joints are widely used in automotive, aerospace and marine applications due to uniform load distribution, superior fatigue resistance, higher strength to weight ratio and less stress concentrations relative to mechanical fastened joints [1-3]. For optimal design, understanding the stress distribution inside these joints is critical to make accurate predictions about their in-service mechanical behavior. There are two types of stresses which can originate in an adhesively bonded joint: mechanical stresses, which originate due to external loads; and residual stresses (locked-in stresses) which can either originate during the bonding process, or when a mechanical load is removed after inducing a plastic deformation.
In an adhesive, these locked-in stresses can be generated either due to the difference of thermo-mechanical properties between the adhesive and the substrates, difference in the moisture content between them or the chemical and physical changes inside the adhesive when it cures [4]. In this study, the focus is on the stress developed during the curing process, which are dependent on the curing temperatures of the adhesive, its thermal and mechanical properties, boundary conditions, and the cooling conditions [5]. Prediction of these residual stresses is critical since they are often attributed to cause premature failure in conjunction with fatigue, creep, corrosion, and wear [6].
A wide range of numerical and experimental techniques have been used to study the residual stresses in composite laminates and are well documented in [7]; however extension of these techniques to adhesive bonded joints has not been fully explored [8-15]. Moiré optical inferometry has been successfully used in measuring residual stresses in adhesively bonded lap joints [16-18]. This technique can however only measure surface strains [19] in limited material configurations. Neutron Diffraction has also been used to measure residual stresses within adhesively bonded double-lap joints [6, 16], but it has spatial resolution limitations and is not capable of measuring residual stress variations over distances smaller than ~1mm. [20].
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Increased Food Shelf-Life In Retail Display Cases Using Sustainably Sourced Filtering Technologies
New Department of Energy requirements for lighting will mandate inclusion of light emitting diode (LED) light sources for the production of retail display cases. These high intensity and highly directional lighting sources provide excellent illumination of products but can induce rapid product degradation resulting in color fading reactions and potentially off-flavors. The purpose of this study was to quantify the ability for recently developed sustainably-sourced filters to mitigate the effects of light induced degradation on fresh Colby cheese and rare roast beef under simulated retail display conditions. Color changes in the food products were quantified as a function of time utilizing the CIE L*a*b* color space and qualitatively via digital imaging. There was no distinguishable difference (both visually and utilizing quantitative colorimetric analysis) between the color change trends of the roast beef under the filtered light and dark control roast beef up to 120 hours of exposure time. Roast beef specimens exposed under non-filtered light reached the maximum color change value of the filtered samples (ΔE ~3.7) approximately 100 hours earlier. However, the filter did not provide additional protection for the Colby cheese samples under the conditions used in this study.
The Novel Silver Based Antimicrobial For Plastics
The use of silver and silver compounds as antimicrobial agents has been known since ancient times. There are several kinds of silver materials like colloidal silver, silver glass, titanium oxide with silver and silver zeolites. In this work, a different silver based antimicrobial for plastics, using carrier a silica to promote the bactericide and fungicide effect of the silver. The silver particles are anchored on silica ceramic particles using chemical process and it composite can be incorporated directly to the polymers. The process of obtaining these additives with antibacterial property is performed by homogenization of
the melt (composting), to produce concentrates of Ag particles (masterbatch) in various types of plastic resins. After preparing the masterbatch, the compound can be used, with recommended percentages in accordance to evidentiary tests of its effectiveness, in all types of plastic transformation processes. Plastics samples in different resins was submitted ISO 22196 test and the silica/silver material eliminated 99.99% of the E. Coli. Eye irritation test was conducted with rabbits to determine the potential for the silver based antimicrobial to produce irritation from a single instillation via the ocular route. Skin irritation test was conducted with rabbits to determine the potential for composite to produce irritation after a single topical application. Under the conditions of this study, the test substance is classified as slightly irritating to the skin. Migration tests was conducted to the composite and the results showed that the migration in polyolefins is according to permit regulatory agency like FDA.
Influences Of Process Parameters On Penetration In A Hybrid Single Shot Manufacturing Of Carbon Fiber/Epoxypolypropylene Structure
The authors detail the creation of a hybrid material structure via the injection of polypropylene (PP) with high ductility into a robust CF/Epoxy thermoset sheet. The purpose of this hybrid method involved combining the inherent properties of both thermoset and thermoplastic materials in a new hybrid structure while reducing the cycle time. The effect of pre-heating time, blank holder force, injection temperature, and injection speed rate on the deformation of prepreg and polymer penetration through prepreg sheets were evaluated. The results of the experimental design based on the Taguchi L18 orthogonal array indicated that the hybrid structures were manufactured with no penetration present in any combinations of parameters. An inadequate deformation characterized the samples created at a lower injection temperature, and pre-heating time, with insufficient adhesion as a result. Although the high injection speed enhanced formability and joinability, no significant effect on deformation and joining occurred from an increase in blank holder force.
Automotive Lightweighting Via Supercritical Foam Injection Molding Of Thermoplastic Olefin
The automotive industry has been transitioning from a primarily metals-based assembly towards a multi-material architecture driven by the need to meet the Corporate Average Fuel Economy (CAFE) standards that mandate automakers to have a fuel economy of 54.5 MPG by 2025. Polypropylene (PP) based Thermoplastic Olefins (TPO) blends constitute a significant portion of the automotive market due to its extensive use in many interiors, exterior and under-the-hood applications. However, lightweighting of PP based TPO blends by foaming often presents numerous challenges - most widely known is a resulting poor A-surface appearance. In this work, Clemson University and our OEM partner are investigating the impact of foamability on PP based TPO, via supercritical assisted foam injection molding. The study investigates the effect of foam injection molding processing conditions (e.g., melt temperatures, injection speed, etc.) on the microscale part performance level (e.g., mechanical properties, cellular morphology, etc.).
Hybrid Process Of Forming-Injection Molding – Investigation Of Polymer Melt Behavior On The Final Injected Part
Due to global competition, manufacturing firms must target innovation in production processes and technologies that allow the mass manufacturing of customized products through highly efficient processes. Motivated by the concept of the hybrid production system, an innovative platform technology, known as Polymer Injection Forming (PIF), was recently developed. In the PIF process, the best-in-class manufacturing technologies in polymers and metals, viz., injection-molding and sheet metal forming, are integrated to manufacture sheet metal-polymer hybrids in a single operation. In this process, the polymer melt serves as a forming medium and deforms the inserted sheet metal during the filling phase of the injection molding process. So far, most studies have focused on the influence of the injection molding process parameters on blank deformation and specification of the final deformed sheet metal part. While doing so, these studies have either totally neglected the polymer part or have only considered its rheological characterization as a forming medium. In this work, for the first time, the melt flow development of the PIF process is investigated, and a schematic flow field is presented. Subsequently, this investigation is extended to the online process parameters which are acquired with a set of in-mold instrumentations. Finally, morphology and crystallinity of cross-section of the samples produced by this process is investigated and compared with the sample produced via conventional injection molding condition.
Failure Analysis Of Automotive Air Conditioning Connectors
Failures occurred within automotive air conditioning system connectors. The cracking was observed within connectors that had been installed in automobiles, which were part of a durability testing program. The focus of this investigation was a determination of the nature and cause of the failures. The results obtained during the evaluation of the cracked connectors indicated that the failures occurred through a brittle fracture, slow crack initiation creep rupture mechanism of the material. However, the cause of the failure was severe molecular degradation as a result of the durability test program conditions. This paper will review the testing performed to characterize the failure mode and identify the cause of the cracking, while demonstrating the analytical procedures used in the investigation.
Investigation Of The Foamability And Resulting Mechanical Properties Of Foamed Thermooplastic Elastomers
Thermoplastic foam injection molding offers various advantages in regard of processing and product design. Due to the foamed core structure, the mechanical part properties differ from the compact references and can be significantly influenced by the processing parameters. At IKV, different thermoplastic elastomers (TPE) with different molecular structures were foamed to investigate the impact of processing parameters on the foam structure and the mechanical properties. Both static and dynamic behavior of the foamed TPE parts was determined. It was found that the mechanical properties of foamed TPE parts change significantly in comparison to compact references.
A Study On The Effects Of The Processing Parameters On The Flatness Quality Of Blown Films Using Laser Triangulation
Blown film extrusion is one of the most commonly used processes for the mass production of thin gauge general purpose films. The vast majority of consumer commodity products, including grocery bags, agricultural films and flexible food packaging films, are produced using this process. Blown films, like many other plastic films, are produced in continuous webs and made available to customers as film rolls. Both for flawless further processing and for the required mechanical and optical properties, plastic films and rolls must meet numerous quality requirements. Among the quality features, the flatness, which describes the planarity of the plastic films in a tension-free state, is gaining in importance with the increasing automation of production lines. The increasing quality demands are mainly the result of the demanding requirements in the further processing steps such as printing or laminating. Non-uniformities in flatness, such as waviness or wrinkles, can limit the printability and laminability of the films and thus lead to product rejects.
Although flatness is a critical quality feature for blown films, flatness quality is currently only monitored by visual inspection on a subjective basis using random sampling. The measurement method presented in this study allows a fast, quantitative and objective evaluation of the flatness quality by measuring the surface topology of plastic films, opening up a new possibility for the quality assurance. By measuring and digitalizing the surface geometry of plastic films, different characteristic values can be derived to assess the flatness quality.
In addition, a quantitative measurement of the film flatness allows a comprehensive characterization of the underlying causes of flatness errors. Accordingly, the measurement method was applied successfully as part of a preliminary investigation to determine the influence of different collapsing geometries on the flatness quality.
Development Of A Temperature Displacement Law For Viscosity Fluctuations Integrated Into The Control Setup Of The Injection Molding Process
Modern injection molding machine technology is able to reproduce machine parameters, such as the movement of the axes, with high accuracy. Nevertheless, different boundary conditions, such as fluctuations in material properties or changes in ambient conditions, influence the quality of injection molded parts. Innovative control concepts can enable a production with a constant part quality despite changing and non-optimal boundary conditions. But these concepts do not take viscosity fluctuation into account although it changes the pressure distribution and thus the shrinkage behavior of the molded parts.
Within this paper, a temperature control setup of the hot runner for compensating different melt viscosities is introduced and implemented. Therefore, a temperature displacement law that regulates the temperature of the hot runner is developed and used to control the injection molding process. Its influence on the process and the part quality are investigated.
Simulative And Experimental Validation Of An Inversed Cooling Channel Design For Injection Molds
Thermal mold design is an important phase during mold construction and determines strongly the resulting part quality and cycle time. Nowadays, part geometries become more complex as well as cycle time becomes an increasingly important requirement.
To support the mold designer in generating an efficient cooling channel design with less iteration loops, a methodology is under development to indicate the location of the cooling channels. Based on the local cooling demand of the part, this methodology proposes an inverse approach where an optimal thermal state of the mold is calculated and a corresponding cooling channel design is derived. A objective function is used to calculate and evaluate the cooling quality of the resulting design. In a process simulation, the developed cooling channel design shows a reduction in part warpage of up to 75 % compared to a conventional thermal mold design.
Specialty Discharge Methods For Continuous Compounders
A brief overview of discharge methods for continuous compounders is presented covering single-screw extruders, melt pumps, centrifugal pelletizers, pressure vessels, counter-rotating twin-screws, along with the B&P Littleford XLT twin-screw mechanism and Rotofeed System. These seven systems are critical subsystems of the entire extrusion process. Discharge methods for specialty processes, if designed correctly, can provide a constant pressure great enough for profile extrusion, continue mixing and/or reacting, cool, or pelletize the product. The correct subsystem can mean the success or failure of the entire process and is highly dependent on material properties.
Process Monitoring Of Induction-Based Adhesively Bonded Lap-Joints
Adhesively bonded joints are an excellent replacement of traditional mechanical joints in the automobile industry. In comparison to mechanical joints, adhesively bonded joints are lightweight and cost-effective in fabrication. Induction-based bonding is gaining popularity as they are relatively quicker than conventional oven techniques. However, the temperature distribution, phase change, and cure time are not as straightforward as conventional oven prepared joints. Thus, it is necessary to understand these parameters in an induction based heating method to produce better joints. In this research work, stress waves are transmitted between adherents that pass through the adhesive interface. The changes in transmission coefficient and Time of Flight (TOF) of guided waves (GW) helps in understanding joint conditions properties such as adhesive phase transition and time of cure during fabrication. A qualitative analysis is reported in this paper to prove the application of guided waves in process monitoring.
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