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.
In the injection molding process, weld lines can occur when two flow fronts rejoin due to either multi-gated molds or obstacles in the mold cavity. The weakness of plastic at weld lines provides serious difficulties for the design and long term durability of injection molded parts. Various methods to reduce the strength loss of weld lines include optimization of material composition, mold design and process conditions. To this purpose, this paper experimentally explores the influence of in-flow on the strength of weld lines for a commercial polypropylene compound reinforced with glass fibers. In-flow is defined as the flow within the mold cavity, below the solidified layer, that continues after the local region of the mold cavity is filled. In particular, the comparison of the weld line strength between specimens manufactured with and without in-flow was carried out and related to the reinforcement distribution in the welding zone.
This paper presents a new manufacturing process for producing functionally graded foam for rapid rotational foam molded composites (RRFM). A new experimental setup incorporates continuous foaming operation using a physical blowing agent (PBA) and a chemical blowing agent (CBA) to deliberately generate a foamed core with varying quality based on preferred direction or orientation. Carbon dioxide will be used as the PBA to produce ultrafine cellular foam. This novel process utilizes a static mixers to create a single phase solution before foam injection phase. In the co-extrusion operation, one extruder will be used for CBA-based fine cell low density foam production and the other for PBA-based ultra-low density polymeric foaming operation.
Copolyester elastomers are high performance thermoplastic elastomers, based on a polyester hard segment and a polyether or aliphatic polyester soft segment. Copolyester elastomers are used to replace thermoset rubbers in CVJ (constant velocity joint) boot applications. These require thermal stability and resistance to greases. Copolyester elastomers are well known for these properties. When the surfaces of the boots come into contact with each other (i.e. at large turning angles) this can cause squeaking noises. Looking at the future, more and more electric or hybrid cars will be built. Until now the squeak noise was muffled by the combustion engine. Electric or hybrid cars require reduced noise emission in dry and humid environments. This paper provides an overview of copolyester elastomer applications for automotive with focus on CVJ boots and noise emission testing in different environments.
This paper presents the idea of “designer polymers” – these are polymers that can be custom formulated to include sensing, computation, and actuation infused throughout the bulk of the material. Designer polymers are useful in the design and fabrication of smart products and we believe they will revolutionize the co-design of complex products. The co-design of smart products involves the simultaneous design of, for example, hardware and the software that executes during the functioning of the device. In our quest to develop designer materials, we have explored a variety of fabrication methods, including insert-molding and 3-D printing, or additive manufacturing.
Tiger stripes of polypropylene copolymers are studied by modeling the mold filling process as a non-isothermal two-phase flow using a level-set method. It has been shown that the Level Set method is capable of modeling the evolution of the flow field at and behind the melt front. An area of large velocity contrast between the skin layer of high shear rates and the center core of low shear rates has been observed behind the melt front under relevant injection molding conditions. The large velocity contrast appears to be a direct origin of the flow instability. The instability in terms of alternative occurrence and disappearance of the oscillatory strain rate is proposed to be a possible root cause of the tiger stripes. The comparison of the materials of different rheology suggests that shear thinning may be a useful property to mitigate the risk with the tiger stripes.
Thermoplastic polyurethanes (TPU) are a versatile class of elastomeric polymers with physical properties that can be tuned to meet a wide range of demanding applications. TPU is known for its elasticity, transparency, abrasion resistance, and chemical resistance. This combination makes TPU an attractive material to replace materials such as rubber or polyvinyl chloride in many applications. However, like many polyurethanes, TPU is prone to oxidation and discoloration during processing and upon weathering. In this paper, combinations of antioxidants, process stabilizers, and light stabilizers were investigated to determine the best additive combinations to reduce the tendency of TPU to discolor.
The on-line evaluation of the effects of process conditions variation during the extrusion process on the kinetics of compatibilization of polyamide 6 (PA6) in a matrix of polypropylene (PP) compatibilized with polypropylene grafted with maleic anhydride (PP-g-MAH) in different locations along the extruder by infrared (FTIR) spectroscopy is proposed in this work. As preliminary results and as a basis for comparing the on-line results that will be shown in the presentation the evolution of dispersion of the second phase of PA6 in the PP matrix is presented here. The area ratio of the peak of carbonyl stretching in amide present in PA6 at 1640 cm-1 standardized to the IR area of the peak at 1170 cm-1 relative to PP is applied to evaluate the evolution of dispersion along the extruder and the effect of the process condition in it. The standard deviation (s.d.) of the area ratio was used to correlate to the changes in dispersion condition when the process temperature, the feed rate and the screw speed were varied.
Silo bags are used for bulk storage of grains in farmland. There are two typical modes of their failure: while being filled with grains, or due to long-term creep deformation during storage. In the past, several numerical studies have been conducted to improve the quality of grains stored in these bags by optimizing the moisture content or CO2 levels. The failure of these bags, however, especially when excessive pressure is applied during grain filling and subsequent creep during storage, is not well understood. Explicit Dynamic Solver in Abaqus (Product of Dassault Systems Simulia Corporation, USA) was used to model polymeric silo bags storing granular material under gravitational loading and pressure. The material computational model for silo bags (film) and the granular material has been developed using material subroutines, which themselves have been calibrated through in-house tensile and creep testing for the film. Numerical analysis of agricultural silo bags has been performed to understand mechanical failure in the bags during installation and usage at different temperatures.
A newly developed mineral fiber-reinforced PC+ABS satisfies all OEM requirements for large, painted, exterior components. It delivers a very low CLTE value, which ensures a high dimensional stability as needed for low gap designs. The low CLTE value is combined with a low density of only 1.24 g/cm3 which facilitates lightweight components and potential cost optimization. Beside the low density, the material offers very good flow properties, which not only permit thin walls but also guarantee a high degree of design freedom, even with large, long moldings. The good flow also speeds up cycle times and contributes to a cost-efficient production process. The new substrate material has proven to provide a nice class A surface of the final component after painting. The good paint adhesion meets the most stringent OEM requirements also after climate aging. Overall, the new mineral fiber-reinforced PC+ABS formulation has proven its technical fit and is a cost-efficient alternative to metal or PC+PET materials for exterior automotive applications. These improved properties of this material will help accelerate the trend to plastic exterior panels in autonomous vehicle since they allow much better pass through of various communication and lighting signals, compared to metal body panels.
Acrylonitrile-butadiene-styrene (ABS) resins are widely used for applications such as appliances, toys, office equipment, sanitary wares, building & construction, transportation and more. Extrusion of ABS covers around 25% of the total ABS market in North America, namely through sheets, pipes, edge bands, and profiles. ABS extruded into sheets and formed into final parts, finds its way into furniture, automotive, buses, trucks, recreational and utility vehicles, sanitary applications, advertisement boards, luggage and doors. For optimum product performance and cost efficiency, the ABS resins require specific attributes. These are an excellent lot-to-lot consistency, a white and thermal stable base color, an adequate UV stability, a low amount of unmelts and a high product purity. Because sheets and edge bands are demanded in a wide range of colors, self-coloring has become a key cost driver through necessities such as color matching, UV absorbers, and optical brighteners. Limited run sizes and regrinding also lead to increased scrap and constant color adjusting. Because the surface quality of thermoformed parts is so critical, presentation of unmelts and high levels of volatile organic compounds in the resins affect aesthetics. This study discusses the attributes of ABS specifically for extrusion and thermoforming, and compares the benefits of MAGNUM™ ABS versus several emulsion ABS. It is intended to provide information to manufacturers of extrusion applications to select the most suitable ABS materials for optimum production performance and cost efficiency.
The primary objective of this work was to evaluate the processing and mechanical, rheological and thermal properties of a 2 and 10 weight percent loading of MCC in amorphous polyamide (APA). Modified, unmodified MCC and commercial MCC (FI-1 fibers) were investigated. Melt-blended composites of the various MCCs and amorphous polyamide were prepared by single and twin-screw extrusion, then injection molded into test specimens. Rheological properties of 2 and 10% MCC filled composites were studied using a rotational parallel plate rheometer. The mechanical behavior of all three filled polymer composites were examined by studying storage and loss modulus with frequency. Also, the influence of moisture content in neat and cellulose reinforced composites were also investigated. These results indicate the need for extensive moisture control for amorphous nylon and microcrystalline cellulose.
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 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.
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.
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.
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.
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.
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.
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 . 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 . Prediction of these residual stresses is critical since they are often attributed to cause premature failure in conjunction with fatigue, creep, corrosion, and wear . A wide range of numerical and experimental techniques have been used to study the residual stresses in composite laminates and are well documented in ; 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  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. . More
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.
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