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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Compatibilization of ABS/PA6 Blends Using Olefin Based Polymers
This study focuses on the morphologies, mechanical and thermal properties of poly(acrylonitrile-co-styrene-graft- butadiene)/polyamide-6 (ABS/PA6) blends compatibilized with methyl acrylate and glycidyl methacrylate grafted polyethylene (E-MA-GMA) and n-butyl acrylate and maleic anhydride grafted, carbon monoxide modified polyethylene (E-nBA-MAH). The ABS/PA6 ratio (100:0, 80:20, 50:50, 20:80 and 0:100) and compatibilizer content (0, 5 and 10 %) are examined as the experimental variables. Compatibilization improves impact strength of the blends. Super-tough blends were obtained at definite compositions (ABS/PA6/E-nBA-MAH: 50/50/5, ABS/PA6/E-MA-GMA: 50/50/5). Dispersed domain size became remarkably smaller for compatibilized blends compared to incompatibilized ones. It was concluded that olefin based copolymers are potential compatibilizers for ABS/PA6 blends.
Laser Transmission Welding of Semi-Crystalline Plastics
Laser transmission welding is an innovative process, which is very suitable for the joining of complex injection moulded parts. When the production demands a high quality of the weld line it is absolutely necessary to consider all the influences of the welding process. While welding semi-crystalline thermoplastics the morphology of the transparent joining partner has to be taken into consideration, because the laser beam characteristics and the amount of energy of the welding process depend extensively on the crystallisation characteristics.Many injection moulding process parameters (e.g. the melt and mould temperatures) affect the cooling conditions of the part, and thereby influence the crystalline structure. Therefore the injection moulding process should be integrated into quality assurance systems for laser transmission welding. In this paper the results of intensive experiments for PBT are documented.
Vapor Transport Properties of Sulfonated Block Copolymers
Polystyrene-polyisobutylene -polystyrene (SIBS) and Polystyrene-polyethylene-butylene -polystyrene (SEBS) block copolymers are materials that are known to have excellent barrier properties to hazardous vapors and liquids. However, when these block copolymers are sulfonated, water and small polar molecules are allowed to be transported through the polymer film. In some instances, this could be beneficial and allow the film to be used as a separation membrane.In this paper, the vapor transport properties of these materials are presented and discussed herein, as they relate to the polymer chemistry and chemical modification of the tri-block copolymer.Results suggest that water permeation is not affected by the structure of the mid-block, however the transport of small organic molecules are affected. It was also found that permeation of polar molecules increases with increasing sulfonation levels within the polymer. The elastomeric character of the tri-block copolymer, coupled with its selectively–permeable characteristics, gives rise to a polymeric membrane with potential for use as breathable membranes.
Opportunities and Challenges for the Plastics Industry in Mexico
The Plastics industry in Mexico is a very vibrant one with total consumption of plastics in 2004 exceeding 4.5 million tons – ranking it 12th in the world. With abundance of hydrocarbon feed-stocks, reasonable wages and proximity to huge market to the North and the South, plastics sector is very attractive and essential to the socio-economic development of Mexico. However, the unique industry infrastructure and other factors have contributed to importation accounting for over 50% of domestic consumption of plastics. This paper will discuss the current situation with respect to domestic production and consumption of plastics, design and fabrication of molds & dies as well as processing machinery, identifying many opportunities as well as critical challenges for the plastics industry in Mexico.
Impact Modified Polyamide-Organoclay Nanocomposites
Ternary nanocomposites composed of polyamide- 6 (PA6) , three types of organoclays and an ethylene/butyl acrylate/maleic anhydride (E-BA-MAH) terpolymer acting as impact modifier for polyamide were melt blended in a twin screw extruder in order to investigate the effects of component concentrations on the final properties. The morphology, melt flow characteristics, thermal behavior and tensile properties of the produced composites were investigated. XRD patterns showed that the interlayer spacing of the organoclays, Cloisite® 25A and Cloisite® 30B increased in PA6-montmorillonite nanocomposites without the impact modifier, as well as in ternary systems. In the presence of elastomer, the MFI of unfilled PA6- impact modifier blend and the MFI of ternary nanocomposites decreased owing to the high viscosity of the elastomer. The crystallinity of the materials decreased in the presence of elastomer and organoclay. Tensile properties of the ternary systems resembled those of binary PA6/elastomer blends. It was concluded that the effect of elastomer was more dominant than the effect of organoclay.
Foaming PS With HFC-134a in Supercritical State
Because of the ban of CFC as an ozone-depleting substance and the undergoing phase-out of HCFC, the foam industry is currently looking at inert gases and HFCs as potential alternative blowing agents. However, contrarily to CFCs and HCFCs that were easily dissolved in the thermoplastic resins and could be readily expandable under relatively mild conditions with a minimum of processing difficulty, these alternative fluids unfortunately lack in solubility and are thus difficult to process. For instance extrusion foaming of polystyrene using HFC-134a is problematic above a concentration of 7wt%. Surprisingly, the pressure associated with this concentration threshold is approximately equal to the critical pressure of the HFC-134a, which may suggest that large clusters of HFC originating from its supercritical state would be responsible for the heterogeneities observed in the cell structure. This issue may be not only limited to HFC-134a as many other alternative gases (carbon dioxide, HFCs, hydrocarbons) may reach the supercritical state under the required processing conditions. Since use of mixtures of physical foaming agents in thermoplastic foam extrusion has been an industrial practice for a long time, the easiest way to circumvent this problem is to add a coagent, with the result of shifting away the critical point (pressure and temperature).
Abbreviated Terms for Plastics - Implications and Challenges
Abbreviated terms are routinely employed in the plastics industry in generic marking of molding products to assist in identification of the plastics for separation in recycling besides in trade and technical literatures. Existing ISO, ASTM and other standards provide clear guidelines for abbreviated terms for polymer families. In practice, however, a wide range of inconsistent abbreviated terms are quite common in the industry. This has significant implications for the general consumers as well as those involved with plastics recycling. The challenge is to arrive at uniform globally acceptable single set of abbreviated terms in order to addressing this issue.
CBA-Based Foaming of Thermoplastics Under Ambient Pressure
Understanding the fundamental mechanisms that govern the foaming process is the most essential universal prerequisite for developing effective processing strategies for fabricating high quality foamed plastic products using any type of foaming technology. Despite chemically blown foaming of thermoplastics under atmospheric pressure has been successfully implemented in rotational foam molding over the last decade, the related open literature does not provide substantial research addressing the fundamentals of this unique foaming mechanism. The present study focuses on clarifying the fundamental foaming mechanisms that govern the successful manufacture of thermoplastic foams using a chemical blowing agent (CBA) under low pressure (atmospheric) conditions. The presented research is mainly based on observing a series of visualization experiments conducted using a custom made visualization system including an optical microscope and a computerized CCD camera imaging system, which was utilized for investigating the behavior of foamable polyethylene (PE) samples prepared by using the compression molding method.
Influence of Carbon Nanofiber Microstructure on Electrical Proprties of LLDPE-Based Nanocomposites
Carbon nanofiber-reinforced linear low density polyethylene (LLDPE) composites were obtained from three different types of nanofibers (MJ, PR-24-PS, and PR-19-PS). A significant drop of volume resistivity was observed at 15 wt% MJ nanofiber content whereas volume resistivity started to decrease only at 25wt% of PR-24-PS or PR-19-PS nanofiber content. Further, micrographs of pure CNFs revealed that MJ nanofibers are twisted or even coiled whereas PR-24-PS and PR-19- PS are fairly straight. Scanning electron microscopy (SEM) revealed that CNFs were well dispersed in composites. We believe that the twisted or coiled structure of MJ fibers led to a better inter-fiber connectivity and reduced electrical percolation threshold.
Flash, a common injection molding defect, arises when melt flows from the cavity into thin gaps between parting surfaces. Besides rules of thumb for eliminating flash, there are few fundamental papers on flash analysis. Understanding flash as a transport phenomenon provides a systematic basis for solving flash problems. The governing equations for the gap flow are established and solved for an isothermal power law fluid, under constant pressure along the parting line where flash begins. Two shapes are investigated, rectangular and ring slits that respectively correspond to modeling flash from straight and curved parting lines. Our equation for flash length, the distance to which the melt penetrates the gap developed between the parting surfaces, is our main result. Further, adimensionalizing not only unifies the results for straight and curved parting lines, but also provides insight into how rheology, pressure and geometry govern flash. Our approach avoids tedious numerical simulation and mold structural analysis. The theory is validated by our polycarbonate flash experiments.
The Promise and Practice of Valve Gate Sequencing
Injection molders commonly use valve gates to reduce cycle times, control gate vestiges and limit gate discharge. The following are real-world examples of sequencing valve gates for balance, pressure control (particularly in family molds), reduction of knit lines, and minimization of clamp tonnage.In-cavity pressure sensing and DECOUPLED MOLDINGSM techniques are becoming more common. When combined with valve gate control these tools help create more robust processes or sometimes processes that would otherwise be impossible. This in turn has reduced scrap, material used and cycle time on a variety of tools.To put these techniques into practice molders need to pay attention to the details required for success.
Hierarchical Description of SEBS Block Copolymer Thermoplastic Elastomers
In this study we investigate the energetics and kinematics of deformation of SEBS block copolymers. The kinematics of deformation is investigated using simultaneous wide angle and small angle X-Ray diffraction on deformed samples. Results show that systematic deformation mechanisms occur in this class of thermoplastic elastomers. Moreover, these mechanisms are related to specific mechanical responses at specific levels of deformation. For the class of thermoplastic elastomers studied herein, the mechanisms include cooperative microbuckling and fragmentation of cylindrical styrenic microdomains, alignment of the fragments in the applied loading direction, followed by strain induced crystallization in selected systems.
Effect of Uniaxial Drawing of Soy Protein Isolate Film on Mechanical Properties
The effect of uniaxial drawing of soy protein isolate film on mechanical properties was investigated to accelerate efforts to develop SPI films with improved properties. The films containing 0 to 30wt% glycerol were drawn uniaxially up to a draw ratio of 2.5. The mechanical properties of the soy protein isolate film were found to be significantly improved after uniaxial drawing. The generation of crystal phase with drawing was not observed fromWAXD and DSC measurements. Therefore, the improvement in mechanical properties is ascribed to molecular orientation induced by drawing of the film.
Effects of Montmorillonite Layered Silicates on the Crystallization Properties of Polylactic Acid
Recently, polylactic Acid (PLA) has been increasingly considered for many applications due to its origin from renewable resources and its biodegradability. Separately, there has been interest in montmorillonite layered silicates (MLS), because of their remarkable ability to improve polymer properties. Strength and barrier properties are particular improvements to PLA that are considered critical. We examine the influence of MLS and processing on the crystallinity of PLA nanocomposites. Screw speed and feed rate of an extruder connected to a blown film die were systematically varied. The materials were supplied by the Naticak Army Research Laboratory and developed by Ratto and Thellen.Increasing screw speed during manufacturing decreases the residence time and is associated with the generation of smaller crystallites. Feed rate is another variable that is considered.Permeability and non isothermal Differential Scanning Calorimetry (DSC) at a single heating rate was reported recently. Here we report on the Avrami parameters of the PLA and corresponding nanocomposites.
Strategies to Balance the Flow in Profile Extrusion Dies
There are two strategies commonly adopted to balance the flow in an extrusion die for profiles: those involving and those not involving modifications of the die land cross section. In this work, a numerical code, which is being developed by the authors to perform the automatic optimization of profile extrusion dies, is used to illustrate the main issues concerning the die design strategies and to show the consequences of their application. It was concluded that the design strategies based on adjustments of the die land cross section generate dies more stable to variations of the processing conditions, but produce profiles with lower dimensional stability. On the other hand, strategies based on modifications of the die land length may be difficult to apply to profiles having significant differences in flow restriction, fact that can be overcame by the use of flow separators. However, this approach affects negatively the sensitivity of the tool and may hinder the mechanical resistance of the produced profiles.
Beam Shaping with Diffractive Optics for Laser Micro-Machining of Plastics with a Femtosecond Laser
Microfluidic devices and micro-electro-mechanical systems (MEMS) have become one of the most interesting and important applications in biotechnology, biomedical, pharmaceutical, life sciences, and agriculture. Research in manufacturing technologies used to fabricate these devices is important for improved quality as well as for time and cost savings during mass productions. A new approach for the fabrication of these MEMS devices is the laser ablation using diffractive optics elements (DOE) for beam shaping. In results described in this report, a 775 nm-wavelength high power femtosecond laser was used to ablate circular channels on polystyrene specimens. This approach to creating channels in the polystyrene was found to be promising even though the DOE used was not optimized for the femtosecond laser wavelength.
The Effect of Polyethylene Catalyst Type and Pigment Concentration on Crystal Growth during Rotomoulding
This work studied the effect of catalyst type and pigment concentration on the impact properties, crystallinity and morphology of rotationally moulded polyethylene (PE) parts. Microscopy, shrinkage and differential scanning calorimetry analysis techniques were used. It was observed that the base PE catalyst had an effect on the extent of crystallinity but that the level of pigmentation had only limited effect on the extent of crystallinity. The reduction in impact performance for turboblended pigmented samples was due to the relatively poor distributive and dispersive mixing of the pigment within the polymer matrix.
Structural and Thermal Aspects of the Performance of Hybrid Moulds with SLS
Hybrid moulds with molding blocks obtained by rapid tooling techniques are used for production of small batches. The mechanical and thermal performance of the inserts is particularly important at the design stage. This paper describes the use of Selective Laser Sintering (SLS) inserts for hybridmoulds. These inserts were experimentally study and the feasibility of this technology for the fabrication of hybrid-moulds investigated. Computer simulations using commercial software were also carried out. The obtained results show a good agreement between simulation and experimental data.
Analysis of Powder and Pellet Melting during Extrusion with a Perturbation Method
It was reported previously that the melting of a polymer during twin screw extrusion can be quantified using dynamic, on-line monitoring of a perturbation technique. Preliminary results suggested significant differences between the progression of melting of Polypropylene (PP) feed pellets and powders. This paper reports additional data on PP and Polyethylene (HDPE) feeds in the form of pellets, powder and pellet/powder mixtures. In addition to a delay of melting in the case of the powder feed, reductions in power intensity of the melting peak were also observed with the pulse perturbation technique. Unexpected behaviors in the melting of powder/pellet blends are described. The perturbation method is further examined by comparing the pulse energy input profiles with the residence time distribution and steady state power consumption over a range of throughput/screw speed (Q/N) operating conditions.
Characteristics of PP/PS/Clay Nanocomposite Produced by High-Intensity Ultrasonic Process
Polymer-clay nanocomposites of various concentrations were prepared by ultrasonically assisted melt blend process. The ultrasonic blend process using high intensity ultrasonic wave was employed to enhance nano-scale dispersion during melt mixing of polymer blend and organically modified clay. The materials studied were linear polypropylene and polystyrene reinforced with organophilic montmorillonite clay (nanoclay) at 3-5 wt% loadings. The effectiveness of the proposed ultrasonic processing technique on polypropylene matrix nanocomposites was evaluated by XRD, rheological measurements and thermal properties. We expected enhanced breakup of layered silicate bundle and further reduction in the size of dispersed phase with better homogeneity compared to the different immiscible blend pairs.Also, it was expected that generation of macroradicals in polymer mixture can lead to in-situ copolymer formation by their mutual combination, which should be an efficient path to compatibilize immiscible polymer blends and stabilize their phase morphology in the absence of other chemical agents.
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