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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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.
A Numerical Study of Scanning Through-Transmission Laser Welding
A numerical model has been developed to simulate the heat conduction during the through-transmission laser welding (TTLW) process. The simulations were performed using the SIMPLER (Semi Implicit Method for Pressure Linked Equations Revised) software. The model was used to calculate the changes in the temperatures at points throughout the heated areas of the parts during the entire welding time. The temperature distributions and peak temperatures generated in the faying surface of welds at same line energy (LE) but different powers and speeds have been predicted and examined. Large temperature differences obtained when keeping LE constant, but doubling both power and speed were calculated and interpreted using this model.
Characterization of the Twin Screw Extrusion Process
In contrast to the well developed field of polymer characterization, the advances of extrusion process characterization lagged far behind. Engineers have to deal with problems such as process scale-up and product quality control primarily by empirical means. Practically no quantitative expressions exist between the operating conditions and the important process parameters such as degree of mixing, intensity of mixing and melting, the nature of polymer melting or plasticization, or energy consumption. We propose along with new supporting data that the parameters introduced previously, ?P/?Q and ?P/?N, that is, energy per unit of additional mass and energy per unit of screw revolution could be used to characterize the melting behavior of a polymer in an intermeshing, co-rotating twin screw extrusion process. The parameters appeared to be independent upon the extrusion rate (Q) and screw speed (N) in the ranges examined (4.5 to 36kg/hr and 100 to 500RPM). We further propose that additional parameters, such as those defining the kinetics of melting, average residence time (for melting and the over all) and residence time distribution obtainable by the pulse perturbation technique may be required in order to sufficiently define a given extrusion process.One can also predict with excellent agreement the observed specific mechanical energy input of extrusion, defined by extrusion power/throughput (P/Q), with simple linear expressions (Eqs. 1 and 2). The parameters c1 (?P/?Q), c2 (?P/?N), and a constant c3, can be determined directly by steady state extrusion experiments without employing pulse or step perturbation methods.
Ultrasonic Plunge Welding of Polypropylene Nonwovens
Polypropylene blown micro fibers with spun bonded cover web made from Polypropylene and polyester fibers were used for the experimental study of the ultrasonic plunge welding of nonwovens. A face centered central composite design of experiment (DOE) with 3 process variables and 3 levels was used to evaluate the effects of vibration amplitude, weld time and weld pressure. In addition to those settings, three different welding profiles were used resulting in forty-five different welding conditions with five specimens welded for each condition. Increasing the welding time generally improved the weld strength until it leveled off. For high welding pressures physical damage was observed around the welding area. Finally increasing the amplitude of vibration resulted in making the welding seam tougher with higher breaking forces.
Constructing Unique Micelle Structures of Charged Block Copolymers via Co-Assembly with Organic Counterions
A variety of fascinating micelle structures have been achieved by the assembly of charged triblock copolymers through the interaction with organic counterions in mixed THF/water solution. Essentially, the formation of toroidal micelles was observed in specific conditions of polymer chain constitution, the chain length of each block, the ratio of THF to water and mixing procedures. Our results showed that final assembled structures can be easily tuned by either varying the chain structure of organic counteirons or changing the ratios of THF to water.
Flash Prevention Due to Skin Solidification
The purpose of this paper is to investigate the role of skin solidification in preventing flash during injection molding of amorphous and semi-crystalline resins. In conventional injection molding, polymer melt is injected into a comparatively cold mold, resulting in the development of a solidified layer. A null hypothesis of this paper is that the development of a solidified layer reduces the exerted clamp tonnage on the machine and may even prevent the formation of flash under high pressures resulting in improved part quality. A set of Design of Experiments was implemented with control factors including barrel temperature, mold coolant temperature, pack pressure and delay time; the characterized responses included part weight, part thickness, and flash length. The results indicated that the addition of a delay time between the injection and packing stages eliminated flashing in this application.
Study of Ultrasonic Welding of HDPE-Based Nanoclay Composites
Clay-based nanocomposites have high modulus, high specific strength, and low permeability. They have become popular in many industries because these material properties can be achieved by the addition of small volume fractions of inexpensive clay particles. Ultrasonic welding of four high density polyethylene nanocomposites with 0 wt%, 3 wt%, 6 wt% and 9 wt% nanoclay was investigated. The effects of weld force, amplitude of vibration, and weld time for energy director joints or weld collapse for shear joints on weld strength were evaluated. Three parameter, three level design of experiments (DOE) were utilized to find near-optimum welding parameters. For the best welding conditions for both energy director and shear joints, increasing the nanoclay content resulted in significantly decreasing weld strength. For energy director joints the decrease in strength with increasing nanoclay content was greater than for the shear joints.
Biomimetic Surface Microstructures and Their Replication to Polymeric Materials
Biomimetic surface structures such as anti-reflective protrusions on the moth eye and self cleaning pillars on the Lotus leaf have a profound influence in the development of technologically important engineering devices and systems. In this study, we prepared microstructured polymer surfaces that mimic the surface patterns on the pronotum and the wing of dung beetles (Phanaeus vindex) using micromolding techniques. The patterned embossing master was fabricated by electroforming the surface of the dung beetle. The electroformed nickel replica was then used to hot emboss on ABS substrates. The replicated polymer surface patterns were found to be comparable with the original surface patterns on the dung beetle.
In-Situ Synthesis of Nanocomposite Systems by Interfacial Polycondensation
In this work, layered silicate- and silica-polyamide 66 nanocomposites are synthesized in-situ by interfacial polycondensation to produce highly dispersed nanocomposite products. The two routes involve either incorporating a highly exfoliated silicate structure from a suspension of silicate platelets in one of the monomer phases or generating a silica hybrid through sol-gel chemistry. Two different approaches in the latter route allow the tetraethoxysilane (TEOS) condensation to occur either simultaneously with or sequentially to the nylon polymerization. Transmission electron and x-ray dispersive scanning microscopy, along with TGA, DSC and FT-IR measurements, are used to monitor and characterize the well dispersed structures produced, which are expected to manifest in enhanced thermo-mechanical properties of the nylon.
Effects of Metallization Coating on Ultrasonic Welding of Abs
Thin metal coating of plastic parts for increased optical reflectivity, improved EMI/RFI shielding, decreased permeability, or for decoration has gained more importance in recent years in automotive, electronics, medical and toy industries. This coating is often found in the weld area and there are concerns regarding its effect on weldability. Therefore, in this work ultrasonic welding of ABS components with metallic coatings was studied to evaluate their effect on weld strength. Two types of coatings were studied: an aluminium coating with hexamethyldisiloxane (HMDSO) as its topcoat and a stainless steel coating. The coated ABS was ultrasonically welded to uncoated ABS. Three factors, weld time, weld pressure, and amplitude of vibration were varied to find near optimum welding conditions. It was found that the aluminum or stainless steel coating had a very small effect on the ultrasonic weld strength for ABS. The maximum weld strength obtained was 28.5 MPa, 28.2 MPa and 26.9 MPa for uncoated, and for aluminum, and stainless steel coated ABS, respectively.
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