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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The Effect of Different Batches of the Same Polymer on the Flow in Flat Coextrusion Dies
Rheological and molecular characteristics (MWD) were experimentally determined for different batches of LDPE. The results show that extensional viscosity may significantly vary for different batches even if shear viscosities and MWDs are very similar. FEM analysis was consequently performed to determine the stability of the coextrusion flow in the flat die for different batches of the material and the effect was found considerable. A recently proposed ‘TNSD sign criterion’ (Zatloukal et al, Int Polym Proc., 16(2) 198-207 2001), which quantifies the relative stretching of the layers in the merging area, was used for this purpose.
An Intelligent Knowledge-Based Plastic Injection Mold Design System
This paper presents an intelligent knowledge-based plastic injection mold design system, 'IKB-MOLD', which was developed based on the analysis of injection mold design process and collection design rules from plastic injection mold design companies. A plastic injection mold object and knowledge representation is propose for detailed injection mold design. Since such representation considers both relationships for assembly and relationships for functional, it is possible for automatically generating assembly tree while satisfying the functional requirement during design process. IKBMOLD integrates the proposed object and knowledge representation with many developed tools in a commercial CAD/CAM software environment. And it has been testified in plastic injection mold design company that IKB-MOLD system can speed up the design process and facilitates design standardization.
Evaluation of Flow Instabilities Using Simulations
Three-dimensional simulations were used to gain insight into the jetting instabilities. With 3D meshing and Navier-Stokes equations, flow instabilities were observed in 3.2-mm thick parts. Inertia produced significant flow instabilities in simulations of polycarbonate and polyacetal. For these materials, this unstable flow correlated with jetting that was associated with slippage of melt along the mold walls. Gravitational effects reduced these instabilities in most materials, but produced highly unstable flow in PBT. No significant instabilities were predicted for polystyrene, polypropylene, polyamide-6, and ABS. In these materials, jetting is usually associated with elastic effects, rather than frictional characteristics. This suggests that the 3D simulations can be used to predict these defects. A viscoelastic constitutive equation should produce more reliable results.
Comparison of Approaches for Optimizing Molding Parameters
The effects of two molding parameter optimization techniques, a manual technique and an automated (software-based) method, were compared with respect to the processing conditions, process stability and reproducibility of the molded parts, and the stress retained in those parts. The software-based process optimization resulted in molding conditions that led to more consistent part weights and dimensions than a manual technique. The parts from the former method, however, exhibited somewhat higher retained stress. This was attributed to the low injection velocities and the packing method recommended in the optimization process. The fully automated process optimization was sometimes limited by the software’s selection of injection velocities and shot size increments that could not be achieved in practice.
Automated Design for the Gate Location of Injection Molds
In injection molding, the placement of a gate is one of the most important variables of the total mold design. In this paper, a methodology that automatically predicts the “optimal” gate location for single-gate injection-molds was developed based on the minimization of the maximum equivalent flow length difference between different fundamental flow paths. The objective of optimization is to achieve a balanced filling pattern design within minimum time. A genetic algorithm was used to search the optimal gate location. The models analyzed demonstrate that the proposed method is promising and the computation time is gratifying.
Evaluating Factors Affecting Shrinkage Predictions
The effects of selected assumptions on shrinkage predictions were determined using two materials, polycarbonate and poly(butylene terepthalate). The linear shrinkage of polycarbonate parts increased with melt temperature, but the shrinkage of PBT exhibited little sensitivity to processing conditions. Although none of the simulations provided linear shrinkage results that reflected these trends, volumetric shrinkage did. Modified flow rates had little effect on the predicted linear shrinkage, but incorporating temperature dependent specific heat and thermal conductivity values produced small changes. Three linear shrinkage models incremented or decreased the shrinkage by 10%, with no model matching linear shrinkage at all processing conditions.
Process Identification of Barrel Temperature Control in Injection Molding: A MIMO Approach
Melt temperature is a key variable in injection molding that has to be continuously controlled during the molding process. Its control is generally simplified due to the dynamic characteristics of the melting process and the barrel zones interactions. Therefore, a thorough understanding of these process dynamics is required to achieve accurate control of melt temperature. Multi-input-multi-output (MIMO) deterministic models were derived and employed for predictive control of melt temperature. Simulations and experiments showed that MIMO model could be used as a good physical representation of the overall system.
Understanding the Effect of Processing Parameters on the Mold Temperature
The mold temperature is one of the most important injection molding parameter, affecting both productivity and quality on the molded plastic parts. The data sheet for various raw materials always give the recommended mold temperature. However, the molds are becoming more and more complex, and as a result it is getting ever more difficult to create proper conditions for effective temperature control. Quite a few researchers have demonstrated the importance of the mold temperature, but, in general, a practical way to determine it is rarely presented. In this work, the software MoldFlow was used to perform cooling analysis with three different injection molds, with different molding conditions, in order to investigate the parameter setting for mold temperature. The analysis of the simulation results showed that cooling water temperature was the most significant parameters to the mold temperature. Empirical model between this factors and the mold temperature was also built. Such model seemed to be effective to estimate the temperature of all the studied molds.
Microstructures of Injection Molded Glass Fiber Reinforced PC/ABS
Microstructure of the injection molded glass fiber reinforced PC/ABS was investigated in the present study. Two types of glass fiber were used to compound with PC/ABS and the compounded materials were injection molded with three moulds of different configurations, respectively. It was found for the specimen molded with the 2 mm-thick sheet mould at the injection speed of 250 mm/s, the glass fibers didn't always flow with the polymer matrix together in the core zone. It was also found the fibers treated for adhesion to ABS appeared to be bound to ABS, while the fibers treated for adhesion to PC/ABS appeared to be bound to PC.
Crystallization Behaviors of Nylon 66 and Nylon 6 Copolymers at High Supercoolings
Crystallization kinetics and morphology of a series of random copolymers of Nylon 66 and Nylon 6 (up to 21 wt%) have been investigated. Optical microscopy with rapid cooling apparatus was employed to measure growth rate at higher supercoolings. Results indicated that the rates of crystallization of Nylon 66 copolymers were reduced with increasing content of Nylon 6 comomoner, and crystallization temperature were moved to lower temperatures. Final spherulites morphology of Nylon 66 and copolymers could be changed from impinged spherulites to isolated spherulites with decreasing size until total amorphous with increasing supercoolings. The melting temperature, crystallinity, and crystal structure of the Nylon 66 copolymers from different cooling conditions were studied with Differential Scanning Calorimetry (DSC) and Wide Angle X-ray Diffraction (WAXD). Crystallinity and melting temperature were found to be lower at higher supercoolings.
Simulation of the Time-, Temperature- and Stress-Dependent Elastic, Viscous and Retarded Creep Behavior
The creep behavior of polymeric materials has been studied, with emphasis on dividing the total deformation into an elastic, viscous and retarded part via a 4-elements-model. It was found that the long-term creep behavior can be satisfactorily predicted based on creep experiments up to 1000h loading duration. An extrapolated Findley-approximation up to a predetermined criterion delivers data-points for long time intervals. The models developed allow a comprehensive description of the creep behavior. With that approach, the simulation of e.g. isochronous curves for arbitrary stresses and temperatures was possible with very good accordance to the real creep behavior.
Photo Degradation Mechanisms of Layered Silicates Polymethyl Methacrylate Nanocomposites
The use of advanced lightweight materials to improve combat survivability has been of crucial interest to the U.S. Army for a number of years. The design, development, and performance testing of these advanced materials is critical for enabling Future Combat Systems and the Objective Force Warrior. Specifically, hybrid organic/inorganic polymer matrix nanocomposites show promise in providing many of the physical properties required (ie. lightweight structure, rugged abrasion resistance, high ballistic impact strength). However, as with any polymer system, these materials are susceptible to degradation over time when exposed to various environmental (i.e. sunlight, moisture, temperature) conditions. This structural degradation (1-4) will eventually comprise the original integrity of the materials’ desired properties. The focus of our research is to exploit nano-technology through incorporation of layered silicates for property enhancement.In this study, the impact of accelerated weathering upon newly developed polymethyl methacrylate-layered silicate nanocomposites materials was investigated. The silicate loading varied from 0 - 5 % by weight. A fluorescent ultraviolet (UV)/condensation weathering tester was selected for the exposure study. The materials were characterized by UV/VIS spectroscopy and FT-IR spectroscopy. The results reveal that the acrlyate linkages undergo a scission reaction upon UV exposure thereby compromising the original properties of the material. Furthermore, these scissions produce a yellowing of the polymer matrix which can inhibit its use where optical clarity in important.
Simulations of Scratch Resistance and Recovery in One and Two-Phase Polymers
We have used molecular dynamics to simulate the behavior of polymers in scratch tests. We start by creating a material on the computer consisting of chains with varying molecular mass, orientation and second phase concentration.Scratching is simulated by moving a force along the surface of the material. We measure the resulting deformation and we study penetration depth and recovery. We find that these depend on the local structure of the material as well as on the distribution of the second phase.Our simulations allow us to better understand scratching and scratch recovery. This helps in the creation of materials with improved tribological properties.
Impact Fatigue Properties and Failure Mechanisms of Glass Fiber-Reinforced Thermoplastics
The impact fatigue properties of four kinds of glass-fiber or glass-bead reinforced polymers were studied through uni-axial and multi-axial fatigue. In performing fatigue tests, the authors paid special attention to the effect of interval times between loading and loading mode on the fatigue properties of those materials. It was found that the numbers of cycles to failure were strongly dependent on the duration of the interval time and loading mode. The failure mechanisms were investigated with acoustic velocity measurements and optical microscope (OM) observations. OM studies revealed that the fatigue life is strongly affected by the features of damage such as breakage of glass, micro-voiding, change in the orientation of glass fibers, and plastic deformation. The degree of damage localization also had a strong effect on the fatigue life. The difference in the damage development mechanisms were found to be caused by the difference in the elastic response of the specimens due to the different loading mode (uni-axial or multi-axial) and the interval time.
An Experimental Study of Accumulating Damage in E-Glass FRP Specimens with Acoustic Emission
Current codes governing the design of fiber reinforced polymeric (FRP) components are generally based on ultimate strength testing. A large safety factor is then imposed for purposes of design. This approach ignores the onset of damage in the component. The onset of damage is related to the structural integrity of the component and its fatigue life.An experimental investigation has been conducted to determine the onset of damage in small coupon specimens with the acoustic emission technique. Damage was found to occur at different stages of loading for coupons made with different resin types and different fiber geometries.
DMA Viscoelastic Analysis of Two Cross-Linked and One Thermoplastic Rubber
Dynamic Mechanical Analysis (DMA) was used to characterize three polymers that display rubbery behavior around room temperature. Oscillatory modulus data were collected at zero degrees centigrade and above for these three rubbery materials: a thermoplastic olefin (TPO), an EPDM rubber and a silicone rubber. The in-phase modulus, out-of-phase modulus and tan ? data were synthesized into mastercurves using the principle of time-temperature superposition and compared. As expected, the TPO, the only non-cross-linked system, showed the most time dependence, while the silicone rubber was very nearly perfectly elastic, basically conforming to rubber elasticity theory. The EPDM data, while still superposable into a smooth mastercurve, showed evidence of an incomplete cure. Subsequent testing and analysis confirmed the incomplete cure. A cured sample of the EPDM polymer behaves in a fashion consistent with classical rubber elasticity theory. These DMA data are also shown to be useful for time-dependent, small-deformation stress and strain analyses.
Effect of Material Properties on the Mechanical and Thermal Performance of Metallocene Catalysed LLDPEs
A range of metallocene and Ziegler-Natta catalysed LLDPEs were prepared by injection moulding to determine the effects of density, molecular weight, MFI and polydispersity on their mechanical performance. Tensile results showed that hexene based mLLPDEs exhibited higher elongation to break while Young’s modulus of the materials was found to be more influenced by density. Impact results demonstrated that metallocene LLDPEs have superior impact strength at room temperature over conventional LLDPEs. Further analysis using differential scanning calorimetry and dynamic mechanical thermal analysis was performed to study the influence of the metallocene catalyst and co-monomer type on the properties of the materials.
Propylene-1-Hexene Copolymer Obtained with Ph2C(Flu,Cp)ZrCl2 Homogeneous and Heterogeneous System
This work deals with metallocene homogeneous and heterogeneous catalysts (Ph2C(Flu,Cp)ZrCl2 and Ph2C(Flu,Cp)ZrCl2/HM) to obtain syndiotactic polypropylene and propylene-1-hexene copolymers. The effects of polymerization temperature, comonomer concentration and different reaction solvents were studied.S-PP of 138/152°C melting temperature was obtained with these catalysts. Both homogeneous and heterogeneous systems showed the comonomer effect. By changing the solvent from toluene to hexane a decrease in activity and an increase in polymer melting temperature and crystallinity were observed.
Characteristics and Properties of Metallocenic Syndiotactic Polypropylene
This work investigates the characteristics and properties of syndiotactic polypropylene produced by Ph2C(Flu)(Cp)ZrCl2/MAO metallocene catalyst system. The obtained s-PP presented melt temperature around 120°C, being more amorphous as the polymerization temperature increased. From the data obtained through HAAKE mixture chambers we could carry out the rheological characterization of the polymer, which presented a non-Newtonian pseudoplastic behavior, as expected. The polymer also had a good mechanical performance compared to conventional i-PP.
Copolymerization of Ethylene and 1-Hexene by Homogeneous and Supported Metallocene Catalysts
In this work, the performance of the homogeneous catalyst system based on Ph2C(Flu,Cp)ZrCl2 was evaluated on ethylene copolymerization and 1-hexene. The influence of the support material was studied using acid mordenite HM zeolite and the characteristics of the produced polymers were also investigated. A study was performed to compare the influence of polymerization solvents as toluene, hexane and hexane/TIBA. An increase in activity was observed in relation to the comonomer addition for homogeneous and supported systems.
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