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.
Polypropylene composites with glass fibers or talc are widely used in various technical applications. In many applications weld lines are formed in injection molding and reduce mechanical performance. When large aspect ratio reinforcements are used this detrimental effect is more pronounced. This results from the preferential orientation of reinforcements in the plane of weld line. In this paper, the hybridization of two different aspect ratio reinforcements is shown to be beneficial to the weld resistance.
This study investigated glass transition characteristics of polymers by using molecular dynamics simulation. The simulation modeled the polymeric fluid with the shifted Lennard-Jones potential theory, and the polymer bond stretching/bending/torsion was simulated with Hook-like model. By cooling the system temperature from melt state to room temperature, we could determine the glass transition temperature. The causes of glass transition can be explained by monitoring the chain energy and structure variation during the cooling process. Different chain length and deformation dynamics of polymeric chain systems were also illustrated. All simulation results were found to be in good qualitative agreement with related experimental and theoretical investigations.
Scanning probe microscopies provide important contributions to the study and optimization of polymer properties. In particular, in dynamical force techniques, the phase measurement yields in many cases to images reflecting tiny variations of the local properties of the sample surface. On that basis, it is possible to extract useful information for samples showing compositional heterogeneity at small scale, for instance blends of hard and soft materials.Here, we present the major morphological features observed with SPM in a series of polymer systems of growing complexity: polymer blends, block copolymers, and hyperbranched polymers.
The linear viscoelastic oscillatory shear properties of a polycarbonate PC and polybutylene terephtahalate PBT, 60/40 by respective weight, blend and its nanocomposites with various concentrations of organically modified organoclay and clay surface treatment were evaluated. The decrease in properties is attributed to a decrease in molecular weight. A 70% decrease in complex viscosity over all angular frequencies is observed. A relatively small decrease in Tg is observed and is attributed to increased compatibility.
The increased use of polymeric materials having outdoor exposure has created a need for a better understanding of the effects of Ultraviolet (UV) Radiation. Many plastics do not perform well when exposed to UV radiation. The exposure to UV radiation significantly affects the physical, chemical, and mechanical properties of plastics materials, thus reducing their life expectancy. Not much research has been done to investigate how stresses will affect the weatherability of plastic materials in outdoor exposure. This paper will show that exposure and/or internal stresses will decrease the displacement and maximum stress.
Two classes of environmentally-friendly polyurethane dispersions have been prepared via prepolymer emulsification process and acetone process. Rheological behavior of these dispersions has been studied as functions of PU-concentration, degree of post-neutralization and temperature. At a critical volume fraction of PU (? ~0.43), a dramatic increase in the reduced zero shear viscosity was detected for the two dispersions. Co-occurrence of thermal-induced gelation and liquid-liquid phase separation was observed for the prepolymer process, while, only liquid-liquid phase separation was discovered both rheologically and morphologically for the acetone process.
Nanoimprint Lithography (NIL) can fabricate sub-50 nm fine structure precisely. However, the processing problems for imprinting include the control of imprinting velocity, polymer flow behavior, the thermal shrinkage of materials at cooling stage and the friction force at releasing step. All of above-mentioned factors will affect the fabrication of nanostructure significantly. Except for investigating these factors experimentally, molecular dynamics (MD) simulation can be adopted to study the effects at different process conditions and obtain further detailed process information. In this article we focus on the effect of different imprinting velocity and the friction at demolding step. And in the future this simulation technology can be further applied to study the making of high-density compact disk, plastic optical nano-device, DNA chip...etc.
During the production of extruded profiles, the calibrator should cool down the profile both swiftly and uniformly. The main difficulty to be faced in the design of these tools arises from the fact that these two objectives are conflicting, i.e., conditions leading to a lower average temperature generally promote a lower temperature homogeneity and vice-versa. There are few ways to improve simultaneously both criteria. As shown in previous works, the most effective alternative is the division of the cooling length into several cooling units separated by annealing zones. In these zones the extrudate temperature distribution homogenizes and, as a consequence, its surface temperature increases (increasing also the thermal energy removal in the subsequent cooling unit), hence leading to improvements in both conflicting objectives.In this work, an optimization methodology (encompassing a numerical simulation code, an objective function and an optimization routine) is used to optimize the lengths of the individual cooling units and of the annealing zones with a view to improve the thermal efficiency of the calibration stage.
The functionalization of polypropylene (PP) by 4-carboxybenzene sulfonyl azide (CBSA) was investigated in a batch mixer. The degree of grafting was studied through FTIR, 1H-NMR and XPS spectroscopy using varying levels of CBSA. Under different reaction temperatures, the grafting degree showed a maximum point at 190°C. The degree of grafting increased with feed azide content initially and then leveled off. The rheological properties of the functionalized PP were also evaluated by oscillatory shear measurements and were found to correlate with the grafting degree results. Finally, the adhesion of functionalized PP to aluminum substrates was found to increase significantly.
It is the aim of this project to distinguish the functionalities of collagen that allows it to attract a Polymer-Induced Liquid- Precursor (PILP) phases to Calcium Phosphate (CaP) and stimulates biomineralization. The system investigated mimics the electrostatic interactions present in collagen through testing surfactants with varying end groups. Self-assembled monolayers micro-contact printed unto gold is used as the substrate for mineralization. Results obtained thus far have been analyzed through optical microscopy, scanning electron microscopy (SEM) and electron dispersive spectroscopy (EDS).
Heat-sealing process is often employed in packaging applications of polymeric films, especially for plastic bags. In this study, effects of heat-sealing temperature and holding time on mechanical properties of heat-sealed parts of poly (lactic acid) (PLA) films were investigated. Peel tests, double edge circular-notched tension (DECNT) tests, and center cracked tension (CCT) tests were conducted with the heat-sealed PLA films. The thermal properties of the heat-sealed parts obtained by differential scanning calorimetry (DSC) were also investigated.
In thermoplastic foaming, phase separation (i.e., bubble nucleation and growth) occurs due to a sudden change in pressure during mold filling that has significant effects on the rheology of polymer flow. An instrumented mold cavity has been designed to capture rheological measurements of the eventual two-phase gas-polymer suspensions. Experimental results for low density polyethylene (LDPE) and thermoplastic polyolefin (TPO) with two types of chemical blowing agents indicated that the rheological properties of two-phase gas-polymer suspensions were sensitive to shear rate, blowing agent concentration, melt temperature and mold temperature. The viscosity of gas-polymer suspensions was reduced in the presence of gas bubbles. A model has been proposed that yields good agreement with our experimental results for estimating the viscosity of two-phase flow in the mold cavity of the injection molding machine.
A self-regulating valve is placed between the extruder and die is to adjust the melt pressure and also reduce the amount of surging related to the screw beat in an extrusion process. The experimental results validate that there is a linear relationship between the control force and output melt pressure, and that the use of a self-regulating valve can significantly reduce the variation in output melt pressure compared to the conventional extrusion process. However, the results indicate that the specified control force and output melt pressure must be carefully selected in extrusion processes to prevent excessive increases in plastication pressure. Furthermore, the response time of the valve limits the dynamic performance of the system, and indicates the need for potential improvements in mechanical and control system designs.
The effects of interfacial shear stress between fiber and matrix, and fiber surface morphology on the fracture toughness of carbon fiber (CF) and glass fiber (GF) reinforced PA 6 sandwich composites are investigated in this study. Both fiber length distribution measurement and single edge notch bending fracture tests were carried out. 6 configurations were produced for this study, i.e. PA 6, composites reinforced with CF (CF/PA 6), composites reinforced with GF (GF/PA 6), GF and CF blend (GF/CF/PA 6) produced via conventional injection molding techniques, whereas the sandwich moldings CFPA 6 skin/GF-PA 6 core (CFs/GFc/PA6) and GF-PA 6 skin/CF-PA 6 core (CFs/CFc/PA6) which were produced using co-injection molding. As a result of rough CF surface, coupled with its capabilities to induce transcrystallinity in the matrix, CF/PA6 have higher interfacial shear stress, fracture toughness and fracture energy values compared to GF/PA 6 composites.. CF also tends to have a very low critical fiber length compared to GF. This is very obvious as the fracture toughness values of CF/PA6 were the highest among all composites. The GF/PA6 configuration was the second lowest, while PA 6 itself recorded the lowest fracture toughness values. Substantial retention of toughness is observed by blending both CF and GF together into GF/CF/PA6. Both CFs/GFc/PA 6 and GFs/CFc/PA 6 sandwich structures show nearly similar toughness values. This is due to the fact that both sandwich composites behave like laminates, i.e. GF/PA 6 and CF/PA 6 laminates combined into a single composite. As such, the superior properties of CF were not efficiently utilized. Fracture energy was calculated on the basis of Kc and Gc relation. CF/GF/PA 6 and GFs/CFc/PA 6 dominate the highest values of fracture energy. This is again attributed to the addition of CF into the sandwich composites.
Injection molding with recycled polycarbonate (PC) and crushed FRP products was fabricated and examined on tensile, flexural and Izod impact test. The specimen of composition filled with 5wt% of FRP and modifier had highest mechanical properties. The composite had approximate equivalent tensile strength and higher Izod notched impact value than that of standard rigid PVC. Composite pipe made of this composition was manufactured by using extrusion process. The composite pipe has extreme high flexibility because in 50% diameter reduction of lateral compression test no fracture ccurred. Consequently, the composite pipe can become substitute of PVC.
It is known that mechanical properties of LLDPE films depend on the length of the short chain branches. However, it is often very difficult to differentiate this effect with the effect of other variables such as comonomer distribution and molecular weight distribution using standard test methods. Furthermore, the structure property relationships for copolymers with different length alpha olefins has not been clearly established. High rate tensile, high rate single edge notch tear, and the essential work of fracture method were used in this paper to differentiate the effect of short chain branch length using several well controlled samples. The crystal morphology of the samples at different stages of deformation were analyzed using DSC, AFM, and X-ray to explain the effect of short chain branch length. It was demonstrated that the tear resistance of LLDPE thin films produced with different length alpha olefins can be differentiated using strain hardening, tear energy, or essential work of fracture at high loading rate. A hypothesis is also proposed to explain the effect of short chain branch length on film tear resistance.
In this study, the effect of the number and size of clusters on the fracture behavior of PP and TPO nanocomposites are investigated. The effect of the particle size distribution and injection molding flow profile are also discussed with respect to the effect of filler morphology on the tensile fracture toughness. Fracture pattern and fracture surface were examined by scanning electron microscopy (SEM). The morphological analysis of crack propagation path and the contribution of nanoparticles were studied by observing process zone formation during crack propagation. A schematic model of nanoparticle distribution in injection molded specimens is also proposed based on fractographic analysis.
Stress corrosion cracking (SCC) results from strongly coupled electro-chemical and thermo-mechanical processes, and this cracking is sensitive to material composition and morphology. There are four stages of SCC such as initiation, individual SC crack propagation, many crack interactions and clusters of crack formation, and finally crack or cluster instability and dynamic growth leading to the ultimate failure. In this paper the mechanism of SCC is investigated by the observation of SCC surface using a scanning electron microscope (SEM). Thermodynamic model of SCC propagation and statistical modeling of SCC initiation based on chemical degradation has been proposed before by the authors. The model predicts a change of the mechanisms of crack growth from chemically driven to mechanical stress control propagation. This prediction is validated by fractographic observations. It provides important information on the change of SCC propagation mechanism by the variation of micro-morphology and striation on the fracture surface. The duration of chemically driven stage of SCC and transition to stress controlled propagation depend on temperature and stress.
Utilizing the injection molding simulation, this paper illustrates a methodology of dealing with manufacturing variance occurring in molded parts. For the simulation, the manufacturing variance is deliberately induced by a small change in processing condition variables, which consequently causes a variation in the rheological properties of the polymer melt entering into cavity. By comparing the simulation results with previously published experimental results, an attempt is made to statistically validate this methodology. In doing so, the effect of different switchover methods during the injection stage is comparatively evaluated. The part weight and dimensions are chosen as the quality characteristics. This study also investigates correlations between part weight and dimensions, as well as between the predictions and the experiments of an actual molding trial.
Biopolymers are generally defined as polymers that are found in nature, derived from nature, or utilized as medical implants. Polymeric biomaterials which are utilized as medical implants are typically characterized for end-use performance as well as processability. While lactic acid is found in the human body, polylactic acid is derived from natural resources and utilized as medical implants. This paper will utilize poly(lactic acid) as an example of a biopolymer where the morphological and isomeric structure has an influence on end-use properties such as mechanical properties, biodegradability, and biocompatibility.
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Brown, H. L. and Jones, D. H. 2016, May.
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ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
Society of Plastics Engineers
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