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 this paper, alternate and synchronous dull and glossy flow marks are studied. The effect of rheology, flow front velocity, mold geometry, melt temperature, mold temperature, and mold surface coatings on flow marks was studied. For the alternate flow marks, it was found that the flow marks did not occur at high injection speeds. The generation of the flow marks is explained by entry viscoelastic instability. For the synchronous flow marks, it was found that coating these surfaces could not prevent the occurrence of the flow marks, although it could alleviate them. Slip is not the cause of the generation of the synchronous flow marks.
This paper presents a true three-dimensional simulation of the underfill flow in the encapsulation of flip-chips. The SIMPLE-based finite volume method (FVM) is combined with the volume of fluid (VOF) method to solve the two-phase flow field and to track the advancement of the resin front during underfilling process. Since the underfill encapsulation is driven by the capillary force, the continuum surface force (CSF) model is employed in the present approach to calculate the surface tension at the resin front surface. In addition, the chemorheology of the encapsulant is also included to consider simultaneously the effects of temperature, shear-rate and degree-of-cure on the underfilling patterns. Several test examples with different dispensing locations or molding temperatures are analyzed to demonstrate the capabilities of the present approach.
Five poly(vinylidene fluoride) (PVDF) resins, R1-R5, of narrow molecular weight distribution (ca. 2.0) but of different weight average molecular weights Mw’s (85 – 250 Kg/mol) were melt extruded in tubular film form with a blow up ratio (BUR) of unity. The objective was to produce a stacked lamella structure that could serve as a precursor for a later process step that converts this film into a microporous membrane. Four of the resins were in pure form R1-R4 whereas the fifth, R5, contained a small amount of plasticizer to facilitate processing due to its high molecular weight. Comparisons were made of how Mw influences film morphology under a given set of process conditions. WAXS systematically showed an increase in crystal orientation as Mw increased for fixed conditions. A Carreau-Yasuda fit of the melt rheological data provided a characteristic relaxation time and this variable was correlated to the respective morphologies produced. It was shown that nearly spherulitic-like textures could be induced with the lowest Mw material whereas highly concentrated fibril nucleated morphologies were promoted with the highest Mw under identical process conditions. It was demonstrated that by blending the resins, R2 & R4, the desired stacked lamellar structure could be fine tuned with regard to morphological features.
Viscosity of polymer melts can be effectively reduced by adding constituent of supercritical fluid (SCF) during plastic processing. The viscosity reduction depends on the amount of SCF added and also the magnitude of shear rate. This research modified a conventional injection-molding machine to investigate the rheological behavior of PP/SCF mixture. By measuring the pressure and flow rate of the melt at a slit die which was attached in front of the nozzle, the true viscosity can be obtained after making Bagley and Rabinowitsch corrections. By using this machinery, the shear rate can be achieved as high as order of 1E4 1/s .
The melt index of a single pellet is measured by combining experimental viscosity determination and simple modeling of the flow in the melt indexer. Special parallel plates are used to quantify the shear rheology of a 5 mg sample, the viscosity data is fit to a Power Law model, and the melt index is calculated. Results from this technique are compared to the results from actual melt index measurements for polyethylenes with a range of melt index values.
Blends of Ethylene-Vinyl-Acetate copolymers (EVA) with metallocene based ethylene-a-olefin copolymers have been studied, with the purpose of exploring their properties and potential in film packaging applications. The effect of blend composition on rheological properties, heat seal, optical and tensile properties has been examined. It is shown that depending on their composition, these blends can offer a good balance of properties and processability.
This study investigates mechanical behavior and reversibility of dynamically vulcanized EPDM / i-PP blends. The composition of these elastomers dictates their morphology, which in turn controls their mechanical behavior. Six compositions are examined under dynamic loading. Dynamic mechanical responses are examined in terms of the Payne effect as a function of composition, cure state, and i-PP molecular weight. The Kraus model is applied and the resulting parameters are explained as a function of morphology.
Processing of polymer melts and solutions is strongly influenced by both shear and elongational rheology. Molecular weight, molecular weight distribution, degree of branching, branch length and their distribution on the host chain are influential on both. In this work the elongational viscosity and first normal stress coefficient are related to molecular parameters of some polyolefins.
Two slit dies with sudden contraction ratios of 4:1 and 18:1 were designed to investigate the effects of pressure and supercritical carbon dioxide (scCO2) content on the entrance pressure drop and rheological properties of PS/CO2 solutions. scCO2 was found to decrease the entrance pressure drop as well as the shear and extensional viscosities of PS.
Two events that coincide in the year 2001 are the NIST centennial year anniversary and the inauguration of the SPE Special Interest Group on Process Monitoring and Control. To celebrate these two events, this paper will highlight polymer process monitoring activities at NIST describing the full range of measurement and sensor developments for real-time monitoring of resin temperature, rheology, morphology, molecular orientation, and dielectric properties of polymers, filled polymers and polymer blends.
Rheology is a discipline that has applications both for analysis of polymer structure and for correlation and prediction of processing behavior. As such, rheology has impact over the entire development of a commercial resin. Described are several projects in the areas of polymer blending, aging and fabrication that illustrate the important role that rheology has played in their execution.
An investigation has been conducted to analyze the influence of different process parameters as well as material properties on the structure of CO2-foamed polypropylene sheets. The use of a linear and a branched polypropylene shows the influence of the rheological melt properties on the foam density and the structure. Using the branched polypropylene, densities down to 140 kg/m3 have been achieved. These samples also show a finer and more homogeneous foam structure than the samples made with the linear polypropylene.
This paper describes the development of blends of recycled polyethylenes suitable for rotational molding. The blends consist of recycled post-industrial polyethylene resins and polyolefin plastomer impact modifiers, produced by single-site (metallocene) catalysts. The rheological properties of the blends were found to be favorable for rotational molding. Rotomolded parts provided satisfactory low temperature impact strength and good tensile properties.
The transient rheological material functions [?(t,?),N1(t,?),?e(t,?) ] of three PP resins are predicted using the multi-mode Phan-Thien and Tanner (PTT) molecular network model. The study also includes the standard quality properties (MFI, XSP, GPC, and DSC) of the resins. The model was coded in C-language, validated with published data (Phan-Thien, 1978) and then used for the prediction of transient material functions. The predictions are in good agreement with the resins' rheological data.
The rheological behavior of polypropylene (PP) modified with nitrile rubber (NBR), within the composition range of 10-30 wt% NBR content, was studied based on the blend ratio, dynamic vulcanization and additives blending effects. Results indicate all systems show a pseudoplastic behavior with an increasing melt viscosity on NBR content. Dynamically vulcanized blends present similar melt viscosity and lower die swell values than corresponding unvulcanized blends. The rheological behavior was correlated with blend morphology.
Post-consumer plastic waste in Australia contains over 50,000 tonnes p.a. of HDPE blow moulded bottles, with half still ending up in landfill. Recycled milk-bottle grade HDPE is known to be too high in molecular weight for processing by injection molding. In this study, the target was to make injection-molded compositions with a content of the recycled material of 75% or higher by blending with commodity plastics. The results of rheological, thermal and mechanical studies of the blends are presented.
The rheological behavior of TPV in shear and extensional is studied to help understanding the flow behavior in various processing operations. The TPV's, which are dynamically vulcanized PP/EPDM blends show in shear flow a typical rheological behavior with an apparent yield stress at low shear rates and a shear-thinning viscosity at high(er) shear rates. In extension the TPV melts appeared not to show strain-hardening. This study discusses the observed behavior in terms of composition.
A polymer flow analysis inside a concentric annular die of an extrusion blow-molding machine was conducted using momentum and continuity balances coupled with the Wagner rheological constitutive equation for six high density polyethylene (HDPE) resins and then used to determine the thickness swell. The rheological measurements included oscillatory behavior, relaxation modulus, steady state behavior, and capillary flow.
The effect of powder characteristics on the rotational molding and sintering performance was investigated. The six LLDPE resins showed comparable rheological and thermal properties. Resins with poor powder quality produced parts with lower density and impact strength. The irregularities in shape due to grinding influenced the sintering results. To eliminate this effect on the sintering experiments cylinders were used. Variations in the sintering results, however, were also observed when using cylinders.
Polylactide (PLA), a new thermoplastic derived from corn, has been developed for extrusion coating applications. Polylactides can be rheology modified to run on high-speed commercial extrusion coating lines to produce packages with unique properties. New packaging systems will be described based on PLA's combination of adhesion, flavor/aroma barrier and heat seal/hot tack strength.
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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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