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.
For decades, fluoroelastomers have been used as polymer processing aids (PPA). Previous works have measured the thickness of the PPA coating, its effects on the polymer/die interface, and proposed several mechanisms of PPA coating. In this work, the coating process of a fluoroelastomer was visualized during the extrusion of a PPA/Polyethylene blend. The apparatus consisted of a capillary rheometer fitted with a sapphire die and a high resolution imaging system. The images obtained show a coating evolution from the adhesion of scarce PPA particles, to the massive wave flow of PPA, and finally the formation of streaks on the die wall. These sequences of images are correlated with the measurements of the die entrance pressure and the appearance of the extrudate.
Over 800MM lbs/yr of polyethylene (PE) powders are used in a very broad array of applications in North America. These PE powders range in size from coarse, 1200 micron (16 mesh) powders, down to extremely fine powders well under 5 micron in size. The various applications for these powders include wood plastic composite lumber, battery separators/membranes, architectural paints/coatings, cosmetics/beauty care, to name just a few.This paper will provide an overview of the PE powder market in North America. The characterization of the various types of PE powders will be presented, as well as the different manufacturing processes utilized to produce these powders. Performance requirements for various PE powder applications will be detailed, and examples presented where PE powder product design provides performance enhancement in selected applications.
Much work has been reported about the deformation of a dispersed single droplet under the flow field of another continuous phase. This investigation has a great significance upon the dispersion or mixing of the multiphase polymer blends. Similar to this, the deformation of a single gas bubble under polymer melt flow field is also well worth studying since its importance upon the dispersion or breakup of bubbles. To obtain the rules of bubble deformation when gas is injected into polymer melt flow field, a series of experiments were made through changing the gas injection pressures. It was found that bubble shapes for the different time periods were changed greatly since its dilatation and the effects of the flow fields. Moreover, the deformation of bubble was severely affected by its volume. Therefore, several different bubble deformation processes were characterized.
Protein and protein based formulations present some interesting difficulties when studied by traditional Differential Scanning Calorimetry techniques. Compared to synthetic polymers, proteins tend to have weak transitions and are more sensitive to thermal effects. Modulated temperature techniques have show some utility in the analysis of these materials, but some issues with kinetic effects, weak transitions, and the time required for screening samples remain. A series of protein-based formulations were studied using high scanning rate DSC. Application of high scanning rate DSC to proteins was found to have some significant advantages in both increasing throughput and in enhancing weak transitions. Not only can throughput be increased dramatically, but very weak transitions like the glass transition of a pure protein could be measured directly.
This paper presents the most recent development in microscale compounding technology in material science. The equipment consists of a 6-inch conical twin-screw extruder co- and counter-rotating and housed in a vertical clamp shell barrel, which can be operated in batch and continuous modes. The design and versatility of this equipment allows the evaluation of a myriad of materials ranging from polymer blends to filled systems and Nano-composites with 5 to 15 grams of sample. It is also possible to monitor changes in the rheological properties of the materials during processing allowing a better assessment of mechanisms such as polymer degradation and stability, reactive extrusion and crosslinking. Comparative analysis with other processing equipment such as mixing bowl and twin screw extruders on model systems and in terms of extent of dispersion and mixing is achieved.
The required performance of polyethylene pipes for gas distribution is firstly described. As an evaluation method for slow crack growth, the relation between crack growth length and time under test was obtained to investigate the stress crack resistance of polyethylene pipes for gas distribution after conducting three-point bending tests at 23 degrees C for fifteen years as the maximum test period. The incubation period leading to crack initiation was much longer and the crack growth was slower for domestic resins. The relation between the stress intensity factor and the crack growth rate of several pipes are also discussed. The full-notch tensile creep test is specified by JIS K6774, which is now under consideration for adoption by ISO as a standard. The data on and the results of the full-notch tensile creep tests have been accumulated for several years to decide whether to introduce new resins or modified resins, and to evaluate the lot-to-lot variation of resin production for the quality control of polyethylene pipes. The full-notch tensile creep test is also applied to the evaluation of fusion joints, especially electrofusion joints, as well as the substrate of pipes. The test results have also been accumulated to determine suitable fusion conditions and to evaluate fusion integrity between different grades of pipes or joints.
Rigid amorphous fraction (RAF) in semicrystalline poly(ethylene terephthalate) is associated with very thin (20- 40Å) amorphous layers confined between the crystalline lamellas in the regions of lamella stacks. In comparison with mobile (regular) amorphous fraction (MAF), it is constrained and vitrifies at much higher than regular Tg temperature, presumably at crystallization temperature, Tc. The structure of semicrystalline PET was probed by positron annihilation lifetime spectroscopy (PALS). Systematic divergences in the o-PS annihilation lifetimes and intensities were observed, as a function of crystallinity. The results indicate that the fractional free volume of RAF as measured by the product of the hole number density and the average hole volume indeed showed a direct correlation with crystallization temperature.
An increasing number of automotive parts are made of engineering plastic for its low cost and superior material properties. The traditional structure analysis for automotive injection-molded part is to perform CAE analysis based on the assumption of one or several isotropic materials. However, the material characteristic of plastic part is extremely dependent on molding process. The process-induced properties, such as fiber-induced anisotropic mechanical properties, might not be favorable to the structural requirement of final products. Besides, the mesh requirement for different analysis purposes might not be the same, either. In this paper, we integrate the CAE analysis of structure and injection molding through data-linking and mesh mapping. This approach shows the effects of mutually dependent analyses have been successfully examined in automotive injection-molded parts.
Premature brittle failures of an injection-molded part made from 20% glass filled Noryl tempted review of product design and material suitability evaluation for the intended application. Fractographic analysis of fracture revealed cracks were present at knit-lines in the part and were due to creep rupture failure mechanism. A stress analysis using finite element analysis technique was performed on the product design to evaluate the stress distribution at the location of fracture. Creep-rupture and stress-relaxation characteristics of the Noryl material were obtained by testing injection-molded samples with a knit line in the center. The usefulness of creep-rupture and stress-relaxation data in product design analysis was demonstrated. The material suitability and part design was assessed with the use of long-term stress-rupture and stress-elaxation data.
Nanoclay reinforced polymer blends exhibit high potential as a new material for CO2 foaming because they can provide higher CO2 solubility, lower gas diffusivity, and better mechanical properties than foams made of homopolymers. In this paper, a polystyrene (PS)/poly(methyl methacrylate) (PMMA)/nanoclay blend was selected to study the relationship among blend morphology, nanoparticle distribution, and foam structure. PMMA serves as the dispersed domain in PS. Blends with different morphology were obtained by changing the nanoclay content and the screw configuration, which were then foamed by using CO2 in a batch system. Effects of nanoclay content on the blendmorphology, rheological properties, and foam morphology were studied. It is found that the highest foam nucleation efficiency appears at the interface of PS/PMMA/nanoclay.
In the pressure-driven disk-flow (PDDF) rheometry, the liquid is pressurized in the center of a pair of parallel disks and flows outward in the radial direction. While an analytical solution to the viscosity can be readily derived for Newtonian liquids, corrections need to be made to determine the actual relation between shear stress and shear rate for non-Newtonian liquids. A data analysis procedure with corrections similar to the Rabinowitsch-Weissenberg correction in capillaryrheometry was developed for the PDDF rheometry, resulting in a relation that correlate wall shear stress with wall shear rate at the exit of the disk flow. Computer experiments with a known viscosity model of a non-Newtonian liquid were carried out using Fluent® to generate data points for the pressure-driven disk flow. The data analysis procedure for PDDF rheometry was implemented and was able to extract the shear-rate-dependent viscosity from the raw data.
Failure criteria of the heat sealed part of oriented polypropylene (OPP) and cast polypropylene (CPP) heat seals made by an impulse type heat-sealing machine were investigated. Circular notches and pre-cracks were introduced to direct failure to specific areas such as inside the seal, at the border or the unsealed part. The notched strength as a function of heat-sealing temperature revealed that the seals were stronger in the transverse direction (TD) as compared to the machine direction (MD). Tensile failure that occurred inside the heat seal is more sensitive to sealing temperature while that at the unsealed part is immune. The stress intensity factor (K1) is generally higher along TD. Within the seal, three distinct zones could be identified with increasing temperature. For failure at the unsealed area, the value of K1 was constant irrespective of sealing temperature along the MD while the trend along the TD is similar to that within the heat seal. The weakest part was identified as the immediate neighborhood outside the heat seal.
This study investigates the spatial distribution of a minor particulate constituent in a transfer molded exposed die paddle (e-pad) leadframe microcircuit package. Packages were polished at three depths parallel to its top surface. Levels 1 and 2 are above the die and leadframe while level 3 is just below the top surface of the die and leadframe. The distribution of area fraction and size of the particulate was analyzed for each level and with respect to the distance from the gate using micro-photographic image analysis. A non-uniform distribution of the particulate material for both particle size and location is evident, and its relations with gate, die and leadframe are interpreted. ANOVA tests were conducted to assess the statistical significance of the variations.
To develop compounds with specific properties and to take full advantage of today’s variety of additives more efficient material development processes are needed. A new method is combinatorial compounding. Based on a twin screw extruder and a following flat film extrusion line compounds are produced and tested with a high frequency. For this the process control has to be altered so that gravimetric feeders continuously change the amount of additives. The composition and parameters specific for the optimization problem at hand are monitored. This information together with Measures of Significance (MOS; parameters or combinations of parameters) is fed into a data base which spans the parameter space. Algorithms known from combinatorial material research help to find a predefined optimum. The optimal compound can than be further tested.In this contribution the equipment, the process and the data management are introduced.
Polymer blends based on poly(ethylene 2,6-naphthalate) (PEN) and poly(ethylene terephthalate) (PET) reinforced with a thermotropic liquid crystal polymer (TLCP) were prepared by a melt blending process. The TLCP component acts as a nucleating agent in the TLCP/polyester blends, thereby enhancing the crystallization of the polyester matrix through heterogeneous nucleation. The lower value of the structural viscosity index for the TLCP/polyester blends was attributed to the formation of TLCP fibrillar structures with elongated fibrils in the polyester matrix, resulting in better spinnabiliy. The higher intrinsic viscosity of the polymer matrix, higher shear rate, and lower viscosity ratio may favor TLCP fibril formation in the polyester matrix.
Since many years, polypropylenes with low amounts of ethylene comonomers (PPR) are used for production of hot-water pipes in sanitary applications. In this contribution we report on a new route for obtaining “biaxially” oriented PPR pipes via a die-drawing process previously developed at Leeds University. This results in a significant improvement of long-term stability as well as hydrostatic pressure and impact resistance, compared to PPR pipes produced under standard extrusion conditions. This unique behavior originates from a non-uniform orientation distribution throughout the pipe cross section, which has been analyzed using X-ray microdiffraction.
The importance of dimensional stability for the automotive industry is evident from the fact that a car consists of a combination of metal, fiber reinforced composites and polymer blends. Metals have a coefficient of linear, thermal expansion (CLTE) in the order of 10-20 x 10-6 /K.The standard way to match typical requirements is the addition of fillers; this leads to an increase in weight and a different property balance concerning E-modulus and impact strength. In contrast to this we describe a new concept to combine low weight, good mechanical properties and dimensional stability. The basis of a changing dimensional stability lies in the surface morphology and is achieved by introducing a layered rubber-PP structure. This change in morphology reduces the expansion coefficients in the important length and width direction, which is accompanied by a slight increase of CLTE in the direction of the thickness. Our goal is, to achieve a material with a very good dimensional stability without loosing primary properties.
Polymeric rigid foams are increasingly used for highly loaded mechanical applications, e.g. as core in foam sandwich constructions in aircraft or automotive parts. So far the mechanical behavior of rigid foams is not determined precisely. Therefore the core of sandwich constructions is not taken into consideration for the mechanical design. This leads to oversizing and extended material consumption. This paper presents experimental results of long-term tests and indicates a theory to take into account the difference of tensile and compressive behavior of foams. This theory is based on a strength hypothesis and can be implemented in commercial finite-element programs. The proposed method leads to an improved mechanical design and as a consequence a reduction of mass of construction parts.
This paper presents a first report from a longterm collaborative programme between Matrix Polymers Limited and the Manchester Metropolitan University. The purpose of the programme is to examine physiochemical mechanisms of the rotational moulding process using a variety of analytical techniques.The effect on the performance of polyethylene (PE) caused by variation of the rotomoulding cooking cycle is investigated using a combination of infrared spectroscopy and melt rheology. Analytical results are correlated with large scale performance characteristics, measured by established industrial assessment techniques such as low temperature impact strength, brittleness, part density development and yellowness index.
The notched impact strength of compact polycarbonate depends on the temperature, thickness (with a tough brittle transition at thickness increases), contribution of sharp notches (transition of the flat tension to the flat stretching condition) and processing parameters.Microcellular polycarbonate foams produced by injection molding process using physical blowing agent (MuCell) with or without gas counterpressure process, shows significantly higher notched impact strength then compact polycarbonate, if the compact polycarbonate is brittle under the same test parameters. When the compact polycarbonate breaks toughly, the notched impact strength of microcellular foams is always significantly lower. Therefore it is very important to pay attention to the test parameters by comparing the notched impact strength between compact and microcellular polycarbonate.
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ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
Society of Plastics Engineers
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