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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Rheology of Heat-Induced Gelation of Chitosan Solutions
Heat-induced gelation was observed above 80°C on a chitosan solution neutralized with a weak base, ? - glycerophosphate. Urea, a hydrogen bonding decomposing agent, was also used in some of these solutions to investigate the presence of hydrogen bonds in the resulting gels. The solution behaviour and gelation process were investigated using linear viscoelasticity.In solution state, the addition of urea decreased the rheological properties due to the reduction of hydrogen bonding interactions. During the gelation tests, the evolution of the storage and loss moduli was monitored as a function of temperature. Heating resulted in sol-gel transition at a critical temperature, the so-called gelation temperature Tgel. It was found that adding urea decreased the resulting gel strength and increased Tgel, corresponding to the retardation of the gelation process. These results indicate that hydrogen bonding is an important parameter in the chitosan physical gels formed, even at high temperature, which is not the usual belief. In parallel, pH and conductivity measurements revealed that gelation was also caused by polymer-polymer hydrophobic associations enhanced at high temperature, due to increased ionic strength.
Melt Grafting of End-Functionalized Poly(Tert-Butyl Acrylate) to Silicon Substrates
This work is part of a study aimed at creating surface grafted polymer layers. After deposition of amineterminated monolayers, poly(tert-butyl acrylate) (PtBA) was grafted ‘from the melt’ to silicon wafer substrates as a function of reaction temperature. The polymer layer of interest in this study was PtBA because it is relatively easy to subsequently substitute the tert-butyl ester groups with other functional groups to create a chemically tailored layer. The thickness of the monolayer and grafted polymer layer were monitored using ellipsometry and static contact angle was used to characterize the surface energy.
Fracture Behavior of Natural Fiber Composites
The fracture behavior of two natural fiber composites was investigated. Tensile and fracture tests were performed on sisal reinforced HIPS and sisal/starch based composites. An increasing trend of stiffness with fiber content was found in both cases, whereas tensile strength decreased for sisal/HIPS composites. A maximum in sisal/HIPS composites quasi-static fracture toughness with fiber loading was observed, while they exhibited lower impact toughness values than HIPS. For the biodegradable composites, fracture toughness increased with fiber content and it depends on fiber orientation. In puncture tests, these composites exhibited higher values of fracture energy than neat matrix and fiber orientation affected the damage zone.
Homocomposites of Poly(Ethylene Terephthalate)
While the advantages of homocomposites over heterogeneous composites are obvious, the fabrication of homocomposites for fast crystallizing polymers is challenging because the melting temperatures of the fiber and the matrix are very close. In the present study, an approach of using poly(ethylene terephthalate) (PET), a slowly crystallizing polymer, to form homocomposites was investigated. Because PET experiences slow crystallization during typical polymer processing, distinct physical forms with a large difference in crystallinity and thus in melting temperature can be readily obtained. In the experiment, highly crystalline PET fibers laid between two amorphous PET films were compressed between heated platens at 180°C, a much lower temperature than the melting temperature of the fiber, and rapidly cooled after a holding stage of 90 seconds. The resulting homocomposites have a tensile strength about twice higher than the non-reinforced PET processed under the same condition.
Morphology Development in Blends of Nanoclay, Polyamide 6, and Polypropylene Processed in a Chaotic Mixer
In this paper, we studied the effect of organically modified montmorillonite clay (OMMT) on morphology development in the mixing of polyamide 6 (PA6) and polypropylene (PP). The clay particles were initially present in the PP-phase. All morphological forms, e.g. lamella, fibrils, and droplets were seen as in blends without clay. Much finer PP-phase droplets were observed during breakup of the fibrils into droplets. The thread breakup studies revealed that the changed interfacial tension due to presence of clay was responsible for finer morphology. In addition, the clay particles in the PP-phase disrupted the break pattern of fibers and expedited fibril-droplet transition.
A Description of the Fluoroelastomer Coating Evolution as a Polymer Processing Aid
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.
Higher Performance Polyethylene Powders
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.
Study of the Interface Deformation when Gas Is Injected into Polymer Melt Flow Field
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.
High Scanning Rate DSC for the Characterization of Proteins
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.
New Developments in Micro-Compounding of Polymeric Materials
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.
Lifetime Prediction for Slow Crack Growth on Polyethylene Pipes for Gas Distribution
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.
Probing the Amorphous Structure of Semicrystalline PET by Positron Annihilation Life Time Spectroscopy
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.
Enhanced Structure CAE Solution with Molding Effect for Automotive Parts
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.
Significance of Creep Rupture and Stress Relaxation Data in Product Design and Material Suitability Evaluation
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.
Foaming of Nanoclay Reinforced PS/PMMA Polymer Blends
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.
Analysis of Pressure-Driven Disk-Flow Rheometry
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.
Effect of Heat Sealing Temperature on the Fracture Aspects of OPP/CPP Seal.
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.
Distribution of a Minor Solid Constituent in a Transfer Molded E – Pad Leadframe Package
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.
Combinatorial Compounding and High Throughput Screening
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.
Fibril Formation of Thermotropic Liquid Crystal Polymer and Polyester Blends by Controlling Viscosity Ratio
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.
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