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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A Technique for Absolute Biaxial Birefringence Measurements and its Applications
In this study, we discuss the applications of a birefringence technique for on-line or off-line quantitative measurement of biaxial orientation in transparent films, sheets, bottles, etc. Absolute values of biaxial birefringence are measured in two directions using a technique based on an incident multi-wavelength double beam and a photodiode array assembly, combined with in-house developed software. Both machine and transverse direction birefringences (relative to the normal direction) are measured simultaneously. Film and sheet of different thicknesses were tested and birefringence values from 0.0005 to 0.25 were measured. The technique was tested on different materials and under different conditions and its applications, particularly for online monitoring of biaxial orientation processes, are discussed.
Processing of Intractable Polymers Using High-Pressure Carbon Dioxide.
A modified extrusion system is used to process a variety of polymers (HDPE, LDPE, FEP, PTFE, s-PS) in the presence of high-pressure CO2. The extruder’s design includes a modified feed section that allows a given mass of polymer to interact with CO2 prior to the extrusion process. This alternative design provides a new and easy route to melt process high melt viscosity polymers of commercial importance such as PTFE, FEP and s-PS. The inherent shear mixing and the presence of CO2 allow for a specific control over the extrudate morphology. Some of the relevant parameters in the process are analyzed and related to the nucleation and plasticization effects brought about by the presence of CO2.
Prediction of the Melting Temperature of Polymers
A generalized equation is introduced to clarify conceptual definitions of copolymer melting temperatures. This treatment incorporates the effects of comonomer volume, crystal length, folding surface free energy and enthalpy of fusion, when comonomers are excluded from the crystallite lattice. Both the Gibbs- Thomson Equation for homopolymers and a modified application to copolymers have also been derived from the proposed equation as two special cases. The equation satisfactorily evaluates the melting temperatures of linear polyethylene homopolymers (including paraffins) and various ?-alkene-ethylene copolymers.
The Effect of Shear-Induced Migration of Conductive Fillers on Conductivity of Injection Molded Articles
Conductive filler particles tend to migrate in nonuniform shear fields such as during mold filling from the regions of high shear stress to low shear stress leading to the loss of conductivity in polymeric articles. In this work, the effect of conductive filler migration on surface and volume conductivity was investigated in conductive compounds of polystyrene and polypropylene and carbon black. Injection molded articles with mean particle concentration of ?c and 3.5?c, where ?c is the percolation threshold, showed volume conductivity values of respectively 10-18 and 10-4 S-cm, while compression molded specimens with same composition offered volume conductivity of 10-4 S-cm. Removal of surface layers from injection molded specimens by excimer laser ablation technique restored the conductivity to 10-4 S-cm. The extent of migration was evaluated in terms of the thickness of polymer layers removed from the surface, which depended on the type of polymer used.
UV Degradation of Recycled Photo-Degraded Polymers
The ultraviolet (UV) degradation of molded bars containing recycled polymer has been studied to determine whether products of photo-degradation act as pro-degradants. Recyclate that had been photo-degraded prior to recycling was mixed with virgin granules to mold new bars. Bars were also prepared from a mixture of virgin polymer with recyclate that had not been photo-degraded.Bars made from blends of virgin and recycled polymer were photo-degraded in the laboratory. For exposures of less than a month, the mechanical properties of both polystyrene and polypropylene were inferior when previously photo-degraded material was included. After extended exposure, the effect of including photo-degraded material diminished but by this time, the properties of the materials were unacceptable.
Polymer/Clay Nanocomposite Foams Prepared by CO2
Polymeric foams are widely used in many applications. In this study, we prepared polymer/clay nanocomposite foams using carbon dioxide as the foaming agent. The effect of clay dispersion (intercalation vs. exfoliation), clay concentration and types of polymers on foam morphology were investigated. It was found that clay nanoparticles serve as an efficient nucleation agent. The nucleation efficiency is affected by both clay dispersion and polymer-clay-CO2 interaction. By controlling nanocomposite composition and foaming conditions, PMMA nanocomposite foams with cell size as small as ~0.4 ?m and cell density as high as ~1012 cells/cc can be produced. These foams exhibit good combination of stiffness, toughness, weight saving and dimension stability. In addition, PLGA nanocomposites foams were also prepared and they can be used for tissue engineering scaffolds.
Copolycarbonate of Bis-Phenol A and 4,4'-Dihydroxydiphenyl
In comparison to a bisphenol A polycarbonate, a copolycarbonate of bisphenol A and 4, 4’- dihydroxydiphenyl has a higher birefringence, higher heat-distortion temperature (HDT), better resistance to boiling water and ASTM Reference Fuel C, higher notched Izod impact strength at thick section and low temperatures, and better resistance to embrittlement after heat aging.The high birefringence and HDT as well as the better resistance to boiling water and Reference Fuel C of the copolycarbonate are attributed to the linearity and rigidity of the diphenylene unit in the copolycarbonate chains. In contrast, its outstanding impact strength under a variety of test conditions is attributed to its propensity to shear yield due to the low rotational-energy barriers of the phenylene rings around the axis of “inter-ring” C-C bonds in the diphenylene units.
Mechanochemical Devulcanisation of Unfilled SBR Vulcanisates
The feasibility of the mechanochemical process for devulcanisation of model sulphur-cured unfilled SBR vulcanisates was investigated. The effect of mechanochemical devulcanisation on crosslink density and gel content of vulcanised SBR was measured using swelling methods. The devulcanised SBR samples were revulcanised utilising the same recipe and curing conditions as used for the virgin compound. The cure characteristics and mechanical properties of the devulcanised SBR were compared with those obtained for vulcanised SBR. It was found that the devulcanisation resulted in a significant decrease in the crosslink density and the gel content. The cure characteristics of devulcanised samples differed from those of the vulcanised samples. The stress-strain results for the revulcanised vulcanisates were comparable to that of vulcanised SBR.
Anionic Copolymerization of Lauryl Lactam and Polycaprolactone to Produce Polyesteramide Tri-Block Copolymer
This paper examines the anionic polymerization of lauryl lactam to polyamide12 and copolymerization of lauryl lactam with a diisocyanate end capped polycaprolactone to produce a polyester amide block copolymer. The molecular weights of polyester polyols used in the preparation of diisocyanate end capped polycaprolactone are varied in this study.The products were characterized by Fourier Transform Infrared Spectrum (FTIR), Differential Scanning Calorimeter (DSC), mechanical properties were measured in a Instron mechanical tester. The influence of the molecular weight of polyol was considered.
Relationship between Structure and Properties of PBT Injection Moldings in the Thickness Direction
Poly(butylene terephthalate) injection moldings have definite skin-core morphology because of the rapid rate of crystallization. In this study, in order to investigate the relationship between structure and properties of PBT injection moldings in the thickness direction, specimens were sliced. Then, tensile properties and microstructure were studied. It was obvious that necking starts at high strain region with increasing depth from surface, and the decrease of tensile modulus and yield stress near the surface mainly depends not on the orientation but on the crystallinity.
Morphological and Mechanical Evaluation of Hybrid Organic/Inorganic Thermoset Copolymers of Dicyclopentadiene and Polyhedral Oligomeric Silsesquioxane
A new class of organic/inorganic hybrid thermoset copolymers have been by prepared by ring opening metathesis polymerization (ROMP) catalyzed with bis(tricyclohexylphosphine)ruthenium dichloride. Dicyclopentadiene (DCPD) and norborylene-substituted polyhedral oligomeric silsesquioxane (POSS) with isobutyl pendent groups have been copolymerized at 60 °C over a range of POSS concentrations. The X-ray structure of the copolymers shows small aggregates of POSS at higher concentrations with uniform dispersion below 10 wt % POSS. These copolymers exhibit a decrease in Tg from128 °C for PDCPD to 114 °C with the addition of 20 % wt POSS. The stiffness, in tension and compression, is decreases with increasing POSS concentration. Additionally, the incorporation of POSS changes the fracture mechanism from shear banding or ductile to brittle failure and is accompanied by a decrease in the fracture toughness of the copolymers.
Characterization of Polymer Resins Produced by Melt Disentanglement
Disentangled polymers (PC, PET) were produced by a patented technology of viscosity reduction by melt disentanglement described elsewhere. The new process generates pellets from original ones supplied by the resin manufacturers, after the melt has passed through a succession of treatment stations designed to reduce their viscosity by a combined effect of shear and extensional force under vibration. In order to understand the characteristic differences between the disentangled resins and the original ones, we submitted the resins to a variety of tests.We show that disentangled resins, produced by melt disentanglement, exhibit novel properties consistent with the fact that they are, indeed, disentangled, ant that the changes depend on their level of disentanglement. In particular, disentangled polymer resins show a higher fluidity, and therefore better processability, when remelted, a lower density at room temperature, a greater gas permeability, and have less Internal Energy, as determined by DSC. For semi-crystalline polymers, both the crystallinity percent and the rate of crystallization are interactively affected by the state of disentanglement of the melt. Benefits will be discussed in the paper and at the conference.
The Effect of Surface Tension and Contact Angle on the Filling Behavior of Flip-Chip Underfill Dispensing Process
In this work, the capillary flow, which is influenced by the surface tension of encapsulant and the contact angle among encapsulant, bumps and substrate of dispensing process for flip chip underfill would be discussed by the theoretical and numerical analysis. The velocity field, melt-front shape and melt-front position are solved using a method base on 3D Collocated Cell-Centered Finite Volume Method. Most of the past studies neglected the dynamic contact angle of encapsulant and the influence of bumps. By applying different dynamic contact angle model parameters, we found that the contact angle changes during flow will influence the flow time greatly. By applying different boundary conditions at bump walls, we found that bump will influence both the flow time and the melt-front. Consequently, the influence of dynamic contact angle and bumps shall not be neglected. By applying suitable model parameters and wall boundary conditions, the flow behavior of Flip-Chip encapsulation is simulated correctly in this work.
Effects of Spinning and Process Conditions on Appearance and Diameter of Electrospun Polyamide-6 Nanofibers
In this work, polyamide-6 in formic acid was used to study the effects of various spinning and process conditions on the appearance and diameter of the ultrafine, electrospun fibers obtained. These influencing conditions include concentration of the solutions, molecular weight of polyamide-6, polarity and level of the applied electrostatic field, and nozzle-to-collector distance. The resulting polyamide-6 fibers were characterized for their appearance and diameter, using scanning electron microscopy (SEM) technique. It was found that the fiber diameter was in the range of 60 to 300 nm. Interestingly, flat fibers were observed when negative electrostatic field was applied on polyamide-6 solutions of high viscosity.
Structure Development during Uniaxial Deformation of PEN Using Real Time Spectral Birefringence Technique
During uniaxial deformation of amorphous PEN poly (ethylene 2,6 naphthalate) films, necking is developed even at rubbery temperatures above the glass transition temperature. To elucidate the structural changes occurring during neck formation and further strain hardening, a real time spectral birefringence technique together with a true stress / true strain measurement technique is applied. These techniques are able to track the changes in birefringence and stress levels as the film is being deformed. The results obtained by these two techniques permit determination of the stress optical constant and the limits at which it starts deviating from the linear behavior as well as large deformation behavior. Further investigation by X-ray and DSC measurements helps to understand and clarify the structure developed during the deformation process of the material.
Effect of Rolling Process on the Uniformity of Extended PTFE
Polytetrafluoroethylene (PTFE) is a remarkable material having a high melting temperature, high chemical resistance, low frictional and dielectric coefficients, etc. Due to its high melting point, PTFE cannot be manufactured by using the conventional polymer process, such as the injection molding, extrusion and blow molding, etc. In this research, PTFE powder–lubricant mixture were carefully prepared and followed by a series of techniques including paste extrusion, rolling and calendering. Effect of rolling behavior on laminated PTFE film was investigated. PTFE were laminated with combination layers of different initial rolling orientations varying from 0 degree, 45 degree to 90 degree in consequent layers. It was found that the rolling direction in each laminate layer affects the pore size of the final extended PTFE film significantly. It was also found that laminate with different combination in rolling direction would influence the characteristics of paste flow and the associated rolling pressure. The deformation on PTFE film with 0 degree laminate was serious. The final pores extend in both vertical and parallel to the rolling direction for the laminated film with 90 degree rolling direction difference in each layer. The laminated PTFE film with laminate 45 degree achieves most uniform distribution of pores.
Effects of Morphology on the Tribological Behavior of Thermoplastics in Sliding Contact
An industry demand for plastic parts that have to withstand tibological stress is to optimize the part performance with respect to friction and wear behavior. By varying the processing conditions during molding formation, the morphology of the part’s surface can be affected significantly. This is essential for the lifetime, e.g. of a plastic gear of bearing. Therefore, an optimum can only be achieved, when the processing is carried out at appropriate conditions. Polyamide-66 as well as two polyoxymethylenes were employed as model materials. The effect of the morphology settings on the tribological behavior of plastic specimens in sliding contact was investigated, and the relationships between tribological and mechanical parameters and the morphology as well as the crystallinity were described.
Plastics Part Design: Low Cycle Fatigue Strength of Glass-Fiber Reinforced Polyethylene Terephthalate (PET)
This paper summarizes our extensive investigation on the low cycle (up to Nf = 5x104, where Nf is the number of cycles to failure) fatigue behavior of short glass-fiber reinforced poly(ethylene, terephthalate), or PET, thermoplastic. The modes of fatigue test include tensiontension, compression-compression, four-point bending (flexural) -- all at frequency f = 1-3 Hz, and flexural fatigue at f = 30 Hz (ASTM D-671). All tests were stresscontrolled with stress ratio R = Smin/Smax = 0.1, except for flexural fatigue at f = 30 Hz where stress ratio R = -1. The fracture surfaces of tested specimens were analyzed using scanning electronic microscopy (SEM).The results from this investigation provide comprehensive, up-to-date information and recommendations concerning methods for fatigue testing of injection molded specimens and models, prediction and optimization of low cycle fatigue properties that play a key role in determining a highly stressed plastic parts life and enduse performance, pre-selection of PET based plastic for various industrial applications.
Production of Thick Microcellular Thermoplastic Sheets
Microcellular foams have largely been explored for thin – sheet applications, with thickness on the order of 1 mm. In this study, the basic batch microcellular process is scaled up to produce thick flat sheets, in the 3 – 15 mm range, from a number of thermoplastics such as PMMA, PS and ABS. It is shown that an unfoamed integral skin of desired thickness can be produced, making it possible to create sandwich structures with a microcellular core and a solid skin. It is hoped that these materials will open up the use of microcellular foams in load bearing applications, and as novel materials for construction.
Fundamental Study of Thermoplastic Foam Structure and Properties
This paper presents “cube” cell modeling development to investigate PE foam compression modulus as a function of material distribution between strut and cell wall, and open cell contents. The model shows that compression has a stronger dependency on cell wall stretch than strut strength. As a result, open cell becomes a critical factor for compression strength. PE foam samples with various degrees of open cell were made. Compressive strength is measured. Modeling results show greatly improved agreement to experimental data by considering the stretch of cell walls and bending of struts parallel to compressive force.
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