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The influence of dissolved gases on the flow behavior of high and low density polyethylene melts was investigated using a capillary extrusion rheometer. Gases were introduced by decomposition of a blowing agent incorporated in the polymer. Data are presented in the form of flow curves (log shear stress vs. log apparent shear rate at the capillary wall), and the data treatment is justified by a continuum analysis which accounts for the change of specific volume of the polymer-gas solution during transit through the capillary. The results indicate the addition of gas in the amount of 0.5% by weight to both high and low density polyethylene melts causes a viscosity reduction of approximately 20% at constant shear rate. The view is taken that the gas increases the free volume available in the system, thereby lowering viscosity. An analysis is presented which indicates that Doolittle's viscosity-free volume equation can account for the viscosity reduction effected by the gas. The experimental observations also indicate that the flow curve discontinuity marking the onset of unstable flow of high density polyethylene is completely suppressed by the addition of gas at the 0.5%w level. This result is discussed in terms of the axial shear stress distribution in the capillary and the suppression of slip mechanisms occurring in the capillary owing to enhanced interpenetration of molecular chains across the slip interface.

Important challenges remain for sustainable design, manufacture, use, and recycling of electronics including materials selection and disassembly time. This paper examines the value relationship between the quantity of plastics separated and the time required for disassembly and segregation. Labor costs for disassembly can constitute a large portion of the total acquisition cost for a recycled material. We report work measurement studies conducted on the disassembly of 21 computers, 22 printers, and 32 monitors manufactured by 27 producers in the years from 1984 to 2001. Results include the weight per total separation time for each plastic part. Each recovered part is identified according to polymer resin using laser Raman spectroscopy by chemometric reference to a library of standards. We extrapolate time as well as the product input required to accumulate various specific types of plastic. We develop disassembly policies and show that they are effective for a variety of computer, printer, or monitor models, which is typical of the random product streams that arrive at electronics recycling facilities. The results demonstrate how new laser identification technology and work measurement can be used for plastics separation planning.

Photopolymers are attractive candidates for high-density holographic data storage because of their high sensitivity and refractive index contrast. We have incorporated several high-index organic monomers into high optical quality acrylate oligomer-based formulations. Using reactivity ratios, reaction kinetics, and component refractive indices as guidelines, a 6-fold increase in Δn has been achieved compared to an initial all-acrylate formulation. Samples prepared from these formulations have been used to write and read >200 high-quality holograms in a given volume of material. This is the first time a photopolymeric medium has successfully been used to multiplex this number of holograms. Using these resins, a protocol for the evaluation of photopolymers as holographic media has been developed.

Isothermal aging has been carried out on low-loss poly(methyl methacrylate) (PMMA) glass at 18°C below the glass transition temperature (Tg). The effect of enthalpy relaxation on light scattering loss of PMMA glass which had no excess scattering was investigated by the use of differential scanning calorimeter (DSC) and light scattering measurement. The light scattering intensity of PMMA glass did not increase with increasing aging time. It is seen that the light scattering loss of glassy PMMA is not affected inherently by physical aging as a result of its approach to thermodynamic equilibrium at a temperature 18°C below its Tg.

Easy-to-fabricate, low-loss optical fibers are described that consist of a pure fused silica core surrounded with a loosely fitting, extruded, FEP cladding tube. Because of their large numerical aperture (NA), these fibers are particularly well suited for the transmission of the incoherent light emitted by light-emitting diodes. Whereas the losses approached those of the core material for small angle excitation (i.e., 7.6 dB/km at 0.8 microm for a Suprasil 2 fiber of 230-m length), they increased to 14 dB/km for a steady-state NA of 0.3. The measured pulse dispersion of up to 30 nsec agrees well with the expected 24 nsec for a stepindex fiber with an NA of 0.3.

A novel type of molded polymeric resin-filled coupler has been built with the goal of making a low cost and manufacturable 1*N multimode optical coupler. The coupler consists of a low index thermoplastic molded cladding piece part containing an optically finished waveguide channel. The channel is covered with a flat lid of the same material and is filled with a high index resin to form a mode mixing waveguide. Optical fibers are inserted into both ends of the channel before it is filled to complete the pigtailed device. The design accomplished all required tasks with just two materials: the molded low index structural part which provides the waveguide cladding, and the high index waveguide core part which provides the adhesive to hold the fibers in place and the optial refractive index matching to reduce reflections. Two different material systems have been used to construct 1*23 couplers. Typical coupler excess losses are less than 2 dB, and the uniformity among all fibers is better than a 1 dB standard deviation. >

The fiber for the sensor is formed by cladding fused silica during drawing with polydimethyl siloxane into which an organic fluorescent dye, 9, 10-diphenylanthracene, has been dissolved. Upon side illumination at a wavelength within the excitation range of the dye, the cladding fluoresces; some of this fluorescence is coupled into guided modes in the fiber core through the evanescent fields of these modes. In the presence of oxygen, fluorescent emission by the dye is diminished. For the sensor described, the rubbery liquidlike nature of the polydimethyl siloxane cladding allows rapid diffusion of gases, and the intensity of the guided fluorescence is observed to drop by 30% in less than 5 s when the ambient atmosphere changes from pure nitrogen to pure oxygen. The advantages of this sensing technique, and some of the possibilities for new sensors based on this principle, are discussed. >

Millions of end-of-life electronic components are retired annually due to the proliferation of new models and their rapid obsolescence. The recovery of resources such as plastics from these goods requires their disassembly. The time required for each disassembly and its associated cost is defined by the operator's familiarity with the product design and its complexity. Since model proliferation serves to complicate an operator's learning curve, it is worthwhile to investigate the benefits to be gained in a disassembly operator's preplanning process. Effective disassembly process design demands the application of green engineering principles, such as those developed by Anastas and Zimmerman (Environ. Sci. Technol. 2003, 37, 94A-101A), which include regard for product complexity, structural commonality, separation energy, material value, and waste prevention. This paper introduces the concept of design symbols to help the operator more efficiently survey product complexity with respect to location and number of fasteners to remove a structure that is common to all electronics: the housing. With a sample of 71 different computers, printers, and monitors, we demonstrate that appropriate symbols reduce the total disassembly planning time by 13.2 min. Such an improvement could well make efficient the separation of plastic that would otherwise be destined for waste-to-energy or landfill. The symbolic methodology presented may also improve Design for Recycling and Design for Maintenance and Support.

Publisher Summary It is noted that optical fiber is considered as a key element in Optical Fiber Telecommunications (OFT). Fiber performance must go beyond simple low attenuation and exhibit critical characteristics for supporting the high speeds and long routes on terrestrial and undersea systems. At the same time, it is required that fiber for the metropolitan and access markets must meet demanding price points. For the traditional long-haul market, impairments such as dispersion slope and Polarization Mode Dispersion (PMD) are considered limiting factors. This chapter reviews the design criteria for a variety of fibers of current commercial interest. A variety of new low-cost fiber designs for the emerging metropolitan and access markets has been discussed in the chapter. The network chain, the design of multimode glass, and the plastic fiber for the highly cost-sensitive local area network market are also explored. Furthermore, the chapter summarizes the current research on hollow core and photonic bandgap fiber structures.

Plastic optical fiber (POF) has long been seen as a potential medium for implementing simple, very low cost optical links, but has not yet found significant application in data communication. In the near future, this situation is likely to change, as a new generation of POF with dramatically improved optical properties becomes commercially available. Unlike conventional POF, the new POF is based on amorphous perfluorinated polymers that are transparent in the near infrared. In order to develop useful fibers based on these new polymer materials, it has been necessary to better understand their fundamental optical properties, and to develop methods for manufacturing low-loss fiber. Since the available manufacturing methods typically result in graded-index POF's with very non-ideal index profiles, the possibility of severe bandwidth limitations has long been a concern. In addition, significant improvements in connection loss will be required to support high-speed systems. In this paper, we describe techniques that we and others have developed to eliminate or overcome these obstacles.

Polymer waveguide technology was exploited to build a photonic switch with enormous bandwidth capabilities at extremely low cost per path. The properties of polymer waveguides allowed the use of a low-cost multielement spatial light modulator in a guided wave application. A 6 x 6 ferroelectric liquid crystal array was used as a switching element to block or transmit light signals between input and output fibers. Visible laser diodes, plastic fibers, PIN detectors, and our proprietary polymeric mixing rod couplers were used to construct the switch. The polymeric fibers, couplers, and switching element allowed eliminating the need to time-division multiplex photonic channels through the switch because the optical paths were no longer costly. This, in turn, eliminated the electronic buffering and synchronization requirements of the switch. This is critical, because signals that can be buffered and synchronized can be switched electronically using GaAs cross-point arrays. Although data-transparent wavelength conversion is acceptable at the inputs and outputs of a photonic switch, buffering and synchronization are not acceptable for some applications. Our low cost polymer waveguide approach also eliminates the need for costly multi-GHz lasers when they are not needed on a per channel basis.

The flow and processing behavior of commercial plastics is determined not only by the characteristics of the base resin but also by the presence of additives of various kinds. In this study the influence of a number of additives on the rheological behavior of molten ABS was investigated using a capillary extrusion rheometer and a Weissenberg rheogoniometer. The additives studied included molding lubricants, rubber impact modifiers, flame-retardant additives, and residual unreacted components remaining from the polymerization process. The mechanisms by which these species affect flow characteristics are described.

Fiber spinning experiments were carried out with an α-methyl styrene/silicone block copolymer under various sets of spinning conditions. The behavior observed was very sensitive to the ambient axial temperature profile employed along the spinline and to the initial melt temperature at the die. By optimizing these parameters, very high draw ratios (>400 to 1) could be achieved. Under less optimum conditions, filament rupture and instabilities such as draw resonance, accompanied by periodic diameter and spinline tension fluctuations, were noted. Tensile stress and axial velocity gradient profiles were obtained along the spinline under a variety of spinning conditions. These profiles, together with an independent: rheological characterization of the polymer, provide insights into the mechanisms giving rise to the various types of behavior observed.

Etude par mesures de desorption. Influence de l'etat d'oxydation du polymere. La permeation n'est pas affectee par l'oxygene lie

Commercially available 25μm thick biaxially-oriented polyvinylidene fluoride (PVDF) film has been poled and investigated as a transducer material by evaluating its mechanical, dielectric, and piezoelectric properties in linear heating rate and isotheremal aging experiments was studied. The piezoelectric strain coefficints, d31 and d32, increase when the film is heatd at 0.5°C/min from 23°C to 150°C, but recover only about one-half their original values upon cooling to room temperature. In isothermal aging log d is linear is log time and between 60°C and 88°C the behavior is characterized by an activation energy of 1.2 eV.

The long term stability of biaxially-oriented poly(vinylidene fluoride) has been examined. In isothermal aging from a few minutes to a Few months, log e vs. time shifts between 6O°C at 88°C are characterized to have an activation energy of 1.2 eV. Data on uniaxial poled commercial film shows agreement with this result. Long term room temperature stability of pyroelectricity over a 10 year span augmented other elevated temperature data in supporting the conclusion that thermally activated processes should not be a factor in device reliability.

A new capillary rheometer incorporated in an instrumented transfer molding press has been developed. This rheometer is effective for determining the viscosity characteristics of thermoset molding compounds under both isothermal and typical molding conditions. In examples of the rheometer's utility, the power law indices of two commercial epoxy molding compounds have been determined to be approximately 0.7. Additionally it has been shown that preconditioning typical epoxy compounds at 47 percent relative humidity causes a viscosity decrease of about 40 percent owing to plasticization of the epoxy resin.

Ultraviolet radiation used for crosslinking prepolymer liquid coatings applied to optical fibers has been found to induce wavelength-dependent optical losses in fibers of certain core compositions. Germanium and phosphorous-doped cores are especially sensitive to radiation exposure and high NA (=0.36) germanium-phosphosilicate core fibers are far more sensitive than moderate NA (=0.23) fibers. The damage is believed to be associated with the formation of color centers in the doped glass network. Uncoated fibers given ultraviolet radiation doses equivalent to those encountered during coating operations exhibit added losses of several hundred dB/km in the near infrared region. Coated fibers of high NA exhibit much smaller, but still significant, added losses. The coating thus acts as a filter for short UV wavelengths which cause the most significant damage. Techniques are discussed for controlling the degree of radiation damage in these fibers.

The shear dependent viscosity and related properties of a number of ethylene polymers of differing molecular structure have been characterized using a capillary extrusion rheometer. The structural aspects of interest were average molecular weight, branching, and the presence of strong intermolecular secondary forces. It was found that average molecular weight influences the degree of shear dependence of the viscosity, branching affects both flow activation energy and the nature of the observed “melt fracture” phenomenon, and intermolecular hydrogen bonding enhances viscosity and activation energy and leads to increased shear dependence of flow behavior. The results are interpreted in terms of specific molecular mechanisms.

The discrete relaxation spectrum of an ABS (acrylonitrile–butadiene–styrene) polymer at 190°C. was calculated by using results from tensile relaxation moduli and the principle of reduced variables. The shift factor was found to conform well to the WLF equation, and the free volume fraction at Tg was calculated to be 0.026 in good agreement with the universal value. The values of the thermal expansion coefficient of free volume were calculated to be 9.8 X 10-4 deg.−1 and 7.0 × 10−4 deg.−1, respectively, from the WLF coefficients and from dilatometric results. The width of the entanglement plateau of the relaxation spectrum was observed to be a factor of approximately 2 larger than that calculated from molecular weights between entanglement couplings determined either from rubber elasticity theory or from an assumed molecular model which discounts the presence of the butadiene in the ABS system. By using Pao's theory, flow curves at 190°C. were calculated both from the discrete relaxation spectrum and from the dynamic modulus. These curves were essentially identical. However, the stress values of these curves were found to be about a decade higher than those experimentally determined from capillary flow measurements. Nevertheless, the shapes of the curves are in good agreement, and an explanation is suggested for existing discrepancies. Flow instability, processing variables, and residual strains are discussed in light of the flow curves and the calculated recoverable shear strains.

The capillary flow instability resulting in extrudate distortion has been studied for ethylene polymer melts using a molecular structure approach. It is found that the instability initiates at a critical value of elastic strain energy independent of (average) molecular weight for linear polyethylene. Once the flow breaks down, a slip interface within the melt is formed near the capillary wall, causing an abrupt increase in volumetric throughput. The velocity gradient within the melt remains continuous through the instability, however. Low molecular weight species present in the molecular weight distribution of linear polyethylene tend to suppress slip. Blends of linear and branched polyethylene exhibit instability behavior characteristic of both components throughout the entire range of composition. Results are discussed in terms of specific molecular mechanisms.

Measurement of the total normal thrust generated in steady torsional flow between parallel plates enables one to determine the normal stress quantity [P11−2P22+P33] as a function of shear rate γ for polymer melts. This measurement has been carried out for two linear polyethylene melts of different molecular weight using a modified Maxwell orthogonal rheometer. It is found that the normal stress curves have similar shape but are shifted from one another both horizontally along the γ axis and vertically. A strong correlation exists between [P11−2P22+P33](γ) and 2G′(ω), where G′(ω) is the dynamic storage modulus in shear, and the two quantities have identical molecular weight dependencies. The manner of treatment of normal stress data for polymer melts of differing molecular weights is explored, with particular regard to the application of the method of reduced variables. In addition, the predictive ability of the Springs four‐constant equation as regards normal stress behavior of polyethylene melts is di...

Relaxation times of polyethylene melts have been measured by Aloisio, Matsuoka, and Maxwell. One implication regarding their observations is that the elastic properties of polymer melts must be time-dependent. In particular, the steady-flow shear modulus depends on the strain rate. Some interpretations of data in the literature have been based on concepts in rubber elasticity where the steady-flow modulus is an equilibrium value, independent of strain rate. We have used Pao's theory for viscoelastic flow together with measurements of relaxation times to discuss the strain rate dependence of the steady-flow shear modulus of melts. The existence of a strain rate-dependent shear modulus leads naturally to a nonlinear relation between shear stress and recoverable shear strain. The conclusions regarding the molecular weight dependence of the modulus also differ from interpretations based on rubber elasticity.

An analysis of the Maxwell orthogonal rheometer for polymer melts is made by using the constitutive equation of White and Metzner. The results indicate that the shear deformation involved is oscillatory and that the storage and loss moduli of the melt may be derived from the measured stress response.

Studies of polymer morphology under ideal conditions approaching equilibrium structures have been shown to be valuable in the development of an understanding of the relationship of properties to structure. Practical fabrication operations do not permit the achievement of equilibrium structures in commercial products and its is therefore necessary to study the effects of processing on the actual structures that result. In addition, an understanding of the effects of processing variables on properties permits the development of fabrication operations which can be directed toward the improvement of properties. Topics covered include the effects of hydrostatic pressure during processing, effects of combinations of pressure and thermal history, relationships between thermal history and crystallization rates in isotactic polymers and the kinetic and morphological effects of flow deformation on crystallizable plastics.

The viscosity of carboxylic‐acid‐terminated polybutadiene increases markedly upon neutralization with mono‐ and divalent bases. These viscosity increases are related to apparent molecular weight, considering the association of the terminal salts as ``polymerizing'' the difunctional prepolymer. For the monovalent alkali‐metal salts, simple end‐group dimerization seems to occur with an average ΔH of ∼−25 kcal/mole. Neutralization with ions of higher valency leads to materials with higher viscosities.

We compare experimental results for tube flow of polymer melts with those computed from Pao's theory. We further present a correlation scheme for the behavior of bulk polymer melts in steady flow and dynamic oscillatory experiments. The correlation is not limited to low shear rates, but is theoretically valid for all frequencies and shear rates. The steady flow shear viscosity is expected to equal or exceed the dynamic viscosity at all frequencies and shear rates. Similarly, the correlation predicts that G exceeds or equals G′ over the entire frequency range. At low shear rates τ12 should correlate with G″ and P11−P22 is given by 2G′. Limited agreement between the experimental results and computed curves for tube flow is observed. The correlation scheme appears to represent the behavior of certain polymer solutions very well but quantitative agreement is not obtained for a linear polyethylene melt. We propose that changes in the relaxation spectrum of the polymer melt subjected to steady shearing can acco...

The capacity of loop transmission systems, such as local area networks (LAN), can be increased by using closed loops of high-bandwidth optical fibers. Since fiber loop lengths are relatively short, it is not crucial to use low-loss fibers. However, the ability to couple information into and out of the fiber loop at arbitrary points along the loop poses a major problem. Current procedures use fiber-optic directional couplers which have to be spliced into the loop,1,2 requiring breaking the loop at prearranged locations and increasing the downtime of the LAN.

A new technique for making optical mixing rod splitters and combiners using plastic materials to form a waveguide-type mixing region has been developed. The resulting devices are somewhat simpler than other previously reported devices.1,2

The fiber drawing and coating process plays an important role in the attainment of high-performance properties of optical fibers. Crucial steps in the process include preform surface preparation and handling, preform heating and drawing, fiber diameter measurement and control, and coating application.

Plastic-clad silica (PCS) fibers having a rubbery silicone cladding offer a distinct advantage for chemical sensing applications in that small molecule chemical species will diffuse through the cladding very rapidly. If a dye is incorporated in the silicone which is altered in color by a chemical of interest, the dye will be affected throughout the silicone volume. Further, because the evanescent tail of the light energy propagating in the fiber core extends into the cladding where it interacts with the dye, the absorption loss spectrum of the fiber is altered by the presence of the dye and by any color changes which it undergoes. The fiber thus represents a distributed chemical sensor in that absorption loss changes which occur anywhere along its length may be detected.

The evanescent field of light propagating in an optical fiber core extends into the cladding; this can cause the optical absorbance of the cladding to affect the transmission loss of the fiber itself. The fact that the evanescent fields of propagating modes in the fiber extend into the cladding also means that the inverse effect is possible: light generated in the cladding can be coupled to guided modes and transmitted over long distances. This work describes a fluorescence-based distributed oxygen sensor which makes use of this process.

Observations were conducted over uniform, exceptionally flat farm land in Illinois during clear weather in July, 1983. Scintillation data were obtained at 116.30 and 172.91 GHz for a path 1.4 km long. Rigorous micrometeorological measurements, some of them path averaging, were made along the path. The results of these tests will be described.

During the past decade, significant advances have been made in the drawing and coating of glass fiber lightguides for use in telecommunications systems. This progress has been the result of contributions from numerous investigators that have added to the legacy of an ancient art as described in a recent review.1 Lightguides for telecommunications differ from other types of glass fiber by exhibiting a combination of unique properties. Critical among these are low loss, low dispersion, dimensional precision, coating uniformity, high strength, and long lengths, all of which are dependent in part, and sometimes entirely, on the drawing process. Techniques and facilities for drawing lightguides differ also from those of other glass fibers. What was once a relatively simple process of drawing a glass into a fiber has become increasingly complex when applied to current designs and applications for lightguides.

Electronics recyclers strive to increase their revenues by balancing the recycling costs of disassembly, shredding, and materials separation against returns from the sale of value added products. While many studies exist that help to clarify the metals and glass recycling potential from end-of-life electronics, much less is known from quantitative models about the optimal disassembly and separation of other materials such as plastics from personal computers. In this paper, the value relationship is examined between the time required for disassembly and segregation with and without the proposed symbolic methodology. Labor costs for disassembly can contribute substantially to the total cost of recovered material. We seek to answer the question: how can the extended supply chain label a large variety of products to reduce the exploration and familiarization activity time prior to disassembly. Work measurement studies were conducted on the disassembly of seventeen computers manufactured by nine producers from 1986 to 1998. The improvement in the initial disassembly processing time with symbolic methodology is examined.