DuPont (Canada)

Mechanistic models for ethylene copolymerization with Ziegler–Natta catalysts contain many kinetic rate constants. Precise estimates of key parameters are required if the models are to be used to obtain reliable predictions of polymer properties for a specified catalyst over a range of polymerization conditions. In this paper, a novel method is developed to assist modelers in assessing whether their model parameters will be estimable from existing or proposed experimental data, and in determining subsets of influential parameters that can be estimated from the data when the complete set of model parameters cannot be estimated. The effects of using different types of data, varying the number of observations per experimental run, and increasing the number of experimental runs on the number of estimable parameters are considered. A method for comparison of the relative effectiveness of different experimental designs for estimating key parameters in gas‐phase ethylene copolymerization is also presented.

High throughput genotyping, phenotyping, and envirotyping applied within plant breeding multienvironment trials (METs) provide the data foundations for selection and tackling genotype × environment interactions (GEIs) through whole‐genome prediction (WGP). Crop growth models (CGM) can be used to enable predictions for yield and other traits for different genotypes and environments within a MET if genetic variation for the influential traits and their responses to environmental variation can be incorporated into the CGM framework. Furthermore, such CGMs can be integrated with WGP to enable whole‐genome prediction with crop growth models (CGM‐WGP) through use of computational methods such as approximate Bayesian computation. We previously used simulated data sets to demonstrate proof of concept for application of the CGM‐WGP methodology to plant breeding METs. Here the CGM‐WGP methodology is applied to an empirical maize ( Zea mays L.) drought MET data set to evaluate the steps involved in reduction to practice. Positive prediction accuracy was achieved for hybrid grain yield in two drought environments for a sample of doubled haploids (DHs) from a cross. This was achieved by including genetic variation for five component traits into the CGM to enable the CGM‐WGP methodology. The five component traits were a priori considered to be important for yield variation among the maize hybrids in the two target drought environments included in the MET. Here, we discuss lessons learned while applying the CGM‐WGP methodology to the empirical data set. We also identify areas for further research to improve prediction accuracy and to advance the CGM‐WGP for a broader range of situations relevant to plant breeding.

This article deals with an inventory problem where the supply is available only during an interval of (random) length X. The unavailability of supply lasts for a random duration Y. Using concepts from renewal theory, we construct an objective function (average cost/time) in terms of the order-quantity decision variable Q. We develop the individual cost components as order, holding, and shortage costs after introducing two important random variables. Due to the complexity of the objective function when X and Y are general random variables, we discuss two special cases and provide numerical examples with sensitivity analysis on the cost and noncost parameters. The article concludes with a discussion of the comparison of the current model with random yield and random lead-time models. Suggestions for further research are also provided.

Abstract During the last 30 years the plastics industry has experienced enormous rates of growth. Due to an increasing demand for high performance plastic materials, the use of extruders as continuous flow reactors for polymers has attracted considerable attention in polymerization and polymer modification applications. This paper is an attempt to present a survey of recent literature on the reactive extrusion of polymers. Experimental and modeling studies for various polymer systems are reviewed and some rheological, modeling, and design aspects of reactive extrusion systems are addressed.

Abstract Over the past four years, we have been developing an in situ surfactant‐washing method to decontaminate soil systems. This study addresses another major step in that development: a field test of the surfactant‐washing method at a site contaminated with polychlorinated biphenyls (PCBs) and oils. A test plot, 10‐ft diameter by 5‐ft deep, was selected in an area of high levels of contaminataion. The study involved applying a surfactant solution on the plot to wash the site material and carry the leachate down to the depressed water table, where it was collected by pumping a recovery well installed through the center of the plot. The leachate pumped to the surface was biotreated to degrade the oils and surfactant, and the PCBs were removed from the leachate by an activated carbon system. Soil cores from the test plot indicated concentrations of up to 6,223 mg/kg PCBs and 67,000 mg/kg oils. The test plot initially contained about 15 kg of PCBs and 157 kg of oils. The hydraulic response of the test plot to washing was monitored by measuring the water levels in wells around the test plot and the fluid pressure and saturation through the plot. These real‐time data were used to adjust the surfactant‐application rate to minimize lateral spread of the surfactant and leachate and the pumping rate to capture all the leachate by the recovery well. The response of contaminant concentrations in the test plot to washing and the performance of the leachate‐treatment system were also monitored during the test by collecting and analyzing samples from the recovery well and from the treatment system. An on‐site laboratory was used for these analyses. During the 70 days of the washing test, 5,375 gallons of a 0.75% aqueous surfactant solution was applied on the test plot at an average rate of 77 gal/day. During the same period, 10,981 gallons of leachate were recovered at an average rate of 157 gal/day. A total of 1.6 kg of PCBs and 16.9 kg of oils (about 10% of the initial mass) was washed from the test plot during the test. Maximum concentrations of 65 mg/1 PCBs and 709 mg/1 oils were measured in leachate samples. The leachate was adequately treated before it was discharged. These test results indicate that in situ surfactant washing is a promising candidate for the remediation of contaminated soil systems.

This 2023 Clinical Practice Guideline provides the biomedical definition of death based on permanent cessation of brain function that applies to all persons, as well as recommendations for death determination by circulatory criteria for potential organ donors and death determination by neurologic criteria for all mechanically ventilated patients regardless of organ donation potential. This Guideline is endorsed by the Canadian Critical Care Society, the Canadian Medical Association, the Canadian Association of Critical Care Nurses, Canadian Anesthesiologists' Society, the Canadian Neurological Sciences Federation (representing the Canadian Neurological Society, Canadian Neurosurgical Society, Canadian Society of Clinical Neurophysiologists, Canadian Association of Child Neurology, Canadian Society of Neuroradiology, and Canadian Stroke Consortium), Canadian Blood Services, the Canadian Donation and Transplantation Research Program, the Canadian Association of Emergency Physicians, the Nurse Practitioners Association of Canada, and the Canadian Cardiovascular Critical Care Society.

Abstract Previous work in the field of salt effect in vapor‐liquid equilibrium and the theory involved are reviewed briefly. Vapor‐liquid equilibrium data at atmospheric pressure are reported for the systems methanol‐water, ethanol‐water, and n‐propanol‐water, each saturated with a variety of common inorganic salts. A simple equation is proposed for the representation of salt effect. An attempt is made to ascertain the theoretical significance of this equation, and in so doing, to relate salt effect in vapor‐liquid equilibrium to the properties of the system components.

Abstract This paper presents a review of the mathematical modeling of two types of polymer electrolyte membrane fuel cells: hydrogen fuel cells and direct methanol fuel cells. Models of single cells are described as well as models of entire fuel cell stacks. Methods for obtaining model parameters are briefly summarized, as well as the numerical techniques used to solve the model equations. Effective models have been developed to describe the fundamental electrochemical and transport phenomena occurring in the diffusion layers, catalyst layers, and membrane. More research is required to develop models that are validated using experimental data, and models that can account for complex two‐phase flows of liquids and gases.

Abstract The carbon‐13 spin‐lattice relaxation times T 1 of the crystalline portion of a set of polyethylenes have been studied. Chain structure and crystallization conditions have been varied over the widest possible extremes so that large differences are developed in the level of crystallinity, the supermolecular structure, and the crystallite thickness. Concomitantly, the observed crystalline T 1 values cover the extraordinarily wide range of about 40–4500 s. They bear a one‐to‐one relation with the crystallite thickness, which is found to be the key structural variable determining this property. A correlation with the temperature for the α‐transition can be established, which implies a similar type of segmental motions for the two phenomena. Major changes in the interfacial structure can also have a drastic influence on the value for the crystalline T 1 . Analysis of the magnetization decay curve also allows for a quantitative determination of the degree of crystallinity, which is found to be in excellent agreement with the corresponding value found from Raman spectroscopy.

A new seismic hazard model, the fourth national model for Canada, has been devised by the Geological Survey of Canada to update Canada's current (1985) seismic hazard maps. The model incorporates new knowledge from recent earthquakes (both Canadian and foreign), new strong ground motion relations to describe how shaking varies with magnitude and distance, the newly recognized hazard from Cascadia subduction earthquakes, and a more systematic approach to reference site conditions. Other new innovations are hazard computation at the 2% in 50 year probability level, the use of the median ground motions, the presentation of results as uniform hazard spectra, and the explicit incorporation of uncertainty via a logic-tree approach. These new results provide a more reliable basis for characterizing seismic hazard across Canada and have been approved by the Canadian National Committee on Earthquake Engineering (CANCEE) as the basis of the seismic loads in the proposed 2005 edition of the National Building Code of Canada.Key words: seismic hazard, earthquake, probability, uniform hazard spectrum, maps, Cascadia subduction, strong ground motions, uncertainty, CANCEE, National Building Code of Canada.

Abstract Maleic anhydride was grafted to the linear hydrocarbon, n ‐eicosane, at 165°C in the presence of the free radical initiator, 2,5‐dimethyl‐2,5‐di( t ‐butylperoxy)‐3‐hexyne. The anhydride has a low solubility in eicosane and a multiple addition procedure was adopted. Grafted product which separated from the reaction mixture was fractionated and analyzed. The fractions contained on average 2–5.5 anhydride units/eicosane residue. 1 H‐ and 13 C‐NMR studies show that the grafts consist of single succinic anhydride rings. At the concentrations of maleic anhydride chosen for homogeneous reaction ( < 0.02 M ) and at 165°C, poly(maleic anhydride) is above its ceiling temperature, so that succinic anhydride radicals cannot add maleic anhydride to form polymer side chains. Instead, these radicals abstract hydrogen atoms to yield grafts consisting of single anhydride units.

Abstract The morphology and impact properties of polystyrene‐maleic anhydride/bromobutyl rubber blends have been studied as a function of interfacial modification and melt processing conditions. It is found that dimethylaminoethanol (DMAE) serves as a reactive compatibilizing agent for these blends and that the addition of DMAE results in a five‐fold reduction In the size of the dispersed phase. Evidence for covalent bond formation between the DMAE and the elastomer and reactive polystyrene phases is presented. The volume average diameter of the minor phase increases significantly as the screw rotation speed and the material throughput increase. In fact, control of various material and processing parameters can be used to effectively control the particle size distribution during compounding. Impact strength measurements are shown to be clearly dependent on the quantity of DMAE in the system as well as the concentration of elastomer. Saturation of the interface with DMAE is shown to be an important consideration.

Abstract Thermodynamic properties of dense gaseous and liquid argon are calculated using perturbation theory based on the hard-sphere potential, together with an accurately determined pair potential function and the triple-dipole dispersion three-body interaction. The first-order contribution of the three-body interaction is calculated both by a Monte Carlo method and by the use of the superposition approximation for the three-body distribution function, with good agreement. Monte Carlo estimates are also found for second-order contributions of the three-body interactions, which prove to be small. Agreement with experiment is excellent at high temperatures and good at low temperatures. Slight discrepancies at low temperatures are probably due partly to the use of the ‘local compressibility’ approximation and perhaps partly to slight uncertainty in the pair potential in the neighbourhood of its zero. This work has been supported in part by grants from the U.S. Department of the Interior, Office of Saline Water, and the National Research Council of Canada. This work has been supported in part by grants from the U.S. Department of the Interior, Office of Saline Water, and the National Research Council of Canada. Notes This work has been supported in part by grants from the U.S. Department of the Interior, Office of Saline Water, and the National Research Council of Canada. Additional informationNotes on contributorsD. Henderson Alfred P. Sloan Foundation Fellow.

Abstract The impact on ground water quality from increasing fertilizer application rates over the past 40 years is evaluated within a glacial aquifer system beneath a thick unsaturated zone. Ground water ages within the aquifer could not be accurately determined from the measured distribution of 3 H and as a result, chlorofluorocarbon (CFC) and 3 H/ 3 He dating techniques were applied. Beneath a 25 m thick unsaturated zone, ground water ages based on CFC‐11 concentrations were greater than 3 H/ 3 He ground water ages by 6 to 10 years, due to the time lag associated with the diffusion of CFCs through the unsaturated zone. Using the corrected CFC‐11 and 3 H/ 3 He ground water ages and the estimated travel time of 3H within the unsaturated zone, the approximate position of ground water recharged since the mid‐1960s was determined. Nitrate concentrations within post mid‐1960s recharge were generally elevated and near or above the drinking water limit of 10 mg‐N/L. In comparison, pre mid‐1960s recharge had nitrate concentrations <2.5 mg‐N/L. The elevated NO 3 − concentrations in post mid‐1960s recharge are attributed mainly to increasing fertilizer application rates between 1970 and the mid‐ to late 1980s. Anaerobic conditions suitable for denitrifkation are present within pre mid‐1960s recharge indicating that removal of DO is a slow process taking tens of years. Over the next 10 to 20 years, nitrate concentrations at municipal well fields that are currently capturing aerobic ground water recharged near the mid‐1960s are expected to increase because of the higher fertilizer application rates beginning in the 1970s and 1980s.

Acrylic copolymers produced via high-temperature solution polymerization are the base resin component for many automotive coatings. These polymers are often manufactured using a semibatch starved-feed reactor policy in order to tightly control copolymer composition and molecular weight. The combination of high temperature and low monomer concentration greatly promotes the importance of secondary reactions, causing observed conversion and molecular weight profiles to deviate significantly from those predicted by classic free radical kinetics. Although the effects of methacrylate depropagation and acrylate branching and scission have been studied during the homopolymerizations of butyl methacrylate and butyl acrylate, there is little knowledge as to how these mechanisms interact during copolymerization. In this work, we experimentally investigate the effect of monomer feed ratio on molecular weight and conversion profiles for high-temperature semibatch solution copolymerization of butyl methacrylate and butyl acrylate. A mechanistic model, constructed and implemented in Predici, provides a good fit to the experimental data set without any tuning of kinetic coefficients or other parameters.

The low temperature modifications of the normal paraffins n-C n H 2n+2 crystallize in three groups (Broadhurst, 1962). The structure is triclinic for n even, 6 < n < 26 (Muller and Lonsdale, 1948; Nyburg and Luth, 1972); orthorhombic for n odd, 11 < n < 39 (Smith, 1953; Teare, 1959); and monoclinic for n even, 28 < n < 36 (Shearer and Vand, 1956). In all of these structures the hydrocarbon chains are linear and in trans configuration. The chains are parallel to one another, the terminal methyl groups forming the surfaces of lamella which are more or less perpendicular to the chain axis. For n < ca.36, it is apparently the interlamellar interaction between end methyl groups which dictates the symmetry. For longer chains the structure is usually orthorhombic and comparable to the structure of highly crystalline polyethylenes. Chains do not fold (as they undoubtedly do in polyethylenes) unless n is greater than 102 (Bidd and Whiting, 1985; Ungar and Keller, 1986). The several crystal forms differ in the manner in which the nearest neighbor chains are related to one another. In the triclinic lattices the packing is such that a triclinic sublattice containing one methylene group is evident. In the other modifications the sublattice is orthorhombic and contains four methylene groups. If the overall symmetry is orthorhombic the long chain axes are perpendicular to the interlamellar surface; the x and y translations, perpendicular to the long axis, are common to both cells. If the nearest neighbor chains are displaced by two or four methylene groups along the chain axis, overall monoclinic symmetry results (Sullivan and Weeks (1970)).

Click to increase image sizeClick to decrease image size ACKNOWLEDGMENTS We are grateful to DuPont Canada, Incorporated, and to the Natural Sciences and Engineering Research Council of Canada (NSERC) for supporting this work.

Abstract Experimental and modeling studies of the free-radical-induced degradation of polypropylene (PP) in the melt phase have been carried out. Experiments have been performed in a single-screw plasticating extruder using a peroxide as the free-radical source. Concentration of the peroxide was in the range 0.01–0.6 wt%. Results in the form of melt flow index (MFI) values, viscosity curves, and molecular weight distribution (MWD) of the produced resins are presented here. Based on these results, a constitutive equation describing the shear viscosity of the melt as a function of shear rate, temperature, and molecular weight has been derived. The extensional viscosity of these resins has been determined as a function of strain rate using Cogswell's analysis of converging flows. A previously developed kinetic model (plug flow) has been used to simulate the changes of the average molecular weights of the MWD, and a sensitivity analysis of this model has been carried out.

Abstract The melt fracture behavior of two Teflon® resins was studied in capillary extrusion in order to identify the critical conditions for the onset of melt fracture and wall slip. These resins were copolymers of tetrafluoroethylene (TFE) and hexafluoropropylene (HFP) and TFE/HFP/PAVE (perfluoro (alkyl vinyl ether)) (PAVE) respectively. The incorporation of the third monomer in the molecules of the resin was found to improve the processability of polymer without substantially changing its rheology. Surface melt fracture (sharkskin) appeared at wall shear stresses greater than about 0.18 MPa, practically independent of temperature in the range of 300 to 350°C. At higher apparent shear rates oscillating melt fracture was observed due to the presence of wall slip and compressibility of the melt. Furthermore, a superextrusion region was identified at apparent rates greater than about 700 s −1 , beyond those where oscillating melt fracture was obtained. In this region, the extrudate appears again smooth. Finally, it was found that the addition of 0.1 % of polyethylene in the resins, reduces dramatically the pressure drop along the capillary die and eliminates extrudate distortion over the whole range of apparent shear rates up to the superextrusion region.

Abstract Random copolymers of ethylene with 1‐butene, 1‐octene, and 1‐octadecene have been prepared using a homogeneous vanadium‐based catalyst system. Comonomer contents determined by 13 C‐NMR analysis of polymer solutions are in the range 1–10 mol%. Crystallinities were estimated by means of density measurements, x‐ray diffraction, differential scanning calorimetry, laser Raman spectroscopy, and CPMAS 13 C‐NMR spectroscopy. The results are compared with those obtained for heterogeneous copolymers of ethylene containing 1–4 mol% 1‐butene. As the comonomer content is increased, the crystallinity decreases. The dimension perpendicular to the 110 plane in orthorhombic crystallites decreases linearly with crystallinity. This decrease in crystallite size is accompanied by an increase in the size of the orthorhombic unit cell. For copolymers containing large amounts of 1‐octene and 1‐octadecene, a second crystalline form appears. Differences in estimates of crystallinity are discussed in terms of looser packing in highly branched copolymers and the extent to which the second crystalline form participates in the phase structure.