Showing papers in "Polymer Engineering and Science in 1982"

Influence of molecular weight and molecular weight distribution on mechanical properties of polymers

Abstract: This work reviews the literature published over the last ten years on polymer mechanical properties as a function of molecular weight and molecular weight distribution, Thermal properties, stress-strain properties, impact, fracture, fatigue, creep, stress relaxation and cracking and crazing are examined for a wide variety of homopolymers and a limited number of copolymers. In general, mechanical properties increase as the molecular weight increases. However, above some limiting molecular weight the mechanical property is usually unaffected. Although much work has been done to describe the effects of molecular weight on mechanical properties, little quantitative correlation exists. The available equations to predict such properties as cracking and crazing, Tg, Tm and tensile strength from molecular characteristics are discussed in detail. However, a more quantitative description incorporating a wider range of mechanical properties would be more useful. This would facilitate use of the vast amount of information available and enable it to be applied more readily to new polymer systems.

Polymer compatibility with and without a solvent

Abstract: A qualitative review of the thermodynamics of polymer systems will be given in terms of three contributions: positional (or combinatorial) entropy, an “international” term and a free volume term. From this one finds that a simple polymer-solvent system phase separates on lowering T to an Upper Critical Solution Temperature (UCST) or raising it to Lower Critical Solution Temperature (LCST), To achieve miscibility of two polymers of high molecular weight, one requires a “specific” interaction, usually a weak charge-transfer complex or a hydrogen bond. Phase separation takes place on raising the temperature to an LCST. These various UCST and LCST are predicted semi-quantitative by the Prigogine-Flory theory. When a solvent is added to two miscible polymers, a new type of phase separation appears since there is an effect of any difference in the strengths of the two polymer-solvent interactions. Phase separation may easily occur in the ternary system where there is none in the three binary systems, and examples will be given. In the case of two highly-attractive polymers in a solvent, a quite different phase separation occurs, sometimes called complex coacervation. A simple Flory-Huggins type theory predicts these phenomena in ternary systems.

Melt rheology of polymer blends

Abstract: The rheological behavior of polymer blends is compared with that reported for emulsions, block polymers and homologous polymer blends. It has been shown that the properties of polymer alloys frequently differ from those of these “model” systems—the principal difference being the lowering of at least one rheological function below the value predicted In the log-additivity rule. Primarily, the most recent (post 1977) results are reviewed. The data obtained by the authors on the flow of poly(ethylene terephthalate)/Polyamide-6,6 are discussed in detail.

The microstructure of injection-molded semicrystalline polymers: A review

Abstract: The microstructure of semicrystalline polymers solidified with and without concurrent applied strain is reviewed. Fluid flow in the filling and packing stages of injection-molding are discussed. Observations of the microstructures of a number of polymers under various conditions are described. In general, the microstructure is extremely inhomogeneous and anisotropic; a skin layer is highly oriented (or, in some cases, finely granular), whereas the core is composed of larger, isotropic spherulites. The principles governing the formation of such microstructures are given. Relations between microstructure and macroscopic properties are briefly described.

Miscibility phenomena in polyester/chlorinated polymer blends

Abstract: Poly(caprolactone) (PCL)/poly(vinyl chloride) (PVC) blends are known to be miscible in the solid state. Recents measurements however indicate that a large number of polyesters are also miscible with PVC if the ratio CH2/CO of the polyester is between 4 and 10. At low CH2/CO ratios, polyesters are too rigid to interact specifically with PVC. At high CH2/CO ratios, the number of interacting groups becomes too small to give miscibility. Similarly, a large number of chlorinated polymers are shown to be miscible with PCL if their chlorine content is high enough. Surprisingly, polyesters are not in general miscible with chlorinated polymers if the mixture does not contain either PCL or PVC. The results presented in this paper suggest that a dipole-dipole interaction, between the carbonyl groups and the C-Cl groups, is responsible for the miscibility phenomena observed in polyester/chlorinated polymer blends.

The Trans-esterification of Bisphenol-a Polycarbonate (pc) and Polybutylene Terephthalate (pbtp) - a New Route To Block Copolycondensates

Abstract: In this work, the exchange reaction taking place in molten blends of bisphenol-A polycarbonate and polybutylene terephthalate was studied. A direct transesterification mechanism catalyzed by titanium residues, present in commercial PBTP, was deduced. The transesterification reaction can be -stopped at various levels by additives capable of complexing the titanium catalyst. This work enhances the possibility of a new approach in macromolecular engineering by directly combining polycondensates in a processing machine such as an extruder.

Effect of sub‐Tg relaxations on the gas transport properties of polyesters

Abstract: The relationship was determined between sub-Tg molecular motions and the transport of O2 and CO2 in amorphous polyesters and copolyesters based on poly(ethylene terephthalate) [PET] and poly(1,4-cyclohexylenedimethylene terephthalate) [PCDT], Modifications of the polyester with certain acid co-monomers restricted the molecular motions that occurred in the β-relaxation region and in turn decreased the O2 diffusion coefficient. The solubility coefficient was unchanged by those modifications. Modification of PET with 1,4-cyclohex-anedimethanol increased the magnitude of the β-relaxation and both the diffusion and solubility coefficients of O2. Similar relationships between the β-relaxation magnitude and CO2 permeability were also found. The temperature dependence of O2 permeability followed an Arrhenius relationship, with different activation energies (Ep) above and below the β-relaxation. The activation energy was smaller below the β-relaxation. Values of Ep above and below the β-relaxation did not depend on the chemical structure of the polymer.

Effect of the addition of ethylene‐propylene random copolymers on the properties of high‐density polyethylene/isotactic polypropylene blends: Part 1—morphology and impact behavior of molded samples

Abstract: Two random commercial ethylene-propylene copolymers (EPM) with different ethylene content have been added to binary isotactic polypropylene (iPP)/high density polyethylene (HDPE) blends by melt mixing in a Brabender-like apparatus. Impact Izod tests and a morphological analysis on the fractured surfaces of broken specimens have been performed and discussed, in order to improve the deficiency in toughness of the binary HDPE/iPP mixtures. The results show that the impact performance of both homopolymers and HDPE/iPP binary blends is strongly improved by the addition of the EPM copolymers. Such an effect is related to the fact that the overall morphology, as well as the mechanism and mode of fracture, are greatly modified by the presence of such additives. The extent is dependent on factors such as the nature of the matrix (HDPE or iPP), the composition, and the chemical structure and/or the molecular mass of the added copolymer.

Numerical Simulation of a Single Screw Plasticating Extruder

Abstract: A fully-predictive steady-state computer model has been developed for a single-screw plasticating extruder. Included in the model are a model for solids flow in the feed hopper; a variation of the Darnell and Mol model for the solids conveying zone; a variation of Tadmor's melting model for the melting zone; an implicit finite difference solution of the mass, momentum, and energy conservation equations for the melt-conveying zone of the extruder and die; and a predictive correlation for the extrudate swell at the die exit. A temperature- and shear-rate-dependent viscosity equation is used to describe the melt-flow behavior in the model. The parameters in the viscosity equation are obtained by applying regression analysis to Instron capillary rheometer data. Given the material and rheological properties of the polymer, the screw geometry and dimensions, and the extruder operating conditions, the following are predicted: flow rate of the polymer, pressure and temperature profiles along the extruder screw channel and in the die, and extrudate swell at the die exit. The predictions have been confirmed with experimental results from a 11/2 in. (38 mm) diameter, 24:1 L/D single-screw extruder with a 3/16 in. (4.76 mm) diameter cylindrical red die. High- and low-density polyethylene resins were used.

An analysis of thermal warpage in injection molded flat parts due to unbalanced cooling

Abstract: To illustrate the potential effect of unbalanced cooling on warpage of flat parts, a simplified two-part analysis is presented. First a computational model for amorphous polymers cooling in an injection molding cavity is presented. The simulation is a finite difference solution of the one-dimensional, transient heat conduction equation with constant material properties. Plastic and mold temperature profiles are calculated through the cooling cycle and the transients from cycle to cycle are included. Temperatures are predicted for both sides of the mold allowing asymmetrical cooling to be analyzed. The model is verified analytically and is in agreement with published data. Secondly, a simplified method of predicting the thermal warpage of a fiat part from calculated temperature profiles is discussed and illustrated. The relative effects on calculated part warpage of asymmetric mold geometry and cooling fluid temperature are predicted with this analysis method. The sensitivity of warpage to these design factors is illustrated for an example part.

Economics of polymer blends

Abstract: Economic, technological, and regulatory pressures gradually narrow the chemical variety of polymers: in 1975, the market share of polyethylene was 40 percent, poly(vinyl chloride), 23 percent, polystyrene, 12 percent, and polypropylene, 11 percent, adding up to 86 percent of all thermoplastics (1-3). The same pressures compel the plastics processor to diversify formulations and production methods. He must resort to new materials (e.g., polymer blends, polymer alloys, and composites) and new methods of manufacture. In this work, the economics of blending will be discussed. There are five reasons to employ polymer blends: higher performance at a reasonable price, modification of performance as a market develops, extending the performance of expensive resins, re-use of plastics scrap, generation of a unique material as far as its processabilitv and/or performance are concerned. In Canada, the cost of blending varies from 8 to about 20 ¢/lb, depending primarily on the volume and the kind of material. The cost effectiveness depends on the total technical and economic environment in which the manufacturer operates; it has to be computed for each case separately. In the text, guidelines and examples are provided.

Studies of epoxy resin systems: Part B: Effect of crosslinking on the physical properties of an epoxy resin

Abstract: An epoxy system consisting of diglycidyl ether of butanediol, DGEB, cured with 4-4′ diaminodiphenyl sulfone, DDS, has been used for a study of the effect of crosslinking density on the properties of the epoxy resin. Because of the low curing rate at room temperature and the low glass-transition temperature, this system was amenable to a wide range of controlled cross-linking density. The crosslinking density was monitored by FTIR (Fourier transform infrared spectroscopy), which followed the change in concentration of the epoxy groups during the curing reaction. The bulk density was found to increase linearly with the crosslinking density. The modulus, the upper yield point, the lower yield point, and the degree of retraction of a deformed sample all increased with the degree of crosslinking. The thermally stimulated depolarization (TSD) β-peak was found to vary with crosslinking density, but the γ-peak was not changed. The TSD a peak was found to decrease in strength, but increased in temperature as the crosslinking density increased. This observation suggests that TSD measurements arc a good monitor of crosslinking density of epoxy resins, particularly near the final stage of the crosslinking reaction.

Recent advances in interpenetrating polymer networks

Abstract: We review the synthesis, morphology, and physical and mechanical properties of IFNs as well as the related pseudo-IPNs, in which only one of the polymers is crossliriked. Recent studies have shown that the degree of phase separation achieved in these materials is strongly dependent on the compatibility of blends of the linear polymer constituents of the IPN components as well as the kinetics of chain extension and the presence of grafting between component polymers. We illustrate this by a series of IPNs consisting of a polyurethane and an acrylic copolymer. The acrylic is a typical automotive enamel. An enhancement in properties results, which is dependent on the amount of grafting and the kinetics of polymerization. Also discussed are IPNs of a polyurethane and an epoxy, which exhibit a synergism in adhesive properties, and IPNs of a RIM polyurethane with several epoxies and unsaturated polyesters. In addition, also reported are the preliminary studies on the first successful preparation of a three-component IPN, consisting of a polyurethane, an epoxy, and an acrylic.

The influence of impingement mixing on striation thickness distribution and properties in fast polyurethane polymerization

Abstract: Impingement mixing in a polyether polyol/butanediol/MDI, thermoplastic urethane system was evaluated using measurements of striation thickness distribution, adiabatic temperature rise, and molecular weight. Adiabatic temperature rise was less sensitive to mixing quality for this system than for the crosslinking ones previously studied. The average of the distribution of striation thickness as measured by optical microscopy on the resultant polymer decreased with increasing nozzle Reynolds numbers, Re. Molecular weight increased and its polydispersity decreased with increasing Re. Morphological data indicate better phase separation in the poorly mixed samples. These results are consistent with relatively slow diffusion for the polyol and thus the preferential formation of unattached hard segments at lower Re.

Mechanisms of flow induced crystallization

Abstract: This paper presents a review of the field of flow induced crystallization from solution. Experimental facts concerning the nature of fibrous nucleation and the “shishkebob” morphology which results are reviewed. The discussion of growth models emphasizes the details of the nucleation control and flow control calculations which have been presented in the literature. A major problem in the development of quantitative models for the growth mechanisms has been the lack of a reproducible growth rate data base and the reasons for this are discussed. The review emphasizes those areas of the field both experimental and theoretical, where further studies are needed before a unified theory of flow induced crystal growth can emerge.

Model of steady‐state melt spinning at intermediate take‐up speeds

Abstract: A model of melt spinning has been developed for speeds above which the effects of gravity, inertia, and aerodynamic drag become significant. The model has as an upper bound the speed at which stress crystallization begins to occur on the spin line. For poly(ethylene terephthalate), these velocities are approximately 750 and 3500 meters/minute. The calculated temperature and velocity profiles are shown to agree with measured values. The stress at the freeze point is calculated and found to correlate well with the spun yarn birefringence which, in turn, is shown to predict uniquely the spun yarn physical properties on a “simple” spin line. The stress-optical coefficient derived from the calculated stress at the freeze point and measured birefringence agrees well with the literature.

A criterion for craze formation

Abstract: A general criterion for craze formation is presented. Crazes are deformation zones that are common to both glassy and semicrystalline polymers. Crazes are composed primarily of fibrils. This paper attempts to describe the process that transforms unoriented glassy and semicrystalline polymeric solids into a fibrous state. The criterion for crazing discussed is a local phase transition. The transition occurs at the draw temperature. Unoriented solid-phase macromolecules, at local high-stress regions, undergo a transition to the elastomeric phase. Rapid extension and accompanying resolidification produce the fibrous morphology of craze fibrils. Cavitation of the deforming rubber phase ocurs because the local length increase is riot compensated for by an overall area decrease. Craze formation in glassy polymers has long been suspected to involve a local solid-to-rubber phase change. To relate crazes in glassy and semicrystalline polymers, one can assume that a solid-to-rubber phase change is required to produce craze fibrils in semicrystalline polymers. The transient melt phase would undergo rapid elongation, causing the formation of extended chain crystallites. These subsequently nucleate the remaining melt, which then crystallizes epitaxially as lamellae. Crystallization during flow would, therefore, be the mechanism of fiber formation.

Compatibilization of the polystyrene/poly(ethyl acrylate) and polystyrene/polysoprene systems through ionic interactions

Abstract: Interactions between anions on one polymer chain with cations on another can lead to compatibilization of otherwise incompatible materials. Thus, if 5 mol% of ∼SO3H groups are attached to polystyrene, and 5 mol% of vinyl pyridine is copolymerized with ethyl acrylate, proton transfer occurs upon mixing, and the pairwise attractive interactions between the resultant ions compatibilize the blend. The same has been observed for the styrene-vinyl pyridine and sulfonated polyisoprene polymer pair. Dynamic mechanical and optical properties are used as a measure of compatibilization.

Studies of epoxy resin systems: Part D: Fracture toughness of an epoxy resin: A study of the effect of crosslinking and sub‐Tg aging

Abstract: The fracture toughness of an epoxy resin system, diglycidyl ether of butanediol, DGEB, cured with 4-4′ diaminodiphenyl sulphone, DDS, has been studied by varying the crosslinking density and state of aging. A stable, but rough, crack propagation was observed with specimens that were 99 percent cured and quenched. When the extent of curing was less than 99 percent or the material was aged for more than 20 min at 62°C, crack propagation was of the unstable stick-slip nature. Aging was found to decrease the initiation fracture toughness dramatically, but the arrest fracture toughness was almost unchanged. This result was associated with a change of relaxation strength of the primary, a, transition with aging. An increase of crosslinking density was found initially to reduce the fracture toughness of this epoxy resin, but the fracture toughness increased after 87 percent of curing. The initial decrease of the fracture toughness was attributed to a decrease of relaxation strength of the primary transition (i.e., the area under the α-relaxation peak), while the increase of the fracture toughness after 87 percent curing was explained by the onset of the stablerough crack propagation, Micrographs taken by scanning electron microscopy-showed possible existence of blunting during crack propagation and a decrease of blunting with the extent of aging.

Mechanistic Studies of Adhesion Promotion by Gamma-Aminopropyl Triethoxy Silane in Alpha-Al2O3/Polyethylene Joint,

Abstract: In order to understand the mechanism of adhesion promotion by organo silane in joints where its chemical reaction with a polymer matrix may be negligible, we studied the role of γ-aminopropyl triethoxy silane (γ-APS) in α-Al2O3/ polyethylene joints. When adsorbed or deposited on α-A12O3/ and moderately dried, γ-APS forms a multimolecular film that is not fully cured. Drying at elevated temperatures for an extended time leads to further curing, resulting in a glassy silane film with a Tg around 108°C, while prolonged dry may cause some degradation. Joint strength is markedly improved by the application of a γ-APS film with a maximum peel strength of 2.3 kg/cm when the silane is applied from a 2 percent aqueous solution. Drying the silane at an elevated temperature prior to joint formation reduces joint strength and also changes the failure mode from cohesive failure through the polyethylene to a mixed mode. Evidence of interdiffusion between γ-APS film and polyethylene at a temperature (149°C) that is above the melting point of polyethylene and the Tg of the silane film was obtained by measuring the Si concentration profile across the interface of the laminate of polyethylene/γ-APS/polyethylene. Diffusion constants in the order of 10−12 cm2/s were obtained, with a teridency toward reduced diffusion as a consequence of extensive drying. DSC results indicate at least partial miscibility of the silane polymer in the amorphous region of polyethylene. It is proposed that the interdiffusion between γ-APS silane film and polyethylene is an important mechanism for adhesion promotion of the joints investigated in this study.

Residual stresses in polymers III: The influence of injection‐molding process conditions

Abstract: Following the evaluation of Residual Stresses (R.S.) in quenched specimens (Part I) and the resulting mechanical-physical properties (Part II), the, present study deals with the effect of injection-molding process conditions on R.S. and the respective properties of amorphous polymers. Melt temperature, mold temperature, injection rate, and injection pressure were the parameters studied. Experimental results indicated that the melt temperature caused two maxima in R.S. The second one reverses from compressive to tensile. In general, most changes occur in the surface regions, while R.S. decreases with increasing melt temperature, as is the case in zones far away from the gate. Furthermore, tensile modulus increased, in general, with rising melt temperature. In the case where the effect of mold temperature was studied, it was found that R.S. are compressive in the surface layers and tend to decrease upon increase in mold temperature and distance from the entrance region. Significant changes in R.S. were also detected in the interior layers. As the mold temperature approached Tg, low values of R.S. were measured, as was the case in quenched specimens. Injection rate affects surface R.S. to a large extent. With low flow rates, tensile stresses were developed in the exterior, reversing to compressive stresses at higher speeds. The reversal in sign depends on the location relative to the gate. Once compressive stresses were formed, further increase in rate caused a reduction in R.S. In addition, variations in tensile modulus, as high as 30 percent, were measured at high injection rates. As far as injection and holding pressures are concerned, experimental results showed that a maximum in R.S. was obtained, with increasing pressure, at the surface. Close to the gate entrance, a reverse from compressive to tensile R.S. was detected at high injection pressures. As in the other cases, injection pressure influenced mostly the exterior layers. Only in zones close to the entrance and at high pressures were high levels of R.S. measured in the core regions.

Rheological analysis of highly loaded polymeric composites filled with non-agglomerating spherical filler particles

Abstract: A non-agglomerating 15 μm diameter stainless steel spherical powder was used as a filler in a low-density polyethylene matrix. The factors investigated included volume loading, the use of surface treatments, and method of applying the surface treatments. The rheological parameters measured to analyze the effect of these factors on the melt behavior of the mixtures were the dynamic viscosity, η*, and the real component of the shear modulus, G′. These parameters showed clear differences in the response of the composites to volume loading, type of surface treatments, and method of surface treatment application.

Processing and commercial application of polymer blends

Abstract: The number of commercial blends has skyrocketed in the past several years and the trend toward blending—in preference to the creation of new polymer structures—has been firmly established. This paper analyzes the reasons for this growth; the types of commercial products, their manufacturer, and their applications; the patent situation; and possible future directions of the industry.

On the dynamics and control of a plasticating extruder

Abstract: In recent years, there have been many papers published on the application of process control to plasticating extruders. Much of the literature concentrates on the more classical control techniques. However, recent research has studied the application of stochastic identification techniques for building transfer function models for the extruder. In particular, the relationship of screw speed to die pressure and temperature has been studied. In the present work, both step tests and pseudorandom binary sequence tests were used to study the process dynamics of a 38 mm Killion extruder having a Iength-to-diameter ratio of 24:1. This study concentrates on the regulation of the extruder pressure in the face of its inherent surging characteristics. Variations in the quality of the feed plastic were studied through pulse and step changes in input polymer composition. Significant control problems resulted from measurement noise, which appeared at the same frequency as the screw rotation speed. Various mathematical filters to reduce the effect of this noise on the control variables were studied.

Batch polymerization of styrene‐optimal temperature histories

Abstract: Optimal temperature histories for the batch thermal polymerization of styrene are determined using Pontryagin's maximum principle. The theoretical predictions are compared with experimental measurements of conversion and molecular weight distribution. The excellent agreement suggests policy improvements in batch radical chain growth polymerizations.

Some solid‐state properties of blends of polyethylene terephthalate and polyamide‐6,6

Abstract: Polymer blends incorporating polyamide-6,6 (PA) and polyethylene terephthalate (PET) and having the following PA wt,% concentrations were prepared: 0, 5, 10, 25, 30, 35, and 100. Samples were obtained by molding in a reciprocating-screw injection-molding machine. The samples were annealed to minimize frozen-in stresses without increasing the crystallinity level in the material. Melting and heat-of-fnsion data, obtained with the differential scanning calorimeter, suggest an overall increased crystallinity in the blends, as indicated by a significant excess heat of fusion. Whereas the neat polymers exhibit ductile failure under both tensile and impact testing conditions, the blends show brittle behavior. Finally, the abrasion resistance of the blends is inferior to that observed for PET but higher than the resistance of PA.

Miscibility of poly(α‐methyl siyrene‐co‐acrylonitrile) with polyacrylates and polymethacrylates

Abstract: A copolymer formed from 30 percent acrylonitrile and 70 percent α methyl styrene by weight, or αMSAN, has been examined for miscibility in blends with various polyacrylates and polymethacrylates. None of the polyacrylates or poly(vinyl acetate) were miscible with α-MSAN at room temperature or above. The methyl and ethyl esters of the polymethacrylate series (PMMA, PEMA) proved to be miscible with α MSAN, but none of the higher homologues were miscible under these conditions. Blends of both PMMA and PEMA with α MSAN exhibited lower critical solution temperatures. The observed cloud points decreased as PMMA molecular weight increased up to 105 where kinetic effects caused an apparent reversal of this trend. Atactic PMMA interacts more strongly with αMSAN than does either isotactic PMMA or atactic PEMA. These structural effects are compared with similar trends found in other systems.

Property‐morphology relationships of polymethylmethacrylate/polyvinylidenefluoride blends

Abstract: An investigation was conducted to establish property-morphology relationships in polymethylmethacrylate/polyvinylidenefluoride (PMMA/PVDF) blends. All blends were compounded in a twin-screw extruder and then processed by injection molding Mechanical properties of blends of various compositions were studied by dynamic mechanical and impact strength measurements. The presence of crystalline regions in blends was determined by Differential Scanning Calorimetry (DSC). Morphology of fracture surfaces of blends was studied by Spinning Electron Microscopy (SEM). PMMA/PVDF blends were found to form compatible mixtures over a wide range of blend composition. Changes in dynamic mechanical properties upon annealing were found to be a direct function of blond morphology. Electron microscopic evidence showed no signs of phase separation. DSC measurements detected crystalline regions in all blends containing 40 percent or more (by weight) PVDF.

Carbon fiber-reinforced composites: Effect of fiber surface on polymer properties†

Abstract: Dynamic mechanical measurements in a torsional (shear) mode have been used to characterize an unfilled epoxy (Epon 828/m-phenylene diamine) and A series of uniaxial graphite fiber (Hercules types A and HM) composites. In unfilled resins containing an excess of the epoxy component, Mc—the average molecular weight between crosslinks—decreases with increasing temperature and duration of cure, suggesting a temperature-dependent side reaction. In fiber-reinforced composites, the dynamic mechanical response is sensitive to fiber type and curing schedule; elevation of Tg by as much as 45°C has been observed. Comparison of the dynamic data with properties predicted by micromechanical models shows only a fair agreement at room temperature, which rapidly worsens at higher temperatures. Surface treatment of type A fibers gives enhanced interlaminar shear strength (ILSS), both at ambient conditions and after hydrothermal aging. Dynamic data for surface-treated systems during hydrothermal aging show a sharper drop in G′ and increase in tan δ. The dynamic data and ILSS results are interpreted in terms of a balance of polymer-fiber interactions, a weak but widespread preferential adsorption of epoxy oligomers on the graphite basal planes at the fiber surface, and a low concentration of covalent bonds between polymer and fiber-surface-functional groups.

Modeling of poly(ethylene terephthalate) reactors: 4. A continuous esterification process

Abstract: A mathematical model has been developed for the direct, continuous esterification process. Influence of process and operational variables, including temperature distribution, residence time distribution, bis(hydroxyethyl)terephthalate recycle, pressure, and ethylene glycol (EG) to terephthalic acid ratio on the reactor performance have been investigated in a range as close to industrial practice as possible. The variables influencing the amount of EG reflux (which governs the energy economy) and side products (which govern the product quality) have been discussed. This investigation provides an analysis of a continuous, direct esterification process, and the results indicate strategies for optimizing productivity and product quality.