Showing papers in "Polymer Engineering and Science in 1988"
TL;DR: In this paper, a review of recent advances in the use of these compounds in immiscible polymer blends and thermoplastic composites is presented, based on their method of addition (in situformation vs. separate addition) and reactivity.
Abstract: The rapid growth in the use of multiphase polymer systems (blends and composites) is undoubtedly related to the availability of methods of controlling the physical and chemical interactions at the interface. Compounds acting as interfacial agents are commonly known as “compatibilizers” in blends, or “coupling agents” in composites; their function is to promote adhesion and enhance overall properties. This paper is a review of recent advances in the use of these compounds in immiscible polymer blends and thermoplastic composites. Polymeric compatibilizers are classified according to their method of addition (in situformation vs. separate addition) and reactivity. Reactive low molecular weight compounds are also listed and their various coupling mechanisms are discussed. It is demonstrated that common routes to enhanced adhesion exist for some types of blends and composites. For example, reactive graft copolymers and certain crosslinklng agents are equally effective as adhesion promoters in blends and composites containing a polyolefin phase.
304 citations
TL;DR: The morphology of compatibilized polyolef in/polyamide blends was found to be significantly dependent on the concentration of an ionomer compatiblizer (polyethylene-methacrylic acid-isobutyl acrylate terpolymer) in the blend as mentioned in this paper.
Abstract: The morphology of compatibilized polyolef in/polyamide blends was found to be significantly dependent on the concentration of an ionomer compatibilizer (polyethylene-methacrylic acid-isobutyl acrylate terpolymer) in the blend. For a dispersed phase content of 10% by weight, a maximum reduction in phase size was observed when only 0.5% by weight of ionomer was added to the blend, A more significant reduction of the dispersed phase size was observed when the minor phase was nylon, due to interactions which exist between the ionomer and the polyamide. These interactions have been confirmed by Fourier transform infrared spectroscopy. At high concentrations of the ionomer, flocculation of the nylon dispersed phase was observed. In comparison to one-step mixing, blends prepared by two-step or batch mixing were characterized by a smaller dispersed phase when nylon was the matrix, and a larger particle size when nylon was the minor phase. The results observed are explained in terms of a speculative model of the interactions occurring across the nylon-polvolefin interface.
205 citations
TL;DR: In this article, the authors explored phase continuity as a function of composition for three two-phase polymer blends produced by mixing in the melt: polystyrene/poly(methyl methacrylate), poly styrene/cis-polybutadiene, and poly(ethylene-propylene rubber).
Abstract: Phase continuity has been explored as a function of composition for three two-phase polymer blends produced by mixing in the melt: polystyrene/poly(methyl methacrylate), polystyrene/cis-polybutadiene, and poly(methyl methacrylate)/ethylene-propylene rubber. The condition for dual phase continuity Is the application of shear close to phase inversion and this can be predicted fairly accurately using the relation
where 1 and 2 are the blend components, η is viscosity, is the shear rate in the mixing device used to produce the blend and ϕ is volume fraction. The co-continuous materials, which we call Interpenetrating polymer blends (IPBs) are non-equilibrium structures and are subject to disruption by changes in flow regime.
177 citations
TL;DR: In this article, a kinetic model for the peroxide-initiated degradation of polypropylene (PP) is proposed and compared with experimental data for the production of controlled-rheology (CR) resins.
Abstract: Results of experimental and modeling studies of the peroxide promoted degradation of polypropylene (PP) are presented. Experiments were carried out, in glass ampoules and in a plasticating extruder. The initiator, 2.5-dimethyl-2,5-bis(tert-butylperoxy)hexane was used as a radical generator. The extruder used had a 38 mm diameter and 24:1 L/D single-screw. In these experiments, the effect of peroxide concentration and screw speed on the molecular weight distribution (MWD) of the polypropylene resin was studied. Samples collected from the experimental runs were analyzed for melt flow index (MFI), flow curve, extrudate swell, and MWD. The measured data are presented and correlations among various parameters are considered. Generally, it can be concluded that controlled-rheology (CR) resins with lower molecular weight, narrower MWD, and reduced viscosity and elasticity, can be produced, A kinetic model for the peroxide Initiated degradation of PP is proposed. Simulations based on this model are compared with experimental data for the production of CR resins. The experimental data were obtained from three sources: (i) industry, (ii) literature, and (iii) present experimental work. The comparison was done in terms of average molecular weights of the resin. Agreement between model predictions and experimental results is quite satisfactory suggesting that this model should find use in commercial practice.
149 citations
TL;DR: In this article, the phase morphology of blends of nylons with polyethylenes and polystyrenes is investigated and the effects of compatibilizing agents are discussed.
Abstract: Investigations of instability of phase morphology of blends of nylons with polyethylenes and polystyrenes and the effects of “compatibilizing” additives or “agents” are described. Annealing coarsens the phase morphology of blends of nylons with polyethylenes and polystyrenes. Phase growth is observed for various periods of annealing time. The addition of compatibilizing agents, specifically maleic anhydride grafted polyolefins to polyethylene-nylon blends and syrene-maleic anhydride copolymers to polystyrene-nylon blends, stabilize the phase dimensions. Styene-maleic anhydride copolymer is found more effective than styrene acrylonitrile copolymer as a compatibilizing agent. The mechanisms of this behavior are critically discussed.
124 citations
TL;DR: In this article, the thermal, dielectric, Theological, and mechanical properties of polyethylene terephthalate copolymers (PHB-PET) have been studied.
Abstract: We present a basic study of the thermal, dielectric, Theological, and mechanical properties of hydroxybenzoic acid-ethylene terephthalate copolymers (PHB-PET). It is argued that they have two-phase structures, one rich in ethylene terephthalate (PET) and one rich in hydroxybenzoic acid (PHB). Polystyrene (PS) is immiscible in 60% PHB-PET (60-PHB-PET) blends. Polycarbonate (PC) is partially miscible with the high PET phase of 60-PHB-PET. PET seems completely miscible with this high PET phase. Shear viscosity measurements on blends indicate that 60-PHB-PET gives rise to large reductions of viscosity. Extrudates and melt-spun fibers have been prepared. The phase morphologies of low PHB-PET blends as determined by scanning electron microscopy indicate ellipsoids or long fibrils of the, 60-PHB-PET in PS or PC matrices. High extrusion rates and melt spinning produce fibrillar structures. The mechanical properties of films, extrudates, and melt-spun fibers were studied. Blends with 10% 60-PHB-PET exhibited significant increases in Young's modulus and tensile strength.
115 citations
TL;DR: In this article, three peaks are attributed to melting of crystallites formed during primary and secondary crystallization processes and to fusion of crystals formed during recrystallizatlon during the melting scan.
Abstract: Poly(elhylene terephthalate) samples were isothermally crystallized from the melt on a differential scanning calorimeter. Subsequent fusion showed three endotherms under many crystallization conditions. These three peaks are attributed to melting of crystallites formed daring primary and secondary crystallization processes and to fusion of crystals formed during recrystallizatlon during the melting scan.
108 citations
TL;DR: In this paper, the main process parameters in vibration welding are the weld frequency, the amplitude of the vibratory motion, the weld pressure, and the weld time, and how these parameters affect weld quality, the conditions that result in the best welds, the weldingability of dissimilar plastics and the effect of fillers such as glass.
Abstract: In vibration welding of thermoplastics, frictional work done by vibrating two parts under pressure, along their common interface, is used to generate heat to effect a weld. The main process parameters in vibration welding are the weld frequency, the amplitude of the vibratory motion, the weld pressure, and the weld time. How these parameters affect weld quality, the conditions that result in the best welds, the weldability of dissimilar plastics, and the effect of fillers such as glass are of interest. To address these issues, a research vibration welding machine in which all the parameters can be independently and accurately controlled and monitored was designed and fabricated. The phenomenology of welding, as determined by experiments on the four thermoplastics polycarbonate, poly (butylene terephthalate), polyetherimide, and modified poly (phenylene oxide), is described.
99 citations
TL;DR: In this article, simple analytical models for the first three phases of the vibration welding process were developed for estimating the molten film thickness, the size of the heat affected zone, and the weld time as functions of the weld parameters.
Abstract: The vibration welding process for thermoplastics is known to consist of four phases: (1) initial heating of the interface to the melting temperature by Coulomb friction; (2) unsteady melting and flow in the lateral direction; (3) steady-state flow; and (4) unsteady flow and solidification of the film after the vibratory motion is stopped. Simple analytical models are developed for the first three phases. These models are used for estimating the molten film thickness, the size of the heat affected zone, and the weld time as functions of the weld parameters: the amplitude and frequency of the weld motion, and the weld pressure. The steady-state film thickness and the heat-affected zone are shown to be very small.
98 citations
TL;DR: In this article, a lap shear joint method was used to study strength development during welding of polystyrene surfaces-the surfaces previously had not been in contact and care was taken to insure rapid wetting of the interface.
Abstract: A lap shear joint method was used to study strength development during welding of polystyrene surfaces- The surfaces previously had not been in contact and care was taken to insure rapid wetting of the interface. The shear stress at failure, τf was measured at room temperature as a function of contact time, t, at constant welding temperatures up no 20°C above the glass transition temperature, Tg. The time dependence of welding could be well described by τfαt1/4. This result is in agreement with predictions of the reptation molecular dynamics model applied to inter-diffusion at a symmetric amorphous polymer-polymer interface. The activation energy for the thermally activated increase in strength development was determined as E = 96 kcal/mol at T = 113.5°C, which compares with E = 93,2 kcal/mole as predicted by the W-L-F theory using C1 = 13.7, C2 = 50 and Tg = 100°C. The polystyrene samples had molecular weights, Mn = 143,000 and Mw = 262.000. The time to achieve complete healing, t∞ ≈ 256 min at 118°C, was found to be of the same order of magnitude as the viscoelastic relaxation time and also with the time required for a polymer chain to diffuse a distance equal to its root mean square end-to-end vector.
96 citations
TL;DR: In this paper, a simple model is developed for the hot melt closely intermeshing corotating twin-screw extruder, analogous to the analysis of the single-crosstitching extruder carried out in 1922 and 1928.
Abstract: In many operations in polymer processing, such as polymer blending, devolatilization, or incorporation of fillers in a polymeric matrix, continuous mixers are used; e.g., corotating twin-screw extruders (ZSK), Buss Cokneaders and Farrel Continuous Mixers. Theoretical analysis of these machines tends to emphasize the flow in complex geometries rather than generate results that can be directly used (1–5). In this paper, a simple model is developed for the hot melt closely intermeshing corotating twin-screw extruder, analogous to the analysis of the single-screw extruder carried out in 1922 and 1928 (6, 7). With this model, and more specifically with its extension to the complete nonisothermal, non-Newtonian situation, it is possible to understand the extrusion process and to calculate the energy, specific energy, and temperature rise during the process with respect not only to the viscosity of the melt, but also to the screw geometry (location and number of transport elements, kneading sections and blisters, pitch, positive or negative, screw clearance, and flight width) and screw speed. To support the theoretical analysis, model experiments with a Plexiglas-walled twin-screw extruder were performed, in addition to practical experiments with melts on small- and large-scale extruders, with very reasonable results, In Part 2, the Buss Cokneader will be analyzed analogously.
TL;DR: In this paper, a model called the island model was developed to explain the results: one assumes that the lines of force as well as propagating cracks tend to concentrate in the more flexible engineering polymer, avoiding the islands rich in the liquid-crystalline phase.
Abstract: Molecular composites, also called polymeric liquid crystals (PLC), are contrasted with the traditional composites; the name heterogeneous composites is proposed for the latter. Advantages of blending PLCs with ordinary engineering polymers are discussed. Results reported for blends of poly(ethylene terepthalate) (PET) with a PLC containing sequences of PET and p-hydroxybenzoic acid (PHB) include thermophysical properties, melt rheology, mechanical properties of solid blends, and scanning electron microscopy of fracture surfaces. A model called the island model was developed to explain the results: One assumes that the lines of force as well as propagating cracks tend to concentrate in the phase rich in the more flexible engineering polymer, avoiding the islands rich in the liquid-crystalline phase. This prevails until the phase inversion occurs. Predictions from the model are fully confirmed by the experimental evidence.
TL;DR: In this article, an elastomeric adduct crosslinkable and compatible with an epoxy matrix was used for coating carbon fibers with an on-line filament winding process.
Abstract: Oxidized carbon fibers were coated using an on-line filament winding process with an elastomeric adduct crosslinkable and compatible with an epoxy matrix. The coating and modifications of the epoxy network were studied by dynamic mechanical measurements. Assuming that apparent activation energies of the secondary relaxation βe of the epoxy network and main relaxation αa of adduct are very different, it is possible at low frequencies to separate the two peaks. The composite material can be described as a three phase system: an epoxy network as matrix, carbon fibers, and a soft interlayer. The mechanical behavior of unidirectional composite materials studied by impact and bending tests is strongly dependent on the presence and the thickness of the coating at the carbon fiber surface.
TL;DR: In this article, it was shown that the Avrami equation can be used to evaluate both the activation energy and activation energy of a crystal growth process and to compare transformation rates when the systems differ in their n values.
Abstract: Over the last four decades, numerous reports have appeared on the physico-chemical kinetics, especially crystallization kinetics, based on the Avrami equation, ϕ = exp [−Ktn] where ϕ is the fraction of material unchanged at time t, K is an overall rate constant and “n” is the Avrami exponent indicative of process mechanism The usage of the Avrami equation has been limited to the determination of “n” and its temperature dependence It is shown that the evaluation of K and the activation energy (E) using this equation is erroneous since K and E are both influenced by “n” although such would be unexpected from the Avrami equation On the other hand, if one uses a modified expression, ϕ = exp[−Kt]n, then in addition to the value of “n”, correct values of K and E are obtained This retains the original correspondence of the Avrami equation to nuclea-tion and crystal growth processes but extends its applicability to (i) correctly evaluate K and E parameters, and (ii) correctly compare transformation rates when the systems differ in their n values Experimental data are presented to support these conclusions
TL;DR: In this paper, the blown film process is studied for both Newtonian and viscoelastic models of the polymer melt, with the existence of more than one steady state bubble profile for a given set of operating parameters; steady axisymmetric solutions vanish suddenly at critical combinations of operating variables.
Abstract: The mechanics of the blown film process are studied for Newtonian and viscoelastic models of the polymer melt. Multiple solutions of the governing equations are possible even for the Newtonian fluid, with the existence of more than one steady-state bubble profile for a given set of operating parameters; steady axisymmetric solutions vanish suddenly at critical combinations of operating variables. Several types of instabilities exist, including one that is analogous to “draw resonance.” The stability of the bubble to infinitesimal disturbances depends on the set of operating parameters that is controlled; control of the bubble inflation pressure is much less stable than control of the amount of inflating air, for example. Heat transfer is stabilizing.
TL;DR: The most promising control techniques are probably optimal control, adaptive control, and their combinations as discussed by the authors, in spite of the highly nonlinear nature of the polymerization process and the high exothermicities and viscosities involved.
Abstract: The control of polymerization reactors is particularly arduous for several reasons; (a) difficulty in specification of the control objectives; (b) high exothermicities and viscosities involved: (c) complicated process dynamics: and (d) problems with measurement of the polymer structure. Computer control has now simplified many tasks such as sequential operations of batch reactors; but no less important, it has made feasible the implementation of elaborate state estimation and control algorithms. The tendency in the polymerization industry and in current research centers is centered on producing ‘tailor-made’ polymers from the view of its microscopic and/or macroscopic structures. To this end, several solutions have been proposed. For example, in the ‘chemical approach’, open loop methods have been developed based on the detailed dynamic models of the processes. Any control technique requires a knowledge of the process to be controlled through mathematical models. These models may be developed either from detailed mass and energy balances, or through empirical input-output or “black-box” techniques. The most promising control techniques are probably optimal control, adaptive control, and their combinations. Optimal control is powerful because it utilizes directly the detailed non-linear plant model. Adaptive control developed for linear plants has already proven satisfactory, in spite of the highly nonlinear nature of the polymerizations. Undoubtedly, improved solutions will be obtained when this technique is extended to non-linear systems.
TL;DR: A review of these techniques with emphasis on the process parameters, polymers investigated, and properties of the resulting materials can be found in this paper, where the productivity of such forming processes has been increased by reducing the level of molecular entanglement among neighboring molecules.
Abstract: Processing plastics below their melting points has been shown to be an effective way to significantly enhance the mechanical, chemical, and physical properties of semi-crystalline thermoplastics. A number of techniques have been developed that are capable of producing highly oriented fibers, films, and shapes. In general, these techniques can be classified as drawing, extrusion, arid rolling, with some very specific modifications having been made to each, that affects the performance of the process. Of particular interest is the rate of production, the range of thicknesses achievable, the uniformity of properties in the product, and the extent, if any, of biaxiality in the product. In recent years, the productivity of such forming processes has been increased by reducing the level of molecular entanglement among neighboring molecules. As an alternate to these orientation processes, techniques have been developed which rely on strain Induced crystallization to enhance the modulus of molded parts and extrudates from a melt. This paper constitutes a review of these techniques with emphasis on the process parameters, polymers investigated, and properties of the resulting materials.
TL;DR: In this article, a detailed model for the prediction of the behavior of batch or continuous emulsion polymerization reactors has been formulated, and an efficient numerical scheme for simulation developed, making use of population balance equations and detailed mechanisms for chemical and physical rate processes.
Abstract: A detailed model for the prediction of the behavior of batch or continuous emulsion polymerization reactors has been formulated, and an efficient numerical scheme for simulation developed. The model makes use of population balance equations and detailed mechanisms for chemical and physical rate processes. The numerical procedure chosen for its solution is orthogonal collocation on finite elements. In this paper, a few comparisons with experimental data are presented to demonstrate the model validity. Finally, a parametric sensitivity study is carried out to identify the most important kinetic and physical parameters. In the sequel, a comprehensive comparison of model predictions with a wide variety of experimental data will be presented.
TL;DR: In this article, the dynamic shear behavior at 200°C of low density polyethylene, LDPE, polystyrene, PS, and their blends was studied.
Abstract: The dynamic shear behavior at 200°C of low density polyethylene, LDPE, polystyrene, PS, and their blends was studied. Two series of blends were prepared containing LDPE:PS = 1:2, 2:1 and 17:3; the first series contained 0, the second 5 wt% of the compatibilizing, partially hydro-genated poly(styrene-b-isoprene) di-block copolymer, SEB. From the Casson plot the relative values of apparent yield stress were found to be G′y > G″y the addition of SEB decreased both these functions, but the inequality remained valid. After subtracting the yield stress values the frequency relaxation spectrum was computed from the relation G″ = G″(ω). The linear viscoelastic functions determined from the spectrum were found to agree with experimental values within a range of error below 5%. The blends were found to be thermorheologically complex with the time-temperature shift factors depending on both temperature and frequency. A compositional dissymmetry of blend morphology was observed: PS dispersed in LDPE formed spheres, while at corresponding concentration LDPE in PS formed fibers. A difference in surface tension of the two polymers, leading to different spreading coefficients (SPE/PS≠SPS/PE), or dissymmetry of the interfacial tension coefficient, could provide a possible explanation.
TL;DR: In this paper, the ratio of rubber to polystyrene phase was kept constant at 1:4 by weight, and the concentration of reactive oxazoline groups in the polystyrenes phase was varied by mixing poly styrene (PS) with a copolymer of styrene and vinyl oxozoline (OPS), and the impact strength and ductility of the reactive blends were found to be up to 73% greater than those of the corresponding nonreactive blends.
Abstract: Acrylonitrile-butadiene rubber having carboxylic acid groups (XNBR) and polystyrene having oxazoline groups, were melt blended in a Rheomix mixer under optimized conditions, The ratio of rubber to polystyrene phase was kept constant at 1:4 by weight. The concentration of the reactive oxazoline groups in the polystyrene phase was varied by mixing polystyrene (PS) with a copolymer of styrene and vinyl oxazoline (OPS). A torque rise observed during blending was found to be related to the concentration of oxazoline-carboxylic acid pairs. This torque rise, and independently measured increases in viscosity, both indicate inter-polymer crosslinkihg. Scanning electron microscopy was used to observe the morphology of the blends. Improved rubber phase dispersion was observed with increasing oxazoline concentration. Instrumented impact strength measurements were made using an unnotched Charpy technique. The plastic yielding was then quantified with the use of a ductility ratio. The impact strengths and ductility of the reactive blends are found to be up to 73% greater than those of the corresponding non-reactive blends. Increasing the OPS concentration beyond 5% results in decreasing impact strength, for as the compatibility increases, the rubber particle size decreases below an effective size for rubber toughening. Similar impact improvement is observed when the major PS phase is substituted with high impact polystyrene (HIPS) containing some OPS.
TL;DR: In this paper, the relationship between chemical structures of various aromatic polyimides and their thermal expansion coefficients was investigated and the properties of low thermal expansion polyimide were elucidated.
Abstract: The relationships, between chemical structures of various aromatic polyimides and their thermal expansion coefficients, were investigated and the properties of low thermal expansion polyimides were elucidated Such low values were observed for polyimides obtained from pyromellitic dianhydride or 3,3‘4,4‘-biphenyltetracarboxylic dianhydride and aromatic diamines which included only benzene or pyridine rings fused at para-positions without a flexible linkage It was proposed that these low thermal expansion coefficients were related to the lineerity of their polymer molecular skeletons In particular, PIQ-Ll 00 (Hitachi Chemical Co Ltd) is one such low thermal expansion polyimide and, it has excellent mechanical properties, thermal stability, and low absorbed moisture content
TL;DR: In this paper, a comparison of the prediction of the theory of rubber elasticity with the experimentally observed variation of the shear storage modulus, G, as a function of crosslink concentration is made.
Abstract: A comparison of the prediction of the theory of rubber elasticity with the experimentally observed variation of the shear storage modulus, G, as a function of crosslink concentration shows that deviations occur when the network strand concentration in diepoxide-diamine polymers exceeds approximately 1.5 mole kg−1. The rapid rise in G above this level is accounted for in terms of the increasing importance of non-Gaussian chain statistics and steric interactions. It is also established that the contribution from entanglements is significant and the behavior over the entire crosslink density range can be described by the following equation
where v and ϵTe are the concentrations of elastically active strands which orginate from fixed points and entanglements respectively, ψ is an empirical constant related to the importance of the non-ideal behavior, and ϕ is the so-called “front factor”. This latter constant is found to depend on the functionality of the network junctions, varying from 0.9, for a system with tetrafunctional junctions, to an average of 0.53 for those networks with trifunctional junctions.
TL;DR: The use of polymer dielectrics, particularly biaxially oriented polypropylene (BOPP), has revolutionized power distribution around the world as mentioned in this paper and has been used for power distribution.
Abstract: The use of polymer dielectrics, particularly biaxially oriented polypropylene (BOPP), has revolutionized power distribution around the world. BOPP film of sub mil thickness has displaced impregnated Kraft paper because of superior dielectric performance, lower cost, and small volume. The polypropylene molecule has a unique set of properties which combine stable dielectric properties in the operating temperature and frequency range along with an adequate dielectric constant. High levels of orientation and a small unbalance of orientation are required to produce films of high dielectric strength over large areas of film. Control of thickness uniformities to approximately ± 5 percent are critical to the reliable operation of the capacitor under load and to control of capacitance in the product. A special fibrillated surface is required which promotes complete impregnation by the dielectric fluid.
This surface is acquired by the development of a specific crystal morphology at one surface of the film. No additives are used to promote this crystalline structure since most additives effect dissipation factor and generate unwanted heat. Similarly, control of contamination (ppm and ppb) is a key factor in the manufacture of film power capacitors.
TL;DR: In this article, the effects of systematically varying the crosslink density on the mechanical relaxations in the glassy region of typical highly crosslinked diepoxide-diamine polymers are reported.
Abstract: The effects of systematically varying the crosslink density on the mechanical relaxations in the glassy region of typical highly crosslinked diepoxide-diamine polymers are reported. Activation enthalpies and intensities for the β relaxation have been measured using a torsion pendulum at 1 Hz. The glyceryl groups, which are thought to be responsible for this process, are divided into a number of categories defined by the structure of the surrounding matrix. Concentrations of these units are calculated using probability theory, and a correlation is obtained with three measures of the relaxation Intensity, In the case of non-stoichiometric networks, variations in the intensity of the β relaxation are interpreted in terms of the simultaneous motion of each class of glyceryl group. The manner in which these processes combine to produce a composite peak appears to be unimportant. For the γ relaxation (−140°C), it is shown that at least four methylene units are needed in the diamine component before the process is observable, whereas only two consecutive methylene units in the center of the diepoxide molecule produce the relaxation.
TL;DR: In this article, a mixture of polystyrene and trichlorofluoromethane was extruded through a slit die having glass windows and bubble nucleation in the flow channel was observed optically.
Abstract: Bubble nucleation in a mixture of volatile liquid and polymer melt under shear flow conditions was investigated, using a light scattering technique. In the study, a mixture of polystyrene and trichlorofluoromethane was extruded through a slit die having glass windows and bubble nucleation in the flow channel was observed optically. A He-Ne laser was used to illuminate the nucleating and growing bubbles. The light flux scattered by the growing bubbles at a fixed angle was detected by a photomultiplier with the aid of a high-voltage power supply. The bubble nucleating site in the flow channel was located using a computer controlled tracking system, which was designed to move the entire optical system automatically in the three dimensional space, and also had the ability to follow the software control command and cooperate with the data acquisition system. When the site of bubble nucleation was located, the coordinates of this site in the flow channel and the experimental conditions were automatically recorded on a floppy diskette by entering a software command. The pressure profile along the flow channel was measured by pressure transducers, with the aid of a microprocessor-based pressure reading system. It has been found that the site of bubble nucleation varies with the position in the direction perpendicular to the flow direction, which is attributed to the nonuniform velocity and stress distributions in the slit flow channel. The present investigation suggests that bubble nucleation can be induced either by flow and/or shear stress; specifically, flow-induced bubble nucleation is the dominant mechanism at positions near the center of the die opening, and shear-induced bubble nucleation is the dominant mechanism at positions near the die wall. It should be mentioned that the bubble near the die wall may also be generated by cavitation brought about by the surface roughness of the wall and also by thermal fluctuations due to the heat transfer between the metal (die wall) and the mixture of polymer and volatile component. The present study indicates that bubble nucleation in a shear flow field can occur at an unsaturated condition. This is in contrast to bubble nucleation under static conditions, where supersaturation is necessary.
TL;DR: In this article, the effect of varying cooling rates during crystallization on the spherulitic structure of poly(butalene terephthalate) was examined using light microscopy, transmission electron microscopy and differential scanning calorimetry.
Abstract: This paper discusses the effect of varying cooling rates during crystallization on the spherulitic structure of poly(butalene terephthalate). Light microscopy, transmission electron microscopy, and differential scanning calorimetry were used to examine specimens. The mechanical properties of the polymers studied were examined by a variety of methods.
TL;DR: In this article, bisphenol-A polycarbonate (PC) with poly (styrene-co-acrylonitrile-butadiene-styrene) (SAN) and poly (acrylanitrile, butadiene,styrene)-polyamide (ABS) prepared by screw extrusion and solution-casting were investigated by differential scanning calorimetry and scanning electron microscopy, and the maximum level of extrudate swell was reached at 0.034 ± 0.004.
Abstract: Blends of bisphenol-A polycarbonate (PC) with poly- (styrene-co-acrylonitrile) (SAN) and poly (acrylonitrile-butadiene-styrene) (ABS) prepared by screw extrusion and solution-casting were investigated by differential scanning calorimetry and scanning electron microscopy. From the measured glass-transition temperatures (Tg) and specific heat increments (ΔCp) at the Tg, SAN appears to dissolve more in the PC-rich phase than does PC in the SAN-rich phase. Also, the decrease of Tg (PC) in PC/ABS blends is larger than in the PC/SAN blends. From the Tg behavior and the electron microscopy study, it is suggested that the compatibility increases more in the SAN-rich compositions than in the PC-rich compositions of the blends. In the study of extrudate swell of the PC/SAN blends and the PC/ABS blends, the maximum level of extrudate swell is reached at 0.5 weight fraction of PC for both blend systems. The Flory-Huggins polymer-polymer interaction parameter (χ12) between PC and SAN was calculated and found to be 0.034 ± 0.004. A similar value of χ for PC and SAN was found with the PC/ABS blends.
TL;DR: In this paper, it is shown that the mechanical properties and/or morphology of a nylon 6 article can depend upon the processing technique (e.g., compression or injection molding) as well as the processing history of the nylon 6 resin itself.
Abstract: The observation of a novel phenomenon is reported whereby the processing history of a nylon 6 leads to a memory effect which in turn affects its crystallization rate from the molten state. Differential scanning calorimetry (DSC) and optical microscopy are the primary techniques used to demonstrate that the melt-crystallization behavior of nylon 6 can be controlled by processing variables. Characterization data is presented to show that obvious parameters such as molecular weight, impurities, monomer and oligomers, etc. are not responsible for the observed changes in crystallization behavior upon processing. It is shown that the mechanical properties and/or morphology of a nylon 6 article can depend upon the processing technique (e.g., compression or injection molding) as well as the processing history of the nylon 6 resin itself.
TL;DR: In this paper, the effects of various parameters on weld quality were systematically studied by first butt-welding polycarbonate specimens under controlled conditions over a wide range of process parameters, and by then determining the strengths and ductilities of these welds by tensile tests.
Abstract: In vibration welding of thermoplastics, frictional work done by vibrating two parts under pressure, along their common interface, is used to generate heat to effect a weld. The main process parameters are the weld frequency, the amplitude of the vibratory motion, the weld pressure, and the weld time or weld penetration; The effects of these parameters on weld quality were systematically studied by first butt-welding polycarbonate specimens under controlled conditions over a wide range of process parameters, and by then determining the strengths and ductilities of these welds by tensile tests, A significant result is the apparent existence of a weld-penetration threshold above which high weld strengths are attained, but below which the strength drops off. Under the right conditions, the strengths of polycarbonate butt welds are shown to equal the strength of the virgin polymer.
TL;DR: In this article, the effects of weld parameters on weld quality were systematically studied by first butt welding thermoplastic specimens under controlled conditions, over a wide range of process parameters, and by then determining the strengths and ductilities of these welds by tensile tests.
Abstract: In vibration welding of thermoplastics, frictional work done by vibrating two parts under pressure, along their common interface, is used to generate heat to effect a weld. The main process parameters are the weld frequency, the amplitude of the vibratory motion, the weld pressure, and the weld time or weld penetration.; The effects of these parameters on weld quality were systematically studied by first butt welding thermoplastic specimens under controlled conditions, over a wide range of process parameters, and by then determining the strengths and ductilities of these welds by tensile tests. The three thermoplastics investigated are poly (butylene terephthalate), polyetherimide, and modified polyphenylene oxide. Changes in the weld pressure are shown to have opposite effects on the strengths of polyetherimide and modified polyphenylene oxide welds; Also, the weld frequency is shown to have a significant effect on the weldability of polyetherimide. The weldability data for these three thermoplastics are compared with data for polycarbonate. Under the right conditions, the strengths of butt welds in these materials are shown to equal the strength of the virgin polymer.