bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of high strain hysteresis loss of nonlinear rubbery polymer
Authors: Kar Kamal K. , Bhowmick Anil K.
Published: April 2004

With the use of the Boltzmann superposition principle, a statistical theory of rubber elasticity, and phenomenological theory, the hysteresis loss at high strain (greater than 100%) of nonlinear viscoelastic materials has been quantified in terms of material parameters. The theory incorporates both experimental and analytical parameters. The experimental results for natural rubber (NR) and styrene‐butadiene rubber (SBR) vulcanizates having variations of loading of carbon black, silica, clay, resin and curatives are in good accord with the theoretical predictions.
Fracture failure processes in polymers. I: Mechanical tests and results
Authors: Liu K. , Piggott M. R.
Published: April 2004

Tensile tests and Izod impact tests were carried out on eight thermoplastics and an epoxy. The results are compared with shear strengths determined previously, and it is shown that for seven of the polymers, the nominal tensile strength is equal to the yield strength and is approximately the same as the shear strength measured by the punch test. (The true ultimate tensile strength is not always a useful concept because the more ductile polymers are radically changed during the tensile testing process.) In shear tests the shear strains can be extremely high before eventual failure. Because of this the Iosipescu test appears to be unsuitable for measuring the ultimate shear strengths of polymers. Classical shear sliding of failure appears to be rare, and instead most of the polymers appear to be failing in tension when tested in the punch test. (Shear is equivalent to tension at +45° and compression at −45° to the shear directions.) The polymers with shear Strengths that are significantly less than the tensile strengths are brittle ones, and these differences are probably due to flaw statistics. Thus the idea first advanced to explain unduly high interface shear strengths in centrosymmetric systems, i.e., that most polymers ultimately fail in tension when tested in shear, appears to be validated.
Relationship between strain rate, temperature, and impact failure mechanism for poly(vinyl chloride) and poly(ethylene terephthalate)
Authors: Green Janet L. , Petty Charles A. , Gillis Peter P. , Grulke Eric A.
Published: April 2004

One approach to the purification of recycled thermoplastic mixtures is selective grinding to induce differences in sizes and shapes between polymers with different compositions. These mixtures can then be separated using one of several technologies including conventional sieving or hydrocyclones. Recycled poly(vinyl chloride) and poly(ethylene terephthalate) often are cross‐contaminated with each other since they have overlapping density ranges and are very difficult to separate using methods such as flotation. Selective grinding followed by physical separation might be a preferred method for separating such a polymer pair if processing “windows” for inducing differences in failure mechanisms can be found. There is a temperature range over which PET fails in a ductile mode while PVC fails in a brittle mode for impact grinding experiments. This range is not accurately predicted by failure mechanism and β‐transition temperature diagrams.
Toughening of unsaturated polyester with rubber particles. Part I: Morphological study
Authors: Maspoch M. L. L. , Martinez A. B.
Published: April 2004

The morphology of rubber‐modified unsaturated polyester is described. In order to modify the particle‐matrix interface, different rubbers were used; BFGoodrich Hycar liquid rubbers and high molecular weight rubbers. Blends of different compositions were prepared. The microstructure of the materials was investigated using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The volume fraction and the particle size of the rubbers' second phase was determined by applying quantitative metallography. The volume fraction of the precipitated phase was higher than the amount of added rubber. Such blends show phase inversion above 35 wt% of rubber.
Protective coatings on aluminum by spontaneous polymerization
Authors: Agarwal Rajat , Bell James P.
Published: April 2004

A novel process to form protective polymer coatings on aluminum using spontaneous polymerization is described. When an aluminum sample is immersed in a partly aqueous monomer solution, polymerization proceeds rapidly on the metal surface, without the addition of initiator, at room temperature. The polymer coatings studied here were formed using styrene (St), N‐phenyl maleimide (NPMI), 2‐methacryloyloxy acetoacetate (MEA), and bis‐maleimide (BMI), monomers, from solutions of different compositions. A possible mechanism for spontaneous initiation and propagation is proposed. The effects of process variables such as polymerization time, monomer concentration, and monomer ratios in feed on the coating thickness and properties are presented. The glass transition temperatures, adhesion strength to aluminum, thermal stability and corrosion resistance of these coatings are reported. The coatings obtained are up to 50 μm thick and conform to the shape of the substrate. They have excellent thermal stability, low dielectric constant, and show very good resistance to corrosion under the ASTM B‐117 accelerated salt fog test. Other monomers and metals may also be used.
Free radical branching of polylactide by reactive extrusion
Authors: Carlson Denise , Dubois Philippe , Nie Li , Narayan Ramani
Published: April 2004

The reactive extrusion of polylactide (PLA) with a free radical initiator resulting in a branched polymer was accomplished. Reaction conditions were in the range of 160°C to 200°C with an initiator concentration between 0.0 and 0.5%. Triple detector size exclusion chromatography, melt flow index, thermal gravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis were used to characterize the polylactide polymers. PLA without initiator showed extensive degradation as was evidenced by a decrease in both molecular weight and melt viscosity. The optimum range for branching resulting in a high molecular weight and low melt flow index polylactide was found to be around 170°C to 180°C and 0.1 to 0.25% initiator.
Modification of nylon‐polyethylene blends via in situ fiber formation
Authors: Chen J. C. , Harrison I. R.
Published: April 2004

Extrusion of nylon‐PE films has resulted in the successful in situ formation of high aspect ratio (possibly continuous) nylon fibers as desired. However, these fibers surprisingly provide no significant reinforcement in uncompatibilized blends. While certain compatibilizing agents appear to give properties more characteristic of a fiber reinforced system, achieving higher levels of reinforcement (approaching those anticipated for fibers containing highly oriented molecules) is judged to be difficult using current methods. Based on analysis of yield stress versus modulus, the act of drawing films appears to have the greatest potential for improving reinforcement beyond the limiting case for unmodified polymers. However, the greatest challenge in realizing this potential lies in overcoming the limited extensibility allowed by nylon under normal conditions.
Segmented block copolymers of natural rubber and propylene glycol‐toluene diisocyanate oligomers
Authors: Paul C. J. , Nair M. R. Gopinathan , Neelakantan N. R. , Koshy Peter
Published: April 2004

Segmented block copolymers were synthesized from hydroxyl terminated liquid natural rubber (HTNR) and polyurethane oligomers based on 1,2‐propylene glycol and toluene diisocyanate (TDI) by one‐shot and two‐shot processes in solution. They were completely phase segregated. Structural features were characterized by infrared and nuclear magnetic resonance spectroscopies. The two‐phase morphology was deducted from thermal analysis and dynamic mechanical analysis (DMA). The soft segment glass transition temperature was about −64°C and the hard segment glass transition was between 70°C and 100°C depending on the polyurethane content. The two‐phase morphology was corroborated by a two‐stage thermal decomposition of the products. The morphology consisted of a heterogeneous dispersion of beads in a continuous matrix. The large size and the nature of the beads suggest that they are independent of the block copolymer structure and are formed by the agglomeration of the polyurethane homopolymers, which remain unbonded to the rubber chains during chain extension. At lower hard segment contents the materials behaved like quasi‐elastomers, and at higher hard segment contents, they were like tough plastics. At intermediate compositions they behaved as rigid elastomers. Variations in hardness and tear strength were consistent with this behavior.
Radiation grafting functionalization of poly (vinylidene fluoride) to compatibilize its blends with polyolefin ionomers
Authors: Valenza A. , Carianni G. , Mascia L.
Published: April 2004

Blends of a crystalline vinylidene fluoride copolymer (PVDF) and a polyolefin ionomer were produced by melt mixing and characterized by a variety of techniques to examine the effect of increasing the level of salt formation on morphology. The PVDF component was also grafted with methacrylic acid by irradiating the polymer powder and subsequently treating it with an aqueous monomer solution. The effect of neutralizing the acid in both polymer components to produce the corresponding zinc salt was also investigated. Compatibilization was accomplished by the addition of zinc acetyl acetonate (ZnAcAc) to the mixture. This increased the viscosity of the polyolefin ionomer phase, comparable to that of the PVDF. The viscosity of the grafted PVDF component did not increase appreciably after neutralization with ZnAcAc. The grafted polymer precipitated and formed a particulate dispersion with in a largely graft‐free polymer matrix. The addition of ZnAcAc to the blend of grafted PVDF and polyolefin ionomer produced a large enhancement in compatibilization, giving rise to the formation of co‐continuous phases that contained encapsulated particles of different size and in various locations.
Interrelationships between P‐V‐T and flow behavior of linear and nonlinear hydrocarbons
Authors: Yahsi Ugur
Published: April 2004

The aim of this work is to determine the branching effect on the flow behavior of alkanes. For this purpose, the zero‐shear viscosity, η0, was analyzed in terms of the Simha‐Somcynsky equation of state, SS‐EOS, using the hole fraction, h = h(P, T) computed from it. For the analysis, η0‐data of the linear and three‐branch alkanes measured in a wide range of temperature and pressure, were used. For the linear species, Utracki proposed a relation, viz. ln η0 = a0 + a1/(h + a2), where a1 = 0.79 and a2 = 0.07 are the universal parameters for linear hydrocarbons and their mixtures. In this work, this relation was found to be valid for the linear but not for the branched alkanes.
Study of electrical phenomena in carbon black–filled HDPE composite
Authors: Lee Gun Joo , Suh Kyung Do , Im Seung Soon
Published: April 2004

Percolation, positive temperature coefficient (PTC), and negative temperature co‐efficient (NTC) in carbon black‐filled HDPE composites, were studied by measuring AC electrical properties. An equivalent single parallel circuit model, which consists of a resistor and a capacitor, was adapted to explain the distribution of carbon black in composite. The electrical conductivity and admittance and phase angle were characterized by measuring the distribution of carbon black aggregates with an impedance analyzer. It was concluded that PTC is due to the deagglomeration or the breakage of the conduction networks caused by thermal expansion and/or crystalline melting of the matrix polymer, and NTC is due to the reagglomeration of the network of carbon black aggregates.
The influence of nucleating agents on the extrusion and thermoforming of polypropylene
Authors: Macauley N. J. , Harkin‐Jones E. M. A. , Murphy W. R.
Published: April 2004

A large proportion of thin‐gauge containers for the food packaging sector is produced via the thermoforming of extruded thermoplastic sheet (1–4). The production of high quality thermoformed parts is critically dependent on the standard of extruded sheet feedstock used. One method of optimizing the properties of extruded sheet and those of the final thermoformed article is through the incorporation of nucleating agents (5–10). This paper discusses the influence of nucleating agents on the extrusion and thermoforming characteristics of polypropylene. The potential of white titanium dioxide pigment particles as a viable nucleation source for polypropylene is addressed. Evidence is also presented that suggests that nucleating agents may play an important role in controlling the extent of physical change taking place in extruded sheet as a direct result of post‐production aging.
A parametric study of the shock characteristics of expandable polystyrene foam protective packaging
Authors: Lye S. W. , Lee S. G. , Tor S. B.
Published: April 2004

The design of expandable polystyrene foam buffers, used as protective packaging for a range of goods, is by and large steeped in heuristics because the design procedures have not been formalized. This paper discusses the application of Taguchi's Method of Parameter Design to the determination of the key design parameters of expandable polystyrene foam end cap buffers. An L18 orthogonal array was adopted for the planned experiments. The eight design parameters considered critical in the design of the cushioning buffers were product centroid‐to‐buffer centroid distance, cushioning area, buffer thickness, wall thickness, material density, rib configuration, rib width, and rib spacing; of these, only buffer thickness, wall thickness and buffer density were found to be significant at a 99% confidence interval. The height of the ribs, being the difference between the buffer and wall thicknesses, is the single most important factor. The buffer cushioning area was found to be not as important as its distribution over the entire load‐bearing area and the buffer configuration. The buffers were designed in Unigraphics II, and the post‐processing of the NC part program for machining on the Hamai vertical machining center. The impact shock testing of the end cap buffers was conducted on the Lansmont Model 65/81 Shock Test System.
A systematic approach for the design of a spiral mandrel die
Authors: Huang Chung‐Ching
Published: April 2004

An effective design strategy is presented for the determination of optimal flow channel geometry of a spiral mandrel die, which can produce annular, thin, and uniform products of polymer melt. This strategy includes two steps: First, a two‐dimensional flow simulation associated with the Taguchi approach is applied to search several sets of die geometric parameters, from which process the flow uniformity is assessed. Second, the optimum one parameter set selected by further considering total pressure drop, mixing degree and residence time distribution (RTD). The strategy is illustrated through the design of a spiral mandrel die with four spirals traveling a full 360°, and the viscosity of polymer melt is assumed to be power law model. The results indicated that the design criteria such as high flow uniformity, low pressure drop, good mixing degree and narrow RTD are difficult to attain simultaneously. For a particular polymer melt, there exists a design window for the geometric parameters; within the window the geometric parameter set may satisfy most of the design criteria.
Shear viscosity of rubber modified thermoplastics: Dynamically vulcanized thermoplastic elastomers and ABS resins at very low stress
Authors: Araki Takumi , White James L.
Published: April 2004

The shear viscosity of PP‐EPDM dynamically vulcanized thermoplastic elastomers and ABS resins were investigated using (a) a constant shear stress creep instrument, (b) a rotational rheometer, and (c) a capillary extrusion rheometer. It was found that stresses exist for some of these materials below which they exhibit only finite deformations. This indicates they exhibit yield values. Much attention was given to measurements of creep at low stresses especially in the neighborhood of yield values. The magnitudes of the yield stresses obtained from these low stress measurements are significantly lower than those obtained using standard extrapolation to zero shear rate of higher stresses from rotational instruments. We also observed a high shear viscosity (∼109 PA s) plateau in the materials of high rubber content. We contrasted our results to those found in the literature.
A multiscale model for polymer crystallization. I: Growth of individual spherulites
Authors: Swaminarayan Sriram , Charbon Christian
Published: April 2004

In this two‐part paper, we present a model for the solidification of semicrystalline thermoplastic polymers that links the microscopic and macroscopic length scales. The model accounts for the important physical phenomena occurring during spherulitic cyrstallization and predicts microstructural evolution. In this first part, we concentrate on the growth of individual spherulites. We present a fast and accurate model that predicts the shape of a spherulite as well as the path of its constitutive lamellae in any thermal situation. In part II of this paper we shall couple this new model for spherulite growth with a nucleation law and a macroscopic heat flow computation, thus enabling us to model realistic crystallization conditions.
Stress monitoring in thin polymer coatings using time resolved fluorescence
Authors: Shiga Tohru , Narita Takeshi , Ikawa Taiji , Okada Akane
Published: April 2004

Stress monitoring in thin polymer coatings was monitored using time resolved fluorescence from organic molecules. The decay time of fluorescence from an organic molecule in a uniaxially stretched polymer coating decreases with increasing tensile stress. The substance 9‐methylanthracene (9‐MeAn) is an effective dye for detecting internal stresses up to 10 MPa. Compared with the traditional bimetallic method, time resolved fluorescence of 9‐MeAn gave reliable values for internal stresses in a thin polymer coating. The internal stress in a polymer coating cured on a glass plate was measured during exposure to an outdoor weathering test. The internal stress diminished significantly in three days. The decrease in the internal stress was caused mainly by light irradiation. Because 9‐MeAn degraded in sunlight, it was a useful probe for stress monitoring only for periods less than two weeks.
Radiation effects of low refractive index, fluorinated methacrylate polymers for fiber cladding
Authors: Bertolucci P. R. H. , Harmon J. P. , Biagtan E. , Schueneman G. , Goldberg E. , Schuman P. , Schuman W.
Published: April 2004

The gamma radiation stability, optical properties, and mechanical properties of 1H, 1H, 3H‐hexafluorobutyl and 1H, 1H‐heptafluorobutyl methacrylate homopolymers and copolymers were determined and compared to poly(methyl methacrylate), PMMA. The aim of this study was to identify polymers for fiber cladding materials that exhibit improved optical radiation resistance and physical properties. Using 60Co source, the samples absorbed 10 Mrads of gamma radiation at 0.04 Mrads/hr in an air environment. UV/Vis transmission spectra were obtained before irradiation, just after 10 Mrads, and regularly thereafter, to track recovery in transmittance. The glass transition temperatures, decomposition temperatures, refractive indices and flexural moduli were also obtained. Poly(heptafluorobutyl methacrylate) exhibited the greatest resistance to radiation induced discoloration and the lowest refractive index of the compositions tested. As the composition of the copolymers increased in hexafluorobutyl methacrylate concentration, both the radiation induced discoloration and the refractive index increased.
Effect of particle morphology on the emulsion stability and mechanical performance of polyolefin modified asphalts
Authors: Sabbagh Amiel B. , Lesser Alan J.
Published: April 2004

Recent federal regulations concenrning roadbed performance have motivated research in polymer modified asphalt binders. Earlier studies on these binders have shown that many of them are susceptible to gross phase separation when the binder is stored at high temperatures under quiescent conditions. This phase separation, in turn, is affected by the initial morphology and storage conditions. In this effort we investigate the effect of particle morphology on the high‐temperature emulsion stability of a low‐density polyethylene‐modified asphalt binder, as well as the concomitant effects on the mechanical behavior. We show for unstabilized emulsions that the dominant phase separation mechanism shifts from coalescence to creaming at a critical particle radius of 4 μm at 110°C. However, stabilized emulsions showed no evidence of gross phase separation for up to 48 hours at 110°C. Dramatically different morphologies were observed for the unstabilized and stabilized emulsions; unstabilized emulsions having teardrop shaped particles and stabilized emulsions having both spherical particles and long cylindrical domains. The mechanical behavior, including the high‐temperature dynamic viscoelastic behavior and low‐temperature fracture toughness, increased with polyolefin content, but was insensitive to the particle morphology.
Melting model for modular self wiping co‐rotating twin screw extruders
Authors: Bawiskar Santosh , White James L.
Published: April 2004

A model for the melting process in a self wiping co‐rotating twin screw extruder is described. Self‐wiping co‐rotating twin screw extruders are modular and starve fed. This leads to melting mechanisms that are different from single screw extruders. The melting process in the modular screw configurations generally occurs in specialized sections such as kneading disk blocks. The model, based on our previous experimental observations, considers the formation of two stratified layers of melt in contact with the hot barrel and solid pellets in contact with the relatively colder screw. In the kneading disk blocks, a part of the solid bed is blocked because of the relative stagger between successive disks. The model predicts both the location of melting and melting lengths in a screw configuration. Calculations for individual screw elements and kneading disc elements are presented first. Melting in a modular configuration of these elements is then considered. The effect of operating variables such as mass flow rate and screw speed on melting is then studied. The model is put in a dimensionless form and the effect of various dimensionless groups is discussed. We make a comparison to the experiment and agreement is good.
Electrocapillary wave studies of different poly(dimethyl siloxane)s
Authors: Seo Yongsok , Skarlupka Randy , Yu Hyuk
Published: April 2004

The monolayer behavior of different end‐functionalized poly(dimethyl siloxane)s (PDMSs) and a block copolymer, poly(dimethyl siloxane‐co‐ethylene oxide) (PDMS‐co‐EO) spread on an oligomeric poly(ethylene glycol) (PEG) substrates, were studied by means of electrocapillary wave diffraction (ECWD). Over a relatively small temperature range (40–70°C), the damping constant was more dependent on temperature than on the wave vector. Different surface layer properties were observed for two PDMS: one terminated with a methyl group (PDMS‐CH3) and the one terminated with a hydroxy group (PDMS‐OH). PDMS‐OH showed a larger reduction in surface tension compared to PDMS‐CH3 because of a higher interfacial affinity with PEG, which indicated that its monolayer surface activity was weaker. A lower surface elasticity of PDMS‐OH than that of PDMS‐CH3 supported that conclusion. The block copolymer showed no surface activity, since the short siloxane moiety did not repel the strong interaction between PEG and the ethylene oxide.
Effect of surface properties on the adhesion between PVC and wood veneer laminates
Authors: Matuana Laurent M. , Balatinecz John J. , Park Chul B.
Published: April 2004

The interface between plastic and wood fibers strongly influences the mechanical properties of a plastic/wood‐fiber composite. This paper presents a means for evaluating the effectiveness of surface treatment on the wood‐fibers in the PVC/wood‐fiber composites by investigating the adhesion between PVC and laminated wood veneers. Wood veneers were first treated with γ‐aminopropyltriethoxysilane, dichlorodiethylsilane, phthalic anhydride, and maleated polypropylene for surface modification. The chemical modification made on the wood surfaces was then characterized using different complementary surface analytical techniques: X‐ray photoelectron spectroscopy and surface tension measurements. The surface tension was determined from the equation of state for interfacial tensions and the measured contact angles of glycerol sessile drops on the wood veneers (both untreated and treated) and on PVC using the Axisymmetric Drop Shape Analysis–Contact Diameter (ADSA‐CD) approach. The adhesion property was evaluated by measuring the tensile shear strength of single lap joints between two wood veneers bonded with a PVC film. The adhesion between PVC and wood veneer laminates was significantly improved when wood veneers were treated with amino‐silane, while no improvement was observed for the other adhesion promoters. Our experimental results indicate that matching the surface tension is not sufficient to ensure good adhesion between PVC and wood veneers.
Simple formulae for the effective moduli of unidirectional aligned composites
Authors: Hui C. Y. , Shia David
Published: April 2004

Simple closed form expressions for the effective tensile moduli of an unidirectionally aligned two phase composite reinforced by fiber‐like or flake‐like inclusions of aspect ratio α are obtained. The case of α ≫ 1 corresponds to fiber‐like inclusions whereas the case of α ≪ 1 corresponds to flake‐like inclusions. These expressions are based on the exact results obtained by Tandon and Weng, who used the Mori‐Tanaka method to obtain the effective moduli of such composites. These expressions are then compared with various empirically based formulae such as the Halpin‐Tsai equation and the Modified Rule of Mixtures equation. It is found that very large discrepancies result when the modulus ratio E0/E1 is sufficiently small compared with the aspect ratio of the flake‐like inclusions, where E1 and E0 are the Young's modulus of the inclusions and the matrix, respectively. Simple criteria for the validity of the rule of mixtures relation are also given. Also, the predictions of the simple closed form expressions are compared to available experimental results and favorable agreements are obtained.
Homogeneous and heterogeneous sulfonation of polymers: A review
Authors: Kučera F. , Jančář J.
Published: April 2004

This paper reviews the various reactions used to sulfonate polymers, especially polystyrene. The mechanisms for the sulfonation of low molar mass compounds are also discussed. The commonly used sulfonation reagents are described, with an emphasis on SO3and its physical and chemical properties. Polymer sulfonations can be grouped into two general routes: one involving homogeneous sulfonation and the other heterogeneous reactions.
Effect of processing conditions on shrinkage in injection molding
Authors: Jansen K. M. B. , Van Dijk D. J. , Husselman M. H.
Published: April 2004

A systematic study on the effect of processing conditions on mold shrinkage was undertaken for seven common thermoplastic polymers. It turned out that the holding pressure was always the key parameter. The effect of the melt temperature is slightly less important. Injection velocity and mold temperature do not show a general trend for all polymers. It was shown that at least for amorphous polymers a simple thermoelastic model could describe all experimental results. For semi‐crystalline materials the model overpredicts shrinkage.
Kinetics of forming poly(butylene succinate) (PBS) oligomer in the presence of MBTO catalyst
Authors: Park Sang Soon , Jun Ho Wook , Im Seung Soon
Published: April 2004

The direct‐esterification reaction of succinic acid (SA) with 1,4‐butanediol (BD) was investigated in the temperature range from 170°C to 190°C with and without a monobutyl tinoxide (MBTO) catalyst. The extent of reaction was measured by the quantity of water distilled from the reaction. The effects of reaction temperature, molar ratio of SA and BD, and MBTO concentration on the kinetics were studied. The experimental kinetics results for uncatalyzed reactions agreed quite well with the Flory model. A new complex model was developed for the MBTO catalyzed reaction, and the experimental results showed good agreement with the complex model.
Preparation and characterization of LDPE/starch blends containing ethylene/vinyl acetate copolymer as compatibilizer
Authors: Prinos J. , Bikiaris D. , Theologidis S. , Panayiotou C.
Published: April 2004

A series of LDPE blends with plasticized (PLST) and granular starch (FILST) were prepared. Ethylene/vinyl acetate (EVA) copolymer was used as a compatibilizer in three different amounts: 10, 25 and 50 wt% based on starch. The blends were studied by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Second derivative IR spectra showed peak shifts similar to those observed in V‐type starch complexes with ethylene/vinyl alcohol copolymers. The possibility for V‐type complex formation is supported by the lower biodegradation rates of the blends containing higher amounts of EVA. Mechanical properties of the blends, especially elongation at break, were satisfactory even for blends containing high amounts of starch (20–30 wt%).
Mechanism of corona treatment on polyolefin films
Authors: Zhang Dong , Sun Qin , Wadsworth Larry C.
Published: April 2004

This paper reviews recent studies on the mechanism of corona treatment of polyolefin films, specifically the chemical and physical changes of this process and the self‐adhesion mechanism. Corona discharge of polymeric films introduces polar groups into the surfaces, which increases the surface energy and, as a consequence, improves substrate wettability and adhesion. The main chemical mechanism of corona treatment is oxidation. In addition, corona treatment can crosslink surface regions and increase the film cohesive strength.
The cause of the grey discoloration of PET prepared by the use of antimony‐catalysts
Authors: Aharoni Shaul M.
Published: April 2004

Heating three antimony catalysts with several glycols and other model compounds in open and sealed vessels with various degrees of oxygen availability was followed by analyses of the volatile products in the head‐space and of the nonvolatile products. Bis(hydroxyethylene terephthalate)(Bis‐HET) and terephthalic acid (TA) plus ethylene glycol (EG) were separately polymerized to poly(ethylene terephthalate)(PET) and TA plus triethylene glycol (TEG) was polymerized to poly(triethyleneglycol terephthalate) (PTEGT). Analyses of the polymers and of the model compounds revealed that: (1) Free glycols or the glycolate moieties in polyesters degrade upon heating in the presence of oxygen to produce equal amounts of CO and CO2. (2) In the presence of Sb(III) species, the CO oxidizes to CO2 at elevated temperatures with the concomitant reduction of Sb(III) to very fine black particles of the elemental Sb(O). This is the cause for the grey discoloration of PET made with Sb‐catalysts. The redox reaction starts at about 200°C and is fully dominant at about 235°C and above. (3) At temperatures lower than ˜200°C, the Sb(III) usually converts to the white Sb2O3 and the CO does not oxidize the CO2.
An experimental comparison of cooling time for cylindrical plastic components using heat conduction models in the non‐conservative and conservative forms
Authors: Dubay Rickey , Bell Adam C.
Published: April 2004

In the manufacture of plastic components, predicting cooling duration and temperature distribution are critical for maintaining optimum productivity costs and part quality. We investigated the cooling cycle of injection molding for cylindrical shaped plastic components. A numerical model was formulated using the full conservative form of the energy equation with temperature dependent polymer properties having continuous equations of state. The cooling time predictions from this numerical method were in good agreement with our experimental results. This model predicted shorter cooling times than the often used non‐conservative heat conduction model that uses constant polymer properties or a temperature dependent thermal diffusivity. Good agreement in cooling time was obtained using the model of Ballman and Shusman and the conservative model for part thicknesses #3 mm. The investigation indicated that the statistical cooling time model of Busch et al. is more suitable for predicting plastic part cooling.
An experimental study on the effect of polymer viscoelasticity on layer rearrangement in coextruded structures
Authors: Dooley Joseph , Hyun Kun Sup , Hughes Kevin
Published: April 2004

Previous work on the layer thickness uniformity of coextruded structures has centered primarily on the effects of differing polymer viscosities in the individual layers. These differences in viscosities result in a phenomenon known as “viscous encapsulation” in which the less viscous layer tends to encapsulate the more viscous layer producing nonuniform layer thicknesses. In this study, the effect of polymer viscoelasticity on the layer thickness uniformity of multilayer coextruded structures was investigated by coextruding multilayer structures through die channels of different cross‐sectional shapes and observing the location of the interface. In order to minimize the viscosity effects, the coextrusion experiments were conducted with identical materials in each layer that were pigmented to allow observation of the layer interface. It was shown experimentally that coextruding identical polymers through channels of various geometries can cause the layers to rearrange. This layer rearrangement appears to be caused by secondary flows that occur in different channel geometries due to the viscoelastic characteristics of the polymer. Layer rearrangement of identical polymers implies that even resins with viscosities well matched for coextrusion may experience nonuniform layer thicknesses when coextruded through large dies.
Modeling warpage in reinforced polymer disks
Authors: Fahy E. J.
Published: April 2004

A circular disk mold is sometimes employed to test how a reinforced polymer will induce part warpage or distortion after removal from an injection mold. These polymer disks are modeled by developing an analogy to axially symmetric disks that have the reinforcement either in the disk radial or tangential direction and warp to a cup or saddle shaped disk during cooling. The governing mechanisms causing warpage are discussed with analytical and numerical models employed to quantify the impact of in‐plane thermal anisotropy on warpage. The cup and saddle warpage formulae that are derived can guide the engineer on estimating the underlying polymer properties as well as evaluating the impact of part design on thermal warpage.
Numerical simulation of multi‐layer flow for polymer melts—A study of the effect of viscoelasticity on interface shape of polymers within dies
Authors: Matsunaga K. , Funatsu K. , Kajiwara T.
Published: April 2004

A two‐dimensional simulation was developed for multi‐layer confluent viscoelastic flow in dies, using a finite element method. The simulated interface shape was compared with the experimental results of previous researchers, and the simulated results were confirmed. Two‐layer and three‐layer flows of two or three kinds of viscoelastic fluids were simulated. Fluids with different non‐Newtonian viscosities and the first normal stress differences were used. The layer thicknesses in dies are mainly determined by the shear viscosity and less by the elasticity of the fluid. The normal stress difference between the fluids forming an interface may be related to interfacial instability, and normal stresses near the interface were examined. The normal stress difference between both fluids was affected by the first normal stress difference and elongational viscosity.
Extrusion of PE/PS blends with supercritical carbon dioxide
Authors: Lee Minhee , Tzoganakis Costas , Park Chul B.
Published: April 2004

The effects of dissolved supercritical carbon dioxide on the viscosity and morphological properties were investigated for polyethylene/polystyrene blends in a twin‐screw extruder. The viscosities of the blend/CO2 solutions were measured using a wedge die mounted on the extruder. A considerable reduction of viscosity was found when CO2 was dissolved in the blend. It was observed that the dissolution of CO2 into PE/PS blends, regardless of the CO2 content used, led to decreased shear thinning behavior resulting in an increase of the power law index from 0.29 to 0.34. The cell structures of foamed PE/PS blends showed a typical dependence of pressure and CO2 concentration, with higher operating pressures and CO2 content leading to a smaller cell size. Also, it was noted that the size of the dispersed PS phase in the PE/PS phase blends decreased by increasing the CO2 concentration, and that the dispersed PS phase domains were highly elongated in the direction normal to the cell radius.
Rheological properties of fumed silica filled Bis‐GMA dispersions
Authors: Kim Sangwoo , Jang Jyongsik , Kim Ohyoung
Published: April 2004

The rheological properties of Bis‐GMA dispersions filled with fumed silica were investigated to optimize the manufacturing process and mechanical properties by using a Rheometrics Mechanical Spectrometer (RMS). Steady and dynamic measurements on the RMS were carried out to obtain shear viscosity and dynamic mechanical properties. The effect of several factors on the rheological properties of fumed silica dispersions was also examined. The factors were a concentration of a silane coupling agent (γ‐MPS), the methods of surface treatment of fillers, silica content, diluent concentration, shear rate, and operating temperatur. From these studies, it was observed that shear viscosity showed an asymptotic phenomenon at a higher concentration than a uniform multi‐layer coverage concentration of γ‐MPS. The silane coupling agent had a significant role in the reduction of tan δ, resulting from a decrease of loss modulus, while fillers decreased tan δ by increasing the storage modulus. In cases where the silica content and diluent concentration increased simultaneously, the Barcol hardness of Bis‐GMA/silica composites was increased, but there was no change in the viscosity of dispersions and diametral tensile strength of those composites.
Comparison of oxidation induction time measurements with values derived from oxidation induction temperature measurements for EPDM and XLPE polymers
Authors: Mason L. R. , Reynolds A. B.
Published: April 2004

Oxidative stability and retained operational utility of polymers used as insulation for electrical cables, such as ethylene propylene diene monomer (EPDM) and crosslinked polyethylene (XLPE), may be assessed by oxidation induction time (OIT) analysis. OIT is measured directly with a differential scanning calorimeter. Using a simplified kinetics model, Gimzewski demonstrated that it is possible to calculate the OIT from measured values of oxidation induction temperature and the activation energy for petroleum lubricants. In the present research, directly measured OITs are compared with OITs calculated from measured oxidation induction temperatures and activation energies for EPDM and XLPE cable insulation. Good agreement between the two methods was demonstrated for these materials.
Prediction of equilibrium polymer blend morphology in dispersed two‐phase flow and comparison with experiment
Authors: Han Chang Dae , Sun Junsuo , Chuang Hsiao‐ken , Lee Je Kyun
Published: April 2004

A theory is developed to predict equilibrium polymer blend morphology in dispersed two‐phase flow in terms of the viscosity ratio and blend ratio of the constituent components. We formulated a system of equations for the ‘One‐Cell Model,’ describing the situation where a spherical droplet of one liquid is dispersed in another liquid, by first considering a pair of Newtonian liquids and then a pair of truncated power‐law fluids. The question posed was: which of the two liquids, A or B, will form a droplet dispersed in another liquid? Finite element method was employed to calculate the rate of the energy dissipated per unit volume when a unit cell, having either Morphology I or Morphology II, was subjected to steady‐state simple shear flow, where Morphology I has a droplet of liquid A dispersed in the matrix phase of liquid B and Morphology II has a droplet of liquid B dispersed in the matrix phase of liquid A. We used a criterion that the morphology that requires a lower rate of the energy dissipated per unit volume in dispersed two‐phase flow is an equilibrium polymer blend morphology. In so doing, we determined the blend composition, at which a matrix inversion takes place, in terms of the viscosity ratio of the constituent components. Theoretically predicted blend morphologies compared favorably with experimental results.
Rheological and mechanical relaxation behavior of a thermally crosslinkable poly(ethylene terephthalate)
Authors: Mather Patrick T. , Romo‐uribe A.
Published: April 2004

A novel terephthalic acid derivative based on benzocyclobutene, XTA, has been used as a comonomer in the preparation of thermally crosslinkable poly(ethylene terephthalate) copolymers. We have examined the rheological properties of a series of such polymers containing varying monomer percentages of the XTA comonomer: 0, 1, 5, 10, and 20. Incorporation of XTA into PET is found to cause dramatic changes in the temperature and time dependence of the rheological material functions, all indicating that the rate of crosslinking between chains in the melt increases as the XTA percentage is increased. The impact of thermal crosslinking on mechanical properties is also examined using dynamic mechanical analysis (DMA) on samples molded at a selected crosslinking temperature for times yielding varying levels of crosslinking extent. DMA results show that the activation energy of the β mechanical relaxation increases significantly, indicating the importance of torsional mobility of the aromatic ring of PET.
Processing and characterization of microcellular foamed high‐density polythylene/isotactic polypropylene blends
Authors: Doroudiani Saeed , Park Chul B. , Kortschot Mark T.
Published: April 2004

In this paper, a study on the batch processing and characterization of microcellular foamed high‐density polyethylene (HDPE/iPP) blends is reported. A microcellular plastic is a foamed polymer with a cell density greater than 109 cells/cm3 and fully grown cells smaller than 10 µm. Recent studies have shown that the morphology and crystallinity of semicrystalline polymers have a great influence on the solubility and diffusivity of the blowing agent and on the cellular structure of the resulting foam in microcellular batch processing. In this research, blends of HDPE and iPP were used to produce materials with variety of crystalline and phase morphologies to enhance the subsequent microcellular foaming. It was possible to produce much finer and more uniform foams with the blends than with neat HDPE and iPP. Moreover, the mechanical properties and in particular the impact strength of the blends were significantly improved by foaming.
Photochemical modification of polymers—photocrosslinking, surface photografting, and lamination
Authors: Rånby Bengt
Published: April 2004

The molecular mechanism, the kinetics and the process development of photocrosslinking of diene elastomers, of high density and low density polyethylenes, and of new linear and dendritic unsaturated polyesters using UV‐irradiation are described. New methods for modification of various polymers by surface photografting are presented, the effects on adhesion and adsorption, and the mechanism of the reactions related to the shortlived high energy states of aromatic ketones as initiators are presented and discussed. The development of surface photografting as a new method for UV‐initiated lamination of various polymer films and sheets is described, the molecular mechanism and the kinetics of the reactions are discussed, and the mechanical and barrier properties of the laminates are presented.
Crosslinking of polybutadiene rubber without any vulcanization agent
Authors: Bellander Martin , Stenberg Bengt , Persson Sture
Published: April 2004

Polybutadiene rubber with 10% vinyl unsaturation has been crosslinked without the addition of any vulcanization chemicals. The crosslinks have been created through treatment at high temperature (240–250°C) and elevated pressure (<293 MPa) in a plunger type mold. The treatment time needed to achieve a crosslinked material is of the order of a few minutes and the reaction rate is shown to be dependent upon the temperature as well as upon the pressure applied. As a result of the severe treatment, some degradation reactions may be expected but careful FTIR analysis shows no increased oxidation. There is some consumption of the vinyl unsaturation, to an amount comparable to the number of crosslinks formed. The presence of carbon black increases the measured crosslink density, as expected, but at higher pressures the amount of extra network material, because of the carbon black, is much larger than at lower pressures, suggesting that the carbon black plays a critical role in the network formation process. The stress relaxation properties in compression of the rubber material were investigated and found to be comparable to those of a peroxide vulcanizate.
Assessment of development and relaxation of orientation in a sheared thermotropic liquid crystalline copolyester
Authors: Wiberg G. , Hillborg H. , Gedde U. W.
Published: April 2004

Shear‐induced chain orientation and relaxation of chain orientation in a thermotropic liquid‐crystalline poly(4‐hydroxybenzoic acid (73mol%)‐co‐2‐hydroxy‐6‐naphthoic acid (27 mol%)) (Vectra A950) were studied by means of transmitted light intensity through crossed polarizers in a shear cell. Shear rates ranged between 4 and 1000 s−1 and the level of chain orientation increased with increasing shear rate and increasing temperature. Overall, the times for relaxation were very short. The longest relaxation times (˜21s) were obtained at the lowest shear temperatures and at intermediate shear rates. At high shear rates, the relaxation times were generally short (˜2s) and independent of temperature. The rapid relaxation of orientation after high rate shearing (100–1000 s−1) indicates that shear‐induced crystallization is inhibited under these conditions. A certain degree of chain orientation was still present although the relaxation as judged by the transmitted light intensity was complete. Signs of recrystallization were observed if the samples were not preheated to 320°C prior to shearing. By simultanecous shearing and cooling, high degrees of orientation were achieved (f ˜ 0.7) as revealed by X‐ray diffraction and infrared dichroism. Infrared spectroscopy showed that annealing of oriented samples at 250°C led to an increase in thermal stability of the orientation with annealing time.