bluuebunny/crossref_metadata_2025 huggingface dataset:
The application of endless‐fiber reinforced polymers
Authors: Menges G. , Minte J.
Published: December 2004

Both in aircraft and automobile construction, the transition from metals to fiber reinforced polymer resins is taking place with increasing regularity. Beginning with the wide selection of possible materials, definite examples of the mechanical properties of construction parts are discussed in this article. Different production possibilities based on fiber winding technology are shown. The application of robots in production is also considered.
The effect of molding time and temperature on the modulus and glass transition of phenolics
Authors: Landi V. R. , Mersereau J. M. , Dorman S. E.
Published: December 2004

The effects of molding time and temperature on the dynamic mechanical behavior of a novolak phenolic molding compound were measured using the DuPont Dynamic Mechanical Analyzer. Large differences were found in the modulus‐temperature response over the range of curing times (10 to 1800 s.) and temperatures (132 to 218°C) employed. Glass transition temperatures increased well beyond cure temperatures at long cure times. In the asmolded condition, samples cured at lower temperature had higher room temperature modulus than those cured at higher temperatures, and the lower modulus corresponded to lower density. Postbaking by steps up to 232°C increased the glass transition above 280°C, and also served to normalize the modulus differences found in as‐molded samples.
Properties of cellulose‐polyester composites
Authors: Zadorecki Pawel , Flodin Per
Published: December 2004

Cellulose fibers were used as reinforcement in unsaturated polyesters. Composites were prepared as laminates with cellulose fibers used in the form of paper sheets. The impregnation was carried out in a vacuum and resulted in a composite with uniform distribution of polyester around the fibers. The polyester was also detected in the lumen of the fibers. The tensile properties were evaluated and compared with tensile properties of glass fiber reinforced polyester. It is found that cellulose fibers increase the tensile strength and modulus of a polyester composite. Immersion of the cellulose‐polyester composites in water caused a considerable water uptake. The presence of water in the composites decreased the tensile properties drastically. Scanning electron photomicrographs of the tensile fracture surfaces showed a lack of adhesion between the cellulose fibers and the polyester matrix in wet conditions.
Optimization of polyester sheet molding compound. Part I: Experimental study
Authors: Fan J. D. , Marinelli J. M. , Lee L. James
Published: December 2004

A series of differential scanning calorimetry (DSC) and molding experiments were carried out to measure the effect of curing agents, namely initiators and inhibitor, on the SMC reaction. Results showed that the induction time, the reaction rate, and the limiting conversion of sheet molding compounds can be modified through the change of curing agents. The SMC resin with a higher concentration of low temperature initiator and molded at higher temperature may cure in a shorter period of time and reach a higher conversion. The shortened scorch time and shelf life can be balanced by adding small amount of inhibitor. Surface quality of molded SMC parts measured by solvent extraction process showed that limiting conversion is an important factor in SMC molding.
Influence of talc's morphological characteristics on the toughness of a composite based on low‐density polyethylene and polypropylene blends
Authors: Ramos M. Arroyo , Matheu J. P. Vigo
Published: December 2004

The toughness of polymer composites based on low‐density polyethylene (LDPE)/polypropylene (PP) blends and filled with talcs of different particle size and particle size distribution was studied applying the two‐variable Box‐Hunter method of optimization. The effect of the polymer matrix composition and percent talc on the Charpy impact strength of the composites, at –30°C, was investigated. The results show a change in the polymer matrix behavior at PP contents of 60% and 75%, depending on talc particle size. At these percentages of PP, toughness exhibits a minimum that becomes lower as the filler content is increased. Optical microscopy shows a nucleating effect of the talc particles for the crystalline polymer. The larger the talc particle size, the higher the nucleation density. The minimum toughness arises at higher PP content in the matrix. At PP contents in the matrix below 35%, the filler has a minimal effect on composite toughness.
Molecular composites based on thermosetting matrix polymers: Poly(p‐phenyleneterephthalamide)‐epoxy
Authors: Moore D. R. , Mathias L. J.
Published: December 2004

Poly(p‐phenyleneterephthalamide) (PPTA) reinforced molecular composites that utilize a thermosetting epoxy as the matrix polymer have been prepared by an in situ polymerization process. The properties of these molecular composites were compared with those of Kevlar pulp‐filled composites that utilized the same matrix formulation. Study of the curing reactions of these systems using Fourier transform infrared, dynamic mechanical analysis, and nuclear magnetic resonance spectroscopy indicated some differences in the reactivity and ultimate polymer structure of these two systems. A comparison of the properties indicated increased tensile strength, modulus, and heat resistance for the molecularly reinforced material over the conventional fiber‐filled system. Examination of the morphology of the molecular composite system showed that aggregated PPTA molecules are formed during the in situ polymerization process. This aggregation phenomenon was found to be due to formation of a liquid crystalline polymer solution during processing and final cure. These findings indicate the possibilities that exist in molecular composite processing for simultaneous control of the properties of the matrix and the reinforcement.
The gel‐phase modulus of high‐impact polystyrene from dynamic mechanical spectroscopy
Authors: Kefalas V. , Theocaris P. S. , Kontou E.
Published: December 2004

High‐impact polystyrene (HIPS) constitutes a mechanically attractive composite, consisting of a glassy matrix and a rubberlike particle phase (gel phase). Dynamic mechanical spectroscopy was performed for the polystyrene matrix for three different types of HIPS as well as for the concentrated gel‐phase material, at the vicinity of the respective glass‐transition temperatures (Tg). An approximate estimation of the gel‐phase modulus was attempted by using known mechanical models. A comparison with experiments was also made. The modulus of the composite was found to be lower than the theoretical lower bound for particulate composites. This was attributed to a separate phase between gel particles and the matrix. A diffusion‐type variation of the modulus of this mesophase layer was estimated, and a correlation between calculated fitting parametric exponents and impact behavior of HIPS was found. Moreover, the Tgs of the materials under investigation were also measured with two independent methods. It was found that all types of HIPS presented higher Tgs than the pure matrix by 5 to 10°C with the highest Tg found being that of the gel‐enriched material. The shift of Tgs to higher temperatures was attributed to an eventual increase of the effective cross‐link density of the matrix because of grafting.
Non‐isothermal crystallization of poly(etheretherketone) aromatic polymer composite
Authors: Cebe Peggy
Published: December 2004

Non‐isothermal crystallization kinetics of poly(ether‐etherketone), PEEK, in the presence of carbon fibers has been studied for APC‐2 composites. Samples of APC‐2 PEEK composite were cooled from the melt at rates ranging from −1 to −20°C/min. A differential scanning calorimeter was used to monitor heat flow during the non‐isothermal crystallization. Effects of cooling rate on crystallization temperature, degree of crystallinity, and conversion rate were studied. We show that the Ozawa analysis fails to provide an adequate description of the non‐isothermal crystallization process in composite PEEK. A modified Avrami analysis was used to describe crystallization kinetics. For the composite material, the change from the primary kinetics of free crystal growth to slower secondary kinetics occurred at about 50 percent relative conversion for all cooling rates. Non‐isothermal crystallization in APC‐2 composite PEEK can be characterized by higher initiation temperature, higher heat flow maximum temperature, and greater relative conversion by primary processes when compared to 450G neat resin PEEK crystallization.
Experimental determination of thermal and adhesion stress in particle filled thermoplasts
Authors: Vollenberg Peter , Heikens D. , Ladan H. C. B.
Published: December 2004

The phenomena of dewetting in filled thermoplastics were studied by light microscopy and were correlated with variations in the slope of stress‐strain diagrams in constant strain rate tests. In such diagrams, kinks in the plots were found to correspond to the dewetting stress. The corresponding local stress at a filler particle is then equal to the sum of the thermal compressive stress and the adhesion stress. It was shown that the adhesion stress was proportional to the reciprocal root of the particle radius. Also, values of dewetting stress predicted for inorganic particles with radii smaller than 2–4 micrometers are higher than the stresses at which crazes and shear‐bands are formed near such particles, indicating that dewetting will not occur in those cases, and adhesion aids may be superfluous.
Processing sequence and the properties of vinyl compounds
Authors: Trujillo Eleana , Richard C. , Schreiber H. P.
Published: December 2004

Acid‐base interaction parameters were measured by inverse gas chromatography over broad temperature ranges for Poly(vinyl chloride), plasticizer, and CaCO3 fillers. Mixing was performed by three routes. In one, all components were added simultaneously, while in others two of the components were premixed, the third ingredient being added subsequently. Mixing was carried on to equilibrium torque readings. The energy requirement for mixing was found to depend on the interaction balance among the components, and to vary with the procedure selected. Minimum requirement was associated with the simultaneous introduction of all ingredients. Higher energies were needed in sequential mixing schemes, presumably because equilibrium partitioning of components was hindered in these instances. Initial mechanical properties of the compounds did not vary greatly with preparation procedure, but upon aging, mechanical property variations became quite evident. Component repartitioning, driven by shifting interaction balances at aging and at test (room) temperatures are cited as responsible. The kinetics of attaining equilibrium mechanical properties also were found to vary with mixing procedure and to respond to the interaction balance concept.
Fatigue crack propagation in mica‐filled polyolefins
Authors: Allard R. C. , Vu‐Khanh T. , Chalifoux J.‐P.
Published: December 2004

Edge notched samples of polypropylene (PP) and high‐density polyethylene (HDPE) containing different mica concentrations were tested in mode I tensile loading. Crack growth was approximated by a non‐linear regression of exponential form using statistical software (SAS). Characterization of fatigue crack propagation (FCP) was made using the Paris‐Erdogan law. The crack front in PP was preceded by a wide plastic zone in which craze developed, leading to a discontinuous crack growth. Using spline functions, a margin between maximum and minimum FCP rates, recorded during the crack progression, is presented along with the average FCP rates. It is shown that mica‐reinforced PP samples exhibit higher FCP rates than unfilled PP. In HDPE, mica reduces FCP rates resulting in a higher resistance to fatigue crack propagation. Effect of test frequency is presented for unfilled polymers and 10 percent mica concentration by weight in both matrices. An increase in the test frequency has no significant effect on FCP rates for both raw and mica‐reinforced PP. Unfilled and mica‐filled HDPE show noticeable decrease in FCP rates with increasing frequency.
Long‐fiber‐reinforced thermoplastic matrix composites by slurry deposition
Authors: Hiscock D. F. , Bigg D. M.
Published: December 2004

A process for producing long‐fiber‐reinforced thermoplastic matrix composites is described. This process, based on papermaking technology, consists of depositing a mixture of a polymeric powder and reinforcing fibers from an aqueous slurry. The degree of homogeneity of the mixture and the subsequent ability to handle the dried sheet have been significantly improved by the addition of less than 5% pulp fibers, based on solids concentration, to the slurry. The dried sheet is then consolidated into a composite sheet with a continuous matrix phase by the application of heat and then pressure. Tensile properties and the degree of reinforcement efficiency of composites produced by this process have been shown to be comparable to those produced by melt impregnation techniques.
Expression of activity of the filler surface of composites in inverse gas chromatography
Authors: Cigánek M. , Dressler M.
Published: December 2004

A new way is introduced to express the interaction coefficient characterizing the surface activity of fillers. The interaction coefficient is a parameter showing how many times greater a specific interaction of a testing solute with a filler surface is than a nonspecific interaction of a hypothetical alkane with the same vapor pressure. A selectin of testing solutes for the determination of the interaction coefficient is discussed. Due to a high surface activity of the studied fillers for polyolefine composites, less polar solutes (furan, dichloromethane, trichloromethane, and benzene) have been selected to study these fillers. New evaluation coefficients of acidity, basicity, and acidobasicity are proposed for a rapid activity determination of a filler surface. These coefficients can be determined from a single chromatogram of the testing solutes. The surface activity of various fillers (calcium carbonate, talc, magnesium hydroxide), as expressed by the interaction coefficient, differs so much that even the differences of surface activities in one filler type (calcium carbonate), dependent on the origin or arrangement, are conclusive.
Interfacial interactions and properties of filled polymers. II: Dispersion of filler particles
Authors: Boluk M. Y. , Schreiber H. P.
Published: December 2004

The specific interaction characteristics and the inherent agglomeration of variously surface coated rutile pigments have been assessed, respectively, by inverse gas chromatographic and powder rheological methods. Standardized methods were used to disperse the pigments in polyethylene and chlorinated polyethylene. Measurements were made of energy requirements for dispersion and of the quality of dispersion attained. It was found that in the non‐polar polyethylene matrix, dispersion processes depended on the strength of pigment agglomerates, but not on the specific interaction potential of the solids. Conversely, in the acidic chlorinated polyethylene, acid/base interactions influenced dispersion but the process was independent of inherent pigment agglomeration.
Weld‐line characteristics in short fiber reinforced thermoplastics
Authors: Vaxman A. , Narkis M. , Siegmann A. , Kenig S.
Published: December 2004

Fibers can greatly improve the mechanical properties of polymers but may also severely weaken molded parts at their weld‐line compared to their bulk strength. The tensile properties and fiber orientation of injection and compression molded fiber reinforced Noryl and polypropylene samples with and without a weld‐zone were studied. Distinct differences in structure and mechanical properties of weld‐containing and weld‐free samples were identified. In unfilled Noryl and unfilled polypropylene, the presence of a weld‐line was found to only have a small effect on the tensile strength and modulus, while in the corresponding fiber reinforced systems, orientation of the fibrous reinforcement parallel to the weld‐line caused a significant reduction of the tensile strength compared to the weld‐free products. The strength ratio of welded and unwelded specimens was found to decrease with increasing fiber concentration. Quantitative determination of the glass fiber orientation distribution within the weld‐line region and in the bulk was carried out by analyzing photomicrographs of polished sections at desired locations.
The effects of molding conditions on the surface composition of sheet molding compound
Authors: McEwen D. J. , Newbould J.
Published: December 2004

An improved internal reflection infrared spectroscopy (ATR) technique (1) has been found to be effective for measuring the relative concentrations of polyester and polystyrene (resin) and calcium carbonate filler on sheet molding compound (SMC) surfaces. The technique has been used to determine the effect of molding conditions on the surface compositions of three commercial SMC materials. The surface compositions of two of the materials, of the same formulation but obtained from different sources, were the same and were unaffected by molding conditions. The surface of the third material (or a different formulation) was found to have substantially less resin than the first two materials. The surface composition of the third material varied with molding conditions, the greatest uniformity being obtained with high molding temperatures and pressures. This study has shown that the ATR technique is suitable for determining the relative surface compositions of SMC formulations. This method will be used to correlate the SMC surface composition to SMC properties, such as surface appearance, paintability, and adhesive bond durability.
Instrumented thermoforming of advanced thermoplastic composites. III: Relative performance of various prepregs in forming double curvature parts
Authors: Dutta A. , Cakmak M.
Published: December 2004

Thermoforming of a double curvature hemispherical cap‐shaped part from different continuous carbon fiber‐reinforced thermoplastic composite prepregs has been investigated. A novel three‐piece matched die mold was used for shaping the prepregs directly from 16‐ply unconsolidated lay‐ups. For poly(ether ether ketone) (PEEK)‐based prepregs, PEEK/graphite fiber unidirectional tapes and commingled knitted three‐dimensional fabric yielded parts that possessed good shape conformity and were free of any major delamination. Encouraging results were also obtained for modified polysulfone (PXM‐8505) based unidirectional fabric as well as PEEK/graphite knitted bidirectional fabrics. Several other prepregs performed rather poorly in forming acceptable quality parts. Fiber alignment was found to be better for fabric prepregs than unidirectional tapes. Both stretching and “draw in” of the material occur during deformation, even though the relative contribution depends strongly on the prepreg form. Our thermoforming studies suggest a cycle time of 10 min or less to form good quality parts, which is an attractive feature, considering that cycle times are typically several hours for conventional thermosetting resins.
Mechanical properties and fracture of an amorphous metallic ribbon/thermoplastic matrix composite with low volume fraction of reinforcement
Authors: Varin R. A. , Ruutopold A.
Published: December 2004

Composite specimens with polypropylene matrix containing up to 1.8 percent volume fraction of amorphous metallic ribbons with the interfacial shear strength ∼0.7 MPa were fabricated by hot compaction under 10 MPa pressure. Their tensile properties and fracture behavior were investigated. It is found that within the investigated range of the volume fraction of reinforecement the composite fracture strength is close to the rule of mixtures predictions. Two types of fracture, matrix and ribbon controlled, are observed. The experimental values of the composite elastic modulus are also close to the rule of mixtures predictions.
Studies on the distribution of reinforcement in composites by energy dispersive analysis of X‐rays
Authors: Rao K. V. , Pandey G. C. , Xavier S. F. , Sharma Y. N.
Published: December 2004

A method has been developed for studying the distribution of fillers and reinforcement in polymer composites by energy dispersive analysis of X‐rays (EDAX). Conventional methods for such studies are based on the morphological examination of the contrast in the micrographs, which indicates the presence and distribution of reinforcement in a matrix. However, in case of hybrid composites, where two or more fillers of similar morphology are present, the conventional methods fail. The approach described here overcomes this limitation and provides a new semiquantitative method of identification of fillers in composites, especially those containing two or more fillers of similar morphology.
In‐situ composites: Evaluation of the adhesion between the thermoplastic matrix and the fibers of liquid crystalline polymer
Authors: Carfagna C. , Netti P. A. , Nicolais L. , Dibenedetto A. T.
Published: December 2004

Mechanical properties of fiber reinforced composites depend on the formation of stable adhesive bonds between the constituents. In order to evaluate quantitatively the adhesion between liquid crystal polymer (LCP) fibers and a thermoplastic matrix of polycarbonate, the single fiber composite test (SFC), utilized for testing glass or carbon fiber composites, has been used. Neither chemical nor physical interaction has been found: the PC and LCP phases are completely incompatible. However, a mechanical friction between PC and LCP was observed during the drawing of the sample when the neck of the matrix started.
Thermoplastics composites with ductile fiber coatings based on UHMWPE: A study on short fiber GR nylon 6
Authors: Mascia L. , Kinsella M.
Published: December 2004

Glass microscope slides were initially used to develop a technique for bonding UHMWPE films on to glass and polyamides respectively, as well as to provide a simple physical model for interlayered fiber composites. Further experiments were carried out on glass fibers coated with UHMWPE from a xylene solution, in order to evaluate the applicability of the above technique and of the physical model in actual composite systems. Although great difficulties were encountered in achieving a well boned uniform coating on the glass fibers the results have confirmed the viability of the approach: the impact strength of compression molded glass reinforced Nylon plaques, measured with an instrumented falling weight apparatus, was increased considerably with only a corresponding small loss in flexural modulus. Dynamic mechanical analysis results indicate that a UHMWPE interlayer substantially increases the tan δ of the short fiber composite over a wide temperature range, albeit with some reduction in modulus.
A comparison of the unidirectional and radial in‐plane flow of fluids through woven composite reinforcements
Authors: Parnas Richard S. , Salem Andrew J.
Published: December 2004

The in‐plane flow of fluids through dense fibrous woven reinforcements was studied to aid the development of constitutive models for use in simulations of composite fabrication by resin transfer molding. As a first part of this effort, both one‐dimensional and radial flow experiments were conducted with Newtonian fluids in several woven glass fabrics. Analysis of the one‐dimensional flow experiments shows that the two experimental techniques are often, but not always, consistent, and both techniques suggest a relationship between the physical structure of the reinforcement and the mathematical structure of the permeability tensor. Preform features at the laminar and interlaminar scales were hypothesized to influence the experimental results.
Thermal analysis of thermoplastic composites during processing
Authors: Yang Heechun , Colton Jonathan S.
Published: December 2004

Unsteady two‐dimensional thermal analysis has been performed on PEEK/AS‐4 fiber thermoplastic composites. To calculate the crystallinity of the composite, a spherulite growth model was applied. A numerical analysis was carried out with variations in mold cooling rate, the prepreg lay‐up, and the composite geometry. The effect of geometry and the cooling rate is significant in the temperature profiles. The degree of crystallinity varies with the cooling rate, but the gradient of crystallinity is small, with the exception of complex geometries at fast cooling rates. The results of numerical calculations are in excellent agreement with the experiments and offer validation of the numerical formulation.
Residual thermal stresses in bismaleimide/carbon fiber composite laminates
Authors: Di Landro Luca , Palonca Alberto , Sala Giuseppe
Published: December 2004

This is a study of residual thermal stresses in composite laminates, due to curing cycles. An extended formulation of Classical Lamination Theory (CLT) is adopted, which is able to take into account geometrical nonlinear effects owed to finite displacements. The approach is applied to square asymmetric laminates that have different dimensions and thicknesses. Final laminate shapes are evaluated after complete curing cycles; they can be cylindrical or saddle‐like, and their equilibrium configuration stable or unstable depending on thickness vs. side length ratio. The same laminates are stacked, press‐cured and the radii of curvature experimentally measured. In addition, they are modeled by means of finite element method (FEM) codes, using both linear and nonlinear techniques. Except for the thick laminates, the results obtained using nonlinear theoretical and numerical approaches show good agreement with experiment. Thermal residual strains are computed from non‐mechanical strains by subtracting laminae free thermal deformations; the corresponding stresses are evaluated through layer stiffnesses. Residual stresses are evaluated both theoretically and experimentally. For thicker laminates the disagreement is mainly due to a mixed viscous phenomenon which takes place in resin interlaminar layers and matrix intralaminae. The share of relaxed stresses is evaluated and methods that include optimal cooling path techniques are suggested.
Effects of water absorption and osmotic degradation on long‐term behavior of glass fiber reinforced polyester
Authors: Castaing Ph. , Lemoine L.
Published: December 2004

Glass fiber reinforced polyester composites, with gelcoat, are widely used as structural materials for hulls, pools, pipes, and tanks in aggressive environments, despite the lack of knowledge concerning their resistance to water in the long term. In addition, these materials may be damaged through an osmotic process, especially when immersed in water, as are boat hulls, and this phenomenon can lead to a delamination of the gelcoat and of the laminate plies. The aim of this experimental study is to evaluate the mechanical characteristics with time of orthotropic laminates subjected to accelerated tests of humid aging. The evolution of the properties with water absorption is followed by a nondestructive test procedure based on vibrational mode analysis. The results are additionally confirmed by quasi‐static bending and shear tests. It is shown that the main effects of water on the composite mechanical properties are the plasticization of the matrix an the osmotic delamination of the plies; on the other hand, gelcoat blistering had no influence on the durability. This paper highlights the need for and the complementarity of both nondestructive and destructive mechanical tests for studying the long‐term behavior of composites in marine environments.
Finite element analysis of polymer melt flow in cable‐covering crossheads
Authors: Fenner R. T. , Nadiri F.
Published: December 2004

A finite element method is presented for the analysis of isothermal non‐Newtonian polymer melt flow in narrow channels of complex shape. The particular application considered is flow in cable‐covering crossheads. The geometric flexibility of the finite element method allows a mesh of triangular elements to be constructed to suit the shape of the flow channel. Computed results obtainable from the analysis include the distribution of polymer layer thickness on the finished cable, together with the extrusion pressure required to maintain a given flow rate of melt. Some typical thickness distribution results are presented as an introduction to experimental verification of the method and its application to crosshead design.
Problems of structural characterization of polymer networks
Authors: Dušek Karel , Ilavský Michal
Published: December 2004

Problems of the characterization of network structure by investigating the network formation and its response to mechanical stress have been analyzed. Attention has been devoted to the effect of reactivity of functional groups and cyclization on the formation of network structure and to problems of obtaining the equilibrium modulus and its relation to the concentration of elastically active network chains (EANCs). It has been demonstrated that a theoretical description of network formation must be based on reliable information on the rules of joining of functional groups and on their relative reactivity; the tree‐like approximation offers a number of structural parameters of the sol and gel including, e.g, chemical clustering of units of a certain type. The main obstacles to reaching the equilibrium modulus are long relaxation, times of lightly crosslinked networks and the occurrence of secondary relaxations. In correlating the equilibrium modulus and the concentration of EANCs, it is necessary to find conditions under which the Mooney‐Rivlin constant C2 can be neglected and to carry out the required corrections of the modulus, if experimental conditions differ from those of network formation.
Entanglement networks of 1,2‐polybutadiene cross‐linked in states of strain. V. Relaxation phenomena and calculations of entanglement trapping
Authors: Carpenter Rick L. , Kan Hsin‐Chia , Ferry John D.
Published: December 2004

Linear 1,2‐polybutadiene is cross‐linked near its glass transition temperature by γ‐irradiation while strained in simple extension with a stretch ratio λo. After release, the sample retracts to a state of ease (λs). From λo, λs, and stress‐strain measurements in extension from the state of ease, the concentrations of network strands terminated by trapped entanglements (vN) and by cross‐links (vx) can be calculated. For vx/vN ≡ R′o > 1, retraction to the state of ease is rapid. For R ≃ 0.3 or less, retraction is slow and extends over many logarithmic decades of time scale. When an eased sample is stretched to λo where the cross‐links do not contribute to stress, the subsequent stress relaxation of the entanglement network toward equilibrium is also very slow if R′o is small. The slow timedependent processes are attributed to a high proportion of untrapped entanglements on dangling branched structures. The concentration of trapped entanglement strands, vN, can also be calculated from the equilibrium stress at λo. The fraction of trapped entanglements agrees rather well with the predictions of the theory of Langley.
Synthesis, characterization, and viscoelastic behavior of single‐phase interpenetrating polystyrene networks
Authors: Thiele J. L. , Cohen R. E.
Published: December 2004

Single phase interpenetrating polystyrene networks were synthesized using a room temperature photopolymerization method. Divinylbenzene was used for crosslinking both networks in most cases; a few IPNs were prepared using acrylic acid anhydride to provide labile crosslinkages in the primary network. The IPNs were characterized by means of equilibrium swelling in toluene. The results of these experiments closely approached the predictions of a swelling equation derived under the assumption that the two networks were elastically independent. Deviations from the swelling equation predictions could be explained in terms of contributions from internetwork entanglements. Small amplitude dynamic mechanical measurements indicated that the presence of the small amount (∼10 percent) of tight primary network chains had no perceptible effect on the linear viscoelastic properties.
A dynamic mechanical study of the curing reaction of two epoxy resins
Authors: Senich G. A. , MacKnight W. J. , Schneider N. S.
Published: December 2004

The curing behavior of two commercially formulated epoxy resins composed of the tetrafunctional amine dicyandiamide and with differing epoxy components, 4,4′‐bisglycidylphenyl‐2,2′‐propane and the tetraglycidyl ether of methylene dianiline, is characterized by dynamic spring analysis. This supported viscoelastic technique is well suited to the determination of the onset of gelation under isothermal conditions but the method is not useful for monitoring later stages of reaction when the resins become more rigid. The activation energy for the curing of the two resins is about 87 kJ/mole (20.7 kcal/mole). Rate constants for the first order curing reaction are given. Additional studies of films cured below the ultimate Tg show that two relaxations can be observed upon heating. The first relaxation occurs near the original isothermal cure temperature with a low activation energy, about 250 kJ/mole, whereas the second relaxation occurs near the ultimate Tg, under the conditions used here, with an activation energy of 500–650 kJ/mole. It is believed that these activation energies provide a unique method of characterizing the molecular mobility of epoxy resins at various states of cure.
Automated torsion pendulum analysis of the formation and properties of a polyphthalocyanine
Authors: Gillham J. K.
Published: December 2004

The cure and transitions of a C10 diamide phthalocyanine resin have been investigated by the torsional braid method. Two relaxations (T′ > Tg and T > Tg) occurring above the glass transition temperature (Tg) are shown to correspond to two relaxations which develop prior to vitrification on isothermal cure. They bear directly on processibility of the material. Also investigated was the coupling between a low temperature transition (∼ − 146°C/2.1 Hz) inherent to the material and a low temperature water‐induced transition (∼ − 76°C/1.9 Hz).
Fickian diffusion of alkanes through glassy polymers: Effects of temperature, diffusant size, and polymer structure
Authors: Chen S. P. , Edin J. A. D.
Published: December 2004

Diffusivities D ranging over six orders of magnitude with values as low as 2 × 10−13 cm2/s have been obtained by a recently developed permeation apparatus, employing a gas‐flow method and a flame ionization detector; Log D for hydrocarbons in bisphenol‐A polycarbonate (PC) at 120°C is proportional to the square of the molecular diameter (d2) as given by the Lennard‐Jones 6–12 potential. This correlation holds even for the nonspherical n‐hexane molecule. The activation energy for diffusion is also linearly related to d2, with values of 9.5 and 23 kcal/mol for methane and neopentane in PC, respectively. Comparison of PC with two similar polymers of higher glass‐transition temperatures (Tg) indicates that our diffusion data do not correlate with the Tg of these polymers. The presence of subsidiary transitions, however, appears to enhance segmental mobilities, increasing the rate of diffusion of the hydrocarbons. The thermodynamic solubility of alkanes in glassy PC can be directly related to their boiling points, and in addition, their enthalpy of solution is linearly related to the heat of condensation of these permeants.
Oxygen transmission through highly crosslinked polymers
Authors: Gordon Gerald A. , Ravve Abraham
Published: December 2004

Highly crosslinked polymers of varying structure were produced by the reaction of poly(glycidyl acrylate) (PGA) and methacrylate (PGM) with a variety of anhydride crosslinking agents: chlorendic (CA), glutaric (GA), maleic (MeA), succinic (SA), and polyrnalonic (pMnA) anhydrides. Topology was also varied by the use of a diluent and a comonomer in the backbone chain. Oxygen permeation measurements were made on these polymers coated onto a polypropylene film substrate before crosslinking. The crosslinking process greatly reduced the O2 permeability which, however, was dependent not only on the degree of crosslinking (yield of the crosslinking reaction), but also on the crosslink density, the chemical nature of the structural elements, and the topology of the polymer network. Thus the most impermeable coating (XPGA/CA) was made not from the stiffest and bulkiest components (PGM and CA), but by the reaction of the bulkiest anhydride (CA) with the more flexible polymer backbone chain (PGA). This is explained in terms of the need for chain flexibility to produce a crosslinked structure of optimum space filling character and network tightness.
Transport in oriented bottles made from polyester resin
Authors: Swaroop Naresh , Gordon Gerald A.
Published: December 2004

Oxygen permeation has been measured in flat sheet as a function of degree of orientation, and oxygen and water transport have been measured in oriented polyester bottles. O2 permeability in flat sheets decreases gradually with orientation on either side of an abrupt decrease by about a factor of 2 after moderate orientation. The bottles tested were all more highly oriented than that critical decree; no significant effect of orientation on water or O2 transport in bottles could be found. Only container intrinsic viscosity (IV) (which is determined by molecular weight, and is therefore a convenient measure of polymer degradation) was significantly related to the transport properties of the bottles. It was found that O2 transport is increased with increasing IV while H2O transport decreased. The explanation for these seemingly contradictory data can be found in the chemistry of degradation of the polyester.
Diffusion, swelling, and consolidation in glassy polystyrene microspheres
Authors: Enscore D. J. , Hopfenberg H. B. , Stannett V. T.
Published: December 2004

The effects of prior thermal and swelling history on the kinetics and apparent equilibria of subsequent n‐hexane sorption in monodisperse, submicrometer diameter, glassy polystyrene microspheres were studied. Repetitive sorption and desorption cycling was compared with continuous sorption and desorption experiments. The apparent equilibrium uptake of n‐hexane in preswollen samples decreased monotonically with the cumulative time under vacuum independent of the cycle frequency or the number of sorption‐desorption cycles. This consolidation was modeled as a first order relaxation process with a single characteristic relaxation time. “As‐received” samples swelled in the presence of the penetrant and the apparent equilibrium n‐hexane content increased monotonically with the time under n‐hexane. The Berens‐Hopfenberg diffusion‐relaxation model accurately describes the cyclic and continuous swelling behavior of the “as‐received” sample. At each temperature studied, a true equilibrium n‐hexane content was approached asymptotically for the preswollen and “as‐received” samples after sufficient time under vacuum or n‐hexane, respectively. Whereas the apparent sorption equilibria were controlled by the cumulative time under vacuum or n‐hexane for the preswollen and “as‐received” samples, respectively, the absorption kinetics are subject to a systematic variation which depends only on the immediate prior vacuum history of the sample. The temperature dependence of the kinetic and equilibrium parameters describing diffusion, consolidation, and swelling suggests a unified molecular interpretation of these diverse glassy‐state transport and relaxation processes.
Finite element solutions for flow in a single‐screw extruder, including curvature effects
Authors: Hami M. L. , Pittman J. F. T.
Published: December 2004

Slow developed flow in an extruder channel has been set up as a two‐dimensional, variational problem using a helical coordinate system, thus avoiding the usual geometrical simplification. Continuity is enforced by an integral form of constraint, and solutions for isothermal, Newtonian flow are obtained by a finite element method for both shallow and deep, highly curved channels. The performance of the solution procedure as a function of Lagrangian multiplier is discussed. Convergence to correct solutions is demonstrated for the shallow channel case. Deep channel results are compared with analytic predictions, curvature corrected according to Booy. Further testing of deep channel results will be made against experimental data.
Mechanical properties of polypropylene‐low density polyethylene blends
Authors: Nolley E. , Barlow J. W. , Paul D. R.
Published: December 2004

Blends of polypropylene (PP) and low density polyethylene (LDPE) were prepared by both batch mixing followed by compression molding and extruder compounding followed by injection molding. Compression molded PP‐LDPE blends were found to have very poor toughness, whereas extruded blends, injection molded without weld lines, were quite tough. Injection molded blend specimens with weld lines were found to be weaker and failed at very low elongations at break. A simple adhesion analysis is presented which explains well the weakness at the weld line expected for incompatible blends. Addition of an ethylene‐propylene polymer with residual ethylene crystallinity was found to be a more effective “compatibilizer” for blends deficient in toughness than a related copolymer with less crystallinity. This effect is attributed to the more block‐like character of the former which permits it to play more nearly the interfacial role required of the ideal blend compatibilizing agent.
Energy transfer and bond strength in ultrasonic welding of thermoplastics
Authors: Frankel E. J. , Wang K. K.
Published: December 2004

This paper describes an investigation into some fundamental aspects of ultrasonic welding of thermoplastics. A simple model was developed to characterize the temperature rise at the weld interface up to the glass transition temperature. Beyond this point, the temperature increases more rapidly and almost directly proportional to weld time. The rate of temperature rise increases with increase of amplitude of vibration. The correlation between weld strength and interface temperature was established using the method of dimensional analysis. It was found that the process can be optimized in terms of weld strength by monitoring the power input. There is an optimal load one can apply to achieve high weld strength. The overall efficiency of the process is rather low in terms of energy usage.
Hot plate welding of plastics: Factors affecting weld strength
Authors: Bucknall C. B. , Drinkwater I. C. , Smith G. R.
Published: December 2004

Welded joints were made under a range of conditions in polypropylene, glass fiber reinforced polypropylene and poly (methylmethacrylate) bars. Melt flow in the weld was investigated by microscopy and by contact microradiography, and weld strengths were measured by tensile tests. The fracture toughness of the weld zone was determined by tests on double edge notched specimens. The study shows that weld strength is strongly affected by hot plate temperature, heating time and melt flow during welding. Insufficient heating or melt flow results in incomplete bonding. Excessive melt flow produces strong transverse orientation. Both reduce strength, but in different ways, which can be distinguished by fracture mechanics tests.
Experimental investigations of shear and elongational flow properties of polystyrene melts reinforced with calcium carbonate, titanium dioxide, and carbon black
Authors: Tanaka Hideho , White James L.
Published: December 2004

Shear and elongational flow measurements on polystyrene melts reinforced with small particles were carried out. The influences of loading level, particle size and surface treatment on shear viscosity, principal normal stress difference, and elongational viscosity were discussed. These systems exhibited yield values for both shear and elongational flow. Experimental values for the ratio of the tensile to the shear yield stress give satisfactory agreement with the predictions of the von Mises yield criterion. The yield value appears to increase with decreasing particle size and may be varied with surface treatment. The principal normal stress difference at fixed shear stress decreases with volume loading of particulates. The results are interpreted in terms of a system forming a gel due to interparticle forces, which is disrupted by a critical distortional strain energy.
Electron‐beam lithography of chlorinated polystyrenes with narrow molecular weight distributions
Authors: Feit Eugene D. , Stillwagon Larry E.
Published: December 2004

Polystyrenes with narrow molecular weight distributions have been chlorinated with only slight broadening of molecular weight distributions to yield materials that are five to six times more sensitive to electron‐beam irradiation. The chlorinated polystyrenes are useful negative resists for electron‐beam lithography. At molecular weights of 3‐4 × 105g/mole, their threshold sensitivities to 20 keV electrons are 1‐2μC/cm2. Their lithographic contrasts are ≥ 1.5; in fact, > 2.0 for the narrowest molecular weight distributions. They compare favorably in these regards to polystyrenes of similar molecular weight characteristics. Lithographic relief images that are 80% of the original thickness of the polymer film can be formed at three to four times the threshold dose.

The degree of chlorination ranged from 0.65‐0.76 Cl/monomer unit. The infrared spectra of the chlorinated materials resemble the spectrum for poly(4‐chlorostyrene). Elemental analysis indicated, however that some addition of chlorine had occurred. More extensive chlorination or chlorination of the higher molecular weight starting materials broadened the molecular weight distributions.

The chlorinated material, a kind of poly(4‐chlorostyrene‐costyrene), is less sensitive than poly(4‐chlorostyrenc) prepared by addition polymerization by almost a factor of four.
Sensitivity and contrast of some proton‐beam resists
Authors: Brault Robert G. , Miller Leroy J.
Published: December 2004

Fifteen negative and four positive resists were tested to determine their proton‐beam sensitivity and contrast. The ratio of the required 20‐keV electron dose (QE) to the required 100‐keV proton dose (QP) ranged from a low value of 7.8 to a high value of 270. In general, the most sensitive resists had the lowest values of QE/QP. This result is explained as being due to incomplete coverage by reactive species at low proton doses because the incident protons are spaced too far apart. The product of QP and the weight‐average molecular weight (Mw) was almost constant for a series of narrow dispersivity polystyrenes over the Mw range of 20,000 to 2,600,000. This product was used as a figure of merit for comparing negative resists.