bluuebunny/crossref_metadata_2025 huggingface dataset:
Grooved feed single screw extruders—improving productivity and reducing viscous heating effects
Authors: Davis Bruce A. , Gramann Paul J. , Noriega E. Maria Del P. , Osswald Tim A.
Published: April 2004

Owing to their high productivity, pressure invariance, and controlled throughput and melt temperature, groove feed systems are becoming widely accepted for the extrusion of pipes, blown films, and blow molded articles. Within the research presented in this paper, a fully instrumented 45 mm extruder equipped with a grooved fed bushing was used to measure pressure distributions, screw and die characteristics, and melt temperature profiles. The screw geometry included decompression and compression zones, and Saxton distributive and Maillefer dispersive mxing heads. The screw and die characteristic curves show the high system productivity where throughputs comparable to 60 and 90 mm conventional extruders were measured. The high throughput induced a dramatic reduction in melt temperature measured at the tip. To better understand and confirm our experimental findings, analytical models were used.
The Sephadex story
Authors: Flodin Per
Published: April 2004

The environment and the circumstances leading to the Sephadex group of products for gel filtration (SEC, size exclusion chromatography) are described. The importance of Porath's and the author's experience from zone electrophoresis is stressed. To be able to get high resolution the technique for packing columns was of decisive importance for electrophoresis. It paved the way for the observation of the separation properties of dextran gels. The synthesis of dextran‐based gels at AB Pharmacia and the development of varieties of them for varying applications are described together with the project leading to their marketing in 1959. The work of the author on gel filtration is summarized. The story is based on publication and memory. Aids to the latter have been laboratory notebooks and other documents still in the possession of the author.
Biodegradable polymers and environmental interaction
Authors: Karlsson Sigbritt , Albertsson Ann‐christine
Published: April 2004

Biodegradable polymers are by definition those that degrade as a result of the action of microorganisms and/or enzymes. The rate of this biodegradation may vary from hours to years depending on the molecular architecture of the polymer in question. Biopolymers like lignin take years to degrade while many proteins and polysaccharides degrade within hours to days. The same is true for the synthetic biodegradable polymers where polyethylene is sometimes regarded as inert to biodegradation while polyanhydrides are rapidly biodegradable. The influence of structure, morphology, and surface area on the biodegradability are discussed, with polyesters and degradable polyethylene (with pro‐oxidant and/or biodegradable additives) as examples. The rate of biodegradation is controllable by choosing the appropriate molecular architecture. In addition to this the environmental interaction of these polymers should be determined. The degradation product pattern of biodegradable polymers should be compatible with the natural degradation mechanisms (i.e., catabolisms).
Selective froth flotation of PVC from PVC/PET mixtures for the plastics recycling industry
Authors: Drelich J. , Payne T. , Kim J. H. , Miller J. D. , Kobler R. , Christiansen S.
Published: April 2004

It was found that strongly alkaline solutions of sodium hydroxide are able to destroy the hydrophobicity of polyethylene terephthalate (PET) whereas the hydrophobicity of polyvinyl chloride (PVC) remains only slightly affected by these solutions. On this basis, a technology involving treatment of PET and PVC particles with alkaline solutions followed by froth flotation of PVC with nonionic surfactants has been developed and tested at a laboratory scale. In both steps of this technology, appropriate experimental conditions, such as concentration of reagents, temperature and residence time, have been optimized through a detailed examination of all these variables on the efficiency and selectivity of PVC separation from PVC/PET mixtures of varying composition. It is demonstrated that using this technology 95–100% recovery of PET and PVC can be achieved in separate products from a variety of PVC/PET mixtures.
Steady shear and dynamic properties of biodegradable polyesters
Authors: Ramkumar D. H. S. , Bhattacharya M.
Published: April 2004

The rheological properties of three biodegradable partially crystalline alipathic polyesters—poly ε carolactone (PCL), polylactic acid (PLA), and polyhydroxybutyrate‐co‐hydroxyvalerate (PHBV)—were investigated. Low shear viscosity (η), first normal stress difference (N1), and dynamic properties (G′ and G″), were measured for each polymer using rotational instruments. High shear viscosity data was obtained using a capillary rheometer. Gel permeation chromatography indicates that both PLA and PHBV undergo degradation during processing. Thermal degradation rate constants for PLA and PHBV were determined from the time‐sweep data. Data indicates that material functions are proportional to the molecular weight for PCL and PLA samples, and directly related to the HV content in the PHBV samples. The relaxation spectra were calculated from the G′ and G″ data using the regularization method and the applicability of the nonlinear Wagner equation was checked on these materials. Results are discussed in terms of variations in the molecular characteristics on rheological properties and their possible influence on the processability.
Optimal cooling system design for the injection molding process
Authors: Park S. J. , Kwon T. H.
Published: April 2004

A computer‐aided optimal design system was developed to improve the performance of a cooling system for injection molding. This was done by minimizing a weighted combination of the uniformity of the part temperature and the cooling time. The CONMIN algorithm was adopted to obtain the optimal design using the special boundary integral formulation and a corresponding design sensitivity analysis formulation. Design variables related to the processing conditions (i.e., inlet coolant temperature and volumetric flow rate of each cooling channel) and mold cooling system design (radius and location of each cooling channel) were considered. Three different optimization strategies are suggested, and three sample problems were solved to demonstrate the efficiency and the usefulness of this optimization procedure.
Characterizations for blends of phosphorus‐containing copolyester with poly(ethylene terephthalate)
Authors: Chang Shinn‐Jen , Chang Feng‐Chih
Published: April 2004

High molecular weight phosphorus‐containing copolyesters, poly(ethylene terephthalate)‐co‐poly(ethylene DDP) (PET‐co‐PEDDP)s, were prepared and characterized with the objective of producing a non‐halogen flame retardant system for practical applications. The phosphorus‐containing copolyester with 30 wt% phosphorus (P30 copolyester) was blended with PET to evaluate their characteristics and flame retardancy. Higher phosphorus content results in lower crystallinity and higher char formation after thermal degradation. The rheological behavior remains similar to that of PET. The P30/PET blend possesses higher crystallization rate than the corresponding phosphorus‐containing copolyester containing equal phosphorus content. Thermal and rheological behaviors of P30/PET blends are similar to PET or the phosphorus‐containing copolyesters. The P30/PET blends are miscible or compatible base on single Tgs detected by DSC or DMA. The SEM/EDX phosphorus mapping image of the P30/PET blend shows uniform distribution of the phosphorus moieties within the P30/PET matrix, another indication of a compatible or miscible blend between the phosphorus‐containing copolyester P30 and PET. Flame retardancy of the P30/PET blend is identical to that of the phosphorus‐containing copolyester with identical phosphorus content. Blending of high phosphorus content copolyester with virgin PET provides a feasible method to obtain a flame resistant PET with LOI greater than 28.
Indentation measurements using a dynamic mechanical analyzer
Authors: Payne Jason A. , Strojny Angela , Francis Lorraine F. , Gerberich William W.
Published: April 2004

A dynamic mechanical analyzer equipped with a diamond indenter tip was used to measure the elastic modulus of polymeric coatings as well as various bulk materials. A fabricated indenter probe was used to indent bulk samples of aluminum and fused quartz, as well as gelatin and polystyrene films in order to compare the micron‐level indentation measurements with sub‐micron (nanoindentation) techniques. The measured moduli were in agreement for ductile materials and thick films (>20 μm), but limited displacement resolution, material cracking, and hydrostatic pressure effects led to diverging values for thinner coatings and more brittle materials.
Measurement of three‐dimensional velocity field in the translational region of a co‐rotating twin‐screw extruder
Authors: Bakalis Serafim , Karwe Mukund V.
Published: April 2004

The velocity field in the screw channels of a co‐rotating twin‐screw extruder was measured using laser Doppler anemometry. Velocity distributions were measured for two screw elements having pitches of 14 and 28 mm, respectively. The magnitude of radial velocity component for both elements was no more than 10% of the magnitude of total velocity. The radial and the axial velocity components were similar for both screw elements. Wider range of tangential velocity values and steeper gradients near the flights were observed for smaller pitch screw element.
Experimental study of the transcription of minute width grooves by injection molding (II)
Authors: Yoshii Masaki , Kuramoto Hiroki , Ochiai Yuuji
Published: April 2004

In the injection molding of substrates for optical discs, precise transcription of the pits and grooves is imperative. In particular, for high density optical discs, molding transcription of minute grooves with widths on the sub‐micron level is required. In this study, in order to quantitatively clarify the relationship between the molding conditions, molding resins, and the transcription, the transcription of minute rectangular grooves (width 0.55 μm, depth 70 nm) by injection molding was studied. Polycarbonate, amorphous polyolefin, and Polymethylmethacryrate resins were employed. A transcription model for the minute groove utilizing the concept of the equivalent thickness of the vitrified layer was introduced, and the relationships between the molding conditions, resin properties, and the transcription heights were verified. Among these resins, amorphous polyolefin, which has the lowest elastic modulus, indicated the highest transcribability.
Carbon black–filled immiscible blends of poly(vinylidene fluoride) and high density polyethylene: Electrical properties and morphology
Authors: Feng Jiyun , Chan Chi‐Ming
Published: April 2004

The electrical conductivity, current‐voltage characteristics and morphology of carbon black–filled immiscible blends of poly(vinylidene fluoride)(PVDF) and high density polyethylene (HDPF) were investigated. Carbon black (CB) had stronger affinity to HDPE than to PVDF, resulting in its selective localization in the HDPE phase. The CB content and PVDF/HDPE volume ratio were the two main factors influencing the electrical conductivity, current‐voltage characteristics, and morphology. At a fixed PVDF/HDPE volume ratio of 1/1, a percolation threshold of 0.037 volume fraction of CB was observed, and that value was much lower than that for conventional CB‐filled polymer composites. At a fixed CB content (10 wt% CB), a maximum electrical conductivity was observed at a PVDF/HDPE volume ratio of 2.75. An increase in CB content in the composites with a fixed PVDF/HDPE volume ratio (1/1) and an increase in PVDF content in composites with a fixed CB content (10 wt%) greatly decreased the domain size of the PVDF phase. A positive‐temperature‐coefficient effect was used to determine the location of CB in the blends.
Diffuse reflectance and transmittance of IR absorbing polymer film
Authors: Ho Wen‐Dar , Ma Chen‐Chi M. , Wu Lieh‐Chun
Published: April 2004

This study employs the ray tracing method to analyze and develop mathematical formulae for the internal reflectance of a free standing thick polymer film. The proposed formulae are then used to simulate the diffuse reflectance and diffuse transmittance. Analysis results indicate that internal reflectance is not a constant and varies with film thickness and absorption property. Internal reflectance of the front surface (irradiated surface) surpasses that of the back surface. In addition, all the internal reflectances decrease with the film thickness and the absorption property. In light of the measured thickness and experimentally determined diffuse transmittance of a polymer film, the extinction coefficient to diffuse IR irradiation can be obtained by interpolating in the graphs provided in this study.
Functionalization of ethylene‐propylene‐diene terpolymer via the alder ene reaction
Authors: Thompson M. R. , Tzoganakis C. , Rempel G. L.
Published: April 2004

An ethylene‐propylene‐diene rubber (EPDM), containing 5 wt% 5‐ethylidene‐2‐norbornene, was functionalized with maleic anhydride through the Alder Ene reaction at temperatures above 200°C in a co‐rotating twin screw extruder. Characterization of the maleated product included FT‐IR, 1H and 13C NMR, and GPC. The degree of functionalization was determined by infrared analysis and by the mechanical properties of an ionic network formed by neutralizing the maleated rubber with zinc oxide. Increased temperature and maleic anhydride reactant concentration were found to improve the extent of reaction. Several Lewis acid species (SnCl2•2H2O, RuCln•xH2O and AlCl3) were tested as catalysts, and they were found to have a small effect on the degree of functionalization. This effect improved with reduced acid concentration. Among the Lewis acids examined, AlCl3 gave rise to the greatest improvement of succinyl anhydride incorporation into the rubber.
A quantitative analysis of low density polyethylene and linear low density polyethylene blends by differential scanning calorimetery and fourier transform infrared spectroscopy methods
Authors: Prasad A.
Published: April 2004

Blends of low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) are widely used for blown film applications. An accurate and rapid test scheme to identify the type and composition of α‐olefin in LDPE/LLDPE blends has been developed that utilizes differential scanning calorimetery (DSC) and Fourier transform infrared (FTIR) spectroscopy techniques. The melting point of LDPE varies with density and usually is in the range of 106°C to 112°C for film grade resins. The DSC thermogram of LLDPE is characterized by a broad range of melting peaks with a lower melting peak around 106°C to 110°C and a higher one in the range of 120°C to 124°C. In a blend with LDPE, the ratio of the two endothermic peak heights changes. At a given weight percent of LDPE, this ratio depends on the type of LLDPE (i.e., the comonomer used). Separate calibrations for butene‐1, hexene‐1, and octene‐1 LLDPEs have been developed to quantify the blend composition from DSC thermograms where the α‐olefin type is successfully identified by FTIR over the entire blend composition range. The calibration curves are applicable to narrow melt index (MI) and density range conventional film grade LDPE and LLDPE resins and are not intended to be used for the metallocene type LLDPEs.
Profile control of plastic sheet in an industrial polymer processing process
Authors: Liang Yue , Kurihara Kazurou , Saito Kunio , Murakami Hiroyasu , Kumagai Kunio , Ohshima Masahiro , Tanigaki Masataka
Published: April 2004

A control system was developed using a two‐degree of freedom control structure with four input variables in the feedforward, and two inputs, the screw rotation speed and the gap of the forming roller, in the feedback loop. The feedforward signals were predetermined from first principles and the operators' heuristic rules for each changeover operation and prepared in a database. At the end of each changeover operation, the values in the database were rewritten by evaluating control performance. The magnitude of the true dead time changed as the production rate was changed. The rate of sampling and control action in the feedback control was adapted in each changeover operation so that the changing time delay was always expressed by a one‐sampling‐step time delay in the discrete models and dealt with by the controller robustness against parameter uncertainty. The developed control system was applied to an actual industrial plastic sheet production line and allowed one to easily perform the changeover operation and reduce material consumption.
Phase inversion during compounding with a low melting major component: Polycaprolactone/polyethylene blends
Authors: Ratnagiri Ram , Scott Chris E.
Published: April 2004

Most of the morphology development in compounding of immiscible blends is known to occur at short mixing times. In this investigation, the effect of rheology of the minor component on its tendency to form a continuous phase at short mixing times is studied. it was shown that phase inversion during compounding can occur even with a low‐melting major component. Four different blends with polyethylene as the high‐melting‐point minor component and polycaprolactone as the low‐melting‐point major component were chosen. Rheological measurements on the individual components were made both in the solid and melt states. Softening temperatures from these measurements were more representative of the observed processing behavior than the peak values as calculated from differential scanning calorimetry data. Compounding runs in a batch intensive mixer indicated that the minor component formed the continuous phase at short mixing times, in the blends with the low viscosity polyethylene. This was shown to correlate with its low modulus in the solid state and its low viscosity in the melt. A ramped temperature protocol during compounding delayed the melting of polyethylene thus preventing phase inversion from occurring. The blends with the higher viscosity polyethylene did not show phase inversion during compounding.
The effects of particle bulk modulus on toughening mechanisms in rubber‐modified polymers
Authors: Chen Xiao‐Hong , Mai Yiu‐Wing
Published: April 2004

The interaction of a blunting mode I plane‐strain crack tip with a periodic array of initially spherical rubber particles directly ahead of and parallel to the crack front in the effective medium is studied by the crack tip‐particle interaction model. The local stress concentrations responsible for rubber cavitation, matrix crazing and shear yielding are obtained by three‐dimensional large deformation elastic‐plastic finite element analysis with a sub‐modeling technique to explore the relationship between these toughening mechanisms. It is shown that rubber particles can act as stress concentrators to initiate matrix crazing or shear yielding but they behave differently from voids at high triaxiality because of their high bulk modulus. Particle bulk modulus affects significantly the hydrostatic stress inside rubber particles as well as the plastic deformation in the ligament between the crack tip and particles. Rubber cavitation or interface debonding relieves the triaxial stress planestrain condition so that extensive plastic deformation can be developed in the toughening process.
A global computer software for polymer flows in corotating twin screw extruders
Authors: Vergnes B. , Valle G. Della , Delamare L.
Published: April 2004

A global computation model for self‐wiping corotating twin screw extruders is proposed. Based on a ID approximated approach, it has been validated by comparison with experimentation and more sophisticated numerical models. It allows one to obtain, for any screw profile including left‐and right‐handed screw elements and kneading discs, the profile along the screws of the main flow variables, such as pressure, mean temperature, residence time, and filling ratio. Owing to the approximations made, this model can be easily and rapidly run on a personal computer or a workstation. Important applications may be found in screw profile design, scaleup, compounding or reactive extrusion.
Dielectric properties of bisphenol‐A novolac type epoxide oligomer as a parameter for cure monitoring
Authors: Koike Tsuneo , Ishizaki Noritoshi
Published: April 2004

Dielectric properties above the glass transition temperature (Tg) have been investigated for three bisphenol‐A novolac type epoxide oligomers (PGEBANs) that have some branching in each molecule in comparison with the diglycidyl ether of bisphenol‐A (DGEBA) oligomer without branching. The relationship between the dielectric relaxation time (τ) and Tg for the branched PGEBAN oligomers is expressed by a modified Williams‐Landel‐Ferry (WLF) equation taking Tg as a variable at fixed temperatures from 70 to 100°C. The WLF‐type relationships between τ and Tg for the two types of uncured epoxide oligomers, the branched PGEBAN and the nonbranched DGEBA, were found to be useful for predicting the Tg of a branched DGEBA‐alicyclic amine system during the middle stage of curing.
Scratch and mar resistance of filled polypropylene materials
Authors: Chu J. , Rumao L. , Coleman B.
Published: April 2004

Pigmented mineral‐filled polypropylene (PP‐PMF) is marketed as a potential alternative to ABS (acrylonitrile‐butyldiene‐styrene) for interior automotive components. However, PP‐PMF is easily damaged by surface scratch and mar, thus limiting its acceptance for interior applications. This study investigates the test methods used to quantify the extent of scratch and mar damage and the effect of different mineral fillers on the scratch and mar resistance of PP‐PMF. Correlation was found between scratch visibility and scratch hardness, which can be measured by laser profilometer. The PP‐PMF specimen with 13 wt% talc is the worst in terms of scratch visibility. Wollastonite filler provided higher scratch and mar resistance, while the addition of 0.5 wt% lubricant showed some beneficial effect.
The effect of PTFE on the friction and wear behavior of polymers in rolling‐sliding contact
Authors: Rao M. , Hooke C. J. , Kukureka S. N. , Liao P. , Chen Y. K.
Published: April 2004

The effect of PTFE on the tribological behavior of polymers in rolling sliding contact has been investigated. The two most widely used polymers — nylon 66 and polyacetal—were used as the base material. Tests were conducted over a wide range of running conditions using a twin disc rolling‐sliding test rig for both the unfilled materials and for the base materials filled with 20 wt% PTFE. The experimental results showed that the friction and wear performance of the PTFE filled polymers was superior to that of the unfilled polymers. In addition the surface cracking that was found in unfilled PA66 and was thought to be responsible for premature fracture of components such as gear teeth was suppressed by the PTFE. It is suggested that a combination of high surface temperature and high surface tensile stress, produced by friction, is required to initiate these cracks and that PTFE, by reducing friction, inhibits crack formation.
Rheological and mechanical properties in polyethylene blends
Authors: Cho Kyucheol , Lee Byung H. , Hwang Kyu‐Myun , Lee Hoseok , Choe Soonja
Published: April 2004

Melt rheology and mechanical properties in linear low density polyethylene (LLDPE)/low density polyethylene (LDPE), LLDPE/high density polyethylene (HDPE), and HDPE/LDPE blends were investigated. All three blends were miscible in the melt, but the LLDPE/LDPE and HDPE/LDPE blends exibiled two crystallization and melting temperatures, indicating that those blends phase separated upon cooling from the melt. The melt strength of the blends increased with increasing molecular weight of the LDPE that was used. The mechanical properties of the LLDPE/LDPE blend were higher than claculated from a simple rule of mixtures, whiele those of the LLDPE/HDPE blend conformed to the rule of mixtures, but the properties of HDPE/LDPE were less than the rule of mixtures prediction.
Numerical simulation of thermoplastic wheat starch injection molding process
Authors: Abbégs B. , Ayad R. , Prudhomme J.‐C. , Onteniente J.‐P.
Published: April 2004

A numerical study is carried out on the thermoplastic wheat starch injection molding process. The simulation is performed using currently available molding software to determine optimal molding parameters. The molding of a standardized sample for tensile test is considered. It is shown that the conventional continuum mechanics equations can be used for modeling the injection molding of thermoplastic starch. These equations are solved using the finite element method. Comparisons with some experimental results are presented, indicating good agreement. Data on the processing of thermoplastic starch and several other basic aspects are also provided.
Characterization of the fracture toughness of rubber‐toughened polypropylene thin plates
Authors: Marchal Y. , Oldenhove B. , Daoust D. , Legras R. , Delannay F.
Published: April 2004

The fracture toughness of PP‐EP (Polypropylene‐Ethylene‐Propylene) blends is studied at room temperature using the “essential work of fracture” (EWF) method. The results obtained by applying this method are compared with those of puncture and tensile tests. Whereas the classical puncture tests do not allow classifying the rubber‐toughened PP‐EP blends, the EWF method proves to be a sensitive technique to monitor the effect of composition and morphology of the blend on fracture toughness. Moreover, the application of the EWF method allows monitoring how the fracture toughness of a material depends on its ability to deform extensively before fracturing and on its capacity to bear some load. A good combination of these two properties thus yields materials presenting an optimal fracture toughness.
Additive group contributions to density and glass transition temperature in polyurethanes
Authors: Fedderly Jeffry , Compton Eric , Hartmann Bruce
Published: April 2004

The method of additive properties was applied to the density and glass transition temperature, Tg, of linear amorphous polyurethanes. This method assumes that certain polymer properties result from the additive effects of unique constituent group properties and that these group properties are independent of their environment. To determine the component properties, 14 model polyurethanes were synthesized. The polymers contained only the following four groups: urethane, phenylene, methylene, and ether oxygen. The densities and Tg's of these polymers were measured. Using these measured values, the known composition of each polymer, and an appropriate additive from, the molar component properties were calculated using a matrix least‐squares simultaneous fit algorithm. An error analysis confirmed that the component values were determined with greater accuracy than literature results. The densities ranged from 1.0 to 1.2 g/cm3 and measured versus predicted densities agreed to within 0.3% on the average. Tg's ranged from −70°C to 70°C and measured versus predicted Tg's agreed to within 1.3% on the average.
Chemical recycling of reinforced polyurethane from the automotive industry
Authors: Modesti M. , Simioni F.
Published: April 2004

R‐RIM PU (reinforced‐reaction injection molding polyurethanes) from the automotive industry (production scrap and parts at the end of their life cycle) can be recycled for the production of new RIM PU by a chemical process. Among the various possible chemical processes (hydrolysis, alcoholysis, aminolysis, and pyrolysis), we have examined glycolysis, a particular form of alcoholysis, for the purpose of obtaining a mixture of oligomers sufficiently similar to a polyol to be used in the production of new R‐RIM PU. Glycolysis with dipropylene glycol (DPG) of R‐RIM PU forms a monophasic product that could be used in the preparation of new, highly crosslinked polymers, similar to those used in the preparation of rigid thermal insulation foams. The same product, because of its high hydroxyl number, cannot be directly re‐used in the production of new RIM PU. Partial substitution of free DPG in the glycolysis product with a triol having high molecular weight forms a homogeneous mixture suitable for production of new RIM PU. This final product has been used in the original R‐RIM application introducing an appropriate optimization of formulation. In comparison with RIM PU obtained from only virgin materials, the loss in properties of molded parts based on even high amounts of regenerated polyol was only marginal.
An experimental study and model assessment of polymer sintering
Authors: Bellehumeur C. T. , Bisaria M. K. , Vlachopoulos J.
Published: April 2004

Experiments were conducted using pairs of particles inside a hot stage microscopy setup with the ultimate objective to study the coalescence, which is a crucial stage in the rotational molding process. It was found that the geometry of the particles had no significant effect on the sintering rate. The sintering rate increases as the viscosity of the resin decreases. However, this effect became less important as the particle size decreased. The experimental results of this study have been compared with the available mathematical models based on balance of viscous and surface tension forces. The model developed by Frenkel and a corrected version by Eshelby predict a faster coalescence than observed experimentally. However, Hopper's model is in relatively good agreement with the present experimental data. Yet there is evidence that mechanisms other than Newtonian viscous flow may play a role in polymer sintering.
Free radical grafting of diethylmaleate on linear low‐density polyethylenes
Authors: Rosales C. , Márquez L. , González J. , Perera R. , Rojas B. , Vivas M.
Published: April 2004

Grafting of preformed polymers is an important method for preparing polymers with functional groups. Lately, the use of extruders as polymerization reactors has increased considerably in industry. However, the knowledge of the total reaction process is still limited. Grafting of diethylmaleate on linear low‐density polyethylenes (LLDPEs) was carried out in solution and in a corotating twin screw extruder. The effects of initiator and diethylmaleate concentrations, temperature, and reaction time on graft content and on crosslinking were investigated. The functionalization reaction was also conducted in the presence of an electron donor material to minimize the amount of crosslinked products in the extruder. The grafted products were characterized by means of FTIR and the thermal behavior of LLDPEs and that of its grafted products was determined.
Interaction of process variables with the fracture behavior of amorphous polystyrene during attrition
Authors: Kubisiak Michael P. , Quesnel David J.
Published: April 2004

This study investigates the fracture of oriented general‐purpose polystyrene. Specimen microstructure was controlled using an extrusion‐sheeting technique where draw ratio, polymer melt temperature, cooling roll temperature, and nip roll pressure changed according to a designed experiment. Sharp‐notched tension results display a 4X difference in longitudinal vs. transverse specimen values. Shrinkage measurements show contraction in the machine direction amplifies with increasing draw ratio. Craze formation is visible only in those specimens tested in the longitudinal direction. Fracture mechanisms have strong orientation dependence and the extrusion‐sheeting process produces an ideal system to study the effect on attrition. Comminution studies illustrate draw ratio has an effect on the final median particle size and width distribution of the powder. Increasing the draw ratio reduces the volume median particle size and minimizes the formation of fine particles. A monotonic fracture mechanism was initially considered but rejected in favor of a low cycle fatigue model based on estimates of fracture strength.
The essential fracture work concept for toughness measurement of ductile polymers
Authors: Wu Jingshen , Mai Yiu‐Wing
Published: April 2004

The essential work of fracture method is explored. The method was used to determine the fracture toughness of a series of toughened polymer blends and the crack resistance of a thin ductile polymer film, which could not be tested using the J‐integral method. A comparison between J‐integral and the specific essential work of fracture was carried out to test the equivalence of the two methods. The effects of geometry on the essential work of fracture and the plane‐stress/plane‐strain transition were studied. It has been shown that the specific essential work of fracture is a material constant, independent of sample geometry, and equivalent to the critical J‐integral. The plane‐stress/plane‐strain transition is found to depend on the nature of the material tested. The sample thickness requirement for valid plane‐strain specific essential work of fracture is discussed, and it is proposed that the size requirement for the plane‐strain specific essential work of fracture may be less rigorous than that for plane‐strain JIC measurement.
Impact and dynamic fracture resistance of crystalline thermoplastics: Prediction from bulk properties
Authors: Leevers Patrick S.
Published: April 2004

The behavior of tough, crystalline thermoplastics in notched impact tests leads to the definition of crack initiation resistance and propagation resistance as two distinct properties, Gc and GD. It is shown here that a single criterion—adiabatic thermal failure of a crack‐tip cohesive zone—can be applied to predict both. Dynamic fracture resistance GD emerges as a geometry independent, though crack speed and temperature dependent, material property, whose minimum value GD,min depends only on temperature and bulk physical properties. GD,min can be measured using a simple pressurized‐tube test. Crack initiation resistance Gc, however, is inherently influenced by geometry and impact speed, although its lower bound is also GD,min. Craze extension and failure of a notched impact specimen, and hence Gc, can be predicted for a specific temperature, given bulk thermal property data and a dynamic stress/strain curve measured by impact bending of an unnotched beam. For materials that comply with the model, sharp‐notched Charpy type impact tests will not arrive at a unique Gc value, while Izod type tests, for which a revised compliance calibration is presented, may fail to establish any Gc value at all.
Photography and microscopy of the instrumented n‐Izod test
Authors: Havriliak S. , Cruz C. A. , Slavin S. E.
Published: April 2004

The ubiquitous n‐Izod test is universal in its use yet condemned by its critics. Rather than criticize the test we have undertaken a course of study to understand it. In this work we report the photographic results taken at short exposure times with various delays after contact is made by the hammer. The photographic studies were made on polycarbonate and on modified and unmodified poly(vinyl chloride) with the notch radius as a variable. These results show that the damage is always contained within the notch. This permits an estimate of the strain rate, which depends on notch diameter. Instrumented n‐Izod measurements show that most of the energy is absorbed before little bending takes place, meaning that the sample is primarily in tension. These observations lead to the conclusion that the test is a high speed tensile test whose strain rate can be varied by changing the notch radius. Microscopic measurements show that, when toughening nylon 6, with small (<200 nm) core//shell particles, the matrix suffers large local ductile deformations without particle cavitation. Rubber cavitation does not occur until after the particles have been deformed by the fracture process.
The effect of the secondary relaxations on the fracture toughness of nylon 6/amorphous nylon 6IcoT blends
Authors: Liu Yun , Donovan James A.
Published: April 2004

The fracture toughness of semicrystalline nylon 6, amorphous nylon 6IcoT, and their blends can be represented as the inherent toughness plus the toughness due to the formation of the crack tip plastic zone. The inherent toughness originates mostly from the molecular alignment near the crack tip plus a small contribution from chain scission. The plastic zone contribution is determined by its size and the energy dissipated by irreversible plastic deformation. The inherent toughness and the energy dissipated in the process zone are temperature dependent and primarily determined by the stress‐induced molecular movement, which is related to the operative secondary β or γ relaxation.
Effective volume changes during fatigue and fracture of polyacetal
Authors: Lesser Alan J.
Published: April 2004

Conventional tensile dilatometry techniques are extended to cyclic fatigue applications to study volume changes that occur during controlled‐load cyclic fatigue of polyacetal. During fatigue, in‐situ measures of the irreversible and elastic volume change are monitored together with dynamic viscoelastic parameters (E′, E″, and Tan δ), and changes in the energy densities (strain energy, potential energy, and irreversible work). The results show that the effective irreversible volume of the polyacetal gradually increases over a wide range of applied cyclic stress. However, at high stress levels and/or frequencies (i.e., low‐cycle, thermally dominated regime), the effective Poisson's ratio of the polyacetal increases as it softens (evidenced by the dynamic viscoelastic data). Conversely, at lower stress levels, the Poisson's ratio continually decreases coincident with decreases in the loss modulus (E″) and the irreversible work density. These results are indicative of entirely different mechanisms governing the low‐cycle (high stress level) and high‐cycle (low stress) regimes. Also, comparisons between tensile and fatigue dilatometry studies show that the dilational‐strain response of samples fatigued at high stress levels are similar to data obtained from monotonic tensile dilatometry. However, the dilationstrain response of samples fatigued at lower stress levels are distinctly different from low‐cycle fatigue and tensile dilatometry.
Designing reliable polymer coatings
Authors: Shaffer E. O. , McGarry F. J. , Hoang Lan
Published: April 2004

A method to predict the ultimate adhesion performance of coatings subjected to biaxial, tensile stress is presented. A set of equations is developed to predict the onset of failure when the locus of failure is cohesive in the coating. The equations also have been extended to predict fatigue lifetime when a coating is cycled from a low temperature to room temperature. To test these equations, the Edge Liftoff Test (ELT) was developed. It consists of fabricating coatings of various heights on a rigid substrate and dicing the latter, so that the edges are 90° to the interface. The parts are cooled and the temperature of debonding is recorded. For thermal fatigue validation, cycles at which the first debond is observed are recorded. ELT results have been collected for a typical epoxy for both monotonic and cyclic cooling. The predictions are in agreement with results.
Cyclic fatigue—crack growth along polymer/glass interfaces
Authors: Ritter J. E. , Grayeski W. , Lardner T. J.
Published: April 2004

Delamination of polymer/glass interfaces was studied under cyclic and monotonic loading using an interfacial, four‐point flexure sandwich specimen. Specifically, crack growth rates along epoxy acrylate/glass interfaces were characterized over a range of velocities from 10−9 to 10−6 m/s as a function of low (10–20% RH) and high (75–80% RH) humidities. For low humidities, interfacial crack growth rates under cyclic loading are almost two orders of magnitude greater than those under monotonic loading with energy release rates G = Gmax of the cyclic loading. At high humidities, interfacial crack growth rates under monotonic loading are approximately equal to cyclic fatigue crack growth rates at low humidity.
Dynamic simulation of microstructure and rheology of fiber suspensions
Authors: Yamamoto Satoru , Matsuoka Takaaki
Published: April 2004

A numerical simulation method has been developed to predict the motion of fiber suspensions in various flows by using the particle simulation method (PSM), in which a fiber is modeled by an array of spheres. The hydrodynamic interaction among fibers is considered by decomposing into intra‐fiber and inter‐fiber interactions. For the intra‐fiber case, the many‐body problem is solved by calculating the mobility matrix for each fiber to obtain the hydrodynamic force and torque exerted on each sphere. For the inter‐fiber case, only the near‐field lubrication force is considered between spheres belonging to different fibers. The methodology was applied to predicting the microstructure and rheological properties of rigid fiber suspensions in simple shear flow and fiber orientation in two‐dimensional diverging flow by combining this method with the finite element method (FEM). In the former, the overshoot of suspension viscosity, due to the transient change of the microstructure, was observed in semi‐dilute to concentrated systems. In the latter, the calculated fiber orientations agreed with expectations of theory.
Generation of microcellular polyurethane foams via polymerization in carbon dioxide. I: Phase behavior of polyurethane precursors
Authors: Parks Kristen L. , Beckman Eric J.
Published: April 2004

On investigating the generation of microcellular polyurethane foam via reaction in carbon dioxide, we have observed that common polyurethane precursors are CO2 miscible, whereas typically fluorinated compounds or specially designed surfactants are needed to solubilize polymers in CO2. Both isocyanates and polyols are CO2‐miscible at workable pressures and temperatures and in useful concentrations to allow generation of polyurethane foams in CO2. By characterizing the phase behavior of several series of propylene oxide and ethylene oxide polyols, we have observed that the combined effects of molecular weight and hydroxyl number fix the location of the phase separation pressures. In general, lower molecular weights and lower hydroxyl mole fractions produce phase boundaries at relatively lower pressures in carbon dioxide. It also has been shown that CO2‐soluble compounds may have a com̀patibilizing effect on less CO2‐soluble materials.
Generation of microcellular polyurethane foams via polymerization in carbon dioxide. II: Foam formation and characterization
Authors: Parks Kristen L. , Beckman Eric J.
Published: April 2004

Microcellular polyurethane foams are generated through phase separation, which is induced by reaction‐induced crosslinking or by a pressure quench. The phase separation conditions are shown to impact the microstructure of the foams. Pore growth will occur through two mechanisms: diffusion of CO2 from polymerrich regions into the pores and also through CO2 gas expansion (boiling of liquid CO2 at reduced pressure). Higher CO2 pressures for polymerization (hence, higher fluid density) provide more CO2 molecules for foaming, generate lower interfacial tension and viscosity in the polymer matrix, and thus produce higher cell densities. Increasing the functionality of the polyurethane precursors increases the Tg of the polymer network and leads to smaller cell diameters by raising the vitrification pressure and allowing less time for CO2 gas expansion to play a role in cell growth. Higher reaction temperatures result in an increase in bulk density as the cell density remains invariant and the cell size drops. The use of the more polar fluoroform as a foaming agent results in larger cells, as it is able to plasticize the polymer network and allow for gas expansion during depressurization. A constant composition method of pressure quench results in smaller cell diameters.
The effect of composition on morphological, thermal, and mechanical properties of polypropylene/nylon‐6/polypropylene‐g‐butyl acrylate blends
Authors: Sathe Sachin N. , Srinivasa Rao G. S. , Rao K. V. , Devi Surekha
Published: April 2004

The effect of concentration of polypropylene grafted with butyl acrylate (PP‐g‐BA) compatibilizer on thermal, morphological, and mechanical properties of polypropylene/nylon‐6 blends has been studied. It was observed that blends with 4.8 wt% concentration of PP‐g‐BA exhibited superior mechanical and morphological properties at all the compositions of PP/Ny‐6. Attempts were made to correlate the experimental data for tensile modulus and strength with existing mathematical models.
Thermodynamics of polymer solutions and blends
Authors: Hoch Michael
Published: April 2004

To describe the thermodynamic behavior of binary and larger polymer blends, the Hoch‐Arpshofen model is used to describe highly asymmetric phase diagrams, and asymmetric enthalpies of mixing, where the miscibility gap and the extremum of the enthalpy of mixing leans toward one of the components. The Gibbs energy of mixing of polymer blends is described as

where z can be mole fraction, volume fraction, or weight fraction. The Hoch‐Arpshofen model contains an interaction parameter W = A + B*T independent of composition and an integer number n (2, 3, 4, …), which defines the asymmetricity of the binary phase diagram and of the Gibbs energy of mixing curve. In a binary system n defines the composition where the Gibbs energy of mixing is maximum or minimum or the composition is where the temperature of a miscibility gap is maximum or minimum. In a binary system A‐B the maximum effect occurs at An–1B. The disorder reaction in polymers is treated as a transformation temperature, and defines T0, the temperature where the ordered and disordered material is equal.
Interfacial property determination for immiscible polymer blends: A model system of polycarbonate/poly(ethylene terephthalate)
Authors: Pham Hoang T. , Sehanobish Kalyan , Rightor Edward G.
Published: April 2004

A model system, a tri‐layer of polycarbonate/poly(ethylene terephthalate)/polycarbonate, was used in this study to investigate the interfacial properties of an immiscible polymer blend system. The model system was compression molded and quenched in three different media: ice, water, and hot water. The interfacial properties of interest were the through‐thickness residual stress profiles and the interfacial strength. A method of estimating the interfacial strength of an immiscible polymer blend was also proposed, enabling the prediction of failure. The method was based on a single‐notch 4‐point bending test. The load at which failure occurred was then analyzed using finite element stress analysis to resolve the interfacial stress, i.e., the strength of the interface.