bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure and properties of poly(vinyl chloride)‐triallyl cyanurate plastisols
Authors: Tai Horng‐Jer
Published: April 2004

Triallyl cyanurate (TAC) has been used as a reactive plasticizer to promote the high‐temperature creep resistance of poly(vinyl chloride) (PVC) plastisols. The resultant crosslinked structure is characterized using gel content and swell ratio measurements as well as Fourier transform infrared spectroscopy. The crosslinking reaction was initiated using peroxide. The effect on the network structure of using a free radical scavenger in the formulation has also been studied. The gel yield and crosslink density in the gel increase with increasing TAC concentration in the plastisol, while the grafted PVC fraction and the residual unsaturation of TAC behave in the opposite way. Introduction of TAC into the plastisol promotes creep resistance at high temperatures, and the logarithmic creep rate was found to decrease linearly with increasing crosslink density.
Impact specific essential work of fracture of compatibilized polyamide‐6 (PA6)/poly(phenylene ether) (PPE) blends
Authors: Chiou Kuo‐Chan , Chang Feng‐Chih , Mai Yiu‐Wing
Published: April 2004

The essential work of fracture (EWF) method has aroused great interest and has been used to characterize the fracture toughness for a range of ductile metals, polymers and composites. In the plastics industry, for purposes of practical design and ranking of candidate materials, it is important to evaluate the impact essential work of fracture at high‐rate testing of polymers and polymer blends. In this paper, the EWF method has been utilized to determine the high‐rate specific essential fracture work,we, for elastomer‐modified PA6/PPE/SMA (50/50/5) blends by notched Charpy tests. It is found thatweincreases with testing temperature and elastomer content for a given specimen thickness. Morphologically, there are two failure mechanisms: shear yielding and pullout of second phase dispersed particles. Shear yielding is dominant in ductile fracture, whereas particle pullout is predominant in brittle fracture.
The effect of scaleup on the processing behavior of a blend exhibiting phase inversion during compounding
Authors: Ratnagiri Ram , Scott Chris E. , Shih Chi‐Kai
Published: April 2004

The scaleup behavior of blends exhibiting phase inversion during compounding in batch mixers was studied. Similar morphological changes were observed during compounding of polystyrene/polyethylene blends of different batch sizes ranging from 12g to 240g. The time to achieve a continuous phase of the major component, polystyrene, was shown to depend on the scale of the mixing device. Based on visual observation of the morphological changes, a constant nominal‐maximum‐shear‐rate scaleup condition was used. Upon a five‐fold increase in batch size the time to phase inversion increased by a factor of 3. This change is explained using a combination of the reduced specific area and reduced mechanical energy input under the experimental conditions. A novel blade design using modular triangular elements was constructed and results from radial and axial scaleup using the new blades are presented. Similarities between the triangular and roller blades are used to highlight the importance of the high‐shear region in determining the softening rate of the polystyrene pellets. The flexibility of the blade design was exploited to study the effect of blade configuration on the time to phase inversion. A relative stagger parameter is introduced to explain the observed dependence. Increasing the relative stagger decreased the stress transfer to the batch and increased the time to phase inversion. Implications of these results for mixing in the kneading sections of twin‐screw extruders is discussed.
Micro‐ and macrorheological properties of polypropylene‐polyoxymethylene‐copolyamide mixture melts
Authors: Tsebrenko M. V. , Rezanova N. M. , Tsebrenko I. A.
Published: April 2004

The influence of polyoxymethylene (POM) additives on micro‐ and macrorheological properties of polypropylene‐copolyamide (PP/CPA) mixture melts with the PP/CPA ratios of 40/60 and 20/80 wt% was investigated. We have shown that the microrheological processes such as deformation of dispersed polymer droplets and formation of liquid polymer streams, coalescence of these streams along the longitudinal direction, migration, and fracture of the liquid streams into droplets can be controlled by addition of a third component that may interact with CPA in a specific manner. The ternary mixture melt viscosity was greater than that of the binary mixture melt viscosity. The degree of viscosity increase depended upon the composition of the binary mixture, the value of shear stress, and POM content. This dependence may be explained by formation of hydrogen bonds between POM and CPA macromolecules. The addition of POM improved the specific PP fiber formation in the matrix of CPA. The latter is valid even for a composition (PP/CPA ratio is 40/60) close to phase inversion. POM migration toward the walls of the forming die occurred in the flow of the ternary polymer mixture melts. For the purpose of realizing the specific fiber formation during the processing of the above mentioned mixtures we recommend an addition of 5% to 10% of POM.
Temporal distributions: The basis for the development of mixing indexes for scale‐up of polymer processing equipment
Authors: Wang Winston , Manas‐Zloczower Ica
Published: April 2004

New and better mixing criteria are needed to assess dispersive and distributive mixing efficiency in polymer processing equipment. Such criteria can serve the purpose of process optimization and machine scale‐up. In this work, the history of flow strength and shear stresses experienced by a number of particles in a twin‐flight, single‐screw extruder serve as the basis to produce temporal distributions of these parameters. In turn, the temporal distributions can be used for developing new mixing indexes for process optimization and scale‐up. Using models for dispersion kinetics and experimental data, calculations of agglomerate size distribution and average agglomerate size can be used as a dispersive mixing criterion.
On‐line ultrasonic measurements of methyl methacrylate polymerization for application to reactive extrusion
Authors: Kiehl Christopher , Chu Lih‐Long , Letz Keith , Min Kyonsuku
Published: April 2004

An ultrasonic measurement system was developed for monitoring the polymerization of methyl methacrylate (MMA) in a model batch reactor and a model twin screw extruder. Conversion of MMA polymerized in a home‐made reaction chamber was compared with results obtained from a differential scanning calorimeter (DSC). The objective is to correlate ultrasonic velocity to extent of reaction based on the model experiments of poly(methyl methacrylate) in solution with MMA. This primary ultrasonic measurement system was applied to the on‐line measurement of the extent of MMA polymerization in a model twin‐screw extruder.
Thermoplastic elastomeric composition based on ground rubber tire
Authors: Naskar Amit K. , Bhowmick Anil K. , De S. K.
Published: April 2004

Ground rubber tire (GRT) is a particulate vulcanizate consisting mainly of rubber hydrocarbon and fillers. Rubber hydrocarbon of GRT (rGRT) has been used as a partial substitute for EPDM rubber in a dynamically vulcanized EPDM/acrylic‐modified HDPE (A‐HDPE) blend. The blends with higher rubber content show poor processability and physical properties, while the compositions with higher plastic content behave like toughened plastics. However, the 60:40 rubber/plastic blend was found to behave as a thermoplastic elastomer, and it was observed that 50% of EPDM can be replaced by rGRT without deterioration in properties.
Effect of non‐isothermal oriented crystallization on the velocity and elongational viscosity profiles during the melt spinning of high density polyethylene fibers
Authors: Makradi A. , Ahzi S. , Gregory R. V.
Published: April 2004

Based on the experimental data of spine line temperature and percent crystallization, a time‐integral constitutive equation has been used together with the degree of phase transformation theory to predict the velocity and elongational viscosity profiles. For the velocity profile, our predicted results are compared to experimental data and good agreement is found. Under a drawing force, the elongational viscosity profile shows a stress softening due to the molecular alignment; then the fiber hardens close to the take‐up point, owing to filament crystallization.
Poly(butylene terephthalate)/ poly(ethylene‐co‐alkyl acrylate)/ carbon black conductive composites: Influence of composition and morphology on electrical properties
Authors: Lagrève C. , Feller J. F. , Linossier I. , Levesque G.
Published: April 2004

Poly(butylene terephthalate)/Poly(ethylene‐co‐alkyl‐acrylate)/carbon black (PBT‐EXA‐CB) blends, prepared through extrusion, were characterized as electrical conductive materials. In the composition range studied (55 ≤ PET % ≤ 75 w/w 5.5 ≤ CB % ≤ 11.1 w/w), various conductive behaviors were observed depending mainly on composition and poly(olefin) crystallinity. The observed positive temperature coefficient (PTC) is quite small compared to poly(olefin)‐CB systems, and our blends do not present a negative temperature coefficient (NTC) on complete melting of the CB‐containing phase, thus offering new possibilities for a regular electric power control. Volume expansion of both PBT and EXA was postulated to be the main parameter responsible for the thermal resistivity evolution through the range +20 to +170°C. A double‐percolation system between both the co‐continuous polymer phases and CB‐particles included in the poly(olefin) phase is postulated to explain these results.
Numerical inversion techniques in the recovery of molecular weight distribution expressed in different transformed domains. Experimental validation
Authors: Brandolin A. , Asteasuain M. , Sarmoria C. , López‐Rodríguez A. , Whiteley K. S. , Fernández B. Del Amo
Published: April 2004

In this work we analyze the feasibility of using numerical inversion techniques for recovering MWD of actual polymers from a transformed domain, specifically the one defined by probability generating functions. We start from known experimental MWDs, transform them, and then apply two different numerical techniques to recover the MWD. We analyze the influence of noise in the calculated probability generating functions on the quality of the recovered molecular weight distributions. We also study how the range of molecular weight selected for the inversion procedure affects the results. We compare the recovered distributions obtained by both methods and suggest a criterion for establishing the reliability of a given solution. We find that this general strategy is appropriate for the recovery of MWDs whether they are monomodal, multimodal, wide or narrow. This provides a tool for the treatment of actual polymerization systems for which there is no analytical solution for the mass balance equations.
Reaction injection molding of polyurethane foam for improved thermal insulation
Authors: Koo Myung Sool , Chung Kwansoo , Youn Jae Ryoun
Published: April 2004

A study on the apparent thermal conductivity of polyurethane foam was carried out. A HCFC (hydrochlorofluorocarbon) gas and carbon dioxide were used as the physical blowing agent and ultrasonic excitation was applied to increase the rate of bubble nucleation. The thermal conductivity of the binary gas mixture was predicted theoretically to estimate the apparent thermal conductivity of the polymer foam. Effects of conduction and radiation on the apparent thermal conductivity of the cellular polyurethane were considered with respect to the cell size and the effect of convection was neglected because of the small cell size. A laboratory RIM machine was designed and built for foaming experiments. The foaming experiments were performed at various processing conditions, and density, apparent thermal conductivity, number of cells, and cell sizes were measured. Best results such as low thermal conductivity and small bubbles were obtained when the polyol was mixed with the HCFC gas and saturated with carbon dioxide at 0.3 MPa, and foamed with ultrasonic nucleation.
Solid‐phase preparation of ultra‐fine PA6 powder through pan‐milling
Authors: Chen Zhe , Liu Changsheng , Wang Qi
Published: April 2004

The engineering plastic polyamide 6 (PA6) was effectively pulverized to ultra‐fine powder through a sell‐made pan‐type milling equipment. A laser Diffraction Particle Size Analyzer and TEM were used to examine the particle size and the distribution of PA6 powder. The results show that the average particle size of PA6 was reduced to micrometer scale only after 15 milling‐cycles and reached 50–80 nm after 30 milling‐cycles. Pan milling decreased crystallinity of PA6 but did not affect its crystal type. Molecular weight and mechanical properties of PA6 dropped slightly during pan milling. The average particle size of PA6 powder could be controlled by adjusting processing conditions including milling time, temperature and the rotating speed of the milling pan.
Photoinitiating characteristics of benzophenone derivatives as new initiators in the photocrosslinking of polyethylene
Authors: Wu Qianghua , Qu Baojun
Published: April 2004

Two kinds of benzophenone (BP) derivatives, dodecyl‐benzophenone (BP‐D) and hexadecoxyl‐benzophenone (BP‐H), used as new photoinitiators have been synthesized by Friedel‐Crafts reactions and identified by ultraviolet (UV) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and elemental analysis. The kinetic characteristics of photoinitiating crosslinking of BP‐D and BP‐H comparing with BP in the photocrosslinking of polyethylene (PE) in the melt and their compatibility with PE resin have been examined by gel content measurement and thermal migration experiments. The results show that these two BP derivatives are excellent photoinitiators, which have better compatibility, less volatility, higher photoinitiating efficiencies, and longer storage time than BP itself. These two new photoinitiators are promising for industrial applications of the photocrosslinking of polyolefins and curing of coats.
Maleic anhydride modification of polyolefin in an internal mixer and a twin‐screw extruder: Experiment and kinetic model
Authors: Cha Jaehyug , White James L.
Published: April 2004

There has been little effort. to quantitatively understand graft copolymerization in batch and continuous mixers. Little information exists on the evolution of grafting reactions with respect to residence time in an internal mixer or along the screw axis in a twin‐screw extruder. In this study, maleic anhydride was grafted onto polypropylene in both an internal mixer and a twin screw extruder. The influence of residence time on degree of grafting in an internal mixer and a twin screw extruder was studied through measuring reaction yields with respect to reaction time in the internal mixer as well as along the screw axis in the extruder. The dependence of the degree of grafting with monomer and peroxide concentration was determined. A free radical kinetic model of the process was developed and compared to experiment. Kinetic parameters were determined.
Residence time and conversion in the extrusion of chemically reactive materials
Authors: Zhu Weimin , Jaluria Yogesh
Published: April 2004

Twin‐screw extruders offer improved control of the residence time distribution (RTD) and mixing in materials such as plastics, rubber and food. Based on the flow and the heat transfer characteristics obtained for a self‐wiping, co‐rotating twinscrew extruder, the residence time and chemical reaction are studied by tracking the particles. For normally starve‐fed twin‐screw extruders, the length of the completely filled section is calculated as function of the process variables using the coupling of the flow with the die. With a model of the solid conveying section, the RTD for the whole extruder is calculated for corn meal at different screw speeds and flow rates. The calculated variation of RTD with the screw speed and the flow rate yields good agreement with observations from many experiments. The variation of the fully filled section length, chemical conversion and mixing effectiveness are also obtained under different operation conditions. Most of the results are in qualitative agreement with experimental results and may be used as guidelines for extruder design and determination of optimal operating conditions.
A uniform phenomenological constitutive model for glassy and semicrystalline polymers
Authors: Duan Y. , Saigal A. , Greif R. , Zimmerman M. A.
Published: April 2004

A phenomenological constitutive model is proposed on the basis of four models: the Johnson‐Cook model, the G'Sell‐Jonas model, the Matsuoka model, and the Brooks model. The proposed constitutive model has a concise expression of stress dependence on strain, strain rate and temperature. It is capable of uniformly describing the entire range of deformation behavior of glassy and semicrystalline polymers, especially the intrinsic strain softening and subsequent orientation hardening of glassy polymers. At least three experimental stress‐strain curves including variation with strain rate and temperature are needed to calibrate the eight material coefficients. Sequential calibration procedures of the eight material coefficients are given in detail. Predictions from the proposed constitutive model are compared with experimental data of two glassy polymers, polymethyl‐methacrylate and polycarbonate under various deformation conditions, and with that of the G'Sell‐Jonas model for polyamide 12, a semicrystalline polymer.
Load‐carrying ability of polystyrene products with molded‐in holes
Authors: Heidweiller A. J. , Van Der Zwet M. J. M.
Published: April 2004

The combined influence of stress concentration, weld line, and local distribution of molecular orientation on injection molded polystyrene (PS) plates with a moldedin hole is described. Birefringence measurements were used to investigate the molecular orientation, and three‐point flexure was used to investigate the mechanical properties. Both blunt notch tests and transverse bending tests were carried out. Blunt notch tests showed a strong variation of the material resistance to fracture around the hole. The molecular orientation increased the material resistance not only at the hole equator, but also at the flow split area. In a large domain, wela line fracture was the dominant fracture mechanism. Transverse bending tests also showed a strong influence of the molecular orientation on the load‐carrying ability. The weld line was definitely the weakest region, but the reduction caused by the weld line itself appeared to be small.
Polyethylene compounds containing mineral fillers modified by acid coatings. 2: Factors influencing mechanical properties
Authors: Haworth B. , Raymond C. L. , Sutherland I.
Published: April 2004

High molar mass medium density polyethylene (MDPE) compounds containing magnesium hydroxide filler, surface‐treated by a range of fatty acid coatings of variable aliphatic chain length were injection molded and subjected to mechanical property evaluation. Surface treatment modifies yield stress and modulus, with property maxima observed close to the monolayer coverage. Acid‐group terminated polyethylene (ATPE) coalings produced the highest yield stress, as a result of physical interaction with the matrix polymer. Retention of high‐energy, ductile mode impact failure of unfilled MDPE was obtained when using short‐chain decanoic acid coating, as a result of enhanced dispersion and reduced particle‐matrix interactions promoting microscopic matrix yielding. A mechanism for enhanced Mg(OH)2 particle dispersion based upon surface energy and molecular adsorption has been proposed, which is consistent with the properties data derived. Fractographic analysis (SEM) has confirmed the predominance of matrix yielding in compounds exhibiting enhanced impact resistance, while X‐ray pholoelectron spectroscopy (XPS) has also highlighted a different crack growth mechanism in MDPE compounds containing coated fillers, which are less prone to agglomeration. In addition, thermomechani‐cal history during processing also modifies physical properties of MDPE/Mg(OH)2 composites to some extent. Anisotropic effects include molecular orientation and filler particle alignment induced by shear stress during injection mold filling, which predominate in compounds containing coated fillers. Overall, the application of organo‐acid coatings reduces polymer‐particle surface interaction and thermody‐namic work of adhesion, leading to improved dispersion and enhanced properties. Appropriate property balances can be tailored by judicious selection of aliphatic chain length and addition level of fatty acid filler coatings.
Effect of starch content on viscosity of starch‐filled poly(hydroxy ester ether) composites
Authors: Zhou Genwen , Willett J. L. , Carriere C. J.
Published: April 2004

The effect of starch volume fraction on starch‐filled poly(hydroxy ester ether) (PHEE) biodegradable composites was analyzed using Mooney, Thomas, Maron & Pierce, and Frankel & Acrivos equations. Corn starch/PHEE materials were extruded using a twin‐screw extruder with starch volume fractions from 0.27 to 0.66. The starch was dried to a moisture content of 0.7% to minimize moisture effect on composite rheology. Dynamic frequency sweep measurements were carried out at 120°C and 1% strain. The equations of Maron & Pierce, Thomas, and Frankel & Acrivos can be used to describe the experimental data. It is found that the relative viscosity at the same shear stress increases with increasing shear stress. The possible existence of yield stress at high starch concentrations was examined using a Casson plot.
Cure shrinkage analysis of epoxy molding compound
Authors: Oota Ken , Saka Masumi
Published: April 2004

EGA (ball grid array), one of the structures Used for semiconductor packages, involves a laminated structure. BGA inevitably involves significant warpage, owing to differences in shrinkage among constituent materials. The extent of warpage is governed by total shrinkage (= cure shrinkage + thermal shrinkage) of the epoxy molding compound that encapsulates the IC chip. In particular, the cure shrinkage exerts great influence on warpage. Cure shrinkage has been understood as the decrease in free volume at the time of curing. However, the cure shrinkage rate cannot be sufficiently explained by the free volume of the cured epoxy resin. We have developed an evaluation method based on the epoxy group reaction ratio, and have eventually confirmed that cure shrinkage depends on the reaction ratio of the epoxy group after curing, and on epoxy group density.
Fluorescence based temperature measurements and applications to real‐time polymer processing
Authors: Bur Anthony J. , Vangel Mark G. , Roth Steven C.
Published: April 2004

We have used temperature sensitive fluorescent dyes, doped into polymer resins, to monitor the true resin temperature during extrusion processing. Two types of temperature sensitive fluorescent dyes were used: mobility dyes and fluorescence band definition dyes. When mixed with the resin at dopant concentrations, the fluorescent dye resides in a molecular neighborhood composed of resin molecules. Under these circumstances, its fluorescence spectrum reflects the resin temperature in its neighborhood. We apply this measurement concept to extrusion processing by using an optical sensor that accesses the machine at standard instrumentation ports. We show that, under processing conditions, the true resin temperature is significantly different from The machine temperature. Two examples of real‐time process monitoring arc presented: first, the effects of shear heating during extrusion were measured, and second, the effects of poor temperature control during extrusion were observed. The effects due to pressure on the fluorescence temperature measurements are examined. The fluorescence temperature measurements are compared to melt temperature thermocouple measurements.
Diffusion‐induced bubble growth in viscous liquids of finite and infinite extent
Authors: Venerus David C.
Published: April 2004

Transport models of diffusion‐induced bubble growth in viscous liquids of finite and infinite extent are developed and evaluated. Results from the present study are compared with results from the often‐cited papers by Amon and Denson (1984) and Arefmanesh et al (1992) and found to be in good agreement. Predictions for the bubble radius and pressure from the finite‐ and infinite‐liquid models are compared over a range of conditions. As anticipated, predictions from the two models coincide at early stages of the growth process, and differ at late stages of the growth process when the equilibrium bubble radius Is approached for the finite‐liquid model. Agreement between the two models at intermediate stages is observed only for relatively low growth rates.
Prediction of molecular weight distributions by probability generating functions. Application to industrial autoclave reactors for high pressure polymerization of ethylene and ethylene‐vinyl acetate
Authors: Brandolin A. , Sarmoria C. , Lótpez‐Rodríguez A. , Whiteley K. S. , Del Amo Fernandez B.
Published: April 2004

We develop a mathematical model able to describe the complete molecular weight distributions of polyethylene and elhylene‐vinyl acetate copolymers obtained in high pressure autoclave reactors. We apply probability generating function definitions to the mass balances of radical and polymer species in the reacting medium. We use three different definitions of probability generating functions, each one directly applicable either to the number, weight or chromatographic distributions. These probability generating functions are numerically inverted to obtain the corresponding calculated molecular weight distribution. The capabilities of two different inversion methods are compared. Predictions are compared with experimental data obtained in an industrial reactor; good agreement is obtained. The approach presented here is applicable to other types of polymerization reactors and post‐polymerization processes.
Coupled diffusion of water and ethanol in a polyimide membrane
Authors: Ni Xiuyuan , Sun Xiaohui , Ceng Dong , Hua Fengjun
Published: April 2004

In this work, the sorplion and steady state permeation of water‐ethanol mixture in an aromatic polyimidc membrane was investigated with the objective of revealing the coupling cherts of water and ethanol in their course of diffusion. The solubility of the watcr‐ethanol mixture in the membrane was determined by means of swelling‐distillation techniques. The sorption behavior was interpreted in terms of the thermodynamic equilibrium equations. The Maxwell‐Stefan mass transfer model was employed as a framework for modeling diffusion. Model equations derived therefrom enable us to cplculate coupled fluxes of water and ethanol from the experimental data. The coupling effects in the diffusion of water and ethanol were revealed by comparing the calculated coupled flux with non‐coupling flux, which was calculated by integration of the Fickian first law using independent diffusion coefficients. Furthermore, the implication of the sole adjustable parameter included in the derived model equations was discussed.
Modeling heat transfer in screw extrusion with special application to modular self‐wiping co‐rotating twin‐screw extrusion
Authors: White James L. , Kim Eung Kyu , Keum Jong Min , Jung Ho Chul , Bang Dae Suk
Published: April 2004

This paper proposes two important models useful for describing heat transfer and temperature profiles in single and modular self‐wiping co‐rotating twin‐screw extruders. One model predicts heat transfer coefficients. Calculations of the barrel and screw heat transfer coefficients are made for various modules in different diameter extruders. We compare the values of the heat transfer coefficients from the model with those from literature. The second model predicts the axial screw temperature profile when the barrel, but not the screw, is heated, Example calculations of the cup mixing and screw temperature profiles are also made for different diameter extruders.
Reactive blending of functionalized acrylic rubbers and epoxy resins
Authors: Dispenza C. , Spadaro G. , Carter J. T. , McGrail P. T.
Published: April 2004

A high molecular weight acrylonitrile/butadiene/methacrylic acid (Nipol 1472) rubber is chosen to control processability and mechanical properties of a TGDDM (tetra glycidyl diphenyl methane) based epoxy resin formulation for aerospace composite applications. The physical blend of rubber and epoxy resin, achieved by dissolution of all the components in a common solvent, forms a heterogeneous system after solvent removal and presents coarse phase separation during cure that impairs any practical relevance of this material. A marked improvement of rubberepoxy miscibility is achieved by reactive blending (‘pre‐reaction’) the epoxy oligomer with the functional groups present in the rubber. The epoxy‐rubber ‘adduct’ so obtained appears as a homogeneous system at room temperature and also after compounding with the curing agent. Depending on the nature and extent of interactions developed between the rubber and the epoxy resin during ‘pre‐reaction,’ materials with different resin flow characteristics, distinctive morphologies and mechanical properties after curing were obtained. The effect of ‘pre‐reaction’ on the resin cure reaction kinetics has been also investigated.
Studies of the aging of nafion®/silicate nanocomposites using 29Si solid state NMR spectroscopy
Authors: Young S. K. , Jarrett W. L. , Mauritz K. A.
Published: April 2004

Sol‐gel reactions of tetraethylorthosilicate were conducted within the nanophase‐separated morphology of Nafion® films to yield Nafion®/silicate nanocomposites. The chemical aging of silicate phase molecular structure when the nanocomposites were exposed to (1) ambient air, (2) applied heat, (3) liquid water, (4) methanol reflux, and (5) heated sulfuric acid was explored by means of 29Si solid state NMR spectroscopy. In particular, the characteristic chemical shifts and relative Intensities of peaks that identify Qn = (HO)4‐n Si(OSi)n molecular subunits in silicate structures were determined for samples exposed to these aging conditions. Shifts in the Q peak distribution reflected the evolution of degree of Si atom coordination about SiO4 units. The coordination states are always Q4 and Q3 although a small Q2 population is occasionally present. Thus, a significant degree of silicate phase coordination can develop despite constraints posed by the Nafion® medium. Percent Q4 increases in all cases but then reaches a maximum after which it decreases, the greatest de‐polymerization being for samples aged in water. The greatest increase in Q4 relative to the un‐aged control occurred for samples heated at 100°C. Exposure to ambient air produced changes in Q4 that were small, but not insignificant. While the initial increase in Si atom substitution around SiO4 units can be rationalized in terms of gradual condensation reactions between residual SiOH groups, accompanied by the liberation of water molecules and their removal from the site of the reaction, the eventual decrease in coordination is not currently understood.
High internal phase emulsion foams: Copolymers and interpenetrating polymer networks
Authors: Tai Huiwen , Sergienko Anatoly , Silverstein Michael S.
Published: April 2004

High internal phase emulsion (HIPE) copolymer and interpenetrating network foams were prepared from 2‐ethylhexyl acrylate (EHA), styrene (S) and divinylbenzene (DVB) using a unique process. The morphologies, thermal properties and dynamic and static mechanical properties of these foams were investigated. The glass transition temperatures and damping properties of the EHA/S copolymer foams vary with its composition. IPN foams with very broad tan 5 peaks were obtained. The damping properties of IPN foams were tailored through changing copolymer composition and monomer composition. The IPN foams based on a copolymer foam and styrene had a broader tan δ peak, a higher glass transition temperature and a higher modulus than tne copolymer foams of similar overall styrene contents. It is therefore possible to prepare novel damping foams based on polyHIPE foams through the synthesis of interpenetrating polymer networks.
Increase of photoluminescence from fullerene‐doped polymers under laser irradiation
Authors: Li G. Z. , Minami N. , Ichio Y.
Published: April 2004

Photoluminescence (PL) from fullerene (C60 and C70)‐doped polymers such as poly(methyl methacrylate) (PMMA), polystyrene (PS), poly(methyl phenyl silane) (PMPS) and poly(phenyl silsesquioxane) (PPSQ) increases gradually under laser irradiation in air (but not in vacuum and in nitrogen) and eventually becomes visible to the naked eye. Concomitantly, the PL peak is broadened and, in most cases, blue‐shifted. No such PL increases are observed for pure C60 films made by vacuum vapor deposition and pure polymer films. Among the polymers used, fullerene‐doped PMMA has the greatest PL increase after several hours of laser irradiation and fullerene‐doped PMPS has the highest rate of PL increase at the initial stage of the laser irradiation. To gain an insight into the mechanism of the PL increase, laser‐irradiated fullerene‐doped PMMA samples were analyzed by UV‐Vis spectrophotometer, FT‐IR, mass spectrometry, GPC and NMR. The results show that the PL increase can be attributed to CH60On‐polymer (or C70On‐polymer) and oxidized fullerene‐polymer adducts formed by some laser‐induced photochemical reactions among fullerenes, oxygen and polymers.
Kinetics of isothermal and non‐isothermal crystallization of poly(butylene terephthalate)/ liquid crystalline polymer blends
Authors: Kalkar A. K. , Deshpande A. A.
Published: April 2004

The melting behavior and isothermal and non‐isothermal crystallization kinetics of poly(butylene terephthalate) (PBT)/thermotropic liquid crystalline polymer (LCP), Vectra A950 (VA) blends were studied by using differential scanning calorimetry. Isothermal crystallization experiments were performed at crystallization temperatures (Tc), of 190, 195, 200 and 205°C from the melt (300°C) and analyzed based on the Avrami equation. The values of the Avrami exponent indicate that the PBT crystallization process in PBT/VA blends is governed by three‐dimensional morphology growth preceded by heterogeneous nucleation. The overall crystallization rate of PBT in the melt blends is enhanced by the presence of VA. However, the degree of PBT crystallinily remains almost the same. The analysis of the melting behavior of these blends indicates that the stability and the reorganization process of PBT crystals in blends are dependent on the blend compositions and the thermal history. The fold surface interfacial energy of PBT in blends is more modified than in pure PBT. Analysis of the crystallization data shows that crystallization occurs in Regime II across the temperature range 190°C‐205°C. A kinetic treatment based on the combination of Avrami and Ozawa equations, known as Liu's approach, describes the non‐isothermal crystallization. It is observed that at a given cooling rate the VA blending increases the overall crystallization rate of PBT.
Thermal behavior of poly(dimethyl itaconate) and poly(di‐n‐butyl itaconate) copolymerized with methyl methacrylate
Authors: Fernández‐Garcia Marta , De La Fuente José Luis , Madruga Enrique López
Published: April 2004

The thermal degradation behavior of random copolymers of dimethyl itaconate and di‐n‐butyl itaconate with methyl methacrylate was studied. The thennal stability of copolymers depends on the structure of the di‐n‐alkyl itaconate comonomer, and on the copolymer composition. The relative thermal stability increases with the methyl methacrylate copolymer molar fraction, following a trend similar to the glass transition temperature variation. The activation energy was obtained by using MacCallum and Tanner's approach. In addition, the thermal degradation of homopolymers was evaluated in inert atmosphere as well as in thermo‐oxidative conditions, presenting different behaviors.
On‐line measurement of polymer orientation using ultrasonic technology
Authors: Edwards Russ , Thomas Charles
Published: April 2004

The propagation velocity of an ultrasonic shear wave can be used to detect anisotropic behavior in the mechanical properties of a solid. Thus, an ultrasonic shear transducer imbedded in an injection mold produces a signal that is sensitive to polymer orientation. This results in a non‐invasive, on‐line technique for monitoring the orientation of polymer in an injection mold cavity during part cooling and solidification. The technique is shown to be quite sensitive for semicrystalline polymers, but much less effective for amorphous polymers. Sensor results are compared to mechanical tests.
Microstructural effects on hot drawing syndiotactic styrene P‐methyl styrene copolymer
Authors: Yan R. J. , Ajji A. , Shinozaki D. M.
Published: April 2004

Crystalline syndiotactic styrene/p‐methyl styrene copolymer (SPMS) has been oriented by tensile drawing at various temperatures between the glass transition and crystalline melting point. The microstructural changes resulting from drawing have been studied using differential scanning calorimetry (DSC) and wide angle X‐ray diffraction (WAXD). WIth increasing draw temperature, both melting temperature and crystalline dimensions of the oriented samples increase. The heat of fusion increases with increasing draw temperature up to ∼200°C. It also increases with draw ratio and draw rate, while the crystalline width increases only with draw ratio. THe amorphous fraction shows a clear glass transition, the temperature of which (Tg) increases with draw ratio. However, Tg decreases somewhat with increasing draw temperature. This is interpreted in terms of the stretching of the randomly coiled amorphous phase molecules.
Numerical simulations of polymer flow in flat spiral dies
Authors: Zatloukal M. , Tzoganakis C. , Perdikoulias J. , Saha P.
Published: April 2004

The flow of a polymer melt through a flat spiral distribution system used in “stacked” type dies was analyzed through three‐dimensional finite element simulations, and predictions of the exit flow variation were compared to experimental measurements. Both isothermal and non‐isothermal simulations were carried out, and the non‐isothermal results were found to be in close agreement with the measured flow variation. It was found that for this particular flat spiral die, viscous dissipation is extremely crucial and may lead to generation of hot spots and to increased flow variation. Finally, the effect of material viscoelasticity on the flow field was simulated by using a CEF constitutive equation. It was shown that neglecting viscoelastic effects due to shear deformation, represented by primary and secondary normal stress coefficients, in the modeling of the flow in the flat spiral dies is a reasonable simplification. On the other hand, extensional behavior should be taken into account for a more suitable description of the leakage flows within this type of die.
Temperature modulated DSC studies of melting and recrystallization in poly (oxy‐1,4‐phenyleneoxy‐1,4‐phenylenecarbonyl‐1,4‐phenylene) (PEEK)
Authors: Kampert William G. , Sauer Bryan B.
Published: April 2004

The thermal and crystal morphological properties of amorphous and melt crystallized poly(oxy‐1,4‐phenyleneoxy‐1,4‐phenylenecarbonyl‐1,4‐phenylene) (PEEK) were investigated. Two different molecular weights were studied by Temperature Modulated DSC (TMDSC) over a broad range of annealing times and temperatures. The lower molecular weight PEEK under all crystallization conditions was found to exhibit secondary crystal melting in the low endotherm region, followed by melting of primary crystals melting in the low endotherm region, followed by melting of primary crystals superimposed with a large recrystallization contribution. Primary crystal melting broadly overlapped with melting of the recrystallized species and contributed to the broad highest endotherm. Recrystallization contributions and the interpretation of TMDSC were partially confirmed by independent rapid heating rate melting point determinations and variable heating rate DSC. The higher molecular weight PEEK showed many similarities but generally had smaller levels of reorganization above the annealing temperature under most higher temperature crystallization conditions. TMDSC provides excellent resolution of recrystallization and related events compared to standard DSC. The broad and substantial exothermic recrystallization in amorphous samples was also examined, showing that recrystallization continues through the final melting region.
Processing enhancers for rotational molding of polyethylene
Authors: Chaudhary Bharat Indu , Takács Elizabeth , Vlachopoulos John
Published: April 2004

Rotational molding is a zero shear process used to manufacture hollow plastic parts. One disadvantage of this process is long cycle times, which are significantly affected by the sintering rates of thermoplastic powder. The objective of this work was to evaluate low molecular weight additives as sintering enhancers for polyethylene and to validate the results in rotational molding. The following additives were blended with linear low‐density polyethylene: mineral oil, glycerol monostearate and pentaerythritol monooleate. The additives resulted in decreased melt viscosity and/or elasticity at low shear rate. The reduction in melt elasticity was particularly significant. Sintering studies confirmed that the additives resulted in significantly faster coalescence. In uniaxial rotational molding, the decreased melt viscosity and elasticity obtained with mineral oil were observed to result in much faster densification and bubble removal. Part thickness was uniform and there was no warpage. Adding mineral oil to polyethylene reduced the cycle time in uniaxial rotational molding and the peak impact strength was identical to that obtained without any additive. Biaxial rotational molding experiments confirmed that the use of mineral oil resulted in shorter cycle time without sacrificing peak impact strength.
Crystal structures and orientation development in tubular film extrusion of syndiotactic polypropylene and isotactic polypropylene
Authors: Choi Dongman , White James L.
Published: April 2004

The differences in behavior of isotactic polypropylene (iPP) and syndiotactic polypropylene (sPP) in tubular film extrusion are qualitatively described. The crystalline form and orientation in the films were characterized using wide‐angle X‐ray diffraction (WAXD) patterns, pole‐figure analysis and birefringence. The sPP films had the crystalline form of the disordered Form I and the a‐crystallographic axis was found to be preferentially oriented in the film normal direction (ND) under the conditions of biaxial stresses. High transverse orientations were developed in the sPP films. In the iPP films, the monoclinic crystalline form was found and the b‐crystallographic axis was preferentially oriented in the ND. The birefringence of the films showed trends very similar to the crystalline orientations characterized by WAXD in both iPP and sPP films.
Modeling the viscoelastoplastic behavior of amorphous glassy polymers
Authors: Drozdov Aleksey D.
Published: April 2004

Constitutive equations are derived for the viscoelastic and viscoplastic responses of amorphous glassy polymers at isothermal loading with small strains. A polymer is modeled as an ensemble of cooperatively relaxing regions (CRR) that are rearranged at random times as they are thermally agitated. At relatively low stresses, CRRs are bridged by links that ensure that the macro‐strain in a specimen coincides with micro‐strains in relaxing regions. When the average stress exceeds a threshold strength for the links, some of them break, and relaxing domains begin to slide with respect to one another. Rearrangement of CRRs reflects the viscoelastic behavior, whereas sliding of micro‐domains is associated with the viscoplastic response of glassy polymers. Kinetic equations are proposed for the evolution of viscoplastic strains and the strength of an ensemble of links. These equations are verified by comparison with experimental data in tensile relaxation tests and in tensile and compressive tests with constant strain rates. Fair agreement is demonstrated between results of numerical simulation and observations for a polyurethane resin and poly(methyl methacrylate).
Thermal stresses and orientations in acrylic sheet
Authors: McDonagh‐Smith A. , Arnold J. C. , Isaac D. H.
Published: April 2004

Two copolymers of poly(methyl methacrylate) with 3% and 10% ethyl acrylate, respectively, were extruded and calendered, with the same line speed and roll temperatures. The residual stresses and anisotropies, induced by the complex processing deformations and temperature variations, were characterized by monitoring the dimensional changes and sample curvatures resulting from subsequent heat treatments. In both copolymers, two distinct recovery regimes were observed: heat treatments just below Tg caused relaxation of residual thermal stresses and at temperatures above Tg led to recovery of chain extended orientations. It was found that the similar processing conditions induced similar residual thermal stresses in the two copolymers, but the higher viscosity of the 3% EA sheet led to greater residual orientations. Across the width of the sheets, little variations were seen in the thermal stresses, but orientations were lower at the edges. Some curvature changes observed following heat treatment well below Tg, were interpreted as resulting from aging effects.
Anisotropic dielectric properties of polyimides consisting of various molar ratios of meta to para diamine with trifluoromethyl group
Authors: Qu Wen‐Li , Ko Tze‐Man , Vora Rohit H. , Chung Tai‐Shung
Published: April 2004

A series of copolyimides based on pyromellitic dianhydride (PMDA) with various molar fractions of 4,4′‐(hexafluoro‐isopropylidene)dianiline (4,4′‐6F) and 3,3′‐(hexafluoro‐isopropylidene)dianiline (3,3′‐6F) were synthesized by a two‐step method. The five different composition copolyimides in the fozrm of {(PMDA+3,3′−6F)m/ (PMDA+4,4′−6F)n were mainly characterized using a dielectric analyzer (DEA) by single surface sensor (in‐plane direction) and thin film parallel plate sensor (out‐of‐plane direction) measurements. DSC, TMA, and XRD were also used to study the structure property. The increasing of molar ratio of para diamine in the copolyimide system up to 35% affected glass transition temperature, coefficient of thermal expansion, in‐plane dielectric constant and out‐of‐plane dielectric constant of copolyimides, correspondingly. The in‐plane dielectric constant was higher than that of the out‐of plane constant for our polyimide films. Anisotropy δε of the dielectric constants was 0.14 for CPI(100/o)a, 0.19 for CPI(85/15)a, 0.11 for CPI(75/25)a, and 0.05 for CPI(65/35)a. The difference in curing history also exhibited an effect on solvent diffusion behavior in our polymer system. Polymers cured at a slower curing rate had smaller CTE than that cured at a faster curing rate, as confirmed by X‐ray diffraction results. Polymers with smaller CTEs had larger dielectric constants at a slower curing rate, and vice versa. The experimental results suggested that CPI(65/35) a with smaller dielectric anisotropy could solve the crosstalk problem and provide equal electrical insulation in microelectronic devices. Therefore, a smaller and faster IC device could, it is hoped, be achieved, with smaller spacing between adjacent metal lines.