摘要:

AbstractThe various efforts up to date on the processing of ultra high tenacity fibers from flexible polymer have been summarized in this report. Some significant parameters correlating well with ultra high tenacity have been found through consideration of experimental results of polyethylene, despite the wide diversity in the processing techniques, degrees of drawing, thermal conditions, and molecular weight characteristics. It has been concluded from those parameters that ultra high tenacity fibers can be only attained by processing techniques satisfying the following structural principles simultaneously:1.ultra drawing with draw ratio above 20 for increasing the number of tie molecules and the degree of molecular orientation.2.reduction of the small angle x‐ray scattering intensity, correlating to an increase in the number of tie molecules.3.increase in molecular chain length for reducing the intermolecular chain slip at polymer chain ends.4.increase the slope of the Griffith plot, a manifestation of reducing defeets and flaws in microfibril

ISSN:0032-3888    

DOI:10.1002/pen.760231302

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractThe post‐curing of a bisphenol A‐glycidyl‐methacrylate based copolymer system at 37°C and 100 percent relative humidity was monitored using Fourier Transform IR (FT‐IR). The dependence of degree of post‐curing on the monomer and initiator components was investigated. The further polymerization achieved by elevating the temperature was measured using differential scanning calorimetry (DSC). The results clearly demonstrated that this free radical curing process was severely quenched by vitrification. Furthermore, a rapid loss in the reactivity to further curing was observed for the material in the quenched state, and this loss in reactivity was attributed to the decay of fre

ISSN:0032-3888    

DOI:10.1002/pen.760231303

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractA novel technique is described which enables reliable fracture toughness measurements to be made in impact test on relatively small specimens of a tough polyethylene. Composite specimens have been made in which a tough polyethylene is sandwiched between two layers of a more brittle polyethylene. The overall fracture toughness is interpreted on the basis of simple additivity of the strain energy release rate associated with each of the component layers. Brittle plane strain failures were obtained for specimens in which the relative thickness of the layers was varied over a substantial range and the fracture toughness of each layer determined by suitable extrapolation. The fracture toughness of the brittle layer obtained in this way agreed well with direct measurements on that material.

ISSN:0032-3888    

DOI:10.1002/pen.760231304

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractThe rheology of polyamic acid (PAA) solutions, precursors of polyimides used in microelectronic device applications, has been investigated by dynamic (oscillatory) shear flow measurements. Frequency dependent storage and loss moduli and dynamic viscosity were measured in the frequency range 10−1to 103rad/s at 23°C. The storage modulusG′ (ω) and loss modulusG″ (ω) exhibited quadratic and linear dependence in frequency at low frequencies respectively, the viscoelastic fluid behavior commonly predicted for polymer solutions from many molecular theories. At high frequencies both dynamic moduli become proportional to ω2/3. The results show that PAA solutions are very high loss viscoelastic fluids, judging from the loss tangent values which far exceed unity. It is suggested that dynamic viscoelastic properties could be used to monitor the degree of imidization since there is a gradual change from viscoelastic fluids to soft viscoelastic solids to hard viscoelastic solids as PAA is converted to polyimides. Onset of non‐Newtonian flow as shown on the frequency dependent dynamic viscosity was in the range 30 to 200 rad/s. The viscoelastic constants, zero‐shear rate viscosity ηoand steady‐state complianceJe0, where also determined from the dynamic data and compared to previous steady sh

ISSN:0032-3888    

DOI:10.1002/pen.760231305

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractA common framework for the analysis of styrene‐acrylic ester systems has been developed by analyzing the pertinent kinetic information. This is shown to lead to a well defined strategy for the design of copolymerization reactors especially in the industrially relevant high conversion region. The existence of stable steady states and its influence on the system parameters has been illustrated for the case of a continuous stirred tank reactor (CSTR). A novel strategy of a CSTR operated with a recycle is proposed. This is shown to lead to an operation in the unique steady state with the added advantage of a high conversion and uniform copolymer composition. This would seem to be the first such analysis in the high conversion regio

ISSN:0032-3888    

DOI:10.1002/pen.760231306

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractAn experimental study of the heating and bonding mechanisms in ultrasonic welding is described. Polystyrene specimens were joined under a variety of welding conditions while the temperatures at the interface and within the interior of these specimens were measured. The power input, amplitude of vibrations, and amount of deformation during welding were measured concurrently. In general, the rate of heating at the interface is greatest at the beginning of the weld cycle, but slows markedly after the interface temperature reaches approximately 250°C. The interface temperature peaks well before the weld is completed. Temperatures within the body increase most rapidly at temperatures near the glass transition temperature. Welded specimens were broken on a special testing apparatus under combined torsional and compressional loads to determine the weld strength. The results show that weld strength is dependent on the amount of energy input and the degree to which material flows out of the interface region. Possible mechanisms for heating and bonding during ultrasonic welding are discussed in light of the observed behavior

ISSN:0032-3888    

DOI:10.1002/pen.760231307

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractAt a fixed vapor pressure p of the penetrant and constant temperature of the experiment, the sorptionS=c/por concentrationcof the ethylacetate vapor in the uniaxially strained low density polyethylene (LDPE) increases most rapidly at low strains. If, however, on the basis of strain relaxation one separates the total strain ϵ into an elastic ϵe, and a plastic ϵpl, deformation, one obtains an almost linear increase of the concentrationcor sorptionSof the sorbate with elastic strain ϵe. The separation of ϵ = ϵe+ ϵpldepends very much on the timeththe sample is kept elongated and the vapor pressurepof the sorbate. The elastic component decreases and the complementary plastic fraction increases withthandp. An almost stationary state is reached afterthof about 1/2h. The calculation of the diffusion coefficientDs1from the first sorption immediately after the stretching is affected by this slow adjustment in the interval 0 ≤th≤ ½hand shows a pseudo maximum at a strain of ϵ∼ = 10 percent. The first desorption experiment and all the later sorptions and desorptions yield the sameDD=DS

ISSN:0032-3888    

DOI:10.1002/pen.760231308

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractThe length reduction of reinforcing fibers in short‐fiber reinforced plastics during processing has been studied experimentally. It has been shown that fiber volume fraction, initial length, and initial state of dispersion have little effect on the final fiber length. In dilute suspension theory based on shearing flow conditions and fiber properties the flow stresses are found to be compatible with the experimental results and results which are found in the literatur

ISSN:0032-3888    

DOI:10.1002/pen.760231309

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractPolymerization of dimethylterephthalate (DMT) and 1,4‐butanediol (4G) carried out in the presence of about 15 weight percent of ethylene‐co‐vinylacetate copolymers (EVA), gave blends with average dimensions of the “soft domains” of a few microns. During polymerization, reaction between EVA and poly(butyleneterepthalate) (PBTP) takes place leading to the formation of macromolecules of PBTP‐g‐EVA and crosslinked EVA in addition to unreacted EVA and linear PBTP. These different chemical structures can be fractionated by selective solubility and quantitatively measured. Their relative amounts depend particularly on the percentage of vinylacetate (VA) in the initial EVA and on the time of reaction. During polymerization there is a retarding effect on the increasing of the molecular weight of linear PBTP which can be ascribed to the lower volatility of the acetate by‐products, derived from the reaction with EVA, which act as monofuncti

ISSN:0032-3888    

DOI:10.1002/pen.760231310

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractThe interest in reaction injection molding of urethane and non‐urethane resins has generated a need for a greater understanding of the molding behavior of these reactive systems. The kinetics and rheology of a given resin must therefore be well characterized in order to understand and model the molding process. This often requires semi‐empirical correlations rather than strict theoretical considerations. A method of fully characterizing such systems by combining adiabatic reactor and IR studies with viscometer data is therefore described. This results in time‐temperature‐conversion‐viscosity correlations which can be directly utilized in molding studies. Such methods are applied to polyurethane and epoxy systems in the work presented here. It was found that very different activation energies are obtained for the same epoxy‐amine system using different kinetic characterization

ISSN:0032-3888    

DOI:10.1002/pen.760231311

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY