摘要:

AbstractThe effects of pressure ranging from 0.1 to 6.21 MPa (0–900 psig) on the curing of unsaturated polyester resins at 110°c were investigated by an approach of integrated reaction kinetics‐rheology‐morphology measurements using a pressure differential scanning calorimeter (DSC), an infrared spectrophotometer (IR), a Haake rheometer, and by using scanning electron microscopy (SEM). Increasing pressure was found to delay the gel effect, and a previously unknown plateau of kinetic‐controlled region in the initial portion of the DSC rate profile was observed. The plateau region was mainly attributed to the crosslinking of C  C double bonds inside the microgel particles, as revealed by the conversions of styrene and polyester C  C bonds measured by IR, gel conversion data and SEM micrographs. The mechanisms of reaction kinetics both at atmospheric pressure and under pressures have also been elucidated by the progress of buildup of microge

ISSN:0032-3888    

DOI:10.1002/pen.760330102

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractCyclic deformation and stress relaxation after cyclic preloading in polypropylene were investigated by using an electrohydraulic, servocontrolled testing machine. The cyclic deformation tests were performed under various sets of strain rate, number of cycles, and strain amplitude in the as‐received sample and a quenched sample. The stress relaxation tests were made after a cyclic preloading in both samples. The distinctive shape of the hysteresis loop, termed a propeller‐like shape, is characteristic of the as‐received polypropylene with large spherulites, in marked contrast to the behavior of metals. The curves at strain amplitudes from ± 1.5% to ± 5% indicate a propeller‐like shape; these loops change into the steady state response as the number of cycles (N) is increased up toN= 30 to 50. The drop of stress in relaxation tests for the quenched samples is smaller than that for the as‐received samples at the same strain levels. This stress drop behavior reflects the difference of spherulite structure. The stress relaxation behavior depends on the morphology, the predetermined strain amplitude, and the process o

ISSN:0032-3888    

DOI:10.1002/pen.760330103

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractFourier transform infrared spectroscopy (FTIR) and carbon‐13 solid state nuclear magnetic resonance spectroscopy (NMR) were used quantitatively (and non‐destructively) to determine the starch content in a series of starch filled polyethylene samples (nominal addition levels range from 3 to 6 wt%). Data acquisition times (including sample preparation and instrument analysis) were typically a few minutes for both techniques. Current methodologies for starch analysis in polyethylene are based upon wet chemical techniques (gravimetric or enzyme analysis). The proposed methods offer several advantages over these traditional methods: they are less labor intensive, do not require chemical reagents, are relatively insensitive to changes in the sample matrix, and are f

ISSN:0032-3888    

DOI:10.1002/pen.760330104

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractBlends of two thermotropic liquid crystalline polymers (LCP) based on 6‐oxy‐2‐naphthoyl and p‐oxybenzoyl moieties and p‐oxybenzoyl, terephthaloyl and hydroquinone moieties have been studied. The blends were prepared by melt mixing using a twin screw extruder. Thermal, rheological, mechanical, and morphological studies were carried out. Based on the dynamic mechanical thermal analysis and the morphological observations, the blends are found to be immiscible. The viscosity ratios of pure LCP melts exceed values of 10 over a wide range of shear rates, with the viscosity of the blends lying between those of the pure components. The prepared blends are shown to be self‐reinforced composites in which one LCP enhances the molecular orientation of the other. Studies of the injection molded bars by scanning electron microscopy indicate a complicated hierarchical morphology with microfibrils of submicron level in diameter, bundled, and intertwined into fibrils of a substantially larger diameter. Due to self reinforcement, impact and tensile properties of the blends show significant synergism when compared to those of the pure LCP components. The properties obtained are remarkably higher than those known for any high performance engineering the

ISSN:0032-3888    

DOI:10.1002/pen.760330105

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractFrequency domain photopyroelectric effect spectrometry (FD‐PPES) is a recent spectroscopic technique that may be used to recover depth profiles of optical absorption in thin films on a noncontact and nondestructive basis. In this work a series of well characterized thermally homogeneous samples were prepared that exhibited continuous or discrete subsurface profiles of optical absorption. Multifrequency FD‐PPES measurements made on these samples were compared to theory using a heat transfer model, which we have developed for a multilayer thermally homogeneous absorber. Excellent agreement between experiment and theory was obtained for these model studies. While both phase and magnitude channels of the FD‐PPES response give depth profiling information, the phase response is especially sensitive to variations in the subsurface profile of optical absorption. By means of the phase response it is possible to determine the number and spatial positions of absorbers in a series of discrete absorbing layers. The FD‐PPES. technique has excellent potential for analysis and nondestructive evaluation of polyme

ISSN:0032-3888    

DOI:10.1002/pen.760330106

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractIn the bulk, the nonlinear viscoelastic response of glassy polymers is due to the irreversible work done on the body by the surroundings. The source of the irreversibility is plastic flow of material near distributed shear bands or microcracks in the polymer. Shear bands and microcracks also form new traction free boundaries in the body. The presence of these new boundaries diminish the load bearing capacity of the polymer. These changes in polymer lattice structure are a mechanism that promotes the release of stored strain energy. If the release of stored strain energy is stress controlled, then at sufficiently high levels of stress to cause a permanent structural arrangement of the polymer chains, polycarbonate and LaRC‐TPI behave as nonlinear viscoelastic materials. If the current stress is less than the maximum stress the polymer has experienced, then the current energy release rate for the propagation of shear bands, crazes, etc., is less than the critical energy release rate. In this instance, damage production is a constant and the material can be modeled using linear viscoelasticity. It will be shown that the stress‐induced nonlinear shift factors are a measure of the rate of damage production in glassy polycarbon

ISSN:0032-3888    

DOI:10.1002/pen.760330107

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760330101

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY