摘要:

AbstractPrevious experimental studies have revealed that the mixing efficiencies of widely used continuous processors such as the single and twin screw extruders depend on the types of screw elements, which are utilized. It is generally recognized that the basic single screw extruder and the fully‐fighted sections of the fully‐intermeshing co‐rotating twin screw extruders are not efficient mixers, in contrast to the specialized mixing elements such as the kneading discs used in co‐rotating twin screw extruders. However, no simulation techniques were available to characterize quantitatively and rigorously the mixing efficiencies of continuous processors. In this study, we have solved the three‐dimensional equations of conservation of mass and momentum, and utilized various tools of dynamics to analyze the mixing occurring in single and co‐rotating twin screw extruders. It is shown that simulation methods can indeed capture the relative differences in the mixing mechanisms of continuous processors like the single and twin screw extruders. The ability to distinguish quantitatively between the distributive mixing capabilities of various continuous processors should facilitate numerical testing of new continuous mixer designs, optimization of operating conditions and geometries of existing mixers and the material‐specific design

ISSN:0032-3888    

DOI:10.1002/pen.760351702

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractIn the present paper an effort is made to model the time‐dependent behavior of high‐density polyethylene (HDPE) with a one‐dimensional integral representation. Owing to the plasto‐viscoelastic behavior of the material, we assume that the total strain can be decomposed into a recoverable viscoelastic strain and an irrecoverable plastic strain. The viscoelastic deformation is represented by the Schapery thermodynamic theory. The plastic deformation is assumed to be accumulated during the loading history. An effective time concept is introduced for the plastic deformation, so that the response due to complex loading can be accounted for. The present representation gives a very good prediction of the responses of creep and recovery, two‐step creep, and constant stress rate loading and unloading. It is also applied successfully to describe the process of preconditioning of semicrystalline

ISSN:0032-3888    

DOI:10.1002/pen.760351703

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractStatistical poly(styrene‐co‐acrylonitrile) (SAN) copolymes with varying mole fractions of comonomer units have been synthesized in a batch reactor. The intrinsic viscosity and gel permeation chromatography (GPC) patterns of model copolymer samples were the basic experimental results. Chromatographic patterns of SAN copolymer samples were converted into molecular weight distributions and afterwards fitted to the theoretical distribution functions. The correlation between the composition of copolymers and the best fitted model distribution (Schulz's two parameters distribution in this case) was established. The treatment of data shows that parameter α is inversely proportional to the content of acrylonitrile units in the sample and indicates the molecular weight interval. Parameterbshows the invariability of the molecular weight distribution s

ISSN:0032-3888    

DOI:10.1002/pen.760351704

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractA bismaleimide (BMI) resin was added to an epoxy system composed of N,N′‐tetraglycidyldiaminodiphenyl methane (TGDDM) and diaminodiphenyl methane (DDM). Cure behavior of theBMI modified epoxy resinswas studied by a dynamic differential scanning calorimetry (DSC) method. Dynamic DSC thermograms of the BMI modified epoxy resins indicated unimodal reaction exothermic peaks. The overall heat of reaction per unit mass decreased with BMI composition. The residual heat of reactions of the epoxy blends cured at 180°C for 3 h increased with BMI composition.Thermal stabilityof the epoxy system improved by incorporating BMI resin.Flexural strength and modulusincreased with BMI composi

ISSN:0032-3888    

DOI:10.1002/pen.760351705

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractAn epoxy‐amine thermosetting polymer, modified by 15 wt% castor oil (CO) or by a commercial rubber (epoxy‐terminated butadiene‐acrylonitrile copolymer, ETBN), was cured in a mold at different heating rates. CO‐modified materials cured at high heating rates exhibited a nonuniform phase separation profile, i.e. a single‐phase transparent core surrounded by opaque layers containing dispersed domains. The resulting structure was explained by simulating conversion vs. temperature trajectories taking place during the cure. Thermal and mechanical properties of uniform and nonuniform materials were compared. These include glass transition temperature, microhardness, yield stress and yield strain in uniaxial compression, and fracture toughness. Some possibilities for further research in this area are

ISSN:0032-3888    

DOI:10.1002/pen.760351706

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractThe desorption kinetics of small hydrocarbon molecules in a low‐density polyethylene (LDPE) film has been simulated via the continuous time random walk approach. A scaling relation between the amount of penetrant remaining in the film during the final stage of the process and the time has been obtained. A constant scaling exponent was obtained for various hydrocarbon penetrants in LDPE. The mutual relation between phenomenological and statistical models has been exploite

ISSN:0032-3888    

DOI:10.1002/pen.760351707

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractWe propose an “optical loss analysis” as a novel nondestructive diagnosis for the thermal deterioration of insulating resins. Using an alkyd resin film, the optical absorptin loss per unit optical path length and the glass transition temperature (Tg, DMA) by dynamic mechanical analysis were measured during heating tests. At longer heating times, values of the optical absorption loss and theTg, DMAincreased concurrently. By rescaling the heating time as a reduced time as a reduced time, a master curve of the deterioration for the resin was obtained. Consequently, when thermal stress is the main cause of the deterioration, one can estimate the degree of deterioration and theoretically the residual lives of resins using this optical loss analy

ISSN:0032-3888    

DOI:10.1002/pen.760351708

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractRecent work on the determination of residual stress in drawn pipes has revealed an error in previous methods used. Such pipes have residual stresses very different from those induced by melt extrusin during conventional pipe processing. In particular, it appears that there are considerable compressive stresses at the bore, and the hoop and axial values are not equal. In an attempt to measure these values, tests were performed on slit rings of varying length, and a pronounced dependence of ring overlap on length was observed. This was contrary to previous assumptions, and a corrected version of the analysis has been developed, which enables the true hoop and axial stresses to be determined by testing rings of various lengths. For isotropic pipes, it has been shown that hoop and axial stresses are roughly equal. Previous results obtained on thin pipe rings can now be corrected by multiplying by the factor 1/(1‐v). For anisotropic drawn pipes, a combination of rings and thin axial strips is used to determine the residual stresses. These pipes can show remarkably low stresses at the bore, which may play a significant part in determining their performanc

ISSN:0032-3888    

DOI:10.1002/pen.760351709

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractIn this study, the viscoelastic behavior of a microcellular plastic was investigated with particular emphasis on the effect of cell size. A poly(ethylene terephthalate) resin containing a polyolefin nucleating agent (CPET) was selected as the test material. In order to investigate the effect of cell size, microcellular CPET samples were produced having a nearly constant density of nucleated cells and a varying cell size. The viscoelastic behavior was investigated using a dynamic mechanical analyzer in tensile mode, and the relationship between viscoelastic behavior and cell size is discussed.

ISSN:0032-3888    

DOI:10.1002/pen.760351710

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractThe viscoelastic behavior of acrylonitrile‐butadiene‐styrene (ABS) terpolymers is studied in the molten state. First, the behavior of the styrene‐acrylonitrile (SAN) matrix is determined. Then, the effect of the degree of grafting on ABS rheological properties is emphasized. A critical degree of grafting (DGc), corresponding to a minimum of the viscoelastic functions in the low frequency region, is determined. It defines a critical thickness of the grafted layer, and is related to the conformation of the grafted chains at the surface of the rubber particle. The DGc affects the morphology of the ABS and also affects the appearance of a secondary plateau at low frequencies. The effects of the rubber particles, of the grafted chains, and of the morphology on the appearance of the secondary plateau at low frequencies are clearly dissoc

ISSN:0032-3888    

DOI:10.1002/pen.760351711

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY