摘要:

AbstractOxygen absorption is a widely used test for measuring polymer stability and antioxidant effectiveness. Commonly, periodic measurements are made using a mercury buret to measure the rate at which oxygen is taken up by the polymer. We designed and built a safe, dependable apparatus that continuously monitors the reaction of a hydrocarbon polymer with oxygen. The instrument operates by recording the frequency with which small, known volumes of oxygen are introduced into the sample tube to maintain a preestablished pressure in the tube. No operator time is required during the test. The instrument readings are readily converted to standard oxygen absorption curves.

ISSN:0021-8995    

DOI:10.1002/app.1973.070170801

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractThe emulsion polymerization of vinyl acetate was studied at 50°C. It was found that the rate of polymerization was proportional to the 0.5 power of the initiator concentration and the 0.25 power of the number of particles. The number of particles was proportional to the power 0.5 ± 0.05 of the emulsifier concentration, but independent of the initiator concentration. The limiting viscosity number of the polymers produced was independent of the initiator concentration and number of polymer particles. It is suggested that the mechanism of vinyl acetate emulsion polymerization is similar to that of vinyl chloride. The linearity of the conversion‐versus‐time curve is explained as being due partly to a decrease in the desorption rate of radicals from the polymer particles and partly to a decrease in the termination rate con

ISSN:0021-8995    

DOI:10.1002/app.1973.070170802

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractMeasurements were taken of flow birefringence of viscoelastic polymeric melts in the upstream reservoir and in the entrance region. Materials investigated were polypropylene, high‐density polyethylene, and polystyrene. Stress‐birefringent patterns, both isochromatics and isoclinics, were formed when a beam of polarized light was sent through a transparent glass cell which consists of a large reservoir and slit die section. Pictures were taken of stress‐birefringent patterns, which were later used to obtain quantitative information on the stress distributions of flowing polymeric melts, with the aid of stress optical laws. Also measured were wall normal stresses in the fully developed region, downstream in the thin slit section, which then permitted us to directly determine the stress optical coefficients of the materials t

ISSN:0021-8995    

DOI:10.1002/app.1973.070170803

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractAn experimental study has been carried out to measure velocities of viscoelastic polymeric melts flowing into a sharp‐edged slit die and in the fully developed region of the slit die. For the velocity measurement, the technique of streak photography was used, in which photographs are made of the movement of tracer particles suspended in a molten polymer. Materials investigated were polypropylene, high‐density polyethylene, and polystyrene. From the photographs, local velocities in the entrance region were determined by measuring the streak length, a reference length, and the exposure time of the camera. A comparison was also made of the experimentally determined velocity profiles in the fully developed region with the theoretically predicted ones, showing a reasonable agreement between the

ISSN:0021-8995    

DOI:10.1002/app.1973.070170804

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractAn experimental and theoretical study has been carried out, as a continuation of our previous investigation, to better understand the problems associated with converging flows of viscoelastic polymeric melts. In the present study, measurements were taken of both stresses and velocities in the converging velocity field of polymeric melts flowing into a tapered slit die, stresses by means of the flow birefringence technique and velocities by means of streak photography. The material used was polystyrene. A theoretical analysis was also made of converging flow, using a modified second‐order fluid model which assumes that all three material functions depend on the second invariant of the rate of deformation. Numerical solutions were obtained of the equations of motion, which give predicted velocity profiles in reasonable agreement with the measured velocity profiles. A comparison was also made of the experimentally determined stress distributions with the theoretically predicted one

ISSN:0021-8995    

DOI:10.1002/app.1973.070170805

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractGasification behavior and its effects on mechanical properties were determined for amorphous polycarbonate (PC) and poly(vinyl chloride) (PVC). Nitrogen‐gasified PC and PVC exhibit interior regions containing gas bubbles surrounded by surface layers of void‐free polymer, while in the helium‐gasified polymers no gas bubbles could be observed. Scanning electron microscope (SEM) observations of the bubbles in nitrogengasified PC indicate that the bubble walls are smooth and featureless (in contrast to the diffuse walls with fibrils of polymer extending into the bubbles observed previously in gasified polyethylene). For both PC and PVC, neither the yield stress nor the elongation to fracture showed any appreciable variation between gasified and ungasified material. The lack of a significant effect of gas bubbles on the drawing behavior in these glassy polymers stands in contrast with the pronounced effect noted with semicrystalline polyethylene. The origin of this difference in behavior and its relation to the crystallization process in polyethylene are disc

ISSN:0021-8995    

DOI:10.1002/app.1973.070170806

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractThe diffusion coefficient of water,Dwm, across homogeneous cellulose acetate membranes of graded porosity ε (water content) are measured. At high values of porosity,Dwmvaries monotonously as ε is varied. At a certain porosity εc, however, there is a sudden change inDwm; and thereafter the change becomes linear again, but with a different slope. Diffusion coefficients are interpreted, through the Stokes‐Einstein relation, in terms of the overall microscopic viscosities ηwmof the membrane matrix. The values of ηwmare then correlated with the equivalent pore sizerof the membranes. It is discovered that the sudden change inDwm(or ηwm) at εccorrelates with similar changes in other properties such as hydraulic permeability and selectivity of the membrane. All these observations are then attributed to the water structure inside the m

ISSN:0021-8995    

DOI:10.1002/app.1973.070170807

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractThe reaction of bisphenol A with a diglycidyl ether of bisphenol A may lead to linear polymers if a selective catalyst is used. Selective catalysts promote linear polymer formation while nonselective catalysts increase the rate of crosslinking. Selectivity in epoxy resin–bisphenol A reactions depends upon the nature of the catalyst used. In order to understand these catalyst–structure relationships better, we measured the effects of catalysts on the rate of polymerization (k1) and the rate of crosslinking (k2) during epoxy resin cures. The knowledge of the ratiok1/k2aids in the selection of catalysts specific for the linear polymerization of epoxy resins. We related this specificity to catalysts basicity. We found that less basic catalysts tend to give largek1/k2values, indicating that little crosslinking occurs with these highly selective catalysts. We demonstrated that the linear polymer obtained from epoxy resin polymerized by triethanolamine, a very selective catalyst, and the linear polymer prepared using 3‐p‐chlorophenyl‐1,1‐dimethylurea, a catalyst with low selectivity, are essentially the same. Finally, we caution that quantitative comparisons of selectivity should be restricted to those reactions whose kinetic reaction orders a

ISSN:0021-8995    

DOI:10.1002/app.1973.070170808

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractThe effects of preoxidation of cellulose samples on graft copolymerization in the presence of ceric salt (Ce4+) as an initiator were investigated. The use of Ce4+as oxidizing agent inhibited the formation of grafts, and the number of grafts decreased as the concentration of Ce4+in the pretreatment rose. In contrast, the samples oxidized with periodic acid (HIO)4or hydrogen peroxide (H2O2) tended to show improved initiation characteristics and gave a larger number of grafts than the unoxidized samples. The reactivity of oxidized samples toward Ce4+was examined and the following results were obtained: The part of easy reactivity decreased in the Ce4+‐oxidized samples but it increased in the HIO4‐oxidized samples; on the other hand, it did not vary greatly in the H2O2‐oxidized samples. Cellulose is probably oxidized to different states by different oxidizing agents, and the reactivity of Ce4+toward these oxidized samples, as one index, seems to be reflected in the graft copolymerization. It was consequently recognized that the graft copolymerization characteristics of cellulose samples could be improved significantly by proper selection of oxidiation condi

ISSN:0021-8995    

DOI:10.1002/app.1973.070170809

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractThe following well‐known equation permits the ready determination ofMnfrom a single osmotic pressure measurement at a known concentration, if the second virial coefficient is previously given:\documentclass{article}\pagestyle{empty}\begin{document}$ \left( {{\pi \mathord{\left/ {\vphantom {\pi C}} \right. \kern-\nulldelimiterspace} C}} \right)^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} = \left( {{{RT} \mathord{\left/ {\vphantom {{RT} {\bar M_n }}} \right. \kern-\nulldelimiterspace} {\bar M_n }}} \right)^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} \left( {1 + {{\Gamma _2 C} \mathord{\left/ {\vphantom {{\Gamma _2 C} 2}} \right. \kern-\nulldelimiterspace} 2}} \right). $\end{document}On this basis, the one‐point method was investigated to determine the number‐average molecular weight. It was found that this method was applicable to commercial polymers. However, in this application, the dependence of Γ2on molecular weight distribution has to be kept i

ISSN:0021-8995    

DOI:10.1002/app.1973.070170810

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY