摘要:

AbstractA comparison of the effect of two structurally similar additives, 1‐benzoyl‐2‐naphthol and 6‐hydroxybenzanthrone, on the rate of photo‐oxidation of polypropylene under conditions of simulated daylight shows that while 6‐hydroxybenzanthrone acts as a prodegradant, 1‐benzoyl‐2‐naphthol is a light stabilizer. Examination of the spectroscopic and photochemical properties of 1‐benzoyl‐2‐naphthol indicates that in fluid solution the photoexcited stabilizer is probably deactivated within the singlet manifold. In glassy solvents at 77°K, on the other hand, triplet formation does occur, but only in molecules in which the intermolecular hydrogen bond of the 1‐benzo

ISSN:0021-8995    

DOI:10.1002/app.1976.070200501

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

年代:1976

数据来源: WILEY

摘要:

AbstractDuring the initial stage of operation, membrance performance in hyperfiltration experiments will be time dependent. For swollen ionic membranes, fluxes show an initial decrease while rejections initially increase in magnitude. These phenomena, also referred to as compaction, can be described by a model proposed here in which the wet membrane thickness decreases in time as a combined response to stepwise changed process parameters pressure and concentration. The response has been described by a linear first‐order differential equation and worked out by use of known concepts of flux and rejection for swollen ionic membranes. Experimental data appear to be in good agreement with model prediction

ISSN:0021-8995    

DOI:10.1002/app.1976.070200502

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe use of poly(phenylene oxide) film to monitor UV radiation is demonstrated, and the results from the continuous monitoring of solar UV radiation at 24 sites throughout the world are presented. The global and diffuse measurements from a temperate and from a tropical site are analyzed in detail, and the effects of season and weather conditions on the UV contribution to solar radiation and the relative importance of the diffuse and direct components of solar UV are discussed.

ISSN:0021-8995    

DOI:10.1002/app.1976.070200503

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

年代:1976

数据来源: WILEY

摘要:

AbstractAssuming that the rate of reaction of an unreacted site in polymer reactions depends upon whether the two immediate neighboring sites on either side (four neighboring sites in all) are reacted or unreacted, differential equations were obtained giving the rate of change ofNnwith time (whereNnis the number of sequences ofnconsecutive unreacted sites with a reacted site at both ends) and solved numerically with the help of a computer.Nnwas obtained as a function of time and also as a function ofM, the total number of unreacted sites. Three sets of values ofkwere tried, one of these relating to autocatalytic reaction, one to autoretarding reaction, and one to the null case in which the reaction rates do not depend upon the neighbors.

ISSN:0021-8995    

DOI:10.1002/app.1976.070200504

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

年代:1976

数据来源: WILEY

摘要:

AbstractMelt rheology and its time‐temperature dependence have long been known to be fundamental properties associated with satisfactory expansion characteristics in vinyl foam. Since much is known about the relationship between rheology and material variables like polymer morphology and system composition, adequate rheological characterization should be quite helpful in polymer design and plastisol compounding.Earlier attempts to study the melt rheology of plasticized PVC foam systems were only partially successful because instrument limitations required that the material be studied at too high shear rate or temperature, or that behavior of specific compositions be extrapolated from data obtained at considerably higher plasticizer level.This paper deals with measurement of the viscoelastic behavior of melts from actual azodicarbonamide foam compositions. The Rheometrics Mechanical Spectrometer was used in the orthogonal mode to study both elastic modulus and loss modulus (viscosity) in the range of shear rates and temperatures which actually occur during commercial utilization of PVC foam compounds. The effects of changing vinyl resin types and plasticizer types and levels were explore

ISSN:0021-8995    

DOI:10.1002/app.1976.070200505

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

年代:1976

数据来源: WILEY

摘要:

AbstractSeveral equations which are used to predict the pressure coefficient of viscosity for amorphous polymers have been examined on the basis of type of information required and equation reliability. These equations can be useful in accounting for pressure effects observed in tubular flow and in other shear geometries. The correlations of Penwell and Porter and of Miller are evaluated and in the perspective of expressions by Matheson and by Eyring. Data on linear amorphous polystyrene (PS), polyisobutylene, poly(vinyl acetate), poly(methyl methacrylate) (PMMA), natural rubber, and polycarbonate are examined and presented. Predictions from the Penwell‐Porter and Miller equations are compared with experimental coefficients at one atmosphere for all data available. For PS and PMMA, it was found that Miller's equation tends to predict values somewhat higher than experiments but is closer to the data on PS and on a high molecular weight PMMA. The Penwell‐Porter equation, on the other hand, tends to predict values somewhat lower than experiments and does a slightly better job for lower molecular weight PMMA. Both equations require WLF or Vogel coefficients andTg‐pressure‐molecular weight data. Miller's equation also requires compressibilities atTgand at the temperature of interest, although an alternate method can be used which only requires average “K” values withoutTg‐pressure or compressi

ISSN:0021-8995    

DOI:10.1002/app.1976.070200506

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

年代:1976

数据来源: WILEY

摘要:

AbstractObservations obtained by other techniques were confirmed by DSC analyses. As the length of the methylene chain increased,Tmdecreased, and crystallinity, heat capacity, and heat of fusion increased. TheTmand crystallinity of the isophthalate esters were lower than for the corresponding terephthalate esters. The values for an odd‐numbered methylene sequence were lower than for the adjacent even‐numbered members. A model was used to calculate the heat of fusion of theoretically 100% crystalline poly(hexamethylene isophthalate) and poly(decamethylene isophthala

ISSN:0021-8995    

DOI:10.1002/app.1976.070200507

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe β‐relaxation atTgof the terephthalate and isophthalate series is due to molecular motions of the backbone chains in the amorphous region, but differs for the isophthalate series in that thep‐phenylene group does not exhibit the free rotation possible for them‐phenylene group. Consequently, the relaxation times of the terephthalate series are longer than for the isophthalate series. The γ‐relaxation (Tγ) for the higher homologues of the terephthalate series cannot be explained in terms of the poly(ethylene terephthalate) analogy. For poly(ethylene terephthalate) and poly(tetramethylene terephthalate), an induced cooperative type of motion of all the moieties is possible, whereby overlapping processes caused by “rocking vibrations” are observed as one γ‐peak. The resolution of the γ‐loss peaks for the above‐mentioned polyesters into components is not possible at the experimental frequency of 110 Hz. For poly(hexamethylene terephthalate) and poly(decamethylene terephthalate), the “rocking vibrations” between the moieties of the skeletal chain are reduced so that even at a test frequency of 110 Hz, the γ‐loss peaks could be resolved into two or three components. In the case of poly(decamethylene terephthalate), three components are resolved; the lowest temperature peak γ1is attributed to hindered motions of the methylene portions, the γ2peak is attributed to motions of the carbonyl group in the gauche conformation, and the γ3peak is attributed to the carbonyl group in the trans conformation of the skeletal chain in the amorphous region. The general observations obtained by other techniques were confirmed by the forced vibration analyses. As the length of the methylene chain increased,Tgdecreased. As crystallinity increased, the β‐relaxation moved to higher temperatures and the damping peak was smaller and broader. The damping peak moved to lower temperatures and increased in size as the length of the methylene chain increased. The damping peak was larger for the isophthalate homologue than for the co

ISSN:0021-8995    

DOI:10.1002/app.1976.070200508

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe time‐dependent response of a viscoelastic liquid to unsteady one‐dimensional stretching deformations was examined. Oldroyd's three‐constant model for a viscoelastic fluid was used. Two cases representing two different stretching histories were analyzed: a sine stretching pulse and a step stretching pulse. The results show that high elongational viscosity may be easily reached in both cases. As the relaxation time of the liquid becomes comparable to the pulse width, elongational viscosity increases with the increase in maximum stretching rates. Conditions to maintain high levels of elongational viscosity at a subsequently reduced stretching rate were given as functions of the relaxation time and initial stretching rates. In view of recent turbulent boundary layer data, the results were used to discuss possible explanations of turbulent drag reduction in polymer solutions. It was concluded that the basic mechanisms for drag reduction in polymer soluations. It was concluded that the basic mechanisms for drag reducation may be related to the effects of high elongational viscosity and local stabilization of small shear disturb

ISSN:0021-8995    

DOI:10.1002/app.1976.070200509

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

年代:1976

数据来源: WILEY

摘要:

AbstractTorsional braid analysis (TBA) (∼0.3 Hz) and differential thermal analysis (DTA) data are presented for the temperature for the region 0–200°C for two series of atactic polystyrenes with narrow molecular weight distributions: (a) anionic series, M̄n= 600–2×106, M̄w/M̄n≃ 1.1; (b) fractionated thermal series, M̄n= 2,000–1.1×105, M̄w/M̄nTgand (b) thatTllreflects chain entanglements, further suggest thatTllinvolves a longer chain segment length and possibly the entire molecule. Comparison ofTllversus logMplots withTversus log M isoviscous state plots based on zero‐shear melt viscosity data from the literature implies thatTllmeasured by the TBA technique corresponds to an isoviscous state of 104–105poises. The employment of narrow molecular weight polymers is presumably responsible for both the linear variation of theTlltransition with M̄n−1(which suggests a free volume basis for the relaxation) and the form of the variation of theTlltransition with logM(which suggests an isoviscous basis for the relaxation). The sharpness of theTllloss peak by TBA decreases with increasing molecular weight and dispersity. The DTA endothermic event corresponding toTllis clearly related to the occurrence of flow since the fused films which result from heating granules to 200°C and cooling to R.T. do not reveal aTllon reheating. If a fused film is crushed, aTllevent is observed on heating. For bimodal blends with M̄n

ISSN:0021-8995    

DOI:10.1002/app.1976.070200510

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

年代:1976

数据来源: WILEY